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  #1  
Old 01-29-2002
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Crew/weight on the Bow

So, you hear it all the time in the racing fleet. Keep the weight off the bow. After the downwind leg, we always try and get the bow crew to wrap as quickly as possible "to keep the weight off the bow". I''m not saying I dont believe that bow weight might be detrimental to boat speed/performance, I would just like to see some real statistics. If anyone has a link or some reference to point me to, I would appreciate it. Any explaination or opinion would be good as well.
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Old 01-30-2002
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Crew/weight on the Bow

Because boats get narrow at the bow, there isn''t much area to hold up weight that is put there. This means that a crew member standing midships may make the boat sink in a half inch, but one at the bow could cause the boottop to be buried several inches underwater. Bows usually flare out rapidly in order to increase bouyancy as a wave approaches so the boat goes over,instead of through it. Putting weight on the bow pushes the bow down so a wider part of the boat has to push more water aside further for the boat to progress. This slows the boat down more than if a thinner part of the boat was cutting the water. There are also issues with keeping weight centered for speed. Spreading weight out may make for a smoother, more seakindly, ride (which may be desireable in certain circumstances, and which is actually designed in to some boats) but it sets up a rythmic pitching movement in the hull that a/causes the bow to dig in (which slows you down) and b/causes the stern to drag (which slows you down too). There are lots of books and articles on it, but that''s my understanding of it. I keep my anchor & chain low & centered, and send the smallest guy with good eyes up to the bow when I need to.
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Old 01-31-2002
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Crew/weight on the Bow

As Paul mentioned, weight on the bow increases pitching which results in an unstable flow over the sails. depressing the bow in moderate to heavy winds has a number of detrimental effects depending on the design of the boat. It pulls the run out of the water reducing the waterline length and reucing the ability to surf. It increases weather helm and in extreme cases can cause a wipe out. It increases the impact with waves.

In lighter air and flat water depressing the bow a little is not all bad. It lifts the larger wetted surface of the stern out of the water and gives the helm a little ''feel''.

As to real numbers, on the Kirby 25 that I had for a number of years, in anything above about 8 to 10 knots of air, it was a quantifiable .2 to .5 knots ever time someone went in front of the shrouds. You could literally watch it on the knot meter which we did on a number of occasions when we were ''labbing'' the boat. It was such and effective brake that when I wanted to slow down a little just before a start I would send to people to the bow until I was ready to accellerate again which combined with fishtailing was the best way to shread off speed.

Jeff
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Old 02-01-2002
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Crew/weight on the Bow

Thank you both for responding. Again, if you can remember the exact articles or references, please send.

Now, just for reference, I''m starting this discussion because I''m tired of the constant yelling to "Get off the bow!!". I feel like this perception of keeping weight off the bow, altogether and in any conditons, seems to be standard, little understood, rhetoric. People just say it/do it, "because everybody does it."

Now, too your reponses.

Point number 1. Weight on the bow causes the bow to sink-True. It follows that this would increase the width of the boat''s entry profile through the water, thereby slowing the boat during the moments that it passes through/over waves or wakes. Is this maybe an assumption? One would truly have to look carefully at the footprint of the boat''s lines at water contact to determine this. Designers mostly look for the average footprint/bootstripe to get the best performance under standard copnditons. It is certainly not the best under all conditions.

Would the entry profile actually widen by such a degree as to see a measurable effect on performance an all boats in all conditions? I don''t know. I don''t believe so. I do recall having read an article (sorry, no recollection on the reference) which was discussing the measurable increase in performance by keeping the water flow across the hull as stable as possible. In fact the article''s statistics seemed to imply that, on average, the flow''s stabilty of water over the hull could affect boat speed by as much as 20%, in some casses. Hence, the all important aspect of a clean smooth bottom. (How much do we spend on paint and weekly/monthly scrubbing?)

So, where I race, San Diego bay, we contend with wavelets (from wind) and the occasional ships wake. Its my experience that keeping the boat level and passing through the small waves (6 to 12 inches), as opposed to going over (allowing the boat to follow its own path up and over) may decrease my speed intitially but allows for increased acceleration and cruising speed more quickly after the wave. Is this due to a more stable flow over the hull? Again, I don''t know. It seems logical. Just as a deeper bow profile seems logical in decreasing my spped.

Point number 2. Spreading crew weight across the boat (instead of centered) can cause pitching. Its key that we have to consider the conditions. In light air (< 10 knots), low wave/swell action conditions, pitching will not occur. (Our situation 85% of the time here in San Diego) If there were pitching I can certainly see how that could drastically affect the flow of air over the sails. (i.e. cause instability in the wind''s flow over the sails).

But, does the pitching motion really increase with say 10% of crew weight moved to the bow? It seems so. The bow goes off waves at a steeper angle with the boats stern going higher over the wave. But at the same time the bow plows shallower through the wave while the stern stays more level at the begining. Maybe the pitching does not increase but, just seems as such. I don''t know without more experience. But, sometimes it doesn''t really seem so.

Minor Point in your responses. Bow down with stern out reduces water line length. Again, this may be significant on some boats, depends on the design. On my brother''s Ranger 26 has pretty steep flare at the bow. Keeping the stern down and pushing the bow down 1 inch actually increases LOW by 1.5 inches. But, on say an ID 35 where the bow is nearly vertical...no change.

Length on the water line though, is only a significant determinant when the boat is actually approaching or at hull speed. Not a common occurance around here. On our Summer Beer Can Series we regularly place first in our class (out of 14) with an average speed of 2-3 knots.

Anyway, all just a bunch of rambling. More opinions the better. I''m certainly interested in more feedback. What I do know is that I am going to spend some time testing various combinations of crew weight-particularly in light wind conditions, against pointing ability and speed/acceleration.

Thnaks again.
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Old 02-01-2002
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Crew/weight on the Bow

If you''d like to dissect this topic thoroughly, please read just about anything by C.A.Marchaj on aero or hydrodynamics. Amazon has offerings that range from $17.50 for used, out of print books, to $120 for his tome, actually called Aero/Hydrodymanics. I can''t remember if he''s an MIT professor and floats his boat in Marblehead, or if he works at McDonnell Douglas and sails out of San Diego on weekends, but that''s the idea.
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Old 02-02-2002
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Crew/weight on the Bow

Tony Marchaj is retired and lives in France.

Jeff
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Old 02-02-2002
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Crew/weight on the Bow

Ahoy, Gentlemen, far be it for me the Pirate of Pine Island to get involved in a disussion on racing but it seems to me from my experence,limited though it is that the only time weight on the bow was advantageous came soley from the fact that our hard chined vessel performed better bow down. My current more traditional hull does not. Hope that clarifies the issue some. Big Red 56
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Old 06-13-2002
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Crew/weight on the Bow

I sail several boats, and we mostly stay off the bow, but an exception is our Catalina 22. For some reason this boat performs best with most of your weight on the bow. It''s not a little difference; it''s like magic how the boats with the big fat guy on the bow pulpit take off.
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