Line for preventer?

[memelet]

I've rigged amsteel lines from boom end to near goosneck with shock cord inside to keep them snug. (Shock cord idea came from BrionT. Very clever!)

I will now run the second part line from the bow back to the cockpit. What kind and what size of line should I use. Boat is 42 feet, main is about 400 sf.

Also, what should be the weak link? Don't think it will be the boom lines. The padeyes at boom are quick hefty with big backing plates. 1/4 amsteel will probably outlive the boom braking. (But my boom wall is very thick.) I'm using a colligo soft shackle blocks at the bow, and thats roughly 10k lbs break. So I'm guessing it has to be the long line that should break, no? But again, what kind of line and what size?

thanks much!
-barry

(rigging is just too much damn fun -- really cuts into time under sail ;-)

[allene]

I can't comment on the line size you need but I can point out some things I observed on my boat, which has the same setup. First, any stretch and the boom can come around as it takes only about 10% change in length in the line from the prevent position to the boom straight back. You are right to use Amsteel as I tried using 7/16 StaSet and it has too much stretch, won't work. It would be OK if you only went from the boom tot he bow but the long run back to the cabin is just too much unless the line is very low stretch. What this also means is that the boom has huge leverage on the line. It just doesn't take that much force on the boom to really tighten up the line. Make sure you do these calculations before picking the line. I use I think 5/16 Amsteel line but just because that is what I had lying around. My boat is 36 feet. I don't think it is too large though.

Allen

[memelet]

Interesting Allen. I've been reading lots of contradictory stuff on preventer line. Some say to use 3 strand to allow for shock loading. Others say staset so as to allow too much stretch.

I've been thinking more like you do, because I will run the lines from the bow back to the cockpit, so clearly 3 strand would be worthless.

thanks!

[Auspicious]

I'm definitely in the "minimum stretch" camp. My opinion may not be worth a lot, but I'm sitting over here next to Evans Starzinger. *grin*

[Brion Toss]

Hi there,
I used to use Sta-Set for the deck pieces, and Regatta Braid for the boom. The Regatta was the short run, so didn't stretch much, but it had enough give that it could absorb shock loads. The Sta-Set was too elastic, though, so I switched to Sta-Set-X. Now that that is becoming scarce, I might go to VPC or the like. Oh, and nowadays on the boom I use Spectra, but with a short piece of bungy cord inserted, for shock load. The Spectra is much lighter, doesn't soak up water, doesn't hang down so readily.
5/16" for a preventer on a 36ft boat? Way overkill.
As for the weak link question, there shouldn't be one; anything in this system that can be counted on to part in an emergency can be counted on to part when you don't want it to.
Fair leads,
Brion Toss

[JohnV]

I'm confused--if Sta-set is too elastic, then why insert bungy in Spectra for shock loads? Or is the bungy just to keep the Scectra taut when it's not in use?
I'm trying to figure out the best combination for my 33-footer.
John V.

[JohnV]

Wait a minute---(smack forehead)---if you put the bungy inside the length of the 12-strand, then stretching the bungy keeps the line taut. But stretch it more, and the dyneema takes over the load.
Elegant.
Wonder if anybody else has thought of it...
JV

[matt the rigger]

The lower stretch the better. I agree with Brian that there should not be a "weak link". And the shock cord in the line has been done for years.

[Brion Toss]

Originally Posted by matt the rigger

The lower stretch the better. I agree with Brian that there should not be a "weak link". And the shock cord in the line has been done for years.

Yes, true, I have done it for years. The first place I saw it was in a 3-strand mooring line. That would have been somewhere around 1980. You'll find a description in the Apprentice. Since then I've been playing with it in a variety of constructions, currently in mooring lines.
Fair leads,
Brion Toss

[memelet]

Sorry for coming back so late; I did not realized I had my responses.

Originally Posted by Brion Toss

Hi there,
Oh, and nowadays on the boom I use Spectra, but with a short piece of bungy cord inserted, for shock load.
Brion Toss

Hmm, I put in the shock cord but really it seems to only keep the line taught when attached to the boom and not in use. It only takes a couple of pounds before the amsteel takes the load. Am I doing something wrong?

Originally Posted by Brion Toss

5/16" for a preventer on a 36ft boat? Way overkill.
Brion Toss

Did I say 36ft boat? Well is 42, so probably not that much different. The 5/16 is the amsteel on the boom. I used that because I had it left over from the life lines.

So I gather that I should warp speed or something similar for the deck pieces?