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Bottom paint in contact with outdrive
walleye
Member Posts: 55 ✭✭
Over the winter I became more educated and aware (via this site!) of outdrive corrosion problems and the need to stay on top of them. Made it down to the yard finally and got a look at my drives (B3s). Some corrosion spots but not as bad as I had feared. I plan to sand down and then prime/paint with Primacon and Trilux 33. However, I also noticed that bottom paint doesn't have a protective barrier around the gimbal housing. The paint was done right up to and is in contact with the housing. There is corrosion beginning around the hub (forward of inside prop) and also corrosion spotting on the bell housing. Leads me to three questions:
1. Is the location of this corrosion likely the result of or exasperated by the bottom paint being in contact with drive? Or is that inconclusive and the corrosion could be happening regardless?
2. P.O. was the last to paint bottom so I'm not sure what type of paint was used. Is all bottom paint a problem if in contact with the outdrive or only if it is copper based?
3. Is there a product I can use to get this paint off around the drives so that I have the needed 2" buffer?
Thanks in advance for the feedback.
1. Is the location of this corrosion likely the result of or exasperated by the bottom paint being in contact with drive? Or is that inconclusive and the corrosion could be happening regardless?
2. P.O. was the last to paint bottom so I'm not sure what type of paint was used. Is all bottom paint a problem if in contact with the outdrive or only if it is copper based?
3. Is there a product I can use to get this paint off around the drives so that I have the needed 2" buffer?
Thanks in advance for the feedback.
Comments
IMO - the main culprit of bottom paint touching the drives was old high solids copper infused bottom coats. I was told that the new coatings pose no problem whatsoever if touching the drives and the real dangers to drives were, in no particular order::
1. cathode system failure
2. not having a galvanic isolator installed and working, particularly when slipped at a marina
3. not using the proper anodes and replacing them when needed
In fact I was told that leaving a (the recommendation used to be 1") gap between the drives and bottom coat risked exposing the transom in that area to osmosis. I checked this with three coating specialists including one who was a chemical engineer for one of the top two marine paint manufacturers and they were all in 100% agreement. The chemical engineer said the "gap" way of applying the bottom coatings was no longer relevant in today's world of coatings.
He did say that if you have an ablative coating on your hull and you add accessories after the fact, for example, underwater LED lights - that you should sand the ablative outer coating off until you "just" reach the barrier coats before bedding the lights with sealant (he recommended 3M 4200) otherwise the edges of the ablative coating, where it meets the installed LED lights, could easily ablate and leak under the light.
I followed this advice when installing my Ocean LED color strobing lights. I also checked with Ocean LED and their technical expert said I had received , "good advice".
That's my opinion based on what I have been told by people who I trust and makes sense to me based on what I have seen of applications within the last 4 or 5 years.
I have seen vinyl ester resins blister - and badly. It is not as frequent as poly esters., but it certainly does happen. I have seen gel coat applied too thick to hulls crack. I have also seen a $4,000.00 osmosis repair to a Rinker built "in this century". When I spoke with Mercruiser they said the new coatings - unless a specialty high copper solids content coating of some kind that would be for pure racing or use off the continental USA -as it would not meet present continental USA EPA standards, would have absolutely no effect on their drives if they were properly maintained. I'm going to be conservative here and say I've seen over 50 cruisers of all brands with the bottom coat touching the drives without any effect whatsoever. When I question the yard/owner regarding leaving a "gap" they all said essentially the same thing - "that's not the way it is done anymore". Based on the best information I could gather I would far rather have my barrier coatings and final coatings applied to my entire hull below the water line. Based on the belief of a guy who I respect immensely who has applied high end barrier coats and final bottom coats to more boats and repaired more hulls than anyone on this forum - his words are if you leave any fiberglass hull in the water long enough it will blister. The nice thing about this forum and owning our boats is that we can read all of the advice on this forum. make a decision and live with the consequences. The beauty of democracy!
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