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-   -   Weather helm and Weight (http://www.sailnet.com/forums/general-discussion-sailing-related/98801-weather-helm-weight.html)

theonecalledtom 04-24-2013 01:59 AM

Weather helm and Weight
 
Spent about 6 hours on a single beat at the weekend, 3 of us sailing a Beneteau 36.7.

One of things we noticed was the massive effect of where the non helmsmen sat on weather helm. With both crew forward of the mast it was possible to completely neutralize the helm, with both in the cockpit (and a full tank of fuel below our feet) the boat was a trying to head up hard in the gusts.

Just thought I'd share it, as I've always focused on sail trim first up to now...

mdbee 04-24-2013 02:15 AM

Re: Weather helm and Weight
 
Chubby friends? :)

theonecalledtom 04-24-2013 02:30 AM

Re: Weather helm and Weight
 
Boat half the weight of my last boat...

blt2ski 04-24-2013 08:50 AM

Re: Weather helm and Weight
 
crew wt and placement can be a BIG factor in weather helm. On my 28' boat, I am moving people about frequently. Down wind especially, not so much for weather helm, but to get the ass out of the water so we are faster downwind! We can gain upwards of 1/4 knot sometimes a half this way.

Marty

theonecalledtom 04-24-2013 10:28 AM

Re: Weather helm and Weight
 
The difference for us was about a quarter turn on the helm - very dramatic.

Every time I've read about it its seemed the main factors to address are traveller, twist, backstay etc but this weight movement has been the biggest single factor I've noticed.

RichH 04-24-2013 11:24 AM

Re: Weather helm and Weight
 
For especially sails made of 'dacron' and NOT rolled-up on 'furlers' .......

The simple answer (for when closehauled), usually ignored by almost all cruisers, is
1. change the mainsail halyard (and/or cunningham) tension ... which repositions the where the 'position of maximum draft' occurs in the mainsail - to rebalance the helm pressure. The more 'fore' where the max. draft occurs, the lesser amount of so-called 'weather helm' (if the boat was set up 'correctly' in the first place).
2. be sure that the headstay is not 'sagging off to leeward' which promotes a boat to 'skid to leeward'.

Several easy steps to determine exactly what is going on when you 'develop' so-called weather helm when attempting to sail 'close hauled':

FIRST is to look at the stern wake ... see if the rudder and keel turbulence wake is coming almost STRAIGHT off the stern; if not, then youre probably skidding and you need to tighten the forestay (via backstay tension).

SECOND, If the stern wake is seemingy 'straight', then you probably have 'weather helm' and you then need to change (usually) to more halyard/cunningham tension until that so-called weather helm is lessened or eliminated. (If you have a 'rudder position indicator' if the 'gage' is showing more than about 4-5 of rudder angle to hold a straight course when 'beating' ... thats 'weather helm', usually easily corrected by (more) mainsail halyard tension). You simply cant do this with sails on 'furlers'.
BTW#2 if youre dragging your rudder almost sideways to correct for 'weather helm', that will result in a slower boat at greater heel angle ... and that greater amount of heeling will also contribute to 'weather helm' in some (non-symmetric hull shape) boats.

Rx: With a boat that was previously set up with 'proper' rigging tension, when you develop 'weather helm', the FIRST thing to do is look at the stern turbulence wake to determine if: 1. boat skidding off to leeward (too loose forestay/backstay); or if, ....
2. actual weather helm (too loose main halyard/cunningham tension).
.... and every damn day requires different tensions depending on wind speed and wave height.

Set-ups:
• Mainsail luff (halyard) tension - How to properly RAISE a woven dacron mainsail - SailboatOwners.com
• Forestay (backstay) tension: http://www.ftp.tognews.com/GoogleFil...f%20Hollow.pdf

theonecalledtom 04-24-2013 01:29 PM

Re: Weather helm and Weight
 
See - adjusting halyards, cunningham, traveller position, outhaul, adding twist in high winds, flattening sails in more normal winds, tightening the backstay (I'll admit to not playing with the forestay much, rig tuning is something I plan on working on learning this year) etc are my normal go to controls. What I'm saying is that, for my slightly fat, 12k lb, 36ft fin keel boat the biggest single effect on weather helm so far, other than reefing, has been moving people around on the boat.

Thank you Gary Jobson for listing this as one of the primary WH controls.

Interesting point on stern wake RichH - in the video here we're sailing unbalanced as it was shot just before realizing the influence - can you tell if we're skidding?


zz4gta 04-24-2013 01:46 PM

Re: Weather helm and Weight
 
http://www.beneteaufirst367.org/clas...ClassRules.pdf
See rule 3.4 B

The 36.7 is a weight sensative boat. Class crew weight is 1,550 lbs. If there wasn't a significant advantage to heavier sailors, then they wouldn't have that rule. Stack 9 people on the rail with one driver (10 total) and it's a huge difference. That's 1500 lbs of righting moment. And that's why you see people hiking when racing. It makes a big difference.

Theonecalledtom, it's really hard to tell if you're going sideways b/c there is nothing to reference the boat against. The waves are fluid, your wake, etc. But judging by heel angle, it doesn't look like you would be going sideways. The 36.7 (like most boats) really suck when you put the rail in the water. Flat is fast.

ajoliver 04-24-2013 04:32 PM

Re: Weather helm and Weight
 
Don't know about Bendy-Toes, but for some boats weather helm can be greatly reduced (and pointing much improved) by raking the mast farther aft. I know this seems counter-intuitive (shouldn't more rake move the center of effort aft - thus causing even more weather helm?), but it works. And again, I cannot testify about any boat but mine.

RichH 04-24-2013 09:53 PM

Re: Weather helm and Weight
 
Quote:

Originally Posted by theonecalledtom (Post 1020855)
Interesting point on stern wake RichH - in the video here we're sailing unbalanced as it was shot just before realizing the influence - can you tell if we're skidding?

Your stern wake somewhat shows that youre skidding but that is best viewed from the cockpit looking back.
The large slack sag in your forestay from what I can see in your video is definitely excessive ... probably the prime reason for the skid and the 'heavy helm'. The very first frame in the video shows absolutely NO jib luff except the very bottom of the tack section ... all the rest has greatly sagged behind the view of the mast.
What your probably feeling as weather helm is the skid's side pressure on the rudder.
At the end of the video the leech of the jib seem VERY tight (probably hooked up to weather) which kind of also suggests and supports the too loose headstay.

I'll try to find some geometric sketch / sail plan of the 36.7 and calc for you what the backstay tension should be to arrive at a 12-15% forestay tension. Is that one or twin backstays?

Nice boat !!!! good video. ;-)


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