Part 1 -
Concept & Application
In an effort to share knowledge and generate
discussion, the following article explains the concept of edge-bonding the
hull planks of a vintage wooden boat. This is the first of two articles, which
covers the concept and application. The second article will be published in
the Fall, and will document the test results - after a Summer of hard use on
Lake Winnipesaukee and on the Vintage Race Boat Circuit.
Yup - that's your Webmeister, edge-bonding his beloved
Obsession with 3M-5200
First - Some Background:
Let's start with the obvious question - why would you
do this to a vintage wooden boat in good condition? Well, in the case of my
Gar Wood Speedster that I have owned and maintained for 25 years now, the objective was to
strengthen and preserve the hull.
In the spirit of Gar Wood and his riding mechanic
Orlin Johnson, I recently upgraded my 454 cubic inch Chevrolet motor to a full race,
510 cubic inch, stroker motor that produces 630 horsepower, and now participate
on the Vintage Race Boat Circuit with my faithful riding mechanic Donnie McLean.
The resulting stress on the hull was causing the planks to "work" excessively.
So I had to somehow strengthen the hull.
After much research, conversation and e-mails with
the Gougeon Brothers (West System Epoxy) and 3-M (5200 Adhesive) we finally
decided to edge-bond the hull planks with 3M-5200 adhesive. This
flexible adhesive would add strength to the hull and retain the
look and feel of a
wooden boat, unlike an epoxy built boat which is stiff and does
Second - the concept of
The concept of edge-bonding is well explained in the
West System publication - Wooden Boat Restoration & Repair. Quoting from page
6, at the end of the paragraph on Bonding for Stiffness - "Edge-bonding the
hull planking with epoxy after cleaning the seams is the single best thing you
can do". There are also some excellent photos of the concept on page 28.
It explains how to clean out each seam by running a saw along a batten, to
remove the old caulk and expose clean wood on the facing edge of each plank
for good bonding. The opened seam is then filled with epoxy. The result being
a much stronger, stiffer hull.
However, we were concerned about using epoxy on a
traditionally built, plank on batten hull. So, after gleaning as much
information as possible from the Gougeon Brothers and 3M, we thought that a
little practical knowledge would round out the discussion.
Maine wooden boat builders are known for producing
great boats that hold up to the rough conditions encountered at sea, so we ran
the project by several of them at the Spring, Maine BoatBuilders Show. All
favored the 3M 5200 for itís tenacious bond, coupled with itís resilient
So, we started leaning towards using 3M-5200 on our edge-bonding project,
but two questions remained. How strong is it, and how workable is it? Using
the same material as our hull planking (3/8" thick Honduras Mahogany), we
setup test pieces, spaced exactly the thickness of a nickel and filled the
groove with slow-cure 3M-5200. After cleanup, the surface of the joint was
left with a concave bevel, much like a traditional deck seam.
Actually, 3M sells two different 5200 formulas. Their "slow-cure" is
tack-free in 24 hours and cures in 7 days, and their "fast-cure" is tack-free
in 1 hour and cures in 24 hours. The slow-cure is stronger, as stated by 3M
and gives a great deal of working time. We found the material to be very
workable. Unlike other similar materials, there is time to get the results you
want even if mistakes are made. They can be cleaned-up and re-done without a
problem. But the stuff is very messy to work with. Be sure to wear gloves !!!
After 7 days of curing time, we cut one of our test pieces into 2 inch
sections. We then pulled and twisted it, and found there wasnít anything we
could do to hurt it. The second test section was placed in a vice, and weight
was added to the opposite plank until noticeable deflection occurred. Finally,
at 75 pounds the plank had moved the width of a pencil line, in relation to
the side clamped in the vice. The weight was left there for 30 minutes and
when removed, the planks returned to perfect alignment. That 75 pounds per 2
inch section equates to 450 pounds per foot, multiplied by the number of seams
on the hull, then by the length of the boat, would result in a very strong,
yet flexible hull. The final decision was made, we would use the slow-cure
3M-5200 for our project.
Third - The Application:
Ok - so much for the concept, now let's talk about
the application - or how we did it. First we found a volunteer to actually saw
or route-out each hull seam - with a 4 inch Makita circular saw. Mike Michaud,
who is currently building a replica of Gar Wood's Miss Detroit III, was
appointed to the task. I just could not bring myself to sawing the hull of my
beloved Gar Wood Speedster. But Mike had a very steady hand, and just followed
the seams by eye with his trusty Makita saw. No guide battens were used. This
was a horrifying process for me to watch, but Mike did an excellent job and I
somehow survived the process.
After the seams were sawed/routed-out, a V shaped
file was used to clean out the seams, and give them a slight V shape. The new,
widened seams were now about the width of a nickel, and ready to be filled
with 3M-5200 adhesive. This ended the first day of the project, so we
celebrated that Saturday night and thought the project would be completed the
next day - wrong !!!
Then came the messy (not fun) part, filling the seams
with black, 3M-5200 adhesive. Anyone who has ever used this stuff will shudder
at this part of the project, and man, did I get filthy. The problem was
getting the thick adhesive into the narrow seams - only the width of a nickel.
So we experimented with various nozzle creations, and ended up using a regular
drinking straw tip, about 1 inch long, taped to the end of the adhesive tube.
It worked, but was very messy and took a long, long time (inch by inch) to
fill all the hull seams. This part of the project took several days.
As the seams were initially filled, we used a
plastic trowel to keep forcing the 3M-5200 into the seams, and then finished
with a round trowel - leaving a recessed, beveled seam - much like a tradition
deck seam. We let the 3M-5200 seams cure for a week before the next step -
sanding and painting.
The final step was to sand and paint
the hull, - using Epifanes #19 black enamel. We first sanded
with 320 grit paper, then a final scuff with Scotchbrite Pads followed by 3 coats of paint. We used our preferred roller/wicking
method, which put down a lot of paint and the results looked sprayed on. Man, the hull was
shinny, and the results look exactly waht we wanted, an extremely strong wooden
hull that still looked like a wooden hull, with the grooved/widened seams. And
because the 3M-5200 marine adhesive remains flexible, the boat
will still "feel" like a wooden boat, strong but still flexing,
unlike an epoxy built boat which is stiff and does not flex.
Finally - The Summary:
In summary, we were very pleased with the results of
edge-bonding project and we want to thank Donnie McLean and Mike Michaud for
their help. The boat looked great, and we were very excited about our enhanced,
strengthened hull. The boat was thoroughly tested that Summer - on Lake
Winnipesaukee and on the Vintage Race Boat Circuit. Five Vintage events were
planned - including, Madison, Detroit, Lake George, Clayton and
Buffalo. In the Fall, we published our test results - check out the link
Click here for Part 2 - Test Results
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