C-Forum

There have been several posts concerning boat repair to which I and others have responded. I learned the basics from an AW magazine article written by the Canoe Doctor, David Brown, of the DC area. Hopefully those with repair problems will benefit as I did from reading David's article. The link to the AW online journal is:

http://www.americanwhitewater.org/journ ... ve/1985/2/

He wrote this in 1985 but it still applicable for repairing todays Royalex.

Michael

So, anyone know the name of the toxic, expensive, micro-short shelf-lifed, specifically designed for ABS "acrylic adhesive" that the Canoe Doctor mentioned in his AW magazine article?

Anyone else use it, and find the repairs worth the effort and expense?

After reading the article I began experimenting with different adhesives. Initially, the best success was with the 3M two-part urethane adhesive (#3532). It is not an acrylic adhesive, but it bonds plastic very well. In 1985 it was used by boaters to bond the plastic extrusion and D-ring set-up to Royalex hulls. This adhesive is a strong structural adhesive, but it is not designed specifically for acrylic plastics. If you have used 3M 3532 you know it expands as it cures. This can cause the a ABS plate to protrude from the hull making it less a streamlined repair on the outer hull surface.

At this point I decided to seek better advice from a distributor of industrial adhesives. Watkins & Associates, in metro ATL, told me about a relatively new line of methyacrylate adhesives that matched the description that David Brown gave in his article. The adhesive was Hysol 9446, a super strong acrylic adhesive with good flexibility after curing. It cost $35 per quart (close to $140 per gallon), six-month shelf life and required the user to wear a organic-element respirator. It needed to be kept at 0 deg. F to ensure the six-month shelf life. I bought my first quart kit in 1986 and used it to repair my Whitesell Piranha. It was absolutely the bomb. You could smack rocks all day and the ABS plate would not come off. I showed it to Nolan and he started using it to bond D-ring extrusions in his canoes instead of using 3M 3532. It turned out that Hysol sold this adhesive to the aerospace industry and in order to meet their stringent military requirements had to state the max shelf life was 6 months at 0 deg. F. David Brown had been employed as a aerospace worker so I thought I must have found something close to what he had described. The adhesive will last up to four years if kept at 32 deg. F when not in use. I used some two-year old Hysol 9446 last summer to bond D-ring extrusions into my Caption and they are holding up great.

Last year I decided to try a new methyacrylate adhesive that Watkins & Associates is distributing for the marine industry. The aerospace industry has driven the price of Hysol 9446 from $35 per quart to $192 per quart over the last nineteen years. Loctite makes a family of methyacrylate adhesives that are designed for adhering acrylics with a strong, flexible bond. They have a one-year shelf life and can be kept at 70 deg. F to maintain the adhesive quality. I have repaired several canoes with it and find it to be equal in performance to Hysol 9446. The cost is $110 per quart kit. It is also offered in smaller quantities, like 12 oz. kits, but I buy no less than quart or liter amounts as that is more economical. I repair canoes for $100 to $150 per job so I recover the cost for the adhesive rather quickly.

As I have posted on here before there is no better way to repair a canoe than with like materials. Plastic repairs last longer than glass and resin repairs on Royalex. It is not an easy job and requires one to invest in tools and materials specific for the job. I believe it is well worth the effort and my customers have agreed. I ran into an old customer who is still paddling a canoe I repaired 18 years ago. It is not his primary boat, but the repair has held up for a long time. With many of our favorite Royalex hulls out of production the only way to keep them on the water is to fix them.

I am at work now and can send you the exact adhesive part numbers when I get home if you are interested in trying a ABS repair. Look in your yellow pages for a industrial adhesive distributor in your area that carries Hysol and Loctite methyacrylates.

Michael

After this weekend I've got a Caption that needs a repair (about a 3 inch rip/crack on the bottom).

Is the Loctite worth the price (given that I have some 3M adhesive in the cupboard)?

P.

p.s. Also some stress cracks on the inner hull, but I don't think a large fiberglass will stay due to flex - is a vinyl patch over these minor cracks worth it?

Where on the bottom of the hull is the crack?

Are the inside stress cracks close to the chines?

You're right in assuming that a fiberglass patch won't flex. A vinyl patch won't be anything more than cosmetic. An interior ABS plate is the best choice to prevent the cracks from spreading. If the 3M adhesive is 3532, it will work. First repair the cracks before you put a plate over them. This can be accomplished with PC7 epoxy paste. It would be best to email me at mrmccurdy at comcast dot net so we can discuss this in more detail.

Michael

A big, hearty thanks to Dixie Boater for his contribution to the C-Forum!

That kind of information is hard to come by, and I appreciate your sharing the bounty of your experience. Knowledgable people Dixie Boater are hard to find.

Thanks for your generousity.

I am happy to share my past experiences and methods of ABS Royalex repair. David Brown was generous in sharing his knowledge in the AW article. Without that I would never have learned how to fix canoes. I want to do the same for others as he did for many of us canoeists.

Michael

Michael et. al.

Here's an update on repair and products for interior stress-cracks on the inside of a Royalex hull... 3M urethane adhesive works better than PC7 epoxy.

2yrs ago I repaired some stress cracks in my hull (propogated from alongside a thigh-strap d-ring & a similar d-ring stress due to an airbag left in the sun - both of these were the hard-plastic d-rings, not vinyl anchors).

After a bit of exploring here, I cleaned 'em up and used 3M 2-part "urethane adhesive" ("2352" or something?) to fill the cracks. It has held fine, no further action from those cracks.

The fiberglass patch over the repair however has mostly come off, it's been flexed/bounced up, but I just keep trimming off the busted bits. I wouldn't bother with the fiberglass again for these little stress cracks.

This summer, I repaired some similar cracks in the same way (drill the ends, "clean"/carve the crack, & fill) using PC7 epoxy instead of 3M adhesive. I also used it to reapir a split in on of the hard-plastic d-ring anchors. After one or 2 uses all the cracks were back!

So, for the record, in my experience, I've had 100% success with 3M urethane adhesive over 2 years, and 0% success with PC7 epoxy over 2 runs. The epoxy seems too brittle for a Royalex hull (the cracks are right in front of the saddle and at the knees where it takes some good flexin'/pounding).

Next cracks I may just try marine goop, as it's much cheaper than 3M adhesive, and people have also reported success with it.

Cheers, Pat.

p.s. FYI, here's the link to the original discussion:
http://cboats.net/cforum/viewtopic.php? ... hlight=pc7

Hi Pat,

I concur that PC-7, by itself, will not hold up to the stresses caused by the hull flexing around thigh or knee strap anchors. I use PC-7 only to restore the strength of a hull with external cracks before I place a ABS plate over the damaged area. The plate is bonded to the the hull (and the PC-7) with a methacrylate adhesive. That is the only way I use PC-7 for a hull repair. PC-7 is too brittle to hold up when the Royalex flexs as you slide over or hit rocks, etc.

Your experience with fiberglass and epoxy repairs is common. While that is a much easier repair method than I advocate, it does not hold up and requires additional patches to be placed around the first patch when it cracks.

3M 3532 Urethane adhesive creates a flexible bond that won't break as easily as PC-7 epoxy paste. Adhesives and epoxies (sp?) have their right and wrong applications for boat repair. One must tailor the adhesive to the repair method.

I have used Marine Goop to fill internal hull cracks and find it to be quite flexible. I have also used it around the edges of a ABS plate repair to "smooth" the transition from plate to hull and create a more streamlined repair. I apply it in thin layers and allow it to cure thoroughly between applications. You can even sand and paint over the cured Goop. Makes for a nice looking repair instad of the ol' ugly black plastic patch.

Keep fixing those boats! That's the only way to learn successful techniques.

Cheers to you my friend!

Michael

[/b]