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Old 02-20-2008
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Boom vang block selection

I am replacing some antique boom vang blocks and need to select the new ones. How would I estimate the working load for the vang on a 35' boat?

Schaefer series 5 is in stock at Defender and fits my selected line size (7/16" - just like my halyards) - but I have no idea if 1800lbs of working load is enough. Sure sounds like "a lot" but then Scahefer says these blocks are "for boats up to 28'" - then again, depends on application I suppose?
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Old 02-20-2008
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Might want to contact Garhauer Marine. They make some really nice gear at very reasonable prices.
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Old 02-20-2008
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Wow.

I have absolutely no idea, though it's perfectly good question. I'd say offhand, as long as it looks as though it can take twice the load of your mainsheet, it's probably okay. Keep in mind that the vang probably takes as much load as any other piece of running rigging on your boat, and plan accordingly...
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Hm, didn't think about that - somehow I thought vang is less loaded, because it has shorter arm of force operating against it - but then again, that may mean less leverage, so may be it is more.

My personal preference is for Ronstan blocks, but the appropriate series aren't in stock at Defender and I don't really have time to go looking around. It would be great to figure out at least a ballpark load for this application.
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Old 02-20-2008
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Quote:
Originally Posted by brak View Post
I am replacing some antique boom vang blocks and need to select the new ones. How would I estimate the working load for the vang on a 35' boat?

Schaefer series 5 is in stock at Defender and fits my selected line size (7/16" - just like my halyards) - but I have no idea if 1800lbs of working load is enough. Sure sounds like "a lot" but then Scahefer says these blocks are "for boats up to 28'" - then again, depends on application I suppose?
I asked the rigging guys at West this same question... I had to replace the vang on my boat as well....

They asked about the square footage of the mainsail, the length of the boom and where the attachment points were. He used that to determine which blocks / mechanical advantage system would work the best.

An 8:1 system can impart alot more force to the attachment points, so I had to take that into consideration as well and refit as necessary. I ended up with 7/16 system for a 34' boat.

I'm sorry I can't provide the "square-footage vs. force needed" stats.

Hope this helps,
Craig
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Quote:
Originally Posted by brak View Post
I am replacing some antique boom vang blocks and need to select the new ones. How would I estimate the working load for the vang on a 35' boat?
If you're replacing them, I'd suggest selecting blocks of about the same physical size and, given modern construction methods make blocks a bit stronger than they used to be, you'll be fine.

The important thing is to not go too small... an exploding vang block would not be a pretty sight. In fact you wouldn't want to be anywhere near it!

Have you considered one of the new-fangled ram setups?
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Old 02-20-2008
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I am trying not to change too much - rigid vang would be nice but I need to sail more before I figure what I want from the rig. I might replace the entire boom at some point anyway.

Original blocks are a bad guide in my case - one is well over 35 y/o - who knows how strong it is. Another is a Schaefer, looks like series 5. I like them, they look very shiplike, and feel solid - but their specs are marginal, 1800lbs SWL.

I just ordered a pre-made Garhauer vang set - it includes both blocks and a line, so its at least $100 less than me buying those things separately. Plus, their blocks have SWL of 2800lbs which sounds about right. They are "modern style" which to me means - ugly, and won't look right on my boat, but I guess I'd rather select function over form.

I found a sort of a guide somwhere on the net, that suggests assuming for wind of up to 20kts about 1.5lbs per sq. ft. of mainsail for fittings on the end of the boom, and 3lbs per sq. ft. for mid-boom fittings. Continuing this further a fitting 1/4 way from the mast, like a vang, would experience double the load at 6lbs / sq. ft. of main. My main is about 230-240 sq.ft. which makes the load in a ballpark of 1400-1500lbs. It goes up as a square of wind force (but then again, I'd be reefing by 20 kts, reducing the sail size). So, Schaefer is marginal and Garhauer is more than enough.

Other manufacturers (Harken, Lewmar) have blocks that look even more "modern" (can't look at those things without squinting) and more expensive.

So that's my research for the day.
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