DIY Diesel Electric Catamaran drives Feasibility ???

[NahanniV]

Hi,

I'm on a Wharam Tiki 46.

I am faced with a broken propulsion system that either needs to be fixed or replaced.

Currently the system is a single BetaMarine 27hp diesel in a central pod. It drives the prop through a 2:1 transmission and a very long (14') lifting drive shaft with a universal joint. Here are some pictures from the original build, if you are interested:
wakataitea tiki46 long shaft system - Wharram Builders and Friends

When I described the system to an engineer friend, he said that "it violates a good number of basic design principles".

The system has worked for about ten years and 30K miles with various problems fixed along the way, but recently the propeller shaft broke.
At this point all the drive leg components need to be replaced. The engine and transmission seem to be in very good condition.

I am looking at replacing the long drive shaft with a Sillete catamaran drive:
https://www.sillette.co.uk/sonic_typ...ran_drive.html
as fitted on Gemini Cats and some Prouts. That should be relatively easy(Ha Ha) and will cost about $6000.

That seems to make the most sense, but I am very interested in an electric option if it is reasonably feasible.

I completely understand that there is no existing battery technology that can reasonably replace Diesel. So, what I am wondering is if I could install a diesel electric system without batteries ?

My (half baked) idea is to replace the transmission with two 10KW generators and two 10KW electric engines (pods ?). The generators and drives would be connected together with some simple electrical switching to control forward/neutral/reverse for both drive engines. The diesel speed would control the motor speed.

Any thoughts ?

[s/v Jedi]

Convert the 27hp to a generator at electric motor voltage. Use two external pods/motors and two controllers. Google for websites and kits.

[a64pilot]

You can do it, it won’t be cost effective nor will it be efficient,but it can be done.
It makes sense if for instance the required engine placement makes a mechanical drive system very difficult.
Maybe a hydraulic drive would make more sense than electric?

Is an outboard an option?

[skipmac]

The suggestion from Jedi would be probably the best solution. With the Beta you have a big piece of the solution already installed assuming it is low hours, excellent condition and not so old that parts are a problem. Have not looked into the details of this particular job but shouldn't be too difficult to bolt a generator section onto the Beta.

However I think it will probably NOT be cheap or simple to add two electric drives to the boat. Without seeing the setup I can picture major fiberglass work to make the mounting for the motors, holes for the drive units, etc and all reinforced to handle the weight and propulsion. Unless you have the technical background this might be an area where you want a pro involved.

Another issue I've encountered when investigating electric power for my boat, all the "marine" electric drive motors I found are really, really expensive, like several thousand dollars for a 5-10 kW motor. Then I look at heavy duty, continuous use rated industrial motors and similar sized units are a thousand or so. A new electric motor for my Prius hybrid which if I recall is around 50 kW or more was around a thousand as well. So far I haven't been able to get a straight answer from any marine electric supplier as to why their motors are so much more than any other electric motor on the planet. It's not like the marine motors are all stainless steel and made that much better. Even if the industrial motors start rusting in a few years you could buy several spares, swap out every few years and still end up cheaper than a "marine" system

[skipmac]

By the way, what basic design principles does your friend say the existing system violate?

[skipmac]

Originally Posted by skipmac

By the way, what basic design principles does your friend say the existing system violate?

Well I looked at the photos and immediately see one thing that looks very problematic to me. That is a very, very long shaft and the support in the photos looked minimal. No way to make it any shorter?

[a64pilot]

I think you could take the hydraulic drives off on any number of industrial pieces of equipment.
This was my last lawnmower, 37 hp and hydraulic drives for the wheels, obviously forward and reverse, very compact and hydraulics and salt water isn’t so bad, electrics and salt water can be a safety issue, especially at higher voltages which you need and high current levels.

[sailingchiro]

I like Jedi's idea. Buy a generator head for lets say 10kilowatt. The 27 hp should have no problem creating the voltage and current for twin electric engines. The Beta is reliable and easy to get parts. It is already plumbed for input and exhaust. The generator heads are plentiful (big truck generators). Use a belt and get the correct size pulleys. All in on the generator, maybe $1000-1500. Make the throttle for the beta adjustable with nut and bolt in order to fine tune the correct voltage. Battery bank for using electric drives for short distances. Electric drives maybe from a electric forklift or electric car. Get the batteries from a Chevy Volt. Twin engine on a catamaran is very nice.
In fact you could hang a house generator AND battery alternator. The house gets 120 volts while the electric engines get their voltage through the batteries. Best of all worlds.
I am normally against electric drives but in your case it does make sense. The long shaft has some weight. The Beta is already installed and ready to work for you. Unfortunately, the Beta isn't worth much on the used market and you would have to replace it with some kind of power. I have seen the Markon 7kw gen heads for $250.00. Just sayin.

[SailRedemption]

With one engine there, I'm with A64, go hydraulic. My dock neighbor has a 65' powerboat with two Cats that drive hydraulic pumps, in which power two hydraulic motors. He can run one engine and have reduced speed with both, or one, prop or both engines. He says he turns the engines on, sets the RPM then uses a throttle for the hydraulic motors. He says it really efficient..

You could fit a pretty good sized hydraulic pump on the Beta and have it run your props via hydraulic motors. Hydraulics very rarely fail, and if the hoses are inside and out of the elements they will last a very long time.

Regarding the diesel electric, I am a mate on a 300' support vessel that is diesel electric. It's not like you can just punch it and go or you will trip a breaker. DC motors would be different(the newest boat my company built is DC and I want to drive it one day and see the difference) but AC you will have a learning curve on throttle response. Now I haven't used a small version of this on a smaller boat, so I could be way wrong here. I just wanted to pass that on.

[a64pilot]

Often with an electric drive, the motor RPM is set, either to keep voltage up, or if AC to keep the Hz correct.
So long as you do most of your motoring at high throttle, this is fine, but slowing down will have the motor at the same high RPM.
Just like a generator.
BIG DC generators are rare, people think alternators make DC, but they don’t, they make pulsating DC, cause they actually out out AC but run it through rectifiers to get pulsating DC.
Of course a battery doesn’t care and is a huge capacitor sort of, so if you had a big battery in-line you ought to get real DC.
Not sure how a DC motor would like pulsating DC, May be fine for all I know.

Often hydraulic drives will leave the motor at high RPM, but there is no need to.
Hydraulic pumps can be amazingly tiny, the 3000 PSI pumps on an AH-64 that each could run the whole aircraft were the size of my fist.

[s/v Jedi]

Everything the hydraulic setup can do, electric can do better. Have you floored the accelerator in a Tesla? Have you felt the power of the drives of the Queen Mary II? For a small boat setup, the controller designed for electric cars are used and they work well.

[a64pilot]

If you want to believe there is something inherently different, do so.
In truth it doesn’t matter what force turns the prop, hydraulic, electric or steam a horse power is a horsepower.
However direct drive is most efficient, and hydraulic drives have far less problems in a salt water environment, everything from being electrocuted to stray current can’t happen with hydraulic, plus it’s pretty simple to rebuild a hydraulic pump, an electronic controller? Best carry spares.

In really big things like ships and Monster draglines electric does do better, but they have nothing at all to do with our little boats any more than the Queen Mary does.

[s/v Jedi]

I’m sorry A64 but I think that for every hydraulic prop drive on a sailboat, at least 100 electric drives are installed. There are perfect out of the box solution made for boats for even the smallest hp applications, all the way down to trolling motors. There are no shorts, no stray currents etc. It’s a clean, simple and very viable option for sailboats.

[skipmac]

While true there are a lot more electric drives on boats I'm not sure that this is an argument that electric is better. Maybe more marketing, consumer perception or other reasons for the popularity other than electric is truly the best option.

If you look at commercial equipment like tractors, earth movers and all related machinery they all use hydraulics, not electric drives. This is equipment that has to run all day, every day, year in year out, generally left outdoors year round and suffers abuse like a commercial fishing boat. Certainly modern electronics are pretty reliable but if something like an electric motor control module dies somewhere in Outer Slobovia you will be out of luck. Blow a hydraulic hose and you can find repair options anywhere there are tractors. If you aren't near any place for repairs I think hydraulic repairs would be possible for most reasonably competent cruisers but those with the ability to repair a solid state electronic device are very rare.

I confess my hands on experience with hydraulics is fairly limited, mainly farm tractors, log splitters and similar but so far all of those have been totally bullet proof for years and years.

I have read that hydraulic drive motors can be a bit noisy. Some say they make a whining noise that can be very annoying. Would love to hear comments about that.

[a64pilot]

Originally Posted by s/v Jedi

I’m sorry A64 but I think that for every hydraulic prop drive on a sailboat, at least 100 electric drives are installed. There are perfect out of the box solution made for boats for even the smallest hp applications, all the way down to trolling motors. There are no shorts, no stray currents etc. It’s a clean, simple and very viable option for sailboats.

I’ve not seen a single one myself, not in small boats anyway.
I have seen hydraulic ferries though, there are some that operate in Savannah Ga and ferry back and forth across the river.