5200 bottom

I built a modified reproduction Chris Craft with cold molding (triple bottom and double topsides) twin engines. All with epoxy glue. All with mahogany solid and okume ply. Everything is solid except the white oak keel where the bottom is separating from the oak rabit at the keel and thru the two piece oak keel. The fasteners are all stainless and solid. I used 5200 to glue the four large Philipine mahogany engine bearers in place (no fasteners) and also in a 5/8 " thick pad under each of the eight engine mounts (no fasteners either from the mounts to the bearers). The boat was launched in 2003 and in water used all summer in 03, 04 and 05, then out on stands in 06,07, and 08 and back in water for 09 and 2010 summer. There are absolutely no problems with the 5200 joints holding the bearers to the ribs or under the engine mounts. I'm tempted to open the bad seems up and use 5200. Do you think polysulphide would be better, and if so, why? and what kind of polysulphide?

 

I wonder if painting the bottom of fiberglass boat with 5200 as a barrier coat would be a good idea. Then you paint bottom paint over it... Should be indestructible.

 

Cost compared to epoxy? Assuming, that is, that 5200 is as impermeable as epoxy. Ease of application? Longevity? What about toughness (beaching, etc.)? And if scraped, while epoxy only would scrape off to a certain depth, would 5200 scrape off in such a way that it tears out a larger gouge because it stretches before tearing?

 

3M 5200 is a miserable adhesive compared to epoxy and your engines and shafts will eventually suffer from the lack of fasteners, which insuring alignment and the sure to stretch out high modulus of elasticity of the polyurethane.

It's difficult to comment on practices like this or the longevity of these types of practices. 3M 5200 is designed as an aggressive sealant and shouldn't be remotely considered in the same class as an adhesive like epoxy. Yes, it has good adhesive qualities, but also permits considerable movement and distortion, both of which are foolish in engine bearers, mounts and other structural elements, where locking down the structural piece is the paramount consideration.

Why you planking is separating from your keel is also a crap shoot. 3M 5200 is a very poor underwater seam sealant, unless it's applied and immediately placed under pressure for a few weeks. If you just pack it into a seam, once the wood get wet, it'll pull out like a big rubbery string. Polysulfide would be a better choice as it'll cling to wet wood, though it should also be applied under pressure for best performance. 3M 101 is the typical single part choice for this goo.

The planking is held in the rabbit by the frames, which are held to the keel by the floors. If you used 3M 5200 in any of these interfaces, then this is the reason your planking is backing out of the rabbit. If this is all fastened and epoxied, then you have other issues, but without pictures and an idea what make and model repro you built, speculation past this would be guess work.

 

5200 as glue

Thanks for your comments Par. Its clear from this and other of your posts that you are not a big fan of 5200. I'm still on the fence about using it on the previously epoxied seems that have opened up at the keel and rabbit. I understand your concern about my using it on the engine bearers and engine mounts but I must say those are two places where there have been no problems at all. Also this is the end of the eighth year after launch and there are no shaft alignment problems. Everyone I've spoken to has said my problem was using the epoxy on the white oak. It simply cracked with the working of the boat and the vibration of these two big engines. The boat is upside down now and the plan I'm considering is:

1) rout out a rectangular trench on the outside of the botom down the center of the keel approx 1/2" deep by 3" wide (1/2" wider than the two white oak keel pieces). Avoid all fasteners. The keel pieces are 6" deep.

2) completely clean out the opened seems (circular saw or router etc.) down 1 to 3 inches below the bottom of the trench, by 1/8th to 1/4 inch wide.

3) soak the trench and cleaned out seems with CPES, let it get tacky

4) pack filler into the seems below bottom of trench and coat the bottom and sides of trench with filler

5) cover with a new piece of mahogany previously treated with CEPS that will fit into the trench maybe protrude proud of the bottom like a long shallow keel.

6) fasten the new piece with stainless screws into the white oak thus putting the filler under pressure.

7) coat entire repair with 2 to 3 coats of epoxy and good coat of antifouling bottom paint.

I'ld really love to hear what you think about this plan.

Hans

 

5200 will separate from wet wood. Polysulfide needs to be primed for good adhesion.

 

I have no advise for people using CPES and 3M 5200 in the fashion you have. There's plenty of documentation , testing and research to back up my "beliefs". The same can be said about white oak and epoxy. I've said for years it works, with proper preparation and now West System's own testing verifies what I've been doing for over two decades.

I'm not sure where you're getting your information, but you're using these products correctly and this is why you are having failures. I've glued white oak for decades with epoxy without a single glue related failure. I've stop using penetrating epoxy for some number of years and testing by the major epoxy formulator reinforces my reasons for stoppage.

 

I have not yet used it for the problem on the bottom. What would you suggest.

 

what do you suggest for a primer?