its less hard than you'd think unless you're really going for long range.

for my sailboat I am getting rid of a 300lbs diesel and a 30gallon fuel tank with a 45lbs PMAC.

That means I have opened up about 465lbs for batteries.

Now, with a sailboat you're never truly out of range -- but the point stands : these things are so much lighter than ICEs on average that there is a lot of opportunity even with battery weight as it is (and it's getting better daily).

I guess there's always the risk for a rig failure.

I looked a bit on doing the same, but came to the conclusion that it will be expensive to fulfil racing rules requiring the boat to be able to maintain speed for 5 hours ie around 25-30 NM range.

As it is now, I have about 500 NM diesel range on my boat, which is basically 3-4 days continuous runtime. Cutting it down to 25nm and 5 hours requires minimally 100kWh.

For a blue water boat, 500 NM is not quite acceptable, but can be fixed with jerrycans for a couple of dollars. An all electric blue water boat would clock in at an unrealistic 2MWh of batteries with a weight at least 20 metric tonnes. 10x the load capacity of my boat.

This is silly, but I've also wondered if you could make a boat that can anchor and recharge batteries from ambient current, sort of like stationary regenerative braking. I'm sure it would take way too long to be worth it, but it was a fun idle thought.

Uh, car batteries are much heavier than most ICE’s. The curb weight on teslas’s are crazy high.

BYD can be lighter because they skip on safety gear and proper structural elements - in my experience.