preventer attachment to boom

[markxengineerin]

In one of the final preparations for my first Atlantic crossing, I'm improving the preventer, copying the design to be "Morgan's Cloud Style". I need to fasten two lines to the end of the boom, one each for port and starboard.

What's the best way to do this? Priorities are strength and not damaging/chafing the boom over time. It would be a bonus to avoid sewing and splicing, but that may be inevitable. Thanks for any ideas. What I'm thinking now is a strap sketched in red, but not sure about terminations for the lines (sketch in blue). Maybe there's an off-the-shelf product for this, maybe based on velcro? I think I've seen that on smaller boats, anyway.

[swisel]

Have you considered a bail as the attachment point?

[markxengineerin]

I had not considered a bail, didn't know what they were called. The dimension is 3.5"- so far I have not found much other than a design I don't like (ebay) and Rigrite (unreliable delivery, I'm leaving in 6 days). I will keep looking.
https://www.westmarine.com/schaefer-...0_007_006.html with a couple spacers maybe?

[wholybee]

Some considerations with a bail. I have an end sheeted boom, with the main sheet attached to a bail. So that was an easy option for me. Having the preventer attached to the bail both creates a strong twisting force on the boom, and pulls the bail forward to the point the bail marks and chafes the boom. Solvable issues, but in thinking about where and how to rig a bail for a preventer, keep those in mind.

I would use a strap made from dyneema. I will probably switch to that on my boat. Dyneema is super easy to splice, so just make a loop around the boom. Then make soft shackles for connecting everything. Once you learn how to make those things, how fast and easy they are, you will wonder why you wanted to avoid them.

[markxengineerin]

I did splice my synthetic rig, just didn't enjoy it much ; )

Few questions on that:
For the "round the boom" section, is it best to have an "endless dyneema loop" or "soft shackle"?

How to fasten each double braid line to this loop? A bowline? Line spliced around a thimble? Line spliced into a loop with no thimble? Other ? I would prefer the bowline, for now, until I have more time. The line will be oversized, so strength reduction is not much of a concern.

[Srpulpo]

Careful not to put it mid boom, we crash gybed once and broke our boom off shore.

[wholybee]

Originally Posted by markxengineerin

I did splice my synthetic rig, just didn't enjoy it much ; )

Few questions on that:
For the "round the boom" section, is it best to have an "endless dyneema loop" or "soft shackle"?

How to fasten each double braid line to this loop? A bowline? Line spliced around a thimble? Line spliced into a loop with no thimble? Other ? I would prefer the bowline, for now, until I have more time. The line will be oversized, so strength reduction is not much of a concern.

There is a way to splice the end of a line into a soft shackle. That is probably what I will do, but my configuration is different than yours, and I disconnect and change sides at the end of the boom, not at the mast. Maybe you could splice an eye at the end of the line. Take the line around the boom, then through the eye, so you can eliminate the strap around the boom.

[Bill O]

If I'm not mistaken, didn't MC use pad eyes for their preventers?

[markxengineerin]

Careful not to put it mid boom, we crash gybed once and broke our boom off shore.

Yes, this is what I'm switching away from. The mid-boom to toe rail system was great in that I didn't even have to go on deck to use it, but the angles were all wrong and I could easily see it damaging a boom if it dipped into the water, for example.

Any eyes in the system seem like they're likely to wear the paint off the boom (not that it's not already worn off/corroding in 20 other areas)

[Rucksta]

Try a T-ball fitting with an eye.

T-ball is the fitting often used to attach shrouds and runners to a mast.
A backing plate is inserted through a slot and riveted to the spar.

It's only minor overkill for a preventer and solves the twisting and point loading problems with bales.

[s/v Jedi]

Put a small pad eye on each side of the boom (at the center of it) where you have the red loop, so that the loop goes through the pad eyes. Make the loop from Amsteel Blue for an easy splice.

Now create two preventer leads, also from Amsteel Blue, spliced to the loop just above the padeye at each side. These leads must be long enough to reach the gooseneck where they have yet another eye splice and are fastened until needed, in which case you simply tie the preventer to that loop.

These eye splices and the endless loop are very easy with Amsteel Blue, you don’t even need tools other than scissors and some cello tape.

[markxengineerin]

I have some extra dyneema that's either 3/16" or 1/4" (hard to tell when it's used), so I'm going to use that for now. Minimum strength is either 4900 or 7700 pounds. I will go up a size or two at some point, but trying to save $ now.

For loop to loop connections, is it better practice to have one or both loops use a plastic thimble, or dyneema on dyneema is fine?

[s/v Jedi]

Originally Posted by markxengineerin

I have some extra dyneema that's either 3/16" or 1/4" (hard to tell when it's used), so I'm going to use that for now. Minimum strength is either 4900 or 7700 pounds. I will go up a size or two at some point, but trying to save $ now.

For loop to loop connections, is it better practice to have one or both loops use a plastic thimble, or dyneema on dyneema is fine?

Dyneema on Dyneema is fine. You can double up the loop around the boom. When you make that splice in place, just do a double wrap, then bring one end through the other, splitting the strands with 6 on each side, just like when you start a Brummel splice. Then you can take some thread and wrap a small seizing around it so that it doesn’t move while tapering and burying the two ends.
I would keep 2” minimum slack around the boom, which should allow the splice without too much trouble

[markxengineerin]

Ah, thanks, good idea on the doubling up

[wrwakefield]

I think Jedi nailed what you need.

I have used Dyneema climbing slings similarly to put a choker near the end of the boom for a preventer in case that is of interest.



Or you can make your own.

Let us know how things turn out. It is always good to learn what others are doing.

Cheers, Bill