[Rhodes22-list] Rebedding Mast Raising Gin Pole Fitting On CabinRoof

[Roger Pihlaja]

Jay,

My recollection is that I had to slightly trim a pair of 2 inch long flat
head screws to fit, but I don't know the final length.  The cabin roof in
that area was a solid sandwich of outer skin, plywood core, & inner liner.
I ran a Q-tip saturated with unthickened epoxy down the ID of each hole in
order to seal off the plywood core against possible water infiltration &
used silicone RTV in each hole during final installation.

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Jay Friedland" <jsail1 at verizon.net>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Wednesday, May 12, 2004 8:51 AM
Subject: Re: [Rhodes22-list] Rebedding Mast Raising Gin Pole Fitting On
CabinRoof


> Nuff said. Through bolting now makes more sense. Roger, do you remember
> bolt length as the barrel nut has the limited depth? Is compression
> between the liner and cabin top a problem- air space, etc.? Launching
> Sat. so this should get the job done.
> Thanks,
> Jay
>
>
> On May 12, 2004, at 8:35 AM, Roger Pihlaja wrote:
>
> > Jay,
> >
> > A couple of years ago, I retrofitted the GBI single handed mast raising
> > setup.  The photo that was enclosed in the earlier post on this subject
> > looks like my gin pole setup.  So, I presume the mounting fitting on
> > the
> > cabin roof is the same.  I thru-bolted the two bolts on the cabin
> > roof.  Use
> > 1/4 - 20UNC SS flat head screws, 5/16 inch ID X 1-1/2 inch OD SS fender
> > washers, and 1/4 - 20UNC SS barrel nuts.  Look on pp. 591 - 592 of the
> > West
> > Marine Master Catalog, 2004 for these pieces/parts.  The stainless
> > steel
> > fender washers & barrel nuts will give you a nice polished fastener
> > that
> > will be very strong, look good, will be accessible for maintenence,
> > and will
> > not be a head banger on the roof of the cabin in the head area.
> >
> > When stepping the mast, the mounting fitting under the gin pole is
> > under a
> > combination of compression loading and shear loading.  The relative
> > proportions of shear load & compression load change as the angle of
> > the mast
> > changes.  Compression loading is the dominant force at the beginning
> > of the
> > lift when the mast angle is low & the gin pole is nearly vertical, with
> > shear loading steadily increasing as the mast gets more vertical & the
> > gin
> > pole lays down onto the foredeck.   The structure of the cabin roof
> > resists
> > the compression load.  However, the only structural elements resisting
> > the
> > shear load are the two 1/4 - 20UNC bolts.  MJM's hypothesis re the
> > screw
> > threads being stripped on the bolt that simply turns is probably
> > correct.
> > As such, the ability of that bolt to resist shear loading must be
> > considered
> > suspect & putting all the shear load on the single remaining bolt is a
> > dangerous proposition.  The consequences of the bolts failing under
> > shear
> > load would be that the base of the gin pole would come free under
> > load.  The
> > gin pole and the mast would go shooting every which way & the forces
> > involved are enormous!  Since there would very likely be someone
> > standing
> > beside the gin pole cranking the winch handle, that person would almost
> > certainly be injured.
> >
> > Please do not attempt to use your gin pole until you get this problem
> > fixed!
> >
> > Roger Pihlaja
> > S/V Dynamic Equilibrium
> >
>
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