Keel bolts - mild steel or stainless?

[Guest]

Keel bolts - mild steel or stainless?

If replacing keel bolts, what are the pros and cons of fitting stainless steel rather than mild steel, does anyone have a view?

 

[tony_brighton]

Thought stainless had to be in air to avoid corrosion

 

[WayneS]

My Westerly 22 which i sold recently has SS bolts into mild keels. 35 years old and they were still great. Had them x-rayed a few years back and they were still in good nick.

Don't know if this helps.

Wayne

 

[brianrunyard]

Same here, lack of oxygen = Crevice Corrosion!

Brian
http://homepage.ntlworld.com/brunyard

 

[Guest]

Have you thought of bronze, similar on galvanic scale to S/S but no crevice corrosion or fatigue. On the other hand most galvanised mild steel bolts seem to last many years as long ast the keel joint is good so is it worth the expense (ie the ones on my folkboat are 40 years old and still fine)

Roly, Voya Con Dios, Glasson, Lancaster http://www.voya.pwp.blueyonder.co.uk//MW1/Intropage.htm

 

[Dipper]

I wouldn't use mild steel. High tensile steel is much stronger. Think of the loads on the bolts as the boat is heeled in rough water.

I changed mine using high tensile steel studding and it was very cheap. Go to a specialist nut/bolt supplier or an engineering firm. When fitted, cover the exposed heads/nuts with layers of car body underseal. This is very cheap, flexible and 'self healing'.

 

[oldharry]

Westerley used stainless on many of their boats, and I have not heard of any failures - but perhaps someone knows different?!

However, Stainless is prone to crevice corrosion when oxygen is excluded, and can fail remarkably quickly - so what was Westerleys formula?

Be aware too that there are several different grades of S/S, and if you use it you must use the right one - ENJ 316 for example will rust out in no time, but I daresay one of our engineers will tell you whether you need A2 or A4 grade - or whatever. Importantly the type normally sold for fastenings in the Chandlery are lower grade, and could have problems underwater.

Another argument against stainless is that it will not tolerate flexing, and fractures very quickly. I know you are not in the habit of running aground, are you? But if you were doing a bilge keeler, the pressure on the keels each time she takes the ground can cause premature failure.

Again - how did Westerly get round that one? Centaurs keels can flap about like a Seagull in a F7 when they get older, but I have yet to hear of S/S keel bolt failure on them.

Mild or HT steel needs to be fully protected, either by heavy galvanizing, or by some sort of coating, otherwise you will be doing it all again in a few years time.... Also, being the same material as the keel, there wil be no galvanic problems asssociated with dissimilar metals.

 

[chippie]

Here in NZ we have just had the rescue of a solo sailor from a couple of hundred miles out into the Tasman sea after he lost his keel. I must try to find out how it was fastened. The funny bit is that the Taiwanese fishing boat that picked him up wasnt going to be in port for five weeks. It was finally arranged for the navy to pick him up from the Taiwanese boat.
I'm not sure if HT bolts can be galvanised--doesnt the heat upset the strength?
I have read lots of warnings against stainless keelbolts but the use of them seems to be fairly widespread.

 

[boatmike]

Please don't use stainless steel below the waterline. I know it has been done and some yards have done so as original equipment and got away with it but previous correspondents are absolutely correct. It can suffer from crevice corrosion. Your options are. Carbon steel heavily galvanised (cheap) Bronze (expensive) Monel (also expensive) Most situations also allow for encapsulating the bolt with liberal amounts of sealant on fitting which is probably the only reason most people get away with stainless screws on skin fittings.