Matching the correct helo to a yacht has lots of variables as I am sure you are becoming aware of. I have flown both the 365 and 109E to ship decks and can tell you the pros and cons of each off line, but the thing about Yachts is that helidecks tend to be an after thought in designing, and even if your vessel does have the deck, is there sufficient load bearing ability and rotor clearance to do the ops safely. You are considering some larger birds (relatively) for this endeavor, so I hope those two variables are well accounted for. How big is the vessel and can you provide a picture of the intended helideck?