Solar dinghy test results

[IGBT]

Finally got a cooler day (77F instead of 105F) and took our Montgomery M17 equipped with a 10kWh battery bank, ePropulsion Navy 6 2024 outboard, pulling a Portland Pudgy dinghy that was carrying four 100 watt solar panels feeding a Victron 150/35 MPPT charge controller.Dinghy was a drag, as expected, but maybe manageable.

We did the same route as last trip except a bit longer (25nm instead of 24nm) over a period of 7 hours 45min, so average around 3.2kts. We did have some headwinds (both coming and going, go figure...canyon river life). Last trip was 24nm at about 3.7kts. 0.5kts is a big hit, no question. Current in the river seemed to be around 0.7kts again..more in the narrow sections.Solar wise, I was quite impressed with this slap together of four 100 watt Renogy panels I had lying around. The day started with heavy clouds and yet we were still getting 95 watts. Around 12:30 the sun would pop out for a minute and I saw 372 watts, which is really decent for our latitude (NE Washington state). The clouds cleared up around 3pm and I was seeing a steady 250 watts, which declined to about 225 watts by 4:30pm, and was 175 watts by 5:30pm as the sun was getting quite low and the panels are just flat on the Pudgy.We tried keeping the power to the motor about 125 watts higher than last time, to account for the drag of the dinghy (so about 625 watts average during the trip) and when the sun was out full, we were getting half of that from the solar panels.

I'll have to think if this is worth taking on the river section of the Great Loop. We kind of want the dinghy for when we have to anchor or tie up to mooring balls, but then again, that drag...

Next step is to get 600 watts of CIGS solar mounted to the boom tent on the sailboat itself and see what that does.

https://www.facebook.com/video.php?v=834219868381533

 

[yabert]

All good data here.
One point who annoy me a bit is the fact you use a 6 kW motor at 10% of his capacity.
Nothing wrong to have plenty of power in case you want, but using a motor at his rated power generally allow it to be in his best efficiency spot.
So it make absolutely no sense to try a 6 kW run, but it could make sense to have a 1 kW motor to increase efficiency.
I wrote could because 1 kW motor can have a smaller prop at different rpm who can cause a drop of efficiency.

But just for fun, I compare Epropulsion data from the 3kW and the 6 kW at 500w and the result are:
6kW at 500W: 9000wh battery / 72 miles of range = 125 wh/mile
3kW at 550W: 4000wh battery / 35 miles of range = 114 wh/mile * (500W/550W) = 104 wh/mile
So, roughly 17% more efficient.
Some food for thought.

 

[yabert]

but then again, that drag

What about building a efficient catamaran like type dinghy?

 

[IGBT]

All good data here.
One point who annoy me a bit is the fact you use a 6 kW motor at 10% of his capacity.
Nothing wrong to have plenty of power in case you want, but using a motor at his rated power generally allow it to be in his best efficiency spot.
So it make absolutely no sense to try a 6 kW run, but it could make sense to have a 1 kW motor to increase efficiency.
I wrote could because 1 kW motor can have a smaller prop at different rpm who can cause a drop of efficiency.

But just for fun, I compare Epropulsion data from the 3kW and the 6 kW at 500w and the result are:
6kW at 500W: 9000wh battery / 72 miles of range = 125 wh/mile
3kW at 550W: 4000wh battery / 35 miles of range = 114 wh/mile * (500W/550W) = 104 wh/mile
So, roughly 17% more efficient.
Some food for thought.

You speak truth.

The problem is there are a few times I predict we will need the true power of a 3hp to 5hp gas outboard and that will require pumping up to 3kW. These times are when fighting heavy current in places around the locks on the Great Loop. On this trip for example, I kept the power at 625 watts almost the entire 25nm so a 1kW Spirit Evo would have been fine. Near the boat ramp, I pumped the power up to 2kW for a short while and we were able to do 4.9kts with the dinghy lashed to our side, about 1kt faster than we were doing at 625 watts. If we ever find ourselves in a 3kt current, being able to do 2kts is going to be better than only being able to do 0.5kts, especially if there is a 1 mile long commercial barge coming in behind us.

The Navy 3 would have been the perfect choice, but the Navy 6 is very little more money, has new improvements in the 2024 design, and I predict will run cooler when used at 3kW input vs running the Navy 3 at 3kW.