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Old 30-01-2012, 21:33   #121
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Re: Sailors Don't Know How to Set Sails ?

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Originally Posted by Ex-Calif View Post
There is a lot going on in an IOR boat with three up in 30 knots. Number one is lack of 5 folks on the rail, number two is probably an assured need to short both the main and the headsail.

With full sail up you had to be 15knots overpowered.
The sails were really stretched out, not flogging, but we were really thinking the leeches would let go any time.
To keep a straight line, we had to keep at least a half turn on the wheel.
Our arms ached!
The owner didn't want to reef even though we suggested it.
Probably because he didn't know how!
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Old 31-01-2012, 00:14   #122
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Re: Sailors Don't Know How to Set Sails ?

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Originally Posted by cwyckham View Post
If you're interested in the theory, the absolutely most accessible book I've found is "The Symmetry of Sailing" by Ross Garrett. It's accessible and correct. A combination that can be hard to find.
Many thanks, will look for a copy of that.

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Old 31-01-2012, 00:25   #123
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Re: Sailors Don't Know How to Set Sails ?

Thank you for all your very interesting and candid replies.
Setting sails properly is a black art and their are a variety of ways to do it for a good many different situations.
It is surprising how difficult it is to find a good course but I am sure if anyone who was skilled suggested running one their might be a few forumites willing to sign up.
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Old 31-01-2012, 04:49   #124
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Quote:
Originally Posted by Surfer Girl
Ex-Calif & S/V Jedi,

You guys are sounding a little bit smug there - not a good look. The title of the thread is "Sailors don't know how to set sails?" (and not "The theory of Hydrodynamics....")

The operative words are 'Sailors' & 'Sails' - both of these are adjustable and/or inter-changeable.
The effect of the keel, dagger board, centre board and rudder on (upwind) sailing performance of a certain sailing craft, although very important, is fixed and non -adjustable (except for hi-tech canting keels). This falls to the naval architect who designed the vessel in the first place; hopefully they got the hydrodynamics right! It either works efficiently in a variety of sailing conditions and points of sail or not. Not much can be done about that unless you have lots of moolah...

FoolishSailor, great synopsis of Sail Trim guidelines!
Smug was not the look I was going for.

But to carry the theme I gues it is not the theory of hydrodynamics but the physics of hydrodynamics.

If the boat is heeling 20+ degrees and one is working main sail trim to solve weqther helm I am only suggesting one is working on the wrong problem. A severely overpowered boat will not balance properly. It startes with understanding the forces involved. Some of the vector discussion was not totally accurate and all of it completely ignored the force that counter all the sail forces. That is the keel.

If the group chooses to ignore the keel in a discussion of sail trim, that's no skin off my back.

It is pretty clear there are a couple of poles. Trim properly or trim "ok." maybe there is an image of lots of work on deck, water crashing over the decks and an uncomfortable ride perpetuated by offshore racing videos. It doesnt have to be like that and as stated earlier by someone 1/2 knot over 14 days adds up to some serious mileage. Add to that the ability to point higher - more towards a destination and the efficiencies can be startling.
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Old 31-01-2012, 04:59   #125
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Old 31-01-2012, 05:38   #126
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Re: Sailors Don't Know How to Set Sails ?

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Originally Posted by Ex-Calif View Post
Smug was not the look I was going for.

But to carry the theme I gues it is not the theory of hydrodynamics but the physics of hydrodynamics.

If the boat is heeling 20+ degrees and one is working main sail trim to solve weqther helm I am only suggesting one is working on the wrong problem. A severely overpowered boat will not balance properly. It startes with understanding the forces involved. Some of the vector discussion was not totally accurate and all of it completely ignored the force that counter all the sail forces. That is the keel.

There is definitely science involved in hydrodynamics but I say theory only because even the experts don't agree (which is often the case). Just look at all the varied hull forms & foils of contemporary racing yachts.

So how do you de-power that severely over powered boat? By trimming the sails (flattening the main, easing the traveller to leeward, etc.) or reefing, n'est ce pas? Good sail trim or knowing when to reef is what creates the balance (along with a good helmsman), you can't change the aspect ratio of the keel or the length of its chord!

And it was me who said that 1/2 or 3/4 knot over 21 days (but 14 will do) will make a big difference in reducing the length of the passage.

I think we're on the same page but perhaps different paragraphs...
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Old 31-01-2012, 11:08   #127
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Re: Sailors Don't Know How to Set Sails ?

Quote:
Originally Posted by Ex-Calif View Post
Smug was not the look I was going for.

But to carry the theme I gues it is not the theory of hydrodynamics but the physics of hydrodynamics.

If the boat is heeling 20+ degrees and one is working main sail trim to solve weqther helm I am only suggesting one is working on the wrong problem. A severely overpowered boat will not balance properly. It startes with understanding the forces involved. Some of the vector discussion was not totally accurate and all of it completely ignored the force that counter all the sail forces. That is the keel.

If the group chooses to ignore the keel in a discussion of sail trim, that's no skin off my back.

It is pretty clear there are a couple of poles. Trim properly or trim "ok." maybe there is an image of lots of work on deck, water crashing over the decks and an uncomfortable ride perpetuated by offshore racing videos. It doesnt have to be like that and as stated earlier by someone 1/2 knot over 14 days adds up to some serious mileage. Add to that the ability to point higher - more towards a destination and the efficiencies can be startling.
Understanding the forces on the keel is critical to understanding how a sailboat sails upwind. However, I don't see how it has much bearing on why heeling causes weather helm, which was the point of the "vector discussion." The keel location has a bearing on CLR, of course, but I did mention the effect of the CLR vs CE on yaw.

The main point I was trying to get across was that the the location of the forward drive force (at the sail CE) was offset from the hull drag force due to the heel of the boat. The hull (and keel) drag force is always pretty close to the centerline. I suppose with a very deep keel, the drag force will end up getting somewhat offset in the opposite direction with a large heel, accentuating the effect.

I think the main effect of the keel is to counteract leeway. Certainly, by heeling over, you'll end up with more leeway as the keel is leaned over (just as the rudder becomes less effective).

I'd love to hear more from you on this if you care to share, as you are clearly one of the most knowledgable on the board when it comes to sail trim and boat dynamics.
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Old 31-01-2012, 11:39   #128
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Re: Sailors Don't Know How to Set Sails ?

Nostradamus,
Try post #87 and click on the blue link. Yes, there are more technical books written but this will get you started on the right track.
Your original post suggesting that most sailors don't know how to set sails might be correct but I would modify your statement to state that most sailors who are self taught and have not read up on the subject don't know how to set sails.
Was Sail Power by Wallace Ross mentioned?
kind regards,
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Old 31-01-2012, 12:38   #129
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Re: Sailors Don't Know How to Set Sails ?

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Originally Posted by SkiprJohn View Post
Nostradamus,
Try post #87 and click on the blue link. Yes, there are more technical books written but this will get you started on the right track.
Your original post suggesting that most sailors don't know how to set sails might be correct but I would modify your statement to state that most sailors who are self taught and have not read up on the subject don't know how to set sails.
Was Sail Power by Wallace Ross mentioned?
kind regards,
I would suggest that some books are good but they can only describe theory. You really need to go out with a really good sail trimmer on racing boats to understand far more than books can convey. I suppose it is like reading the Karma Sutra. You have to actually do it to know how difficult some things are to get right without ending up in a real mess.
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Old 31-01-2012, 13:10   #130
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Quote:
Originally Posted by cwyckham

Understanding the forces on the keel is critical to understanding how a sailboat sails upwind. However, I don't see how it has much bearing on why heeling causes weather helm.
Modern sailboats are specifically designed to cause weather helm when they heel beyond their optimal angle of heel. This is a safety feature so that when boats are over powered they broach and round up versus power up and "round down" with the potential for a jibe in heavy weather.

When you feel weather helm it is your boat telling you to reduce heel and adjust the sail plan.

The reasons for weather helm are in the hull design and sail plan. Instead of thinking of the sails and the keel laying at an angle when at heel instead think of them in two dimensions and see the change in the profile and thus the change in the CE in this manner. The combination of the change in wetted surface and the keels profile in relation to this combined with the fact that the jib looses pressure faster than the main when the boat heels causes the boat to want to round up ie weather helm to compensate.

If you have weather helm you need to change sail plan by depowering your sails.


Once your boat is at optimal heel, each mono hull has an angle that is usually around 11 to 15 degrees you should avoid heeling more if possible. If your boat wants to heel than it is time to depower.

You should depower in approximately the following order, it you have two masts there are some small changes, but in principle this works for all boats. Once your boat is back to ideal angle stop going down the list

1. Tension all control lines. Start with foot of main, then luff, then leech
2. Tension backstay to open top of leech
3. Travel down main
4. Open leech more by easing boom vang slightly

At this point it is time to reduce the sail plan. Once you start reducing sail plan you need to really watch for weather helm as sailors tend to not reduce both sails equally. I.e. start furling genny without reefing main. If you adjust one you need to adjust the other.

If you are really in the **** and sails are fully reefed and you are still over powered then you need to consider changing your sailing angle and entering storm tactic mode which would be a different discussion and I am sure covered in detail somewhere else.

Bottom line is that weather helm is designed into boats and is an indicator that it is time to do something
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Old 31-01-2012, 13:44   #131
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Re: Sailors Don't Know How to Set Sails ?

Optimal heel of a mono is zero.
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Old 31-01-2012, 13:47   #132
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Re: Sailors Don't Know How to Set Sails ?

Yes, practice is necessary.
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Old 31-01-2012, 14:25   #133
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Quote:
Originally Posted by ctl411
Optimal heel of a mono is zero.
Not true. The designed wetted surface is usually optimised to increase waterline while reducing wetted surface at a given angle. The optimal efficiency of a sail plan is zero degrees of heel as that presents the most surface as to the wind. So in light air where you are not reaching your hull speed you get maximum efficiency and as the wind pipes up the boat heels and the water line increases to give you a faster max hull speed and even though the sails don't present the same surface area to the wind there is ample power and at this point less wetted surface and more LWL is more important for speed.
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Old 31-01-2012, 15:49   #134
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Re: Sailors Don't Know How to Set Sails ?

Speaking as a mechanical design engineer with, I suspect, a better than average understading of the physics of air-flow past sails and water-flow past hull and appendages, I'd suggest that it is disingenous to suggest, as been suggested here, that it is important to understand that physics in order to improve sail trim.

The physics of catching a thrown baseball is relatively complex too - quadratic equations of motion derived from Newton's Laws, even assuming that you negect wind strength, wind direction and air resistance. If you take into account wind & air resistance, you probably neglect local non-laminar flow. How about altitude and its effect on both air resistance and gravity? What about Coriolis force? Hell, what about relativistic effects such as Time Dilation / Lorenz Contraction? If one needed to undersand all that physics in order to catch a baseball, nobody would be catching 'em, yet we all can. Most of us can do it without even thinking about it, too. Sure the physics is interesting, but hardly necessary.

And I'm not suggesting that it isn't worth reading up a little on the physics - both hydrodynamic and aerodynamic. Interesting; yes. Vital; no. People were sailing, and sailing well, long before half the physics was articulated.

Speaking as somebody who does about equal parts fully crewed racing (on numerous different boats, including our own) and short-handed cruising on our own boat, I'd suggest time would be better spent investigating all the things that can be adjusted, and inquiring as to what one, theoretically, can hope to achieve through adjustment of that particular thing, and then actually sailing and adjust each thing, in a variety of conditions, to see how that actually manifests in reality.

But different strokes for different folks
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Old 31-01-2012, 15:50   #135
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Re: Sailors Don't Know How to Set Sails ?

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Not true. The designed wetted surface is usually optimised to increase waterline while reducing wetted surface at a given angle.
Ah but there we go into racing rules and the weird boat shapes as the result of those. If all racing rules are ignored, then the keel can only exert a righting moment when there is some heel, but it should be limited as much as possible. Our waterline length is optimized when upright just fine

Sailing upright is not very macho so many boats put the rail down in the water anyway. \

ciao!
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