The keel bolts are, in fact, not bolts at all but are lengths cut to appropriate size of 1" Whitworth continuous studding, i.e. lengths of round mild steel bar that are threaded along their entire length.
Mild steel is used rather than High Tensile steel as H.T. steel corrodes much faster than Mild Steel: we prefer to use Mild Steel rather than Stainless because there could be corrosion of the threads in the cast iron Keel itself due to the difference between iron and stainless steel in terms of galvanic corrosion and because in time stainless steel is prone to enbrittlement. At least with mild steel it is obvious that the bolts need to be checked whereas stainless could be left forever in the mistaken belief that because it is stainless it never needs checking. The threads in the keel are, after all, just as important as the bolts.
The studs are screwed into the cast iron keel to a depth of 2" - 3" prior to fitting the keel and the studs offered up into the holes in the hull; subsequently, the keel nuts are tightened down onto heavy washers or plates according to their position. To check the keel bolts it will be necessary to remove them and dependent upon the length of time since installation there may be different methods required to affect removal. Before attempting to remove the nuts or studs give the nuts and studs a prolonged soaking in "Plus-Gas" or some similar penetrating oil.
In the simplest of cases, it may be sufficient to lock one nut against another. First loosen the existing nut, then run on another nut and tighten the lower nut against the top nut using two ring spanners. Having locked the two nuts by further unscrewing the lowest nut the stud will come out. Remove the studs one by one replacing the first before removing the second and so on.
In more stubborn cases it will sometimes be necessary to run the nut close to the top of the stud and arc-weld the nut to the stud thus transforming the stud/nut combination into a "bolt" which can then be removed with either a ring spanner or a heavy duty box spanner with a long, very sturdy, through bar. If this later method is adopted shield the fibreglass from any sparks from the arc-welder and check that if an inboard engine is connected to the keel in any way break the connection or welding may ruin the alternator.
If the bolts are in good condition they may be replaced having covered the lower part with a good water repellent grease and using plenty of Mastic under the nut and washer.