Getting Into Electric Power Catamarans

The 6kW motor arrived last week, and we got out on the water with it today.

It worked well; good power and speed. But we experienced ventilation (also referred to as cavitation) approaching top speed.

Transom could be a bit lower. Also, ePropulsion makes an 'anticavitation plate', so that's another option.

On one run I saw over 20km/h, so around 13mph. Assuming that holds after fixing the ventilation problem, that's right in line with my estimates.
 
Hi again SlowCo!

The motor comes with two propeller, differing mainly in pitch. I'm using the higher-pitch propeller, due to the pitch involved being more in line with my expected top speeds. The lower-pitch propeller has about 30% less pitch, so would likely only achieve around 10-11mph. I could see that propeller coming in handy if I was able to carry enough load to drop the top speed of the higher-pitch propeller down below that number, or perhaps if I was towing something heavy.
 
The cavitation would indicate that a different prop could bring even higher top speed without the ventilation and be more efficient. I would hook up a watt meter to see how much amp draw there is at different intervals/speeds. And try an even larger/higher pitch prop to see the difference.
 
SlowCo said:
And try an even larger/higher pitch prop to see the difference.
Click to expand...
Unfortunately, there's only one other pitch of propeller available, and it's lower pitch, not higher.

The control for the motor includes an instantaneous watts readout (and speed). I will definitely plot those two values at various wattages (1kW, 2kW, ...). I did notice that I was able to achieve the same speed as the top speed of the 2.2kW motor (11km/h) at lower wattage than 2.2kW. Due to a more efficient propeller than is on the smaller motor, no doubt.
 
There must be higher pitch/faster (aftermarket) props from different manufacturers that can be made to fit?
In the trolling motor world there are guys making their own props or using model aircraft props with surprising results (higher speeds @ less amps so longer trips):


[youtube]QfNWmJ2DbgM[/youtube]


[youtube]hIXckCOSuWg[/youtube]
 
I'm all for going faster/further on the same power/energy. Unfortunately, my searches for aftermarket propellers for the ePropulsion Navy 6.0 Evo don't reveal any sources.

Of course someone could measure the mounting pattern and integrate that into a new propeller design, but that someone would not be me.

I also feel like 13-14mph is the right speed for the 6kW power level and this boat. This is based on other quoted speed/power points.

I got the transom lowered by almost exactly one inch (as much as will fit the current parts). Just waiting for a dry-and-not-too-cold day to test it.
 
We got out on the water a few days ago with the transom lowered one inch. At first it would still ventilate at top speed, then I trimmed the motor in five degrees and that pretty much cured it.

It was windy and rough, as can be seen in this rear-facing video:

https://www.dropbox.com/s/kmsuo94jgmygkeq/GP010001.mkv

I saw 20.x km/h on the readout, so about 12.x mph.

Here is a photo that shows the trim angle:

https://i.imgur.com/NwvLsaF.jpg

It would still ventilate in the worst of the waves. I'm pretty sure the so-called Anticavitation Plate would cure the problem the rest of the way, and probably allow me to go back to a straight-ahead trim angle, and maybe even allow raising the motor back up to the original height.
 
Most above-the-deck parts have been removed, in preparation for installing better front seats, and probably moving the old front seats to the rear (doubling the seating capacity).

PtnJ2IF.jpg
 
New front seats and motor controller installed.
qc2NzXJ.jpg

I wanted a storage bin under the pilot seat too, but the vertical helm supports don't leave space to get your feet through when entering/exiting. I have a plan to eliminate those supports, but not right away.
QIoGiiD.jpg

The passenger seat swivels, and both seats fold down and lock when folded. The storage bin is lockable via padlock.
 
I took this yesterday evening after installing the rear seats (which are just the front seats I replaced).

SVjmO0O.jpg
 
Honestly I kinda think that is really fast. There will be a point where more power will yield less gain in speed. That would blow my trolling motor Grumman canoe out the water in a race. Especially around the 1:16 mark. Its fast and quiet. The wake is the loudest thing lol.
 
The motor consumes 6kW maximum. Speeds around 12.x mph. Hopefully can pick up a bit more with the transom raised back to the original height. It's an inch lower in the video; was lowered to reduce ventilation, but I have the Anticavitation Plate installed now.
 
I've been told by the boat manufacturer that speed is proportional to the square root of power. I have a few data points that are consistent with that claim. My current battery pack holds 10kWh, and reserving 10% leaves 9kWh. Here's a table of power, speed, range for 9kWh total energy consumption:

1kW, 5.3mph, 47.7-mile range
2kW, 7.5mph, 33.8-mile range
3kW, 9.2mph, 27.6-mile range
4kW, 10.6mph, 23.9-mile range
5kW, 11.9mph, 21.4-mile range
6kW, 13mph, 19.5-mile range

Once my motor-mount situation is stable, I can get better confirmation on at least the first two columns of that table.
 
Very decent numbers. So a few hours of touring/boating if using between 2 to 4 kW. And 7.5 to 10mph is a nice speed to cruise.
 
Another testing session.

https://www.youtube.com/watch?v=ZvkUB6qncTg

This is with the Anticavitation Plate added. That allowed me to return the trim angle to zero and still avoid ventilation.

Speeds were virtually identical, around 12.5 mph (20 km/h).

The transom has been raised back to the original height since that video was made, so next time out will test that configuration.
 
Is having a gas generator to provide 10kw of power to the motor not in the cards as a backup?

bobkart said:
I've been told by the boat manufacturer that speed is proportional to the square root of power. I have a few data points that are consistent with that claim. My current battery pack holds 10kWh, and reserving 10% leaves 9kWh. Here's a table of power, speed, range for 9kWh total energy consumption:

1kW, 5.3mph, 47.7-mile range
2kW, 7.5mph, 33.8-mile range
3kW, 9.2mph, 27.6-mile range
4kW, 10.6mph, 23.9-mile range
5kW, 11.9mph, 21.4-mile range
6kW, 13mph, 19.5-mile range

Once my motor-mount situation is stable, I can get better confirmation on at least the first two columns of that table.
Click to expand...
 
I'd do something like that with propane (LPG), if a light enough and quiet enough generator could be found. Most I see are around thirty pounds per kilowatt (120/240VAC output), although I've found one or two that output 48VDC that are lighter (per kilowatt).

https://www.parkergas.com/2022/02/07/is-propane-a-cleaner-fuel/

I'd not connect power straight from the generator to the motor. I'd use the generator just to charge the batteries. Basically a Serial Hybrid. But most likely I could get away with considerably less battery capacity in that configuration. I don't need a 10Kw generator; even 3kW would make a big difference in my range.
 
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