Stiffening a boom

[Steve Laume]

During the NE winter meeting the subject of loose footed mains and boom strength came up. The presenter did not seem truly comfortable with stating that our old booms would be just fine with the loading of a loose footed main. Someone suggested an external stiffener. Things moved on and I didn't get a chance to talk to the guy who suggested it and seemed to know a great deal about spars in general.

My boom is mid sheeted with only two attachment points as Cape Dory set it up originally on the CD-30. If I sight my boom, it has a very slight upward bend to it even when it is not under load. I know of one CD-30 that broke her boom and would not want to repeat that situation on Raven.

I have seen welded on stiffeners which would work very well. It would also be a pretty costly and involved process. The biggest problem I would have with going that route would be that the boom would have to be recoated in some way.

Is there an effective bolt on arrangement for stiffening a boom? I believe Bob Emmons slid another section inside of his new one. Weight considerations? How to best gain effectiveness? Would you only do the mid section where the sheets attach? This seems like a bit of a science and something I could screw up if not done right. To complicate things a bit more, it would be nice if the sides of the section did not increase in width so all of my hardware would still fit.

Has anyone, other than Bob, who happened to have an old boom done anything along these lines? Should I just not worry about it? Recommendations and advise would be much appreciated, Steve.

[Russell]

Has anyone, other than Bob, who happened to have an old boom done anything along these lines? Should I just not worry about it? Recommendations and advise would be much appreciated, Steve.

I say do not worry about it. Its designed to handle the loads. Even boat with a traditional main origonally, any time reefed it becomes loose footed. So yes our booms are strong enough and designed to handle loose footed with midboom sheeting. Sure booms sometimes break, just like anything else on the boat can. Ussually these things happen due to accidental jibes while over canvassed and such. Sometimes they are just flukes or a result of existing damage. If another CDs rudder fell off, would you be rushing to drop and rebuild your rudder? Failures happen, but one or even more incidents is not proof that the entire line is prone to it.

Unless you are aware of critical or potentially critical damage to your boom that could lead to failure, I would not worry about it.

[sharkbait]

I agree with Russell that the boom should not require any additional stiffening. However, if I wanted to I would just inject liquid expandable foam into the boom to stiffen it. If you have internal lines in your boom then you would have to install pvc tubing for the lines before injecting the foam.

[Neil Gordon]

Even boat with a traditional main origonally, any time reefed it becomes loose footed.

True, but the reef also shortens the lever.

[rtbates]

I do not believe that the foot of a mainsail has much force applied to it no matter how it's rigged. And that's why going loose footed casues no more stress on the boom.

I could be wrong, but I really doubt it. As a trial, the next time out grab the foot and see how much force is there.

[Duncan]

As I understand it, the leverage that breaks mid-sheeted booms comes from the point loading on the clew. This is not lined up with the mid-sheeting position, which is why you see three bails there on most boats.

This existing leverage would be marginally increased by a loose-footed sail, but I think that's just an incremental factor in the existing imbalance.

Seems to me that the best thing you could do for your boom is sheet it from the end. That lines up the loads better.

I took a a quick look at the 30C sail plan, and it seems like the boom goes almost to the end of the cockpit. That way, the sheet shouldn't be too much in your way, and the traveller would also be in a pretty good spot?

[Warren Kaplan]

Steve,

I was talking about that with Michael Heintz at the time of the presentation. There are a lot of loose footed mainsails out there and yet the incidence of fractured boom reports on CD30s seems almost unheard of.

I wonder if the compromised boom on Bob Emmons' boat was a unique situation, perhaps a flaw limited to that particular boom, and not indicative of a general design problem.

[Michael Heintz]

I agree that the boom failure of Bob's Redwing may more be an example of a unique equipment failure rather than a design flaw. I do not believe that loose footed mains would contribute to that failure. I'm not sure what Bob had.

As Warren points out, we have rarely heard of a CD boom failures such as Bob's.

It turns out that on the day of Bob's boom failure, I was sailing somewhere behind him on Buzzards Bay. I was sailing Macht Nichts CD 30 MK II 1987,with loose footed main. I can tell you it was a nasty day even by Buzzards Bay standards. It was blowin stink and the chop of the Bay had us bouncing around like a bukin bronco. If ever there was to be an equipment failure that would be the day!!!!!

[Argo]

I realize that this conversation is old... but I thought I add my two cents. I have a 1986 Cape Dory 30 which I sailed from Marthas Vineyard to the Bahamas going as far south as Clarence Town Long Island. I snapped my boom in half when I jibed accidentally off North Carolina. A new boom would have cost me half of what I had to live off of for the rest of the winter and I sure as hell didn't want to hang around waiting for a boom to be shipped to me in NC while it got colder and colder.

I had made a mast and spars for a haven 12.5 a few years back and I figured I'd just make a wooden boom and keep going. I got some advice from a friend who makes wooden spars back up in New England and in a few days made a solid boom 3.5" in diameter with the pith running dead center from one end to the other. Cost me about $50 for materials.

I rigged it up just like the original boom with the sheeting in the middle but made it loose footed for simplicity's sake. I raised it for the the first time and immediately took it down because it bowed like crazy, with the low point where the sheet attaches. After taking it down I attached the foot of the sail to the boom using loops of webbing so it was no longer a loose footed sail. I also spread the connection points of the sheet out more to spread the load on a wider area. I raised the sail again in light wind and it was a little better but it was still bowing like crazy and I was afraid I would snap it again. I switched to end boom sheeting, raised the sail and the boom was straight as an arrow. There was visibly much less stress on the boom.

Now after close to 5 months of sailing its still holing up well and I'm quite confident in it. Now that I'm thinking of getting a real deal aluminum boom for the boat I wouldn't go back to mid boom sheeting unless the spar was a lot beefier. On the CD30 there isn't a lot of space between the sheet and the wheel but it's enough space. When sailing sheeted in tight the boom is never really dead center over the wheel and I'm usually sitting on the high side anyways. I keep the sheet block attached to a quick release shape shackle and when I'm motoring I put it off to the side attached to the stern pulpit rail.

The Cape Dory 28 has the same sized tube stock for its boom and it sheets on the end, which now seems to me to be a smarter system. I wouldn't be surprised if there was some copy and past engineering... add two feet ...a bit more sail area ...sheet it in the middle and there's the Cape Dory 30. While I'm sure it worked mathematically in the design process I'll bet that the Cape Dory 30's boom in particular was pushing the limit more than other Cape Dory boats.