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-   -   Mainsheet load on 31ft boat (need new block and cleat) (http://www.sailnet.com/forums/gear-maintenance/73352-mainsheet-load-31ft-boat-need-new-block-cleat.html)

MarkSF 04-04-2011 10:58 AM

Mainsheet load on 31ft boat (need new block and cleat)
 
I need to replace the mainsheet block / cleat assembly on my Bristol 31.1. I looked at Garhauer, and they do 2000lb or 2800lb rating. Sounds ample for my boat? (180 sq ft mainsail)

Is the 2800lb one over the top? is 2000lb enough, or should I go for the extra margin?

There's no traveller, just a swivel that the block is attached to. Would be very surprised if the swivel is rated for 2000lb, so any suggestions for uprating that would be welcome.

zz4gta 04-04-2011 11:54 AM

It's around 600-700 lbs, so the 2000 lbs would be way overkill. As moast Garhauer products are. Is it a single block with a cleat? Double? Tripple? What is the current purchase?

MarkSF 04-04-2011 12:32 PM

There are two blocks under the boom, and the cleat block is a double. It looks like 3:1 purchase.

GeorgeB 04-04-2011 12:40 PM

MarkSF, I just happen to have the formula to calculate sheet loads.

((Maximum expected windspeed) ^2*(sail area in square feet))/232

When I plug in your 150 square feet and 25 kts wind speed, I get a load of 404 pounds which is well within the smaller block’s specs. To get to a thousand pounds of load, or half the block’s rated strength, you need to sail in 40kt breezes. No reason to “over kill”. Garhauer makes a pretty good block (ball bearings, etc), they are just a little “industrial” looking. They will be at the boat show and if you can wait, they usually have pretty good show prices. I had to google the Bristol 31.1 to get an idea of your rigging set-up and I saw an ad for one being sold in Alameda. Is that yours? If so, my boat is not to far from yours so PM me if you have any questions about the area. We’ve been sailing out of the Estuary for many, many years and love the close proximity to the Central Bay and the Ocean.

tommays 04-04-2011 03:03 PM

On a much smaller J24 for example its 4:1 and i would sure not want any less :)

The biggest issue is more the peek loads during tacks and jibes and is what has broken plenty of hardware over the years

MarkSF 04-04-2011 03:15 PM

I think it's actually 4:1. Guess I don't understand pullies much!

zz4gta 04-04-2011 03:36 PM

According to sailboat data, he has ~180 sf of main. Also, from looking at pictures, it's a 4:1 puchase on the mainsheet. So the block will need to be a double w/ becket and cam cleat.
Try one of the following.

http://www.defender.com/images/602157.jpg
http://www.islandwaterworld.com/prodimg/p271648.jpg
Or something like the 2611 below, but a double
http://www.twinsrecreation.com/asset...2608_PPM_2.jpg

KeelHaulin 04-06-2011 12:45 AM

I think I would stay with the two separate blocks on the boom, they are track mounted and you don't know what maximum load the track can handle in the event of a hard gybe. You might also consider going to a cascade system or double line sheet to gross/fine trim the sheet. Harken has systems like these, but they have a single block at the top. You might ask a Garhauer or Harken rep about it next week at the boat show.


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