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-   -   gybe preventers (http://www.sailnet.com/forums/seamanship-navigation/29260-gybe-preventers.html)

Kacper 02-16-2007 09:16 PM

gybe preventers
 
Hey all,

When running, when is it SAFE to rig main and jib preventers and when is it NOT SAFE?

I've heard of people being stuck and being knocked down because of wind shifts or something else.

Also, when is it a good idea to put your jib out on a pole, and how do you do this exactly? I have never tried it, and running wing and wing is the most difficult tack for me.

When running I release my main as much as possible (so it's almost touching the spreader), but it seems to jerk around quite a bit.

Thanks,

Kacper

sailingdog 02-16-2007 11:28 PM

Generally, a boom preventer is only used on longer dead-downwind runs. Rigging it for short ones can be a nuisance. A boom preventer isn't going to cause the boat to be knocked down unless you come around quite a bit... from a downwind run to a beam reach or so on the opposite tack. If your sailing skills are so poor that you can't keep on a downwind run, then you probably should be out there as that's over a 90 degree shift in wind and boat direction combined. Granted, it does happen, but should be pretty unusual, especially on open water. I prefer a boom brake to a boom preventer, as I believe a properly setup and designed boom brake is better and safer than a preventer is.

If you're running almost dead-downwind, you should probably have a boom preventer rigged, to prevent the boom from crossing the boat and injuring people in the case of an accidental gybe.

I've never heard of a jib preventer... The jib isn't all that dangerous, given that it doesn't have a large metal boom attached to the bottom of it to wield like a club.

To pole out a jib, you have to have a ring setup on the mast, like you would for a symetrical spinnaker. Then you take one end of the pole and attach it to the jib sheets, like you would on a spinnaker, and then make the other end to the ring on the mast. Now, if you're going DDW, then you might want to pole the jib out on the side opposite the mainsail, and sail wing-on-wing, to increase the effective sail area.

As for the main sail jerking around... can you describe what you mean by "jerking around" a bit more clearly, it's a bit vague.

Kacper 02-17-2007 02:17 AM

hey sailindog,
Sorry, when I said "jib preventer" I meant poling out the jib, which I've never done.

Yes, in this case I am always doing DDW. I find that in light winds, say if my boom is on starboard, and I turn to starboard just by 10 degrees this causes an accidental gybe.

By jerking I mean, it the boom comes aft and forward in a violent kind of way, espcially if we go over a wake or over a wave. This usually happens in lighter winds.


Kacper

sailingdog 02-17-2007 07:47 AM

Using a preventer and tightening up on the boomvang, if you have one, will help prevent the boom from doing that.

chris_gee 02-17-2007 09:26 AM

The boom vang will stop the boom rising. If you are ddw your boom as you describe it maybe at say 100 -110. Altering course 10 gives you 110 -120, whereas the wind must be at >135 to give a gybe. A minimum change of 15. You could get some movement from a wake or very likely flukely winds in the light which could set off a gybe but in the light it wouldn't matter too much but it can be disconcerting. You wouldn't need a preventer then.
In fact what can easily happen with minor wind fluctuation and steering wanderings is that rather than being ddw you are sailing by the lee and and a further small turn that way is added to by the resultant change in apparent wind easily accumulating in total to put the wind ahead of the boom and gybe you.
You would be better off not sailing ddw in those conditions but bearing off say 20-30 and gaining boatspeed and vmg. Then you would find that having the boom to leeward gives you some extra degrees of margin, a minimum change of 45, making a gybe unlikely.

Valiente 02-17-2007 02:32 PM

I use a modified sort of preventer set-up. I rig a pair of four-part tackles, with cam cleats on the bottom blocks, to a mid-boom bail. One tackle leads to a port mid-ship cleat, forward of the boom and one leads starboard. To gybe or wear the boat in heavy air, I can loose the weather preventer, and haul in the lee as I steer with my legs on the tiller. I use the mainsheet as a boom brake to fine tune the process when I am on my new broad reaching course.

This differs from the usual preventer-to-the-bow and back set up, but it's worked for me in 30 knots. Here's a picture of the set up prior to hoisting the main. I suppose you could call it a "split vang", as well, except that these are rigged for the whole day of downwind sailing.
http://i169.photobucket.com/albums/u...preventers.jpg

rtbates 02-19-2007 03:21 PM

Dead downwind, twin headsails are much better. If you must use your main you might find that sailing slightly off dead downwind is both faster to your waypoint and much more comfortable. Or you might try just dousing the main and sailing with a big headsail only. Downwind the main is a pain. There is also a product called a BoomBrake that basically adds a friction system to keep the boom from slamming over.

lharmon 02-19-2007 05:37 PM

Boom Brake
 
To prevent gybes I really like the Dutchman boom brake. Especially since I have a lot of guests that like to "drive". Holding +/- 15 degrees is not a bad job for a rookie. Downwind I love it. If an accidential gybe occurrs, the boom is managed and will come across slowly if it has to. Dutchman info is http://www.mvbinfo.com/dp_03_BB_brochure.html

Razman23 02-19-2007 06:09 PM

Take a look at this. This should help out some.

http://www.youtube.com/watch?v=QZadjhHANCk

And on a side note, it also proves the oldest rumor in the world.

When you get two sailboats close together, they will end up racing each other. :O)

fendertweed 02-22-2007 12:34 PM

just to clarify on the whisker pole... do you tie both jib sheets through the end of the pole? Recommend type of knot?

Thanks,
Jon


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