Fasteners

[starlightventure]

I am restoring a 1956 38 foot carvel planked yawl. Some of the original through hull galvanized carriage bolts have rusted the heads off. The rust went into the mahogany planking where the carriage bolts seat and caused some of the shoulder to become deteriorated and black.

Dose anyone know weather I should replace these galvanized bolts with bronze, Or would that be worse by setting up corrosion between the iron rust deposits in the surrounding wood ?

[Todd D]

If you replace some of the fasteners with bronze and leave iron in the boat you will accelerate the deterioration of the remaining iron. I would say either replace all the iron with bronze or stick with galvanized. Is the planking fastened with iron or bronze?

[starlightventure]

The planking is fastened with about 160 3/8 x 4" through hull galavanized carrage bolts with one 2 inch stainless screw on either side of said bolt about 400 of them. Mahogany planks 1 1/4 x 4". Five through hull valves are bronze. The stainless prop shaft is suported by a 1/8 x6"x24" stainless plate, fastened to the exterior hull wth stainless screws.

[Roger Cumming]

If there are only 70 bolts and 140 screws in the planking why not replace everything with bronze? This seems like a very small amount of fasteners for a 38' hull. As you are probably aware the stainless fasteners are not reliable below the waterline and should be replaced. 140 bronze #14x2" screws will cost only about one dollar each, but the 3/8" bolts in bronze would cost much more, perhaps $10 each. Would 3/8x4" machine screws work? They are much less expensive.

[starlightventure]

I have found hundreds of stainless steel screws below the water line. I called the last owner and he said they were installed 9 years ago. Upon removing these 2 inch stainless screws I can see that the condition is like brand. The screw slots are as sharp as a knife.

The few bronze screws would not come out, the heads broke off, the screw slots stripped out, they had to be drilled out.

Because of this find I have decided to replace 160 through hull 3/8 x 3 1/2 rusted galvanized lag bolts with 316L stainless. It is a low carbon superior metal made for salt water and much stronger than bronze.

I believe that the novice use of 18/10 stainless , the most common, with a higher carbon content that dose turn black and pitt in salt water has caused a miss conception on the superiority of this saltwater resistant metal.

From my observation I would only use 316L stainless to fasten a boat.