preventer attachment to boom

[kish]

Originally Posted by 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

The shock loading on the boom on a crash gybe will cause the mechanical bail attachments [rivets] to fail. [Don't ask how I know this!]

I have used 50mm [2 inch] non dynema {polyester ?} webbing, double wrapped around the boom. It is terminated in a sewn eye similar to jack stay webbing. You can then attach a polyester [preferably] or dynema line of your choice to it.

This webbing is analogous to car seat belt material, which has some stretch ability, to protect the wearer and by analogy will avoid damage to the boom.

[s/v Jedi]

Originally Posted by kish

The shock loading on the boom on a crash gybe will cause the mechanical bail attachments [rivets] to fail. [Don't ask how I know this!]

I have used 50mm [2 inch] non dynema {polyester ?} webbing, double wrapped around the boom. It is terminated in a sewn eye similar to jack stay webbing. You can then attach a polyester [preferably] or dynema line of your choice to it.

This webbing is analogous to car seat belt material, which has some stretch ability, to protect the wearer and by analogy will avoid damage to the boom.

The stretch comes from the preventer itself, not from the loop around the boom or the short tail to make it accessible with the boom outboard. The preventer line itself is 1.5 times the boat length, which is more than enough for stretch.

[SVTatia]

Have you considered a boom break? I had one on my previous boat and it eased 2 accidental jibes that could have been disastrous.

[Hoodsail]

If you choose a boom brake, make certain you match your boat length to the correct boom brake based on the manufacturer/s recommendation. I've used the Dutchman brake and rigged it 2/3 down the length of my boom from the mast, then forward to a shackle along the toe rail and finally back to the cockpit. The brakes arent cheap, hundreds of dollars based on your boat size, but sure beats a crash gype in heavy weather. thnks

[dcreasoner]

If you don't expect to use your outhaul much, just tie your two preventers (two round turns and two half hitches to minimize chafing) where you have the red line, then lead the preventers all the way forward, and back into the cockpit. Be careful not to allow the preventers to chafe on the shrouds. Once you get across the Atlantic, you will likely remove them, so no need to drill holes in the boom.

[s/v Jedi]

I now realize that many sailors don’t know the easy way for preventers.

If you take a long line, tie it to the boom, then go forward to a bow cleat and tie it off, or go through a block there and lead it aft to the cockpit… those are all the HARD way of doing this.

Instead, you make the preventer in two parts. One is the long line but it isn’t tied to the boom: as it comes back from the bow, outside everything incl. the capshrouds, you tie it to your lifeline just aft of the capshroud.

On each side of the boom you create a short lead that is always attached to the boom. To deploy the preventer, you tie them together like in the video below.

Note that this easy method also works when the boom is already all the way out.

https://www.youtube.com/watch?v=4KPk5JMvkJU

[GreenWave]

Originally Posted by s/v Jedi

I now realize that many sailors don’t know the easy way for preventers.

If you take a long line, tie it to the boom, then go forward to a bow cleat and tie it off, or go through a block there and lead it aft to the cockpit… those are all the HARD way of doing this.

Instead, you make the preventer in two parts. One is the long line but it isn’t tied to the boom: as it comes back from the bow, outside everything incl. the capshrouds, you tie it to your lifeline just aft of the capshroud.

On each side of the boom you create a short lead that is always attached to the boom. To deploy the preventer, you tie them together like in the video below.

Note that this easy method also works when the boom is already all the way out.

Well Hollywood may have delayed the Emmy's but this post/video gets my nomination for "Best in Show"!

[nmccubbin]

We put a 3/8” U-bolt on each side, about a foot forward of the aft end of the boom
Easy if the end of the boom is open
You can buy the SS bolt any marine store

The preventer line has an eye splice in the U-bolt
Fwd end of line to a cleat on the boom. We extend it with a sheet bend when setting up.

[Happ]

Originally Posted by 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.

Racing boats use a Velcro wrap around the boom for their outhauls. Put 3 or 4 wraps on and attach your lines. Quick, easy, and affordable.

[argonauta1]

[ATTACH][/ATTACH]

The attached displays my solution. Note I learned the hard way not to over tension the preventer. It lead to over stressing the luff which ended up breaking the main halyard at the mast head. That is why you will note a heavy duty bungee in the assembly which I added later. The bungee is/was available from West Marine

[s/v Jedi]

Originally Posted by argonauta1

[ATTACH]Attachment 279599[/ATTACH]

The attached displays my solution. Note I learned the hard way not to over tension the preventer. It lead to over stressing the luff which ended up breaking the main halyard at the mast head. That is why you will note a heavy duty bungee in the assembly which I added later. The bungee is/was available from West Marine

Sorry but not good. Things breaking is the clue that it is wrong and a bungee cord isn’t the solution.

What you do here is a sheeting method. Boats without travelers often use such setups. I have something like this on my mizzen and a block and tackle like that to put on my rail as a replacement sheet in case of long passages reaching like that for days.

A preventer pulls the boom forward, not down. This is why the line goes all the way to the bow.

[argonauta1]

Well, the setup took me from Australia across the IO up the Red Sea through the Med and across the Atlantic with no issues.

I belatedly realized the importance of understanding the transfer of stress points in the main sail rig which can happen when a preventer is used. You will have noticed that the aft end of the boom is not rigidly fixed but moves up and down as the mainsail flexes. An overly tightened preventer will inhibit that movement. Thus the stress transfers to the next vulnerable point which is where the main halyard turns 180 degrees at the masthead sheave.

The bungee eases the stress by acting as a shock absorber if the preventer is mismanaged. When one reviews a stress diagram of a mainsail rig it becomes obvious. At the time the bungee was not incorporated. I was blissfully ignorant of these nitty grittys thus I broke my main halyard in particularly heavy downwind conditions mid Pacific.

[Dockhead]

Originally Posted by 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

This is a very good solution


The choice between strap, bail and padeye for the attachment greatly favors strap from the point of view of strength and least compromise to the strength of the boom. It's the way to go if you don't have a dedicated preventer fitting like Selden rigs often do.


As to how to attach it -- I have Wichard forged snap-eyes spliced to the ends of my preventers. This is easy, but a dyneema soft shackle is probably better -- stronger, and no metal to fly around in case of a kerfuffle.

[Dockhead]

Originally Posted by s/v Jedi

Sorry but not good. Things breaking is the clue that it is wrong and a bungee cord isn’t the solution.

What you do here is a sheeting method. Boats without travelers often use such setups. I have something like this on my mizzen and a block and tackle like that to put on my rail as a replacement sheet in case of long passages reaching like that for days.

A preventer pulls the boom forward, not down. This is why the line goes all the way to the bow.

A agree! Get rid of that!

This reminds me of the infamous preventer which killed two people on the Platino. It's simply wrong!

Here's a whole article on it called "Amidships Preventers -- A Bad Idea Which Can Kill" https://www.morganscloud.com/2018/10...that-can-kill/ According to Morgan's Cloud, this arrangement increases the loads by 24x (!)

Preventers should ALWAYS be rigged ALL THE WAY TO THE BOW, and to the END OF THE BOOM. They should be set up quite snugly in order to eliminate slop and snatch loads. Dyneema is the right cordage for preventers. NO BUNGEES!!!

[Dockhead]

Originally Posted by argonauta1

Well, the setup took me from Australia across the IO up the Red Sea through the Med and across the Atlantic with no issues.

I belatedly realized the importance of understanding the transfer of stress points in the main sail rig which can happen when a preventer is used. You will have noticed that the aft end of the boom is not rigidly fixed but moves up and down as the mainsail flexes. An overly tightened preventer will inhibit that movement. Thus the stress transfers to the next vulnerable point which is where the main halyard turns 180 degrees at the masthead sheave.

The bungee eases the stress by acting as a shock absorber if the preventer is mismanaged. When one reviews a stress diagram of a mainsail rig it becomes obvious. At the time the bungee was not incorporated. I was blissfully ignorant of these nitty grittys thus I broke my main halyard in particularly heavy downwind conditions mid Pacific.

Reminds of the friend who told me he'd been smoking since he was 17, and never had a problem. He was diagnosed with lung cancer the next year.