Wooden Boat People
By McKenzieDriftBoat.com
another screwy question for the restoration experts
hello again. I'm a former engineer, I tend to worry about the small details. I'm also an experienced carpenter that's done lots of weird remodels involving lots of rotten wood and fasteners so I know how I'd normally deal with this situation but the things I normally build don't have the constant mechanical stresses that a boat has so failure is less likely and has less potential for tragedy.
The issue I'm writing about is that most every screw in my boat is corroded, some to the point of being almost gone, and most every screw hole is surrounded by soft wood. The boat is a 25-30 yr old Tatman 16x48 that's in overall good shape. I've recently finished getting the chines off, none of the screws were holding it to the boat. Only the sealant/adhesive was keeping the chines on but it's some tenacious stuff and those chines were going no where so I'm guessing this is the 3M 5200 (reminds me of pink erasers). From what I can tell, once this stuff set up the only thing the screws were doing for the chine was promoting rot. If I didn't need to remove the chines for other reasons I think I could have pulled the screws, plugged the holes with epoxy, and called it done. Now I'm pondering the screws from the bottom into the frame. Many are so far gone that there's no way I'm getting them out so the only choice would be to put new screws in place next to the old ones. I'm worried that this my cause problems since too many screw holes into these small frame pieces may promote cracking. It appears that this pinkish sealant was used for the rest of the boat so I'm wondering if I need to worry about these screws. I'm guessing they haven't been holding anything together for a long time and there appears to be no problems with the wood separating so maybe this 5200 is doing what needs to be done and there isn't an actual mechanical problem here but rather only my dislike for corroded screws that's the issue.
So...would you worry about replacing them? If they need to be replaced then I'll also need to be carefully fill each hole with epoxy so there's something for the screws to hold on to. Another option is to leave the screws and drive ring shank nails where I have good wood. Perhaps I should mention that I will be sealing the entire bottom in epoxy once this is done.
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Replies to This Discussion
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Permalink Reply by Rick Newman on
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Jeff, I haven't seen nor heard of any pink adhesive therefore I cannot comment on that. I often peruse the WoodenBoatForum.com and remembered something about wierd things happening with screws in wood. Here's what I found.
"The phenomenon is referred to by shipwrights as ‘iron sickness’ or ‘nail sickness’ It is particularly
serious on oak and teak-hulled vessels (e.g., the Edwin Fox in Picton). The
chemical interactions between ferrous metals and timber are complex and not
well understood. There are all sorts of factors involved, including the possibility
of galvanic cells being set up between one end of a fastener embedded in wood
and the other end exposed to the atmosphere, especially when chloride ions
are present. Acid timbers (e.g., teak) are more prone than neutral timbers (e.g.,
kauri). For some inexplicable reason the less susceptible a timber is to fungal rot
the more likely it is to suffer from iron rot. Rot fungi seem to have an inhibiting
effect on iron rot. There is only one way to control iron sickness, and that is to
stop the iron corrosion. Either remove the offending fixtures and fasteners, or
coat them with some corrosion-inhibiting substance."Here's a link to the place I found it.
http://forum.woodenboat.com/showthread.php?88931-restoration-adheri...
Something else I found was from Bob Smalser a highly repected boat builder, gun restorer, etc, that said you can either deal with the rot now or later. His concept was to either remove the offending metal or seal it in with a really good sealant.
A common method often mentioned is to remove as many fasteners as possible and epoxy in a plug providing a new, fresh material to refasten. When it proves difficult to remove the screws some folks fashion a cutter from tubing with a couple of teeth ground into the annulus. since you are dealing with soft woods it is pretty easy to drill around the offending fasteners to remove a plug of rotted wood. Then you can repeat the process of plugging and epoxying in fresh wood.
I have not yet tried these techniques but the reports and pictures I observed on WooodenBoatForum showed success. It won't be much fun but it seems like a reasonable manner to restore your old boat and prevent further rot damage. I have just started a repair of a Sawyer Light Oar. It had apparently had a rubber "boot" over the tip. Under that boot there must have been some damage and water was trapped and a great location for rot was formed. several inches of the Douglas Fir suffered from rot, It seemed to be stopped by the glue between the lamination and traveled through the cells of the wood for an inch or two. As I cut the oar apart I found that the rot had traveled to small pockets not connected directly to the rot. My point is there can be hidden pockets so look carefully.
Something I observed one of the "old" pros A.J. DeRosa do is to sister a new frame member next to a questionable one and then attach the screws into that one.
I hope this information helps, you might use the search function to see if there is any useful information hidden in previous posts. One thing about the search box is you may have to ask the question several ways to find answers. I sometimes find the longer the phrase I put in the better the results.
Good luck,
Rick Newman
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Permalink Reply by Jeff Gent on
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thanks for the info. I know some woods are hard on metals, cedars especially which are also rot resistant so that go with the above, but I'm guessing the corrosion in this case is from salt water since the corrosion for some screws is so extreme that the screw is almost completely gone and these are the ones that were under a UHMW shoe where any salt water could not be rinsed off.
I also have a pair of old oars with very rotten tips caused by those rubber tip protectors that trapped water. I'm pondering using Coat-it on the tips of my other oars but have wondered if that would do the same thing.
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Permalink Reply by Randy Dersham on
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Hello Jeff,
I'm pretty sure that "pink" stuff is 3M 5200 in the color they call tan. That is what came with my Tatman kit in 1996.
For the bottom, I agree that if the bottom is solid then the 5200 is doing it's job and you should not have to replace anything if there is no rot other than the screw holes. I'd recommend that you remove the screws, drill out the soft wood with a tapered drill, then fill the hole with a tapered plug and epoxy.
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You'd be the one to know, thanks. I said pink, but it's not brilliant pink...more like the color of classic pencil erasers.
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Permalink Reply by Phillip Westendorf on
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Jeff,
Here's a link to a Hollow Screw Extractor, it should work to remove the bad screws. Then do as Randy suggests.
http://www.highlandwoodworking.com/set3hollowscrewextractors.aspx
G'Luck
Dorf
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oh no....another tool that I just HAVE to buy. I hate it when that happens. Thanks for the link, some of the screws have enough solid material left that my easy-outs have been working well but I'll need something like this for the rest and I'm guessing I could find lots of uses for these in the remodeling work I do. They're basically mini hole saws with no guide drill. I've used hole saws before without a guide bit, almost impossible to make a clean hole, so I'm thinking I'd also want one of those jigs for turning a hand drill into a mini-drill press.
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Permalink Reply by Rod Anderson on
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one way to guide a hole saw without a bit is to drill a hole of the same diameter through a piece of plywood, maybe 6" X 6", clamp the piece of plywood so the hole is over your 'target' and drill away. worth a try...
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