Excellent. Thanks very much. Anyone have any other pointers?
How many hours do you have? How many multi hours? Low time pilots, non professional pilots, pilots who do not fly weekly, might not yield the expected safety from twins. Accidents in twins are more lethal than Singles.
I have heard owners who keep excellent maintenance and who have deep pockets describe their annuals sometimes breathtakingly expensive. I had a lawyer acquaintance who claimed his Turbo Aztec nearly bankrupted their three man Law partnership until they 'fire' sold it.
I'd be considering a Cherokee 6/260 or Cessna 205/6/7 series. 6/7 seats 1600 lbs useful load same fuselage of the Seneca. 1 engine. 12 GPH fuel consumption 130 knots. Your mission is never more than 50 miles away from land at the half way point, you can mitigate most of that with altitude glide to safety. Even if going farther out you can Island hop without being out of glide distance from a beach. Not to mention it will be easier to have pristine maintenance on a single engine than on any twin.
I think much of the safety most of us expect about twins is an unrealized myth unless you are trained hard, recurrent trained often and stay proficient weekly (if you do not have thousands of hours) and even then there is a question of much, much higher kinetic energy due to higher speeds required at talk off and landing speeds and weights of the twins.
There is a saying "How far can you fly on 1 engine in a twin?" Answer: "that 2nd engine will take you all the way to the crash site."
Since the water is warm it is not as much a real survival issue as it would be in the cold great lakes. That and your relatively short mission over water, plenty of sand bars and pleasure/fisher boats in the area.....I just do not see the need or risk.
There is a saying that at its most basic flying costs about 3X fuel. So on one hand you have $6 per gallon times 12 gph=$72 fuel and $220 total costs or 24 gph = $144 fuel and $440 total cost.
If you take out the inflexible part of the trip such as run up, taxi, take off and approach the twin at 30 knots faster has no sizable benefit in reducing the total number of hours flown. So it might not be exactly 2x the cost but it may be close.
I believe that you may be accepting ALL POSITIVE ASSUMPTIONS about owning and flying twins and in practice it might be safer in a better maintained and easier to stay qualified pilot in a single.