[einherjar]

I've got a new project I would like to get some input on.

It's a large old houseboat. 44' steel, 16,000lbs. Currently powered by twin Chrysler 225 V8's.

The motors are such a hassle all of the time that it hardly gets used because there is something wrong with it. The boat is used just for slow cruising (3-5kts) up and down the river. Usually not more than 8 miles normally. So the hp / high speed that the current engines provide are not that important.

To me it seems like the high torque properties of electric motors would be a great feature for a boat like this. Sure it weighs a lot, but size the prop accordingly and you can push a lot at low RPM.
Also battery capacity might not have to be that large due to the normally short distance and low speed that it travels.

Initially I was thinking a pair of heavy duty DC motors no more than 36-72v. There is a generator in the boat too, so there will still be some gas involved. I've heard it's a bad idea to do DC with the possibility of gas vapor near by, so maybe AC is better. Also the possibility of a single motor driving both props, though then most likely I'd lose the option of pivoting (one F one R). As it is a large displacement boat heavy batteries isn't the much of an issue. Probably make a couple of packs so one can be charging via solar / reserve while the other is used.

Any input on size of the motors and type and project in general is appreciated.

 

[samborambo]

What did you decide to do with this in the end?

For your application, a pair of industrial cast iron AC induction motors running off VSDs would be fine. They're designed for 100% duty cycle and are hard to break. There are some online calculators to work out power vs water speed based on your hull LWL.

You'll need a higher voltage battery pack for a standard AC induction motor (at least 1.4 times the AC motor voltage). The other option is to rewind the motor for low voltage. Motor rewinders will do this if you provide them the spec you want.

If you go with standard industrial motors, you can use standard VSDs but connect the battery pack to the DC bus inside the VSD. You could even get away with one VSD and a reversing contactor to run both motors with V/Hz mode (can't do vector/FOC drive in parallel).

Sam.

 

[Duncan]

Hi
Ref your boat - at 3 - 5 knots - you are getting into horse drawn territory! - a single horse can pull a 40 ton barge at walking pace

So you really don't need much power

The secret of efficiency with a water screw is large amounts of water pushed back slowly - so a big low rpm prop is best

I don't know about sparks and corrosion but a pair of forklift motors running on 48v would give more than enough power

 

[Emyr]

The secret of efficiency with a water screw is large amounts of water pushed back slowly - so a big low rpm prop is best

Big low rpm Archimedes screw, yeah?

 

[Duncan]

A large three blade prop is a LOT more efficient than an Archimedes screw

 

[nucleus]

I think you need the power reserve in case the wind comes up.

Also, the safest route prop-wise is to stick to what is already there.

I think a pair of HPEVS AC-9's could be the ticket.

 

[Duncan]

And the safest way to do any conversion is not to do it

 

[brian_]

Also, the safest route prop-wise is to stick to what is already there.

That would make sense if the intention was to operate at similar speed as the original configuration. It seems that the intention is for slower operation.

 

[boekel]

I think you need the power reserve in case the wind comes up.

Also, the safest route prop-wise is to stick to what is already there.

I think a pair of HPEVS AC-9's could be the ticket.

Yes for power reserve!

old prop can be a start when you don't know your motor characteristics, then adjust until right.

old prop usually means you need a big rpm reduction (you'll need that anyway in most situations).

 

[Peterboat#1]

I am nearly their with my conversion, my old forklift motor is mated to the propshaft batteries and controller mounted and cabled up. This week its other wiring and and a test run hopefully.
My boat is 57 x 12 and weighs over thirty tons and I am happy cruising the inland waterways at 3 -4 mph. Charging is taken care of by 3.6 kw of solar on the roof.
In the end I suspect I will be fine tuning the propeller, but you never know it might be right

 

[boekel]

I am nearly their with my conversion, my old forklift motor is mated to the propshaft batteries and controller mounted and cabled up. This week its other wiring and and a test run hopefully.
My boat is 57 x 12 and weighs over thirty tons and I am happy cruising the inland waterways at 3 -4 mph. Charging is taken care of by 3.6 kw of solar on the roof.
In the end I suspect I will be fine tuning the propeller, but you never know it might be right

What kind of reduction gear do you use?

 

[Peterboat#1]

What kind of reduction gear do you use?

Its direct the original diesel worked through a 2 to 1 gearbox, the top revs were 3100, the electric motor I have chosen has a 1680 rpm at 48 volts.
I have used a 60 volt system but dont expect to get anymore rpm,and to be honest dont want to do the 7 - 8 mph this achieves anyway.

 

[boekel]

Its direct the original diesel worked through a 2 to 1 gearbox, the top revs were 3100, the electric motor I have chosen has a 1680 rpm at 48 volts.
I have used a 60 volt system but dont expect to get anymore rpm,and to be honest dont want to do the 7 - 8 mph this achieves anyway.

Be carefull when testing, you -do- need a reduction gear, don't burn out your motor!

 

[Peterboat#1]

Be carefull when testing, you -do- need a reduction gear, don't burn out your motor!

Oh no! It is a series motor which I understood to have lots of torque at low rpm so thought it would be ok. I will monitor the temp of it whilst on test to see how it performs

 

[boekel]

Oh no! It is a series motor which I understood to have lots of torque at low rpm so thought it would be ok. I will monitor the temp of it whilst on test to see how it performs

yes that's good for a car, on a boat it doesnt matter you want continuous power in a boat, and if you turn too slow you don't have enough power.

Higher voltage = higher RPM

what controller do you use?

 

[Peterboat#1]

yes that's good for a car, on a boat it doesnt matter you want continuous power in a boat, and if you turn too slow you don't have enough power.

Higher voltage = higher RPM

what controller do you use?

Curtis PMC 1205M-6B403 400A DC Series Motor Speed controllor

I suspect I am going to find out whether things are ok this week. I have various gadgets to let me know what amps its drawing etc so I will post the results. I was rather hoping that because I had matched the rpm of the moto,r to rpm of the gearbox all would be ok

 

[boekel]

I was rather hoping that because I had matched the rpm of the moto,r to rpm of the gearbox all would be ok

that is correct if the continuous power of the motor is the same as the power of the engine that came out.

 

[Peterboat#1]

that is correct if the continuous power of the motor is the same as the power of the engine that came out.

I can always reduce the pitch on the prop, if the motor cant hit the revs that it did with the diesel engine, this week I hope to be trying it and as I say will report back.
For test purposes I will put my timing light on it and see what it says for RPM

 

[boekel]

good plan, I usually also test with original prop first.

most of the times the pitch has to be halved, but that's probably a coincidence...

try not to use more than 250 motor amps at first (depending on the motor, what current / power is it rated at? diameter?)

 

[Peterboat#1]

good plan, I usually also test with original prop first.

most of the times the pitch has to be halved, but that's probably a coincidence...

try not to use more than 250 motor amps at first (depending on the motor, what current / power is it rated at? diameter?)

12 inch in diameter and 18 long I will look at the plate tomorrow, its not a problem to remove and repitch the prop so its a plan if it doesnt perform. I will watch the amps carefully which is why I am doing everything right first time