[Rhodes22-list] A fix for the short furler

[Roger Pihlaja]

Bob,

I'm not quite certain what I'm looking at in those pictures.  I understand
you had to make new plastic end bushings because the old ones were probably
old & brittle & disintegrated when you tried to remove them.  But, what are
you going to do with the center bushing?  Are you planning to join the two
pieces of the furling tube with the center bushing vs. welding them
together?  If so, how do you plan to immobilize the top & bottom pieces of
the furling tube so they can't rotate relative to each other?  Remember, the
head of your genoa is bolted to the top of the furling tube.  During
furling, the required torque to turn the furling tube is applied at the
furling drum at deck level.  The tack of the genoa is tied to the furling
drum, so it must rotate with the furling drum.  But, the furling tube design
assumes the furling tube will also transmit the torque up to the head of the
genoa & cause the entire headsail to wrap around the furling tube in sync.
If your extension is not somehow locked to original lower part of the
furling tube; then, the torque will have to be at least partially
transmitted by the luff tube on the genoa.  This load will take the form of
a distributed shear load all down the length of the luff tube.  Sailcloth is
intrinsically at its weakest against this sort of shear loading & this
twisting action will shorten the life of the sail, although I can't say by
how much.  In addition, I would think the sail shape will look pretty odd
with the leading edge of the sail all twisted out of shape.

Assuming I've analyzed your plan correctly; then, plastic is a poor choice
for the material of construction of the center bushing.  Consider
refashioning that center bushing out of Al 7075-T6 aluminum alloy & using at
least three
10-32 UNF oval head stainless steel set screws on the top & bottom sections
to immobilize them relative to each other.  I would also epoxy these set
screws in place during assembly.  It won't be as strong as welding & it will
be also be heavier; but, it should lock the upper & lower sections together
and hold them in proper alignment for a long time.

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Robert Dilk" <Robert.Dilk at TRW.COM>
To: <rhodes22-list at rhodes22.org>
Sent: Monday, September 27, 2004 9:28 AM
Subject: [Rhodes22-list] A fix for the short furler


> Here is my solution.
> I was unable to remove the  original split bushings intact, so I
> measured and designed these from scratch.
>
> Note the two end bushing and the center bushing . I will use the center
> bushing to connect the of furling tube to the new extension.
>
> The new Forestay is due in Friday. I will tell you how it works out.
>
> Bob
> S/V Knot Necessary
>


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