Posted by Grant Headifen on June 29, 2010 under Bareboat Charter, Crew, Sail Trim, Skipper | 
I once sailed with an ex-submarine captain who would turn the boat through a tack extremely slowly. When asked why, he had several good reasons.
(1) Look behind you as you come about. If you are leaving swirling water eddies behind the rudder, these are a sum of kinetic energy that was previously in your sailboat but has now been released to the water. What does that mean? If you jam the tiller over during a tack you will loose momentum – slowing down your sailboat more than you need to. If you execute an easy steady turn leaving the kinetic energy in the boat, you’ll maintain kinetic energy in the boat.. Thus when you come out on the other side your boat still has speed. Still not convinced? You’ll remember from docking that the boat carries a lot of momentum. Put the throttle in neutral and the speed bleeds off very slowly. Ever been skiing? Execute a few cutting turns and you’ll see how fast your speed drops. Same concepts when tacking.
(2) A slower turn also allows your crew a few extra seconds to get the jib sheet in tight before the real heel and tension comes on. This is really important because once you’re heeling over on the new tack it is more difficult and slower for the crew to tension up the jib sheet to it’s appropriate trim. It’s pretty frustrating as helms person when you’re perfectly on the new tack and you’re watching the crew floundering around cranking slowly on the winch and the jib is still only half in. You’re probably yelling “get it in get it in” and watching others pull past. What I’m doing here is putting a little responsibility back on you. With a slower turn, the crew can get the jib sheet almost all the way in by hand before the tension comes on.
(3) The swirling water eddies left a signature in the water that could be picked up by submarine hunting satellites. Not that this is relevant to sailing really but it was just his well formed habit.
The point is – when you’re the helms person, maintaining speed through the tacking maneuver is a balance between your boat’s momentum profile and your crew’s efficiency in getting that sheet in. It’s not about jamming the wheel over to the other side as fast as possible.
Just goes to show you that slow is faster. Ask the tortoise!
Posted by admin on June 22, 2010 under Bareboat Charter, Coastal Navigation, Crew, Sail Trim, Skipper |
Leeway is just one of those things that is a law of the universe that we have to put up with. It’s just like gravity. Still with gravity – the advantage is that it’s highly predictable. And so then is leeway.
Leeway is the sideways slip motion of our sailboat down wind from the pressure of wind against our boat and sails. It results in a course that is less than desirable.
Leeway Slips Your Boat Side Ways Down Wind
Airplanes suffer from the same issue. When flying in a cross wind, the plane crabs (slide slips) downwind. The course becomes different from the heading.
Not accounting for leeway will have you sailing (or flying) in a fairly unnoticeable arc to get to the mark. To represent an example with a mark to the north and a westerly crosswind, here’s what happens; you aim for the mark at 000, your boat slips sideways to the west. Now your mark is at 359 but you don’t really notice it. After a few minutes your mark is at 358 still in noticed. Minutes later your heading is 355 then 350 etc. All because you keep aiming at the mark but you’re being pushed to the east by the wind. Your course over ground becomes an arc and is the long way around.
The prudent sailor will account for the leeway and sail a constant heading depending on their known leeway of say 350 for the example above. The sideways slip motion will deliver them to the mark in a straight and shortest line.
Now that we’re in the electronic age, navigators will plug in the destination to the gps. The autopilot which is cross talking to the gps takes care of the rest. The gps analyses the cross track (the boat’s distance away from a straight line to the mark) and feeds back to the autopilot the proper heading to minimize this in real time. Thus resulting in a straight course to the mark.
I’m doubt that during the Wednesday/Friday night beer can race such electronic methods are utilized. So I’m suggesting that to take line honors and win the bottle of rum at your club race by taking account of leeway.
Leeway is particularly more prevalent when you are sailing on a close haul or close reach and can be as much as 20 degrees depending on the wind conditions, water conditions, your sailboat design, your apparent angle with the wind and how your sails are set.
However, other than buying a new boat, the only thing that you have control over is the trim of your boat and sails.
Here’s a couple of general rules to follow:
- Over sheeted sails cause more sideways force and thus sideways slip (leeway). Fly the telltales diligently.
- Aim for a position to windward of the mark you’re trying to go around. The more you are sailing on an upwind course, the more the degrees upwind you should aim.
- The higher the wind speed, the higher above the mark you should aim.
- In general, on a close haul, allow 10-15 degrees. Adjust this less if the wind is light, more if the wind is strong. Reduce this amount linearly as you bare away from the wind.
When doing serious navigation we absolutely must account for leeway and an excellent understanding of how your boat performs leeway wise is essential and how to solve for it once you know it. NauticEd developed an educational navigation video solving a leeway and current exercise at http://www.youtube.com/watch?v=1LQcFOGSJQs
Using a gps and a nice steady windy day, you can do a simple determination of your sailboat’s typical leeway.
(1) Begin sailing on an angle slightly off a close haul direction and with a recognizable land marker dead ahead.
(2) Measure your speed
(3) Douse the sails and begin motoring at the same speed in exactly the same direction.
(4) Take note of your gps course.
(5) Deploy the sails and turn off the engine.
(6) Continue to aim for the same point on land.
(7) Now read out your gps course.
(8) The difference in course angles will be your leeway
(9) Repeat for different points of sail
(10) Repeat for the opposite tack.
(11) Repeat on different days with different wind strengths
Note that:
(a) this method is relatively immune from current because you have normalized it out by performing the motoring task.
(b) this method will not account for the leeway due to the hull of your boat presented to the wind.
We hope you enjoy your bottle of Rum!
Posted by admin on June 16, 2010 under Crew, Sail Trim, Skipper, weather |
During the Americas’ Cup campaign in New Zealand in 2003, I saw one of the best explanations of this on a TV interview with the Greg Butterworth, the Tactician for the Alingi Team.
Most of us sort of understand the concept and we’ve been left with the answer of “Well – weather helm is better because it’s safer.” But few explanations go into how it gives your boat a sailing advantage.
The definition of weather helm and lee helm is simple and it is easy to remember which is which. If you have a tiller, weather helm is when you have to pull the tiller to weather (toward the wind) in order to keep the boat going in a straight line. Lee helm is when you push the tiller to lee (downwind) in order to keep the boat going in a straight line. We’ve probably all felt this slight pressure required on the tiller when underway.
Your boat can be tuned to give weather helm or lee helm. Rake the mast forward and you move the center of effort of the wind forward which causes your boat to want to turn downwind. Rake the mast back and you move the center of effort of the wind back causing your boat to want to go upwind to weather.
When your boat gets rounded up – you just experienced massive weather helm. No matter how much you pull the tiller to weather, you can’t stop the boat going to weather. Dumping the main sail moves the center of effort forward thus reducing the weather helm.
The basic perception of weather helm being safer comes from this effect: if you let go of the tiller, it will automatically go to center because of the water flowing over the rudder and because the rudder is pivoted at its leading edge. Now there is no rudder force to counter the desire of the boat to turn up wind to weather so the boat does exactly that. It turns to weather and rounds up slowing the boat down and reducing forces on the rig. Conversely, lee helm means that if you let the tiller go the boat will turn away from the wind, heel over more increase forces on the rig.
So from a safety point, weather helm is good. BUT there is another advantage that we’re not generally taught. Holding the tiller to weather means that there is a slight pressure on the rudder to windward. This actually MOVES THE BOAT TO WINDWARD as it slices through the water. And we all know what that means, race advantage!
The Weather Helm Advantage
The illustration shows how the water pressure from weather helm creates a sideways force on the rudder tending to push the boat to weather.
Now Greg Butterworth went on to explain that there are other cool things you can do. One is to put a little trailing edge swinging control surface on the keel.
The illustration below shows this effect too. For us pilots, this is much like a trim tab on a wing of a small airplane. The trim tab creates the ability to adjust the lift at that point on the aircraft and thus create a balance of forces. The issue to remember here is that you’d need to trim the tab the other way when you tack over.
A control surface on the keel
So there you have it. While we’ve all been understanding the lifting effects of the wind over the sail, the other fluid that we’ve ignored is the water under the boat and how we can gain lift from it too.
Next time you’re out sailing on a nice steady 10 knot breeze, come up on a close haul, trim the sails perfectly so that all your tell tails are flying smoothly. Then notice what pressure you’ve got on the helm. Note that if you’ve got a wheel, weather helm will be a tendency to apply downwind turning pressure on the wheel (which is the same as pulling a tiller upwind right?). Ideally you should have slight weather helm. If not, you should probably not jump right in and start raking your mast back. Talk to a mast tuning specialist in your area first.
Posted by Grant Headifen on June 8, 2010 under Crew, Sail Trim, Skipper |
Rounding up is caused by many factors. One is too much wind and force aloft which tends to heel the boat over. This reduces the amount of rudder in the water and thus the rudder’s effectiveness. Another factor in rounding up is the center of pressure of wind on the sails is too far aft which then pushes the aft of the boat downwind and thus the front of the boat up wind.
The NauticEd SailTrim clinic discusses this topic and so what we wanted to do was test it out for sure. So last weekend we took out a friend’s Beneteau 373 to test out an anti-round up theory. Read on to find out the results of our experiment.
First though, we must first understand wind shear. The phenomenon of wind shear is pretty easy. Wind moves faster at the top of the mast than is does at the water level because the stationary water slows the down the wind in close proximity.
Secondly, consider the concept of true wind vs apparent wind. Which is best understood by imagining driving your car in a cross wind with your hand out the window of the car. At stand still you would feel the wind coming from the side of the car. The faster you go, the more you feel the wind coming from the front of the car. But when a gust of wind comes (which is just an increase in true wind speed) then you would feel the wind shift back more to the side. When relating this to a sailboat, if your boat was standing still, the wind at the top of the mast would be the same apparent direction as at the cockpit level albeit, faster (from the wind shear phenomenon). However as your boat picks up in speed the apparent wind moves forward BUT because of wind shear it shifts forward less at the top of the mast. IE at the top of the mast the wind tends more to the direction of true wind direction because the true wind speed is higher. Thus at the top of the mast the true wind is more aft than apparent wind. Aft means it is coming from a direction further towards the back of the boat. Get it?
So – whether you get it or not. The fact is: at the top of the mast the wind is higher in speed and more aft than at the cockpit level.
Figure A and B show the boat speed, true wind and apparent wind vectors for cockpit level and top of the mast. Obviously in both cases, the boat speed vector must be the same. The true wind vector is obviously the same direction but due to wind shear it is longer (faster) at the top of the mast. This results then in the apparent wind direction being more aft. IE in this case from 135 deg to 125 deg.
Wind shear and apparent wind phenomenom
Thirdly, you should understand that if a sail is sheeted in to tight it creates more heel. This then is exactly what is happening at the top of the mast. Even though at the bottom of the sail you may have perfectly trimmed the sail, the top of the sail is sheeted in too tight against higher wind speed. No wonder you’re getting excessive heeling. And excessive heeling creates round ups.
This is now quite a revelation! It means that the top of the main needs to be “out” further than the bottom of the sail for it to operate efficiently. This is usually indicated by the top telltale. Often the leeward telltale will be stalling at the top of the sail. Especially in high wind because of the phenomena above.
The top of the mainsail needs to go further out so that the starboard telltale can fly smoothly
Thus the top of the mainsail needs to be let out further so that the leeward telltale can fly smoothly. This is commonly referred to as twisting the sail out at the top. Except people believe you are just spilling out (wasting) the wind at the top. Not quite so now, as you’ve just learned. Twisting out the top of the sail is letting the top of the sail fly according to the direction of wind it is feeling.
In the illustration, you can see the top telltale on the downwind side is fluttering. If you let out the main at the top, the wind can reattach to the sail on the leeward side and the telltale will fly smoothly reducing the force aloft.
Understanding all the above. How do we stop rounding up?
Option one: Obviously the first and safe option in higher winds is to reef the sail.
Option two: Let out the traveler which is what most people do when hit by a gust. Just so long as you realize what you’ve done is not twisted the top of the sail out – all you’ve done is let out the mainsail from top to bottom and thus depower the mainsail. This reduces the force aloft and thus the heel. It also moves the center of effort of wind on the sails forward which reduces tendency to round up. The trouble is that you spend all day fighting gusts with still quite a few involuntary round-ups.
Option three: Let out on the mainsheet. Here again you’ve depowered the entire mainsail to handle the gust. Still, it works.
Option four: Permanently reduce the force aloft by letting out further on the mainsail and tightening up on the traveler. The trick here is to bring the mainsail bottom back in again using the traveler. Yes, bring the traveler to windward up past the center point. Most sailors are reluctant to do this because they’ve been taught that it detaches the wind on the leeward side. But not when you’ve let out the mainsheet. In effect, by letting out on the mainsheet, you’ve allowed the boom to rise up and the leech of the sail to slacken. This creates the desired twist at the top and allows the top of the sail to fly according to its apparent direction. At the same time, the bottom of the sail can fly according to its apparent direction.
By trimming the traveler and mainsheet together you can manage the twist at the top of the sail as desired yet still keep power on the bottom of the mainsail. Keeping power on the bottom of the mainsail keeps your speed up which also increases the effectiveness of the rudder. Increasing the effectiveness of the rudder means it can hold more against any turning effect created by the shifting of center of pressure backwards. Wow – see how it is all connected.
What happened on our 15 knot gusty sailing day? Well, not one round up.
So to summarize, the sailing lesson here is when in higher winds bring the traveler up and sheet out the main. You’ll also need to release the boom vang a little. Letting the boom vang out allows the boom to rise which loosens the leech (trailing edge) of the sail and allows the top part to “twist out”.
This and many other finer sail trim concepts are discussed in NauticEd’s Sail Trim Clinic at http://www.nauticed.org/courses/view/sail-trim.
Posted by Grant Headifen on June 3, 2010 under Bareboat Charter, Skipper |
Here is a question posted by one of our students today with our response following.
On 6/4/10 1:54 PM, “Ted” wrote:
I have recently started through your courses in the hope of chartering next winter. My own boat is a 25′ Catalina. From your information it appears that I will not receive credit for my days on water due to my boat being under 28′. Is that correct and therefore will I not be able to progress beyond crew level 0?
Thank you for your time
Ted
>>>>>>>
Ted
Some of your small sailboat experience is counted. However, the sailing certification and experience that the yacht charter companies are requiring is that their customers have some experience on larger sailboats before they responsibly release a sailboat to anyone on a chartered sailing vacation. As you can imagine, sailing experience is a major factor for them in lending out their charter sailboats. When we consulted with the major yacht charter companies in the world to put this program together they were adamant and rightly so that a proper and valuable sailing certification would include some big boat time.
My advice would be to buddy up with some one the local yacht club who has a larger boat to gain the experience you’ll need.
You will be able to advance to Skipper as soon as you log 5 days more on a sailboat 28ft or longer whilst you are acting as master of the vessel.
I hope that answers your question.
Sincerely
Grant Headifen
Educational Director
