We looked into this quite a bit before we went cruising. I eventually got an engineer
to come down to the boat and take a look at it for me. We have a Lagoon 440
... we extended the davits with a horizontal tube and fitted 5 solar panels
on the top complete with tilting Stainless Steel
frame ... and we hoist a dinghy complete with 30HP outboard engine
and 2 x petrol tanks
and a heavy anchor
and we NEVER remove the engine
under sail ... have been sailing in all weather
conditions like this for the last 3 odd years full time, crossed the Atlantic and the Pacific ... the trick ... the Way we tie the dinghy to the boat.
Surprisingly the davit tubes are 'sprung'! They are fitted to the boat with the inside tube bracket at an offset to the bulkhead ... and then the offset braket is cranked down by tightening the bolts which pre-bends the tube in the opposite direction to which a load will cause it to straighten (not sure I'm being clear here but trying to be) - anyway, the engine gets tilted on the dinghy and the dinghy gets strapped by cargo rachett straps over the davits which pull the dinghy into the stern of the boat. The painter is tied off to the main horn cleats
keeping the front of the dinghy in position and then a cargo strap is placed on the leg of the dinghy engine and ratcheted to the other side rear horncleat. The dinghy is now snug between the stern and the underside of the davit and in a sense becomes part of the structure. To make it even better for severe wind
and sea state we had 'handles fitted' to the sides of the solar
panel frames (great as handholds when getting in and out of the dinghy too) which allow for cargo straps to pull up toward the roof of the patio area and down to the handles at the step closest to the water
on both sides. That further supports movement of the structure, however, we only had to do this once in very large seas and winds gusting over 60 knots ... the entire structure was solid!
I would recommend the use of a structural engineer
to save you a lot of money
in modifications ... look rather if there can't be a 'tie down' solution. You may be able to get some idea from photos on our blog here ... Impi: HURRICANE STORM YACHT PREPARATION ... boat remaining in the water
Anyway .. 40 hp may be pushing the envelope a bit ... our 30hp is 2 stroke
so maybe lighter than the 4 strokes ... the dinghy is a double floor heavy duty fiberglass
... it is a heavy dinghy at 3.8m length. Oh ... and we did build a bracket in the dinghy to have the lift
perfectly aligned with the spacing of the davits
Took a look at the post I suggested but the engine is down as opposed to up ... you may get a better glimpse on one of our videos on youtube ... although it was not filmed for the davits one can see the dinghy and straps in some frames ...