<font size=3>At 10:04 17-10-98 -0400, Bob McLeran wrote:

I have had excellent results with NidaCore.
I am putting the finishing touches on a complete reconstruction of a
29" offshore having replaced stringers, built new ribs, redone the
sole both inside the cabin and the whole aft deck, replaced the transom
and built a brand new windscreen, all using NidaCore. This material is
impervious to oil, gas, diesel, hydraulic fluid, water, coca-cola,
coffee, etc.. The person actually doing the work was extremely skeptical
about using this material but once he started using it, there was no way
he was going to go back to using marine plywood for coring material. He
was most pleased with the flexibility of the material and the manner in
which it would bend into any shape  he needed.  It comes in
different thicknesses, depending on your needs. We used  1, 1/2 and
5/8 inch throughout for the project. For the stingers and bulkheads we
simply bonded the number of required panels together to reach the desired
thickness.
We replaced the aft deck just 5 years ago but water got underneath and
the resulting rot, which we thought was only the deck, actually extended
down into the stringers and, as we found out later, into the transom. We
also had a design flaw in the bulkhead connecting the cabin top to the
aft deck. The bulkhead was not extended all the way down through to the
hull ( it reached only to the deck)  resulting in a weak connection
which had to be repaired every couple of years.Here I started with the
idea of replacing the deck and have now rebuilt the entire boat. There is
no such thing as 1 little project when it comes to a boat.
The material is lightweight and we reduced the gross weight  of this
boat by about 800 kgs. This material also soaks up about 1.5 times the
usual amount of resin that would be used with a wood core. However this
just seems to add considerably to the stiffness and strength of the
stuff. I can personally testify that this rebuild has resulted in a boat
much stronger then when it came out of the showroom some 15 years
ago.
I decided to go with the NidaCore because it cost just a few dollars more
per sheet than the marine plywood I would normally have used here in
Venezuela. The marine plywood manufactured and available here is not of
very high quality, and that is an overstatement. The boat was also
"heavy" for the type and length.  The flexibility, ease of
use, lightweight, and imperviousness to most factors causing rot and
relative minor additional expense over wood made the decision easy. My
original goal was to replace the deck but after pulling up the old deck
and seeing the extent of the repairs required I just decided to do such a
great job of rebuilding that the boat would last another 25 years without
having to do anything other than polish it and change out the engines
when the time comes.. Not being a naval engineer or the like,  I'll
let you know how everything works out once the boat goes back in the
water (about 3-4 weeks from now).
The NidaCore people can be contacted at [1] 561-287-6464, 3240 S.W. 42nd.
Ave.Palm City, FL 34990. Their web address  is
<www.nida-core.com>. Hopefully they improved their web site over
the last 5-6- months.
I hope this helps.
Steve
</font>

Would it be possible to do the repair from below and avoid cosmetic damage
to the deck?  I wonder if foam in place expanding foam would work?
Ron Rogers

I think that doing the repairs from below would cause more even more
cosmetic damage (in the interior of the salon - removal of lots of teak
handrails and teak supports, entire finished false ceiling, etc), and
wouldn't work as well.  Expanding foam definitely would not be the
answer since I doubt if it would have the necessary strength AND if done
from below would be difficult to impossible to keep in place.

The problem with the deck is that the teak has delaminated from the top
layer of fiberglass, the fiberglass (top and bottom) has delaminated
from the core, the core structure (which originally was some sort of
plywood in 4x4 squares) has delaminated from itself and much of it is
water logged.  As it turns out, most of the structure of the wooden core
was not rotten, only water logged.  If I could have figured out a way to
dry it out, in theory I could have reimpregnated it with epoxy (there
are several ways to do that) which would have also relaminated the top
and bottom layers of fiberglass to the core.  I would still have had to
remove and refasten all the teak strips after the work on the core since
the teak had delaminated from the top layer of fiberglass.  AND, I
couldn't have done the core work without removing at least some of the
teak decking, even if I'd chosen to dry and reimpregnate!

So, all things considered, the best way to go about it seemed to be to
just open it all up, remove the water logged core, let the edges dry
out, and then rebuild the core using the technique I mentioned in
earlier posts.

I have now removed all the teak, most of the top fiberglass lid, and the
core material.  This past weekend I added some lengths of 2X8 where the
core had been, and then placed 3/8" plywood over the entire thing to
keep it dry (hopefully) through the winter months.  I refastened the
mast (which was removed to get the core up) to a piece of 2X8 which runs
the entire length of the open area and rests on a couple of beams - the
whole thing is solid enough to walk on, and I can still use the boat
since I can walk on the plywood deck.

After removing the mast, I discovered that the stainless steel lag
screws which held the bottom mast plate to the "step" penetrated not
only the core but the bottom (interior) layer of fiberglass, and it had
no backing plate on the interior side of the boat.  Top that off with
the fact that the screws weren't imbedded in anything (like epoxy to
prevent water contamination of the core) and I'm not surprised that
water had worked its way into the core.

The next time I buy a used trawler . . . . !!!!

"Ronald C. Rogers" wrote:

--
Bob McLeran                              rmcleran@ix.netcom.com
M/V "Sanderling"                        Docked at Point Patience Marina
Hailing port: Wianno MA                      Solomons, MD
Hampton 35 Trawler

Randall, I haven't tried or read anything about what you propose, but
why bother with the plastic barrier as long as you're going to imbed the
teak in 5200 or a similar compound anyway?

I am going to use a technique that I have tried, and that is to imbed
the teak in thickened epoxy - it works and is absolutely water proof.
It's described in The Gougeon Brothers on Boat Construction, and in more
detail in their publication #002-550 Fiberglass Boat Repair &
Maintenance.  Their telephone # is 517-684-1374 if you want to order.
(They also have a great pub on vacuum bagging!)

I rebuilt my lazarette hatch using epoxy, and it worked very well.  In
essence, a layer of thickened and blackened (with graphite) epoxy is
laid down on the repaired deck, then the teak strips are set in the
epoxy and fastened at the edge (or in evenly spaced holes) with screws
and washers coated with a release medium (use a kitchen spray) - each
screw holds two strips of teak if fastened at the edge.  The thickness
of the screws determines the spacing between the strips (I used #10 and
got 3/16 inch spacing which was about what I had with the original
deck).  After the epoxy sets, remove the screws, and fill the holes (and
any gaps in the space between the strips) with the same blackened epoxy
mixture.  That fills ALL the holes that were created when the deck was
fastened down, and leave NO deck screws into the underlying core.

The advantage to me of using this method (and I think it would work with
yours, also) is that I can reuse the teak strips I removed from the deck
before rebuilding the core.  I'll clean them up to remove the caulking
(have them sitting in my carport now), then saw off the little ledge
that's cut into one side of each strip which created the pocket into
which the caulk was placed.  I put them on upside down so I don't have
to worry about the damage done when I removed the bungs and screws.
After the deck is down, I'll redrill the old screw holes from the top to
a uniform size, and fill those holes with the blackened epoxy as well.
This gives the appearance of black "bungs" but I'm satisfied with the
look and I'll only have to buy a few teak strips (a few are not usable
due to breakage or hardware holes)!!!!  If you wanted, you could color
the epoxy to make it a color closer to teak, and then it would have the
appearance of teak "bungs."

Hope I'm not boring the rest of the list with this stuff.

Randall Jacobs wrote:

--
Bob McLeran                              rmcleran@ix.netcom.com
M/V "Sanderling"                        Docked at Point Patience Marina
Hailing port: Wianno MA                      Solomons, MD
Hampton 35 Trawler

Robert H. McLeran wrote in part:

I'd like to pass on a tip that a marine surveyor gave me last year.  I
have not tried this approach but it does sound interesting, particularly
for small areas of wet coring.

The theory is to use a vacuum pump to reduce the air pressure in between
the two fibreglass layers to the point where the water will boil.  The
water vapour would then be removed by the vacuum pump.

1. Drill a grid of 1/4 inch holes into a small wet area of the coring.

2. Lay the end of the suction hose flat on deck near the centre of the
   section you are working on.

3. Cover the entire section with burlap to allow unimpeded migration of
   air and vapour.

4. Cover the burlap with a heavy guage poly and tape all edges to the
   deck to create an air-tight seal.

5. Run the vacuum pump for about 24 hours.

6. When a moisture meter indicates the coring is dry, inject epoxy into
   the holes to fill all voids.

This should be done in small sections at a time (I can't recall if it
was 2 or 4 square foot sections).

If this procedure has any merit, perhaps one of the engineers on this
list would be kind enough to refine the procedure and also calulate the
amount of pressure reduction that would be required at a given
temperature.

Hope this helps.

--

Bruce Gelhorn
M/V "Single Malt" (Mainship 34)
Vancouver, BC