Galvanised bolts

[MM5AHO]

Speaking as a galvanizer....
As has been said, beware electroplated zinc. It's likely to have about 5 microns of zinc versus about 50 on hot dip galvanized.
And then there's centrifuge hot dip and non-centrifuged materials. The difference again is thickness of zinc.

Generally the life expectancy is proportional to thickness of zinc.

As to threaded rod versus bolts: If you cut the end of threaded rod to get length right, you'll have a steel exposed end. While there'll be some protection from circumferential zinc, in a marine environment this might not be enough.
Threaded rod is almost certain to be centrifuged.
Bolts also likely to be, but if you buy black steel (uncoated) then get them galvanized without centrifuging, and then use a die nut to remove surplus zinc that will block the threads, you'll have the thickest galvanizing normally available. If you don't get galvanizing done much, give these to a friendly fabricator to gain from their buying power and to avoid minimum changes.

 

[NormanS]

Speaking as a galvanizer....
As has been said, beware electroplated zinc. It's likely to have about 5 microns of zinc versus about 50 on hot dip galvanized.
And then there's centrifuge hot dip and non-centrifuged materials. The difference again is thickness of zinc.

Generally the life expectancy is proportional to thickness of zinc.

As to threaded rod versus bolts: If you cut the end of threaded rod to get length right, you'll have a steel exposed end. While there'll be some protection from circumferential zinc, in a marine environment this might not be enough.
Threaded rod is almost certain to be centrifuged.
Bolts also likely to be, but if you buy black steel (uncoated) then get them galvanized without centrifuging, and then use a die nut to remove surplus zinc that will block the threads, you'll have the thickest galvanizing normally available. If you don't get galvanizing done much, give these to a friendly fabricator to gain from their buying power and to avoid minimum changes.

That was what I did, when I needed lots of bolts, for an old wooden fishing boat conversion.
(For clarity, black bolts, and got them galvanised).

 

[Roger Bailey]

Not quite sure what black steel is but The Real Wrought Iron Company can supply round wrought iron bar. I got some 1" to make new keel bolts for my boat which has a cast iron ballast keel. A local blacksmith forged the counter sunk heads on one end and I wormed the threads myself. I didn't galvanise the bolts but gave them a couple of coats of metal primer. When inserting the bolts I greased them well and once they were started up into their holes I poured a little liquid rubber compound into the top before driving them home. The new bolts were a good tight fit and I hope that the rubber compound has filled any gaps. I think they should be good for 20/30 years.

 

[sideshowbob]

Was that expensive? I was going to have a go at replacing the bronze keel bolt we have in our cast iron keel that is causing some deterioration to the oak floor that it passes thro'. I suspect that originally the builder knew exactly what he was doing but this particular bolt is the easiset to access and hence has been in and out a few times by various yards to appease the the standard survey report line of 'draw keel bolts for inspection'. Its probably not insulated from the iron anymore and causing an issue at the top end. The oak floor will need replacing as well. not looking forward to this and I havent been impressed by any of the galvanising I have seen of late so was a bit concerned as to what to use.............. All the other bolts and associated structure look OK otherwise.

Not quite sure what black steel is but The Real Wrought Iron Company can supply round wrought iron bar. I got some 1" to make new keel bolts for my boat which has a cast iron ballast keel. A local blacksmith forged the counter sunk heads on one end and I wormed the threads myself. I didn't galvanise the bolts but gave them a couple of coats of metal primer. When inserting the bolts I greased them well and once they were started up into their holes I poured a little liquid rubber compound into the top before driving them home. The new bolts were a good tight fit and I hope that the rubber compound has filled any gaps. I think they should be good for 20/30 years.

 

[Tranona]

Was that expensive? I was going to have a go at replacing the bronze keel bolt we have in our cast iron keel that is causing some deterioration to the oak floor that it passes thro'. I suspect that originally the builder knew exactly what he was doing but this particular bolt is the easiset to access and hence has been in and out a few times by various yards to appease the the standard survey report line of 'draw keel bolts for inspection'. Its probably not insulated from the iron anymore and causing an issue at the top end. The oak floor will need replacing as well. not looking forward to this and I havent been impressed by any of the galvanising I have seen of late so was a bit concerned as to what to use.............. All the other bolts and associated structure look OK otherwise.

Think I would use 316 stainless and ensure the hole is lined with a good sealant. I did this on my wooden boat after both wrought iron (original) and mild steel pitch coated both failed. The former lasted 20 years but all waisted where they went through the oak keel - one came out in two pieces! and the latter showed the same trend after 12 years. current bolts Actually 20mm bar threaded each end) have been in since 1992 with no sign of likely failure. Used polysulphide for sealant.