Electric propulsion - stops or stalls - any experience ?

[Pete7]

Originally Posted by Skipper Lee

Jeepers, I don't know why my photos come upside down or sideways?

Sorted for you. If you are using a smart phone to take photos, I find it useful to run them through Microsoft Paint first to either re-size them or sort the orientation.

Pete

[seandepagnier]

I started using electric propulsion many years ago and it's fairly reliable. The motors which are submerged in a pod failed by water leaking into them. This happened to me as I started with trolling motors and also used a brushless rc motor with planetary gears in this arrangement. Eventually when 3 of failed this way I did not replace them, so I will avoid using motors that are submerged despite better cooling.

I was and continue now with electric propulsion mostly for the challenge and proof of concept. Mechanized propulsion is just not essential for sailboats and it never was.

A lot of the electric conversions posted here seem to be re-using the inboard arrangement. Be wary of this as it's not designed for a very high efficiency because of the many compromises made for an engine which you no longer need to make for an electric drive. For example, there is a reason pedal powered kayaks use 16 inch propellers. For a 28ft monohull you need a 4-5ft diameter propeller to achieve 90% efficiency, so in most cases you will achieve 20-30% efficency with typical inboard engine bronze propeller of 14 inches, which is significant running on battery power which has limited density. If you can use larger propellers it greatly helps with efficiency.

A 2:1 reduction from motor to propeller is questionable. I am currently using an 11.5:1 reduction, but I think in the future would like to use a 15:1 or 20:1 with a larger propeller. My beam is 4ft and the propeller 32 inches diameter. I would prefer a 40 inch diameter propeller. The ratio really depends on the electric motor and propeller, but a larger reduction allows you to use a much smaller and cheaper electric motor which saves a lot of cost and weight. The larger propeller more than offsets the efficiency loss in the belt, and the loss of 2:1 or 8:1 is about the same anyway.

Putting a propeller in the inboard location reduces efficiency because the propeller passing the hull is not in clean flow of water, and stuffing box has friction. This also limits how much you can increase the size of the propeller because if the prop is too close to the hull the larger prop will not increase efficiency as it normally would. This is rather significant, and putting the propeller far away from the hull is desirable. It's better not to copy what people with engines do, because they have different design requirements and compromises and they also don't really care about energy efficiency very much. This is plainly clear just from the way people with engines use their boats.

The next thing to consider is the propeller material. Realistically bronze is obsolete. A carbon fiber propeller is actually cheaper to make and much stronger so it can be thinner and have less drag and higher efficiency. More importantly it can have a high aspect ratio compared to bronze which greatly improves efficiency.

For ultimate reliability, the first thing I put on the boat is an efficient sculling oar. On my 27ft boat I could maintain 1.4 knots for hours. I sculling up to 10 miles in a day, but generally it is useful to get to wind or maneuver in harbors or re anchor which is usually not far to move. It has superior maneuverability and is more reliable than an electric motor. Also, a lot more fun and interesting to watch, and much better in cold weather. I have not spent more than $10-$15 to build one. I have seen a lot of sculling oars which were not built correctly and are therefore not very efficient. A good sculling oar is between 80 and 90% efficient which takes a large propeller to equal. As I have sculled more than 100 miles in total and have built 4 oars each one improved from the last, I can say for a 28ft boat for example, this should be installed and working before electric propulsion is considered.

An electric sculling oar would probably be superior to most electric drives discussed here for most people. The efficiency would be more than twice that of powering an inboard propeller, and maneuverability much better. Also it would have a lot of other advantages such as being able to manually operate it as well, but strangely this idea I have so far not seen.

[carstendenmark]

Hi Sean, welcome !

I guess your Crowther trimaran will move at 0.5kt, if you fart !
For my type of boat, sculling is not an option.

The efficiency will surely get better with a bigger, slow rotating and well designed prop.
It would be really nice if you could post us a sketch of design for a larger diameter prop with lower pitch, that can replace an existing prop on a saildrive or shaft, as most of us will "just" make a conversion, not make a completely new propulsion system.

For my own project, I am thinking of getting a used feathering 3-4 bladed prop and then exchange the blades to (3D-printed) design.
Think of submarine prop or containership prop, blade shapes.

I need to have adjustable gear ratio to fine tune = tooth belt drive.

[Skipper Lee]

Fascinating Sean,
Yes for Sculling oar,
No for 5 foot prop on my under 90 ft sloop,
My goal is to keep it a bit more Realistic or I would simply set up an Electric long tail style 27 foot sailboat.
Perhaps my longtail could share the notch in the transom where the sculling oar rests and just be removable and tie it to the high side rail when its windy enough to sail?
Upwind 5 ft prop forward, downwind 5 ft prop astern.
Thus: your 5 foot prop would work and I figure that it would be at least 80% more efficient. Yes for the diagrams and please also post a diagram of the electric sculling oar concept, That's Do-able.

But seriously folks,
Sean, you sound very informed and I love to see engineers push the boundaries but most of us converting to E-driven cant have it so the 4-5 ft prop is the first thing to hit the beach, I also don't have room for that much reduction gear under the cockpit.
We just need to work within the general platform we were dealt, Remove diesel add electric motor, make it pretty good, Sail the boat.
Also it has to sort of resemble a sailboat IMHO, especially underwater.
Thanks for the thoughts on the sculling oar and the carbon fiber prop,
Those are great ideas...

[carstendenmark]

Thanks, Lee ! You really rock !

A question to all :

Do you buy items for your conversion from western countries and suppliers ?

We need to replace bad components.
Where to get the spare parts ? Home, or only from China ?
Where to get them, 10 years from now ?
(If you want to sell your boat, you must convince the new owner, that the parts are replaceable.)

I can still get most parts for my swedish 10 HP Volvo Penta MD6B, put into my boat in 1976 (not cheap, but AVAILABLE).
Not that I want to do that anymore, but I CAN.

Is it possible for you to get the controller, the BMI, or any of the batteries replaced, when you're cruising other countries (well, even at home) ?

It can last several months to get a spare, even living in safe EU or US, if you order from outside of your home turf.
Your sailing season might be gone, when you finally receive it.

Is it worth to save a few bucks to buy outside of your home ground ?

Be sure that everything electronic is available in your home country.
BUY QUALITY.

If you buy crappy stuff, buy two to have a spare, if needed !
Oh, oh, then it's not cheap anymore, right ??
And, will you rely on your spare part of same kind, if the first has already failed ?
The time spent on exchanging bad stuff could be spent on SAILING !

Mechanics are everywhere, no problem. Can fix anything.
But electronics sucks.

Guys, please keep this in mind during your conversion.

[Skipper Lee]

Hey thanks Carsten,
Just keeping in good humor is enough for me these days.
Looking at your boat I wonder if you can ditch the 40 year old Sail-drive and just glass in a shaft log and use a really short shafted E-drive? that removes a lot of rolling gear and seems possible at a glance of your boat on sailboat data. It seems the Thunderstruck system I used could handle that. I attached the invoice for your perusal. I did notice the 48V charger is Asian,
I am going to look into the Carbon prop blades as the next level.
I just want my boat to be all it can be, Not looking for a miracle.
I am ordering a spare motor and a spare throttle and belts just for ballast. I haven't heard of a speed controller going off line but I know its what I don't provision that'll take me out.
That's why I want to get it set up as simplistic as is possible, like no chain or rubber coupler, as in single shaft, rugged installation Etc.
I think E driven Marine systems will pan out over time for tons of users with reasonable expectations and have little maintenance issues.
Batteries however will likely remain the weak link. 2 switchable separate 48 V banks would be great but just spent 23.00$ more for my single set of 6 Firefly batteries than I initially spent on my boat.
Regarding failures, the electric pump still down my water well is from the 80's my electric washer and dryer is even older, yet in comparison my 2008 Jeep engine horribly ate itself 2 years ago. and the previous truck didn't have a much longer life.
In my city there's thousands of I.C.E repair shops and 4-5 electric motor rewinders.
HMMM.

[carstendenmark]

Thanks, Lee !
Where do you sail in Alberta ?

Batteries will get cheaper, even for quality LiFePO4's with BMS on-board.
Initially I'll run for a small bank, in an electronic setup so the bank can be expanded.
I am just cruising daytrips for now, and usually don't sail in very rough conditions.

It's a big job to replace a saildrive with a shaft drive !
So, first I will find out if I can convert the S100 saildrive, if it is still in good health.
It is supposed to handle up to 23 HP, so I think that will do.

Removing the horizontal shaft and the forward/reverse gear to the Volvo and use the vertical shaft by making an extension to it. Then the motor can be placed next to the shaft, toothbelted.
There will be lots of room when the diesel is out, so the batteries can be where it was. An extention bank can be installed mid-ship.

Basically I only need my motor for getting in and out of marinas and to get in position when anchoring. It is a SAILboat, not a motoryacht.
For a start I will charge by marina shore power, with a charger that can handle a genset input. We even have 400V 16A plugs, so I don't have to wait too long for a charge. Just need a charger and converter which can handle it.
As I'm saving on the batteries, I can afford a portable genset, perhaps a Honda EU22i. That will be nice to have to get moving in super-calm conditions (there are actually days with NO wind in Denmark), and at anchor to charge and electro cook.
She will then be a hybrid boat, put I'm not fanatic making a pure electroboat. Solar panels can wait. I can charge for several years from shore, for the cost and maintenance of solar panels.

Here are some shallow sandy waters, so I like a setup, where I can reverse her out of trouble by engine power, if I'm stuck. I need a motor which are capable of giving me a good burst of power !
Probably I can couple two 48V banks together for jumping to 96V, temporarily :-) ? The big prop in the setup will help too.
Just an idea...

[Skipper Lee]

As it's on a trailer, initially I will put her in one of the Alberta lakes (Sylvan Lake)next spring for trials.
Later next season I will move it to B.C on the Okanagan Lakes about a full days drive from here(that's where I bought it and my Son and grandchildren live).
I will move it the next spring to the sea at Vancouver BC, my old sailing grounds where I had a 40 ft Wharram Cat and a 26 ft Plywood (Thunderbird) sloop for many years.
Finally I want to sail it to Mexico the following year to another friends place when I will be finally retired. Then likely get something else about twice as heavy and a few feet longer
I've sailed some in Thailand with friends Prout 39 Cat, Jeanneau 43 DS and have done some racing there (X-99) and Bareboat chartering in Cuba etc.
Basically when Covid shut travel down for 2020 I bought this boat to play with while Working from home.
Anyway I just like a good project to keep my sanity and keep thinking.
I also have bought a new 2000 watt gen if needed to keep it moving albeit slowly.
So far I am having a blast with it.
Cheers.

[carstendenmark]

Seems not many people are having trouble with electric boats so far.
That makes me feel, that this is the right way to go :-)


Cheer up Skipper, the vaccine will soon end your troubles. Give it half year, max.
I'm "stuck" in China for now (well, not exactly unhappy about that, as there are no more infected...), and I will return home to Denmark to my boat etc. when the danes finds a way to control the virus better. I hope that's going to be in the spring.

In the meantime - investigate in the best solution for me, and hopefully others to enjoy it too, when finished.

[NPCampbell]

Originally Posted by seandepagnier

The next thing to consider is the propeller material. Realistically bronze is obsolete. A carbon fiber propeller is actually cheaper to make and much stronger so it can be thinner and have less drag and higher efficiency. More importantly it can have a high aspect ratio compared to bronze which greatly improves efficiency.

There are 2 problems with carbon fiber propellers.

1) Carbon fiber is extremely strong in tensile strength and stiffness but poor in mechanical toughness (brittle), fracture toughness and impact toughness (Izod, etc) due to basically having zero yield strength. Bronze is between 2 and 20 times stronger in impact strength. Banging a wrench against a bronze prop will put a nick in it, however, the same to carbon fiber will possibly fracture it. Care must be taken to avoid propeller strikes against the bottom, floating obstacles, ropes, etc.

2) Care must also be taken that a carbon fiber prop is completely electrically isolated since carbon/graphite is the most cathodic of all elements. If carbon comes in contact with a metal drive shaft it will eat the anodes (and everything else) at an incredible rate.

[seandepagnier]

Originally Posted by NPCampbell

There are 2 problems with carbon fiber propellers.

1) Carbon fiber is extremely strong in tensile strength and stiffness but poor in mechanical toughness (brittle), fracture toughness and impact toughness (Izod, etc) due to basically having zero yield strength. Bronze is between 2 and 20 times stronger in impact strength. Banging a wrench against a bronze prop will put a nick in it, however, the same to carbon fiber will possibly fracture it. Care must be taken to avoid propeller strikes against the bottom, floating obstacles, ropes, etc.

This a good to point out, that carbon is not superior in all ways.


I'm not sure the prop will be damaged from striking rope, but maybe from harder objects. My maximum rpm is only around 200, so I'm not worried about damage as much. If bronze is 2-20 times better in impact but the propeller speed is 1/10th as fast because my propeller is so much larger and slower, then the carbon should do ok. I have already dropped it on the end and it damaged the boat without damaging the prop.


I think it depends on planned use, but I don't think the carbon prop will just fracture and I can't just fracture carbon tapping it with a wrench, I would have to hit it as hard as I can which is a lot faster than it is moving spinning at 200rpm.

All the high efficiency electric boats I have found, none of them use bronze props.

2) Care must also be taken that a carbon fiber prop is completely electrically isolated since carbon/graphite is the most cathodic of all elements. If cardbon comes in contact with a metal drive shaft it will eat the anodes (and everything else) at an incredible rate.

I think it's easy to isolate from the shaft. Mine is isolated, but I also keep the prop out of the water when I'm not using it, and the shaft is a stainless threaded rod of 316, so we will see how long it holds up.




I'm still pondering how to make the electric sculling oar. For this a wooden oar can achieve high efficiency because for example, on a 28ft boat, and the pivot at the deck, 8ft shaft and 6ft blade, it's sweeping an area similar or maybe a little more than a 5ft diameter propeller than is fully submerged. A ball screw is about 90% efficient converting the small lightweight and cheap brushless motor into linear motion. Two buttons, or a twist handle with forward/reverse with variable speed on the paddle can provide "power assist" sculling, but a fully automatic system would need feedback sensors to provide the drive signal.

[mghorton]

Have you looked at the Kiwi feathering props? I had one on my Dufour 35 a few years back and loved it. Blades are made of some sort of high strength plastic and easily replaceable, although in five years of use, I never needed to replace one.

[The Sun King]

I have run into a couple of problems with electric propulsion. Most concerning was controller overheating. I did my testing in cold weather and started my trip in warm weather. I had originally designed for 2 motors, but that was too much power, so an extra controller was in place. I channelled airflow to cool things until I could obtain a fan. Now each controller is equipped with its own fan. You might consider redundancy for critical parts that you can't buy just anywhere. I carried the second motor as a spare, but the motor was never an issue.



Another problem, which you could also encounter with a combustion engine, was prop fouling on the Mississippi. When the water is rising, there is wood in the middle of the river. Everything from twigs to trees. Deeper prop depth could avoid that, but I am rigged for shallow water. I carry a spare prop but have never used it. Ideally, the worst outcome, here, is a tripped breaker and getting wet to clear the debris, though sometimes you can clear by reversing. I only got fouled when approaching 49 barge tows!



One other issue was a motor modification. I advanced the brush timing to make the motor much more efficient in forward. That included being efficient in generation. The controller saw this as a sign that it should not go into reverse if there was much forward motion. This involved technique to avoid problems. The extra efficiency was very useful during multiple cloudy days or during long night runs. Most people won't be modifying their own motors or even using brushed motors, but I prefer them. The advanced timing also virtually eliminated brush and commutator wear.

[carstendenmark]

Thanks, Sun King ! Would you think, that choosing a controller aimed for double power output without fan cooling would have eliminated your problem ?

I consider a controller, geared for maximum power, or some more, so it runs smooth at normal operation, and with fan cooling, just in case.
A saying is (well, not in aviation), that doubling your size of gear will make it run forever.

A fan cooled unit will do the job fine, I guess, but are there anyone here who knows about a controller that is fresh water cooled (can use the same cooling water, that runs through my 18KW motor) ?
Just curious...

[Skipper Lee]

I did put the biggest heat sinc on the controller and it will be fanned on demand. I also mounted the controller vertically with the sinc vanes up/down so as to not trap the heat under the controller. I've noticed on line some folks mounted their controller flat on a board without a heat sinc, it likely would/could overheat like that.
I should consider provisioning an extra controller as well.

Merry Christmas to all.
I got Cornells World Cruising Routes#8 from my girl. Yippee!
I also got every Nav light and all new interior lights all in LED from Santa Lee.
And a Blue Seas AC/DC panel with fancy gauges from ..............Santa Lee.
And 2 sweet Hella interior Fans ,and a wire stripper and a great terminal crimper and adhesive terminals that shrink on.
Sadly I did not get a large bag of tinned copper wire in a variety of gauges,
although I suspect I didn't get the wire as a precaution against me not being found at turkey chopping time, LOL.
Seasons Greetings.