T-Pain Is On A Boat: Re: [Electric Boats] Hydraulic motor drive with Hybrid Electric and Diesel Motors

Saturday, May 18, 2013

Re: [Electric Boats] Hydraulic motor drive with Hybrid Electric and Diesel Motors

It's not clear why an 18 HP diesel engine driving a pump driving a hydraulic motor driving a propeller has an efficiency gain over a diesel engine driving a propeller. And then to add the complexity of a second, smaller 3 HP electric motor driving a separate hydraulic pump which then pumps in parallel with the 18 HP diesel-driven pump. Ignoring any inefficiency in a reduction gear, if we assume 98% efficiency in each component of the diesel driven motor, that's a 4% loss in efficiency in the first chain (diesel to pump to hyd motor to propellor would be .98*.98*.98 = .94). I have no idea how to calculate the parallel lash up (solar cell to battery to motor to pump to hyd motor to propellor) but it's sure to be way lower total efficiency than the other path.
While I kind of like the idea of using hydraulics -- they can be quite efficient -- it seems like you've drifted away from the KISS principle.

On Fri, May 17, 2013 at 11:44 PM, reesekc <kcr@kcrproducts.com> wrote:

I have a Hughes 35.5 Sloop of which I just removed the Atomic Four motor with a V-Drive. I am planning to replace the motor with a hybrid hydraulic drive system. A hydraulic motor will be used to drive the propeller shaft; and to power this motor, I'm planning on installing a 3 HP electric motor with pump; as well as an 18 HP diesel also with a hydraulic pump. The plan is to connect the motors in parallel with check valves to prevent back flow, so the motors may be used independently or together.

The electric motor will be supported with solar panels and a small battery bank. The diesel motor will drive a larger pump and of course have an alternator for general electricity and recharging the batteries.

I believe the hydraulic pump/motor system is simple and reliable, and I also like the idea of hybrid power system which greatly reduces the battery bank size. I've done a search through past posts, but I could not find much on "hydraulic motor driving a propeller". If anyone could steer me to a previous thread, or if anyone has some comments on the plan, I would appreciate input.