Is there any reason why I cannot hook an electric motor direct to a BW velvet drive?

[nolakennedys]

Seasons Greetings all!

I have been thinking about this for a while. Is there any reason that anyone may have to not mount and couple direct a similarly rated shaft output electric motor in replacement of the main engine directly to the reduction gear (in this case a model 72 Borg Warner velvet drive)?

In the Coast Guard our Detroit Diesel 6V53s were direct connect and the gear ratio was 1.5 to 1 or 2:1 if I remember correctly. More RPM, more speed. The premise should be the same. Just would like some community feedback. I think it may be better than a direct connect from electric motor to shaft. Thank you all and stay safe out here!

[jimbunyard]

What's your 'idle speed' on those electric motors?

If you're talking about standard, single speed motors, I don't think it will work practically.

If you're talking about variable speed motors, what's the point?

[tkeithlu]

Thrust could be a problem. On my 4-53 DD, the thrust comes right through the BW tranny and against a thrust plate on the fly wheel. Is your electric motor ready for that?

Are the RPMs at rated power the same? If the electric motor spins faster at power, the propeller could be a problem.

[nolakennedys]

Originally Posted by jimbunyard

What's your 'idle speed' on those electric motors?

If you're talking about standard, single speed motors, I don't think it will work practically.

If you're talking about variable speed motors, what's the point?

Hi Jim,
I am not sure on the idle speed. The idea I am toying with is replacing the aging diesel with a similar spec drop in electric motor. So the idea would be yes - a variable speed electric motor with output the same or close to what the diesel does currently.

The train of thought outside of going electric motor is to use the reduction gear as a "dampener" for load to the shaft. Most of the setups I am seeing are direct connect setups. That seems like it may cause more issues in the long run than a setup through the reduction gear.

[nolakennedys]

Originally Posted by tkeithlu

Thrust could be a problem. On my 4-53 DD, the thrust comes right through the BW tranny and against a thrust plate on the fly wheel. Is your electric motor ready for that?

Are the RPMs at rated power the same? If the electric motor spins faster at power, the propeller could be a problem.

Good questions sir, thank you! I will find out. The electric motor type has not been selected yet, but the idea is to get as close as possible to thrust load specs of the original engine - all other things remaining the same. Propeller definitely could be affected and I will check into that if I decide to pursue the idea.

[Searles]

The shaft thrust is taken on the thrust bearing built into the aft end of yours BW gearbox,the drive plate does not take propeller thrust .⛵️⚓️

[redneckrob]

Originally Posted by jimbunyard

What's your 'idle speed' on those electric motors?

If you're talking about standard, single speed motors, I don't think it will work practically.

If you're talking about variable speed motors, what's the point?

Your question doesn’t make a lot of sense. What would the point be of putting in a single speed electric motor? Who in the world would want to operate a boat with a single speed engine of any type? Why wouldn’t you want a variable speed motor?

[jimbunyard]

Originally Posted by redneckrob

Your question doesn’t make a lot of sense. What would the point be of putting in a single speed electric motor? Who in the world would want to operate a boat with a single speed engine of any type? Why wouldn’t you want a variable speed motor?

Hmmm... In the real world, most high (as 'understood' by the public; 50-100 hp [the comparitively miniscule EV component aside]) horsepower electric motors are single speed. As worded, the OP asked for a response seemingly based on the current standard, i.e. single speed, necessary torque motors,

Of course, my point was only to demonstrate that there probably isn't any need for a hydraulic transmission with a variable speed/torque electric motor; as such, the question makes perfect sense.

The technology is old enough that the question can actually be easily answered by perusing the abundantly available information on existing systems.

If I were interested in pursuing the topic, my first search would be something like 'medium marine electric drives'.

[valhalla360]

The motor should work fine.

Of course, you aren't going to spec a single speed motor. Idle speed would be 0RMP and largely irrelevant.

It would be very unusual for the thrust to go into the engine via the crank shaft, so that shouldn't be an issue.

Do make sure your bilge is dry in the vicinity of the motor.

Many EVs skip the reduction gearing and transmission but there should be no harm in retaining it other than a slight loss in efficiency.
- Electric motors can generate peak torque from 0 RPM, so for the same HP, they generally have an easier time turning the prop (the prop diameter & pitch may be slightly different).
- By reversing the current, you can reverse the rotation of the prop without the need for a mechanical transmission.

Electric motors are easily better in just about every way compared to ICE. The challenge is storing sufficient energy. If you have no intention of motoring more than a few miles between plugging in, storage really isn't a big issue. If you plan to coastal cruise anchoring out covering 30-50miles per day, storage is a big issue.

[redneckrob]

Originally Posted by jimbunyard

Hmmm... In the real world, most high (as 'understood' by the public; 50-100 hp [the comparitively miniscule EV component aside]) horsepower electric motors are single speed. As worded, the OP asked for a response seemingly based on the current standard, i.e. single speed, necessary torque motors,

Of course, my point was only to demonstrate that there probably isn't any need for a hydraulic transmission with a variable speed/torque electric motor; as such, the question makes perfect sense.

The technology is old enough that the question can actually be easily answered by perusing the abundantly available information on existing systems.

If I were interested in pursuing the topic, my first search would be something like 'medium marine electric drives'.

In the real transportation world where high hp electric motors have been in use for decades, i.e. train locomotives, they obviously use variable speed electric motors, and we're quite obviously talking about a transportation application, not a conveyor belt motor! I don't think the question is about if a transmission is needed for an electric motor, even in applications where a constant speed motor is used a variable pitch prop is used to change power settings, not a transmission. The question is if it's possible to minimize the rework of the entire engine compartment by more simply replacing the ICE motor with an electric one without having to also rip out the transmission.

This is a pretty specialized question and the OP correctly came to a pretty specialized place where it is most likely that someone who knows what they're talking about could answer that specific question. I too am interested in hearing from that expertise here on this subject. Telling someone to do a Google search in response to such a question here is not only singularly unhelpful but really a bit insulting. If you can't help, just remain silent, but it adds no value to tell someone to do a generic Google search in this situation.

[Scubaseas]

Originally Posted by tkeithlu

Thrust could be a problem. On my 4-53 DD, the thrust comes right through the BW tranny and against a thrust plate on the fly wheel. Is your electric motor ready for that?

Are the RPMs at rated power the same? If the electric motor spins faster at power, the propeller could be a problem.

I doubt this about thrust being transmitted to the crankshaft. Typically there is a thrust bearing in any transmission. Now how you handle the torque of the motor needs consideration. If it's a face mounted electric motor it should be OK. If the motor was used as a 90* load to shaft like a K frame then you need to have a frame plate that will bolt up to the reduction gear without shearing itself off said frame plate.

[Jack C]

My Velvet drive has a raw water cooler. Does yours? If so you would have to add a water pump">raw water pump.
I see no benefit of using the velvet drive. Add a thrust bearing if the electric motor does not have one.

The Velvet drive is bolted to the engine which sits on flexible engine mounts. What will support the drive's weight when connected to an electric motor?

[Pete7]

Originally Posted by valhalla360

Many EVs skip the reduction gearing and transmission but there should be no harm in retaining it other than a slight loss in efficiency.

I thought it was the other way around it that electric motors were more efficient at higher revs, but to use in a boat they need a reduction gear to bring the speed of the prop down to about 1000 rpm or you loose through propeller losses. The other advantage of the reduction gear is it can incorporate the thrust bearing which neatly solves the problem.

Pete

[valhalla360]

Originally Posted by Pete7

I thought it was the other way around it that electric motors were more efficient at higher revs, but to use in a boat they need a reduction gear to bring the speed of the prop down to about 1000 rpm or you loose through propeller losses. The other advantage of the reduction gear is it can incorporate the thrust bearing which neatly solves the problem.

Pete

Electric motors are pretty efficient at any speed.

Of course it depends on the exact motor you spec. Put a high RPM japanese motorcycle engine in a boat, you will need a deep reduction gear as they are low torque high RPM motors.

But typically, electric motors hold an advantage as they can develop peak torque at any RPM, so you don't need a low gear to help get the prop turning.

If you look at Tesla and other EVs, they largely scrap the transmission as it's not needed. Even early EVs from 30yrs ago, people would often start in 2nd gear as electric motors generate so much low end torque 1st wasn't needed.

[David Rainbow]

As to the question of constant speed, A vessel could still be controlled by such a single speed unit with the addition of a variable speed propeller. Up until very recently a Island Shipping company based in Cairns Australia used a container vessel with many power hungry refrigerated containers consuming a great deal of their requirements from a shaft alternator. The vessel thus maintained a constant shaft (RPM) speed even whilst undertaking manoeuvring tasks like docking. Being controlled by propeller pitch and rudder with a short burst of forward tunnel thruster to straighten her up once alongside.