I'm about to start a project on an older Chriscraft

BruceK said:

Boatgm, owner builder of "Carabao"(Tagalog for water buffalo)will be impressed with the Philippines mahogany timber choice(see his post under "Homebuilt").
Sounds like you are on the home run,shaping timber to put her back together.Must be a relief.
Those thousands of screws,are they s/steel, or silicon bronze or ...BruceK[/QUO
Tough couple of days, The silicon bronze screw god decided to test us. On the starboard side of the boat the number ten 1-3/4 screws stopped cooperating. We had been extracting screws with a Grabit extractor which is a combination drill and easy out in one bit. Screws that we had trouble with were easily removed using this nifty tool. Unfortunately the starboard side stopped cooperating and I had to resort to drilling off the heads of the screws and pulling planks over the top off what ever remained of the screw heads. The planks came off in chunks.
these screws were damaged by what looks like electrolysis. I have never seen this before, the screws were pink and the outer layer peeled off like a nut shell. They looked like the zink had been leached out of them. this is really disturbing as this got worse below the water line. I don't have a clew as to what would cause this. If this is a reaction to bottom paint, how and why. This job may have really gotten hateful. We had a hell of a time getting the screws out of the wood on the hull sides, I don't even want to think about fighting these out under the boat. Anybody ever experienced screws being eaten away like this?

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Scary Tough couple of days said:

Okay, I’ll put in my 2.5 cents and hope this helps. - - > But, please realize I’m talking about bottom and other location refastening/replanking jobs I assisted shipwrights on in boatyards some 40 +/- years ago; and they were always on boats that were strictly in New England area's Atlantic salt water... none ever having spent time in fresh water, far as I knew. So, my memory may be fuzzy and Atlantic salt is a bit different than Pacific, and, the yacht harbors were usually overcrowded with too many hot leads from 120 v shore power dangling around the water as well as boats not having nearly as good a common ground running throughout the boat to anodes... such as usually is in today’s boats.

The old fasteners we’d remove or “sister fasten” were usually galvanized or bronze. Monel fasteners were scarcely used but lasted very well and if the planks were soft needing replacement the Monels would usually reverse right out for replacement with new. Corroded/rusted galvanized fasteners were the worst to deal with because they would too often be rusted to the point where they would break off at the surface (if we drilled off the head and pried the plank off first). With galve’s, when we did not need to remove an OK plank, we would simply sister fasten and leave the threaded core, shank, and head of the original galve still embedded. Bronze fasteners would corrode somewhat and seem to get skinny. When we could off screw them on a plank that was to remain we would simply drill a bit larger hole in the same hole and screw in a bit larger fastener of the material the boat owner had agreed to pay for. Otherwise we would sister fasten. Few boat owners would use Monel as replacements due to cost. Yankee screw drivers and cut off screw driver shanks tightened into electric drills (often Sears Craftsmen drills) were the usual means of installing new fastenings. The bronze seemed to considerably outlast the galvanized. I do not recall working on boats with stainless fasteners nor installing stainless.

In my opinion the older bronze fasteners needing replacement from loosing their mass to get skinny and loose in their holes were eaten by electrolysis that permeated the berth areas of hot harbors combined with poor maintenance/replacements of zinc anodes. The Chris you are repairing may have been berthed in a hot harbor and not had anodes well maintained regarding the fastener conditions you are experiencing. Not that I well understand it – but – boats with big battery banks can also develop 12 v corrosion on a boats metal parts... unless the boat’s entire battery system can be isolated and separated from the boat’s structure.

Good luck!

Art

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THD said:

Scary-I don't think that it is electrolysis, but just normal corrosion from the bronze silicon being in damp wood for a lot years. Even fully bedded and with a sealed bung, the screws get and stay damp. The bronze in the alloy corrodes over time. When we bought and rebuilt old Trumpy's, we always refastened with monel. Expensive, but virtually corrosion proof. We also ran into some of the same problems mentioned where the screw would break off right at the neck and could not be removed. We would drive those down a bit and put a little epoxy filler on top and then drill new holes and sister screw (I am not too sure I like that term!!).

Refadtening is a huge, time consuming and tedious job. There is no easy way to do it. I don't envy you the task.

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Scary said:

look closely at the fasteners. the green layer on the pink screws flakes off and is about .010 of an inch. the green screws are coming out of the same frame above waterline. They are solid and don't show any of the tendency to flake off. Interestingly the aluminum mufflers are strapped to these frames with bronze screws and aluminum straps. The wood contact area is destroyed by electrolysis and we may have to sister the sister frames effected. I'll try to post some pictures tomorrow. The aluminum strapping is mostly destroyed as well. I have seen wood ruined by stray electrical current from poorly grounded" bonded" pumps and motors. this is the first time I've seen it caused by dissimilar metals without electrical connections.

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OFB said:

Any chance there could have been an over zinc issue at some point? Be interested in seeing the damaged wood. Was there any white fuzz with a non salty taste too it present on that damage?

Oh so many questions.

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OFB said:

Art my written word is , bad !

On wood boats the anode sets up an electrical flow or current against the metals under water. Part of that will be through the hull. Over protetcion can damage the wood through this proccess.

Old wood boats get a chance to experience lots and lots of marine experts. Some upon seeing an issue will believe the addition of more anodes will solve an issue when in fact it unbalances the system.

Thats just way too simple of an explanation but my written word usualy just confuses.

My guess is there be several issues goin on within this vessel. It can be a bit of a game.

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