As with hybrid autos, generator / battery / electric drive rigs have
advantages and disadvantages.

One hp = 750 watts, about.

a 5 hp generator produces about 3750 watts of electricity steady state,
a little more for a second or two startup, whatever the voltage /
current output might be.

An electric motor might be able to provide more horsepower than that
for a short while, using batteries as "nitro" for your boat, while
otherwise smoothing the power available or even recharging at a dock.

Small batteries will provide short bursts of "overdrive" for a short
period, larger ones proportionately.

The weight you might save in batteries could be compensated for by a
better generator.

If you can cruise at about 4 hp, you will be able to use a kilowatt for
amenities, topping up depleted batteries, etc.

If you can sail and use the prop to charge batteries, you may have the
best of all worlds.

If you don't mind pottering along at about half or 3/4 of calculated
hull speed, you can do it on surprisingly little power, if you are not
bucking a strong wind, and if you can use tides and currents to your
advantage, may get where you want so long as time is not of the
essense.

There is a lot to think about, here. There will be some
transformational loss, ie torque to electricity, battery charge /
discharge losses, and electrical to torque efficiency.

Motor / generator combined devices are becoming more practical and
efficient all the time. Quebec Hydro holds patents for a wheel motor /
generator, and has offered info for developers, but strangely, will not
respond to me, perhaps if GM or Ford were to call in francias?

CTC offers a Chinese wheel motor / generator brake battery assisted
bicyle for under a grand, it's about 1/2 horsepower.

We are on the cusp of many new things, soon. The attitude display
promises to be interesting.

Terry K