I have several VHF sets - 2 metre amateur - that do marine band as well, and use them in our vehicles (the Mrs has a legit requirement due to her job, but the reality is that nobody much gives a f round here anyway!).
You can unlock/widen any Icom or similar handheld or base set (mine are mostly Icom IC2100/IC2200 base sets) but I'm not sure how - UK ones are restricted to 144-148 MHz but export ones like mine will do 136-174MHz. However none are waterproof so would either need an Aquapac for a handheld or a boat with a roof for a base set.
A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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