> Judy
>
> I had not been aware that there were coefficient of expansion problems
> between the wood with which the Potter rudders are made and bronze bushings.
> There would not be a problem in my use of the bushings if the bushings broke
> loose from the epoxy--the problem would be if the epoxy came loose from the
> wood. That would let the water into the plys of the wood, and I/we'd be
> back where we started.
>
> What do you think of the idea of overboring the bolt hole, filling it with
> epoxy, and drilling the pivot bolt hole through the epoxy? Do you see a
> problem with that solution?
I didn't express that coefficient of expansion stuff it very clearly..... mea
culpa.... I made it sound more complicated than it is. Let me try again
<shaking the fuzz out of my brain> I think we're in 99 percent agreement here
.
I don't see any problem with using the bronze bushing inside the hole. Au
contrair, mon frere, it's a great idea. My compliments to you for re-
inventing it in the context of your rudder problem. As you point out, you
have two needs: protecting the wood from water, and protecting the wood from
being chewed up by the pivot bolt. Your solution sounds like it meets both
needs very well.
I don't know If I would bother bonding the brass bushing inside the hole to
the wood. I'm no materials engineer, but I'm guessing that the bond probably
wouldn't last through too many episodes of getting overheated n the car in
the summer and being dunked into cold water. (Come on you engineers out
there, what about an educated answer???)
I'd use epoxy resin to seal the wood inside the hole and and to provide water
barrier. Then I'd just slide in the bronze bushing and put the bolt thru it.
The bronze bushing sounds find to me, but I don't have a bronze one, so I'll
probably use nylon when I gratefully copy your idea.
The whole issue of differing coefficients of expansion doesn't sound like it
applies in this situation, since the bronze doesn't HAVE to stay bonded to the
epoxy. It would be an important consideration, or so I've read, in other
situations like sealing a plexiglass window to a fiberglass hatch -- you'd
have to use caulk that remained very flexible and could stretch and compress.
>
> To the best of my knowledge all of the Potters that have ever been built (
> that had kick up rudders, any way) had the rudder components made of ½ inch
> plywood.
My #266 1985 P-19 came with a *solid* (not laminated) 1-1/8 inch thick
mahogany kick-up rudder. I put a thin layer of reinforcing fiberglass around
the pivot bolt area because there was evidence of prior water damage and
surface deterioration of the wood. I sealed it with four layers of West
System epoxy for a moisture barrier and 6 or 7 coats of Armada Finish for a UV
barrier. I replaced the old, weathered tiller with a brand new laminated one.
I put thick aluminum guiding/reinforcing plates on both sides of the rudder at
the pivot hinge joint. I felt I needed that to handle anything SF Bay could
throw at me -- with monster winds and currents if you go to the less protected
parts of the Bay. Maybe it's "overkill", but it's my boat and I can do it if
it makes me happy.
For an even greater security blanket, I intend to make a spare one piece
emergency rudder out of 1" plywood and put a fiberglass laminate skin around
it. I'll buy an extra set of guedgeons for it and mount them on the blade. I
have a spare tiller on board already (a one inch pipe would do if you want a
cheap option). I plan on carrying a complete, assembeld spare rudder/tiller
on my boat. (If I can just get it to fit somewhere on the P-19....)
>Sooner or later these will break because the plys are weakened
> because of water leaking into them. With the P-14's/15's you are limited to
> ½ inch plywood because of the width of the fittings that go around the
rudder
> head and that fit into the gudgeons--you can't even use 5/8 or 3/4 inch
> plywood to make it stronger. You COULD ust thicker plywood and rout a
groove
> for the fitting, I guess...
I really ought to look at some P14/15 rudders before I make suggestions, but
as long as you guys will forgive me if I am talking absolute trash here goes
<reckless grin>:
Ouch! Routing grooves in plywood? Sorry Tom, as much as I like your bushing
idea, I think this one just doesn't float. (but I'll bet you knew that)
Talk about water penetrating the laminated layers of wood......
Isn't there some way you can use wider gudgeon fittings and matching pintles
on a P14/15? Then you can a) get a thicker piece of solid mahagany for the
rudder blade, and shape it to a nice foil (which I haven't a clue how to do
but I have friends who do) or b) use the plywood rudder as a plug and put 1/8"
of glass laminate all around it. (I could probably do a decent job on that
option.)
If your rudder has seen better days, why not replace it with something better
than the original????
>
> Anyway, this is a real live design/materials problem that all Potter owners
> have, and as you said, the blessed thing is going to break at exactly the
> worst possible moment. It would be nice to a) have everyone aware of the
> problem and b) have a fix ready.
On a gentle lake, the worst possible moment for something to break is probably
when youre headed back to the marina to get more cold beer <grin>. On an
angry ocean.... well that's another story.
<Warning -- self-impressed opinion coming. You guys are flattering me too
much lately. First all those cyber marriage proposals and now somebody even
asks for my opinion.I!! <grin>>
Okay, I'll get serious here. But it's just a reasoned opinion. Remember, I
don't know diddly about rudders on the little Potters.
In my opinion, marine grade plywood has no place below the waterline unless
it's got a thick skin of glass laminate over it. Heck, to my "purist" way of
thinking, plywood is just marginally acceptable for cabin doors (and only if
you maintain it faithfully). The idea of a 10 year old, unglassed, imperfectly
maintained, 1/2 inch plywood rudder *ON THE OCEAN* makes me really nervous.
However, it's probably not a big deal on lakes or well-protected bays.
If you put several layers of glass over the blade and used larger gudgeon and
pintle fittings, I think that would be okay. In essence, you'd be glassing
over a plywood plug, using the plug as a shape for your foil. Or you could
make a nice foil shaped blade out of solid mahagany. Rudder gudgeons and
transom pintles can be purchased in several widths and strengths. If you'd
like, I can look some up in my catalogs and get prices and working loads for
you.
Anybody who has read my previous posts knows where I'm coming from. My repair
and design solutions tend to be a bit over-engineered. I love sailing, but
the sea and wind occassionally scare the %^&* out of me. me. I like to think
that I'm a relatively brave person, but part of me wants *every* bit of
insurance I can have. Over-engineered stuff gives me a warm fuzzy feeling.
As always, your mileage may vary.
Judy B.
Judith Blumhorst, DC
HMS18/P19 Sail Captain, Potter's Yachters
WWP-19 #266 "Red Wing"
SF Bay, CA
>
> Regards
>
> Tom Grimes
> P-14 #363 Far Horizon
> Muncie, Indiana
>