boom preventer

[Sumner]

..... A classic preventer is attached to the boat near the bow. Once tensioned it will not allow the boom to swing any significant ammount at all.

View attachment 130656

I run my two preventer lines to the bow like above and in that situation they recommend having the line attach as far out on the boom as practical as shown above. I use the bail for the mainsheet. Not optimal but still past the mid-point of the boom and it has worked well and is easy to access as far as putting the lines on or off,

Sumner
==================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas

 

[walt]

Bud, correct about what I am planning and thanks for that diagram, makes it easy to see how you would get rid of any swing - and the shock loads associated with the swing. Im still inclined to just do the very simple thing I mentioned as it addresses the actual problem I did have dealing with the whisker pole but I have to accept a compromise for not having all that extra rigging. I also like the vang idea for its simplicity and you can see in the picture that it would limit the swing to a pretty small angle. The one danger I would still have is someone getting clocked while standing high going into the companionway. Plus a fairly big shock load. If you are standing inside the cabin or sitting in the cockpit.. not a safety issue. In the picture you can see where I had my issue. I was coming back on the left side of the picture after removing the whisker pole, boom swung around from where it was to the side I was on.

 

[BudGates]

I occasionally sail with a buddy (on his boat) who has a hard time keeping track of where the wind is coming from. I almost always move his vang to act as a preventer when he's at the helm, even on a reach. It has saved my head a few times.

I can't take credit for the diagram. If I had drawn it I wouldn't have spelled "cleat" with an "h".

 

[arknoah]

Regarding preventers.... if you find the use of a preventer necessary on a regular basis... (I rarely use one when daysailing) then it would be very simple to rig one up permanently without having to mess with the vang or other specialized hardware. Here goes: Establish an attachment point on the boom with a strip of webbing. Attach two lines to this point... one for each side... run each line forward to a small block located ahead of the mast near the toe rail... the lines then double back to a conveniently placed cleat. There is no need for purchase. Nylon line can be use to provide shock absorption. The lines are left attached... only employed when needed....otherwise left slack when sailing so boom can move naturally. When you bear off on a broad reach or run and the seas are bumpy you may want to apply the preventer... simply grab the appropriate line and cleat it.... voila ! you're good.

Yep. This actually makes sense to me -- thanks!

 

[catalanc]

Not sure what it is, but I think I'm warming to the polar chart ....

I agree with Jackdaw that technique trumps hardware, but this could come in useful while learning. I am a little paranoid of knocking myself overboard (I mostly sail single handed) or the Admiral when she is on board. I typically center the boom before making a turn sailing downwind but I sail on Lake Dillon where the wind changes quickly and can take me by surprise. Something like this would be useful.

So, anyone out there have a preventer installed on a Catalina 22 (MK II). Where/how did you put the preventer on the boom and where/how did you run the lines?

Thanks for the info.
cec

 

[thinwater]

From your discription it sounds like your preventer is attached on the combing by the cockpit. If you move the attachment forward this effect becomes less. A classic preventer is attached to the boat near the bow. Once tensioned it will not allow the boom to swing any significant ammount at all.

View attachment 130656

This does not always work well. The problem is the angle and the length of the line. With only ~ 3-4% stretch, the boom can move far enough back to jibe. As you can easily see, once the boom moves back just a few feet, with the wind on the wrong side, the force stretching the line becomes enormous. You need a very low stretch line and the spreaders cannot sweep back too far, and the vang/sheet/preventer need to be snug against each other.

 

[walt]

If I ever do something like Sumner did on his Bahama trip where he had the autopilot on for long periods of time, I would definitely go with a proper preventer that limits almost any movement at all from the boom. Another "bad" thing about a method that allows the boom to partially swing is that it seems to me you increase the chance of trading an accidental jib for a knock down. Tradeoffs for simplicity vs all that extra rigging.. I will add one thing about the preventer that also seems to be illustrated here - when I am in control of the boat, I dont think I need the preventer, Ive never come close to having an issue. Its when someone else or something else (like an autopilot) is in control of the boat that it becomes at least more important. You may have great technique where you dont ever come close to needing it but maybe your wife (which was my case) or friend or the autopilot may not even know about the possibility of an accidental jibe.

 

[Pilgrimtex]

I have a 37 ft Beneteau. I used decenders as a boom brake but they are hard to find the proper tension. Too tight and the boom won't shift for you and too loose and you may as well take it off.
What I use now is the safest method which is a gybe preventer. I mounted a pad eye in the bow with a block and a line from the cockpit to the block then to eyes I installed on the boom. Positively prevents accidental gybe and easy to adjust by just popping a clutch mounted for it. Also helps in light winds by loading the boom to prevent slapping from boat rolls.
Forgot friends crossing the Atlantic had two accidental gybes in a storm which required the boom and mast be replaced on their 53 footer in Portugal. They did not have a preventer.

 

[thinwater]

There are only 2 situations where I find it helpful:

• Wing-and-wing. Keeping the genoa full requires sailing a few degrees by the lee.
• Bumpy and light winds. I actually connect it to the midships cleat and just use it to steady the boom.

In fact, the wide traveller of a cat makes an full accidental jibe impossible if the traveler is locked down. There's not that much main sheet out.

Another thing that REALLY helps is using nylon or even climbing rope for the traveler lines. This really takes the sting out, yet the stretch under working load is trivial. Try it. I learned my lesson after trying a Dyneema traveler line. That was stupid, like jibing against a brick wall.