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  #21  
Old 12-16-2010
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Quote:
Originally Posted by Sabreman View Post
On small boats, I see the advantage to keeping the boat heeled in light air - to keep the boom in one place and to keep it from flopping back and forth. Ignoring the mechanics of keeping the boom in place, without exception, everyone that I've asked has not had an answer why the boat should be heeled. It makes no sense, less sail area is exposed to the wind when it's needed most. I'd really like to see a real answer to this since it's puzzled me for years.
On most sailboats, heeling them to leeward and slightly bow-down in light air usually reduces the amount of wetted surface, which reduces the amount of drag. When the boat is oriented slightly bow-down, that raises the fat stern, which decreases wetted surface.
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Old 12-16-2010
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On most sailboats, heeling them to leeward and slightly bow-down in light air usually reduces the amount of wetted surface, which reduces the amount of drag. When the boat is oriented slightly bow-down, that raises the fat stern, which decreases wetted surface.
I'll buy that! Makes sense, but in the way of a followup question, I've always been schooled to stay aft to keep from burying the bow and creating more drag. Was I schooled wrong? As an aside, we're slightly bow-down (1") at the dock, without crew. So maybe I'm all set up!

On flat bottomed sleds, does the same hold true?
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Old 12-16-2010
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Sabreman, my last comments applied only to sailing to windward in light air.

With regard to a flat bottomed sled, it depends on whether tipping it in any given direction has the effect of reducing wetted surface. As I imagine a flat bottomed sled, tipping it one way or another probably wouldn't help.

Last edited by Sailormon6; 12-16-2010 at 04:11 PM.
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Old 12-16-2010
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understood
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Old 12-16-2010
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Smack, If you are looking for some simple formula that says for a given windspeed and AWA, put X pounds on the rail, you are not going to find it. Too many variables. Optimum sail selection, trim, heel and rudder angles are all part of the dialing in process when preparing for the racing season. For example, when I went to a tapedrive main, I had to readjust my whole game plan especially for stiffer wind conditions. You can certainly flatten the sails in order to depower them, but you will bleed speed when you do. You trim for maximum power and use your rail crew to flatten the boat and reduce weather helm. As a helmsman, I want to start putting guys on the rail when I start seeing a rudder angle in excess of ten degrees. When the wind is blowing twenty-twentyfive plus, I will have everyone on the rail and use only one guy to do all the trimming. I will also sit on the rail. I even do this when doublehanding. Read the RRS’ pronouncements and you will see that a lot of appeals have centered around the use of “moveable ballast”. It has a big impact even it you can’t distill it into a single, simple formula.

In regards to light air conditions, inducing a heel will generate weather helm which will get the boat pointing more efficiently and increasing VMG. The big difference between a cruiser and a sportboat, is you can induce heel with only the forepeak and mastman on the lower side (and hidden behind the genoa, he, he.) on the sportboat.



Last edited by GeorgeB; 12-16-2010 at 04:43 PM.
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Old 12-16-2010
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While you are right that at some point heel angles need to be controlled with sail choice and trim, rail weight figures prominently in how much drive and how much drag the boat produces. While there is an optimum drive and optimum heel angle for any wind, how you attempt to achieve these ideals is a balancing act of sail trim and crew weight.

When you talk about the impact of rail meat, you really need to look at the whole equation and not just crew weight. Righting moment is the center of that weight times the righting arm. The righting arm is the dimension between the center of the weight of crew and the center of buoyancy. In most boats as a boat heels the center of buoyuancy moves to leeward.

So If we use the boat in your picture as an illustration, it would appear that the boat is heeled approximately 25 or so degrees (measured with a protactor rotated so that the measurement is adjusted for the focal point of the picture appearing to be off axis with the boat), (which, BTW 25 degrees is probably too high a heel angle for optimum speed. They seem to know that onboard since you can see that the mainsail trimmer has dropped the traveler and is vang-sheeting the boom to leeward in an attempt to flatten the boat and compensate for the weigh of two crewmen who are off the rail and up on the bow)

In the picture, the center of the crew weight is probably something like 5 feet off the center line of the boat. I'm seeing 9 guys on the rail and two on the bow. Assuming, all of the 11 guys are on the rail that is probably something approaching 2,500 lbs as they are dressed.

Again, eyeing the picture, the center of buoyancy at that heel angle has shifted approximately two feet to leeward. So that means a lever arm of roughly 7 feet, which when multiplied by the crew weight results in a righting moment that crudely would be somewhere around 17500 foot pounds (7 feet x 2500 lbs=17,500 foot-pounds).

To put this in perspective, lets assume that the boat in question has a 4500 lb bulb on its keel and that bulb is 8 feet below its center of buoyancy. At a 25 degree heel angle that bulb would be approximately 3.4 feet to windward of the centerline of the boat, which when you add the 2 feet that the center of buoyancy has shifted to leeward, results in a righting arm of 5'-4" and a righting moment around 24,000 foot-lbs.

In other words, the crew has achieved roughly 75% of the righting moment of the keel bulb with only 55% of the weight. That is pretty efficient, especially since the boat is not being penalized in their rating for the crew weight.

To touch on a couple of the fine points raised above. These days virtually all racing rules limit crew number and/or crew weight to prevent people from putting together a 'beef trust' and kicking butt in heavy going and from going too light in light air.

As has been pointed out, on crack race boats, this crew weight is used very strategically. In light air race-boats are often heeled to leeward and trimmed slightly bow down. This does a number of things. One of the big ones is that heeling a modern boat perhaps 10 degrees moves the wetted surface to the round of the chine and away from the flat of the bottom (a cylindar has less wetted surface per capacity, than an flattened oval) which reduces wetted surface pretty dramatically. Bow down also reduces wetted surface pretty dramatically by moving more of the wetted sruface to the cylindrial bow sections and away from the flatter stern sections.
Trimming to leeward and bow down trims some 'feel' into the helm and a bit of lift, so that the helmsperson can use a minimum amount of helm and yet hold a course.

Another advantage is that when a boat is heeled over gravity pulls the sails into a more proper shape so that any wind that encounters the sail is encountering a foil shaped object. Lastly, very often in light air the wind has a vertical component, falling slightly downward, and the heel angle exposes the sail more perpendicular to the wind.

Normally larger heel angles mean more leeway, but in light air, there rarely is enough side force that leeway is as much of a problem as simply maintaining forward motion and building apparent wind speed.


Jeff

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Last edited by Jeff_H; 12-16-2010 at 05:33 PM.
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Jeff - I'm not sure if you're referring to my Avatar...

In that photo, you are correct that we are at about 25 degrees. I agree that we're heeled a bit much. Conditions were fluky in the St. Mary's River at the end of Gov Cup this August. About 10-18 kts depending on where you were.

We carried 8 crew this year. I was driving and had one trimmer (in black). we were preparing to tack and he'd just eased the genoa slightly (a little early). They guy in orange was tucking under the boom and the rest of the crew (5) were moments from switching sides. The main was centered but extremely tight with a stretched leech. Not sure that I liked that, but the sail was flatter.

At the time, we had too much weatherhelm. Since then, we've replaced the genoa and a new main is coming in a couple of months. The sails in the photo (especially the main) are nearly dead. The genoa delaminated about a month after the photo was taken. We hope to see significant improvement next year.

BTW - Great assessment.
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I was actually referring to the photo in Smack's opening post. It was a little larger picture and so easier to see and measure. I must admit that I have enjoyed your avatar which is a great shot of your boat doing what a sailboat is meant to do.

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Quote:
Originally Posted by Sabreman View Post
I'll buy that! Makes sense, but in the way of a followup question, I've always been schooled to stay aft to keep from burying the bow and creating more drag. Was I schooled wrong? As an aside, we're slightly bow-down (1") at the dock, without crew. So maybe I'm all set up!

On flat bottomed sleds, does the same hold true?
All race boats benefit from keeping weight in the right place for the given conditions. The downhill weight to the rear you describe is for higher winds and waves when keeping the rudder in the water is job #1. In light air as someone else mentioned, many boats like weight at the mast and out of the stern to get the 'rear' out of the water. Hiking to windward makes a very large difference on most boats. It makes a huge difference in being able to power up the headsail to get through chop, keeps the boat flatter and measurably faster, and allows more sail area, and until you're at theoretical hull speed upwind, every little bit helps. Weight to leeward in light air upwind is equally important, as is using crew weight to help gybe and tack the boat with as little rudder movement as possible. It's faster. If a boat length or two doesn't matter to the skipper, then he/she's a rock star with blazing boat speed, or heading a program that just isn't going to be very competitive in a good fleet. Good preparation, good starts, good trim/sail handling, good driving, quick gear changes (including getting crew weight in the right place), and good tactics win races. When any of the above are lacking, at the best, you'll be wildly inconsistent in your results, but most likely, you're not going to in the running for the pickle pickle dishes at all.
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Old 12-16-2010
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Weight plays a huge part in racing, So much that with my Olson 30 the class is limited to 1100 lbs of crew weight on the boat. They move that down to 1000lbs for the nationals.
By moving the weight around depending on conditions can gain you up to a knot easy.
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