[Rhodes22-list] Bow pulpit

Rik Sandberg sanderico at earthlink.net
Sun Feb 22 10:48:03 EST 2004


One more issue with a bowsprit.

I don't know if Barney trailers or not, but a bowsprit hanging 2 feet out in 
front of the boat is sure to interfere with the bow stop on the trailer upon 
launching and retrieval. Plus, whatever is used for a brace on this piece is 
going to be in the way of pulling the boat all the way to the stop.

Just one more little thing to consider.

'Course all of this is assuming that Barney really meant bow sprit and not bow 
pulpit. I'll probably be munching happily on all these words as soon as 
Barney clarifies that point. :-)

Rik

On Sun, Feb 22 2004 10:33 am, Rik Sandberg wrote:
> 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
> > > >
> > > > __________________________________________________
> > > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > >
> > > --
> > > 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
> >
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
>
> __________________________________________________
> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list



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