Spars for 1928 McInnis 24’ catboat

In the wood gathering phase of an authentic reproduction, stickering green oak, LL yellow pine, and Atlantic white cedar. Found a spruce main and boom from a donor hull of the same era, they seem sound, minor checks, workable, prob ca 1970s refit.

Is it practical to take a 28’ x 6 1/2” spruce mast and shave it to make a 26’ boom, ditto shaving a 23’ x 4 1/2” boom to make a 16’ gaff, both tapered? How would one go about shaping these spars?

If this can be done, I can devote the $$$ saved to the cost of a new main, which will be 35’ x 8”, also tapered, likely costly…still trying to source it.

 

Hi jangr, If it was my project, I'd consider sourcing a lathe with a chuck big enough to hold 6 1/2" , and a place to mount the tailstock 28 feet away, run it at low speed to reduce / avoid whipping out of balance, and make a very sturdy and heavy moveable tool bar to hold the wood turning chisel on, then doing it one section at a time, checking progress with a long straight edge and a critical eye. Probably need a heavy moveable and adjustable steady rest as well, to minimize turning an oval / ellipse / odd shaped spar. Then use sand paper or emery tape and long board to finish the rough surface created due to low speed turning. It has great potential to turn into a disaster though. Maybe ask around local wood machining establishments for options and suggestions, and pay for a professional to do a good job quickly. Then you just cut to length, do prep work, and epoxy then varnish.

 

Seasquirt, tooling out a mega lathe was my first thought also. But after 50 years both pieces have some age related warp, maybe 1/4” on the boom in particular. Wobble would be a real problem, hard to avoid an oval shape.

Now thinking to make a straight, flat, first cut, with individual patterns for each segment of taper. Use each pattern to mark each taper segment on the flat cut, rotate 90 degrees , making 4 more cuts in sequence. Could use the patterns again to mark the 4 corners, set the saw at 45 degrees, make 4 more cuts. Pretty confident I could make a rough tapered octagon, then work the edges with a draw plane, using the patterns as a guide. Sand the rough blank to finished size with a longboard and critical eye.

Does that sound reasonable?

 

Slicing corners off was how the original was shaped.

 

<sigh> No, maybe, yes. Mast like this where done on a spar bench. Shaft lathes (which can be 60ft x 5ft BTW) are specifically big shipyard equipment for rotating items cannot be used for wood because of the natural density variations in the natural material. (Personally I blame the conceptual problem on Norm Abram and The New Yankee Workshop which promoted the idea of "wood machining" vice "wood working".) There are many texts, both period and modern, that explain how to get out a mast or yard of either solid stock or built-up. Two that come readily to hand are Basil Greenhill The Evolution of the Wooden Ship and Chappell's Boatbulding. Both are the same method for round or oval masts...squaring, then tapering, 8ing, 16ing, 32ing if you wish, then a rounding plane and sanding. What this this method also allows you to do is to transition the shape of the spar as necessary from a square foot, octagonal at the partners, round in the body, and the square again at the head for the peak fitting. All traditional, and much less timely than trying for a perfect "machining" setup.

Edit to add: Francis Kenney's edition of Skene's Elements of Yacht Design also has a whole section devoted to the made-up wooden mast that are not round.

 

Try this 5 part series. I took a quick look through and it has almost everything in it.

 

The first thing you must check is if the donor spars are hollow or not. If they are the probability of beeing able to modify them is slim, and the work required is equal if not greater to making something from scratch.
Unfortunately for you there are spars buildt up from two halves where it's not immediately obvious that they are hollow.

If they are solid there's no problem using them, jehardiman explained how it's done.

 

Sorry, forgot that you are using donor spars. Rumars is correct, the existing material would end up too thin (and therefore too weak) if you just reused a hollow spar by cutting the outside down, see Kenney's book.

 

Thanks all. I have Chapelle’s Boatbuilding, aka the Bible, and have read through the process, pg 553 onwards. The only difference is that I won’t have a flat surface to work from until I make the first cut. I’ll do that with a piece of ply clamped level on top, blocked on the underside. When I roll the spar with the flat cut facing up, and level, I can mark it with my taper pattern. Repeat until I have the tapered, octagon, the rest is pretty straightforward.

 

When trimming your final corners, a simple sharp hand plane may do a smooth job, if you don't over do it; or an old style spoke shaver could do it, before sanding. You could also start on making new tapered birdsmouth spars, for if the old wood spars fail.

 

Squirt - I am not sure a birds mouth spar would work strength wise. The sail plan is already aggressive, 490 ft2 on a 30’ mast (deck to peak), so the 8” base diameter is specified in solid spruce. The construction plan has 3” oak mast partners backed up by 4 inverted knees running back to the frames for and aft. Since it’s a catboat, the mast is only 15” aft of the bow, so there’s not a lot of room to go for more diameter/expanded partners. Not to mention the single 3/8” SS forestay running to a bronze ‘duckhead’ eye, which trails 6” aft on deck, and 40” down the stem band. I feel like this particular style of boat would be a challenge to convert to a birds eye mast, tho I would be happy to be proven wrong.