Re: [bolger] hollow mast progress
What was the outside dimensions, and wall thickness of your mast?
I have a hollow birds-mouth mast, doug fir, 3-1/2 at the partner, 7/8 inch
wall thickness. Don't seem to have any problems with it, other than it is a
bit heavy.
No blocking, hollow all the way.
I have a hollow birds-mouth mast, doug fir, 3-1/2 at the partner, 7/8 inch
wall thickness. Don't seem to have any problems with it, other than it is a
bit heavy.
No blocking, hollow all the way.
----- Original Message -----
From: <fraser.howell@...>
To: <bolger@egroups.com>
Sent: Friday, July 28, 2000 6:19 PM
Subject: [bolger] hollow mast progress
> A couple of months ago I built a hollow (unstayed) mast for my Chebacco.
> I liked the description of the "birdsmouth" technique that appeared in
> Woodenboat, and thought it would be neat to run the halyards inside. I
> was quite happy with the thing until it broke. No warning, sudden,
> compound fracture. Just like Prada.
>
> I think that it had been weakened during stronger winds, as it failed
> under moderate conditions, with a reef in the main. It certainly had
> stood up to far greater stress. The break started at the partner, with a
> vertical failure across 2 strakes, then a split that went up to the boom
> jaws, where the remainder let go.
>
> The material was clear white spruce, glued with epoxy. The glue didn't
> fail, the wood did. It might be that the stiffness of the hollow mast
> concentrated the stress, progressively crushing the material in the way
> of the partner.
>
> I still like the concept, and I'll build another. I'll try protecting
> the area between the partner and boom by wrapping it in epoxy and cloth,
> and I might try carbon-fibre. I'm open to suggestions.
>
> It seems like a lot of work, but the mast was that much lighter and
> stiffer that the boat went much better to windward, and I still have the
> exit blocks, which were the most expensive part.
>
> I kept the old solid mast, so am still in business.
>
> Cheers
> Fraser Howell
>
>
>
>
>
> Bolger rules!!!
> - no cursing
> - stay on topic
> - use punctuation
> - add your comments at the TOP and SIGN your posts
> - add some content: send "thanks!" and "ditto!" posts off-list.
>
--- Inbolger@egroups.com, "Ron Badley" <badley@s...> wrote:
mine reinforced his mast with carbon and had it fail right at the
partner in a similar manner to what you describe. Carbon is
quite brittle and stiff. Wrapping with glass and epoxy would be
better, and kevlar even better than that (for protection, not for
splicing the mast), but what I think you need is something between
the
partner and the mast that has some give to it to spread the load, so
you're not stressing the wood across the grain so much. Leather?
Rubber? What's customary? You could also try increasing the area of
the partners and making them taper away from the mast just a little
at
the top.
Of course a solid plug where the partner is won't hurt, and I think
wrapping with enough eglass and epoxy, done intelligently, would be a
good way to fix the mast.
> Hi Fraser,I think the wrapping with carbon idea would not be good. A friend of
>
> From what you say it sounds like the mast broke due to failure
> of the wood snip
mine reinforced his mast with carbon and had it fail right at the
partner in a similar manner to what you describe. Carbon is
quite brittle and stiff. Wrapping with glass and epoxy would be
better, and kevlar even better than that (for protection, not for
splicing the mast), but what I think you need is something between
the
partner and the mast that has some give to it to spread the load, so
you're not stressing the wood across the grain so much. Leather?
Rubber? What's customary? You could also try increasing the area of
the partners and making them taper away from the mast just a little
at
the top.
Of course a solid plug where the partner is won't hurt, and I think
wrapping with enough eglass and epoxy, done intelligently, would be a
good way to fix the mast.
Hi Fraser,
From what you say it sounds like the mast broke due to failure
of the wood rather than the building method used, good to hear
as I like the method also. I'd suggest making the new mast
solid in the area where it passes through the deck and tapper
out the solid core over quite a long length (I'm not sure how
long your mast is). A tapper for this type of mast can be
achieved by cutting a long "V" in a dowel. If this is done the
mast will not be susceptible to crushing at the deck. I doubt
carbon will fix the problem for next time. You have to be
careful how carbon us used. As carbon is _very_ stiff if it's
not tappered out over a large area the mast could break off
right where the carbon ends.
Ron
Kismet 31 "Big Bird"
From what you say it sounds like the mast broke due to failure
of the wood rather than the building method used, good to hear
as I like the method also. I'd suggest making the new mast
solid in the area where it passes through the deck and tapper
out the solid core over quite a long length (I'm not sure how
long your mast is). A tapper for this type of mast can be
achieved by cutting a long "V" in a dowel. If this is done the
mast will not be susceptible to crushing at the deck. I doubt
carbon will fix the problem for next time. You have to be
careful how carbon us used. As carbon is _very_ stiff if it's
not tappered out over a large area the mast could break off
right where the carbon ends.
Ron
Kismet 31 "Big Bird"
>From:fraser.howell@...
>To:bolger@egroups.com
>Subject: [bolger] hollow mast progress
>Date: Fri, Jul 28, 2000, 4:19 PM
>
> A couple of months ago I built a hollow (unstayed) mast for my
> Chebacco.
> I liked the description of the birdsmouth technique that appeared
> in Woodenboat, and thought it would be neat to run the halyards
> inside. I was quite happy with the thing until it broke. No warning,
> sudden, compound fracture. Just like Prada.