nearly lost my boom.

[skkeith]

Couple days ago in a decent wind while relaxing for a bit I just happened to look at the attachment point of my main sheet to the boom, which is mid boom via a traveler. (Islander 28). The stainless eye in the boom was broken off on one end and just barely holding the block by luck. I will get a photo up when I can...

The broken part is some kind of stainless plate and eye with a slot in the boom. The eye sticks out the slot and the plate is riveted to the boom on the inside.

Any recommendations for replacing this? It seems a bad design. I have a loose footed main now, any reason not to go with a soft shackle around the boom here?

[Knotical]

Not sure I follow you when you say “nearly lost my boom” - is it that the mainsheet connection has broken or come loose?

Surely you have a gooseneck and topping lift, right?

How about a boomvang?

A photo will be nice, close-up and from a little further showing all the attachments.

You will need to investigate why the mainsheet plate broke.

[Brioche]

That is a fairly common way of attaching a high-stress padeye. Attached from the outside you are relying on two small rivets or screws. Mounted from the inside, the ends form sort of their own backing plate, and rivets mainly serve to hold it in place.

Stresses on the mainsheet can be pretty high, especially when you tack or jibe so if you want a soft shackle it would need to be well secured in position, and would take a lot of wear and tear from movement as well.

I am not sure how much pressure from sails got translated to the middle of the boom with bolt ropes or similar arrangements. Obviously, with a loose footed sail you are now turning every bit of stress into bending forces at the midpoint -- but that is the way the boat was designed.

[JPA Cate]

You can use sewn webbing strops. The sailmaker can sell you what they use. We have used flat pad eyes on the boom to keep the strops located where they're supposed to be.
The webbing spreads the loads, too.

We broke the boom to main sheet shackle under way, once, and having permanently rigged preventers made it possible to control the boom when the main sheet couldn't.

Ann

[skkeith]

I will post a photo when I get back. I have no topping lift, just a fixed vang and a traveler (attached at different points). No preventers either (probably a mistake). How should I rig preventers...? Also what is the name for the in boom fitting I am looking for, and where might I source one?. I will pull the bad one and post it eventually...

Thanks everyone!!

[skkeith]

I went and got the boom it looks like I might have major issues. Here is the overall layout, you can see the broken fitting at the right of the boom

Here are a couple pictures of the bent fitting with the paint still on. You can see the cracks where the boom metal deformed.

Here is the end that broke close up

and here is the base plate.

I notice it s not just bent down but also to the port:

I seem to have a similar bend in the attachment of my vang

Looks like the slot in the boom has been somewhat cracked due to side to side torque.

I am worried about the slot in the boom being too weakened to re-use. However I was thinking it might work to make a much oversized stainless T to fit (drilling new holes). I was also thinking I would tap the plate instead of riveting. What about the vang seat (or whatever you call it). This is clearly not burly enough, it is aluminum.
How should I proceed here?

[Renoirpierre]

Sorry about you boom issues. Glad you are alright.

I would probably drill a small hole at the end of each crack and then Weld the cracks up.

This is a part that looks like it gets a fair about of fatigue and side loading. I would probably suggest building something that you could rivet to the boom to capture a soft shackle or webbing strops to keep them from sliding along the boom.

If you were to use a preventer I would attach it to those strops to prevent causing an additional bending moment on the boom.

From a load perspective I would like to see the main sheet attachment connect near the end of the boom but that may require some additional adjustments.

[JPA Cate]

Yes, you were on the way to having the boom break. Yes, it can be repaired. You will want to "sister" it, both inside and out, with a long sister for spreading the loads. Also, don't sheet the main down so hard. [We were doing that: it started the cracks that caused the boom to fail later, and we could see the differences between the old and new breaks, and understand how it happened.] Reef earlier.

You'll also want to replace the attachment for the boom vang to the mast. I would think mounting the new one to a new backing plate would be adequate. If you use stainless steel, be sure to isolate it galvanically (we've used cut up inner tube material for this, or Duralac anti-seize). If you have tears in the aluminum of the mast, the mast will need a "sister", too, and reinforced the same way as the boom, sisters in an out, the new vang fitting can be installed. Also, you may need to develop a lighter hand with the vang. The multiplication of force that we can apply can overwhelm the strength of attachments.

Our preventers are a three part tackle mounted by a strop over the boom, that has D rings on it for the blocks for the preventer line. There are fiddle blocks with two sheaves at the chainplates for the capshrouds. It goes up to the boom block then back around the fiddle block, and in our case, back to either the primaries or secondaries whichever is available at the moment, and we are able to control the boom through fairly heavy weather gybes with them. It is not the recommended way of rigging preventers; but it has worked for us.* In heavier weather, we have to use running backstays, so being able to plan the gybe ahead and ease the boom quickly across has been convenient for us.

Ann

*Use the CF Custom Google Search under the search button too find threads about how to rig preventers, there are explanations why to not do it the way we do. We've run double preventers this way since Jim had his Yankee when I met him, and they have worked for us this way for a long time. The day we broke the boom, we were able to stabilize the forward part of the boom with the preventers, and drop the sail, willy nilly on the deck, then seek out a sheltered spot (trees on the cliff to break up the wind), and tidy everything. Big nuisance. But we found a rigger who had mast sections that fit for the sisters, and whom we hired to do the sistering.

A.

[UFO]

When re-doing go to 1/4" Monal Rivets - Use Tefgel or similar for corrosion and once you have fixed it up just make a quick dyneema strop with an eye either end and go over the boom and both eyes onto the block for a safety back up.

[Tin Tin]

So when you had a standard mainsail, the foot rope would go down a slot in the top of the boom, so when tension was applied to the center main sheet the boom would have bent in the middle but would have had tension from the sail offsetting to some extent, tension on the main sheet would take belly out of sail as the boom bent more. Now the only point the sail touches the boom is at the ends. When you tension the main sheet there is no resistance other than the end of the boom this will weaken mid boom because of the lever effect from the end,. So you could alleviate these forces with end boom sheeting.

[Dockhead]

I would just second everything Ann said. Sister and weld it up, then use a webbing strop to attach the mainsheet instead of the padeye, and you'll be good to go.

This kind of failure is why I don't like mid-boom sheeting -- not at all.

But vangs have the same problem. We broke the boom of a Discovery 67 last year in the middle of the Atlantic, with the help of a hydraulic vang . It had been broken before, it turns out, so I don't blame myself entirely, but it's easy to forget how much stress can be generated with all that leverage. I'm trying to be a little more careful with the vang on my own boat, after that. Fortunately my Selden rig has a boom one size oversized for the boat and built like a brickhouse, but again -- all that leverage can break probably anything if you're not careful.

[skkeith]

Thank you everyone you may literally be life savers. I have some followup questions:
* On the sistering technique are we talking welding or screwing or rivets? If we are talking mechanical connectors any reason not to tap? If we are talking welding how??

* On the 'webbing strop' Dockhead, would you mind elaborating more on the construction, size, materials, etc.

* On the 'vang attachment' the existing fitting appears under sized, without any backing plate (the boom is tapped). I was thinking to just fabricate a sold 1/2" piece of aluminum which is the correct dia. for the vang. Cutting to shape. I think the under sized original (welded) fitting was causing rotation and additional torque. I was planning on using the existing holes tapped in the boom without a backing plate. Should I re-consider?

[JPA Cate]

Hi, skkeith,

Ours are screwed together, with s/s countersunk hex head screws on about 5" centers, suitably isolated galvanically.

Our strops are made from 2 inch wide nylon webbing, sold here in Oz as "seat belt webbing". They have trhree wraps around the boom and are stitched in place using heavy whipping twine.

Sorry, but I don't agree with the underlying assumption that the vang attachment was undersized for your Islander. It seems to me that you have been heavy handed (as we were). Note also, that both Dockhead's and our booms are a lot longer than yours (ours is a tad over 17 ft., and the sections would be thicker; and Dockheads, suitably larger for a 57 ft. Moody.) There's no harm with adding a suitably hefty backing plate to help spread the loads, but you really also need to understand how much your own strength is increased by the mechanical aids, and modify how you do things.

Ann

[Dockhead]

Originally Posted by JPA Cate

Hi, skkeith,

Ours are screwed together, with s/s countersunk hex head screws on about 5" centers, suitably isolated galvanically.

Our strops are made from 2 inch wide nylon webbing, sold here in Oz as "seat belt webbing". They have trhree wraps around the boom and are stitched in place using heavy whipping twine.

Sorry, but I don't agree with the underlying assumption that the vang attachment was undersized for your Islander. It seems to me that you have been heavy handed (as we were). Note also, that both Dockhead's and our booms are a lot longer than yours (ours is a tad over 17 ft., and the sections would be thicker; and Dockheads, suitably larger for a 57 ft. Moody.) There's no harm with adding a suitably hefty backing plate to help spread the loads, but you really also need to understand how much your own strength is increased by the mechanical aids, and modify how you do things.

Ann

Again, everything Ann says

Minor quibble -- I would use polyester, not nylon webbing for the boom attachment.

What's great about this is that it distributes the force around the whole boom, rather than point loading a padeye. Much gentler. But note that this still doesn't make the boom invulnerable -- so you still have to be careful cranking on the mainsheet against the resistance of the leech.

Don't ask me how I know. Many of us have made the same mistake.

And with your next boat, try to find something with end-boom sheeting.

[skkeith]

Thanks everyone. Ann I am sure you are right about me being too heavy handed, the undersized comment only referred to the diameter of the vang attachment which does not fit the vang diameter properly and allows play/rotation.
Anyone hazard a guess at the recommended breaking strength for the webbing?