The newfies used to put Turbo 400 transmissions in their lobster boats. I don’t recall if they would shift or just run them in a particular gear.

When I was young, my dad had several boats ranging from his ex desert storm fountain to several commercial fishing boats. He was very interested in this particular east coast dory with a turbo 400 in it. I have no idea how well it worked. I don’t recall ever seeing it in the water.

What I do know is that higher speeds need more power, it’s not like cruising in a car in the highway where you can shift into overdrive because you aren’t using much of the engines power. This is more like towing a massive trailer in a head wind at 85 mph… probably not shifting into overdrive.

Here… it’s a thing. Not a common thing and you likely need to use a fee drive for length.

https://www.offshoreonly.com/forums/do-yourself-boating-budget/317670-turbo-400-transmissions-boats-questions.html

Makes sense for a diesel where you have a narrow rev range.

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