View Full Version : figuring out spar dimensions

01-08-2008, 08:44 PM
hello all - My husband and I have come across a pretty little 23' cruising sailboat (fiberglass..) but she's in a hole she dug for herself in someone's yard where hurricane Katrina left her. I plan on making some spars for her and was wondering if anyone knew the rule of thumb when it comes to determining spar diameter, etc.

I plan on gluing up the mast and boom. As there is no surviving rigging or sails and the boat is a model built in a small shop in Louisiana, I have no idea of rig dimensions. To my best guess, the mast will be around 26' and the boom will be 11'. How thick will I need to make the mast and boom? I intend on making them solid. Any suggestions on making these spars using lumberyard stock? We're on a budget... Of course feel free to speak up if anyone feels trying to find a suitable old aluminum mast would be smarter/cheaper/better/safer, etc...

01-08-2008, 10:17 PM
We need more info! :)

Pictures? I presume this is a sloop rig? Stayed rig? Do you have any of the hardware? (I hope so, because your budget is shot if not.) Do you have the sails? If so, does the main require a slotted mast or does it need a track?

The more you tell us, the more helpful we just might be. Or at least we'll have something more to argue about.

Roger Cumming
01-08-2008, 10:40 PM
First call the shop where the boat was built if it still exists. If not, consult a yacht designer/naval architect who can draw a sail plan from which you can build the spars. I suspect, however, you would have already done that and want instead to do everything yourselves. I would note the dimensions (length, beam, draft) and weight of your found boat and then survey the world of 23' cruising sailboats. When you find at least 10 that are very similar in dimension and weight note their sail plans. Note the sail areas and spar dimensions. You will become familiar with several similar designs and from this you will be able to sketch a sail plan. Also, seek out sailors with some sailing experience with similar sized boats. Ask them for advice.

With a sail plan you can establish the dimensions of the spars and then build them. Lumberyard spruce is acceptable for the mast. Laminate it in 3 layers, tapering it. Pick out good planks. Similarly, pick out some good Douglas Fir from the lumberyard for the boom, which should also be laminated A heavier wood for the boom is usually best. The rigging hardware can be purchased from catalogs. The rigging itself can also be procured from catalogs but will take some ingenuity on your part, depending on how much if any of the original is left.

If you think of the sails and rigging of the boat as the engine, you will have built the engine for your boat! After this you will want to build a whole boat. Good luck. And keep us posted.

01-08-2008, 11:18 PM
Advice from the cheap seats here in the Forum: if you can come close to the presumed sailplan with several options from common 23' cruising boats, look at the used sail lofts to see what is available. Pick up the sails first, then build the rig to fit.

Alternately, when you figure out what size of sail and rig she had, look around for both sails and spars from other Katrina boats that may have lost the hull but had everything else survive...

Ian McColgin
01-09-2008, 06:31 AM
It's likely that she originally had aluminum spars so you'll get little help regarding the scantlings.

It's also really clear that you need guidance as you left out several major considerations:

Deck stepped or keel stepped? The latter can be somewhat lighter than the former.

Chainplate layout? Is she meant to have just a pair of shrouds or lowers as well? Is there any sweep? This will tell you a lot about whether the rig is meant to be played with by mast bending, and will give you some notion of how much beyond pure colum strength is needed.

Fractional rig or masthead? Again with how far from a pure colum the mast must go.

In the extreems, a mast can be a pole - unstayed like catboats and the modern Freedoms and Nonsuchs - or a colum, like some ultralight but highly stayed rigs where the mast is the least mass that can withstand the compression strain of the stays. Most masts are a bit of both.

Once you decide on the basic rig - height, sail plan, stay pattern - then you can readily determine scantlings suitable to available wood for either a solid or hollow mast and if the latter, box or bird's mouth.


Jay Greer
01-09-2008, 09:38 AM
Since what you are asking is part of my profession, I can't in good conscience overstep the considerations of this forum, or myself as to a gratis solution. However, if you are willing to do some research, you might do as others have advised and find yourself an existing boat that has a well designed rig that is pleasing to your eye. You could then find a boat that has similar displacement and hull dimensions that is rigged with a wooden mast, one that has a published set of spar plans available. There are many published rigs that are out there. A good source of information could be to check out the various books written by some of the greatest designers of wooden boats such as:
L. Francis Herreshoff, William Atkins and Uffa Fox. This will give you the insight you need as to scantlings and proportion you are seeking. One word of advice is to avoid taking that which is complicated to sea!

01-09-2008, 10:51 AM
Several books written by a CHAPPELLE will give you definitive scantlings for your mast, including the taper that will be strong and look proper. The scantlings you'll find in his books for spars are authoritative.

01-09-2008, 11:03 AM
Thanks a lot. After some research (some of which involved a shovel) I've found the spar and sail dimensions. The mast is cabin stepped, although the step is missing, there are two sets of chainplates, and the rig is not fractional (full?). She's got a full but shallow keel (about 2'10").

The boom is 11' and the mast is 26'.

I intend on looking for a suitable set of used sails and modifying those dimensions if necessary. Any rough guesses on how thick to make the mast and boom? Also, what is the scarf ratio for masts? Yes, I see the hint to do more research myself, and I'd glady figure this one out if any of you could come up with a way to get this beast on a trailer (that hasn't been constructed yet)!

01-09-2008, 07:49 PM
At the risk of high criticism, I'll venture to guess that your mast will want to be in the neighborhood of 3" by 4" A square, hollow mast will be the easiest and cheapest to build. You'll want to taper it up top, but that's not hard to do, either.

The size depends on lots of things -- not just the sail area, but the wood you use and how the mast is stayed and the weight of the boat. The more wire, the lighter it can be. The lighter the boat, the lighter it can (and should) be.

As to getting it out of the ground -- how badly is it stuck? I'd start by pumping water all around it to loosen things up. Then you'll need a hoist of some sort. A relatively simple A-frame structure with a chain hoist might do it if you can get straps well under the ends of the hull.

Once again, we love pictures of these problems.

01-10-2008, 11:21 AM
here's a picture... Sorry it's small..

01-10-2008, 06:45 PM
That doesn't look so bad, as far as the extraction goes. If you know someone with a front-end loader or want to spring the cash to hire one, you could probably get straps under the boat and use the heavy equipment to lift the boat up by the straps, drive it back to the road and set it down on the trailer. Knowing the boat's weight before you start would be a very good idea. Is there any kind of builder's plate on the boat? Also, you'll want to measure how deep the keel is from the waterline before you can find or build a trailer that will be suitable. By the way, modifying a trailer is probably no more costly than building from scratch.

01-10-2008, 08:51 PM
Your dimensions are close to those of a Catalina 22', of which 22,000 were made. There are (used) sails, masts booms and rigging for sale all the time on various owners' sites, e-bay etc.