New electric propulsion build (small sailboat)

[KTP]

We have gone down the rabbit hole on another electric propulsion build.

This is a Montgomery 17 sailboat built in 2013. A fine little sailboat with a camping cabin, perfect for gunkholing. It is beachable (with a kick up rudder) but has a 600 pound lead fixed keel, about 1.75 foot draft with CB up.

We have owned a 2005 M17 since 2008 but got this additional one on a road trip on a whim (had truck, had no boat attached, felt like something was missing).

We have sailed these boats quite a bit with a 2.5HP Yamaha outboard, a 6HP Tohatsu, and a Torqeedo 1003 and later a 1103 (the non geared brushless model).

The 6HP is overpowered, the 2.5HP is right at the correct power for almost all conditions if run near WOT, although it will move the boat very comfortably at 4 kts with 1/4 throttle. Both engines are loud and make the cuddy cabin smell of gasoline and exhaust. I have never really liked them and always hated firing them up. We switched out from the 2.5 to the 6 only because the 2.5 started leaking oil in the water (probably shaft seals) and I was not in a location to have it fixed.

If we take it day sailing to locations where I know the water, we leave behind the gas outboards and take the Torqeedo. It only has a 900wh battery but if we sail and are careful, it is enough. Yes there is range anxiety, and I did consider just getting 2 or 3 more batteries, but at $1000 a pop, that does get pricey fast, plus the annoyance of switching them out every 45 minutes if WOT. At WOT it is close to the Yamaha 2.5, maybe a hair slower.

Enter the new build (kind of crazy).

The motor is a E-propulsion Navy 6.0 (2024 model). This new model has been redesigned, dropping the weight from 80 pounds to 66 pounds, with a smaller (hopefully as efficient) brushless motor underwater. The old Navy 6.0 motor static thrust with the larger prop was 278 pounds, which is quite impressive, but I do not have numbers on this new model, just some various reports of people using it and liking it compared to the old model.

The battery bank is LiFePO4, comprised of two banks, one on the forward port side and one on the starboard side. Each bank weighs 88 pounds, comprised of four 12.8V 100AH group 24 size LFP with bluetooth BMS and low temp charge protection. We considered going with a Epoch 48V battery for each bank, they have a nice unit but it is 95 pounds and I was unsure if I wanted to lug two of those in and out of the tight forward compartments. We plan to remove the batteries often, for long term storage and other use cases, and 22 pounds is a lot easier to move than 95. The price is about half for the eight group 24 vs 2 of the Epoch 48. It was a hard decision though, and other factors went into it (we have a mountain location with a 24V inverter power which could make use of the 12.8V in a 2s config).

Anyway, the total battery is 10,240 watt-hr and weighs 176 pounds. The weight is nice and forward in the boat. The previous owner had a 66 pound gel 12V battery for the small systems (lights, depth, etc.) and we have replaced that now with a Victron 48V to 12V DC-DC converter at 20 amp output that weighs less than 5 pounds. We also removed 2 sand bags he had placed in that forward compartment (evidently for better sailing). So the weight change isn't bad, and is pretty balanced now. The Navy 6.0 (2024) is as mentioned 66 pounds, and the old Tohatsu 6hp gas was 57 pounds. We also carried a 3 gallon gas tank in the back compartment that is now gone, and 3 gallons of gas is 20 pounds. I think all in, we are a tiny bit heavier, but nothing noticeable, and if anything, better balanced.

Performance is yet to be determined as we are still building it all, but my expectations are that we will rarely if ever need to use the Navy 6.0 at more than 3kW. Could have gone with the 3kW model but the price diff is pretty small and I wanted the bigger motor for future uses. I expect and hope that the performance at 1kW input is somewhat similar to the Torqeedo 1103 at full throttle (1100 watt input). If that is the case, we should have 10 hours of potential motoring at 4.5kts (45nm range). At 2000 watt input it should easily be the same output as the old Yamaha 2.5hp gas motor, which would give near hull speed in calm conditions (about 5.3 kts). That would mean 5 hours of motoring with a range of 26nm.

Charging would be done at home since this is a trailer sailboat, or possibly at a marina. The boat has twin 48V 18.5 amp chargers, each drawing 12 amps max at 120VAC. Thus a 30 amp shore power could charge both banks in about 5 to 6 hours.

A fair amount of work and expense, but a fun project, and still learning new things even though we have been doing stuff like this for many years. For example, I discovered Amphenol Surlok power connectors, which are now my new favorite 200 amp power connector that is IP67 when connected.

[KTP]

Finished up the 48 volt install, everything works well, just waiting on the motor now. We have the IP67 connectors ready to plug in on the transom.

[Statistical]

That looks like a solid install. Electric is ideal for daysailers. Outboards are loud, smelly, and have a bad habit of being a pain to start if they have been sitting for a while.

The push button convenience of electric is solid for a low stress day on the lake. Will be curious to see your real world range tests at various speeds.

[mbianka]

Originally Posted by KTP

Finished up the 48 volt install, everything works well, just waiting on the motor now. We have the IP67 connectors ready to plug in on the transom.

Nice install. I converted to EP in 2008 and never looked back. Up graded last year from four AGM batteries to a single 48 volt 105 AH Allied Lithium battery. Only two connections to maintain and all accessible from inside the cabin.

[sailingharry]

Sounds like a well thought out plan, and a near ideal use case for EP. It is also refreshing to see that your calculations and analysis have not bought into magical EP equivalent horsepower. Your idea that 2kw should do what your 2.5 HP does is probably quite accurate, since the math says that 2kw is 2.7hp.

[KTP]

Originally Posted by sailingharry

Sounds like a well thought out plan, and a near ideal use case for EP. It is also refreshing to see that your calculations and analysis have not bought into magical EP equivalent horsepower. Your idea that 2kw should do what your 2.5 HP does is probably quite accurate, since the math says that 2kw is 2.7hp.

Yes, we have some years of playing around with electric already, in both a inboard 10kW on a 34 foot PSC and a lot of time using Torqeedo 1003 then a 1103. Also have used a 2.5HP and the 6HP on our 17 footer.

Realistically, the big boat should have stayed diesel, but battery prices are dropping so much that even it is viable for a weekend cruiser if upgraded to a big LFP bank (for the same weight cost as the smaller lead acid AGM).

The small 17 foot sailboat we had a recent experience while sailing on a large lake with just the Torqeedo and its 915wh battery. We had been out all day and the wind died, while still 5nm from dock. The Torqeedo had only 46% charge left (because we had used it on our dinghy during the day). We dropped it down to 200 watts and did the 5nm at about 3.5kts, arriving with 19% charge.

Makes me think the 10kWh bank is going to feel so nice.

[SaylorMade]

Looks nice.

That is a lot of kWh for a 17 foot boat.
I converted last year on a 27' 7,000 lbs boat and went with 12 kWh.
After having used the setup for the first full season I feel that I would've been fine with just 6.

But yeah with the prices these days it's just nice to have a lot of range.

[KTP]

Today we took out the boat with the new motor (ePropulsion Navy 6kw). We kept the wattage going into the motor right around 500 and saw speeds of about 3 kts going up the river and 4.4kts coming back down, so evidently there was about 0.7 kt of current. Total trip time was 6.5 hours and total distance traveled was 24nm. We used 54% of one bank (5.12kwh per bank) and so we used 27% of our total battery capacity doing this 24nm trip up and back. Thus one could estimate our max range would be 88nm at this speed and power input. There was also some use of the same bank by our 12V fridge and VHF/depth sounder. We have these running off a Victron 48V to 12V converter, 20 amp. I would probably say 250 watt-hr went to those as a guess.
There was no wind and so we just motored, never even broke out the sails. We don't have any solar mounted yet so no idea how much that would have helped on this little test trip. I was pretty hot in the sun, so I think we could have at least gotten back 1200 watt-hr over this entire 6.5 hour trip if we had 600 watts of CIGS mounted. That would put our range at over 150nm for traveling during the daytime hours.

I have in mind a trip up the inside passage (Canada, west Coast) since we go to Blaine a lot. That would really put this thing to the test, but I want to get the solar sorted first. Have fabric on order to make a 8' x 7' boom tent and really interested in the BougeRV 200 watt CIGS panels on that (three) after watching a video of a guy running over them with a tractor, drilling 10 holes in them, dragging them face down at 25mph on a ATV on a gravel road, then cleaning that dirt off by body surfing on it. The sucker was still putting out 80% of rated power all beat and scratched up. I think they would work for the Great Loop trip (probably more sun than the inside passage).