A word of caution with 2WD tractors. A bloke here who had a Rigid Raider tried recovering it with a 2WD Ford tractor (a lot bigger than a Fergie) and totally wrecked the launching beach with it, digging big holes everywhere.
Main problem in that case being the RR is a heavy old barge and a 2WD tractor (regardless of make) is largely designed to gain traction on its rear wheels via weight transfer from the trailer/implement - hence the fact most tractor-trailers have the wheels at the back of the trailer and a very heavy noseweight, to load up the driven rear wheels.
A boat trailer of course usually has a light noseweight to allow on-road towing by a vehicle with suspension, so you don't get either the weight transfer, or the grip, that a tractor needs to perform properly.
I guess it wouldn't really be a problem on a proper surfaced slip but without the weight over the rear wheels (and assuming you haven't compensated by filling the rear tyres with water or fitting wheel/3 point linkage weights) you don't have as much traction as you might expect. However the gearing is excellent compared to anything else, and a 4WD tractor is a completely different story.
Brakes on older tractors are also almost universally crap... we've got 3 old Fordsons on the farm (by old I mean 1950s/1960s) and none of the brakes work on any of them.
A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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