Since a boat like that didn't have manual brakes as an option you'd be stuck either trying to make something, or make something work.

A properly setup manual brake system isn't any harder to stop than a power setup. Pedal travel will be the only difference.

I've had plenty of power and non-power braked Mopars, both all drum and drum/disc setup and never noticed any difference in how the brakes "felt". Unlike Chevys which were very noticeable to me.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.