burgundyben
Well-known member
Perhaps easier to cast a new keel?
Boring studs out of a cast iron keel
- Thread starter mog
- Start date
Leonidas
Member
Why try to re-invent the wheel and risk loosing your keel at sea?? It is not a big job to lift the boat and remove the keel to a proper machine shop that can drill out and remove the old studs and have new ones made to fit the existing holes in the hull. Even if the boat is on a concrete stand, you may be able to drop the keel by digging the ground sufficiently in way of the keel. 600 kgs of keel is not beyond the capacity of a fork lift truck and a transportation trailer.. Suggest you use a marine quality stainless steel for the studs and when fitted on the boat you encapsulate them so that the bilge water is kept out of the theaded part. Also ensure you use a good sealant for the joint between the bottom of the hull and the upper section of the keel. Trying to drill out, machine etc in situ is a lot more time consuming , expensive and with dubious results. Adding extra holes in the hull to relocate the studs, you will only be weakening the area which is designed to carry the weight of the keel ( even if you plug the old holes)
ghostlymoron
Well-known member
I would check what the existing studs are made from before replacing them. If mild steel replace like with like as crevice corrosion can cause problems with stainless.
See link to Vyv Cox's website http://coxengineering.sharepoint.com/Pages/Crevice.aspx
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Norman_E
Well-known member
The OP says they are cast in J shaped studs.
A question for Vyv Cox. As studding is generally available in mild steel, bright zinc plated, would you use that or insist on un-plated steel?
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vyv_cox
Well-known member
I cannot think of any reason why not, except that the zinc plated stuff will undoubtedly be mild and therefore the weakest available. Black steel may well be stronger, although strength is rarely an issue I think. The vast majority of boats nowadays have stainless steel keel bolts, I suspect so that it is always possible to withdraw them, unlike steel ones which could rust in to the keel.
As with all bolts, no matter the material, they rely on being dry in situ. The sealant applied before bedding is critical.
30boat
N/A
I'm curious.How does the OP know for sure that the studs are J shaped and not regular threaded rod?I always thought that casting J shaped studs in was done with lead keels because the softer metal wouldn't be strong enough for threaded studs.
mog
New member
Thank you all for contributions so far.
Where we are now;
Casting a new keel will cost at least £2000 and why go to all that trouble?
I will not be entertaining any DIY solution and have found a Steam Railway engineering business in Devon who have agreed they have the kit and skill to do the job.
J studs; I was advised by other owners of MARCON yachts that this was the method used in production but I dont know this for absolute certainty. In any event I will be attempting to unscrew the studs before taking the keel to Devon. If my info is wrong and they unscrew then I will replace them with 316 stainless 1in BSW (Vyv Cox, are there any issues I need to be aware of with the dissimilar metals in contact?) or black steel if the consensus of advice is that way. If they do not unscrew or snap off in the attempt then the steam engine folk get their chance. I Am thinking that we should look to just clear the old threads and retap with either M30 3 coarse thread or 1 1/4 BSW depending on availability and clearance hole size?
Furthwer comments or suggestions on this plan are most welcome
I will be sandblasting and priming the repaired keel and am aware of the need for speed in this process to avoid instant iron corrosion. What type / brand of primer would ppl recommend?
Finally for the bedding sealant I have had mant differing views. What is the tried and tested preference of the contributors here?
Thank you all again and I finally feel like i am closing in on the answers to this awkward problem.
Nick
MOG
vyv_cox
Well-known member
The only issue with dissimilar metals is keeping the water out. The vast majority of boats use 300 series stainless steel keel bolts, although I am not certain that it is 316, or even if that is strictly necessary. I would screw them into the keel using a sealant, rather than an adhesive, in case they ever need to be withdrawn again. When refitting the keel to the boat use plenty of sealant to cover the keel surface and provide a water-tight joint. I cannot advise the best sealant for this as I suspect it is quite specialised, I would consult with someone who does it frequently.
superheat6k
Well-known member
For bedding i would use a polysulphide mastic, on my first boat we used 6 tubes of boatlife then watched at least three of them squidge out as the joint was pulled up. Sadly boatlife is no longer available.
When the joint is pulled I would aim for a gasket around 3-4mm thick left, so place some rubber spacer pieces of this thickness in a few positions around the top surface of the keel, and the spread a generous layer of mastic right around these to prevent you pulling the joint up too much that too much mastic gets squeezed out. Pull up with a light firmness then allow several days for the mastic to cure. Check with the mastic makers that it will set in this situation.
When the joint is pulled I would aim for a gasket around 3-4mm thick left, so place some rubber spacer pieces of this thickness in a few positions around the top surface of the keel, and the spread a generous layer of mastic right around these to prevent you pulling the joint up too much that too much mastic gets squeezed out. Pull up with a light firmness then allow several days for the mastic to cure. Check with the mastic makers that it will set in this situation.
mog
New member
sealant
I just pulled this from a suppliers website about mastic sealants. Thanks for the lead and application advice.
Nick MOG
Polysulphide (Polymer) sealants
We stock a small selection of alternative but equivalent polysulphide (sometimes known as polysulfide) mastic joint sealants. There are newer technology polymer-based alternatives these days such as Modified Polymer (MP) & Modified Silane (MS) mastic joint sealants available, and although polysulphide sealants are still sometimes specified, the majority of end users will accept polymer-based mastic joint sealants as a newer alternative and agree that this technology is superior.
I just pulled this from a suppliers website about mastic sealants. Thanks for the lead and application advice.
Nick MOG
Polysulphide (Polymer) sealants
We stock a small selection of alternative but equivalent polysulphide (sometimes known as polysulfide) mastic joint sealants. There are newer technology polymer-based alternatives these days such as Modified Polymer (MP) & Modified Silane (MS) mastic joint sealants available, and although polysulphide sealants are still sometimes specified, the majority of end users will accept polymer-based mastic joint sealants as a newer alternative and agree that this technology is superior.
mog
New member
Thank you yet again Vyv.
I am reassured that my amateur plan should produce a professional repair and hopefully extend the life of my yacht another 40 years when properly executed.
I forgot to also mention in my previous summary that I have taken the advice about 3 times stud diameter as depth of bury and have advised the Loco engineers that a bore of 4 inches or 100mm will be required.
M30 coarse threaded bar is probably easiest to find but if the Steam guys can make in BSW more easily and cost effective then that would suit too.
I will photograph and video each step of the process so hopefully those who follow this path at a later date can benefit from the collated wisdom I have been so grateful in receiving.
Nick
MOG