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  #21  
Old 03-27-2013
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Re: Mainsheet size?

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Originally Posted by Stumble View Post
Med,

If its going to be trimmed from the winch, then none. Perhaps 2:1 at the most.

If we assume that a maximum sheet load is 3,000lbs, and the winch has a 40:1 purchase that means the max handle load should be around 10lbs. Add in a little extra for friction loss and you still have way more purchase than you need.

The typical design for a winch trimmed main is to have a double ended sheet so you can fast trim at 1:2, then at 1:1, then on the winch at 40:1. More than this is just silly on a moderate size main like yours.
By double ended do you mean european or german mainsheet where it goes to 2 winches? I don't have 2 winches.... What I would like to be able to do is hand sheet until it is blowing a bit, then use the winch when needed. As others have pointed out, the main is the first sail on my boat to be reefed, so I expect that with modest purchase I could be sheeting it by hand on most days.

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  #22  
Old 03-27-2013
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Re: Mainsheet size?

Med, if you want to be able to hand sheet it primarily, with the winch available as a backup, then you should probably size it based upon controlling it that way. Assuming a 1500lbs max load trimmed by hand, you would need something like a 30:1 purchase arrangement. This is why on mid boom sheeted mains they pretty much have to be winch controlled. The rough number is that a person can exert around 50lbs of force on a line for brief periods. Beyond this it isn't practical. On my Trip 40 we had a 24:1 and a cascade 48:1 on the main, but it was still pretty marginal.

By switching to a winch, you immediately get somewhere in the 40:1 range in low gear, meaning even a 2:1 or 3:1 additionally while nice, isn't really necessary. The downside to additional purchases is that you also increase the amount of line you need to crank in, and the amount of tale left in the cockpit. Which may or may not be an issue depending on your boat.

If I was setting up a winch driven system, I would just assume that I was going to use it most of the time. Otherwise on a sail this big you have to have a major increase in necessary purchase.
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  #23  
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Re: Mainsheet size?

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Originally Posted by MedSailor View Post
My new setup will be going from the boom, through a fiddle block a couple times, then forward to the mast, down to the deck, around a deck organizer, then to a rope clutch and finally a winch. Any thoughts on how much purchase I should have for my 400sqft sail before the winch?

This is what I have in mind, though I'm really hoping that I don't need a deck organizer near the mast AND at the winch....


Thanks for all the help so far.

MedSailor
I think my main is aproximately the same size as yours.
I have a German double ended system, when we rigged this the choice was 1:2 or 1:4, chose 1:4 (with a 1:40 winch). Reasoning was that it would be easier to go from 1:4 to 1:2 if we wanted to change....
We still use 1:4 as it give some more leverage while sheeting in by hand.

As for leading the sheet to the winch it all depends on where the winch is located.
We use a the secondary cockpit winches, so the sheet go from the goose neck down to a block at the chain plate (see picture - note the attachment is at the bottom of the turnbuckle - and this solution have been cleared with a competent rigger)
Used a Dyneema loop


The best advice is to try out the lead using some blocks and rope.
Remember to test all boom positions, you don't want the sheet self adjust while tacking.

My sheet winch (one)
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  #24  
Old 03-28-2013
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Re: Mainsheet size?

Quote:
Originally Posted by Stumble View Post
Med, if you want to be able to hand sheet it primarily, with the winch available as a backup, then you should probably size it based upon controlling it that way. Assuming a 1500lbs max load trimmed by hand, you would need something like a 30:1 purchase arrangement. This is why on mid boom sheeted mains they pretty much have to be winch controlled. The rough number is that a person can exert around 50lbs of force on a line for brief periods. Beyond this it isn't practical. On my Trip 40 we had a 24:1 and a cascade 48:1 on the main, but it was still pretty marginal.

By switching to a winch, you immediately get somewhere in the 40:1 range in low gear, meaning even a 2:1 or 3:1 additionally while nice, isn't really necessary. The downside to additional purchases is that you also increase the amount of line you need to crank in, and the amount of tale left in the cockpit. Which may or may not be an issue depending on your boat.

If I was setting up a winch driven system, I would just assume that I was going to use it most of the time. Otherwise on a sail this big you have to have a major increase in necessary purchase.
All good points, though as I work though both winch, and winch-less systems I still think there is an argument for a moderate amount of purchase. With a 4:1, by the math, it looks like I might be able to hand sheet up to 10kts. I realize that the reality will be different as friction from blocks will make it harder, the rope clutch adds resistance but generally makes hand sheeting easier etc. I will probably also be able to hand sheet off the wind.

Even without any hand sheeting, the 3/4:1 purchase has the advantage of being easier on my blocks and cabin-top hardware (except the traveler car) Without some purchse I would need a turning block at the mast rated for 6000lbs and rope clutches rated to 3000lbs. I'm finding that those are hard to find in the size line (and cost bracket) that I'm using.

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  #25  
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Re: Mainsheet size?

We started out with a 4 part winchless sheeting system.. we're now up to 6 parts for better control. The good bearing blocks reduce friction considerably.

Makes controlling gybes much easier/less scary too.

btw our main is 41P/14E.. similar to yours??
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Re: Mainsheet size?

Quote:
Originally Posted by Faster View Post
We started out with a 4 part winchless sheeting system.. we're now up to 6 parts for better control. The good bearing blocks reduce friction considerably.

Makes controlling gybes much easier/less scary too.

btw our main is 41P/14E.. similar to yours??
I'm a little lower aspect. 42'P (luff will be 41) 17'9" E (foot will be 17'3"). Lots of roach, especially at the head of the sail for a total of 398.25sqft. (400 square feet to me)

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  #27  
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Re: Mainsheet size?

For the traveler car end, is there an advantage of this kind of block

over this one?


Less friction???

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  #28  
Old 03-29-2013
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Re: Mainsheet size?

no difference. the double sheave is done on the larger sizes because if you have lower sheave that is 4" then the top one would need to be 6" and that makes a very tall block. it done to keep the assembly as low a profile as possible
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  #29  
Old 03-30-2013
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Re: Mainsheet size?

Med,

As overboard mentioned they are used to try and control the block size. When dealing with large line size (1/2" or larger) keeping a 8:1 turning radius means the smaller block should be at least 4" which would mean a 6" upper wheel minimum to give enough clearance.
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