DIY Electric Inboard

[fritz3000g]

I just participated in a thread where a sailor was describing how he made an electric inboard using an outboard lower unit, a 60v electric motor, and some batteries.

Anyone else done anything like this? How's it working?

[TrentePieds]

Shouldn't be very difficult to do if you have a lathe and a drill press and know how to use them. That's that part out of the way, and the prop will spin beautifully when you feed juice to the motor.

The real question, when you are talking boats, is how are you gonna supply the juice, how much of it can you carry, and how long will what you can carry last you?

You tell us how you are going to employ a boat driven via a notion as antique as electric propulsion. Then, and only then, can we tell you if you are onto something worthwhile, or whether you are barking up the wrong tree :-)

All the best

TrentePieds

[barnakiel]

If you do the engineering part right, why not.


Note possible mistakes in that thread, e.g. where the running time is discussed (not 4 hrs, but rather like 1.5hrs) and only if you forget the engine is S2-60min rated. Etc.


El motors are fine in boats. The challenge is always DA JUICE ...


Cheers,
b.

[fritz3000g]

Estimated pricing for a 4hp equivalent motor:
DC Motor: $300 (60V 3kw)
Batteries: $1500 (5x200 AH 12v)
Generator: $800 (2000 WH inverter)
Lower Unit: $200 (used)

Could run off batteries for 2 hours at full throttle (to drain down to 50% battery capacity), or much longer at 1/2 throttle. That would be fine for most sailing days or motorsailing. On an all-motoring day you'd need to run the generator.

With the generator running, it would still be much quieter than an outboard, and you could put the generator in any well-ventilated location (i.e. not next to cockpit).

[barnakiel]

Skipped the controller and the cable prices? Why?



This thick copper is not what you reprocess from skip. It is $$.


As I have said, you CAN'T run it 2 hours because it is rated 1hour. Offset? Well, no longer 3kW but rather like 1.5-2 kW. Good only if your boat is small and your your tides are wee.



?



I too want an el boat. Except every time I draft, I hit the battery cost / weight wall. Plain batts are only good for max 5 years. High end batts are $$$.



Etc. so I say it works. An equivalent outboard and fuel come out cheaper though. And are simpler to fit too.



b.

[fritz3000g]

Originally Posted by barnakiel

Skipped the controller and the cable prices? Why?

No good reason. That's probably another $300-500 depending on cable length.

Originally Posted by barnakiel

As I have said, you CAN'T run it 2 hours because it is rated 1hour. Offset? Well, no longer 3kW but rather like 1.5-2 kW.

Wow - interesting. I've been looking at electric motors for years and never noticed a duty cycle limitation like that. Guessing (and I suspect this is high) that a motor with a 12 hour duty cycle is twice as much.

4 hp isn't much, I realize. Enough to move a 26' sailboat (4000 lbs) at 4 knots, is my guess.

Originally Posted by barnakiel

An equivalent outboard and fuel come out cheaper though. And are simpler to fit too.

Agreed. The inboard electric is tempting though. An inboard gas motor would introduce smells into the cabin.

[TrentePieds]

Quote: "4 hp isn't much, I realize. Enough to move a 26' sailboat (4000 lbs) at 4 knots, is my guess."

On flat water, in a dead calm, yes. With any wind and slop, no. For use in and out of the marina, which is all you get for an hour's running time, pretty dodgy, cause you might well wind up having to SAIL (heaven forfend!) into your finger slip at the innermost end of the marina.

Better stick with a quiet little four-stroker OB :-)

TP

[fritz3000g]

From the guy who actually runs this system:

Well it is a sailboat, full power is more like 80 to 100 amps. I have never run it that high you are just pushing water at that point. I can run it at about 4 mph which is a good clip for my boat @ I think it was about 40 or 50 amps. mostly I run it at 2 mph that's 10 amps. I use cheap menards Exide batteries group 27 6 of them 5 for the 60v system and one for the 12 volt house. the 12 volt feeds off of the 60v via a step down. 6 solar panels keeps them in balance. I have a Honda generator that I used to use 2000. that would keep me moving with the on board 10 amp 60v charger. But I am building a diesel alternator @ 60v about 25 to 35 amps. If it works well I will build a better alternator at about 80 amps. That means that I can charge the batteries in about 30 min to an hour between 50 and 80%, the area that the batteries will accept the most amps. The key really is to not use the generator at all. But it is there just in case. 10 hp Diesel ICE takes very little fuel. Batteries are less than $600 and last 2 to 3 years. I might go with Trojan 12v @ $165 next year just to see the difference. My whole system is based on living off grid not traveling by prop power. The batteries are mostly for the house, the prop is just an extra advantage of my system. By the way the lower unit was Free! and my Diesel alternator will be about $500.00 and will blow a generator out of the water. speed control is a simple https://kellycontroller.com/shop/contro ... ntrol-box/

So... as long as you're ok with running at 2 mph (no wind, no tide) it works fine. In a pinch you can turn on the generator and/or up your speed to 4 mph. Also, I could probably get a larger motor for not too much more money to give myself the option of upping my speed further if need be.

[Adelie]

Originally Posted by fritz3000g

No good reason. That's probably another $300-500 depending on cable length.


Wow - interesting. I've been looking at electric motors for years and never noticed a duty cycle limitation like that. Guessing (and I suspect this is high) that a motor with a 12 hour duty cycle is twice as much.

4 hp isn't much, I realize. Enough to move a 26' sailboat (4000 lbs) at 4 knots, is my guess.

Agreed. The inboard electric is tempting though. An inboard gas motor would introduce smells into the cabin.

36yr old out of tune 4.5hp 2-Stroke pushed my 4,000lb 20’ boat with 18’ LWL at 5kt.