A two strap lift
wouldn't be recommended as this places a lot of point load on each strap. The ballast casting on this particular design carries a high percentage of longitudinal stiffness in the hull
. This is a trick L. Francis learned from his father and one he bragged about and used in many designs. Without the ballast the hull
is "floppy" especially fore and aft. This is why you don't want a two sling lift
. A three sling would be much better, maybe an "I" beam temporary attached along the keel
too, to keep the hull from doing something weird, like rip the deck
carlins and sheer clamps out of their respective locations.
The logical locations for a 3 strap lift would be the aft strap at frame bay 41, which is right at the very end of the flat portion of the deadwood assembly. This is the thickest portion the deadwood assembly and being under the aft end of the cockpit
and just forward of the mizzen, a fairly solid location. Next and would seem the natural location is frame bay 28, directly on the frame, which is the CG location too. It's also under the forward end of the trunk cabin
so a full width deck
step and fuel
bunker bulkhead are located. The last would be frame 13.25 (the one after frame 12), which is located just under the forward side of the fore mast
step. This is on the angled up portion of the hull in the forward quarters, so you may want to rig a preventer to keep it from "creeping".
If the ballast casting was in place you could use a two point lift and place the straps at the very locations L. Francis intended for the steamer hoist. If a temporary "I" beam was installed, you could also use these two point locations, which are shown on the plans.
I mention this because the 3 1/4" deep keel
timber, isn't all that much material to be asking to support the 10 tons of 55' monster on top of it. The only areas of the keel that have much meat are the hoisting ring locations and the "posts". My point being a two sling lift will likely hog the hull if too close together or rip out the sheer clamps and carlins if too far apart.
A set of gantry style hoists could be rigged, possibly motorized, each set at the locations I've mentioned. If it was me, I'd make a really stout cradle
for the boat and hoist the cradle
with the boat in it. This way the boat doesn't really come into play, assuming the cradle is truly stout. This cradle could be used over and over during your other planed moves.
Lastly, I have a home made power chain fall. It's a regular 3 ton chain fall, but I've rigged up a wooden gear
to accept the hoisting chain. The wooden gear
has an in feed and out feed guide of sheet metal and the whole 2 pound contraption is run by an electric
drill that I chuck up to it. Just keep tension on the chain and it'll run up what ever you hang from it. I could easily see a long bit of pipe with three gears attached, all threaded through the hoisting chains of three gantry hung chain falls. One electric motor
with a speed controller, maybe stolen from a router table. Yea, a bit of contrivance, but nice, uniform control with more heft then necessary, just in case your local experts where way off.