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Old 19-08-2010, 23:03   #1
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Full Length Crack in Underside of Wooden Boom

Bought the boat last week:

Had hoped I'd looked at everything:

Went to get the boom from his house...

and found a crack running the full lenght along the under-side of wooden boom. ... but not full depth

Solid Oregon , Crack is not right thru.

Has (some-time in the past) previously been filled with epoxy.

But is still cracking and that previous repair is now cracking too.

My idea?

1. Fill with runny epoxy.
2. run a strip of 1" fiberglass tape along.
3. coat that too
4. let dry
5. sand
6. seal
7. sail

Suggestions? comments ? questions?
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Old 19-08-2010, 23:31   #2
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It's possible this is just a check, but it should be addressed. If it's had epoxy in it, the owner knows it's there, so ask them about it.

A check will continue to open and close depending on moisture content unless you encapsulate the boom. For a boom of the size I suspect, you'll be fighting a losing battle to encapsulate without a heavy sheathing, so skip the cloth. It'll just delaminate anyway. Bond the crack with thickened epoxy.


Reef out the crack (you don't know what's in there, so make sure by cleaning it out good). Wet it out crack with straight epoxy (very important), then mix up some thickened epoxy. I'd recommend a milled fiber (West System 403) and silica (West System 406) batch, say 50/50 with a touch of wood flour for color. Make the mix peanut butter in consistency and pack the crack full, trowel flush with the surface. If you wrap the boom with clear plastic sheeting (while the goo is curing), you can smooth out the fairing, sanding process quite a bit.

Then sand, varnish/polyurethane to suit and reassemble the hardware.
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Old 19-08-2010, 23:36   #3
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I'm hoping some of our wood experts can jump in on this.
Is it a solid boom from a single piece of timber? Or laminated from multiple pieces?
If from multiple pieces is the crack at a joint?
How old is the boom and how was it stored?...If its been stored say in an air conditioned room or is fairly new it may be cracking due to drying out/curring.
Do you know what the wood type is?
Some pictures would help.
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Old 20-08-2010, 05:20   #4
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I have to assume the Original post was actuate, James. He did mention a solid spar and that it was Oregon (Aussie for Douglas fir). One would have to expect they've looked for seams, end grain orientation, etc.

Pictures would be helpful, though I doubt the repair strategy I offered will change any, unless he didn't notice it was a built up spar, rather then a solid hunk of fir.
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Old 20-08-2010, 05:25   #5
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How is the boom made? Is it box construction, solid, laminated? Knowing that will help members give you more accurate suggestions.
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Old 20-08-2010, 05:58   #6
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Bluestocking's main boom is 17ft of douglas fir made up of 3 vertical laminations. When i got the boat, a glued line had opened up on the underside between a ckeekpiece and the centerpiece. The previous owner held it together with hose clamps
I cleaned out the joint with a hacksaw blade and packed in a filled epoxy blend.
A small hairline crack opens from time to time, but nothing major
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Old 20-08-2010, 08:06   #7
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I am assuming it is a solid spar, made onf one timber. what you have appears to be what is called a radial check, and it is normal to have happen as solid wood dries..there are ways to prevent it in drying lumber, but it still happens..thing is, a radial check can be beneficial, in that it relieves stress in the wood without sacrificing much stregnth...I would (wood?) not recommend adding more material to a the epoxy that is already there ( I am making assumptions here) because what happens is the wood expands and contracts with it's moisture content, and as you add material and the wood contracts, there is additional force added to the sides of the crack..keep it up and pretty soon you have a split all the way through instead of a relatively benign condition.

Blue Stocking, you are probably ok with that hairline crack, it's just the wood working.

In most cases if the check is small, I would simply coat the inside of the check with thin epoxy to seal it and keep it from rotting, then the wood can work and flex without having a splitting wedge to work against. Unless it interferes with the rig or flexes too much..in which case a new spar is called for.

Yes, I have a Sawmill, and no, I did not stay at a holiday inn last night..
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Old 20-08-2010, 17:34   #8
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thanks for you input

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