Dropping the Keel

This looks like the sort of place where there are people that will know about dropping a keel.

I am looking advice on dropping a fin keel to inspect the keel bolts.

Background
I have a small crack in the keel which may go beyond the gel coat. There are no internal leaks from nuts, but I have decided it is time to check the keel bolts and fix the crack and also re-fare the bottom of the boat and keel at the same time.

I have seen a keel dropped and reattached before and the process looked fairly simple, provided you have a crane that can lift the boat. Searching the net for other methods used include creating a frame to support the boat in a fixed position and a separate frame to lower the keel into, but then maneuvering the keel back on might be more difficult.

To get an idea of the size of the project the boat is a 40 ft fiberglass mono hull with a fin keel attachment. The keel bolts are in line and there is what is called a deadwood stub (glassed) below this there is an external lead keel. The keel proportions are the same as the Farr 12.2 meter.

Questions
So my main question is once I have dropped the keel and checked everything is OK with the bolts and come to be reattaching the keel what adhesive should I use? I have read and heard different things, i.e. that there are special glues/sealants that are extremely powerful that are used to attach keels. One rebedding compound that is mentioned quite a lot in relation to keel bedding is 3M 5200. There are probably others...?

Another method also used by others is to epoxy mixed with micro-balloons or perhaps chopped glass fibers to produce a sort of paste that has a consistency somewhere between peanut butter and honey.

Some people also recommend adding "Pentamid" to the epoxy to make it more flexible, but not sure if I want any flexibility at all.

Apply this to the cleaned, dry roughened surfaces on both the boat and the top of the rudder. Then lay a smooth mound of the epoxy mix on top of the keel in the middle running fore and aft about an inch or more high. This mound will push out any air as the keel and boat come together.

I have been tossing up another additional protection against future cracks and leakage, but have not seen any it done anywhere else. I was thinking that I could use 5200 (or epoxy+Pentamid) in a small ring around the actual bolts and epoxy paste everywhere else. The idea is that if the epoxy cracks the 5200 being flexible will still provide a seal to prevent water access to the bolts and therefore any galvanic corrosion. I am not sure exactly how this would work in practice.

Then lower the boat onto the keel, do up the bolts (not one at a time but using a pattern). I think the the bolts then should be retorqued (using a torque wrench) to the same average toque as before they were removed. The retorquing the bolts needs to happen while the boat is still on the hard and with boat sitting back on the keel and other supports. The question here is that when the boat goes back in the water the keel will be pulling down rather than pushing up, so perhaps the boat needs to be support and some weight taken off the keel when retorquing the keel nuts. In any case the important thing in this phase is to not have the boat wobble or move before the rebedding adhesive is set. If the boat does move you could end up with a gap. But easier said than done, any ideas?

After the keel is set clean the excess epoxy paste away and wait a day or so before fairing in some new glass around the keel base. At this stage I was thinking of building up the base of the keel so the join was a bit more rounded and better supported so the keel is less likely to crack again. To do this I would sandblast to remove the gel coat around the keel and build up layers of epoxy and cloth cut to cover an increased area with each layer.
different thickness. How can I get heavy cloth to stick when applying it to the bottom of the boat? I am guessing apply a coat of epoxy wait till it starts to go off and lay the cloth on top, then paint on some new epoxy before the initial coat completely sets.

Does this sound reasonable?

Many production boats are shipped with keel unattached and it is then reattached on arrival. So I am wondering what technique and adhesives are used in these cases?

Anyone had any experience with this?

 

Dropping a keel is a big job, if there are signs of any cracking in this area you are right to investigate, if there is srtuctural damage it will have to be ground out and repaired well, if there has been any movement consider beefing up cross keel structure such as floors. If she is a production boat its likely to be stainless bolts and they will have been torqued up real tight as its a lead keel it will creep over the years so they may well go slack. As for bedding its a waste of time using epoxy or hard setting compound you should be using a two pack polysulphide or similar. If you have a gantry with the boat hanging in slings on chain blocks it makes the job easy, And dont let the ballast fall over!

 

Seems to be a duplicate thread.... see http://www.boatdesign.net/forums/fiberglass-composite-boat-building/dropping-keel-25327.html