Dear Group,
I am interested in some feedback on pontoon construction. I have
looked at several designs for wood pontoons with fiberglass over them.
I would not be building something huge, perhaps about 18 feet max. Has
anyone had experience building a pontoon? I have built wood/fiberglass
construction before, but never a pontoon. Ideas on floatation foam and
bulkheads? Proper support for deck attachment? Etc. Thanks a ton for
any feedback.


M Russon

If you plan on using pressure treated plywood or lumber, there is some
concern that neither polyester or epoxy resins will stick for very long
to the new preservatives they now use. Also the new formulations are
very corrosive to metal so all fastenings and fasteners would have to
be compatible. If epoxy won't stick to the stuff, I would also wonder
about any glues and adhesives. Sam

On 26 Aug 2005 18:17:51 -0700, "Sam" wrote:

If you plan on using pressure treated plywood or lumber, there is some
concern that neither polyester or epoxy resins will stick for very long
to the new preservatives they now use. Also the new formulations are
very corrosive to metal so all fastenings and fasteners would have to
be compatible. If epoxy won't stick to the stuff, I would also wonder
about any glues and adhesives. Sam

Sam,
Thanks for the reply. I was going to use a non pressure treated
plywood, most likely a marine grade ply on the deck and an exterior
grade on the actual pontoons prior to fiberglass. I am a bit gun shy
of the pressure treated wood since i believe they still use arsenic as
a chemical in that stuff. Any other suggestions for the actual
pontoons?

MRusson

Just be careful when creating "hard points" that you spread the load
smoothly out to the skins. Any abrupt change in loading such as occurs at
the edge of a metal backing plate will lead to failure in that area.

Prime areas for concern include deck attachment points and bulkhead to skin
joins.

Big epoxy fillets are good; as are stacked backing plates of decreasing size
with the largest and limpest next to the skin.

Roger

http://home.earthlink.net/~derbyrm

"M Russon" wrote in message
...
Dear Group,
I am interested in some feedback on pontoon construction. I have
looked at several designs for wood pontoons with fiberglass over them.
I would not be building something huge, perhaps about 18 feet max. Has
anyone had experience building a pontoon? I have built wood/fiberglass
construction before, but never a pontoon. Ideas on floatation foam and
bulkheads? Proper support for deck attachment? Etc. Thanks a ton for
any feedback.


M Russon

MRusson wrote:
I was going to use a non pressure treated
plywood, most likely a marine grade ply on the deck and an exterior
grade on the actual pontoons prior to fiberglass. I am a bit gun shy
of the pressure treated wood since i believe they still use arsenic as
a chemical in that stuff. Any other suggestions for the actual
pontoons?

MRusson
I would divide the pontoons into watertight sections for emergency
flotation and skip the foam which would only add redundacy, price,
weight and a good starting point for rot. I would also make each
watertight section inspectable with a hatch or seal big enough to make
the inside accesable for repairs, etc. The hatches wouldn't have to be
store bought but could be made of plywood that was secured in place
with screws and sealed with a non-permanent caulking, say silicone or
White Lightning house caulk as opposed to 5200, as you wouldn't have to
open them but once a year, more or less. The bottom corners (chines?)
of the pontoons will have to be slightly rounded for the fiberglass to
wrap around without creating air pockets and they should also be
reinforced with extra layers of glass or something like angle iron
imbedded in caulking as they will recieve more wear than elsewhere. Try
to avoid, by proper design, water sitting on top of the pontoons for
long periods of time. The weak point of pontoons and catamarans is the
system/deck that connects them and the tendency for them to twist in
waves and wrack/wreck the boat. Some people replace rotted decks, and
you might consider building a new deck, with pressure treated plywood
topped with rubber roll roofing for flat roofs that comes in wide
enough sizes for one piece to cover the whole deck. It is glued down
with contact cement or some similer adhesive and then indoor outdoor
carpeting is glued to the rubber for a leakproof deck. Sam

On 27 Aug 2005 10:35:05 -0700, "Sam" wrote:



MRusson
I would divide the pontoons into watertight sections for emergency
flotation and skip the foam which would only add redundacy, price,
weight and a good starting point for rot.

This makes good sense since i was thinking the same thing. I like the
idea of skipping foam. Every old boat i have seen had rot developing
around the foam locations.


I would also make each
watertight section inspectable with a hatch or seal big enough to make
the inside accesable for repairs, etc. The hatches wouldn't have to be
store bought but could be made of plywood that was secured in place
with screws and sealed with a non-permanent caulking, say silicone or
White Lightning house caulk as opposed to 5200, as you wouldn't have to
open them but once a year, more or less.

I like this idea since it would provide a repair point for each
section in the event water somehow got into the pontoon section. Would
it be wise to also glass the interior seams for greater strength and a
better resistance to rot? This way if water got into the section, it
would puddle in a glassed section rather than bare wood.

The bottom corners (chines?)
of the pontoons will have to be slightly rounded for the fiberglass to
wrap around without creating air pockets and they should also be
reinforced with extra layers of glass or something like angle iron
imbedded in caulking as they will recieve more wear than elsewhere.

I would think a heavy roving layered in a bi-directional fashion over
a rounded edge could provide a stable corner. I could hold back the
plywood from butting into the other side and leave a gap at the
corner, and perhaps inset a radius tube or pipe etc.

Try
to avoid, by proper design, water sitting on top of the pontoons for
long periods of time.

A slight convex angle to the pontoon top perhaps?

The weak point of pontoons and catamarans is the
system/deck that connects them and the tendency for them to twist in
waves and wrack/wreck the boat.

Would these "hard points" at which the deck attaches to the pontoons
be better if they actually flex around a bit during use? Perhaps a
rubber mount of some sort? I wonder if a set of heavy lag bolts
secured and epoxied into the pontoon top, and sealed, could be
modified to act as a pin rather than a bolt. The deck could sit on top
of the pontoons and be pinned into place with rubber cushions under
the deck to provide flex and movement. ??????


Some people replace rotted decks, and
you might consider building a new deck, with pressure treated plywood
topped with rubber roll roofing

EPDM roof liner perhaps?

for flat roofs that comes in wide
enough sizes for one piece to cover the whole deck. It is glued down
with contact cement or some similer adhesive and then indoor outdoor
carpeting is glued to the rubber for a leakproof deck. Sam

Sam, GREAT info...........)

M Russon

On Sat, 27 Aug 2005 13:02:55 GMT, "Roger Derby"
wrote:

Just be careful when creating "hard points" that you spread the load
smoothly out to the skins. Any abrupt change in loading such as occurs at
the edge of a metal backing plate will lead to failure in that area.

Prime areas for concern include deck attachment points and bulkhead to skin
joins.

Would these need to be a fixed hard point on the pontoon top? Could
these be made flexible somehow? Rubber mount points with steel pins
perhaps? I can see the pontoon top flexing and cracking with a small
hard point with a sub-standard backing plate. Could bulkheads in the
pontoons be inceased in size or more placed in the pontoon to help
overcome the flexing? I would like to attach the deck directly to
hardpoints at the bulkheads of each pontoon. The idea was to have a
bulkhead in the pontoon at every other deck mount point. If the deck
is 18 feet long, i could space the bulkheads at 24" apart inside each
pontoon. I could space the deck supports at 12" on center and bolt
through every other one to the pontoon tops. I think that 24" on
center at the deck supports is too far apart and would make for a
spongy deck.


Big epoxy fillets are good; as are stacked backing plates of decreasing size
with the largest and limpest next to the skin.

The larger the better?


Thanks Roger.....

M Russon

Flexible mounts is a whole different subject. The point I was making has to
do with transferring the load to the skin. It needs to be a smooth
transition. Otherwise the skin flexes at the "step" and eventually breaks.
Note that a flexible joint doesn't really cure this since I'm talking about
the stresses at the perimeter of the backing plate. Eventually the joint
will reach its limit and ask the skin to pick up the load. I believe you
can see this in the crazing of the fiberglass hulls around the chain plates
and winch mounts on some of the less well designed production boats.

Bulkheads are good. They transfer the load to the skin around the whole
perimeter of the pontoon rather than just to a spot on top, but do fillet
them generously to the skin around the whole perimeter. I'm sure there's a
practical limit (diminishing returns), but I don't know what it is. My gut
feel is that a 2" radius would be good. (??????) Maybe with a 6" belt of
epoxy/fiberglass applied to the inside first.

As for having the pontoons move independently of the deck (and of each
other), it sounds good, but I'd look for someone with first hand experience.
Could you get the same effect by having a flexible deck? What kind of sea
states are you expecting to handle?

Roger

http://home.earthlink.net/~derbyrm

"MRusson" wrote in message
...
On Sat, 27 Aug 2005 13:02:55 GMT, "Roger Derby"
wrote:

Just be careful when creating "hard points" that you spread the load
smoothly out to the skins. Any abrupt change in loading such as occurs at
the edge of a metal backing plate will lead to failure in that area.

Prime areas for concern include deck attachment points and bulkhead to
skin
joins.

Would these need to be a fixed hard point on the pontoon top? Could
these be made flexible somehow? Rubber mount points with steel pins
perhaps? I can see the pontoon top flexing and cracking with a small
hard point with a sub-standard backing plate. Could bulkheads in the
pontoons be inceased in size or more placed in the pontoon to help
overcome the flexing? I would like to attach the deck directly to
hardpoints at the bulkheads of each pontoon. The idea was to have a
bulkhead in the pontoon at every other deck mount point. If the deck
is 18 feet long, i could space the bulkheads at 24" apart inside each
pontoon. I could space the deck supports at 12" on center and bolt
through every other one to the pontoon tops. I think that 24" on
center at the deck supports is too far apart and would make for a
spongy deck.


Big epoxy fillets are good; as are stacked backing plates of decreasing
size
with the largest and limpest next to the skin.

The larger the better?


Thanks Roger.....

M Russon

Roger,
Thanks for the reply. I would not be expecting particularly rough
water when using the pontoon boat. My biggest concern would be the
occasional bumps and potential rough water that would stress the
pontoon to the point of cracking any hard point on the pontoon. I have
been thinking about what you said concerning the flexible mount and
it's relation to proper backing of the hardpoints. It would seem the
best answer is to mount the deck securely at each bulkhead and fix it
solid to the pontoon. I could construct the deck to "twist" a bit as i
believe the factory built pontoons do. The pontoon would of course not
roll side to side, but the deck could move with the pontoon. Aluminum
has it's advantages for flexibility, but i believe it weakens and
cracks over time due to repeated twisting. Having the bulkheads act as
the anchor point, and distributing the hull and deck stresses across
all the bulkheads at the same time seems the best answer. The deck
would literally have to tear the bulkhead apart in order to separate
from the pontoon. This would still allow the pontoons to be separated
in individual compartments with inspection holes in the top, and allow
repair to be performed in the event of a crack somewhere. I believe
the worst stresses the boat can see sometimes come from the trailering
and hauling of the boat to the water and back. Now you have my brain
cranking along....)...

M Russon



On Sun, 28 Aug 2005 03:07:33 GMT, "Roger Derby"
wrote:

Flexible mounts is a whole different subject. The point I was making has to
do with transferring the load to the skin. It needs to be a smooth
transition. Otherwise the skin flexes at the "step" and eventually breaks.
Note that a flexible joint doesn't really cure this since I'm talking about
the stresses at the perimeter of the backing plate. Eventually the joint
will reach its limit and ask the skin to pick up the load. I believe you
can see this in the crazing of the fiberglass hulls around the chain plates
and winch mounts on some of the less well designed production boats.

Bulkheads are good. They transfer the load to the skin around the whole
perimeter of the pontoon rather than just to a spot on top, but do fillet
them generously to the skin around the whole perimeter. I'm sure there's a
practical limit (diminishing returns), but I don't know what it is. My gut
feel is that a 2" radius would be good. (??????) Maybe with a 6" belt of
epoxy/fiberglass applied to the inside first.

As for having the pontoons move independently of the deck (and of each
other), it sounds good, but I'd look for someone with first hand experience.
Could you get the same effect by having a flexible deck? What kind of sea
states are you expecting to handle?

Roger




http://home.earthlink.net/~derbyrm

"MRusson" wrote in message
.. .
On Sat, 27 Aug 2005 13:02:55 GMT, "Roger Derby"
wrote:

Just be careful when creating "hard points" that you spread the load
smoothly out to the skins. Any abrupt change in loading such as occurs at
the edge of a metal backing plate will lead to failure in that area.

Prime areas for concern include deck attachment points and bulkhead to
skin
joins.

Would these need to be a fixed hard point on the pontoon top? Could
these be made flexible somehow? Rubber mount points with steel pins
perhaps? I can see the pontoon top flexing and cracking with a small
hard point with a sub-standard backing plate. Could bulkheads in the
pontoons be inceased in size or more placed in the pontoon to help
overcome the flexing? I would like to attach the deck directly to
hardpoints at the bulkheads of each pontoon. The idea was to have a
bulkhead in the pontoon at every other deck mount point. If the deck
is 18 feet long, i could space the bulkheads at 24" apart inside each
pontoon. I could space the deck supports at 12" on center and bolt
through every other one to the pontoon tops. I think that 24" on
center at the deck supports is too far apart and would make for a
spongy deck.


Big epoxy fillets are good; as are stacked backing plates of decreasing
size
with the largest and limpest next to the skin.

The larger the better?


Thanks Roger.....

M Russon