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NauticEd International Sailing Education is the proud title sponsor for the May 12th 2016, Oregon Offshore International Yacht Race. Two of NauticEd’s practical sailing schools, Island Sailing Club and Vancouver Sailing Club are a significant part of this title sponsorship and many of their students are participating.
The race, in its 40th year is 193 miles long and begins off the coast of Astoria, Oregon and finishes in the harbor at Victoria, British Columbia.
As part of the education sponsorship, NauticEd is giving away 6 Captain’s Sailing Education Packages to 6 lucky participants. This represents over a $2000 donation to the cause of keeping people save on the water with advanced sailing education. View the contents of the Captains package below. This represents extensive and vital education for all sailors wanting to sail more than 20 miles off shore or over long distances.
All participants are encouraged to create a new account with NauticEd whereby they will receive 2 FREE NauticEd courses, Navigation Rules and Basic Sail Trim and a FREE sailor’s electronic logbook.
Students of Island Sailing Club and Vancouver Sailing Club are encouraged to join in on the race.
WINNERS: If you are a winner of one of the 6 Captain Education Packs, sign up for a free account at www.NauticEd.org/signin then send us an email. Once we verify with the Committee your prize, we will drop the 12 sailing courses into your curriculum. Congratulations!
ALL OTHERS: Set up a free account at NauticEd here Sign in to NauticEd you will automatically be given two free courses and a free sailor’s electronic logbook. You’re Welcome!
We think this is the world’s best sailing App and for good reason.
NEW APP WAS UPDATED ON SEPT 20th 2015
First off, it is free (that’s good) and second off with that you get NauticEd’s free course on Navigation Rules. Pretty soon we’ll also add NauticEd’s FREE Basic Sail Trim Course.
In addition, any course that you have invested in with NauticEd automatically appears on your App. And to top that off, you can also take your tests for all your courses on the App offline. That’s a big wow!
There is zero reason not to download the App – and imagine if everyone did and took the FREE Navigation Rules Course. You could stop worrying about if the “other guy” heading at you knows the rules or not. So spread the word generously.
Bored in the doctor’s office? Take the Free Rules of the Nautical Road test!
If you think this is the greatest idea on the planet or at least just a very good one, please like us on facebook.
Posted by Grant Headifen, Global Director of Education – NauticEd.
One of the greatest things I love about my job is the ability to apply the latest technology to the sailing education industry – it is so exciting to be leading the world in this area.
And – today comes as a greatly awaited day for us to announce one of the bigger innovations in not only sailing education but in the entire community of eLearning itself.
I’d like to introduce Nano-Forums!!!!!!!!
Please watch this video and you’ll see why our Sailing Nano-Forum is so innovative and such a benefit to the sailing community at large – You’re Welcome! It represents a MASSIVE investment in technology over the past 6 months. Ummm like really REALLY massive but we think it’s worth it!
We think you will really enjoy it.
Oh and btw since this is new technology to the world and we invented it, we are coining the phrase NANO-FORUM right here right now!
What it ultimately means is that we all now can collectively crowd source information in targeted specific areas and re-use the crowds knowledge for educational drill down topic purposes in a way never been done before.
Just watch the video – you’ll get what we are talking about.
Please engage in the Nano-Forums through out our courses. Look for the SeaTalks button at the top right of every page of the course.
Start by taking the FREE Navigation Rules Course at:
It is pretty amazing – you can now see the content of all your sailing courses in your curriculum offline AND take the tests offline. Once you reconnect, the test results are sent up to the cloud. i.e. it does not matter where you take the test – on iOS or on online on your computer.
NauticEd Sailing App
It is pretty amazing – you can now see the content of all your sailing courses in your curriculum offline AND take the tests offline. Once you reconnect, the test results are sent up to the cloud. i.e. it does not matter where you take the test – on iOS or on online on your computer.
Right now it’s for iOS – an Android version is coming.
Also in the App, is the ability to add to your new style logbook (launched in 2014). So on the dock after a day of sailing, just right there – add the day and it will show up in your sailing resume.
A really amazing feature is that you now carry your sailing resume and certificate with you on your phone at all times and can email it in an instant to anyone.
If you like this post – please LIKE it on facebook and g+1 it – it really helps us grow. Thanks!
Tides are often intimidating to sailors and so, many sailors tend to try not to sail in tidal areas or just ignore them hoping that if they stay deep enough there is little to worry about.
The point of this article is to de-intimidate you about tides by explaining the predictive nature and how to access information easily about the local conditions.
But first let’s start with an intimidating situation to set the worst case then we’ll take it up from there.
On a recent trip to the UK we visited Ilfracombe in the south west coast of England. This whole area and further up the coast towards Wales exhibits one of the highest tidal areas on the planet. Ilfracombe has a 9 meter tide – that’s 30 feet for imperial speakers. The point of the visit was to experience this, get the photo and write about it. What we didn’t plan on was a real life threatening situation – not really but sort of – close(ish) – kinda -could have gotten bad – well, at least wet. Read on.
Here is a pic with the tide mostly in in Ilfracombe.
The tide is in – boats happily floating
Here is the same place a few hours later.
The tide is out – boats sitting on the bottom high and dry
9 meters – 30 ft is huge. Ilfracombe as a normal diurnal tide meaning there are two high tides and two low tides every day. From high tide to low tide is around 6 hours and 20 minutes. The rate of water movement for all that to take place over 6.3 hours is hard to conceptualize. As we walked along a flat beach – it seemed like every lap of the waves caused the water to progress up the beach about 6 inches. To experience it is an awesome wonderment.
Throughout the day as we watched, rocks covered and uncovered and some turned into rather large islands from nothing.
Not only is the vertical movement of the tide a concern, but the currents produced from the moving water is of a potential greater concern. We went out fishing on a kayak and were constantly weary of our position moving relative to the land and of the swirling directions of the current flow. 300 meters out we were being pushed in one direction quite fast, 2-3 knots, but closer in we were drifting in the opposite direction at 1-2 knots. And most of the time it was hard to even get the line on the bottom due to the current. According to the extremely hospitable local we stayed with and took us fishing, every year many people have to be rescued from the current. Mostly just due to the under estimation of the conditions. I’m a pretty good and fast swimmer, it takes me about 20 minutes to knock out 1 km in the pool with no waves. That’s swimming at about 1.5 knots. Thus even I would be swept out faster than I could swim.
So what actually happened was that one of our party climbed down onto some rocks to get a better place to fish. An hour later he turned around and was completely cut off from the land by the rising tide. Since it was about half tide the water level was rising quite quick and was pouring over a weir about 6 inches of flow height into a basin created by a walk way that was completely covered and thus stopping his escape. We saved his sole by dropping me off the two person kayak onto land and Martyn returning to go get him. Actually pretty funny and I was grateful it happened to create the story here but… this is the stuff that you hear about. My friend was simply not used to and did not expect such conditions from any experience he has had in the past. Night time and a few waves and cold water and it could have been lights out.
The Rule of Twelves
Slack water occurs at or close to high and low tide. At this time the water is hardly moving and so fishing and swimming can be safe (ish). The highest current times occur at or close to ½ tide. However there is not a linear scale. It’s on a sinusoidal scale and is approximated by the following rule of twelves.First, the rule of twelves is not entirely accurate but it’s not a bad way to think about a rising or falling tide.
The tide rise and fall approximates a sinusoidal curve i.e it starts out slow then increases the fastest at about half tide then slows down to a very slow finish.
See the following animation (best viewed with Chrome or Safari). This is a tide rising over a 6 hour period using the rule of twelves as a basis for tidal rise.
When you push the play button the rising tide goes slow and not much has happened in the first hour, But by 3 the tide is rising fast. In the last hour the tides is rising to it’s final completion slowly.
Thinking linearly you would say that the tide has to rise 30 feet over approx. 6 hours that means 5 feet per hour. But the animation shows 2.5 feet in the first hour. Between 3 and 4 it averages 7.5 feet per hour and the last hour is 2.5 feet. This then is how the rule of twelves helps you approximate a tide in your head.
With the Rule of Twelves you start out with 1/12th rise in the first hour. Then 2/12ths rise in the second hour then 3/12ths rise in the 4rd and 4th hour. Then back down to 2 /12ths in the 5th hour and 1/12th in the 6th hour.
This is an ok approximation to the sine curve. In addition, tides are only approximated by a sine curve. So realize when applying this rule, that it’s an approximation. But not too too bad actually.
In our Ilfracombe 30ft (9m) example here is what the rule of twelves looks like and assuming a 6 hour tide (which it is not there it is 6:20 between high and low tide)
End of hour
total 12ths inc
tide height ft
Now in reality take a look at this below. This is a screen shot from the World Tides App for Ilfracombe on Sept 27 2014. It shows an 8.1 meter (26.6 ft) tide rise on that day. Low tide is at 2:20pm and high tide is at 8:40 pm. The low tide is 1 meter above the printed chart reported datum. Thus the rise in height that day will be 8.1 meters. (Chart Datum in the UK and most of the world is set at lowest attainable tide levels (LAT) in the USA it is set at Mean Low Low Tide (MLLW)).
Tide at Ilfracombe on Sep 27th 2014
I then plotted the rule of twelves prediction on top of this tide shape. You’ll notice a fairly decent difference.
Tide with rule of twelves plotted
Now in addition – note that the blue area rise and fall of the tide is as predicted and not actual. However, since tide data is so well known, you are well served by assuming the predicted tide will be very close to actual. More on that in a minute.
So really what does this all mean. It means carry with you your iPhone or Android and have it loaded with a tidal App.
Here’s the link for the iOS version: World Tides 2014
And here is the Google play store search results for tides: Android – Tides search
With a tidal App you have accurate access to the tide heights at any time of the day in virtually any port in the world. You can see if the tide is coming in (flooding) or going out (ebbing). If you know your eta at a port then you can simply pull out your Tide App and see what height the tide will be.
In addition – most tide Apps DO NOT need a connection to the internet after it is initially downloaded. The data is stored on your device. How is this so? Tides are wonderfully predcitable and we have got them so figured out that the accuracy is usualy with in a few inches at any time. This is because for hundreds of years now we (humankind) have been measuring the height of the tide at points all over the world and comparing those measurements to the positions of the Sun and the Moon. Since the Sun and Moon exactly repeat their combined cycle every 19 years, the tides repeat themselves to the exact heights and cycles every 19 years. It took a lot of work from a lot of people BUT now we have it. Tide prediction is accurate and the data is at your finger tips 24/7.
Don’t be afraid of tides.
In our Coastal Navigation course we have a very detailed discussion of tides going through the theory of prediction, how to predict at subordinate stations and lots of discussion about how to handle current flow due to tides. It is the best Coastal Navigation course available.
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Have you ever been to Greenwich? If you haven’t, make sure it is on your bucket list. Not only is it a delightful place with a spectacular view of London and the Thames River, but it is the real birth place of “Longitude” and home to some of the most amazing master mathematicians of the burgeoning modern times of the 17 and 18oo’s.
The zero degree line of longitude was selected and placed in Greenwich in 1751 and then later in 1851 it was moved a few feet to align with a new telescope placed at the now zero deg. zero minute, zero second longitude position. This designated line placed on earth is a humankind determined and positioned line. It stretches from the true north pole to the true south pole.
The zero mark could have been placed anywhere on earth. It was placed in Greenwich because of the incredible work being done by the Royal Observatory mathematicians and astronomers. They needed to set a zero point and what better than exactly underneath their telescope The axis of spin of the earth also passes through the north and south poles. This is unlike the zero degree latitude line of the equator. This line is a universally given line and can not by randomly placed by humankind.
In the 1700’s in bars and cafe’s all over the topic of the times was that determining Longitude on the ocean was akin to perpetual motion – it was seemingly impossible. Yet the challenge was there and £20,000 had been put up as cash incentives to inventors to help solve the issue. £10,000 of which was ordered by the King as prize money to the person who could solve it. Longitude was that illusive!
If you understand that in those days because of ships not knowing exactly where they were, there were many shipwrecks costing lives but also huge amounts of money. Thus global positioning was imperative. Latitude had been pretty easily solved much earlier. If you do a noon shot of the sun to determine its angle above the horizon then compare this with tables of the suns angle on a specific day of the year you get your Latitude. But longitude had no such luxury of determination.
I had the luxury of recently visiting Greenwich and was delighted to see and learn about one of my favorite topics. Longitude. Here I am with one foot in the eastern hemisphere and one in the western hemisphere.
The zero degree Meridian Line in Greenwich
What was particularly awesome about my trip was that the Maritime Museum in Greenwich was displaying a whole history tour of “Longitude” and I was actually able to see the time pieces that John Harrison invented to allow ships to keep time at sea and thus solve the Longitude problem and collect the Kings prize.
I highly recommend this short read of the book Longitude.
Variation aka Declination
We discuss Variation/Declination heavily in our NauticEd Coastal Navigation Course. This is the difference between the charted true north and what will read on your compass due to the earths magnetic poles not aligning with the axis poles. Interesting enough, one means used to determining rough longitude int he old days was to take a measurement of the variation. True North can easily be measured by the north star in the Northern hemisphere and magnetic north by a compass. This difference combined with a variation map of the world allowed approximate longitude determination. The method was rudimentary at best and provided no accuracy.
On that same topic and quite interesting also is that a very accurate global map of variation exists today and is programmed into every magnetic field chip used to determine compass directions. Your smart phone can tell you magnetic North and this is measured by the electronics measuring the earth’s magnetic field. To go from magnetic north to true north, the phone needs to know where on the planet it is. Once this is known (usually via GPS measurement) it applies the known table of variations and can then show also true north.
Here is also a great website resource to see your position on earth but also find your variation.
It’s astounding to know that these guys back in the 1700’s knew all this and were the discoverers of this knowledge. Another part of this whole story is bought to life by Cook’s first voyage in 1769 to Tahiti. He was sent there by the Royal Astronomical society to measure the times that Venus was to transit the sun. This was predicted by Haley more than 40 years earlier. By comparing the measurement of times of the transit from many different locations on the planet, the mathematicians of that time were able to calculate the distance to the sun. AND the nailed it within hundredths of a percent.
Here is the picture I took of Cook’s Monument in Tahiti at the place where he measured the transit of Venus across the sun in 1769.
Cook himself used John Harrisons Chronometer (Watch) on his second voyage around the world. Cook’s logbook notes about 6 months into the trip, said that he believed more and more that Harrisons time piece was to be the way of the future.
I really hoped you enjoyed this little trip through the discovery of knowledge that we all use today virtually in our everyday lives. Whether we are aware of it or not, Latitude and Longitude is touching us manytimes every day in our every way.
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Posted by Director of Education on January 30, 2012 under Celestial Navigation | Comments are off for this article
This weekend I visited a very special and historically significant celestial navigation place. It’s called Mercury Bay and it’s in the Coromandel Peninsula in New Zealand. Cooks beach lies on the edge of Mercury bay and is thus named after lt. James Cook, the famous world explorer of the 1700’s. Cook visited Mercury Bay in his ship the Endeavour between November 5th and 15th, 1769. Cook also named the bay thus because this is the place where he and his astronomer Charles Green set up to watch the solar transit of Mercury on November 9th. So why would he do this? What’s the big deal?
The Memorial at Shakespears Head, Cooks Beach
The Royal Astronomical Society knew of the coming solar transits of Mercury and Venus in 1769. With funding from the King, they sent out many people to observe these celestial events in different parts of the globe. The observations would help in determining much about distances in our solar system. Cook’s first stop was to be Tahiti to observe the Venus transit, then after that he had been directed further south to find a great southern continent that was assumed to exist. In October 1769 he came upon New Zealand whereby he waited until November 9th to observe the Mercury transit.
As a side effect of these observations, some accurate longitude information could be determined from the observation posts. In those days, calculating longitude accurately in remote locations was almost impossible because you needed to know the time in Greenwich, the 0 degree longitude datum. But with out a time piece that would stay accurate on a rolling sea how could you know the time?
In theory here’s how the longitude determination simply works. Let’s just say that the event would take place at Midnight Greenwich time. But the Endeavour’s crew observed the event to take place at noon local time. That would mean that Cook was 12 hours away from Greenwich. Since the planet rotates in 24 hours and there is 360 degrees in a circle, 15 degrees represents 1 hour.
As a quick aside explanation of that. Let’s say you know the time in Greenwich is 1 pm yet the local time where you are is 12 noon. You are 1 hour away from Greenwich and thus 15 degrees west. This is how time relates to longitude.
Thus, in the example, Cook would have been 12 x 15 = 180 degrees away from Greenwich. Cook would have gained the local time by observing the apex of the sun to obtain the local accurate noon time. Plugging in the real numbers then, the Royal Astronomical Society of England was later to determine the longitude of a place about 300 yards west of the river at the east end of Cooks beach by comparing the time of the occurrence in Greenwich and the time at Cooks beach (plus a few other factors like diameter of the earth etc). The observation place on Cooks beach is 174 deg 45 min west. Cook went on through March 1770 to draw a very accurate map of New Zealand charting most of the coastline almost exactly. Also as a result the Royal Astronomical Society was able to determine a measurement of the Earth to the Sun. Their results differ only 1/8th of 1 percent from today’s measurements. All pretty impressive I say and thus making Mercury Bay a worthy place of historical significance.
Place where James Cook observed the transit of mercury
Several years later Cook returned to New Zealand carrying the latest technology, a chronometer. Commonly known today as a watch. The watch invention was very significant because it was immune to the rolling seas. Knowing the exact longitude, Cook was then able to reset his watch to the correct time upon arrival in New Zealand noting the daily offset in seconds the watch would have suffered on the trip between England and New Zealand. He then went on to use his watch to calculate and reposition accurately all of the Pacific islands he discovered and revisited from his previous visit, again taking into account the time offset.
View of Cooks Beach - No wonder he stayed here 10 days
The NauticEd celestial navigation course written by Captain Ed Mapes is a great start to understanding the technical details of calculating longitude using a noon shot of the sun. Take the NauticEd celestial navigation sailing course today.
One of Cook’s favorite Pacific islands besides New Zealand was Tahiti. Tropical warm waters, an abundance of fresh fruit and friendly people was one of his reasons. Speaking of Tahiti, if you obtain the NauticEd sailing certification of Bareboat Charter Master rank before June this year, you’re invited to get on a jet liner fly at 500 miles per hour and captain your own luxury modern sailboat using a wonderful GPS in our sailing flotilla starting June 16 this year. Can you imagine giving that invitation to Cook? Count yourself lucky, but only if you take advantage of this offer.
Visit our Sailing flotilla opportunity in Tahiti
I guess we’ll have to visit the place where he observed the Venus Transit – come join us.
What the heck? Take the plunge and a jolly good worthy life challenge – become a NauticEd Bareboat Charter Master and Yacht Master now!
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.
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.
Recently on our NauticEd flotilla with the Moorings to the Kingdom of Tonga we wanted to pass through the Fanua Tapu Pass which is a gap in the reef to get to the eastern islands of the Vava’u archipelago. Normally the gap is marked by a series of buoys, however the latest storm ate them.
The pass is well documented by two waypoints. Traversing using a GPS map, however, was out of the question because Tonga is one of the last places on earth to be accurately placed on the world coordinates. Yes you’re reading that right – the islands are not actually where the maps say they are and especially reefs and rocks are not where they are positioned on the maps. That’s pretty absurd for this day and age but it’s true. Call the Moorings base in Tonga for your self.
Navigation is performed using good old eyesight (some of our eyesights are older than others) coupled with map reading skills, a depth sounder and a keen watch out on the foredeck.
So anyway we had to get the first waypoint dead on to pass through the reef. The first waypoint was 18 deg 43.914 min South and 173 deg 59.12 min West. Our position was 18 deg 44.902 South and 173 deg 62.014 West.
So it’s a bit funny trying to hit a point like this because you’ve got to be able to work with a few obvious things but understanding the principles makes it much easier. First you’ve got to know which directions you need to be heading based on the hemispheres you’re in.
In the northern hemisphere to increase the latitude you’ve got to head north but in the southern hemisphere to increase latitude you’ve got to head south.
Similarly, in the eastern hemisphere to increase longitude you’ve got to head east where as in the western hemisphere to increase longitude you’ve got to head west.
OMG how do you remember that? Especially in the heat of the moment with waves and rocks all around you and your life depending on it.
I’m sure there is a memonic for it but it’s best to understand the principle first and below is the way where I can best understand it. For me, I find that principles are better than memonics.
Imagine you’re standing on the intersection of the prime meridian (below grenwich) and the equator. You’re at 0 deg Latitude and 0 deg Longitude. Move in any distance to the North and the latitude increases North. Move any distance to the South and the Latitude increases South. Now place yourself at about 17 degrees south latitude. Move North and you’re moving towards the equator and towards 0 deg Latitude.
So in principle then, if you understand this; move towards the equator you’re decreasing the Latitude no mater which north or south hemisphere you’re in. So in our example above our latitude was greater than the waypoint so we needed to head towards the equator. We were in the southern hemisphere so we needed to head north.
IE when dealing with latitude – just figure out if you need to head towards the equator or not. That should take care of that from an understanding principles point of view.
Longitude. Back to our Prime Meridian/Equator intersection. Looking towards the North pole, everything towards your left is West Longitude right? And everything towards the right is East Longitude. So anything from England, past the Americas and all the way around to Hawaii is West longitude. Any everything from England, past Asia and all the way to Australia and New Zealand is East Longitude. This is why the USA is known as western society and Asia is known as eastern society.
So now you just got to know where you are East or West. In Tonga we were on West Longitudes. So anything back towards the Americas or England from that point was decreasing the Longitude numbers towards the zero prime meridian in Grenwich. Which meant to get to our waypoint we had to head East to the America’s.
So overall we needed to head to the North and to the East. Next we looked at what was the relative differences between desired and present positions for latitude and longitude. The longitude difference was about 3 times that of the latitude difference. This means we needed to head more east than north.
In the old days (I mean the old old days) before longitude could accurately be determined, traders would head north from Africa and purposefully miss England far far to the west of England. Then once on the latitude (easily discovered by the angle the north star makes with the horizon) they would then travel East. This ensured they would miss all the potential dangers. Hundreds of ships were being lost due to the difficulty in accurately determining the longitude. In early 1700’s the King of England offered a 10,000 pound reward to figure out how to accurately determine Longitude. For those of you interested, watch the history channel show on this or read the book “Longitude”. Both are excellent!
So lets go back to the principle. Where ever you are you should establish this before any issues come up. IE if you’re on a bareboat charter – answer these questions before you leave the base.
Am I in the southern or northern hemishere? Then based on that, embed into your head which way do you go to increase/decrease latitudes. Should you head towards the equator or away.
Am I in Eastern Longitudes or Western Longtiudes? Then decide which continent you should head to decrease or increase longitudes.
Here’s a little test then. You’re in the Aegean Sea at:
36 deg 56 min North Latitude, 27 deg 19 min East Longitude
you want to get to:
36 deg 57.897 min North Latitude, 27 deg 17.295 Min East Longitude.
Which way should you be heading?
Simple enough – we’re in the North Eastern hemisphere. We want to increase the latitude so we need to move away from the equator and thus head north. We also want to decrease the longitude and head towards Grenwich England which means head west.
Both are almost 2 minutes in difference and so the VERY APPROXIMATE direction should be North East. We say VERY APPROXIMATE because the latitude lines and longitude lines are not the same distance apart and vary according to latitude. The closer to the poles the closer are the longitude lines. Therefore the heading would be more north of northeast.
In this blog we’re placing quite an importance on this concept. The reason being is a funny (potentially not so funny) story attached. On the Tonga trip one of the crew was an ex Airforce Navigator. He got turned around for a second in the reef because we were heading east to reach the waypoint but his brain was telling him to head west. The reason is that he was used to Navigating around New Zealand which is in the Eastern Longitudes. Tonga is just on the otherside of the 180th Meridian in the Western Longitudes. Whoops being turned around in the middle of reefs is NOT good. There were rocks all around us and correct decisions had to be made fast.
OK and here’s a real scenario to scare you into taking this blog and the NauticEd sailing simulator serious. A family member falls overboard at night and you hit the MOB button on your hand held GPS. You’ve got the lat and long where they went over. By the time you get turned around and the sails down with all the confusion – all you’ve got is their lat and long and yours and a compass. How do you save your family member’s life?
MOB is at 16 deg 33.250 min N and 62 deg 11.501 W
You are at 16 deg 33.200 min N and 62 deg 11.595 W
Which way do you head? Quickly now the current is drifting them away from that position.