Replacing Bilge Keel Bolts

louisderry

louisderry

Well-Known Member
Joined
16 Oct 2012
Messages
146
Visit site
Hello all,

I currently have a fishing boat that has been totally gutted it is a bilge keel boat. The bilge keels were attached using m6 roofing bolts made from steel. They had rusted completely so I removed them all and dropped one of the bilge keels. I've rebedded the keel with a sealant and added m8 A4 stainless steel bolts with a 2p size washer - 14 in total. the orignal plan was to have squares of teak wood on the inside then a washer then a nut but due to the wood cracking when tighting the keel bolts iv'e decided to stick to bolts, washers and sealants only.

I can't decide if I should glass over the top of the bolts as well or if I should fibreglass over the keel on the outside also. Am I over cooking? obviously the keel needs be solid and withstand impact??

Will a good sealant /adhesive and m8 bolts be okay or should I glass ? :confused:
 
Last edited:
Glassing the bolts in is not a good idea as you will seal in any moisture. Best is to use good spec bolts and ensure the joint is well sealed against water ingress.
Personally I wouldn't glass over the keels externally but apply a decent paint system including blasting to Swedish standard 2.5 and immediate priming with zinc rich primer. You have the ideal opportunity to make a good job of it while you have the keels off and it should last many years.
 
Okay doke- The joint is definitely now well sealed and the ballast in the keel is concrete anyway my only real concern was making it hardy enough to take an impact if needed. I'm not sure if they were the original bolts but ethier way what's replaced them is definately stronger. :encouragement: the bolt heads will be well anti-fouled covered and wont be exposed.
 
Last edited:
I'm an ignorant Australian and not entirely, in fact not at all, sure of the installation

But there appears to be a contradiction

How can the bolt heads be well antifouled and also not be exposed?

Antifoul seals nothing.

Jonathan
 
i have steel bilge keels also a centre main cast iron ballast im also replacing the bolts whats recomended steel or stainless steel?
bolts are 140 mm long .
 
Niander said:
i have steel bilge keels also a centre main cast iron ballast im also replacing the bolts whats recomended steel or stainless steel?
bolts are 140 mm long .
Click to expand...

Digging around all that I can find was steel apprently has slightly more give than stainless (not sure on this though) and once stainless is below the waterline it will want to be covered anyway as it doesn't remain stainelss without oxygen.
All of which I can't confirm- need a further dig!
 
From the mention of antifoul I have a feeling that there may Ben some crossed wires here. Most sailing boat keel bolts are bolted down into the keel from inside the hull: they hold the keel in position using threaded holes in the body of the keel without going all the way through the length of the keel.
The OP seems to be indicating that he has through bolts holding what we might call stub keels in place. He talks about coach bolts: that is bolts which go right through the keel and take a nut on the end to hold the keel in place, hence the talk of antifoul and sealing them..... If I'm right, then I'd put sealant round the external end of the bolts as well as the internal end, just to make sure that water doesn't penetrate the bolt hole.
 
louisderry said:
Digging around all that I can find was steel apprently has slightly more give than stainless (not sure on this though) and once stainless is below the waterline it will want to be covered anyway as it doesn't remain stainelss without oxygen.
All of which I can't confirm- need a further dig!
Click to expand...

There is plenty of oxygen in seawater. How many propshafts corrode away? The big problem is stainless steel in wood that remains wet. In these circumstances the oxygen level is reduced considerably and corrosion is almost inevitable. I answered a question in last month's YM on this topic, in that case about chain plates (the same letter was in PBO but no answer was given). There are several examples on my website.
 
The big problem is stainless steel in wood that remains wet. In these circumstances the oxygen level is reduced considerably and corrosion is almost inevitable.
Yes but im wondering because mild steel will also rust in these condition but what will rust through faster stainless steel or mild steel?
 
duncan99210 said:
From the mention of antifoul I have a feeling that there may Ben some crossed wires here. Most sailing boat keel bolts are bolted down into the keel from inside the hull: they hold the keel in position using threaded holes in the body of the keel without going all the way through the length of the keel.

Many small bilge keelers have steel plate keels, these are normally through bolted through flanges welded to the top of the plate. My understanding is this is what the OP has - how else would they have been fastened on with 'roofing bolts'?


The OP seems to be indicating that he has through bolts holding what we might call stub keels in place. He talks about coach bolts: that is bolts which go right through the keel and take a nut on the end to hold the keel in place, hence the talk of antifoul and sealing them..... If I'm right, then I'd put sealant round the external end of the bolts as well as the internal end, just to make sure that water doesn't penetrate the bolt hole.
Click to expand...

FWIW my Trident built 1972 has ballast stub bolts threaded in to the ballast casting, and steel bilge plates held with 3/8 Whitworth bolts. All are glassed over inside, and are as good as the day they went in. Its a PoaJ opening them up to check, but we never get keel bolt leaks on Tridents, and the few that have had their bolts pulled for checking have been 100% intact. In fact the Owners Association would very much like to hear from anyone who has had trouble with them! We still dont know after 50+ years whether anything can go wrong with them! Not something I would want to do, but it seems to have worked well enough!

I would be wary of using even A4 stainless on a wooden hull because of oxygen deprivation causing corrosion, but in a GRP hull it seems to be OK.

I am a bit concerned that just using penny washers on the inside of the is enough. The keels can be subject to big sideways loading if they hull drags sideways across the ground round a swinging mooring on a rising tide, for example. Depending on the thickness of the hull lay up (assuming it is GRP, I would want to put in some means of spreading the load, perhaps using a steel plate inside stopping the bolts from bulling through. D pends how thick the hull is on the bilge.
 
Niander said:
The big problem is stainless steel in wood that remains wet. In these circumstances the oxygen level is reduced considerably and corrosion is almost inevitable.
Yes but im wondering because mild steel will also rust in these condition but what will rust through faster stainless steel or mild steel?
Click to expand...

When I installed 316 keel bolts in my wooden boat in 1992 I cleaned all the holes, painted epoxy in them and bedded the keel in polysulphide and canvas, making sure the sealant went around the bolts. Still there and no signs of weeping around the join or any leaks. Not pulled a bolt yet, but pretty confident they are still sound. The original mild steel bolts from 1963 were replaced in 1987 by which time they were perfect examples of how such things corrode - 2 came out in 2 pieces. The second set were already corroding in 1992.
 
Niander said:
The big problem is stainless steel in wood that remains wet. In these circumstances the oxygen level is reduced considerably and corrosion is almost inevitable.

Yes but im wondering because mild steel will also rust in these condition but what will rust through faster stainless steel or mild steel?
Click to expand...

My 1972 motor sailer has wooden bilges, a small wooden keel and wooden above-water strakes, all fastened with galvanised steel bolts. I am gradually replacing all several hundred of them, most of which are in a very poor state. However, none of the wood has fallen off after 45 years but many leak water into the boat.

The answer, as with all corrosion problems, is to keep the water out. Bed stainless steel bolts in plenty of sealant and/or epoxy and they will last indefinitely. The Blakes seacocks on my 1985 Sadler are held on with stainless countersunk bolts in sealant, every one of which is as new.
 
Admitting I know nothing of the design,

I was twitchy as the OP suggested his first thought was to use teak pads, between washer and hull, and they split - so he was dispensing with the teak and using large penny washers. Mention of hull material has been omitted but if new teak pads split and the hull is wood and old I'd then worry that the hull was strong enough to take the load with small washers, as someone has mentioned - large washers, or a long beefy strip drilled for each bolt, would be a better option.

My interpretation of the design is that the keels are boxes, with a flange for the bolts, and the box has been filled with concrete, which explains why the bolts are external. If the keel is off it would be easy to make up a long stainless strip with perforations to match the bolt holes for the flange on the keel (though it might need to be short strips to fit in the interior). Maybe instead of a long strip on each side, short strips from side to side.

If stainless is not the best answer for the bolts, and there seems to be conflicting advice? what is the alternative. Galvanised construction bolts?

Jonathan
 
Neeves said:
If stainless is not the best answer for the bolts, and there seems to be conflicting advice? what is the alternative. Galvanised construction bolts?

Jonathan
Click to expand...

I have never tried pricing larger bolts but fasteners in wooden boats nowadays are probably more often made in silicon bronze. Plenty available on Ebay. Adequate strength and excellent corrosion resistance.
 
I cannot think that a few bolts are going to be expensive - but its not my wallet.

But ignoring costs, silicon bronze or galvanised HT steel bolts. I'm sure that HT bolts can be adequate, or more so, strength. How would corrosion resistance compare - in this application.

Or is that 'how long is a piece of string' - galvanising can be variable??

Jonathan
 
Hello all , sorry been away for a few days. To confirm the boat is GRP and the yes the bolts don't come out of the keel itself like they would do traditional. There is is 14 m8 bolts scatted around the outside of the keel thru the fibreglass and not in the concrete.
I think i'm going to go down the route of cutting stainless steel strips as advised to add strength as the washers are not to bad but i'd rather get it sorted 100%. Shame as i've just come from Brighton and forgot about that stainless steel yard there where they have a large bin of stainless steel offcuts would of been ideal!

Thankyou all for the feedback/advice.
 
You must log in or register to reply here.

Share this page

Top