Part 1 - Concept & Application

William E. John III


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 not flex.

Second - the concept of edge-bonding:

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 properties.


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 our 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 below !!!

Click here for Part 2 - Test Results


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