Originally Posted by mrez
It is kinda strange to me why this idea is not getting more traction. It looks like a very good compromise. I can without any problem do DIY lithium battery
which gives me enough to maneuver in marinas
with the electric engine.
Hybrid doesn't really line up well with typical cruising boats power needs.
It works great in cars because they go from zero demand at a stop light to high demand accelerating, followed quickly by low demand approaching the next stop light...and so on. Hybrids are great at smoothing out power demand vs power production.
For cruising sailboats, you wind
up with a few scenarios:
- Day cruiser who mostly goes out for day sails
. Pure electric can work
fine as you just need enough to get in and out of the marina and you can recharge from shore power
. But annual fuel
usage just getting in and out of a marina is negligible to begin with so not much point in adding the cost & complication of a hybrid.
- Coastal cruisers. If conditions are good, they may sail...in which case the motor
type doesn't matter. If conditions are not good for sail, most will crank up the motor
and put in 20-50miles. But once you get up to speed, power demand tends to fairly steady, so they hybrid doesn't get to do it's power smoothing trick. If not carefully designed, it can actually reduce efficiency...at best it will be roughly the same efficiency.
- Ocean crossing
cruisers. These are really a tiny percentage of cruising boats. Even more so, when you consider new boat
purchases. They largely operate as coastal cruisers with occasional long crossings. During the crossings, they almost exclusively sail.
So the question is, who are you marketing
the hybrid drives to and how much will they benefit?
A more viable approach is a pure electric with a small generator
backup allowing for a moderate range under battery. Example:
- On our 34ft catamaran
with 25hp outboard
, we were around 10kw to maintain 6.5kt cruise
- As coastal cruisers, a 50mile day was a long day. Usually, we were around 20-40miles.
So a 20kw electric outboard
(roughly equal to 25hp and already available...check elco) is a simple bolt on power train. Under typical conditions, it would only use 10kw but you can put out the full amount if you need it, so we aren't sacrificing capability.
- A 45kwh battery bank (about half the size of a tesla) would give 4hr at cruise
speed with a 5kwh cushion. Resulting in about a 28 mile range under battery alone.
- Add a 5kw generator for periods of higher demand (which is often done for house loads anyway).
- Battery alone, would likely cover 2/3 of our travel days with shore power
recharging the batteries
- On longer travel days, we could run the generator which would allow up to 8hr at cruise speed (40wkh battery bank plus 8hr*5kw = 40kwh from generator). In a pinch we could continue at reduced speed (probably 5.0-5.5kt) using purely the generator output but based on our experience that would have been very rare.
- If we aren't pushing the drivetrain for range, the battery bank could be diverted to house loads. 12hr at 1.5kw at 50% duty cycle is 9kwh, which is viable for running the aircon overnight without the generator running. So if you are just doing a short run to an anchorage for the evening, you could avoid running the generator but still enjoy aircon.
This would be more expensive compared to just a standard outboard with a small built in generator but not by a huge amount (particularly for a new boat). Once set up, should be a very nice system that can get most miles on electricity from shore power but hit 98% of the capability of a pure ICE propulsion