Electric Dinghy Conversion

[boathealer]

We have converted our dinghy (Whaly 270) from an overweight (for us) Suzuki 9.9 EFI to a 5hp equivalent electric motor and a pair of lithium batteries.

We think this will work really well for us since we have an abundance of solar energy available. Was hoping to plane with one person, but the combination of short waterline and 5hp is just not enough.

Testing specifics for our setup and a few photos below. Full project report, if interested, is here:Electric Dinghy Conversion

 

[High Wire]

How long does it take to recharge from, say 50% SOC?

 

[boathealer]

How long does it take to recharge from, say 50% SOC?

Depends on the charger you choose to mate with the batteries. With a full-capability charger, it would probably be about 2 hours. But the charger would be big and expensive. The batteries themselves can take a 75A (1C) charge current.

I am currently under test with the small charger (lower size/cost) we have selected to use (only 12A output current). I estimate about 6-7 hour charge time with this charger, but from today's testing 20-30% SOC, not 50%. Would be considerably less time for 50% SOC.

 

[stubones99]

Cool conversion! Is there anything keeping the batteries centered in the compartment? I would be worried if they might take a lateral hit and the hold down support could dig into the battery case.
Is there enough surface area on the boat to install glue down PV sheet to have it generate power in the sun?

 

[boathealer]

Cool conversion! Is there anything keeping the batteries centered in the compartment? I would be worried if they might take a lateral hit and the hold down support could dig into the battery case.
Is there enough surface area on the boat to install glue down PV sheet to have it generate power in the sun?

Good eye! Thanks for the caution.

The bracket for the charging port and the bracket for the cutoff switch are aluminum "L" pieces that are secured to the bottom of the hold down board. They each butt right up against the batteries. I put some rubber trim pieces along the edge to keep them from abrading the battery cases. That and the 'pointy' end of the compartment should keep them in check.

Not a lot of flat surface area on the dinghy Plus, it would take A LOT of solar area to make a difference with a 2kW motor. That's why I put so much battery capacity in - we'll just juice up from the mothership.

Best,

 

[ranger58sb]

We have converted our dinghy (Whaly 270) from an overweight (for us) Suzuki 9.9 EFI to a 5hp equivalent electric motor and a pair of lithium batteries.

I was surprised in the other thread you mentioned that 9'6" dinghy weighs 154-lbs.

FWIW, the 10" (310) RIB we had weighed only 135 lbs...

Anyway, I'd consider electric, next time. The Suzuki EFI 15 we had was pretty decent, but our dinghy usage is relatively lightweight.

-Chris

 

[boathealer]

I was surprised in the other thread you mentioned that 9'6" dinghy weighs 154-lbs.

FWIW, the 10" (310) RIB we had weighed only 135 lbs...

Anyway, I'd consider electric, next time. The Suzuki EFI 15 we had was pretty decent, but our dinghy usage is relatively lightweight.

-Chris

Everything's a tradeoff. Rotomolded plastic is heavy by nature.

I don't think you'd find any language describing that RIB as "Indestructable".

 

[boathealer]

I was surprised in the other thread you mentioned that 9'6" dinghy weighs 154-lbs.

FWIW, the 10" (310) RIB we had weighed only 135 lbs...

Anyway, I'd consider electric, next time. The Suzuki EFI 15 we had was pretty decent, but our dinghy usage is relatively lightweight.

-Chris

Everything's a tradeoff. Rotomolded plastic is heavy by nature.

I don't think you'd find any material describing that 310RIB as "Indestructable".

 

[ranger58sb]

Everything's a tradeoff. Rotomolded plastic is heavy by nature.

I don't think you'd find any material describing that 310RIB as "Indestructable".

Yep, excellent point!

-Chris

 

[DDW]

It is too bad these engine manufacturers feel they must lie (or at least be misleading) about the power output. 2KW is 2.6 hp - not 5 - even at 100% efficiency. With two of those you might actually plane!

Other than that, I love your conversion, and have been very happy with my ePropulsion 3 hp "equivalent" (really 1.3 hp) motor.

 

[boathealer]

It is too bad these engine manufacturers feel they must lie (or at least be misleading) about the power output. 2KW is 2.6 hp - not 5 - even at 100% efficiency. With two of those you might actually plane!

Other than that, I love your conversion, and have been very happy with my ePropulsion 3 hp "equivalent" (really 1.3 hp) motor.

Thanks.

Torqeedo does have this information on a page one-click-down from their main page - albeit not prominently displayed and requiring some technical slight of hand - Performance and Efficiency
.
.

 

[boathealer]

Another data point from a longer test run today.

Left motor running when we got back. Automatic cutoff and subsequent motor calculation showed 73Ah (@24V) used until cutoff. Relion batteries rated at 75Ah.

Last three full charging cycles by Victron charger after motor cutoff showed right at 76Ah put back in.

I think things are pretty well calibrated now!

 

[Swfla]

With your current charge system. You could do two excursions a day minimum. Using it as a ship to dock/beach from anchorage is ideal with non-planing speed. It's not for everyone but I imagine a good number of cruisers would be nodding yes!

 

[boathealer]

With your current charge system. You could do two excursions a day minimum. Using it as a ship to dock/beach from anchorage is ideal with non-planing speed. It's not for everyone but I imagine a good number of cruisers would be nodding yes!

Yes. An obvious tradeoff.

Our cruising style, boat, and "threshold of pain" puts us squarely in the "not for everyone" category.

It helps that we have a 2'10" draft and can get a 'head start' toward any shore-side locations with the big boat!

 

[cardude01]

Cool project!

I recently picked up a fiberglass “barge” boat and I’m looking to see if I can swap out the noisy 3.5hp Tohatsu for the “3 hp” epropulsion Spirit 1.0 plus. The barge definitely doesn’t plane, it’s a 14’x 7’4” 500 LB catamaran, or maybe a monohull with a tunnel is a better description. Each hull is about 3’ wide.



The current gas outboard will push the boat at 5 mph at wot, but we normally cruise around 4mph at about 2/3 throttle to keep the noise down.

I saw some data on the epropulsion Spirit 1.0 with the older gen 1000w battery and it pushed a 1200lb sailboat at 4mph for 3 hours allegedly. I’m wondering if I can get similar performance with this barge, or would the sailboat hull be more slippery and efficient than my flat bottomed barge?

https://0220afca-6e42-4f45-a99f-036...d/77b59c_2452318b99544cf4bc557961bde03aee.pdf

 

[boathealer]

Cool project!

I recently picked up a fiberglass “barge” boat and I’m looking to see if I can swap out the noisy 3.5hp Tohatsu for the “3 hp” epropulsion Spirit 1.0 plus. The barge definitely doesn’t plane, it’s a 14’x 7’4” 500 LB catamaran, or maybe a monohull with a tunnel is a better description. Each hull is about 3’ wide.

That sounds like a fun thing to play around in!

I would guess those hulls are less efficient than a sailboat, but at 3-4mph it probably doesn't matter a whole lot.

 

[Nomad Willy]

Cardude,
The barge has a lot of resistance TBS but resistance can be overcome.
It’s a small boat. Try a 10hp on it. Bet you’ll be thrilled w the speed.
And running at half throttle will probably be rather quiet.
See if you can borrow a trial engine.

Edit;
That “barge” will definitely plane.
10hp should actually be enough.

 

[cardude01]

It has a 30lb thrust cheap Minn Kota trolling motor on the bow, and that will pull it along about 2mph or so (calm water no current/wind), so maybe the hull is not all that inefficient?

 

[DDW]

It appears to have a lot of wetted area and very hard chines, so I can't imagine it being real efficient until it comes on plane. How about the larger eProp? If it were my experiment, I'd borrow a couple of different size gas engines and see what the characteristics were. Keeping in mind the claims of electric vendors must be discounted - 1 hp is about 800W regardless of what the may advertise.

 

[Nomad Willy]

Efficient?
Seen very few that are less efficient.

At the speeds you’re talking FD like this rowboat/sailboat is efficient.
Notice in this photo how the stern curves up. The water at and just beyond the stern is hardly disturbed at all. Lightweight and a FD stern at low speeds is the key to efficiency.
But with 10hp or so that “barge” boat will plane depending on weight.

 

[cardude01]

It appears to have a lot of wetted area and very hard chines, so I can't imagine it being real efficient until it comes on plane. How about the larger eProp? If it were my experiment, I'd borrow a couple of different size gas engines and see what the characteristics were. Keeping in mind the claims of electric vendors must be discounted - 1 hp is about 800W regardless of what the may advertise.

Yeah I would really like to do some experimenting before I haul off and spend $2000 on that epropulsion outboard. The battery on the Spirt plus is almost 1300 watts, so is it really only about 1.5 HP? If that’s all it is wide open it doesn’t sound like enough. I run this 3.5 hp gas engine at 1/3 to 1/2 throttle usually.

 

[ranger58sb]

I've been thinking about a) an electric dinghy, and b) treating ourselves to a steering wheel.

Our main usage would be anchored/moored boat to dock, or boat to sandbar for the dog. (We're currently dog-less, actually.) Any additional usage -- longer distance sightseeing, etc. -- could be easily tailored around whatever the propulsion system might support.

The AB Alumina or the Highfield Classic center console RIBs -- or similar -- look to be what I'm thinking of, but also way fancier than we would care about. And they seem to want an arm and a leg for those, too. OTOH, they do sort of illustrate what's in my mind. Light weight (comparatively) would be a goal.

The Elco electric outboards look like a decent propulsion option. Either the 24V EP-5 or the 48V EP-9.9 would seem viable. A couple Group 31 AGM batteries in a 24V system would seem to be most economical, even though that path would weigh more than a L-Ion power supply. Four Group 31 AGMs in a 48V system sounds like beginning to get weight-prohibitive. The two L-Ion power supplies weigh much less; in fact both 24V and 48V weigh the same 55-lbs. The 24V L-Ion power supply cost doesn't put me off... but the 48V version is getting on toward serious bucks$$$.

The RIBs I mentioned recommend 20-30 horsepower. I don't so much care about going fast, don't necessarily care about planing... but I wonder if the 5-hp/24V version on a ~300-lb RIB (plus motor, pax, and "stuff") might be a bit tooooo tiny. In fact, maybe even the 9.9-hp/48V system might be too puny, too.

Hmmm....

-Chris

 

[Nomad Willy]

Our cooking propane seems to last a long time.

But I think some heating appliances are less efficient w propane fuel. One of the reasons I chose the Wabasto for heating. Not sure though.

 

[DDW]

Yeah I would really like to do some experimenting before I haul off and spend $2000 on that epropulsion outboard. The battery on the Spirt plus is almost 1300 watts, so is it really only about 1.5 HP? If that’s all it is wide open it doesn’t sound like enough. I run this 3.5 hp gas engine at 1/3 to 1/2 throttle usually.

I think the Spirit Plus has the same motor as the Spirit (the battery is slightly higher capacity) The motor is 1000W so if 100% efficient 1.34 hp by definition. The prop is slower turning and larger than the gas, practically I'd expect it to be about the same as the gas at 1/3 or 1/2. Keep in mind that at displacement speeds, the resistance rises exponentially, so doubling the power may only get you a small increase in speed. For example I think with my Spirit and Bullfrog dinghy, 500 watts power gives about 3.6 knots and 1000 watts about 4.1 or so. The extra power is useful for punching through a chop or against wind. I got 4.6 knots wide open on a supposedly 5 hp gas outboard.

 

[rslifkin]

With the larger, slower turning props the electrics are generally better optimized for low speed thrust. That's why they claim a 1.5hp electric has the "same thrust" as a 3hp gas outboard. At low speeds, it likely does. But assuming a dinghy that will plane, the higher powered gas outboard will move it faster.

 

[cardude01]

I think the Spirit Plus has the same motor as the Spirit (the battery is slightly higher capacity) The motor is 1000W so if 100% efficient 1.34 hp by definition. The prop is slower turning and larger than the gas, practically I'd expect it to be about the same as the gas at 1/3 or 1/2. Keep in mind that at displacement speeds, the resistance rises exponentially, so doubling the power may only get you a small increase in speed. For example I think with my Spirit and Bullfrog dinghy, 500 watts power gives about 3.6 knots and 1000 watts about 4.1 or so. The extra power is useful for punching through a chop or against wind. I got 4.6 knots wide open on a supposedly 5 hp gas outboard.

Hey thanks. I appreciate those real-world numbers. This barge weighs about 500lbs; not sure how that compares to the Bullfrog.