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Old 06-25-2007
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Wind angle to sail

So I had a great weekend of sailing. I was able to leave the pier and return in a sailor like fashion. (i.e. under sail) as the lake is very weedy by the pier this was a huge accomplishment for me. The weeds actually choke off the entire area. Many times I have had them stop the boat or kick up the rudder. The first few times that happened it was quite a sight but now I am ready, with my oar in hand. The rudder kicks up and the oar takes it's place.

Now on to the questions. is there a general rule of thumb as to what angle the sail should be placed at in relation to the apparent wind? I know when sailing close hauled the sail is sheeted in but on more of a beam reach I am having trouble finding a good trim. My boat only has a mainsail.

Also are single sail dinghy more sensetive to the wind than a dinghy with a jib and mainsail?
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Old 06-25-2007
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I sailed with a Nasa Engineer who had never been sailing before, we were moving right along. He started discussing the physics of sailing and how the wind must be at 90 degrees to the sail in order for 'proper' propulsion to take place.
this he explained is why the sails are moved by the sailor 'to acheive the 90 degrees angle.'

I am not an engineer, nor a practicing Rocket Scientist. Never thought of this theory before or since except for today.

having both a single sail sunfish and a jib/ main Hobie 16. I can notice the wind better on the sunfish but make better use of it on the Hobie.

i enjoy both but for different reasons Don't overthink life, just enjoy the ride
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Old 06-25-2007
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Well it's obviously not rocket science.

The front of the sail generates lift, the back of the sail generates drag. The optimum angle should be about 35 deg, but it depends on the point of sail you're on, the type of sail you have and the boat and wind speed. The short answer is something less than 45 deg, generally. Practically speaking, let the sail out until it luffs and then pull it in until it stops.

Also, in general, the sensitivity of the boat increases with more sail area and less weight.

Last edited by CapnHand; 06-25-2007 at 11:56 AM.
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Old 06-25-2007
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The engineer was talking through his hat.
Generally the sail should be trimmed to the point where the luff is just filled. However it gets more complicated because what you are after is maximum forward force, not maximum sideways or total force. Going into the wind the maximum total force will be with boom in the centre. The best direction being to windward just where the sail properly fills. However on a single sailed boat that will give healing but little forward drive. Maximum forward drive comes at an angle of the boom to the wind of about 22 degrees. This holds for a beam reach but for beating you also have to consider the effect of how close to the wind you are sailing on distance sailed.
Effectively upwind try the boom just over the edge of the transom. On a beam reach you can let it out more than you think for forward speed not healing. On a broad reach or run it is more a matter of projected area ie the sail at 90 to the wind.
With two sails it is more complex in that the jib is more important and the main may be trimmed harder to help the jib air flow.
I am not sure what you mean by asking if a single sail is more sensitive to the wind. The answer is no, but two sails are a bit more complex.
Once you get the initial hang of it, you will learn more by racing even for fun against other boats of the same design. If your friend is going faster look at what he is doing different, and gradually you will get a feel for how things interact.
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Old 06-25-2007
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Originally Posted by CapnHand
Practically speaking, let the sail out until it luffs and then pull it in until it stops.
You mean I have been doing it right? I think I should write that next to the tiller on my little sailboat (which I will loan to just about anyone that expresses an interest in learning).
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Old 06-25-2007
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nolatom will become famous soon enough
Most new sailors tend to overtrim, since a sail will "tell" you when it's undertrimmed (by luffing) while an overtrimmed sail won't give you such an obvious reminder, you'll just be going slower.

Off the wind, the old saying is,"When in doubt, let it out".

When you sail closer than a beam reach, you'll have to trim in more than you think, because your speed has a greater tendency to "pull" the apparent wind forward, and you have to trim in to avoid a luff.

Think about iceboats..they can go 60 knots in a 20-knot wind, because their speed creates much more apparent wind speed than does the "true" wind. Same thing with your boat, but to a much lesser degree. This is why you may be at 45 degrees to the true wind close-hauled, but the apparent wind (on you telltale yarn) may be more like 25-30 degrees. It's like those vector problems you used to do in geometry.

All this will come with experience. Eventually, try some racing (crew for someone to start with) and you'll see more clearly how critical proper sail trim is for speed.
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Old 06-25-2007
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I am guessing that you are sailing a Butterfly. It has been many years since I was on one. That was my first sailboat. I have been sailing scows for 30+ years. I have sailed with main, jib and spinnaker on the E scows and am currently sailing a C scow which is 20' with a large main sail.

As to your first question, "what angle the sail should be placed at in relation to the apparent wind?" There are two things in play here. Sail trim and the angle you steer at. If you want to sail as close to the wind as reasonably possible. You should have the sail trimmed so that the blocks at the back of the boom are nearly over one another. Depending on wind strength will determine how tight the main sheet should be trimmed. Too tight and you will see the leach of the sail get too rigid and it may cup to weather and not allow good air flow. Too loose and you will see the sail luff. There is a fine line that you can play with here. For now just pull it in so the back of the boom is slightly to leeward of the center line on the boat. Even if it is over the lee corner of the transom you would be ok.

Steering, you should be at about a 30 - 45 degree angle to the wind. Keep your mainsail trimmed the same and practice feathering upto and off of the wind and learn to feel that magic spot where the speed seems to be the best. If you have tall tales on your sail, in the luff about a foot back from the mast and 3 feet above the boom, They should both be streaming straight back when you are at the proper trim and steering angle.

Try to go out in a moderate condition with rather calm waves, lack of boat chop, and only play with one or the other factor at a time. You will find with different wind conditions your main sheet trim will change as will the angle steered. Also try to keep the hull at about a 15 degree angle, the lee rubrail about an inch out of the water. That is the fastest angle for your hull shape.

When it comes to reaching, a big mistake people make is in not using the boom vang to help hold down the boom a little. More vang with more wind. Try going from closed hauled to a reach, slowly letting out the sail as you steer down off of the wind. Then steer back up again slowly trimming. You want to be glancing off the wind. Your boom will end up when on a broad reach about 2 - 3' off the transom. You will learn from this type of exercise how to get your best speed. We feather up and off the wind to maintain speed when racing. My boat is constantly changing. As you get better at it you will find that changing trim on the sail and body weight movement will steer the boat rather than using the rudder.

As to a single sail (cat rig) versus main and jib ( sloop rig ) being more sensitive. They each have their own level of sensitivity. I find a sloop rig easier to sail and feel what the wind is doing. I spent many years sailing a 16' scow ( M-16 class, sloop rig) and found it difficult at first to read the sail and feel what was going on when I got on the C Scow ( cat rig). Now they are both easy. I prefer a sloop rig but on our lake in Southern Wisconsin, we have 20 C Scows racing every Tuesday and Sunday. I like the action and earning bragging rights for a day or two.

Good luck

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Old 06-25-2007
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thanks for the great replies.

6string, I sent you a PM. I think we may be sailing on the same lake.
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