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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation > wind conditions and reefing
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


Thread: wind conditions and reefing Reply to Thread
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Topic Review (Newest First)
09-25-2012 06:15 PM
AdamLein
Re: wind conditions and reefing

Quote:
Originally Posted by MarkSF View Post
Your first paragraph presumes wrongly that righting arm is only related to distance from axis of rotation.
It does not. I can make the same argument using only the horizontal component of the distance, which is what I was actually intending.

I guess what I'm not sure about is the vertical location of the axis of rotation, relative to the crew's COG.
09-25-2012 05:29 PM
MarkSF
Re: wind conditions and reefing

Quote:
Originally Posted by AdamLein View Post
Presumably the folks on the high side are as far or farther from the axis of rotation than the folks on the low side. So their righting arm is as long or longer.

I say "as far or farther" because the center of buoyancy shifts to leeward, which I think implies that the axis of rotation shifts to leeward as well.

Your first paragraph presumes wrongly that righting arm is only related to distance from axis of rotation. There's a vector component too. Righting moment is proportional to the horizontal component of the distance, as it's gravity acting on the weight, doing the work.

Think of 3 people on each side, with the boat at an extreme angle of heel. The 3 on the high side could be directly over the centre of rotation and despite being a long distance away from it, the horizontal component of their distance is zero and hence they provide no righting moment.

The 3 on the low side are the same distance from the centre of rotation but their horizontal component is maximised. They are making the boat heel more.

Generally the effect of ALL weight above the waterline is to reduce the righting moment, and the more the boat is heeled the more the effect.

The exception is when the weight is on one side, but the effect of that still drops as you heel and can reverse in effect at extreme angles.
09-25-2012 04:27 PM
AdamLein
Re: wind conditions and reefing

Quote:
Originally Posted by MarkSF View Post
In that case the effect is likely to be minimal at best, and could even make the boat tip more. The guys on the high side, when heeled, could be over the centre of mass, while the low side have a considerable arm. As the boat heels more, mass higher up has the effect of reducing the righting moment.
Presumably the folks on the high side are as far or farther from the axis of rotation than the folks on the low side. So their righting arm is as long or longer.

I say "as far or farther" because the center of buoyancy shifts to leeward, which I think implies that the axis of rotation shifts to leeward as well.
09-24-2012 02:29 PM
MarkSF
Re: wind conditions and reefing

In that case the effect is likely to be minimal at best, and could even make the boat tip more. The guys on the high side, when heeled, could be over the centre of mass, while the low side have a considerable arm. As the boat heels more, mass higher up has the effect of reducing the righting moment.
09-24-2012 02:20 PM
AndreasNYC
Re: wind conditions and reefing

I was thinking I would strap them to the bottom of the kheel for maximum leverage.

Actually our cockpit is pretty small so where where sitting 3 on the high side and 2 on the low.

A
09-24-2012 01:46 PM
jameswilson29
Re: wind conditions and reefing

Quote:
Originally Posted by AndreasNYC View Post
How much difference do you think the extra people made?
Andreas
It depends on how large your friends are...

Probably made quite a difference, even on a 13K lb. boat with a 34% ballast to displacement ratio. With an 11' beam, you had all that weight positioned 3-5' windward of the center of buoyancy, probably just about in line with the center of the displacement/gravitational pull of the boat.

Of course the weight is high in the boat. Next time, see if they will all huddle belowdecks on the windward side... or in the bilge...
09-24-2012 11:38 AM
AndreasNYC
Re: wind conditions and reefing

So I have discovered that putting a reef in my headsail solves 90% of the problem
We where out on Saturday with 5 people on the boat.
I saw the wind was more than predicted so we used the rolling furler to reduce the jib from a 130% (or maybe 150%?) genoa to jib sail size. After that she handled fine in 26 knot winds. Heeled up to 30 degrees while going upwind at a nice clip. (7 knots)
How much difference do you think the extra people made?
Andreas
09-16-2012 05:10 PM
JBIZZ
Re: wind conditions and reefing

Not familiar w/ your boat but in lets say 30 knots or more I personally would just use the motor. I've got a Sabre 28 @ 7800 pound displacement, w/ fin keel & 4.5' draft. In 25 knots I would just use the main alone w/ no reef (my dad would have the genoa up as well). I grew up racing w/ my dad so I have a little different perspective. We were once in a race w/ 25 knot winds & 30 Knot gusts. My dad decided to fly the spinnaker, which no one else was doing in the race. It was a lot of fun until we broached but he decided to continue to fly the spinnaker until we broached again & water started pouring into the cockpit. It all depends what your comfortable at. If you feel your heeling to much you can ease the main or reef it or fall down.
09-13-2012 04:37 AM
chef2sail
Re: wind conditions and reefing

W have ez- jacks which are out of the way at the mast so our full batten main is not hung up on them. After havinbg lazy jacks for years these are a huge improvement. Thye even have a system for deploying from ther cokpit although we dont do that.

You can make these also if you are so inclined, but they really arent that expensive.

Dave
09-11-2012 01:36 PM
MarkSF
Re: wind conditions and reefing

My old lazyjack system was removed last month, and now I'm finding it much easier to put the mainsail up, and change reefing, especially when close reaching on the jib.

I designed a new system that would allow each side of the lazy jacks to be lowered independently or together. for raising the sail or reefing.The two lines that go up to near the top of the mast would go around blocks, then come back down the cleats on each side of the mast. The old system terminated at the top of the mast.

If you wanted to get really fancy you could bring the two "lazy jack halyards" back to the cockpit.
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