Keelbolts Swan 41

I am intending to purchase a swan 41 to replace my steel cruising boat of 20 years ownership from new. I am confident that all important points on what will be a 30 year old boat can be evaluated by a surveyer, however there is one area that concerns me. I believe that the keel bolts were stainless steel cast into the lead keel. Lead and stainless will form a galvanic couple that will corrode the stainless, especially if there is not much oxygen to replace the oxide layer. I think that there is a chance that the stainless bolts will get pitting and crevice corrosion just where they leave the lead. Unfortunately there seems to be no way of checking this except by removing the keel completely.

   Have any of the Swan owners ever removed the keel on their boats? If so what was the state of the keel bolts? Has anyone else ever had concerns on this point, and has anyone devised a means of inspecting the bolts? ( Do they unscrew from the lead?)

Cosmo Little (Falmouth, UK)

I had the same concerns when considering the purchase of my 1969 vintage Swan 43.

I did receive keel boat dimension, embedment and torque data from Nautor's techincal department.  Visual observations of the keel bolts inside the bilge was impossible due to the bolts covered with fiberglass and resin. I had the surveyor conduct a torque test on two random keel bolts I had exposed from the fiberglass and resin and they did not turn at the specified torque setting.  They were also sounded with a hammer and sounded OK.

 Visually from the outside the keel and keel/hull joint did not reveal any obvious distress.

My surveyor felt confident enough that the keel bolt design and specs were still adequate and I purchased the boat.  Short of dropping the keel I believe there is no good way to check the bolts.

All of this also is dependent on how hard a life and any groundings the boat may have experienced.  Dropping the keel on my boat would entail removing all water tanks (easy job) in the bilge and the mast step (not so easy).

If you are trying to establish a budget for this work you can contact Jamestown Boat Yard in Jamestown, Rhode Island.  They have quite a bit of experience with older Swans.

Good Luck

Hiro

Cosmo, I have a 411 from 1977. Fours years ago I took off the keel to inspect and carry out some repairs to the fairing / sheathing etc.

On the 411 you need to remove the engine as one keel bolt is under it. We found absoltely no problems with the keel bolts. We did find that some diesel had soaked into the surface of the grp layup around the bolts in the bilge so took the opportunity to clean this up and replace the effected GRP layup.

We then replaced all the mastic seal between the keel and hull stub and replaced the sheathing which covers the keel joint. This is constantly splitting on the 411 at the front of the keel but is only cosmetic. 

The job took five days.      

Cosmo, I have a 411 from 1977. Fours years ago I took off the keel to inspect and carry out some repairs to the fairing / sheathing etc.

John and Hiro,

Thank you for your replies. I obtained the keel bolt data for the 41 from Nautor, and it seems way over engineered, there are 10 M24 bolts and 1 M20 bolt, all in type 316 stainless. I calculate this as a safe working load of 90 tons. I have now made a first inspection of the boat I hope to buy, and there are no crack marks or signs of movement between the keel and the hull whatever. This slightly surprised me, having a suspicious mind it occured to me that the join could have been faired while the boat was resting on the keel after the last liftout. It will be interesting to see what my surveyor has to say on this when we make a further inspection in a few weeks.

Cosmo Little

Dear Cosmo,
That's absolutely normal for an (S&S...) Swan, don't be surprised at all!
Fair winds
Matteo (38/067)

I am intending to purchase a swan 41 to replace my steel cruising boat of 20 years ownership from new. I am confident that all important points on what will be a 30 year old boat can be evaluated by a surveyer, however there is one area that concerns me. I believe that the keel bolts were stainless steel cast into the lead keel. Lead and stainless will form a galvanic couple that will corrode the stainless, especially if there is not much oxygen to replace the oxide layer. I think that there is a chance that the stainless bolts will get pitting and crevice corrosion just where they leave the lead. Unfortunately there seems to be no way of checking this except by removing the keel completely.

If you are seriously worried about this problem, and there is no doubt that silicone bronze or monel bolts are more saltwater resistant in lead, then you can opt to have the bolts tested by ultra sound. This is a process used by the US navy on their nuclear submarines to test fasteners. The readout gives a pretty accurate full depth chart of the bolt and will show crevice corrosion and 'wasting'.