[Rhodes22-list] Bow pulpit

[Rik Sandberg]

Michael,

I do not disagree. However, I have seen many "protrusions" on the front of 
sailboats, or powerboats too for that matter, that were made of FRP and would 
be considered by most folks to be a "bowsprit". I have not however, EVER 
seen, after walking past a few hundred boats, a "bow-pulpit" made of FRP. I 
am certainly not the last word on anything boat related, but I think Barney 
may have his terms confused here. A FRP bowsprit type appendage would, in my 
mind, be more plausible than an FRP bow-pulpit. Just want to be sure that 
Barney and the rest of us are really on the same page. :-)

Bottom line here is that whatever Barney hangs off the front of his boat, if 
it's made of FRP, the first time he bumps a dock, it's likely to bust into 
many small pieces. FRP can be fairly strong for it's weight, but it is not 
particularly tough (able to bend) or forgiving like a metal part would be.

Personally, If I was going to make a sprit for an R22, I would use a metal 
frame on the outside, with a wood filler in the middle. No matter what one 
hangs out there, one is going to have to have some kind of brace down to the 
bow to support it.

I also agree that an anchor roller is both easier and probably better. Doesn't 
look as "shippy" though. :-)

Rik


On Sun, Feb 22 2004 09:42 am, Michael Meltzer wrote:
> I thinks it is the same issues, 2 feet long is big, figure one inch depth,
> 6 inch wide, is asking for it, thier is also the issue what loads are going
> to be on it, either a forstay or anchoring will need a brace(using the
> trailer eye as a chainplate?). Most likely will get more milage from using
> a stainless anchor roller hanging forward a few inches.
>
> MJM
>
>
>
> ----- Original Message -----
> From: "Rik Sandberg" <sanderico at earthlink.net>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Sunday, February 22, 2004 8:59 AM
> Subject: Re: [Rhodes22-list] Bow pulpit
>
> > Roger,
> >
> > I agree with your assessment for the use of composites for a bow pulpit,
> > or for that matter any rail or stanchion on a boat. But, I wonder, could
> > Barney be thinking of a bowsprit??? I know that's not what he said, but
> > sometimes folks don't yet know the proper term for a particular part.
> > It's possible that this is the case here.
> >
> > My apologies for making wild assumptions if this is not the case. :-)
> >
> > Rik
> >
> > On Sun, Feb 22 2004 04:14 am, Roger Pihlaja wrote:
> > > Barney,
> > >
> > > The material properties of FRP composites (fiber reinforced polyester
> > > or "fiberglass") do not lend themselves to building long "skinny"
> > > structures like bow pulpits.  For example, Young's Modulus for 316
> > > stainless steel is about 28,000,000 psi while Young's Modulus for a
> > > typical FRP composite is only about 6,500,000 psi in the axial
> > > direction (oriented along the fibers) and 1,800,000 psi in the
> > > transverse direction (oriented at 90 deg to the fibers).  Since the bow
> > > pulpit is too "stupid" to know which way the fibers should have been
> > > oriented during lay-up for any given load situation, such structures
> > > must be designed using the lower value for Young's Modulus. Young's
> > > Modulus is a measure of the inherent stiffness of a material.
> > > Therefore, FRP composites are only 1.8E6 / 28E6 = 0.0643 X as stiff as
> > > 316 SS.  In order to have an FRP composite bow pulpit that was
> > > acceptable stiff, the legs and railing would have to be so thick that
> > > there would be an excessive amount of windage up on the bow.
> > >
> > > In addition, FRP composites are not ductile like metals.  In other
> > > words, when an FRP composite is stressed beyond its yield point, there
> > > is some internal damage.  Some of the glass fibers break and the
> > > chemical bond between the polymer matrix and some of the glass fibers
> > > fails in shear. This damage is cumulative and irreparable.  The next
> > > time the damaged FRP composite is loaded, it yields at a lower value of
> > > stress than before & more internal damage occurs.  However, since the
> > > damage is internal to the composite structure, it may not be visible on
> > > the surface.  This cumulative damage can progress to the point where
> > > the bow pulpit might fail when someone merely leaned on it.  In
> > > contrast, when a metal is stressed beyond its yield point, it can
> > > deform and bend a lot before failure.  After the deformation, the metal
> > > is said to be strain hardened & the yield stress is actually greater
> > > than before the incident.  This is why it's nearly impossible to
> > > straighten a piece of tubing back to its original shape after bending. 
> > > In a collision situation, the 316 SS bow pulpit might come away bent. 
> > > But, as long as there were no visible cracks and the mounts were not
> > > pulled out of the foredeck, the bow pulpit would still be safe to lean
> > > on. With an FRP composite bow pulpit, you wouldn't know unless you ran
> > > an ultrasound nondestructive test on it.
> > >
> > > Bottom line - for long "skinny" structures like bow pulpits that have
> > > to withstand shock loading & have a safety function, FRP composites bad
> > > - metals good.
> > >
> > > Hope this helps.
> > >
> > > Roger Pihlaja
> > > S/V Dynamic Equilibrium
> > >
> > > ----- Original Message -----
> > > From: <bestpestcontrol at earthlink.net>
> > > To: <rhodes22-list at rhodes22.org>
> > > Sent: Sunday, February 22, 2004 12:32 AM
> > > Subject: [Rhodes22-list] Bow pulpit
> > >
> > > > from Barney-- Has anyone seen a fiberglass bow pulpit on a Rhodes 22?
> > > >
> > > >
> > > >
> > > > it looks to extend about 2 ft in front of the bow. Im thinking of
> > >
> > > installing one on my rhodes
> > >
> > > > __________________________________________________
> > > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > >
> > > __________________________________________________
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> >
> > --
> > Rik Sandberg
> > Long Prairie, MN
> > S/V Happy Little Girls 2
> > Pacific Seacraft Flicka
> >
> > All things significant are small and slow
> >
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
>
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