Using the TT35 as a solar-electric trawler

[Nomad Willy]

That’s what I was thinking .. hydraulic pump.
But there are much more power losses pumping the hydraulic fluid though the small tubes.
And the prop shown lacks the efficiency that Scott Harris is looking for.
But ZF is a big company and could easily use bigger tubing, larger dia and higher aspect ratio prop blades.

Here's what I mean about a high aspect ratio prop. Blades that are long and fairly narrow. Sailplane wings are long and narrow for the same reason.

 

[REO]

I gave up on an Albin 27 electric conversion. Here are the issues.
Good Stuff
My 62 hp diesel is loud. The 6.5 panda generator is much quieter.
The electric drive is silent if I want to harbor hop and charge at a marina.
The difference in fuel consumption is not big issue to us.
Bad stuff
We use our boat for long distance trips and avoid marinas. Running a generator all night is not desirable.
The cost of battery replacement combined with the generator fuel makes this an expensive way to power a boat
Even with a generator I worry about range under challenging ocean passage conditions.
In the end I decided that a diesel engine was best for long range passages where a marina may not be available for quiet and cost efficient charging.

I do have one question. The calculations based on watts used to power my Albin at 5 knots showed about 5 hp. I doubt that a 5 hp outboard motor could move my boat at 5 knots. It seems to me that changing the pitch on a small outboard motor would not work because the motor power curve would cause it to stall. Isn't it the fact that an electric motor has full torque at any rpm that allows it to push a heavy boat with a small amount of hp? There have been a lot of really helpful calculations in this discussion, so maybe it was already explained and I missed it??

 

[Nomad Willy]

Outboards have small props.
Small OB’s have even smaller props per hp than that .. really small.

 

[BandB]

BandB,
Pardon me but how do you know that?
Why should his information be false?

The individual providing him the information has a history of his speed and fuel numbers on TT35's being significantly overly optimistic. The numbers may be valid in theory but not in practice. One problem has been weights being considerably more than initially anticipated.

Now, that's also common with fuel numbers quoted on many boats. Numbers quoted are often perfect conditions, light load. On a relatively light, semi-displacement boat, current and wind and seas can make a significant difference as can another few thousand pounds of equipment. One needs to be very careful in accepting such numbers from builders. Not so crucial to most on day to day usage. However, I know one 97' boat that was designed for long distances (and there are many other examples) that the buyers quickly found out had several hundred miles less range than "promised" by the builder.

 

[twistedtree]

I gave up on an Albin 27 electric conversion. Here are the issues.
Good Stuff
My 62 hp diesel is loud. The 6.5 panda generator is much quieter.
The electric drive is silent if I want to harbor hop and charge at a marina.
The difference in fuel consumption is not big issue to us.
Bad stuff
We use our boat for long distance trips and avoid marinas. Running a generator all night is not desirable.
The cost of battery replacement combined with the generator fuel makes this an expensive way to power a boat
Even with a generator I worry about range under challenging ocean passage conditions.
In the end I decided that a diesel engine was best for long range passages where a marina may not be available for quiet and cost efficient charging.

I do have one question. The calculations based on watts used to power my Albin at 5 knots showed about 5 hp. I doubt that a 5 hp outboard motor could move my boat at 5 knots. It seems to me that changing the pitch on a small outboard motor would not work because the motor power curve would cause it to stall. Isn't it the fact that an electric motor has full torque at any rpm that allows it to push a heavy boat with a small amount of hp? There have been a lot of really helpful calculations in this discussion, so maybe it was already explained and I missed it??

It was 5kw for 5kts, not 5ph. So more like 7hp. But not a huge difference.


What an electric motor's torque would let you do is turn a larger prop slower. But no matter how you slice it, it will take the same 5kw to move the boat whether is comes from a high rev gas engine or a low rev electric engine. The difference will be the required gearing and prop size/pitch to match the motor's 5kw output point with boat movement at 5kts.