I just finished up a 15 ft. X 2.5 inch mast and an 11 ft. gaff spar
using this method and am well satisfied. I constructed a "spar lathe"
from directions in the jan 2004 Wooden Boat Magazine that made sanding
the mast a 50 minute or so affair. The rig turns the mast at about 200
RPM while I walked up and down with a belt from a belt sander turned
inside out. The Arch Davis Designed Penobscot 17 the spars are for
goes in the water Labor Day Wekend. Sometime after I'll post a site
with the details. Great design, fun to build, and (hopefully) fun to sail!
Jeff
Jonathan wrote:
This guy Frank Hagan has a good illustration of the "proper"
birdsmouth set up, as well as a number of tips in building.
http://users2.ev1.net/~fshagan/bm.htm
In the horror show I created by not thinking to count my pieces, I got
frustrated enough to overlook one of his other caveats, which was to
have the screw part of the hose clamps in various parts of the mast
instead of aligning them. If you inadvertently align them, you seem to
put enough pressure on *one* strip that induces a slight bow in the mast.
I plan to set the spar so that the bow is bowing aft and I will
explain that in an unstayed rig I wanted to "pre-bend" for sail shape,
as there is no backstay to shape the mast with.
I'm not sure I can sell that to my 12 year old, she's pretty good at
sniffing my BS 
but, it's worth a shot
Jonathan
Brian Whatcott wrote:
Ah yes: that explains it.
I was interested in the fishmouth approach - I hadn't run across
this method before.
I started by asking myself: Why wouldn't I saw on a 22.5 degree
angle? This would be economical in the spar material: only the kerf
would be lost. But visualizing the clamp up, it would be a nightmare,
I'm su the fishtail approach is largely self aligning I'd think.
And your approach ought to be very warp resistant.
I recall that the 2 part sandwich approach that I used allowed a
little bowing to show up after a year or two.
I also recall that a hollow shaft loses 5% of its strength (in torque)
while losing 25% of its weight, for a 50% of radius, hole.
Brian Whatcott Altus OK
On Sun, 15 Aug 2004 06:54:41 -0400, Jonathan
wrote:
No, it uses 8. I used 1x4 fir decking and got 3 strips per board,
and I inadvertently used all nine instead of discarding one
In the process of clearing a space to lay out the mast for gluing,
checking all of the 45 degree cuts for full cut through (my saw
depth changed without my input after the first 4 cuts, and two
strips had to be cleaned up with a Sandvick scraper)
I forgot to discard one of the lengths I was wondering why the
hose clamps I used to glue it up were suddenly too short when they
had plenty of room on my test, a 2 foot spar.....
*Fortunately*?, my epoxy mix was thick enough to fill most of the
gaps. There are a few places I will use the West syringes to fill
some hairline spaces.
I was wondering if anyone would catch that goof
Jonathan
Brian Whatcott wrote:
On Sat, 14 Aug 2004 22:16:33 -0400, Jonathan
wrote:
Took a detour to work on Ocean Planet for two weeks and to make a
mast. Interior is painted. Almost there !
http://home.comcast.net/~jonsailr
Nicely illustrated! But the mast uses 9 45 degree segments?
you have a gap or two, I reckon.
Brian Whatcott