I discovered that most of the balsa core mateiral in the deck of my
18-ft boat is either rotten or fully wet. I am in the process of
removing all the core material from the entire deck. Now I need to
figure which alternative core materials I should use for these two
different areas:
1. Deck area that don't have any weight-bearing hardware.
2. Deck area where the T-top is anchored on.

For the deck area that don't have any weight-bearing hardware, I am
thinking of getting something like Corecell or Divinycell that are made
from PVC and won't rot. I am thinking of getting them in plain sheets
instead of sheets that have been scored (cheaper and in the correct
thickness). But according to the supplies web site, plain sheet of
those materials cannot be contoured to curved shapes. I am wondering
whether I can at least bend the plain sheet just a little bit -- like
1" drop for every 30". Is the plain sheet so rigid that I cannot even
use a bag of fertilier to conform it to a slight curve on the deck when
I bed it with wet epoxy? The other question is whether epoxy will
adhere well with those synthetic core materials.

For deck area where the T-top is anchored on, I am thinking of using
either marine grade plywood encapsulated with epoxy or many layer of
fiberglasses and epoxy. Will marine grade plywood still rot? Which
material is better for this area anyway?

Thanks in advance for any suggestion.

Jay Chan

Sheet core-cell can easily be bent to the kind of curve you describe.
If it's obstinate, some kerfs cut on the table saw will do the trick. Apply
kerf-side up so they can fe filled later with light bog.
Bond the sheet down with epoxy-microspere slurry.
If the sequence of your construction will be to re-build the deck from the
bottom skin up, one way to provide higher-strength patches for the
attachment of loaded hardware would be to cut windows in the foam where you
want said patches to be, then after the foam's bonded down, fill the windows
with high-strength (like Cabosil) filler (Use slow hardener or they'll
exotherm badly. ), sand flush, apply the top skin and Bob's your uncle.
Just remember where the patches are.

. If it's
wrote in message
ps.com...
I discovered that most of the balsa core mateiral in the deck of my
18-ft boat is either rotten or fully wet. I am in the process of
removing all the core material from the entire deck. Now I need to
figure which alternative core materials I should use for these two
different areas:
1. Deck area that don't have any weight-bearing hardware.
2. Deck area where the T-top is anchored on.

For the deck area that don't have any weight-bearing hardware, I am
thinking of getting something like Corecell or Divinycell that are made
from PVC and won't rot. I am thinking of getting them in plain sheets
instead of sheets that have been scored (cheaper and in the correct
thickness). But according to the supplies web site, plain sheet of
those materials cannot be contoured to curved shapes. I am wondering
whether I can at least bend the plain sheet just a little bit -- like
1" drop for every 30". Is the plain sheet so rigid that I cannot even
use a bag of fertilier to conform it to a slight curve on the deck when
I bed it with wet epoxy? The other question is whether epoxy will
adhere well with those synthetic core materials.

For deck area where the T-top is anchored on, I am thinking of using
either marine grade plywood encapsulated with epoxy or many layer of
fiberglasses and epoxy. Will marine grade plywood still rot? Which
material is better for this area anyway?

Thanks in advance for any suggestion.

Jay Chan

wrote:
I discovered that most of the balsa core mateiral in the deck of my
18-ft boat is either rotten or fully wet. I am in the process of
removing all the core material from the entire deck. Now I need to
figure which alternative core materials I should use for these two
different areas:
1. Deck area that don't have any weight-bearing hardware.
2. Deck area where the T-top is anchored on.

For the deck area that don't have any weight-bearing hardware, I am
thinking of getting something like Corecell or Divinycell that are made
from PVC and won't rot. I am thinking of getting them in plain sheets
instead of sheets that have been scored (cheaper and in the correct
thickness). But according to the supplies web site, plain sheet of
those materials cannot be contoured to curved shapes. I am wondering
whether I can at least bend the plain sheet just a little bit -- like
1" drop for every 30". Is the plain sheet so rigid that I cannot even
use a bag of fertilier to conform it to a slight curve on the deck when
I bed it with wet epoxy? The other question is whether epoxy will
adhere well with those synthetic core materials.

For deck area where the T-top is anchored on, I am thinking of using
either marine grade plywood encapsulated with epoxy or many layer of
fiberglasses and epoxy. Will marine grade plywood still rot? Which
material is better for this area anyway?

Thanks in advance for any suggestion.

Jay Chan


Plain Corecell will bend that sort of curve easily. It's a bit more
expensive than Divinycell but resists impacts better. Do you drop a
lot of heavy objects on your deck?

Epoxy sticks very well to all these synthetic cores.

If you use plywood:
- coat it with epoxy as you suggest.
- when you go to through bolt/screw on the T-top, first drill an
oversized hole. Then fill the hole with thickened epoxy. Wait for it
to cure. Then drill the smaller hole through the thickened epoxy.
Even if the caulking fails, water shouldn't get to the plywood.

I'm not wild about using plywood as a high density core but real high
density core is very expensive. (except for www.bateau.com's Renicell
but you probably don't need a whole sheet!)

Evan Gatehouse

Glad to hear that Corecell has enough give to be bent slightly to match
the curve of my deck surface. I will order Corecell or Divinycell soon
(depending on price).

Also thanks for mentioning the steps to re-inforce the fasteners for
weight bearing hardware. I have already planned to do this for all the
hardwares on the deck regarding if they are weight bearing or not
(currently, none of the hardware on the deck have any re-inforcing
bedding -- water leak and rotten balse core). e question is whether
this is good enough for supporting a T-top. You see, the T-top in this
boat is quite heavy duty (relative to the size of the boat), and I will
be mounting all sort of things into it in the nwar future (such as an
electrical box, VHF radio, antenna, GPS...). Obviously, the fasteners
of the T-top will be under a lot of stress. I am wondering whether a
small area (like 4"x4") of epoxy bedding (with colloidal silica filler)
is good enough to handle the load considering the fact that the
surrounding area will only be light weight core material. I am
wondering whether I should spread the load by using a 12"x12" marine
plywood as the core material to anchor the T-top and then adding epoxy
bedding surrounding each fastener of the T-top.

I figure that Cabosil is the same as colloidal silica that I am
planning to use. Good to know that I am on the right track.

Jay Chan


Jim Conlin wrote:
Sheet core-cell can easily be bent to the kind of curve you describe.
If it's obstinate, some kerfs cut on the table saw will do the trick. Apply
kerf-side up so they can fe filled later with light bog.
Bond the sheet down with epoxy-microspere slurry.
If the sequence of your construction will be to re-build the deck from the
bottom skin up, one way to provide higher-strength patches for the
attachment of loaded hardware would be to cut windows in the foam where you
want said patches to be, then after the foam's bonded down, fill the windows
with high-strength (like Cabosil) filler (Use slow hardener or they'll
exotherm badly. ), sand flush, apply the top skin and Bob's your uncle.
Just remember where the patches are.

. If it's
wrote in message
ps.com...
I discovered that most of the balsa core mateiral in the deck of my
18-ft boat is either rotten or fully wet. I am in the process of
removing all the core material from the entire deck. Now I need to
figure which alternative core materials I should use for these two
different areas:
1. Deck area that don't have any weight-bearing hardware.
2. Deck area where the T-top is anchored on.

For the deck area that don't have any weight-bearing hardware, I am
thinking of getting something like Corecell or Divinycell that are made
from PVC and won't rot. I am thinking of getting them in plain sheets
instead of sheets that have been scored (cheaper and in the correct
thickness). But according to the supplies web site, plain sheet of
those materials cannot be contoured to curved shapes. I am wondering
whether I can at least bend the plain sheet just a little bit -- like
1" drop for every 30". Is the plain sheet so rigid that I cannot even
use a bag of fertilier to conform it to a slight curve on the deck when
I bed it with wet epoxy? The other question is whether epoxy will
adhere well with those synthetic core materials.

For deck area where the T-top is anchored on, I am thinking of using
either marine grade plywood encapsulated with epoxy or many layer of
fiberglasses and epoxy. Will marine grade plywood still rot? Which
material is better for this area anyway?

Thanks in advance for any suggestion.

Jay Chan

Evan Gatehouse wrote:
wrote:
I discovered that most of the balsa core mateiral in the deck of my
18-ft boat is either rotten or fully wet. I am in the process of
removing all the core material from the entire deck. Now I need to
figure which alternative core materials I should use for these two
different areas:
1. Deck area that don't have any weight-bearing hardware.
2. Deck area where the T-top is anchored on.

For the deck area that don't have any weight-bearing hardware, I am
thinking of getting something like Corecell or Divinycell that are made
from PVC and won't rot. I am thinking of getting them in plain sheets
instead of sheets that have been scored (cheaper and in the correct
thickness). But according to the supplies web site, plain sheet of
those materials cannot be contoured to curved shapes. I am wondering
whether I can at least bend the plain sheet just a little bit -- like
1" drop for every 30". Is the plain sheet so rigid that I cannot even
use a bag of fertilier to conform it to a slight curve on the deck when
I bed it with wet epoxy? The other question is whether epoxy will
adhere well with those synthetic core materials.

For deck area where the T-top is anchored on, I am thinking of using
either marine grade plywood encapsulated with epoxy or many layer of
fiberglasses and epoxy. Will marine grade plywood still rot? Which
material is better for this area anyway?

Thanks in advance for any suggestion.

Jay Chan


Plain Corecell will bend that sort of curve easily. It's a bit more
expensive than Divinycell but resists impacts better. Do you drop a
lot of heavy objects on your deck?

Epoxy sticks very well to all these synthetic cores.

If you use plywood:
- coat it with epoxy as you suggest.
- when you go to through bolt/screw on the T-top, first drill an
oversized hole. Then fill the hole with thickened epoxy. Wait for it
to cure. Then drill the smaller hole through the thickened epoxy.
Even if the caulking fails, water shouldn't get to the plywood.

I'm not wild about using plywood as a high density core but real high
density core is very expensive. (except for www.bateau.com's Renicell
but you probably don't need a whole sheet!)

Evan Gatehouse

Thanks for confirming that Corecell plain sheet should have enough give
to be bent slightly. I also have a feeling that Divinycell is cheaper
than Corecell. But this may become irrelevant now. Turn out the
boating supplier cannot ship large plain sheets (store pickup only). I
may be forced to buy small sheets that have scored. Oh well...

Thanks for the tip of using a combination of marine plywood as core
material and epoxy bedding to secure the T-top. This sounds very
practical.

If you don't have a good feeling about the use of plywood as core and
high density synthetic core is very expensive, I am wondering what you
would have suggested.

What's about the idea of using fiberglass and epoxy alone (solid thick
fiberglass, no core) without using marine plywood for the T-top? Then,
there is nothing to rot and must have a lot of strength, and I don't
need to buy a whole sheet of marine plywood. The only thing that I am
not sure is whether this solid fiberglass is stiff enough. If it has
some give, I am afraid that it will transfer load to other anchoring
points of the T-top and may cause spider crack on the gelcoat in the
other anchoring points (the T-top has two anchoring points on the deck
and four anchoring points on the console). I am just hoping that a
5/8" thick solid fiberglass deck will be rigid/stiff enough to absorb
most of the load. Any idea?

Jay Chan

Noah's Marine has half-sheets of core-cell at good prices. They can ship.
It's perfectly OK to piece it together.
The function of the core is to keep the skins a constant diatance apart and
to bear shear loads. Cored panels as they are thicker in section are stiffer
than solid glass panels. Foam cores need help in this only where there are
heavy compression loads, as from fastenings.
The drawback of plywood core is that when water gets to it, it'll rot. And
it's heavy.

Jim Conlin wrote:
Noah's Marine has half-sheets of core-cell at good prices. They can ship.
It's perfectly OK to piece it together.
The function of the core is to keep the skins a constant diatance apart and
to bear shear loads. Cored panels as they are thicker in section are stiffer
than solid glass panels. Foam cores need help in this only where there are
heavy compression loads, as from fastenings.
The drawback of plywood core is that when water gets to it, it'll rot. And
it's heavy.

Thanks for the tip. In that case, I can ask the vendor to cut the
plain sheet in two or three pieces in order for UPS to ship. The other
option is buying scored sheets that are small in size and can be
shipped.

If I understand you correctly, a solid fiberglass panel should be great
for the T-top to anchor on as long as it is as thick as a cored panel.
Of course, I will not make the whole deck in solid fiberglass; that
would be too heavy. I will use solid fiberglass in the small areas
where the T-top is anchored on.

Jay Chan

wrote:
Jim Conlin wrote:

Noah's Marine has half-sheets of core-cell at good prices. They can ship.
It's perfectly OK to piece it together.
The function of the core is to keep the skins a constant diatance apart and
to bear shear loads. Cored panels as they are thicker in section are stiffer
than solid glass panels. Foam cores need help in this only where there are
heavy compression loads, as from fastenings.
The drawback of plywood core is that when water gets to it, it'll rot. And
it's heavy.


Thanks for the tip. In that case, I can ask the vendor to cut the
plain sheet in two or three pieces in order for UPS to ship. The other
option is buying scored sheets that are small in size and can be
shipped.

If I understand you correctly, a solid fiberglass panel should be great
for the T-top to anchor on as long as it is as thick as a cored panel.
Of course, I will not make the whole deck in solid fiberglass; that
would be too heavy. I will use solid fiberglass in the small areas
where the T-top is anchored on.

Jay Chan

Solid fiberglass is a good option for through bolting hardware. But
you don't need the solid glass to be thick as the core unless you can
only get to the top side of the sole. If you can get to the bottom,
you can taper the core out to nothing and make the solid glass about =
3/4 the bolt diameter. For a cockpit sole, where you might not be
able to get to the back side, then a solid glass laminate will have
to be the same thickness as the core. Just slightly larger than the
footprint of the mounting base is enough.

Evan Gatehouse

Evan Gatehouse wrote:
wrote:
Jim Conlin wrote:

Noah's Marine has half-sheets of core-cell at good prices. They can ship.
It's perfectly OK to piece it together.
The function of the core is to keep the skins a constant diatance apart and
to bear shear loads. Cored panels as they are thicker in section are stiffer
than solid glass panels. Foam cores need help in this only where there are
heavy compression loads, as from fastenings.
The drawback of plywood core is that when water gets to it, it'll rot. And
it's heavy.


Thanks for the tip. In that case, I can ask the vendor to cut the
plain sheet in two or three pieces in order for UPS to ship. The other
option is buying scored sheets that are small in size and can be
shipped.

If I understand you correctly, a solid fiberglass panel should be great
for the T-top to anchor on as long as it is as thick as a cored panel.
Of course, I will not make the whole deck in solid fiberglass; that
would be too heavy. I will use solid fiberglass in the small areas
where the T-top is anchored on.

Jay Chan

Solid fiberglass is a good option for through bolting hardware. But
you don't need the solid glass to be thick as the core unless you can
only get to the top side of the sole. If you can get to the bottom,
you can taper the core out to nothing and make the solid glass about =
3/4 the bolt diameter. For a cockpit sole, where you might not be
able to get to the back side, then a solid glass laminate will have
to be the same thickness as the core. Just slightly larger than the
footprint of the mounting base is enough.

Evan Gatehouse

Thanks. I will keep the formula (glass-thickness = 3/4 bolt diameter)
in mind. This will come in handy.

I have very little (or no) access to the back side of the deck where
the T-top footing is. Sound like I will need to make the solid
fiberglass as thick as the deck.

Good to know that the fiberglass bedding area only need to be slightly
larger than the footprint of the T-top mounting base. This settles the
issue. Thanks.

Jay Chan

Evan, i've thought that the 'puck' that's in place of the core under a
loaded fastening only needs to have the compression strength to bear the
fastening loads and be non-decaying. In that case, most any high-strength
bog will do the job. Why glass?


wrote in message
ups.com...
Evan Gatehouse wrote:
wrote:
Jim Conlin wrote:

Noah's Marine has half-sheets of core-cell at good prices. They can
ship.
It's perfectly OK to piece it together.
The function of the core is to keep the skins a constant diatance
apart and
to bear shear loads. Cored panels as they are thicker in section are
stiffer
than solid glass panels. Foam cores need help in this only where
there are
heavy compression loads, as from fastenings.
The drawback of plywood core is that when water gets to it, it'll rot.
And
it's heavy.


Thanks for the tip. In that case, I can ask the vendor to cut the
plain sheet in two or three pieces in order for UPS to ship. The
other
option is buying scored sheets that are small in size and can be
shipped.

If I understand you correctly, a solid fiberglass panel should be
great
for the T-top to anchor on as long as it is as thick as a cored panel.
Of course, I will not make the whole deck in solid fiberglass; that
would be too heavy. I will use solid fiberglass in the small areas
where the T-top is anchored on.

Jay Chan

Solid fiberglass is a good option for through bolting hardware. But
you don't need the solid glass to be thick as the core unless you can
only get to the top side of the sole. If you can get to the bottom,
you can taper the core out to nothing and make the solid glass about =
3/4 the bolt diameter. For a cockpit sole, where you might not be
able to get to the back side, then a solid glass laminate will have
to be the same thickness as the core. Just slightly larger than the
footprint of the mounting base is enough.

Evan Gatehouse

Thanks. I will keep the formula (glass-thickness = 3/4 bolt diameter)
in mind. This will come in handy.

I have very little (or no) access to the back side of the deck where
the T-top footing is. Sound like I will need to make the solid
fiberglass as thick as the deck.

Good to know that the fiberglass bedding area only need to be slightly
larger than the footprint of the T-top mounting base. This settles the
issue. Thanks.

Jay Chan