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Old 14-05-2022, 15:53   #1
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Dyneema or nylon webbing as strop for preventer

I want to rig a more substantial preventer for an upcoming offshore passage. In the past I have run some 1/2" double braid StaSet to the boom bale. I instead want to get the attachment point out to the end of the boom, then bring the double braid forward to a turning block at a bow cleat, and back to somewhere near the cockpit. Maybe a cabin top winch.

Aside from the final location, my dilemma is about the material for making the strop. I have 1" nylon webbing and some Dyneema line, 1/4" and 5/32", as options. I've seen suggestions of nylon webbing. I could speedystitch eyes into the nylon webbing but that seems like a working load limit ~ 900lbs, not to mention the strength of my speedystitch loop. The webbing however seems like it would be less prone to slipping. For webbing or Dyneema I would make it long enough to wrap around the boom once. I would also put eyes in the ends of each and use a soft shackle to join the double braid eye splice to the strop. I have thought about running the strop around the boom just aft of the slide that holds the clew in place so that would keep the strop from sliding forward.

Any thoughts or recommendations?
Thanks,
Harry
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Old 14-05-2022, 17:12   #2
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Re: Dyneema or nylon webbing as strop for preventer

Here are my thoughts:

1. I would connect the preventer as close to the point where your main sheet attaches to the boom as possible. If you connect to the end of the boom, youíd be setting up some unnecessary forces between the middle and the end of the boom.

2. You want the front of the preventer as far forward as possible. What you are really trying to achieve is the widest angle possible between the connection point and the boom when it is fully to leeward.
Most people attach the preventer while itís close to centre and therefore attach the other end near the beam as it looks like the widest angle - which it is until the boom is fully eased.
However, thereís always a compromise between the ideal location and whatís useable when you decide to rig a preventer at 3 am in heavy weather

3. I donít see any reason not to use Dyneema line for the preventer. You probably already have some on board, itís easy to work with, itís more than strong enough and itís designed to be used in the various winches and cleats that you already have around the boat - particularly in the cockpit.

Finally, remember that you want the preventer to be easy to rig, easy to tension but also easy to release in a hurry if you need to.

Hope that helps!
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Old 14-05-2022, 17:18   #3
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Re: Dyneema or nylon webbing as strop for preventer

Harry, my only suggestion is that you should consider where is the weakest link. If you do accidentally broach and things go wrong something is likely to break. I donít mean add in a really weak link, but consider where is the weakest link. For example, if you use all dyneema then the weak link might be the boom. The ocean is more powerful than we think and takes great pleasure in sending us back to the chandlery for a stronger fitting..
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Old 14-05-2022, 17:38   #4
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Re: Dyneema or nylon webbing as strop for preventer

Thanks for the input so far.

1) The preventer will be 1/2" or 7/16" double braid poly. It will work much better in the winches and clutches. The question of dyneema is as a strop vs. 1" nylon webbing.

2) I have always understood that it is best to have the preventer as close as possible to the end of the boom so that if the end of the boom goes in the water during a broach the boom does not break at the middle.

3) Having a "weakest link" being a nylon strop instead of the boom (assuming dyneema isn't going to be the failure) is an interesting idea.

Thanks,
Harry
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Old 14-05-2022, 17:46   #5
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Re: Dyneema or nylon webbing as strop for preventer

Quote:
Originally Posted by hlev00 View Post
I want to rig a more substantial preventer for an upcoming offshore passage. In the past I have run some 1/2" double braid StaSet to the boom bale. I instead want to get the attachment point out to the end of the boom, then bring the double braid forward to a turning block at a bow cleat, and back to somewhere near the cockpit. Maybe a cabin top winch.

Aside from the final location, my dilemma is about the material for making the strop. I have 1" nylon webbing and some Dyneema line, 1/4" and 5/32", as options. I've seen suggestions of nylon webbing. I could speedystitch eyes into the nylon webbing but that seems like a working load limit ~ 900lbs, not to mention the strength of my speedystitch loop. The webbing however seems like it would be less prone to slipping. For webbing or Dyneema I would make it long enough to wrap around the boom once. I would also put eyes in the ends of each and use a soft shackle to join the double braid eye splice to the strop. I have thought about running the strop around the boom just aft of the slide that holds the clew in place so that would keep the strop from sliding forward.

Any thoughts or recommendations?
Thanks,
Harry

If the strop is made as a loop, the stress on the stitching is halved.


Don't use a Speedy Stitcher (sewing awl). Buy a palm and needles and learn how to use them. Much faster, stronger, and more versatile. If you read a sail making book you will find either very, very few, or zero references to sewing awls. There are many reasons.
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Old 14-05-2022, 17:55   #6
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Re: Dyneema or nylon webbing as strop for preventer

Would a nylon strop be stretchier and put less of a shock load on the boom in the event of an 'episode'? Keeping the boom from breaking would be a good thing.
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Old 14-05-2022, 18:47   #7
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Re: Dyneema or nylon webbing as strop for preventer

FWIW: All our attachments to the boom are made via strops made from three layers of 2 inch "seatbelt" nylon webbing, hand stitched in place. We use simple clamps made from sheet aluminum to keep them in place along the boom. Have used this technique for thirty odd years now with zero failures. We replace them if chafe shows up or the nylon shows signs of sun damage.

We have ~ 3/4 boom sheeting and a vang/preventer three part tackle permanently lead from near the mid point to a hard point near the chain plate on each side, with the fall coming back to the cockpit and the secondary winces via a clutch. This allows very easy use as a preventer and is a powerful vang as well. Had a similar setup on our previous boat, and between them we've logged some 140,000 miles. In that time we have not had an issue with dipping the boom end in the water, but I suspect that it could happen in the right (wrong!) conditions... however, I have better things to worry about. Meanwhile it is so easy to use as a preventer that it is always in use when the wind is much aft of the beam.

We don't fear sailing DDW or even a bit by the lee. There have been countless times that the wind got on the wrong side of the sail and it gybed it... and nothing much happens. Pretty soon the autopilot (or wind vane on previous boat) cirrects the course and it gybes back. Meanwhile the boom never moves and the boat stays under control.

I know that some folks think this a foolhardy approach, but IMO the proof is in the pudding of experience.

Anyhow, the nylon strops have worked flawlessly!

Jim
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Old 15-05-2022, 17:42   #8
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Re: Dyneema or nylon webbing as strop for preventer

We use 1/4" Dynema for the boom length. I wove an Eye in ea end, loop the Drnema thru the eye over the bail near the mast end, and pull it fwd to near the mast. I rigged a double bungee, hooked to the mast end of the boom and with the hook on the other hold the Dynema Preventor in place until needed. I use 12mm line, thru a 3" block secured to the foredeck and have both lines running back to near the cockpit. One end has a large clip on it, stored hooked to a stanchion base, and the other goes thru a block and to the secondary winch. When I need the Preventor, I simply unhook the Dynema end from the mast, connect it to the large clip, and with the winch pull the boom out as I release the M/S Sheet...keeping both tight. The boom is captured between the 2, and goes nowhere. We've had the system rigged and in regular use for some 5 years now-really works well. The Dynema is light, strong, and easy to handle....works really well.
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Old 15-05-2022, 18:03   #9
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Re: Dyneema or nylon webbing as strop for preventer

I like saicrazy description. Dynema setup on the boom and 12mm line led forward to block gets my vote
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Old 15-05-2022, 18:41   #10
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Re: Dyneema or nylon webbing as strop for preventer

@sailcrazy I like the sound of that. It seems similar to someone elseís setup I saw. Can you describe again where you attach the outboard end of the dyneema. You said a bale. Is that one in place specifically for your preventer? Or did I misunderstand where that end attaches?

I also like what @JimCate has done.

Whatever I do now will be temporary until I can do something more permanent. For example several have mentioned d-rings or other attachment points specifically to manage the preventer.

Thanks,
Harry
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Old 15-05-2022, 19:26   #11
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Re: Dyneema or nylon webbing as strop for preventer

as Chris JHC posted, attach the preventer to the boom very near to the attachment of the mainsheet. Keep the forces in line so you don't break your boom.
Dyneema is plenty strong, but doesn't cleat well, so that is something to consider.
We leave a Dyneema pendant attached permanently to the boom, and when we want a preventer, we add a length of stout polyester line to the pendant and take it to a cleat with 2:1 advantage.
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Old 15-05-2022, 20:37   #12
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Re: Dyneema or nylon webbing as strop for preventer

hlev00...we have a semi-circular bale almost at the end of the boom. The M/S sheet attaches to it. And I attach the Dynema length to it, too....one on each side. I made a small loop on the end of the Dynema, and just put the loop on one side, then pass the other end thru it, and tighten....no knots, no chaff. Aand then the Dynema length along each side of the boom to the bungee hook near the mast-simple, but always in place and easy to get when needed..
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