My Potter 15 rudder is made of 4 pieces. The top is a solid core about
10"x15", with two pieces of plywood screwed to it on either side measuring
10"x30". The solid blade mounts between the plywood, below the solid top.

One side of the plywood is falling apart, and the other side isn't doing
much better. I went to the lumber yard today to buy some plywood to replace
the bad parts. They have Marine Fir and Marine Okoume. They told me that
neither will be durable; they have to be covered with fiberglass. If that
is true, it certainly explains why the original is falling apart, as it is
not covered in fiberglass.

I bought a piece of fir, which I will cover with spar varnish just to get me
through the end of the year. This winter I will rebuild the whole thing.
(neither the top core nor the rudder blade are looking real good either).

What is the story on plywood? Is nothing suitable for marine use without
being fiberglassed? Would solid wood (3/8") substitute? Any advice on how
I go about doing this so it is durable would be appreciated.

What is the story on plywood? Is nothing suitable for marine use without
being fiberglassed? Would solid wood (3/8") substitute? Any advice on
how I go about doing this so it is durable would be appreciated.
Thinking about it, how about making the top core and one side out of one
piece of solid wood, and then using a second piece of solid wood for the
second side? I could partially resaw the core/side to remove most of the
wood (where the rudder blade goes), and rout out the balance. That way it
would all expand evenly, since it is all the same wood oriented the same,
without any pesky plywood.
Would it be strong enough?

Toller wrote:
My Potter 15 rudder is made of 4 pieces. The top is a solid core about
10"x15", with two pieces of plywood screwed to it on either side measuring
10"x30". The solid blade mounts between the plywood, below the solid top.

One side of the plywood is falling apart, and the other side isn't doing
much better. I went to the lumber yard today to buy some plywood to replace
the bad parts. They have Marine Fir and Marine Okoume. They told me that
neither will be durable; they have to be covered with fiberglass. If that
is true, it certainly explains why the original is falling apart, as it is
not covered in fiberglass.

I bought a piece of fir, which I will cover with spar varnish just to get me
through the end of the year. This winter I will rebuild the whole thing.
(neither the top core nor the rudder blade are looking real good either).

What is the story on plywood? Is nothing suitable for marine use without
being fiberglassed? Would solid wood (3/8") substitute? Any advice on how
I go about doing this so it is durable would be appreciated.

Thinking about it, how about making the top core and one side out of one
piece of solid wood, and then using a second piece of solid wood for the
second side? I could partially resaw the core/side to remove most of the
wood (where the rudder blade goes), and rout out the balance. That way it
would all expand evenly, since it is all the same wood oriented the same,
without any pesky plywood.
Would it be strong enough?

Toller,
One should very much wonder about the individual that told you that
marine fir would not be durable enough.
The difference between the marine PW and others is 2-fold.
1- PW graded as marine has no voids in the core.
2- The bonding adhesive has very low water permeability (it used to be
better than exterior, but common exterior now usually uses the same process.

Time was all small boats that were not clinker plank (even some that
were) were made from marine plywood, and some are still out there.
I have made rudders and centerboards from marine PW.

Fiberglassing PW will just assure that it never has a chance to dry out
(Oh- sure it is completely encapsulated - with ZERO porosity or
permeability - Right - )

You can make PW cheek pieces and replace those on the rudder. What you
make them from is not of much consequence in actual fact.

The plan you outline in that last paragraph sounds like a whole lot of
work.

Matt Colie
Lifelong Waterman, Licensed Mariner, Congenital Sailor
and Third Generation Boatbuilder

Or, you could simply buy a replacement from West Wight...

http://www.westwightpotter.com/

...maybe even upgrade to their 'Kick Up Beaching Rudder'?

The issue with Douglas Fir plywood - marine or otherwise - is that is
'checks' - or cracks along the outer ply layer. Water can ingress
along these cracks, and the rot process begins.

The solution is to cover the plywood with fiberglass (stops the
checking) and epoxy resin (stops the water). The application of these
materials should be considered carefully, meaning that additional
research into 'fiberglass and epoxy plywood encapsulation' should be
undertaken before starting.

Note that any screw / bolt holes in or through the rudder / tiller are
an area of concern.

Common practice (for bolts) is to drill an oversize hole, fill with a
thickened epoxy slurry, allow to cure, then re-drill with the
appropriate sized hole. In this way, water never gets to the wood.
For screws, much the same except allow the crew to penetrate the wood
for about 1/2 its length, i.e. 'drill oversize' for 1/2 the length of
the screw.

Anyway... good luck!

MW

A few thoughts:
Ply, since it is laminated, is much more resistant to warping than solid
wood. It's also able to take impact and strain without splitting as solid
wood might. Provided you can keep the water out, it's a very stable
material.
Ply is, pound for pound, really strong. Good marine ply is void-free and
uses waterproof glues. I build stitch and glue kayaks, where the 4mm (3/16")
ply is encapsulated in epoxy resin - about 4 coats on each side. Our 'yaks
take a pounding on our rocky beaches, and I've yet to damage the ply itself.
Provided you epoxy seal both the inside and outside surfaces with multiple
coats of resin, or even fiberglass cloth soaked out with epoxy, making sure
you seal the end grain really well, there's no reason the ply won't outlast
any solid wood, and possibly you
:-))
Make sure you use epoxy, and not polyester resin - the poly doesn't stick to
things or hold them together
nearly as well.
BTW - that Potter is one sweet little craft - used to admire them greatly in
our sailing days, before we downsized and simplified things to kayaks and
canoes.

"Toller" wrote in message
...
My Potter 15 rudder is made of 4 pieces. The top is a solid core about
10"x15", with two pieces of plywood screwed to it on either side measuring
10"x30". The solid blade mounts between the plywood, below the solid top.

One side of the plywood is falling apart, and the other side isn't doing
much better. I went to the lumber yard today to buy some plywood to
replace the bad parts. They have Marine Fir and Marine Okoume. They told
me that neither will be durable; they have to be covered with fiberglass.
If that is true, it certainly explains why the original is falling apart,
as it is not covered in fiberglass.

I bought a piece of fir, which I will cover with spar varnish just to get
me through the end of the year. This winter I will rebuild the whole
thing. (neither the top core nor the rudder blade are looking real good
either).

What is the story on plywood? Is nothing suitable for marine use without
being fiberglassed? Would solid wood (3/8") substitute? Any advice on
how I go about doing this so it is durable would be appreciated.

On Sep 10, 12:00 pm, "Toller" wrote:
My Potter 15 rudder is made of 4 pieces. The top is a solid core about
10"x15", with two pieces of plywood screwed to it on either side measuring
10"x30". The solid blade mounts between the plywood, below the solid top.

Those side pieces are called the rudder cheeks. I've replaced mine on
a 21 foot mahogony strip saiboat. They get a lot of stress when
running before the wind with waves comming under the transom and
trying to change your course on you. I just used ordinary fir plywood
without any voids in it. It should be thick and stong. The thickness
might be determined by the hardware used to hang the rudder off the
transom (pintles and gudgeons) although you can rout the plywood to
accept narrow hardware.


One side of the plywood is falling apart, and the other side isn't doing
much better. I went to the lumber yard today to buy some plywood to replace
the bad parts. They have Marine Fir and Marine Okoume. They told me that
neither will be durable; they have to be covered with fiberglass. If that
is true, it certainly explains why the original is falling apart, as it is
not covered in fiberglass.

I bought a piece of fir, which I will cover with spar varnish just to get me
through the end of the year. This winter I will rebuild the whole thing.
(neither the top core nor the rudder blade are looking real good either).

What is the story on plywood? Is nothing suitable for marine use without
being fiberglassed? Would solid wood (3/8") substitute? Any advice on how
I go about doing this so it is durable would be appreciated.

"Wm Watt" wrote in message
oups.com...
On Sep 10, 12:00 pm, "Toller" wrote:
My Potter 15 rudder is made of 4 pieces. The top is a solid core about
10"x15", with two pieces of plywood screwed to it on either side
measuring
10"x30". The solid blade mounts between the plywood, below the solid
top.

Those side pieces are called the rudder cheeks. I've replaced mine on
a 21 foot mahogony strip saiboat. They get a lot of stress when
running before the wind with waves comming under the transom and
trying to change your course on you. I just used ordinary fir plywood
without any voids in it. It should be thick and stong. The thickness
might be determined by the hardware used to hang the rudder off the
transom (pintles and gudgeons) although you can rout the plywood to
accept narrow hardware.

Rudder Cheeks eh? What is the piece between the cheeks called?
Mine are 3/8" ply, routed down to 3/16" at the hardware.

What did you put on them to waterproof them?

On Sep 12, 1:17 pm, "Toller" wrote:

Rudder Cheeks eh? What is the piece between the cheeks called?
Mine are 3/8" ply, routed down to 3/16" at the hardware.

What did you put on them to waterproof them?-

Paint. For the edges anything you have handy will do. They are not
going to be under water. If I were doing it today I'd spread polyester
resin along the edges where it can soak in to keep moisture from
penetrating. Epoxy, polyurethane varnish, or even linseed oil if
that's what you have at hand.

I'd also smear polyester resin on any places which would chafe, for
example if the tiller is inserted between the cheeks (I don't know
what that's called), or the rudder rotates between the cheeks ("kick
up" rudder) . Polyester is good for abraision resistance. I use it on
my home built boats where parts might rub. I coated the inside of a
dagger board trunk with it. Just the resin, no fibreglass
reinforcement. Or epoxy if that's what you have.

"Wm Watt" wrote in message
oups.com...
On Sep 12, 1:17 pm, "Toller" wrote:

Rudder Cheeks eh? What is the piece between the cheeks called?
Mine are 3/8" ply, routed down to 3/16" at the hardware.

What did you put on them to waterproof them?-

Paint. For the edges anything you have handy will do. They are not
going to be under water. If I were doing it today I'd spread polyester
resin along the edges where it can soak in to keep moisture from
penetrating. Epoxy, polyurethane varnish, or even linseed oil if
that's what you have at hand.

I'd also smear polyester resin on any places which would chafe, for
example if the tiller is inserted between the cheeks (I don't know
what that's called), or the rudder rotates between the cheeks ("kick
up" rudder) . Polyester is good for abraision resistance. I use it on
my home built boats where parts might rub. I coated the inside of a
dagger board trunk with it. Just the resin, no fibreglass
reinforcement. Or epoxy if that's what you have.

I have epoxy (and linseed oil and polyurethane varnish) but hesitate to use
it since it is not UV stable.
I have never used polyester, but have heard it doesn't adhear worth a damn.
That is not your experience I take it?

Toller wrote:

I have never used polyester, but have heard it doesn't adhear worth
a damn. That is not your experience I take it?

A lot of things - including the 40' ply and fiberglass Newporter
ketch - were made with polyester resin. Does it stick as well as
epoxy? No. But it isn't exactly easy to get off either.

When I had a sizeable sailboat I used it (with fiberglass) on anything
I made of ply - trunk cabin deck, dog house, hatchs, etc. - and never
had any adhesion problem in the 20 years I owned the boat.

Consider the number of cars that have had dings filled with Bondo.
Bondo is polyester resin and talc. Have you seen many chunks of Bondo
along the roadside?


--

dadiOH
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