There is a common misconception that you have to have a "dive" specific boat to dive from, something like that dive resort's boat (you know the 50 foot flybridge sedan cruiser) you visited last spring has but as can be seen from this eclectic list almost any boat will do for diving. No jetskiers have shown up yet but anything that floats can be dived from. There are only a few dive specific boats ever made, dive boats are built by their owners, not bought (kinda like Jeeps).
I like a boat I can put on a trailer and tow 3,000 miles. This allows us to explore from the Gulf of Baha to the frigid Great Lakes to the muddy coast of Texas down to the warm waters of the Gulf Stream. Obviously I value portability, some want a 45 footer and just figure if they get there they will do it in the boat and not behind a pickup truck. Either way, my point is, one of the first choices to make is do you want a trailer boat or a boat that will stay at a marina forever? After you figure that out you can move on to outboard vs inboard and all the other this brand vs that and cabin vs cuddy vs center console, new vs used etc.
Right up front is the cost of fuel going forward. A 26 footer with twin 250s will burn fuel at prodigious rates, maybe 1.0 MPG, a 17 foot open skiff with a 90 might get 8 MPG. Is it just you and your wife? or is it the entire local dive club, in which case maybe a "club" purchase is in order?
Dogs, wives (husbands), airplanes and boats are really hard to share.
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