> Have you done this w/ your boat, Judy? Has anyone else with P19s from
> the era of ours?
>
> You are indisputably correct about the tuning (static and dynamic) of
> a fractional rig, but I have always been hesitant to try dynamic mast
> bending on Ursa Minor. Have you noticed the section on that mast? It's
> positively _massive_ for the application, far larger and stiffer than
> on comparable boats. I wonder if it wouldn't take entirely too much
> stay tension to effect an appreciable bend. Or at least way too much
> to be categorized as safe. Did your rigger take this into account?
>
> Regards,
>
> Bill Combs
> WWP 19 #439 (Aug 1987)
> "Ursa Minor"
> Fort Walton Beach FL
> ttursine@gnt.net
>
Hi Bill (and Dave Kautz too),
The adjustable backstay was part of the original HMS18 design by Herb
Stewart. As was the "massive" DM6 mast. As were the 1/4" shrouds and the
shroud chainplates we all even on the newer P19s.
The only thing that's different from his original rig design on my 1985 P19
is the bow chain plate (which my rigger thought was strong enough but kind of
a weird way to do it). Dik Dickerson's HMS18 #11 (?) came with an adjustable
one identical to mine. They all came with the wooden compression post, the
1/4" shouds/stays and the same shroud chainplates we all have on our P19's.
I trust the competency of the designer of the HMS18/P19, Herb Stewart. I
trust designed a rig/hull/mast/compression post that was strong enough for
the adjustable backstay he put on it. Herb Stewart designed the adjustable
backstay as part of the original rig design, so I feel safe using it. It's
that simple to me. The original design by Herb Stewart was sound.
If the boat was built according to Herb Stewart's specification, the
adjustable backstay wouldn't worry me. The only question in my mind would be
"did the builder make hull and hull/chainplate strong enough to take it or
did he skimp on the construction?" The rigger inspected my boat and thought
it was. Nothing but the mast flexes visibly when you tension the backstay
and compress the mast column. Just as it should be.
I change the tension on my backstay all the time. Bruce Little, the previous
owner, did too. With no apparent damage to the boat. In the almost 15 years
of using an adjustable backstay on Redwing, no shrouds have ever ripped loose
from the boat and the mast has never come crashing down. The compression
post hasn't been pushed through the hull and the cabin roof is just fine
(it's solid fiberglass between the mast and the compression post. There's no
core to crush)
And yes, the rigger was the one who showed me how to tune the shrouds/stays
and showed me how much bend to put in the mast safely. The P19 carries so
little sail area compared to the rigging that he wasn't worried about the
wires, turnbuckles, etc failing. The stays/shrouds are manifestly strong
enough, his only concern was the hull and chainplates attachments and he was
satisfied with them.
Like I said, I only have to bend the mast a little to get an appreciable
flattening of the mainsail draft. Bending it certainly increses the
compressive load on the mast column/compression post and the tensile load on
the stays and shrouds, but my rigger didn't seem to be worried.
BTW, since the newer P19's have a ligher DM5 mast, the compressive loads on
the stays/shrouds and the rest of the rig would be less then for our heavier
DM6 masts on the older P19s. The mast on the newer boats is identical to the
DM5 mast manufacturerd by Dwyer company. As for the strength of the mast, Mr
Dwyer personally told me that he thought the mast was plenty strong enough to
take it.
I use the original equipment (adjustable backstay) that came on my boat all
the time. If anybody has doubts in his own mind about the safety, don't do
it.
Best,
Judy B