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Keel bolts in Stainless Steel, Oh. No!!!

No No No No !!!

I, together with many others, read with some horror the stories of owners fitting so called wonder metal, 'Stainless' bolts

Stainless steel, in any grade or form, must never be used as a fastener, under water. Stainless is only stainless, i.e. corrosion free, if it is surrounded with Oxygen. No matter what grade of stainless!!  In the oft times damp, wet environment of boats and their keels, this is not a good place to be for S/S.  On Deck OK.

I have three S/S bolts that were extracted from a members boat, after one of my earlier articles. They are very badly corroded away, in just three years. I have seen S/S bolts that have looked as if a worm has crawled through them!! They also suffer an unseen corrosion, a crystalline break up of their structure, only detectable by X-ray.


Type 316 or A4 Stainless bolts after 3 years!!!

Did you know that it rots twice as fast as cast iron if just left on it’s own in a water sodden timber?

An owner once fitted these and claimed that when removed the amount of corrosion was minimal, however how does he know when that visible corrosion started? I bet it was a week last Tuesday, and by next year the keel falls off! Alarmist! Not a bit of it!! If you want to go looking for it, there is a cast iron keel just off the baffle at Bradwell, fell off an E-Boat when the S/S bolts rotted through!! Age of boat, less than 10 years!!!

Wisely the owner has decided to replace his bolts with the best material for the cast iron keel, mild steel, galvanized if you like, to give a bit of protection against ordinary rusting, and coated in grease and mastic sealant too.

Just to end this, and to put my money where my mouth is, I drew two of my own bolts this winter. I chose the easiest to get at, and the most difficult, because that’s the one a surveyor will ask to see!

After failing with a standard spanner, I purchased a ¾ drive tommy bar and socket, then with the help of an extension on the handle, got enough leverage to shift them. They are of course mild steel, galvanized. They came out as shiny as the day they went in, during the building of ‘Fiddler’s Green’, about 15 years ago. They have done 11 seasons afloat, plus a couple of winters too. Next year I might pull another couple, but in the meantime I am more than happy.

I appeal to all owners to check their bolts, 10 years is a normal period between checks, a little birdy tells me that there are some out there that have not seen the light of day for 25!! What faith.

Just to re-iterate, with a cast iron or steel keel or even steel box and concrete, Mild steel bolts, galvanized.

For lead keels, bronze, (or if wealthy, ‘monel’ metal.)

Please no suspect keels on our boats!!

John Williams,


In our 2006 refit we, or rather my crew and helper, Keith, removed another keel bolt, came out with a bit of grunt, sticky mastic!!  Bolt and threads like new!  Mild Steel Galvanised, 15 seasons use!  We have removed a different keel bolt every couple of years for the last 6 years.  All are good.


The bolt removed from Fiddler's Green.




Here is Alan Lonton with a freshly drawn iron bolt from his WW 'Bonita', launched 7 years ago.

The bolt was weeping water into the boat slightly, so has been wet and in drawing it to reseal it we can see there is not a mark on it, it will go back as it is, resealed in more mastic! What price a Stainless bolt in those circumstances??

John, April 2007



                            As an addenda, here is a reply I posted on the Forum in November 06.  Might help others.



Removing the bolts from the bilge keels should be relatively easy, they are normally dome headed coach bolts and provide they are not badly rusted away, a good clout from the inside should have them out.

I take it you are going to have the bilge keels either remade or re galvanised.. either way when refitting use a good boat mastic, I recommend SikaFlex, and I would coat the keel and the bolts in Epoxy to prevent water getting at them and provide an insulator for the copper based anti foul we use. This will prevent electrolyse between the different metals.

The main keel might be more difficult, only because the bolts go through a deeper, thicker timber section. rusting on the bolts will cause them to jam.

I had tapped some bolts and they have shot out the underside, others I have bashed for hours! Bear in mind the boat needs to be high enough off the ground and the bolt heads not obstructed with chocks! Spent hours once bashing a bolt against the trailer it was sat on! shuffled the boat 2 " and the bolt fell out!

If they stick and you are drifting them out with a bronze or Stainless bar, ( often a bit of old prop shaft!) The top end of the old keel bolt might open up... To get round this I have centre punched a mark in the middle of the end of the old bolt, then drilled a 6 mm hole down the middle of it for an inch or so 25mm. This allows the keel bolt to collapse on itself, rather than swell out.

The bolts should have a clearance round them in the timber, filled with mastic.. If they have they will come out OK.

I had one set that had no clearance and the slightest rusting caused them to stick! Took me months to 'persuade' them out. Made a puller to fit round the other end eventually... once I had bashed them far enough to see the other end!

When refitting do not be tempted to use Stainless. It will rot twice as fast as cast iron if it gets wet!

No, with a cast iron keel used galvanised steel, with a lead keel either Monel, (if you could afford it) or more commonly bronze.

If you are removing bolts use it as an opportunity to increase the ballast. The E24 should have a minimum of 1020lb, the E26 1660lb, but 2000lb is more like it! Bear in mind bilge keels (Side keels) will also have to be slightly deepened to allow the boat to sit approx upright ..

Bilge keels should be about 2" shallower than main keel. This allows weight to be always taken by main keel.

To add extras keel weight, Steel plate 25mm thick, flame cut to shape, slightly undersize so it can be faired off with epoxy putty, is the easiest way these days.

Can I just add Paul, that there will be timber blocks beneath the keel in the recesses in the cast iron, these can be prised out or they will simply come out as you start to drive the bolts down.

As it is leaking and 35 years have elapsed, I would expect at least one to be rusty. They should be 5/8th bolts in 3/4 inch holes, if they are you have a chance! my first set were 3/4 in 3/4 holes, what a pain!

Those are the ones that some had to be fought every mm of the way, with a special made puller at the end, turning 4 threaded bolts in a flat plate, pushing up against the bottom of the keel, to remove them. In some respects I was lucky, as there was a nut on the underside I could remove to get my plate in....

Needless to say when I refitted the bolts I made then 5/8th as per the plan, in those 3/4 holes! To my knowledge they are still there, mild steel galvanised, sealed in Sikaflex! no leaks!

Hope this helps,