Thread: New box boom build for lugsail - Goat Island Skiff

That buzzing sound you hear is the fly on the wall named Dave. He had this on the "nice to have" list and would love to let everyone else do the hard work first. If the fly buzzes away periodically it's because he has car repair work to attend to that keeps him from doing boaty stuff.


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Your mission Paulie is to have a completed and fully tested box boom to show me at Mystic!


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An attempt to read through https://www.woodworkforums.com/f169/s...-skiff-156481/ reminded me why I stopped following that thread. Too much engineering for my poor brain to follow. But after a look at the Wiki, I'm thinking douglas fir, 12mm thick, 60mm tall x 50mm wide, fir inserts in the ends and WRC spacers at a few points in between. I'll glass the ends, just like the standard boom, and add a layer where the downhaul attaches.

So, the only question left is taper. I'm thinking taper in the vertical direction but not the horizontal. But should I bother? Will it cut enough weight to be worth the extra effort? Will it compromise strength too much?

Originally Posted by davlafont

Your mission Paulie is to have a completed and fully tested box boom to show me at Mystic!

As long as I don't have a broken box boom to show you! I have a tendency to test things to the breaking point.

I'm about to begin building the spars for my Pathfinder build so your thread will be good for me, too!

My GIS sail is set loose-footed with mid-boom sheeting.

My original box boom was 6mm Okume sides, 12mm cedar top & bottom, with cedar spacers and mahogany plugs. I tapered the bottom but not the top or sides. There is no FG wrap. This produced a surprisingly light and stiff boom. No failures with this boom.

My second box boom was 12mm cedar, lap-joined with cedar plugs and spacers. It was slightly larger in cross-section than the original and untapered. Again, no FG wrap. It works but was not a significant improvement over the original. No failures with this boom.

What I plan for the Pathfinder (I can use the GIS sail for the main in a lug yawl sail plan) is 9mm Okume sides, 10mm cedar top&bottom, with DF plugs and cedar spacers. I don't plan to use any FG wrap with this one either.

Bob Wessel
Fenwick, MI
Building Gardens of Fenwick, a Welsford Pathfinder
Karen Ann, a Storer GIS

Originally Posted by paulie

I'm thinking taper in the vertical direction but not the horizontal. But should I bother? Will it cut enough weight to be worth the extra effort? Will it compromise strength too much?

I'm willing to bet the weight reduction would be undetectable, and the strength uncompromised (or undetectable). But don't discount the aesthetic effect. Elegance can add 2- or 3- knots to your apparent speed (i.e. speed in the eye of the beholder).

Bob, how much taper did you apply?

Bob, you are saying that cedar w/o any glass is strong enough? This is good to know. Cedar would be significantly lighter and less expensive than fir. I would prefer to use it if I can.

How clear was your cedar? No knots? Small knots? Did you scarf out pieces that looked wonky or did you use continuous pieces? I can get "mostly clear" cedar 2 x 4s pretty cheap, but I'd pay a lot for "really clear".

David, I like the way you think. I was even thinking of painting the tips of the spars white for the same reason. I'm a total attention whore on the water. Half the fun of taking the Goat out is getting all the stares and positive feedback. If a bit of taper buys me more, it's worth it!

Dave,

There wasn't much taper in my original box boom. I'll see if I can find a photo or two showing what I did.

Paulie,

The original boom used cedar fence boards - which was pretty knotty and needed scarfing to get useable lengths. That boom has a distinct crook in it, the result of poorly aligning the scarfs. But even with the crook, the boom has worked remarkably well, I just won't use fence boards again as a source for spar material.

For the second boom, I used 12' pieces of reasonably clear 4/4 rough cut white cedar (readily available here in central Michigan) milled (a band saw and thickness planer are my friends) to size. Yes, it is strong enough without FG - with this caveat: I don't sail as hard as some or in as strong of winds as some but I've never felt the boom was near the breaking point.

Bob Wessel
Fenwick, MI
Building Gardens of Fenwick, a Welsford Pathfinder
Karen Ann, a Storer GIS

Thank you for that info! Headed to the lumber yard right now.

Sent from my cell. Please excuse typos and brevity.

Photo of the original box boom (aft end closest) :


DSCF4665 by bob.wessel, on Flickr

Photos of second box boom:

Note the knots.


DSCF5824 by bob.wessel, on Flickr

Aft end. Note I didn't sand this very much - 3 coats of epoxy and a couple coats of varnish.


DSCF5826 by bob.wessel, on Flickr

Thanks for the pics! They will help with my build.

There's been a change in my plans. I got sidetracked on the way to the lumber yard -- had to go pick up my son at the train station and the yard was closed by the time I was finished.

But I found something in the garage I might like better. I had totally forgotten that I had one piece of douglas fir left over from my build. It's nice stuff -- clear with close, straight grain. But it has a crack down the middle, so I had set it aside. But I can work around that crack and when cutting for the boom. It should work great.

The only problem is that it has been out in the garage soaking up moisture for 2 years. I brought it down the basement, where it is crispy dry, but it will take some time for it to dry sufficiently. I'll have to wait some days before I start cutting.

If 10mm cedar doesn't break, I may go even thinner on the fir. Trying to decide now how gutsy I want to get on that.

Uh, the cedar was 12mm, not 10mm, just pointing that out to make sure you don't get too crazy planing you DF.

Have you measured the moisture content of that DF with a moisture meter? I'm no expert but lumber is often air-dried in the open - exposed to the elements so I'm not sure I understand how your DF would be soaking up moisture in your garage. Not saying it isn't, just that I don't understand your statement.

On a side note, I'm not so convinced that the weight of the boom is something to become frantic over. I'm thinking that stiffness (of the boom) is more critical than weight. That is part of my reasoning for going with 9mm Okume for the sides of my Pathfinder boom. Of course, the Pathfinder is a heavier boat than the Goat so weight of the spars isn't as critical. On the other hand, since I am using the Goat sail on the Pathfinder, I want the sail, boom and yard package interchangeable (the masts are - and have to be - different) between the two boats. The yard will get a bit of attention to make sure it is stiff enough (I think the current one is, but it needs to be replaced - besides, if I'm building a new boom I may as well build a new yard to match).

Remember, that was 12mm cedar not 10mm...

Got it! 12 not 10.

My garage is unheated, uninsulated, and 100 yards from the beach. It currently has puddles of standing water on the floor, as it frequently does, and our biggest problem out there is keeping the mold at bay. The board was sitting on the floor within a few feet of the puddles. I might shrug all that off except that my son had a bad experience a couple of months ago. He made a table for his dorm room from some spare sapele from the same spot. The boards shrank enough in the first week at school that a sizable gap opened up between them. It didn't quite ruin his work, but it is very noticeable.

I'll give the wood a few days in the dry basement with a fan blowing before I start measuring and cutting.

Oh, okay... guess I should ask for specifics before offering generalized suggestions.

Looking forward to your progress. I'll try to document what I'm doing with my spars, too.