Electric boat conversion

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IanDoyle

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Hi All,

Does anyone have experience or knowledge around converting a boat from using a diesel engine to a hybrid electric power system.

So this would mean a large battery bank powering a electric motor and a generator to recharge the batteries and / or drive the motor when they are empty. The obvious advantages would be a completely silent boat when running on batteries and a mostly silent boat when the genny is running, altho this is dependent on sound insulation etc. Would also mean that you could recharge when hooked up to shore power and trickle charge with a solar panel. At a high level the diagram below describes the ideal scenario

https://www.fischerpanda.co.uk/res/48v_1x10kw_Shaft_BMV_GENSET_1.pdf

I currently have a 38' Broom cruiser with a Perkins diesel which runs very well so probably not something that I'm going to do soon but the idea of a silent boat with a fully electric drive system is awfully appealing! The boat itself should be well set up to do this (I'd hope anyway). The engine comp is quite large and very accessible, currently has a hydraulically driven prop but I'm guessing I would just connect the motor direct if I converted? Depending on cost, I'm thinking something like a 6 or 8Kw 48V Generator with a 600a Li-ion battery bank.

Wondering if anyone has done this or has any advice etc.

Thanks,
Ian
 
Perfectly possible if you have more money than sense, but the viability of it is low as the huge extra weight of the batteries and the complex charging needs alone would outweigh any advantages in such a small boat, and it would lead to poor handling and the loss of space. Other issues would be insurance as a home installation would bring huge potential liabilities and the resulting huge premiums and this is even before the risks which are currently known and one risk is Li-ion batteries exploding, and once they explode they are difficult to extinguish.

I could add more.
 
This is a story that I read a while ago, about the conversation of a Beneteau Swift Trawler 34 to hybrid
https://www.boats.com/reviews/beneteau-swift-trawler-34-hybrid-shockingly-good-hybrid/
https://www.passagemaker.com/cruise...et-a-first-look-at-beneteaus-hybrid-prototype
As far as I know it never got beyond this prototype.
As it piggybacks the Diesel engine, the diesel also recharges the battery bank. And it can be recharged from shore or generator.
This gives you the option of using your existing Perkins and not buying a generator.
This could save a lot of money, until you feel that you have a viable system that’s worth investing more money in.
 
How about using wind ?
You could feasibly use a large sheet or something attached to a pole and work out how to harness a breeze using ropes , winches and knots .
Perhaps go as far a rigging a system to vary the surface area of let’s call then “sails “ to adjust speed and wind conditions .

You never know you might even be able circumnavigate the globe @ nil diesel expense with a contraption like this :)

Solar panels or a wind generator as well but only for the beer fridge :)

I realise it’s a different mind set on this particular forum ,having a boat that does not rely on its engine(s) :):):)
 
I was talking to whitelighter about this the other day.

A d12 weighs 1175 kg empty. Add oil and water probably 1250 I have2 so 2500kg

I have another 2700kg if diesel

So 5200 kg in total. I don’t know what an electric engine weighs let’s day 600kg the pair

That leaves 4600 kg for batteries.

Google tells me an 85kw Tesla battery pack weighs 540kg so I can have 8.5 of them giving 724kw of power

I have no idea what this means in real life on a boat however ... my Range Rover does 30 to the gallon. My boat about 1.

If a Tesla does 300 miles on a battery using an efficiency of 30:1 suggests my 8.5 batteries will get me about 85 miles. Not my current 250 mile range but it’s a start ! Yesterday I did 30 miles ish to es trenc and back. With shore power I am fine to charge. At anchor not so useful !
 
jrudge said:
I was talking to whitelighter about this the other day.

A d12 weighs 1175 kg empty. Add oil and water probably 1250 I have2 so 2500kg

I have another 2700kg if diesel

So 5200 kg in total. I don’t know what an electric engine weighs let’s day 600kg the pair

That leaves 4600 kg for batteries.

Google tells me an 85kw Tesla battery pack weighs 540kg so I can have 8.5 of them giving 724kw of power

I have no idea what this means in real life on a boat however ... my Range Rover does 30 to the gallon. My boat about 1.

If a Tesla does 300 miles on a battery using an efficiency of 30:1 suggests my 8.5 batteries will get me about 85 miles. Not my current 250 mile range but it’s a start ! Yesterday I did 30 miles ish to es trenc and back. With shore power I am fine to charge. At anchor not so useful !
Click to expand...

Even with shore power it would take 80 hours to recharge on 32A supply if drained to 20%, assuming no other losses or power consumption going on. If you’re enjoying air con etc while you charge it would take even longer!
 
Anders_P42 said:
Even with shore power it would take 80 hours to recharge on 32A supply if drained to 20%, assuming no other losses or power consumption going on. If you’re enjoying air con etc while you charge it would take even longer!
Click to expand...

Most Mariana’s I goto have 3 phase power which will help

I am not suggesting I do it but the power range etc is better than I thought !
 
jrudge said:
I am not suggesting I do it but the power range etc is better than I thought !
Click to expand...
Are you sure it is, J?
I am not saying that your train of thought is totally wrong, but your conclusions make me suspect it could be.
I mean, an electrical-only planing boat which gives, for the same total weight, one third of the range of the equivalent diesel version with the same performance? Without doing any math, that just doesn't pass a quick sanity check, imho.

I suspect that you might have not considered the "same performance" bit.
Of course if you are assuming to use the boat at D speed only it makes a helluva difference, but in this case you should make the comparison with a single diesel of less than half the size of each of your D12s...
Which brings the diesel range well into 4 digits, as opposed to the 250 you mentioned.
Which is bound to be at P cruising speed, surely?
 
on page 16 of this months MBY there is a small feature about battery and solar powered catamarans. Initially aimed at tourist boats but they are considering a full cruiser 12m long. Apparently it will run 14 hours at 7 knots, top speed 14 knots and at low speeds it will just keep going as long as the sun shines. In the med that would be very useful as the sun shines most days, but the wind doesn't always blow the right way or at all. Arguably better than a sailing boat as you can run fast-ish to escape bad weather or get home a bit quicker.

Give it another 10 years of battery and solar panel advances and it could well be the future.
 
BruceK said:
Im curious as to how you would keep the Li-On batteries cool when drawing that kind of amperage.
Click to expand...

electric car batteries have a liquid or gas coolant pumped through the assembly with a heat exchanger/heat pump to manage the temperature. Should be easy to do the same with electric boat batteries.
 
Kashurst, fine for automotive use with free flowing air at sufficient speeds, but a marine variant is a totally different kettle of fish.

Now, graphene batteries will be a different kettle of fish and one I am eagerly awaiting real time data from in actual use.
 
MapisM said:
Are you sure it is, J?
I am not saying that your train of thought is totally wrong, but your conclusions make me suspect it could be.
I mean, an electrical-only planing boat which gives, for the same total weight, one third of the range of the equivalent diesel version with the same performance? Without doing any math, that just doesn't pass a quick sanity check, imho.

I suspect that you might have not considered the "same performance" bit.
Of course if you are assuming to use the boat at D speed only it makes a helluva difference, but in this case you should make the comparison with a single diesel of less than half the size of each of your D12s...
Which brings the diesel range well into 4 digits, as opposed to the 250 you mentioned.
Which is bound to be at P cruising speed, surely?
Click to expand...

My “methodology “ tried to compare like for like. Seems a Tesla motor weighs 35 kg so I possibly over did the weight of the motors.

Remember this is using 5 tonnes !! Of batteries to replace the 5 tonne of iron and fuel. That is almost 9 Tesla batteries that would take a car 2500 miles so 80 ish does seem feasible
 
How much would 8/9 Tesla batt packs cost ?
How much life expectancy, ballpark 5/7/ 9 years ?
Finally someone has already touched on recharge time issues @ marinas but what about the marina not taking too kindly to the expense it’s sacrificing in a fixed service charge agreement ? I mean as a marina operator would you prefer the li ion guys to be on PAYG leccy .Certainly fund there own 8/9 worth of “ Tesla “ batt pack recharge unit ?? Which they presume take with them to a visiting berth to hook up ?

It’s do able but the infrastructure isn’t there yet in marinas .
Columbo in Naples do a SY hybrid .Part small Diesel engines part leccy li ion motors .
40 to 55 M with a leccy only range in single figure so D speed only of single digit km,s .
The diesel(s) are a generators , only the leccy motors conect to the prop shaft(s) .
It’s very quiet and there’s an odd silence as it wafts in / out of the marina .Theres on in La Nap on its 2nd Owner .
Interesting the first owner( one of the Sultan of Oman’s 50 offspring ) spent £79 M on the new build and asked 4 years later €39 M . A Russian owns it now .

Green credentials ? Highly debatable.
 
You would still need a diesel geny or a few .

Here’s why .......

As you go larger up from a Greenline hybrid 35 to a more useable space wise 45 to 65 ftr ,then you hit the wall of other leccy essential consumption like your air con and even basic 220 / 240 sockets , cook top , lights , nav gear , autopilot, electro hydraulics for rudder , flaps and passerelle and tender crane , and hi low ........etc etc .

Unlike a car in a decent specced Med boat those things are gonna grab a huge chunk of a li ion ( or A N Other batt ) % .
Further diminishing the juice available to turn the prop(s) .

So if there no way round a geny for boat home comforts then it feels like the hybrid route is the way Fwds .
Leccy motor turns the prop( s) , geny s provide leccy .Ok some can be stored in the now smaller batt bank .Remember to knock some weight off the 5/6 ton of “ iron + fuel “ to add back geny(s) and there fuel .

And then it s only D speed which a eco warrior isn’t gonna worry about - I guess ?
 
Last edited:
jrudge said:
Porto. Who ever said you didn’t need a gen.

My weigh swap leaves the gen in place. Let’s not go off on a tangent
Click to expand...

Your std geny that came with the boat ( when it was a regular planing diesel ) won’t be enough to feed the topping up of the li ions AND feed the home comforts and boat running list once above a certain size .
So if you are reduced in say a 60 ftr to running a geny all day if you want to go more than 9 km,s away from a charge point at D speed .Then why not use your mains at 6/700 rpm and existing acid bats / geny

Carry on with D12 ,s or what ever ?
Irony is @ anchor the li ion boat of any decent size will be the only ones with genys running :)

There’s been a couple of days this week , blustering day time heat whereby we have turned the geny on to power up the Aircon ( a 42 000 btu - inside st cabin temp 42 degrees ) on our way back to our berth to initiate a cool down .
A hour later when docked it’s now below 30 inside and dropping .Bed time 22 on the shore power .
How much shore power out of a typical 32 A is gonna be left over to top up the li ions for morning
.?

Passage planning an all li ion even with std geny will be problematic.
Like a Tesla buy 10x worse in the Med .

Any benefits above 35 ft basic boat are marginal at best or worse if it’s a fully specced Med boat .
 
Last edited:
Porto. Where do you get 32a power from?

Three phase will give you 64x3 for a start.

Time to charge. Sure. Never said it was perfect but given you have overnight and many people stay local it could work who knows.

Running gen is nothing odd. Mine has just been on for 2 days as it was humid and hot on anchor. That is what they are designed for to run and run and run
 
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