TDW - the one you show if the loop slips 'over' it will jam tight. The 'ears' on the rescue-8 prevent this.
Rich, good man, thank you. I'm still trying to find one of those horned or eared versions. We've not had a problem with ours but I take your point and better to be safe than etc etc.
Looking at the Wichard it doesn't look a great deal stronger than either what we have now or the CMI so I doubt stronger is required. One point though, when used as a boom break the lines go through the descender very differently than when it used for climbing, most importantly it is also used upside down.
My preventer is a long bit of 6mm rope from one stern cleat, along to the amidships cleat, up to the mainsheet fitting on the boom and down the other side and back.
At the boom fitting i have tied a loop and the loop is attached to the fitting with a couple of turns of 4 mm line that should have a breaking strain of a few hunderd kilograms.
I bought a mountaineers "descender" like the photo of the red one in the posts above for about $10 but I have stopped using it as this system is simpler and beter.
The idea is not to stop the boom flying across under all circumstances. It is to stop it flying across at the same time as the boat gybes accidently (a second or 2 later is fine). Or to stop the boom coming across from a wave and rolling etc.
I want the 4mm line to break before the boat is pinned down aback.
In the video below you can see how mine is set up - its not in closeup, but you'll get the idea Its the light coloured lines either side of the main sheet at the boom. I am running pretty deep downwind and you can see the boat rolling so this is where a preventer is good. Not so you can sail by the lee with thumb in bum and mind in neutral!
I can't get the YouTube video to embed properly Can someone tell me how?
- stretchy is good as it absorbs dynamic loads, IMHO
- stronger is better, just make sure you can release the preventer easily and in a controlled manner when you have to
- snap shackles are quick and convenient, but they break at the most inopportune times (like, in the middle of an uncontrolled jibe), so if you're going to use one go oversized. (I have a snap shackle on one side and I tie a knot on the other because the shackle broke)
- I prefer end-boom preventers as you're less likely to break the boom, especially if you drag the boom in the water as you roll to and fro, which happens sometimes in downwind sailing when the seas get up
My preventer is set up with a line port and starboard from the cockpit to big blocks on the bow and from there outboard back to the shrouds where the lines are attached when not in use. There is a single, stretchy line attached to a bail at the end of the boom that is long enough to run to the gooseneck where it's cleated off when not in use. To rig the preventer join the port or stbd line to the one on the boom and tension it from the cockpit. The disadvantage of this set up is that you need to reset the preventer after a jibe/tack.
In sizing the line....go to a good rig shop and ask what they recommend (and why).
AWESOME! Congrats. Those are sweeeet boats. Send a pm if you are ever in the South Bay....
Where do you normally sail? I've been sailing out of Redwood City a lot. Not so much now the boat is in Alameda. I might move it back to RC but I'm going to try Alameda for a month or two then make up my mind.