Mast size

[dforrestrichards]

I was given an 18 foot v-hulled skiff a few weeks ago. It needs to be rigged entierly. How would i go about finding how large the mast should be. I would like to gaff rig it. The boat came with some head sails. It does not have a bowsprit. Any help at all would be great. Thanks,
Forrest

[Art Read]

You plan on rigging stays and shrouds? If not, make it as beefy as you can get away with. The gaff rig is fairly "forgiving". I'm thinking a tappered spar about 4 - 5 inches unstayed, maybe 3 - 3 1/2 or so stayed. Look at similar boats and see what works for them maybe?

[Russell Sova]

Most gaffers didn't have tapering masts. Hillair Beloc in "Sailing the Sea" suggests no taper for a gaff. For a boat that size 3 to 3 1/2 stayed would be perfect. An unstayed 5 incher would surely be weight disadvantage.

[Wooden Boat Fittings]

Parallel-sided as far as the hounds, so that gaff jaws and masthoops (and lacing, for that matter) don't (a) jam at the bottom or (b) slop round at the top.

I agree that three-and-a-half inches diameter should be enough, and maybe as a skiff she could get away with no shrouds. But a gaff can put a fair wringing strain on the mast all the same and I think shrouds would be appropriate from the hounds -- and cap shrouds too if you were thinking of setting a topsail.

Mike

[Ed Nye]

Go here
web page (http://www.carlsondesign.com/#Professional_Shareware)
and scroll down until to get to the mast design software. Download it, plug in your stuff and it will tell you what you need to know.
Ed

[Bruce Taylor]

From Skene's:

P = wind pressure (Square feet of sail area X 1.15)
L = Length of mast in inches
Safety Factor for small gaffer = ~2
15,700 = Pi X fibre stress of spruce (5,000)

Max. diameter of solid spruce mast (in inches)equals the cube root of (16PL X Safety factor / 15,700)

[Art Read]

Re: mast taper... My plans show quite a bit of taper. Granted, it's fairly consistant diameter 'twixt the gooseneck and the point where the gaff jaws will land when set, but it DOES taper below the goosenedk towards the step and above the jaws, thru the hounds to the truck. A perfecly "untapered" spar would look a bit akward, no? (5 inches WOULD be pretty ungainly for that size boat. But 3 1/2 unstayed would make me nervous. Go with shrouds and at least a forestay or perhaps choose a more forgiving rig?)

[mmd]

John Leather's "The Gaff Rig Handbook" gives ratios for spar tapers, including gaff-rigged masts.

[brian.cunningham]

Ed, way :cool: program!

Bruce, I put your formulas into a spreedsheet.
Thanks for the info.

As you know I'm building a schooner gaff rig.

In order to get the two equations to come out equal you need to select "Heavy Ocean Cruiser" from the displacement type.

Multihulls are not on the list though. My boat is really light for the rig I'm using, but putting as mast on a multihull is like setting it into concrete!

[ 09-30-2003, 01:10 AM: Message edited by: brian.cunningham ]