Welcome, Neal!
What is the ratio of the drive leg?
Does your combustion engine couple directly to the sail drive or does it have a transmission between it and the sail drive?
The combustion engine has a horizontal output. This goes through some sort of transmission with a 90-degree output to mate to the vertical shaft of the sail-drive.
With the engine decoupled, how easy/hard is it to turn the shaft by hand?
Most systems I've seen talked about here, mine included, aim for a prop-rpm of about 1000rpm. The motor I have in my system has a constant of 50rpm/Volt, which is fairly common in motors for our application. To use that motor in a direct drive setup would mean operating it at about 20V. But to push my boat at 5.5kts takes about 5kw of power. At 24v, that translates into about 200A of current, which means more heat in the motor coils, a bigger controller and bigger wiring, bigger batteries, etc. The fan on my motor can't move enough air at 1000rpm to keep cool, so I run my system at 48V and use a 2.55:1 gear transmission. This gets me 2500 motor rpm and 980 shaft rpm at only 80-100A draw from the batteries. Motor runs cool to the touch. Prop turns at an efficient range. Motor controller doesn't spend all its time near max output, and the wiring is not as big and spendy. Everyone is happy.
I would say to keep the sail-drive since it is already installed and working. You may need to consider a new prop since I believe most omc drives were coupled with gas engines, which have higher rpm output than diesels. So depending on the transmission, you might have too shallow of a pitch on the prop for an efficient electric drive.
I know they make some nice compact planetary gearboxes that can sit between your motor output and sail-drive input so you have plenty of options on that front. You would probably need to get an adapter plate machined to fit between the C-face (common motor interface spec) of the transmission to the OMC input face.
The project is very doable and will give you a nice clean engine room with lots of room (a shocking amount of room, really) to mount batteries and the various electronics.
Welcome to the list!
/Jason
On Mar 20, 2018, at 00:58, 'Myles Twete' matwete@comcast.net [electricboats] <electricboats@yahoogroups..com> wrote:
From a new member:
Hi,
I am looking at converting a omc sail drive to electric and was hoping to find out a bit about this. wondering on the propeller is it advisable to use existing lower drive (not certain as to terminology yet) or replace with direct?
Thanks for any thoughts and am excited about possibilities and any suggestions.
Sincerely,
Neal
Location: Lake Michigan, McKinley Marina, Milwaukee WI
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Posted by: "Jason (Electric Boats) Taylor" <jt.yahoo@jtaylor.ca>
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