Advice needed on inboard electric power components.

[Rich Jones]

I'm thinking of possibly re-powering my Palmer fantail launch this winter. The 12 year old, 80 lb. thrust trolling motor that I cannibalized for power works OK, but I blew the reverse function of the switch this summer. I could try to fix that, install a new trolling motor or go with an inboard.

For purposes of this thread, let's talk about inboard power.
My problem with inboard is that you just can't buy a system off the shelf and I have no idea how to design one or where to get the components: motor, controller, prop shaft, prop and whatever else I would need. I've googled electric motors for boats and can only find stuff that costs $5,000. That would be a deal breaker right there.

Anyone have sources for this stuff or any other advice they can offer?
Thanks!

[WX]

There are inboard power units on the market.

[WX]

There are inboard power units on the market.
https://ecoboats.com.au/products/ele...nboard-motors/

[cstevens]

Also https://www.elcomotoryachts.com/. I've been drooling over their setup for a while now.

I'll bet that the smallest motor would work great for the Palmer:

https://www.elcomotoryachts.com/ep-6.shtml

Pricing is on the Elco site as well which is a refreshing change from most companies selling diesel motors:

https://www.elcomotoryachts.com/quote-request.shtml (it says request a quote but once you select the motor and options if gives you the cost right then).

And... it's too expensive given your criteria. Darn, I'd sure like to see someone install one!

[Rich Jones]

The Elco site is the one I was looking at. Nice motor but the price is ridiculous.
There has to be something out there cheaper. I've heard of cobbling together an old golf cart motor, but that's not a route I'd like to take.

[nedL]

In the early 80’s i worked for a shipyard that had a sideline of building reproduction fantail launches. We build them with gas, steam and electric versions. For the electric version the owner of the yard sent me to a golf cart dealer where I picked out three of their best junkers and arranged to have them delivered to the shipyard. I stripped out the motors and controllers, and then used the components to power the electric launches. They actually worked pretty well.

[Ron Carter]

If you could stand the battery weight I'd bet you could cannibalize an old 36v golf cart for motor and controller. Shafting, sealing the shaft and prop all ought to be pretty straight forward. Cross posted because I type slow.

[Rich Jones]

In the early 80’s i worked for a shipyard that had a sideline of building reproduction fantail launches. We build them with gas, steam and electric versions. For the electric version the owner of the yard sent me to a golf cart dealer where I picked out three of their best junkers and arranged to have them delivered to the shipyard. I stripped out the motors and controllers, and then used the components to power the electric launches. They actually worked pretty well.

If I went that route, is the prop shaft hooked directly to the motor or is a pulley and belt system necessary? Also, do you remember what size and pitch the prop was?

[Don Z.]

Not sure on costs, but try these guys:
http://www.annapolishybridmarine.com

Mike at Electric Yacht may be able to help as well.

[Don Z.]

If I went that route, is the prop shaft hooked directly to the motor or is a pulley and belt system necessary? Also, do you remember what size and pitch the prop was?

My only thought on that is shear pin... You can easily slam from forward to reverse on an electric, the motor doesn't care. The shear pin does though. May be useful to have a design where the shear pin is inside the hull... so if it goes, you can play with it without getting wet.

[Ensio]

I have been told that electric motor bearings cannot take much thrust so there should be a python drive or similar thingy there. Belt drive if there is no room for the motor in somewhat straight line. Batteries are usually the most xpensive part.

Also the usual stuffing box wastes a couple of hp’s so some version of the water lubricated shaft seal would be a good idea...

[nedL]

If I went that route, is the prop shaft hooked directly to the motor or is a pulley and belt system necessary? Also, do you remember what size and pitch the prop was?

Let me do some thinking and try to remember what I did almost 40 years ago. Lol

The prop selection wouldn’t be tough. If I understand your intended use (based on your posts here), you don’t need to worry about ultimate performance and efficiency, so once you have your motor in hand to know the RPM range you can use any one of the online prop calculators to find out what prop will put you in the speed range you want. My guess will be somewhere around a 12x9. That will put you in the small range of what was used in the small (14-16’) mahogany runabouts and speedboats. eBay is where I would look. They used to be able to be found cheap there (~$50).

Go with a 1” prop shaft. That will be the easiest to find a prop and stuffing box for.

[cstevens]

Also the usual stuffing box wastes a couple of hp’s so some version of the water lubricated shaft seal would be a good idea...

Hmmm. I can't find any actual data on this but I'd be very surprised if the stuffing box friction losses are anywhere near that large. First, a "couple of hp's" is pretty huge when you think about it. Compare to a 2hp outboard. Does it really take that much power to overcome the friction in the stuffing box? I can turn the shaft on my 34' boat pretty easily by hand, so I'm thinking no. And then it's also worth pointing out that a traditional stuffing box *is* a water-lubricated shaft seal. If there is a lot of friction there then it's too tight. I'm guessing that with modern teflon packing a traditional stuffing box is actually pretty efficient. Not trying to argue against dripless seals (although they have their own problems that can be catastrophic) but just worth making that decision based on some real info.

But back to the immediate question. I started writing up a bunch of thoughts on using golf cart motors (mostly pro) when I came across this site:

https://www.goldenmotor.com/frame-bldcmotor.htm

The 48v 3kW BLDC Motor seems perfect for the Palmer. Motor and controller together would be about $600. They also sell electric outboards so they should have some familiarity with boat applications and may be able to provide technical advice as well.

One further point about the question of a thrust bearing. Electric motors are designed to take a certain axial load. Whether a thrust bearing is needed would depend on the axial load rating of the motor and the anticipated load in the specific application. The motor supplier should be able to provide the info needed here. But it's worth noting that the Elco setup, which seems very well engineered, *does* incorporate a thrust bearing. Probably not a bad idea to use one.

It looks like you could put together the full setup for around $2,000 for the motor, controller, batteries, motor mount fabrication, thrust bearing and other misc. parts. Still not cheap but a lot less than the Elco cost.

[GregH]

Have a look at this- http://www.thunderstruck-ev.com/

I've not yet purchased anything from them, but am seriously considering one of their units for my 18' Catboat build.

[cstevens]

Have a look at this- http://www.thunderstruck-ev.com/

I've not yet purchased anything from them, but am seriously considering one of their units for my 18' Catboat build.

There you go. The 5kW kit looks like it would work nicely. And it's worth noting that they say:

If you choose not to use a gear reduction, it's important to install a thrust bearing somewhere in line with the prop shaft, as most motors are not rated for axial/thrust loads on the shaft.

So there you go.

[Paul Pless]

a humble suggestion

[NickW]

I know this is a UK organisation but it may provide info and/or links to other sites.
https://www.electricboatassociation.org/index.php

Nick

[Rich Jones]

Have a look at this- http://www.thunderstruck-ev.com/

I've not yet purchased anything from them, but am seriously considering one of their units for my 18' Catboat build.

A very interesting site! Thanks. $2,000 for motor kit and another $600 for the recommended gear deduction. Plus whatever the cost for stuffing box, shaft and prop. Let's say $3000 for the whole setup. Gives me lots of think of. With any inboard, I'd lose some cockpit space also.

[cstevens]

I like Paul's humble suggestion myself, but not for the mechanically disinclined for sure.

I'm also not sure I understand the point of the reduction gear in the Thunderstruck setup. A reduction gear is meant to match the engine RPM to the prop at the motor's ideal operating speed. But electric motors don't have an ideal operating speed. And unlike an I.C. motor, electric motors deliver full torque at the lowest RPM and torque drops as rpm increases. So running the electric motor at full speed and then using a reduction gear to get the right shaft RPM seems like needless complexity to me.

Now it's possible that the Thunderstruck motors are high-rpm, low-torque, in which case they might need the reduction gear to produce enough torque to turn a prop large enough to move a displacement sailboat, which is their target market for that kit. So a) you might be able to do without it on the Palmer or b) you might want to find a motor with a higher torque rating.

[cstevens]

...so I just revisited the original build thread so I could refresh my memory on the cockpit layout and found these photos.





And now I don't think you should change a thing. She's perfect and why mess with perfection? Buy a new trolling motor and keep using her.

[Rich Jones]

...so I just revisited the original build thread so I could refresh my memory on the cockpit layout and found these photos.





And now I don't think you should change a thing. She's perfect and why mess with perfection? Buy a new trolling motor and keep using her.

That is what I really want to do. Right now it has an old 80 lb. thrust motor that is used for both propulsion and steering. I'd like to replace it with a twin 80 lb. (160 lb. total) thrust pod that MinnKota makes for mounting on outboard motors. It would fit perfectly on my skeg and I would add the rudder from the original design. The rudder post could go up the same tube that I used for the trolling motor.
However, I spoke to MinnKota and they don't recommend the motor for main propulsion. It could be that MinnKota is just covering their butts by saying that the motor is meant for auxillery use only. Plus, the battery drain would limit cruising time. Right now, I have one set of batteries, but the boat is wired for another set, which I would add. That said, I generally don't go out for more then a couple of hours anyway. I have also seen several boats that use a trolling motor for main power, including one that is commercially built.
Another drawback of the trolling motor is speed. They are built to push a big boat slowly. At present, I get a top speed of 5.5 mph at full charge. After an hour of cruising at 4 mph, my battery is down 25%, but I can still get 5mph if wanted. Doubling the power would not double my speed. I'm thinking a new top speed of about 7mph. Hull speed is around 6mph with my 16' waterline and 4' waterline beam.
I have experimented with RC plane props and get a bit more speed and range, but they are fragile and I have no way to replace one out in the middle of the lake if it broke. With the inboard, speed would be no problem.
The bright side with the MinnKota pod is ease of installation, low cost ($1,200) and I don't have to mess up the woodwork in the cockpit.
So, it's either that or go with the inboard, with which I'd have more power then I'd ever need or could use.
Decisions, decisions. The much more expensive inboard option would be much harder to get past my wife.
I'm trying to hold onto my money to pay for our daughter's wedding next June. I suppose I could buy the expensive motor and hold her wedding reception in the basement. I'm sure she'd understand....

[Garret]

Of course your daughter would understand - but how would you know after having been disinvited from the wedding & divorced? Just kidding, I doubt it'd be quite that drastic...

I'm glad to see that you're exploring possibilities & this is a good crowd to bounce things off. Looking at that clean uncluttered cockpit makes me lean towards replacing the outboard you used. It was 12 years old, right? I'm not sure I understand why the twin 80's. Is that to go from 0 to 6 in 2 seconds instead of 5? Planning on pulling a water skier? Here's a 200 lb. thrust motor for $350: https://www.ebay.com/i/253137075013?chn=ps

I think this is a KISS situation - but that's just me.

[cstevens]

Rich, I wonder if this motor would work?

https://www.electricpaddle.com/



It uses a high aspect ratio prop like the ones you were experimenting with and it might give you more speed than the trolling motor which, after all, is meant for trolling not running a boat at hull speed. I haven't tried it myself but I've seen one and I think it's a pretty nice unit. Yeadon has tested one - you might talk to him about it.

[Rich Jones]

Of course your daughter would understand - but how would you know after having been disinvited from the wedding & divorced? Just kidding, I doubt it'd be quite that drastic...

I'm glad to see that you're exploring possibilities & this is a good crowd to bounce things off. Looking at that clean uncluttered cockpit makes me lean towards replacing the outboard you used. It was 12 years old, right? I'm not sure I understand why the twin 80's. Is that to go from 0 to 6 in 2 seconds instead of 5? Planning on pulling a water skier? Here's a 200 lb. thrust motor for $350: https://www.ebay.com/i/253137075013?chn=ps

I think this is a KISS situation - but that's just me.

I just looked up that 200 lb. thrust trolling motor. Made by Cloud Mountain. I looked at their website and I'm just not sure it's a true 200 lb. thrust motor. And for $429 new? Seems too good to be true.
The problem with using a regular trolling motor as opposed to the pod is that I'd void the warranty the minute I butchered it in order to install it. For that price, though, it is tempting.
I'm thinking also that I could maneuver better with the prop wash hitting a rudder instead of the motor just turning as it is now.
A new 80 lb. thrust MinnKota goes for almost $900. That's the saltwater version, which is what I'd get. I boat in fresh water, but you never now. The double 80 lb. pod goes for $1200, so might as well go with that. Plus, I don't have to butcher it to install it.

[Garret]

But Rich - everything on eBay is always top quality & exactly as advertised! The price is awfully good - might want to do some googling about their reputation?

[Rich Jones]

But Rich - everything on eBay is always top quality & exactly as advertised! The price is awfully good - might want to do some googling about their reputation?

I read a few reviews about they call 200 lb. and 250 lb. motors. They never use the word "thrust", which is strange. One review says that's it nowhere near that level of thrust but does push his 14' canoe at 5.5 mph.
I will do some more googling on it.

[openboater]

Did you see this inboard setup ?

https://www.boatdesign.net/attachmen...ric-pdf.93696/

[jpatrick]

That is what I really want to do. Right now it has an old 80 lb. thrust motor that is used for both propulsion and steering. I'd like to replace it with a twin 80 lb. (160 lb. total) thrust pod that MinnKota makes for mounting on outboard motors. It would fit perfectly on my skeg and I would add the rudder from the original design. The rudder post could go up the same tube that I used for the trolling motor.
However, I spoke to MinnKota and they don't recommend the motor for main propulsion. It could be that MinnKota is just covering their butts by saying that the motor is meant for auxillery use only. Plus, the battery drain would limit cruising time. Right now, I have one set of batteries, but the boat is wired for another set, which I would add. That said, I generally don't go out for more then a couple of hours anyway. I have also seen several boats that use a trolling motor for main power, including one that is commercially built.
Another drawback of the trolling motor is speed. They are built to push a big boat slowly. At present, I get a top speed of 5.5 mph at full charge. After an hour of cruising at 4 mph, my battery is down 25%, but I can still get 5mph if wanted. Doubling the power would not double my speed. I'm thinking a new top speed of about 7mph. Hull speed is around 6mph with my 16' waterline and 4' waterline beam.
I have experimented with RC plane props and get a bit more speed and range, but they are fragile and I have no way to replace one out in the middle of the lake if it broke. With the inboard, speed would be no problem.
The bright side with the MinnKota pod is ease of installation, low cost ($1,200) and I don't have to mess up the woodwork in the cockpit.
So, it's either that or go with the inboard, with which I'd have more power then I'd ever need or could use.
Decisions, decisions. The much more expensive inboard option would be much harder to get past my wife.
I'm trying to hold onto my money to pay for our daughter's wedding next June. I suppose I could buy the expensive motor and hold her wedding reception in the basement. I'm sure she'd understand....

You said it at the top: This is what I really want to do.

So do that. Or a reasonable facsimile. Don't bother with power you don't need. Don't bother with speed you don't want. Why try to push the boat beyond hull speed? You know that's a losers game when it comes to power. Explore the MinnKota some more and others. Doesn't Torqeedo make a pod that would work? They are expensive, I realize. But at least they will back it as a main source of power whereas MinnKota seems reticent.

Your boat simply screams: Slow & pleasant cruise. Embrace it. Don't succumb to the dark (go faster) side.

Jeff

[Rich Jones]

You said it at the top: This is what I really want to do.

So do that. Or a reasonable facsimile. Don't bother with power you don't need. Don't bother with speed you don't want. Why try to push the boat beyond hull speed? You know that's a losers game when it comes to power. Explore the MinnKota some more and others. Doesn't Torqeedo make a pod that would work? They are expensive, I realize. But at least they will back it as a main source of power whereas MinnKota seems reticent.

Your boat simply screams: Slow & pleasant cruise. Embrace it. Don't succumb to the dark (go faster) side.

Jeff

As far as speed is concerned, I just want to reach the boat's true potential, which is faster then it goes now with the 80 lb. thrust motor. I've no desire to go screaming over the waves. No succumbing to the dark this for me!
Toqueedo does have a nice pod which is both expensive and would require a well to be built in the fantail.
I'm probably overthinking this whole thing. Another trolling motor would probably do me just fine since the boat is not going to get everyday, extensive use.
Just thought it would be a good idea to explore inboards.

[JimConlin]

For that length and hull form, 5.5 Kts. is as fast as it's going to go.
More power won't get you significantly more.

[Rich Jones]

For that length and hull form, 5.5 Kts. is as fast as it's going to go.
More power won't get you significantly more.

Not unless I'm surfing down the face of a wave. God, let's hope that never happens!!
I fully realize that doubling the power will not double the speed. But, I'd still like to have a motor that can get me to hull speed. The motor on there right no does not.