Galvanised or SS bolts?

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hhummeli

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I am fixing my sail boat from 1949 which has mahogany hull on galvanised steel frames. My problem is the chainplates which are SS which are originally fixed to the hull with galvanised rivets which go thru the galvanised frames. There is oak frames in the middle of the galvanised frame and the chain plate to keep them separated.

Question is: should I use galvanised bolts (quite hard to find) or change them to SS? They are all above waterline and therefore they don't get in contact with water.

hh

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They don't come in contact with the water until they do, such as when you are on a screaming reach and the deck is just touching the surface of the water. However, they are in a position where they can be easily withdrawn say 12 months after installation so that you can see if there has been any degradation. If there hasn't, you're home free. Don't forget, it's not the heads that you have to be concerned about, but the parts of the bolts which are buried in the structure of the hull.
Peter.

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If the stainless is electrically separated from the galvanised frames I would go with stainless.
stainless is more noble than the zinc galvanising.
How long had the rivets been in use and how bad were they?

If there is an electrical connection I would opt for zinc as galv bolts are relatively inexpensive and hopefully would corrode before the frames as they would get some splashed seawater.

Galv bolts are widely used in outdoor construction, try to find a supplier to the building/construction industry. Make sure they are hot dipped.

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Hi,

I just had a horrendous failure of a 10mm 316 bolt that held a step in my cargo space. The step is of course not critical, but the way the bolt failed was an eye opener. I always knew that SS is a crappy material, but that was the final straw.

I am replacing all critical fasteneings with mild steel, 8.8, or 12.9 depending what strength I need.

Then I use plenty of grease or anti-seize compound, wrap in cloth or off-cuts of cordage drenched with plenty of grease and cover afterwards with another layer of cloth painted with tar emulsion. My boat however is not a "yacht" but a "workboat" and looks and shiny things dont interest me, just strength and safety.

regards ongolo

<hr width=100% size=1>So what......... it floats
 
Thanks for the replies.

The galvanised rivets were mostly in good shape. The ends - which some brave men hammered in 1949 - were quite badly corroded. Also the other ends on some of the rivets were partly rusted under the bungs and in future I don't like the idea of rust within mahogany planks. The steel frames are still ok.

The bolts will be in contact with the steel frame since it is quite hard to insulate the bolt from the frame.

Good thing with this problem is that it will be quite easy to check the new bolts: just take the bung away and remove the bolt. I may go with the galvanised if I can find some good hot dip ones.

hh

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Another choice?

Our (external, galvanised steel) chainplates are secured with bronze bolts which pass through the teak planking, the oak frames, and the galvanised wrought iron hanging knees. In the case of the top bolt this also passes through what we British call the shelf and what the Americans call the clamp. The nuts are hardened up on bronze washers against the iron knees.

This arrangement was suggested by the late Peter Brown, a vastly experienced designer of wood yachts, as a replacement for the original mild steel galvanised bolts, which were fitted when she was built in 1937, and which were pretty nasty.

Yes, I know it is a mixture of metals, but there are two points to consider:

1. The area is usually dry, unless sailing with the rail under, which we do, but not for 95% of the boat's life!

2. Much more important - the less noble metal, the galvanised iron, will corrode in preference to the more noble, and since there is more iron than bronze some wastage can take place before any ill effects are seen. In practice, this means that the first sign of trouble is a rust weep on the topsides (easy cure, take the chainplates off and re-galvanise) not the sudden failure of a hidden bolt.

<hr width=100% size=1>Que scais-je?
 
If you want to go with galvanised bolts, we bought loads of galvanised bolts, washers, nuts, all-thread & screws from a company called Bunner Galvanising. They were always very helpful, prices very reasonable and the quality of galvanising was great.
Bunner Galvanising, Bentinck St, Liverpool L5 9TR
Tel: 0151-207 0081
Fax: 0151-298 2929


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<A target="_blank" HREF=http://www.davey.co.uk/>Davey</A> do galvanised fasteners amongst other interesting stuff, but they only sell to trade, so you'd have to chat up your local chandler, or pretend to be one yourself

cheers,
david

<hr width=100% size=1>What we are dealin' with here is a complete lack of respect for the law....<P ID="edit"><FONT SIZE=-1>Edited by penfold on 08/06/2004 13:18 (server time).</FONT></P>
 
Hi again and thanks,
I will be looking for galvanised bolts but I need to find them a little closer than from UK since I live in Finland.

Since the chainplates are inside the hull and visible the ends of the bolts and the nuts are easily checked. It will be a nice experiment to connect a voltmeter between the bolt and the chainplate. Luckily the Baltic Sea's water is not as salty as the Atlantic so the corrosis will be quite slow. Also the chainplates will only in very rare instances be under the water due to the high freeboard. Biggest challenge will be chainplates holes (3 on both sides) in the covering board and how to get them watertight.

hh



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a footnote, re bronze bolts

I clobbered the port aft chainplate getting off some scrubbing posts singlehanded - it caught on the post, with the momentum of nine tons of boat moving at at least a knot and a half - and unsurprisingly it got bent.

What I had not noticed until I asked Mike Illingworth of Robertsons to look at it was that the upper bronze bolt had been pulled. All I saw was a slightly bent chainplate, but Mike pointed out that the slot on the head of the bolt had closed up somewhat, as the bolt deformed under the shock loading.

I reckon a lesser material might have snapped within the wood, invisible, but the bronze just str.e.t.c.h..e...d!

As it was, since I had not noticed the damage, we went in for a race, followed by a season's fairly hard sailing...

<hr width=100% size=1>Que scais-je?<P ID="edit"><FONT SIZE=-1>Edited by Mirelle on 10/06/2004 12:22 (server time).</FONT></P>
 
galanised! stainless does not like being surounded by wood they will break.galanised will rust but slowly youll have years of security give them a coating of galanised paint and put some polysulphide compound in the hole befor the bolt goes in probably last forever! and galvanised bolts can be found everywhere

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