So replacing wood with new plywood means I can cut out a shape of any size
and replace it with a close to equal piece of plywood correct? Just glass
the old plywood to the new plywood, right? No concern over how big a piece
of plywood is, etc? I could use two pieces of plywood for one hole? etc


It appears I've got more rot than I had expected (although the transom feels
strong otherwise).

I've pulled out about a 1 foot x 1 foot section around the drain plug and am
evaluating whether there will be anymore to go too.. Have drilled a bunch of
holes in the lower inner part of the transom to see how far it spreads and
allow all the wood to dry up before my final decision



wrote in message
ups.com...
It's too late to do any more than slightly slow the problem by sealing
the exposed wooden surfaces of the drain hole.

If you like this boat and plan to keep it, you will want to cut the rot
out of the transom. Be sure to go a few inches beyond the point where
you "think" the rot ends when scarfing in the new piece. You should be
able to cut away part of the fiberglass on the outside of the transom
and spoon out the punky wood, cut a new piece of the best marine ply
you can find, and then glass up the exterior again.

This is a great chance to learn from the bad practice of the original
builder. Any hole drilled through a wooden member- transom, stringer,
etc for the purpose of draining water should have the edges sealed up
to prevent water from wicking into the surrounding area and promoting
rot. If it were my project, I would cut the drain hole large enough to
accept a drain plug with a bronze collar fitting. Seal the edges of the
hole with a layer of glass and resin, and then bond the bronze collar
into the sealed hole- perhaps using epoxy.

One rot gets a foothold, it is relentless. Transom rot on small boats
is fairly common, and as most are outboard powered it is double
trouble.

On Thu, 09 Jun 2005 19:17:13 -0400, Chris wrote:

[I have rearranged the order so that it flows chronologically]

wrote in message
ups.com...
It's too late to do any more than slightly slow the problem by sealing
the exposed wooden surfaces of the drain hole.

If you like this boat and plan to keep it, you will want to cut the rot
out of the transom. Be sure to go a few inches beyond the point where
you "think" the rot ends when scarfing in the new piece. You should be
able to cut away part of the fiberglass on the outside of the transom
and spoon out the punky wood, cut a new piece of the best marine ply
you can find, and then glass up the exterior again.

This is a great chance to learn from the bad practice of the original
builder. Any hole drilled through a wooden member- transom, stringer,
etc for the purpose of draining water should have the edges sealed up
to prevent water from wicking into the surrounding area and promoting
rot. If it were my project, I would cut the drain hole large enough to
accept a drain plug with a bronze collar fitting. Seal the edges of the
hole with a layer of glass and resin, and then bond the bronze collar
into the sealed hole- perhaps using epoxy.

One rot gets a foothold, it is relentless. Transom rot on small boats
is fairly common, and as most are outboard powered it is double
trouble.


So replacing wood with new plywood means I can cut out a shape of any
size and replace it with a close to equal piece of plywood correct?
Just glass the old plywood to the new plywood, right? No concern over
how big a piece of plywood is, etc? I could use two pieces of plywood
for one hole? etc


It appears I've got more rot than I had expected (although the transom
feels strong otherwise).

I've pulled out about a 1 foot x 1 foot section around the drain plug
and am evaluating whether there will be anymore to go too.. Have drilled
a bunch of holes in the lower inner part of the transom to see how far
it spreads and allow all the wood to dry up before my final decision




I didn't see the original thread. If it is a fiberglass boat with a
plywood core, then you are probably right. You can probably get away
with putting in a whole bunch of plywood more or less however you want,
But don't leave any voids, and take steps to ensure that the new plywood
is bonded to the adjacent old plywood. You may have to use some kind of
adhesive filler for this. Epoxy, with filler, for example.

On the other hand, if it is a plywood boat with a thin layer of
protective glass, or glass on only the outside, then you are probably
wrong. In that case you will probably need to scarf in the plywood very
carefully.

I'm not an expert, so take my advice with a grain of salt. But the whole
idea behind sandwich construction is that the core experiences mostly
compression loading, and the skin experiences mostly tension.

Of course, this means that you have to do a good job tapering the
fiberglass thickness where you meld old glass with new glass. I think I
have seen a 12:1 ratio recommended. That is, if the glass is 1/8" thick,
you would taper over 1-1/2".

--Mac

Yes it is a fiberglass boat, a 15.5' v type hull.

The wood from the drain plug and the first foot at the boot seems to be
rotten.. We'll see how much though, letting it dry out now.


"Mac" wrote in message
news
On Thu, 09 Jun 2005 19:17:13 -0400, Chris wrote:

[I have rearranged the order so that it flows chronologically]

wrote in message
ups.com...
It's too late to do any more than slightly slow the problem by sealing
the exposed wooden surfaces of the drain hole.

If you like this boat and plan to keep it, you will want to cut the rot
out of the transom. Be sure to go a few inches beyond the point where
you "think" the rot ends when scarfing in the new piece. You should be
able to cut away part of the fiberglass on the outside of the transom
and spoon out the punky wood, cut a new piece of the best marine ply
you can find, and then glass up the exterior again.

This is a great chance to learn from the bad practice of the original
builder. Any hole drilled through a wooden member- transom, stringer,
etc for the purpose of draining water should have the edges sealed up
to prevent water from wicking into the surrounding area and promoting
rot. If it were my project, I would cut the drain hole large enough to
accept a drain plug with a bronze collar fitting. Seal the edges of the
hole with a layer of glass and resin, and then bond the bronze collar
into the sealed hole- perhaps using epoxy.

One rot gets a foothold, it is relentless. Transom rot on small boats
is fairly common, and as most are outboard powered it is double
trouble.


So replacing wood with new plywood means I can cut out a shape of any
size and replace it with a close to equal piece of plywood correct?
Just glass the old plywood to the new plywood, right? No concern over
how big a piece of plywood is, etc? I could use two pieces of plywood
for one hole? etc


It appears I've got more rot than I had expected (although the transom
feels strong otherwise).

I've pulled out about a 1 foot x 1 foot section around the drain plug
and am evaluating whether there will be anymore to go too.. Have drilled
a bunch of holes in the lower inner part of the transom to see how far
it spreads and allow all the wood to dry up before my final decision




I didn't see the original thread. If it is a fiberglass boat with a
plywood core, then you are probably right. You can probably get away
with putting in a whole bunch of plywood more or less however you want,
But don't leave any voids, and take steps to ensure that the new plywood
is bonded to the adjacent old plywood. You may have to use some kind of
adhesive filler for this. Epoxy, with filler, for example.

On the other hand, if it is a plywood boat with a thin layer of
protective glass, or glass on only the outside, then you are probably
wrong. In that case you will probably need to scarf in the plywood very
carefully.

I'm not an expert, so take my advice with a grain of salt. But the whole
idea behind sandwich construction is that the core experiences mostly
compression loading, and the skin experiences mostly tension.

Of course, this means that you have to do a good job tapering the
fiberglass thickness where you meld old glass with new glass. I think I
have seen a 12:1 ratio recommended. That is, if the glass is 1/8" thick,
you would taper over 1-1/2".

--Mac

One piece is much better. Those joints in the wood have little strength.

"Chris" wrote in message
...
So replacing wood with new plywood means I can cut out a shape of any size
and replace it with a close to equal piece of plywood correct? Just glass
the old plywood to the new plywood, right? No concern over how big a
piece of plywood is, etc? I could use two pieces of plywood for one hole?
etc


It appears I've got more rot than I had expected (although the transom
feels strong otherwise).

I've pulled out about a 1 foot x 1 foot section around the drain plug and
am evaluating whether there will be anymore to go too.. Have drilled a
bunch of holes in the lower inner part of the transom to see how far it
spreads and allow all the wood to dry up before my final decision



wrote in message
ups.com...
It's too late to do any more than slightly slow the problem by sealing
the exposed wooden surfaces of the drain hole.

If you like this boat and plan to keep it, you will want to cut the rot
out of the transom. Be sure to go a few inches beyond the point where
you "think" the rot ends when scarfing in the new piece. You should be
able to cut away part of the fiberglass on the outside of the transom
and spoon out the punky wood, cut a new piece of the best marine ply
you can find, and then glass up the exterior again.

This is a great chance to learn from the bad practice of the original
builder. Any hole drilled through a wooden member- transom, stringer,
etc for the purpose of draining water should have the edges sealed up
to prevent water from wicking into the surrounding area and promoting
rot. If it were my project, I would cut the drain hole large enough to
accept a drain plug with a bronze collar fitting. Seal the edges of the
hole with a layer of glass and resin, and then bond the bronze collar
into the sealed hole- perhaps using epoxy.

One rot gets a foothold, it is relentless. Transom rot on small boats
is fairly common, and as most are outboard powered it is double
trouble.

I was also thinking that once I put some wood in there (however much is
required), then I may put a long piece of 2x4, or 4x4 that goes the width of
the boat. This piece could be glassed to the inner back, and the floor at
the back. If that doesn't add strength then I don't know what will.

Again, right now, the top part when the motor mounts is solid, and it
appears that the rotted area is about the lower foot...


"Bill McKee" wrote in message
ink.net...
One piece is much better. Those joints in the wood have little strength.

"Chris" wrote in message
...
So replacing wood with new plywood means I can cut out a shape of any
size and replace it with a close to equal piece of plywood correct? Just
glass the old plywood to the new plywood, right? No concern over how big
a piece of plywood is, etc? I could use two pieces of plywood for one
hole? etc


It appears I've got more rot than I had expected (although the transom
feels strong otherwise).

I've pulled out about a 1 foot x 1 foot section around the drain plug and
am evaluating whether there will be anymore to go too.. Have drilled a
bunch of holes in the lower inner part of the transom to see how far it
spreads and allow all the wood to dry up before my final decision



wrote in message
ups.com...
It's too late to do any more than slightly slow the problem by sealing
the exposed wooden surfaces of the drain hole.

If you like this boat and plan to keep it, you will want to cut the rot
out of the transom. Be sure to go a few inches beyond the point where
you "think" the rot ends when scarfing in the new piece. You should be
able to cut away part of the fiberglass on the outside of the transom
and spoon out the punky wood, cut a new piece of the best marine ply
you can find, and then glass up the exterior again.

This is a great chance to learn from the bad practice of the original
builder. Any hole drilled through a wooden member- transom, stringer,
etc for the purpose of draining water should have the edges sealed up
to prevent water from wicking into the surrounding area and promoting
rot. If it were my project, I would cut the drain hole large enough to
accept a drain plug with a bronze collar fitting. Seal the edges of the
hole with a layer of glass and resin, and then bond the bronze collar
into the sealed hole- perhaps using epoxy.

One rot gets a foothold, it is relentless. Transom rot on small boats
is fairly common, and as most are outboard powered it is double
trouble.

On Fri, 10 Jun 2005 04:23:57 +0000, Bill McKee wrote:

One piece is much better. Those joints in the wood have little strength.


I don't think the joints in the core NEED much strength. I mean, you can
use Styrofoam as a core, and that can be broken easily by hand. Also,
balsa core is not very strong laterally, but it is an excellent core
material (unless it gets wet).

With cores, the important thing is that it adhere well to the skin, and
that it have good compression strength. Butted plywood with, say, epoxy
filler at the joint, should make a good core.

But then I am not a mechanical or structural engineer or naval architect,
so take my opinion for what it is worth.

--Mac


"Chris" wrote in message
...
So replacing wood with new plywood means I can cut out a shape of any size
and replace it with a close to equal piece of plywood correct? Just glass
the old plywood to the new plywood, right? No concern over how big a
piece of plywood is, etc? I could use two pieces of plywood for one hole?
etc


It appears I've got more rot than I had expected (although the transom
feels strong otherwise).

I've pulled out about a 1 foot x 1 foot section around the drain plug and
am evaluating whether there will be anymore to go too.. Have drilled a
bunch of holes in the lower inner part of the transom to see how far it
spreads and allow all the wood to dry up before my final decision



wrote in message
ups.com...
It's too late to do any more than slightly slow the problem by sealing
the exposed wooden surfaces of the drain hole.

If you like this boat and plan to keep it, you will want to cut the rot
out of the transom. Be sure to go a few inches beyond the point where
you "think" the rot ends when scarfing in the new piece. You should be
able to cut away part of the fiberglass on the outside of the transom
and spoon out the punky wood, cut a new piece of the best marine ply
you can find, and then glass up the exterior again.

This is a great chance to learn from the bad practice of the original
builder. Any hole drilled through a wooden member- transom, stringer,
etc for the purpose of draining water should have the edges sealed up
to prevent water from wicking into the surrounding area and promoting
rot. If it were my project, I would cut the drain hole large enough to
accept a drain plug with a bronze collar fitting. Seal the edges of the
hole with a layer of glass and resin, and then bond the bronze collar
into the sealed hole- perhaps using epoxy.

One rot gets a foothold, it is relentless. Transom rot on small boats
is fairly common, and as most are outboard powered it is double
trouble.

Mac wrote:
I don't think the joints in the core NEED much strength. I mean, you can
use Styrofoam as a core, and that can be broken easily by hand. Also,
balsa core is not very strong laterally, but it is an excellent core
material (unless it gets wet).

You can use Styrofoam but you shouldn't.

With cores, the important thing is that it adhere well to the skin, and
that it have good compression strength. Butted plywood with, say, epoxy
filler at the joint, should make a good core.

With cores, the most important property is the shear
strength. Obviously if it doesn't stick to the skins it
isn't core... Transoms should have a higher compressive
strength - balsa is good, plywood is o.k., high density foam
(= 120 kg/m3 is ideal)

But then I am not a mechanical or structural engineer or naval architect,
so take my opinion for what it is worth.

--Mac

I am a m.eng. and naval architect

Evan Gatehouse

On Sat, 11 Jun 2005 21:10:47 -0700, Evan Gatehouse wrote:

Mac wrote:
I don't think the joints in the core NEED much strength. I mean, you can
use Styrofoam as a core, and that can be broken easily by hand. Also,
balsa core is not very strong laterally, but it is an excellent core
material (unless it gets wet).

You can use Styrofoam but you shouldn't.

With cores, the important thing is that it adhere well to the skin, and
that it have good compression strength. Butted plywood with, say, epoxy
filler at the joint, should make a good core.

With cores, the most important property is the shear
strength. Obviously if it doesn't stick to the skins it
isn't core... Transoms should have a higher compressive
strength - balsa is good, plywood is o.k., high density foam
(= 120 kg/m3 is ideal)

As long as it is not polystyrene? ;-)

But then I am not a mechanical or structural engineer or naval architect,
so take my opinion for what it is worth.

--Mac

I am a m.eng. and naval architect

Evan Gatehouse

Thanks for chiming in! It's always nice to have people who actually know
what they are talking about.

So, to come back to the OP's question, if a transom is originally
constructed with fiberglass skins and a plywood core, and some of the
plywood is rotten, would it be OK to replace the rotten parts with several
pieces of plywood butted together? Or would it be better to scarf in one
piece of plywood to replace the rotten area?

I guess another way of asking the question is, would butt joints in the
plywood core significantly weaken the transom?

I am thinking that they would not weaken the transom.

--Mac

Thanks for chiming in! It's always nice to have people who actually know
what they are talking about.

So, to come back to the OP's question, if a transom is originally
constructed with fiberglass skins and a plywood core, and some of the
plywood is rotten, would it be OK to replace the rotten parts with several
pieces of plywood butted together? Or would it be better to scarf in one
piece of plywood to replace the rotten area?

I guess another way of asking the question is, would butt joints in the
plywood core significantly weaken the transom?

I am thinking that they would not weaken the transom.

--Mac

If they are relying on the core for stiffness and strength,
then butt joints would be weaker. I wouldn't do it on my
boat for example.

I would cut off the outer skin near the transom corners,
chisel and then grind out all the plywood and rebuild the
transom

Evan Gatehouse

If the transom is suspect, check out http://www.transomrepair.com, they
have a whole system for removing all of the wood in the transom and then
filling the space with a pourable resin/chopped filler system. I was going
to use this in my 21' Mako (the Mako factory approved), but sold the boat
before it needed the work (just had a few rotten spots, but the majority of
the transom has still been strong).

Cheers,

--
Steve (remove anti spam XYX in return address for correct email)
http://www.gulf-stream.net/patandsteve