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fullkeel

Able Bodied Seaman

Posts: 43

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Sep 28 10 12:47 PM

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David, I have read about how you reduced weather helm by moving the headsail forward and shortening the boom.  I was wondering if the same effect could be achieved by increasing the height of the rig?


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#1 [url]

Sep 29 10 5:11 AM

Actually the opposite would occur if you raised the rig height. A taller rig will apply more leverage to the mast, causing the boat to be more tender and heel more. As a sailboat heels, the underbody shape becomes asymmetrical--the more she heels the more asymmetrical she becomes, and that shape will increase weather helm. Additionally, you would need to reef earlier for any given wind speed. 

The easiest way to reduce weather helm, without making any permanent modifications is to take a reef earlier. Reefing a marconi main moves the center of effort forward, thus reducing weather helm.

Restoring a Bristol 29 in my backyard. www.bristol29.com

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fullkeel

Able Bodied Seaman

Posts: 43

#2 [url]

Sep 30 10 9:19 PM

hi david, makes total sense.  how about this take:  could you increase the height of the mast enough such that it would allow the boom to be shortened so it does not extend into the cockpit area and still maintain the power of the rig?

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#3 [url]

Oct 1 10 5:53 AM

To shorten the boom so that it extended only to the aft cabin bulkhead would mean your boom would only be 8 feet long. In order to raise your mast enough to have the same sail area in the main, your mast would need to go to over 50 feet. That would make the boat incredible tender, not to mention the extra weight would throw everything out of balance. I don't see that as a possible solution.

Restoring a Bristol 29 in my backyard. www.bristol29.com

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tm

Fiberglass Sander

Posts: 6

#4 [url]

Feb 13 13 9:11 AM

Hi all,
I am looking to reduce weather helm in my B29 by moving the main sheet traveller forward. It seems that Hereshoff's comments were that if there is too much weather helm when going to wind it is time to reef.  I prefer to keep full sail at 20 knots, when the boat is really in her element, and I am not keen to to alter the mast, boom or mainsail just yet.  So I am thinking of moving the main sheet traveller forward, as it is now positioned aft of the cockpit, in order to move the sideways force forward in the boat and reduce the effect.  Does anybody have any input or experience with repositioning the main sheet traveller (and boom block) for this purpose? Any comments are appreciated.
Thanks, TM

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#5 [url]

Feb 14 13 6:22 AM








In theory this might seem logical, but in fact, where the mainsheet sheets to the boat has no effect on weatherhelm. If you move your sheeting point to a traveller forward of the companionway, you will likely bend your boom in a big wind. 

Weatherhelm is the difference between the center of lateral resistance on the keel, and the center of effort from the sails. The CE will be aft of a vertical line drawn from the CLR and that difference is called the lead (rhymes with seed). The more lead--the more the CE is aft of the CLR--the more weatherhelm. 

The only way to reduce weatherhelm is to move the CE point forward. When you reef the main you do just that (the smaller the triangle, the more the CE moves forward). If you move it forward of the CLR you will have lee helm (drop your main and sail on your genny and you will see what I mean). 

To move it forward you need to either move the mast forward, which you can do by adjusting your rigging (it will help a tiny bit but on the B29, not enough to be really noticeable). You can move the jib forward using a bowsprit, you can shorten the boom and reduce the size of the main, or you can sail with a reef most of the time. The problem with the B29 is the giant main that was encouraged under the old CCA racing rules. Making the boat stiffer can also help a little bit so you could add ballast into the lowest point in the bilge. 

Whatever you do, don't mess with the rudder. Changing the shape of the rudder does not affect weatherhelm, it will only ruin the sailing qualities of the boat.

Good luck,

David






Restoring a Bristol 29 in my backyard. www.bristol29.com

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#7 [url]

Feb 17 13 9:23 AM











That’s not a silly question at all, but one that is hard for me to answer. Hull speed relates always to wind speed, and weatherhelm is a reaction to wind speed upon the current sail plan. One man’s nuisance is another man’s patience and so weatherhelm might be a nuisance in one day’s sailing but not in another’s. Obviously as wind speed increases for the same sail plan to stay on the same heading you will have to crank in more rudder as weatherhelm increases. The more lee rudder the more drag which slows the boat.  On some boats, weatherhelm will actually overcome the rudder and the boat will round up into the wind regardless of how much the tiller is hauled to weather. I have seen Catalinas do that often, but I think spade rudders are more easily stalled than keel attached rudders. Luckily the Bristol rudder will not stall that way, but at some point the helmsman’s patience is overcome and it’s easier to reef than to continue.
On one of the first sails in my B29 back in 1988, the weatherhelm was so strong that I broke the original Bristol cast bronze tillerhead. I would classify that and the resulting fire drill when I was suddenly holding a tiller no longer connected to the rudder as slightly more than a nuisance. That’s when I decided to look into the ways to reduce WH and make to boat more pleasant to sail.
Alll that being said, I would take a guess that at around 5 knots of boat speed, if you are sailing close, you will be needing more than 5 degrees of rudder to stay on your heading. Beyond that it’s up to the skipper to decide when to reef, or luff the main or change the heading to reduce WH.
Cheers,


David








Restoring a Bristol 29 in my backyard. www.bristol29.com

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rpicciotto2004

Able Bodied Seaman

Posts: 29

#8 [url]

Feb 17 13 11:50 AM

thanks david.  great answer.  as far as i am concerned, 73 years on the planet have almost taught me to be patient, and unless there is overwhelming need for speed, at 5 kts to weather under the 100% jib, the accompanying head seas are enough to make me think seriously about putting one reef in the main.  so much for gerontology.  

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tm

Fiberglass Sander

Posts: 6

#9 [url]

Feb 18 13 8:37 AM

Thanks David.
Your explanation makes sense.  It looks like reefing is my best option.
Waiting for warm winds.
TM

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