Iron Nails

I acquired a 30' commercial forestry cruiser built in '39 with iron nails. She's been partially refastened in the past but needs to be completely redone. My question is what to refasten her with? Hot dipped galvanized boat nails are still available and they did last a very long time on her first run, but they aren't intended for long life. It's a mystery that they did. As there's no easy way I'll be able to remove all traces of iron from her hull, so bronze screws are out. I've considered stainless, but below the waterline sounds like a recipe for corrosion as bad or worse than iron nails. Nails below the water and screws above?

 

Is this boat hooked up to shore power? If not then bronze would be my choice but very$$
I would go with US made galvanized nails heavily coated.

 

But again, with other iron still in the hull you'd have electrolysis with bronze screws added.

 

66 years ain't bad. Why start experimenting with new materials?

 

Can you actually get iron nails, as opposed to steel nails ? Pure iron certainly does not rust at anything like the rate of steel.

 

It depends on the steel. For example, manganese makes steel much more corrosion resistant. Pure iron was never available and it is not very good for nails.

 

Iron would be too soft for nails, I imagine.

 

Yes. Pure iron is more expensive than Monel or bronze too. I only see it in laboratory conditions.

 

Nails in 1939 would have been made from steel rather than wrought iron.

When the boat was built the expected useful life for it was probably fifteen or twenty years which meant iron fasteners would be satisfactory.

 

What are the conditions of the wood in the planks, particularly plank ends, and frames around the fasteners?

 

Wrought iron is approx.
Element Content (%)
Iron, Fe 99-99.8
Carbon, C 0.05-0.25
Phosphorus, P 0.05-0.2
Silicon, Si 0.02-0.2
Sulfur, S 0.02-0.1
Manganese, Mn 0.01-0.1

 

The nails I was thinking of were http://www.architecturals.net/boat-cut-nail-3-14-galvanized/

The boat is fir on oak. The planking is in pretty good shape considering the age, with only a few small areas needing replacement. There is some iron sickness to be sure. I intend to remove the interior to get at the hull, but so far have only found a few frames that are cracked.

 

Those nails are made by Tremont: http://www.tremontnail.com/
Tremont catalog page for galvanized boat nails: http://store.tremontnail.com/cgi-bin/tremontnail/items?mv_arg=32

 

The problem with ferrous fasteners isn't that they rot, but they also ruin the wood in the holes they live, during the rotting process. The surrounding wood becomes "infected" and there's not a lot you can do, except cut it out, replace with good, clean and solid material (dowels usually) and start again. If the fasteners weren't "working" too badly, drilling and plugging can be all it takes. It's a tedious and time consuming task, but worth it. If the fasteners have left egg shaped holes, you'll likely have other issues (oxide contamination, leaching, etc.) and much larger repairs need to be made. This type of fastener repair requires you use the same or similar species of wood for the frames AND the planking. For example, if she's cedar over oak, you'll need oak for the frames and cedar for the planking. It's a pain in the butt, though the right way to do it.

This is a common set of issues to contend with, so have a pro look her over and pull some fasteners to get a good idea of what you're working with. With some luck, you have some really bad spots, but mostly just some repairs and refastening.

 

A shipwright told me to not bother with digging out at the old nails but just sister them with new holes and fasteners. It's not exactly Bristol, but this is an old work boat, not a rare Herreshoff mahogany schooner. If she doesn't last another 70 years that's okay, she was only designed to last 20.

The only possible way I'd consider drilling out the old nails would be to use a narrow hole saw and cut out the entire nail and iron sick area and glue in a trunnel. But with such light construction as this boat was made, I would be worried that even glued, drilling fairly large holes through the frames would weaken them too much. I'm not sure it's been done on a boat of this size so have no idea if that's feasible. I like the idea to get rid of all the bad wood and those rusty fasteners, but drilling them out, gluing in new wood plugs, and then drilling for fasteners and plugging them, is too much work.