RE: [bolger] Re: Hollow Mast Plug
- Hello Guys
Interesting thread but HEY think simple. The simple solution has already
been sugessted but we seem to have ran right past it.
I've built several smallish birdsmouth spars and assisted with two really
big ones for a 38' catamaran. In each case we only had the simplest of gear
(a tablesaw and a roughy at that).
You should be building a birdsmouth spar light enough so it NEEDS
reinforcement at the partners and other points such as spreaders etc,
otherwise it'll be too stiff. The WoodenBoat article suggests that the
stave thickness can be very light, and I would stick to the "light" formula
DON'T try driving plugs in later, you'll go nuts trying and do a lousy job
as the epoxy will drive out as well. You need to do a test fitup of the
staves and plugs, the plugs must be a loose fit so the workmanship isn't at
all critical. Make sure you taper the plugs by cutting "V's" down the ends
( like a reverse scarf - several books have pictures) and drill through them
if you plan on internal halyards ( yuck - too complicated). We have often
made our plugs as separate birdsmouths assemblies, its so easy to do. Use
epoxy a bit thicker than normal on the plugs so it doesn't run out.
Plaster epoxy on the whole lot and assemble.
I'm a certified "wood butcher" and even I have made some quite nice spars by
these methods. Incidentally the birds-mouth technique has been around for a
long time ( I've seen it in a English book published in the 1960's) and is
technically very very good. I would never build another spar by any other
method now. The big spars we built for the Cat came out lighter than
aluminun, were stiffer and have been around Cape Horn!!!
Regards - Foster
Southland, New Zealand
> consider laying up an external collar of epoxy saturated fiberglass
> carbon fiber. By applying the fabric in increasingly wider strips the
> reinforcement would be tapered, preventing a hard spot that would
> concentrate forces and invite failure of the mast (this would be a
> problem with an untapered internal plug, as well). Also, such a collar
> would be much easier to apply, and the application of
> adhesive could be
> better controlled and evaluated. I do not think it would have to be
> particularly thick to achieve the desired increase in strength,