Running Fix Explained
Coastal Navigation iPad eLearning App
This week we uploaded our updated Coastal Navigation course to Apple for publishing on iTunes as an interactive eLeanring App. We’re very excited about this update because of the HTML 5 animations we’ve used to explain some of the concepts. At the bottom of this post, we show you how to essentially get this App for free.
Specifically in regards to this post, no where on the web have we seen a decent explanation of how to do a very simple and elegant position fix using only one land position. The concept is called a running fix. In fact all we found was very poor, long, complicated and sometimes wrong explanations of how it works. Certainly we found no animated interactive explanations. So as usual, at NauticEd we have broken down the seemingly complicated to the very simple.
Play this animation below then read the explanation and solution below – then watch the animation again.
The Example Problem is:
You are sailing along on heading 57° psc (61° Mag) (47° T) your knot meter reads 5 knots. You are passing Horton Point Light to your starboard. At 1548, a hand held bearing shows that the bearing to Horton Point Light is 119°Mag (105°T). You decide to do a running fix. At 1615, the bearing to Horton Point Light is 160°M(146°T). Determine your running fix position.
The time elapsed is
1575 -1548 = 27 minutes (/60) = .45 hours
@ 5 knots you will travel 5 x 0.45 = 2.25 NM
You draw the true bearing line of 105° T to Horton Point Light. You then draw a vector 2.25 NM long in a direction of your heading 47° T starting anywhere on the 105° line. You then draw another line parallel to the first 105° T bearing that intersects the end point of the 2.25 NM vector. Finally, you draw in your second bearing line of 146° T. Where the 146° T line intersects the parallel 105° T line – you mark as your running fix position.
The theory behind this is simple but not usually explained. Initially you must lie on the 105 degree line somewhere but you don’t know where. You know that over the time elapsed you will travel the 2.25 NM from some where off the initial 105 deg line but you don’t know from where – yet. The parallel 105 deg line projected forward means that you will also lie somewhere on that projected line, again – somewhere. By doing the second bearing, off any object, the intersection of that bearing with the projected line means you must be at that point (given that your speed and heading were accurate).
LAT 41° 07.55’ N and LONG 72° 28.8’W
You can then draw your running vector from the fix position back to the original sighting line if you like to find your original position. This will also be your track.
Pretty slick ah? You’ll never be confused about a running fix again – and I bet you’re now wanting to get out on the water and practice next time out. Imagine trying to explain this using text and a paper book – yuk. Ahhhh no wonder people don’t like slogging through books anymore. In what?, less than a minute you grasped this concept fully.
eLearning is where it is all at.
Show off to your friends next time you’re out about your new found knowledge.
>>>> How to get this App for FREE <<<<
This above is the kind of stuff NauticEd is all about, but we not only break this stuff down to the simple using incredible multimedia eLearning techniques, but we back this up with an internationally recognized sailing certificate accepted by yacht charter companies world wide.
So here’s the deal that we will keep up for a few days in celebration of this App launch – invest the NauticEd Coastal Navigation online class using this promocode - 15degreeswest – and we’ll give you $15 off the regular online course price. This gives you access to the Online Coastal Navigation course and the associated test and certificate recognition.
If you have an iPad … When the App comes out in the next few days, the price of that is going to be $14.99. This means you’ll be getting the App essentially for free. The App does not include the test – it is solely the course content. As always with our iBooks or Book Apps – you need to invest in and pass the test to gain certificate recognition.
Scratching your head? What we mean is buy the online Coastal Navigation course now using the promocode and then apply the 15 bucks you save towards the App – we’ll let you know when that’s available. Then complete the test and – bang – it gets attached to your sailing certificate.
Invest in the Coastal Navigation Class now and save $15
Or – if you’re really ready to get going properly why not invest in the BareboatCharter Master bundle of courses. The Coastal Navigation Course is included and you get a bonus of the Electronic Navigation course for free AND you save a ton of $ over the A La Carte Prices AND if you use this promocode – 15degreeswestbbcm – over the next few days you’ll still save the $15 above. That’s the best deal ever!!! (NOTE: this code will also work for the Captain’s Bundle of courses)
Invest in the Bareboat Charter Master Bundle of courses (includes the Coastal Navigation Class) and save $64.50
On our most recent yacht charter tot he Bay of Islands New Zealand we encounted one day with reasonably high swell and only about 10 knots of wind. Being on a broad reach was not the ideal heading for this but alas this is the direction we wanted to go – from the Bay of Islands up to the Cavalli Islands.
During the sail one of our precious crew became a little seasick. The proven cure I’ve always found to work is to have that person steer the boat. It takes about 5 minutes and viola – they’ve been so hard concentrating on helming that the seasickness has gone.
Later on in the week another became sick on a long sail. This time I administered a nice hot cup of freshly made ginger tea. We ground up the fresh ginger root and poured boiling water over it then strained off the root after a minute and served the tea. Besides being quite tasty and refreshing the tea did it’s job of fixing the seasickness with in 10 minutes. Having ginger on board is is paramount to enjoying a good feed of sashimi after your catch. So ginger up when doing your provisioning.
Ginger fixes seasickness
There is another good preventative measure that one should take before pulling anchor. And that is to have a good pooh. Yup that’s right strange as it seems it helps. Of course having one underway is always proven to work as well because the moment you go below to indulge in this behavior you will instantly puke – which is actually a good way to fix seasickness anyway. I.E. don’t go below unless you instantly want to puke. Now having a good puke does work but the instant this happens you’ve got to eat more food to help settle the stomach no matter how bad you feel after a puke – eat! It works!
Other methods I’ve seen work is the electronic shocker watch. It’s a strap you wear around your wrist that administers a small electric shock on intervals.
If your a druggy there are non natural methods that can also work like patches and ingested drugs. Unfortunately our western culture tends to believe a drug method first rather than the natural ones. Me, I’d rather not put too many chemicals into my body and try the natural proven ones first.
Int eh bareboat charter course we go through just about everything you’re going to encounter on a bareboat yacht charter sailing vacation. Knowing this kind of information can make you a hero and an admired leader.
Take the Bareboat Charter course now
On the way back
Currently we’re working on a cool project with SimRad to create a training simulator for a gps device. But to do that and to write the code and the statement of work for the programmer we had to be very clear about the math behind it all. At least to me, it’s all pretty interesting and so I thought I’d share it here. Kinda like “the making of…” in movie talk.
With traditional coastal navigation you are plotting positions on a chart then measuring the angles and distances. That’s all pretty easy and well described in the NauticEd Coastal navigation course. But once you start to do it electronically, you’ve got to have the mathematics of it all well understood in order to write the code. Turns out it’s again pretty easy but you’ve got to reach deep into some brain cells to drag out the trigonometry you’ve so desperately tried to forget from high school days and thought/hoped you’d never use again.
But this is a worthwhile read because you’ll exit out understanding the principles, which is really the point of the sailing blog entry.
So here’s one snippet of what we did:
We simulated a vessel moving at 20 knots that can be controlled using the autopilot. We input a static current to the east at 2 knots. For this scenario and for any direction the vessel is moving, we want to present the following variables in real time as they changed:
- Bearing to Destination – BTD
- Distance to Destination – DTD
- Course to Steer to reach destination – CTS
- Speed Over Ground – SOG
- Time to Destination – TTD
- Position of the vessel
The difficulty comes in with the current. You can’t just head towards your destination because the current will drag you off. So you’ve got to solve for a triangle where you have limited information and the triangle is not a right angle triangle.
We decided early on in the simulation to work in meters and meters per second because it makes the math a lot simpler. Also just by universal convenience meters per sec is ½ speed in knots. Thus 20 knots = 10m/s.
In a first example, the destination is at a point 500m to the north and 1000 m to the east of the vessel. Since we know the instantaneous position of the vessel and the position of the waypoint, we know the instantaneous distance to the waypoint. I say instantaneous because the vessel is moving.
Solving for Distance and Bearing to Destination
That’s a good start however the vessel is not moving at 20 knots towards the target. Due to the current the resultant vessel speed over ground is slightly different. To visualize what’s happening we drew this triangle. We added the current vector to the bearing vector to create a Course To Steer vector.
Vessel heading versus resultant track
There is a further complication however, since the whole process of getting to the destination doesn’t necessarily take 1 hour. We can’t say that the current vector is 2 nautical miles long. Thus in the distance triangle above we only know two variables, the angle (a) and the distance to destination – that’s not enough information. Instead we have to draw a velocity triangle whereby the current is 2 and the vessel speed is 20. Fortunately this triangle is exactly the same shape as the distance triangle. In that triangle we know three variables, vessel velocity, current velocity and the angle (a). Thus we can proceed to solve for the entire situation.
Solving for velocity triangles and distance triangles
Here’s the painful part from the ol days
A/sin(a) = B/sin(b) = C/sin(c) it’s called the sin rule.
The lower case letters are the angles and the upper case letters are the triangle side lengths opposite the same lower case letter. IE length A is opposite the angle a.
Just bare with us if that scares you. Actually it’s pretty simple from here you just have to plug and play. What it means is that if you know 3 pieces of information about any triangle you can find the others.
The first thing well solve for is the angle b. To do this, use the velocity triangle. The three pieces of information that we know are the current speed vector length, the vessel speed vector length and the angle to destination (a).
In this quadrant ie angle to destination is less than 90 deg, the Bearing to Destination is 90 minus the angle to the target ie BTD = 90-(a)
Solving the sin rule for angle (b) then
(b)= arcsin ( current x sin (a)/(vessel speed)) = arcsin (B x sin (a)/A)
= 2.6 deg
Since all angles in a triangle add to 180 the angle c must = 150.9 deg. This is the course that you would steer to arrive at the target due to the current.
The luck of it is that this is the same angle to plug back into the distance triangle
IE (c)= (c*).
Now we can return to the distance triangle because we know enough variables. If we plug the two known angles (a) and (c) in to distance triangle we can solve for the distance A*. We need to know A* because the vessel attempts to travel along this path at 10m/s but ends up at the destination. Solving for the time it would take the vessel to attempt A* is the same time it takes for the vessel to actually travel to the destination. IE the vessel is helped by the current.
From the sin rule:
A* = C* x sin(a)/sin(c) = 1027.2 meters
and at 10 m/s the time elapsed is 102.72 sec = ~ 103 seconds
The vessel actually travelled 1128 meters in 103 seconds thus the
SOG = 1128/103 = 10.9 m/s = 21.8 knots
The distance that the vessel was pushed to the east by the current = Set =B*
Set= current speed(drift) x time = 1 *103 = 103 meters.
So for this tiny moment point in time:
- BTD= 63.4 degT
- CTS=60.9 deg T
- DTD = 1128 m
- TTD = 103 sec
- SOG = 10.9 m/s
In coding all this up and since the vessel is moving we have to solve all these at each instant in time using location information from the last moment in time. Again not too difficult it just takes a bit of thought in laying it all out.
If you know the velocity of the vessel over ground (solved from above) and the increment in time, you can calculate the change in position. This is done in Cartesian coordinates Ie x and y directions
- Change in X = velocity in x direction times the time increment = Vx x dt
- Change in Y= velocity in y direction times the time increment = Vy x dt
Where Vx and Vy are solved from the angles calculated from above and SOG
So the position at this instant is now the position at the last instant plus the distance travelled in the increment in time.
We have to solve all this for each instant in time because the vessel is also changing direction from input from the autopilot. In a real situation the position information is being gathered from the actual gps not the last instant. Altho some smarter systems will use this for predictive situations.
Another level of complexity is added in when you consider other quadrants. For example in the below drawing, the current works against the vessel. Note the SOG has slowed, the angle b reduces the CTS, and the triangle is quite different. Thus in the code we have to add a lot of if/then statements to determine what quadrant were working in to determine which formula to use.
Solving the velocity and distance triangles
OK ADMITTEDLY THAT MIGHT HAVE BEEN A BIT HEAVY GOING
Hopefully this gave you some insight into:
- Some principles behind coastal navigation
- Help in understanding electronic coastal navigation
- Some insight into what we do at our sailing school to provide great sailing education
We can’t wait to deliver the SimRad Electronic Navigation simulator and training tool to you.
If you’re interested in properly understanding how to navigate a vessel using charts then take the NauticEd Coastal Navigation Course. Once we finish the electronic navigation simulator we’ll embed it into the Navigation sailing course.
Coastal Navigation Sailing Course
Tides and tidal currents came to mind today as I strolled along the harbor’s edge watching the behaviour of some sailboats racing. Remembering a recent race regatta series I participated in in the Auckland New Zealand harbor last winter also brought up this topic of tides and tidal current. In one race in the series, we were racing back up the harbor while the tide was ebbing (going out). Consequently, the current was racing in the other direction. Our tactic was to stick to the sides of the harbor as close as possible where the current is the least. Unfortunately all the other boats knew to do this as well and this created a pretty big mess of all the fleet tacking on top of each other. “Starboard” was the call of the day as each boat established their stand-on position over the other. Every now and then one boat would break out and try to brave the current instead of the tacking mess only then to rejoin the fleet as they were dragged backwards. It was pretty exciting actually, although our skipper was stressing a little.
There was pretty much nothing we could do except tack tack tack and keep a very diligent watch for traffic ducking and tacking to give way when required. The skippers were trading expletives with each other across the water more in this race than I’d seen in any other. LOL
How Tidal Flow Works in a Harbor
In a channel, current will run strongest in the deepest parts typically towards the center, unless there is a bend in the channel then the current will run strongest on the outsides. Just think about the last time you watch water flowing in a river to visualize. So your best bet when trying the go against the tidal current is to hug close to the sides and on the inside turn if possible. At an extreme case I had a friend in Sydney harbor who won a race by waiting out the worst part of the tidal current by throwing down the anchor. Not sure if that’s against any official race rules but it’s pretty funny.
Also take note that current flows “relative” to the tide period but slack water does not necessarily match high and low tide times especially in harbors. Tidal current is determined by the local effects of the upstream harbour shape and weather, not just the sinusoidal tidal period. That comes as a big revelation to some. In fact, I physically had to show my skipper prior to the start of a race one day last winter.
Real Example of Tides in a Harbor
Observe the following which is Auckland New Zealand harbour, one of the more heavily raced harbors in the world.
Chart of in Auckland Harbour
Now look at today’s tidal period;
Sinusoidal Tide in Auckland Harbour
- High tide: 3:52 am
- ½ tide at 6:55 am ebbing (going out)
- Low tide: 9:57 am
- ½ tide 1:07pm flooding (coming in)
- High tide: 4:16 pm
- ½ tide: 7:22 pm ebbing (going out)
You might assume that minimum current occurs at high and low tides ie 3:52 am and 9:57 am and 4:16 pm while the max current occurs at ½ tides at 6:55 am and 1.07 pm
But now look at today’s current predictions:
Tidal Current in Auckland Harbour
- Min current flow was at 3:15am (45 minutes before high tide)
- Max current flow ebbing was at 5:16 am (1 hour 39 minutes before ½ tide ebbing)
- Min current flow was at 8:15 am (1 hour 45 minutes before low tide)
- Max current flow flooding at 10:54 am (2 hours 13 minutes before 1/2 tide flooding)
- Min Current flow at 3:51 pm (25 minutes before high tide)
- Max current flow ebbing at 5:57 pm (1 hour 25 minutes before ½ tide ebbing)
A quick analysis of this shows that the current matches in time the flooding tide more than the ebbing tide. This empirically supportis the statement above about how the upstream shape determines the current flow out.
As a specific example, lets say it is 8:30am on the day shown. From a tidal analysis you would think that the tide is ebbing and so an early morning race out of the harbour you’d probably stick to the centre of the channel. However the prudent sailor doing a current flow analysis would see that the current has already turned to flood and would stick to the sides of the channel. All things else being equal, prudence would win.
- Don’t assume that the current is slack at high and low tides
- Stick to the edges of the harbor when going against the flow
Navionics Electronic Chart
In this article I used the Navionics iPhone app. I pressed and held my finger over the diamond shaped T to get the tidal info and the diamond shaped C to get the current info. When you have such an electronic chart, look for these diamond T’s and C’s scattered through out. On iPhone and iPad simultaneously push the home button and the power button to get a screen shot.
Tide and Current icons on an electronic navigation chart
Rule of Twelve
While we’re on the tidal topic I might as well discuss the rule of twelve regarding a sinusoid. It’s a good general piece of knowledge to know since tidal heights generally follow a sinusoid shape (except in weird tidal places in the world like the Solent in England where two high tides occur about 1 hour apart).
In the first 1/6th of the time between high and low tides, the height changes by only 1/12th of the full amount
In the next 1/6th the height changes by an additional 2/12 (=1/6)
In the 3rd 1/6th ie half tide the height changes by an additional 3/12 (1/4)
Adding 1/12 + 2/12 +3/12 = 1/2. So at half tide, the height has changed to ½. That makes sense but looking back and assuming a diurnal tide (6 hours between high and low), in the first hour the height has only changed by 1/12th. That’s insignificant. At the end of the 2nd hour the height has changed by a total of 3/12ths = ¼. That’s still pretty insignificant.
What this means is that if you’re relying upon the tide to increase the depth in a shallow area, then even with a 10 ft (3m) tide, 2 hours after low tide, it has only come up 2.5 ft (0.75m). Best you wait until half tide at least when the ½ of the height change has occurred (5 ft (1.5m) in this example).
NauticEd Coastal Navigation Sailing Course
For a full discussion on tides, tide table, how tides work and why there are two tides in one day when the earth and moon only rotate relatively about each other once per day, take the NauticEd coastal navigation sailing course. You’ll also be able to brush up on your navigational skills which isn’t at all a bad thing.
Coastal Navigation Sailing Course
This article was written by Grant Headifen, Educational Director for NauticEd Online Sailing School
Where were you over the holidays? Sailing?
If you tried to email us over the holidays, you would have gotten a polite “out of the office notice”. We were busy catching up with our Canadian friends who have been sailing the world with their three kids for the past four years on a 42 ft PDQ Antares Catamaran. Early last year we meet up with them in New Zealand in the Tasman Bay (see the video in New Zealand). This year we meet with them in the inland water ways around Brisbane and the Gold Coast of Australia. Sailing with the Ellsay’s on Stray Kitty is a real insight to the lifestyle of world cruisers. They’ve certainly got it down and watching the kids in action with the lines and fenders was pretty impressive. This adventure was particularly interesting because of the intercoastal navigation issues in and around all the waterways. So here, I thought I’d relate a few stories as highlights of the issues and proof that both theory and practical knowledge is king.
Waterways south of Brisbane
One beautiful sunny afternoon we were anchored at a place called Jumpingpin. We went for a walk along the beach and came across a uniquely Australian experience by encountering a group of wallabies hoping across the sand.
Jumpingpin - A popular day stop (so long as you anchor properly)
After a nice stretch along the beach we returned to the boat just in time to beat an approaching thunderstorm. And in Ausy fashion, this one turned out to be a real beaut. About the time winds reached a peak of 40 knots we realized the washing was still on the lifelines and my bald head got a real pelting with the huge sideways rain drops as I brought in the now drenched washing. All the while that I was doing this, Chis, the skipper was pulling out fenders ready to fend off any of the at least ten yachts that were now dragging anchor.
To make matters worse, the tidal range in the area is around five feet. This creates particularly strong tidal currents in the narrow waterways. As the thunderstorm pelted us, the tidal current had risen to about 5 knots and was flowing in the same direction as the wind. This put huge forces on the anchors and it was pretty hair raising to see how fast the boats that had drug anchor were flying by. As an observation, almost all of the boats that had drug anchor and were now trying to reset them were using CQR plough type anchors.
The Dreaded CQR Anchor. Leave it at home.
Stray Kitty uses a Rocna roll type anchor and it held fast. Of course, in typical style of many boaters, the scope used was also way to low on boats that were dragging. And so we were able to watch the comedy of anchoring errors unfold in front of us. In reality there was no comedy. Some of the dragging boats were coming way too close, way too fast.
Boats anchored at Jumpingpin. Anchor scope too small and CQR Anchors caused dragging.
Next, one of the boats that re anchored abeam of us did it a bit too close and so as the current reversed later that night we began to come dangerously close. We elected to raise anchor and reset further out into the channel. However this presented quite a challenge with site selection. The wind was flowing in one direction whilst the current was in the other, and, we knew the current would again reverse before we awoke. Couple this with the difficulty in determining distance at night from other boats made us both glad of our previous anchoring experiences and knowledge. The worse scenario consequence of dragging anchor in the night and being washed out of the protected albeit high current waterway into the huge breakers coming in thought the cut was not one I wanted to spend to much time thinking about.
Another challenge was the markers. First off, Australia abides by IALA-A system which is opposite to the America’s IALA-B system of navigational marks. I.E. red right returning doesn’t work – it’s green on your right when returning. And in the USA the intercoastal water way fairly consistently uses green to seaward along the full length of a waterway with specially marked intercoastal day marks. IE heading from New Jersey past Florida and onto Texas you would keep green intercoastal daymarks on your left. In Queensland, they don’t seem do that and so the green and red swap inconsistently up and down the waterway.
Red Day Marker
Sometimes the red and green swap sides, some times they don’t. They seemed to use the yellow special purpose marks to designate a channel intersection rather than a preferred channel marker with red over green or green over red that is used in the USA.
Special Purpose Marks designating a channel intersection
Twice we were caught out nearly heading onto a sand bar because the day mark swapped over. The Australian navigation system also uses cardinal marks. Being able to read these quickly kept us out of trouble when it came to isolated dangers.
East Cardinal Mark (Safe Water to the East of this mark)
On top of all that, sand bars move and so your highly relied upon GPS map showing the exact position of the day marks can’t be trusted. When sand bars move the local coast guard move the day marks to remark the proper deep channel. So you can be looking at your GPS telling you that the channel is in one place when the marks tell you some thing else. Which do you trust? You have to trust the day marks.
Waterway Chart. Even with GPS don't rely on the chart. Follow the day markers.
Twice we had to turn right angles to follow a day mark went the GPS was telling us that the depth was one foot. Of course a slow and easy pace combined with the depth sounder readings is essential. Still, when you have only two feet to play with below the keel, sometimes it’s not the greatest comfort.
We tried our best to time our sailings each day with the changing tidal current so that it would help our speed. On the day that we approached Surfers Paradise this was not the case however and our 7 knot though the water speed only gave us a three knot SOG (speed over ground) due to current. On one particular day we had to ensure that we crossed under powerlines at half tide or lower due to the height of Stray Kitty’s mast.
Under Sail (actually me just posing for the shot)
As hairy as I seem to have made the above sound, we definitely had a spectacular time visiting this area. It’s off the beaten track when it comes to top charter locations around the world and probably for good reason due to the complexity and also due to the spectacular and more popular Whitsundays area to the North.
There are two highly relevant NauticEd sailing courses to this article. The first is the NauticEd Anchoring a Sailboat Sailing Course. I’d venture to say that none of the power boats that drug anchor that day would have done so if they’d taken this course. First thing they’d have done was to leave the CQR in the garden at home and secondly they’d have understood scope a little better. Surely those people are embarrassed that they drug so badly.
The second course that would really help someone enjoy our intercoastal venture as much as we did would be the Coastal navigation sailing course. This course teaches in depth the navigation marks of both IALA-A and IALA-B systems including cardinal marks.
The other comfort to the whole trip was having very experienced world cruisers on board. After a hard day of tidal currents, thunderstorms, crazy reversing navigation day marks and shallow waters we were rewarded with gourmet type dinners under the southern sky. The crew of Stray Kitty, after living on their cat every day for the past four years, did not sacrifice food quality one bit and were even able to whip up a birthday cake for me on the 31st.
The Crew of Stray Kitty (next to their Christmas Tree)
Other tasty delights on the menu were kangaroo, pork roast, shrimp pasta, steaks, roast turkey, gammon (cooked in the oven on board), plenty of salads and cookies. Some great Australian and new Zealand wines were poured on top of the above in the warm southern hemisphere summer over the Christmas and 2011/2012 new year.
Christmas Dinner Table Setting Aboard Stray Kitty
Thanks to Stray Kitty and her Crew!!!!!!!!!!!
Christmas Dinner with Alexandra, Andrea, Grant, Ryan, Christine, Cari, Chris, (Vanessa photographer - Nikon D3100) on Stray Kitty - a 42 ft PDQ Antares Catamaran
The posting here is not a course in celestial navigation by any means. However it’s meant to simplify a few principles for you so that you’ll at least have some sort of celestial orientation. And… perhaps it’ll inspire you to learn the aging art.
This was written by Grant Headifen, Educational Director of NauticEd. NauticEd provides online sailing courses and Sailing Certifications accepted by charter companies worldwide.
Latitude: In the northern hemisphere, finding latitude is simple using one of the greatest gifts to human kind – The North Star. What ever angle the northern star is at from the horizon, that’s your latitude.
Imagine you’re an ant sitting on the top of an apple looking at a spot directly above you on the ceiling then the spot is 90 degrees from the surface you’re standing on. If you’re standing half way around the apple then you’d barely see the spot but it would be horizontal to the surface you’re standing on and so the spot would be at zero degrees. And if you were ¼ of the way down the apple then the spot would be at 45 degrees etc. ie the northern star is the spot on the ceiling to us.
You can also find latitude using other celestial sightings but they involve table lookups and are slightly more complicated. Not meant for this post and also note that there are a few more complicated variables not taken into account during this simplistic explanation like the height of your eyeballs above the earths surface etc etc. But at least you’ve now got the principle.
Longitude: Now this is a fun one and in an incredibly easy principle. But years ago (early 1700′s) while the principle was easy then the execution was difficult. Read on to see why.
The earth rotates through 360 degrees in 24 hours. That’s 15 degrees per hour. By convention, when the sun is at it’s highest point in Greenwich, it is noon in Greenwich. That means that at a place that is 15 degrees to the West of Greenwich the sun will be at it’s highest point one hour later. Six hours after Greenwich the sun will be at it’s highest point somewhere in over the USA and 12 hours later the sun will be at it’s highest point in New Zealand.
Animation of time zones
So if we know the time in Greenwich and sun just reached its highest point where we are then we can calculate our longitude.
Lets do a few examples. If it is 6 pm in Greenwich and the sun just peaked overhead here, then I am 6 x15 degrees to the west of Greenwich which is 90 degrees West which is right near St Louis Mo.
If the sun peaked overhead in Los Angeles what time would it be in London.?Well LA is 118.15 degrees West (from Google earth). Divide that by 15 degrees per hour and we get 7 hrs 53 minutes. Now since the times zones are created in bands this would round up to 8 hours. Thus it would be 8pm in London.
You’re sailing in the Greek islands in the Mediterranean and a little bird just told you your latitude is 34 deg 54 minutes north but failed to tell you the longitude. Fortunately you have your handy sextant and just as you take a shot, the sun just reached its apex overhead. You look at your watch and the local time is 12:10:48 pm. Where are you?
Since you’re in time zone B you are 2 hours ahead of Greenwich. Thus the time in Greenwich is 10:10:48 am. And since the sun peaked just now (=noon) then you are 12:00:00 minus 10:10:48 = 1 hour 49 minutes and 12 seconds from Greenwich. Putting this into decimal time this is 1.82 hours. Multiply this by 15 degrees per hour and we have 27.3 degrees East or 27 degrees, 18 minutes East.
You’re in the harbor north of the town of Kos on the Island of Kos.
That was incredibly easy, so why all the hoopla back in the 1700′s? The King of England even offered up a ₤10,000 reward to anyone who could solve the issue of Longitude. The above math was well known but the issue was telling the time. No one could accurately keep time at sea. After 27 years of work on the project, John Harrison, finally invented the Chronometer more commonly known as the watch. The watch was not susceptible to the sudden crashes of waves at sea and thus kept proper time.
James Cook on his second trip around the world in 1772 sailing on Rendezvous, took Harrison’s watch with initially much skepticism. Stating that he’d give it a try. After six months at sea, Cook stated that the Chronometer would almost certainly become the way of the future for Navigators. Cook then went on to reposition many of the Islands in the Pacific including Tahiti, his favorite island. His map of New Zealand astounds people even today with its accuracy.
Again there were a few simplistic assumptions taken in that explanation. But now, at least you understand the principle of longitude determination from a noon shot of the sun. You can also determine your latitude from a noon shot of the sun as well using tables and a bit of math. Again beyond this posting.
If you’d like to delve deeper into these topics, NauticEd provides online sailing lessons and an Introductory Celestial Navigation Sailing Course, or maybe you’re just happy with your handy boring ol GPS.
How to Heave To
The books simply say to tack the boat and leave the head sail cleated to windward and turn the wheel all the way to windward (tiller to lee). While that’s correct, there are a lot more things to think about to pull it off correctly. This article is part of the training in the Skipper Sailing Course and is written by Grant Headifen, the Educational Director.
There are a few reasons you might want to heave to.
- Lunch, simply taking a rest, or instructor debriefing
- Storm Tactics and Reefing
- Man over board recovery
- Boarding by another vessel (ie, crew change during a race, or law enforcement safety inspection)
A Cool Trick about Heaving to!
The first thing to think about is (if you can) lie in a heave-to position so that your boom is on the port side. Why? So that you’re technically sailing “on starboard tack”, putting you in a more advantageous stand-on position with regard to the Navigation Rules vis-a-vis other sailboats “on port” tack. Wouldn’t want to disturb our lunch now would we? It’s not a big deal but just something most people may not have thought about.
What is Heaving To?
When you are successfully hove-to, your sailboat will be in a stable situation with the mainsail and headsail still up. Your forward speed will be minimal and you’ll be sliding downwind slightly. This makes it an ideal strategy for the situations above. Essentially you’re under full sail but nearly stopped! Cool eh?
How Heaving to works
The mechanics of the heave-to situation is that the forward speed of the boat has dropped to a minimum because the head sail is back winded (aback) and the main sail has been eased out far enough to reduce nearly all of the forward driving lift on the sail. The backwinded head sail creates a large turning moment on the boat to turn it downwind. As the boat turns downwind however the boat tends to pick up a little speed. As the boat picks up a little speed, the windward locked wheel causes the rudder to turn the boat back upwind, killing off the speed. It creates a little see-saw action. You can adjust the see-saw action by adjusting the set of the headsail, the mainsail, and the rudder angle. Each boat will see-saw a little differently in differing wind conditions and due to the distances of the rudder and the headsail center of pressure positions around the hydrodynamic pivot point of the vessel. Once the boat is settled, by making small adjustments to the angle of the rudder, the amount the mainsail is eased, and by the “depth” or flatness of the headsail, a skilled operator can make very useful adjustments to the exact way in which the boat is lying to the wind and seas. Practice practice practice! When that storm comes, you’ll be glad.
How to Heave To
Once you’ve got it down, you’ll enjoy having this little skill under your belt but you’ve got to practice it a few times. To enter into a hove-to position, if practical, start out on a on a port tack with the headsail sheeted in tight. Tack the boat slowly onto a starboard tack (bleeding off some speed while head-to-wind) but leave the headsail cleated (ie don’t tack the headsail). Turn the boat so that you’re on a close reach (60 degrees off the wind) and let out the mainsail most of the way out so that it is luffing. Now wait until the rest of the boat’s headway speed bleeds off. That’s the key part. If you turn the rudder to windward (the wheel to windward or the tiller to leeward) before the speed bleeds off, the momentum of the boat may carry it through another tack. Once the speed has bled off, turn the rudder all the way to windward (wheel to windward or tiller to leeward) and lock it in that position (lashing the tiller).
Heaving to in a Storm
It’s really important to realize that this is a completely wise thing to do in a storm. With a huge caveat, make sure you have plenty of sea-room distance to leeward on the track of your hove-to reckoning, avoiding shoals, or the other hard stuff (like land!). Heaving-to in a storm gives you and your crew a rest from the elements. And it can be a safer means of riding out a storm rather than trying to sail it out. The boat is in a completely stable position. You should probably lower or deeply reef the main or raise a storm trisail (very small mainsail) as well as a small headsail to reduce loads on the rig. Here’s the kicker that is really cool – since the boat will be slipping sideways, a wake is left to windward. Any breaking waves hit this “slick” and flatten out, thus reducing the wave action on your vessel. Now that’s really cool.
Heaving To in a Sailboat in a Storm
A Heave To Must
When you’re settled down into the heave to position and every thing is balanced, use a preventer line to “prevent” the boom. This will prevent the boom from slapping around wildly with sudden variable gusts, save wear on the rig, prevent an accidental gybe or worse yet a bonk on the head if you need to go forward.
Using Heaving to in a Man Overboard Situation
Heaving to can be a very effective crew over-board recovery technique. The very moment the victim goes over the side you can crash tack the boat and go into a heave-to position. You must be sure that the victim is able to swim, that they did not sustain injury whist falling. It’s your call on this one but it’s a technique not often taught and so isn’t considered in the panic but, it will keep you from getting too far away from your friend in the water which is clearly the biggest danger. Me? I’d still get the engines on. On that topic, the biggest danger they say from turning on the engines is not chopping your friend up, you’re smart enough not to do that, it’s from getting a line wrapped around the prop in all the panic. So just make that’s part of your “engines-on” routine in crew over-board practice. Next time you’re out practice man (or woman) over board.
There you have it, you’re now a heave to expert. NOT! You haven’t practiced it enough yet! And while you’re out there practicing it, have fun. Or should it be the other way around???
Learning to sail is easy with NauticEd Qualified Crew Member Course !
Qualified Crew Member Course
Imagine if you could just hang out at the yacht club every day – how much you’d learn from everyone. That’d be cool. Well … now you can!
It’s a very cool piece of technology we just installed on the NauticEd site. It’s called DisQus and the concept is based on crowd intelligence. It shows how the power of the Internet can beat out a boring ol’ book. Thousands of websites have already introduced it and it’s ideally suited for you and NauticEd.
On every page through out all of the NauticEd sailing courses you can now discuss (Disqus) the topic at hand and read what others are saying about the topic. For example, lets say you know a few things about how to dock a boat using spring lines but are a bit confused about backing into a slip. Right in the course you can add your springing off knowledge and ask all other students their opinions on reversing. When any one comments and adds to those comments you’ll be sent an email (if you want). You can add pictures and diagrams if you want. Our part is to use the crowd intelligence to improve our sailing course material for everyone.
You can even invite facebook friends to join in on the conversation and help out.
Crowd-Intelligence with DisQus and NauticEd Sailing School
How cool is this? Now you’re tapping into the knowledge of thousands of other NauticEd students – wow that’s a big yacht club with a lot of combined experience. You’re not on your own any more. It’s not just us and our authors pontificating about sailing – it’s a real open discussion and conversation in real time.
But like any party or social – you can’t just stuff your mouth with cake and listen – you’ve got to add your two cents. And you can’t be rude because people are watching and the bouncers will bounce you out. So come on join in – ask questions and post your knowledge.
To kick off, I’ve gone in and asked a few questions and posted a few comments in each course topic. I invite you to join me and start new conversations. Like who gives way – the paddle board or the sailboat? Do you know the answer?
Login and give us your opinion to the Rules of the Nautical Road topic embedded in our Rules course.
And to celebrate the launch of crowd intelligence via DisQus, we’ll award a free sailing course of choice to a student randomly picked from everyone who participates in the conversations over the next week (through May 25th) . Hint, the more you talk the more we’ll notice.
We’ll see you on NauticEd.
You see this – what do you do? What should you have done?
Last week, Editor and Chief of Sail Magazine, Peter Nielsen, and I chartered a 38 foot catamaran from the local Moorings Base in the Bay of Islands, New Zealand, on a bareboat yacht charter. Peter was writing a story about sailing in the south pacific which will come out later this year (keep and eye out for it). We snapped some great shots, did some great sailing, caught lots of snapper and ate like kings in some of the most beautiful bays. The Kiwi weather really turned it on for us and the New Zealand Tourism board will be happy as Peter had a great time and surely will be writing up the Bay of Islands as a must see sail area.
So we sailed up into the Kerikeri inlet to the north of Moturoa island and past the stunning Black Rocks – where in the old days whales were so abundant here that whalers used to harpoon the whales from these rocks. The wind was 20 knots out of the north so it made for a nice beam reach into the inlet. On the way back we decided to do a run through the Kent Passage. About 100 meters back I noticed power wires crossing from the mainland to Moturoa Island.
Kerikeri Inlet - Bay of Islands New Zealand
“Hmmmm”, I said to Peter “what do you think about those”.
“Hmmmm” replied Peter.
We both looked at the GPS which noted nothing on the electronic chart.
A quick consult of the paper chart showed the following image with a very hard to see thin line.
Not much information and no height datum.
“Hmmmm” we both said
We could now see a sign on the shore warning of the DANGER. But we could not read the specifics.
“Hmmmm” one more time. 30 meters to go!!!!!
With out any more hesitation and with prudence taking over, we brought the boat up into wind, turned on the engines and motored the boat away from the lines.
We got out the binoculars and were able to see the sign marking which indicated 23 above MHHW.
From the manual in the chart table, the mast height above the water line on a Leopard 38 is 19.1 m. That made it safe to proceed.
MHHW is the mean higher high water. This is the average height of the high tide during spring tides. Bridges and power wires are marked as such to indicate safe passage at these times. This is opposed to chart datum depths which are marked as MLLW.
So the lessons learned here:
- If you’re unsure of situations like this bail out. We did the right thing. Not that we were under any time constraint, but there is no time constraint that is worth really messing up like what could have happened.
- Know your mast height. When pilots get rated for an aircaft they spend hours and hours studying the characteristics of an aircraft. Yet when we go charter a boat – at best the Yacht Charter Base will spend maybe an hour with you.
Off the top of my head, here’s a list of boat characteristic specifications that you should know about when chartering a Sailboat on a Bareboat Yacht Charter sailing holiday.
- Mast height
- Keel depth
- Offset of the depth meter (some charter companies add in a 5 ft offset below the keel, some do it at the keel, some do it at the water line and some don’t even know)
- Beam Width (for unfamiliar marinas)
- Number of water tanks
- Max cruising revs for engines
- Boat speed at max cruising revs
- Length of anchor rode
- Reefing wind speeds
Typically, you’re not going to be too concerned about fuel capacity with a week to 10 day long yacht charter, but it’s prudent to watch fuel usage.
There is a lot of other things to learn about a charter boat like locations of safety gear etc. But this is more about the boat dimensional characteristics. Please feel free to add to this blog about any other dimensional specifics you believe are important.
I’ll end the post with a bit of humor.
Even if you don’t have one on your sailboat charter – one day you’ll be helming someone else’s boat with an Electronic Wind Meter and you certainly want the owner to be confident at what you are doing. There’s a couple of secrets so read on.
He’s what happened – I took out two guys who were experts at racing at their local yacht club. The trouble for them was they both kept on having to look around the bimini on our 373 Beneteau to get a peak at the wind vane at the top of the mast. I tried to tell them to use the electronic wind meter 18 inches from their face but they’d have nothing of it. It wasn’t pure enough. Then day turned to evening and evening to night. IE no wind vane watching at night … and they now had sore necks.
Wind meters are cool, and given the right calibration they’re pretty accurate. The resolution is greater than eyeballing the wind vane and thus you can be more consistent with your angle to the wind. I’m necessarily saying they are better than wind vanes but I’m definitely saying that being both vane and meter skilled adds to your sailing abilities.
Here’s a typical Wind Meter – it shows that the wind is 42 degrees to starboard. You’ll see a red dot at the bottom. Next to the red dot are the words TRUE and APP (apparent). The dot represents which wind direction the meter is measuring. In this case Apparent. For a discussion on True vs Apparent Wind see the NauticEd Skipper Course. The green and red don’t mean any thing other than green is the starboard side of the boat and red is port.
Typical Wind Meter
LEARNING TO SAIL WITH AN ELECTRONIC WIND METER – SECRET NUMBER (1): This goes to working with wind vanes as well. When making heading adjustments, keep your head out of the boat. This means DON”T watch the meter or vane as you turn the boat. You’re guaranteed to over shoot your desired new heading. Also it’s dangerous traffic wise. Watching the meter or vane means you’re not looking out for traffic during a turn. IE When driving a car and turning at an intersection you never would look at the speedometer. It’s too dangerous and besides what’s the point, you can best judge a safe speed in the intersection turn by the rate things are going past your car. Same same – watch things outside the boat when you turn.
Imagine this – make a 90 degree turn in your car using a compass and stay exactly in the center of the lanes. Well maybe Al Pacino (acting as a blind guy) in the oscar winning movie Scent of a Woman could do it but me? Never in 100,000 trys. Again – same same why would anyone make a 10 degree adjustment to their heading looking at the wind vane or wind meter. You can’t stay in the center of the lane (new desired heading).
I’ll provide an example scenario: Assume you’re sailing along on 40 degrees apparent (your wind meter and vane point 40 degrees off from the front of the boat). You notice the wind direction changes to give you a 10 degree lift (a lift means the wind direction has changed so that the wind meter or vane points more towards the aft than before – in this case now 50 degrees). You want to turn upwind to bring the wind back to 40 degrees. Here’s how to make the turn: Pick out something on the horizon dead ahead then pick out something 10 degrees upwind from that point. Turn the boat to the point with out looking at the wind meter or vane. Once you are now sailing at the new point, check how you’re doing against that 40 degrees and make another adjustment in the same manner.
This was so basic it’s not too much of a secret, but you’d be surprised … one time teaching in my sailing school I actually had to cover up the wind meter as I could not get my student to stop watching the meter and to watch the horizon instead. As soon as she started watching the horizon her whole sailing world changed. She could hold a course, tack, gybe make adjustments with out over shooting – everything. Her whole problem was that one little point.
Here’s another scenario similar to a wind meter/vane turning problem – your navigator says to come onto a new heading of 160 degrees. Don’t watch the compass during the turn. First determine how many degrees the turn is, pick out a point on land or even a cloud to turn to. Make your turn watching out side the boat – then check your heading.
LEARNING TO SAIL WITH AN ELECTRONIC WIND METER – SECRET NUMBER (2): Don’t teach new people at the helm anything about the wind meter or the wind vanes. It’s too confusing – First, just have them focus on sterring to points on the horizon and making turns to new points on the horizon that you pick out for them.
LEARNING TO SAIL WITH AN ELECTRONIC WIND METER – SECRET NUMBER (3): Don’t stare at the wind meter and try to figure out which way you should turn the helm to make the meter move in any one particular direction. That’s too hard because it’s backwards from what you’d think and guaranteed you’ll get it wrong when some one embarassing is watching. And as above, make sure when you’re explaining the wind meter to a new helmsperson that you disallow them from similarly using it to figure out which direction to turn.
Instead, the wind meter should be used to determine how many degrees off the desirable wind angle you are and if the turn should be towards the wind or away from the wind. That’s all. Example – lets say we want to be flying 30 degrees APP off the wind. Using the wind meter above, we’re 12 degrees away from 30 and we are heading too far down wind. So lets pick out a point on land or a cloud that is 12 degrees upwind (the what? Port or Starboard) from our current heading.
The NauticEd Skipper Course is chocked full of tips like this one. Get started today and register for the NauticEd Skipper Sailing Course
Have you played with our FREE Sailing simulator, NED? We use interactive tools like this to quickly and effectively teach sailing skills.
NED the Sailing Instructor