so since we're well into winter now, i've decided im not happy with the aluminum mast i scavenged last season(just looks wrong on the boat, also way to many bolts, nuts, plates to hang up the sail on ), so i'm going to build a wooden one. its -39 C today with the wind chill (thats about -33F) anyway you cut it, too cold for anything but dreaming up boat projects !!
the box on my skipjack is 2.75 x 3" so i'm wondering if i can use a sold piece of stock for the bottom (below the hinge) that is 2.75 x 3, then taper the rest of the mast (box style) to 2.75 square? will this be strong enough, or will it need to be solid?
2 3/4 by 3", tapering to 2 3/4" square, isn't much taper. You could easily make a 2.5" (side to side) by 3" (front to back) and taper this (above the hounds) to 2" square. This would look better and be lighter, still having plenty of strength and stiffness.
In fact, a 2.5" square section, from the base to the hounds is just fine and still over kill for this rig. I like round spars myself, but these should be 2 3/4" or 3" round, with the same wall thickness (minimum 1/2" on a 2.5 section, 9/16" on a 2 3/4" and 5/8" on a 3" mast. Most folks use 3/4" thick stock (1 by) for the wall thickness, but this just makes a heavy mast. The lighter the mast, the easier to raise and the better the boat sails too, so make every effort to build a light stick.
As for solid, well this is an easy thing to make, but a bear to lift and causes the boat to heel more, unnecessarily. If I was making a mast for your boat I'd make the base 3" square and taper to 2.5" at the hound, then taper to 2" at the head, above the hounds. This makes a nice meaty stick, that looks right, but not one that's overly heavy.
Technically, you can go smaller in diameter, but most think these look too dainty.
so, if i am going to a tabernacle system, how long should the supports extend up each side of the mast? is there a formula to ensure the proper support?
A tabernacle setup depends on how you'll use the sail and how the ail is attached. You can calculate the loads or just make it stout enough. 1x4 hardwood cheeks or 2x4 softwood will be stout enough, though 2x4's will be bulky. The amount of mast below the pivot depends on how you'll raise it and where the gooseneck will live. I like tabernacles to permit power mast raising, either with a winch or tackle. The longer the distance between the pivot and the purchase at the bottom of the mast, the easier hoisting is. If you're just going to "walk it" up, then the tabernacle cheeks don't need to be very tall.
Attached is a square mast building technique I've used, to offer round mast looks with less intimidation. It's a standard box section, with rabbited corners (standard practice on box mast), but it also has corner pieces, which are easy to install. I build the mast is two halves, then glue these together. It also makes tapering easy, as you just whack off an edge on the table saw, before you rabbit.
The finish nails are just to hold it together until the glue dries. Then you pull them out or cut the corners off with them still in place. The gray line is the stock that's removed in the rounding process.
Attached is the building sequence, from left to right, top to bottom. We start with the drawing, then assemble the two halves, nail and glue together. On the bottom the corners are whacked off at 45 degrees, making an octagon, which looks good below the gooseneck. Next it's cut again at 22.5 degrees. These cuts can be done on the table saw easily. The last one is rounded with sand paper.
Before epoxy and birdsmouth techniques, this was a common way to get a round mast using basically straight cut.
wow thats great, thanks paul !
A quick question for Paul: just out of curiosity, about what sort of weight is one to expect, roughly, for a mast like you described?
Thanks,
Mike
Weight is dependent on species selected, diameter, taper and wall thickness. Assuming a 16' stick with a 3" heel and continuous taper to say 2" - an eastern white spruce mast would be about 9.25 pounds. Sitka spruce would be 9.75 pounds and Douglas fir would be 12.25 pounds. This doesn't include glue or fasteners and assumes a 20% wall thickness.
A relatively straight sectioned mast up, again 3" heel with a slight taper to the hounds, say 2.75", then tapering to 1.75" at the head - white spruce would be 11 pounds, Sitka would be about a 1/2 pound more and Douglas fir about 15 pounds.
A solid mast of these dimensions would be roughly 25.5 pounds for Douglas fir, 20.5 for Sitka and 19.5 for white spruce, so a significant savings, especially if old, busted up and having to hoist it on your shoulder at each outing.
Personally, a 20% wall is a conservative figure for a well stayed rig. 15% or 17% wall thickness would save more weight, but you'd want a well tuned rig. A gaffer with a well tuned rig seems a bit of a misnomer, so maybe just 20% after all.