One diesel & One electric

[jdaltonpe]

I have been researching water generating systems and it is obvious that the most efficient production of energy from moving thru the water is with a regenerating electric motor. For long distance cruisers the electric motor is a bit of a worry because of the need to motor long distance thru the doldrums, etc. What if you were to replace one diesel with an electric motor on a cat? You could still maneuver well in tight spots, use the diesel to make miles when the wind dies and use the electric motor to make power when on passage. Anyone ever try this? Am I missing an obvious problem with this idea?

[bibbjs]

Funny, we have been talking about the exact same thing...

[BigBeakie]

Are you aware that you may be able to put enough solar on the boat so that you can motor on solar alone? We will have 4kW solar and will motor at 4.5 knots for a 50' 13T cat. Since we will be in the tropics where there are long periods of low to no wind, this is very attractive. Silent, and very economical in the ROI for the solar panels.

Otherwise consider a DC genset that gives you cruising speed, and you can put it where you want it for maintenance access.

[Redreuben]

There are other factors to this equation to consider such as your need for water making and water heating both of which use diesel power well.

[valhalla360]

Depends what your goals are.

Yes, a diesel in one hull with an electric motor in the other is quite viable for propulsion. Using intelligent design and operation, it should cost little if anything extra and offer some efficiency benefits. There have been a few threads discussing this recently.

If you are talking electric house side loads, solar on a cat makes far more sense than hydrogenation. It's easy to install enough solar to cover all but air/con (technically it can be done but it starts to get silly and uneconomical).

If you are talking propulsion...obviously, hydrogenation doesn't work. Also, expecting the prop designed for propulsion to extract power, is far less efficient than one designed for power extraction. It can work but it will create a lot of drag compared to the power extracted.

PS: don't get sucked into magic electric HP. You aren't going to push a 50' cat at 4-5kts with 5hp...otherwise, they would be outfitting 5hp diesels in 50' cats. Displacement cruising boat speed is determined by HP not torque. HP doesn't care what the power source is. Whatever HP you decide is needed for a particular boat is the HP you need regardless of fuel source.

[rabbi]

Originally Posted by BigBeakie

Are you aware that you may be able to put enough solar on the boat so that you can motor on solar alone? We will have 4kW solar and will motor at 4.5 knots for a 50' 13T cat. Since we will be in the tropics where there are long periods of low to no wind, this is very attractive. Silent, and very economical in the ROI for the solar panels.

Otherwise consider a DC genset that gives you cruising speed, and you can put it where you want it for maintenance access.

A 50ft cat motoring 4.5kn on 5.5HP sounds ambitious. Not saying it's impossible but just doesn't match my experience.

Plus that 4kWp rarely means 4kW available so in the morning or evening hours this 50ft cat will have to cope with 3-4HP.


That said the original idea of one side diesel and one side electric may be strong enough for maneuvering, and even generate a enough power for the house loads on longer passages. I remember I have seen a Catalac for sale with such a setup.
The main problem is: This is DIY with no off the shelf components or experience available, so may need some experimenting (read: wasted $$).

[DotDun]

Originally Posted by BigBeakie

Are you aware that you may be able to put enough solar on the boat so that you can motor on solar alone? We will have 4kW solar and will motor at 4.5 knots for a 50' 13T cat. Since we will be in the tropics where there are long periods of low to no wind, this is very attractive. Silent, and very economical in the ROI for the solar panels.

Otherwise consider a DC genset that gives you cruising speed, and you can put it where you want it for maintenance access.

When will we see the results of the tests? Until then, 4KW and 4.5kts on a 13T boat, is theory.

[bibbjs]

I'm not so sure that 4kW and 4.5 knots on 13T is not achievable...in clam seas, no wind and no current. There are plenty of times that this is perfectly acceptable as well. The big problem that was found with the electric hybrid cats of 2007-08 was not the calm seas condition, but when the winds and waves were up. In this case, they were woefully under powered. Having one diesel and one electric may well be the way to overcome this.

[hpeer]

Once upon a time we saw a cat with 2 Diesel engines that drive hydraulic pumps that drive hydraulic motors. If I understood correctly hydraulic normally each engine/pump drove its own motor but either engine could be switched to either motor or one engine could turn both motors.

I have casually wondered about something like that for a monohull. Use two smaller diesels, run a hydraulic pump for propulsion and another to run a gen set. Now you could also put in a big battery set with an Electic pump and some wind/solar and have an very flexible system. You could drive the boat with either diesel or electric. One diesel could be down without hurting the boat. Carry a spare hydraulic pump and maybe main motor.

You would probably also need to carry spare hose, fittings, presses, dies, fluid, etc.

A bit off the topic but sort of related.

[bibbjs]

The hydrostatic drive idea is also a very interesting one, particularly with sail drive boats like cats. It lets you have the engines where you can get to them and the drive system somewhere else entirely. The main drawback to this kind of system is the size of oil sump needed to keep the system operating at ideal conditions (aeration and temperature are issues). The interesting part of this system is it configures almost exactly like the electric/genset hybrid. The drawbacks are that hystat pumps and motors are expensive and run at high pressures. Proper maintenance is more critical than a gear driven transmission.

[valhalla360]

Originally Posted by hpeer

Once upon a time we saw a cat with 2 Diesel engines that drive hydraulic pumps that drive hydraulic motors. If I understood correctly hydraulic normally each engine/pump drove its own motor but either engine could be switched to either motor or one engine could turn both motors.

I have casually wondered about something like that for a monohull. Use two smaller diesels, run a hydraulic pump for propulsion and another to run a gen set. Now you could also put in a big battery set with an Electic pump and some wind/solar and have an very flexible system. You could drive the boat with either diesel or electric. One diesel could be down without hurting the boat. Carry a spare hydraulic pump and maybe main motor.

You would probably also need to carry spare hose, fittings, presses, dies, fluid, etc.

A bit off the topic but sort of related.

I've seen one and heard about a couple others but they were all a single diesel that is plumbed to run both props.

My understanding is they aren't very efficient and are quite noisy. If you are doing this, may as well just go with a single diesel generator and use electric motors...still won't be as efficient as straight diesels but less rube goldberg.

This is where diesel in one hull and electric in the other comes in. You can get that peak efficiency with the diesel when running fast for a long period of time and the advantages of electric when you don't need lots of power.

[Capt. Ray]

4kW is just over 5HP and it's easy to test - hip-tow your yacht with a 5HP outboard motor on your dinghy. It's not quite a fair comparison because torque on an electric motor is very different from torque out of a small combustion engine, and an electrically-driven propeller on your boat will have a lot more "bite" than the tiny prop on your outboard, but on a calm day with flat water I would not be surprised if you can achieve 3.5 knots, maybe more on the OP's boat. I have achieved over 2 knots with a 100-ton steel ketch with a 20HP outboard as a comparison.

For motor-sailing or simply keeping moving in a becalming, I would normally be very happy to get 3 knots on a passage, that's 75 miles a day, so for this application I think it is an excellent idea.

Originally Posted by DotDun

When will we see the results of the tests? Until then, 4KW and 4.5kts on a 13T boat, is theory.

[BigBeakie]

[I][When will we see the results of the tests? Until then, 4KW and 4.5kts on a 13T boat, is theory./I]

The results of Kato, a 66' Schionning G-Force 2000 with cruising displacement of 12.5 to 13T has been published by Australian Multihull World in issue #144 May/June 2017 pp. 22. Note that this data is almost now a year old, so this is not late breaking news for those who wish to evaluate real data!

The data from actual measurements up to 4 kW, not theory, is as follows:

Power from Battery > Boatspeed flat water

1kW > 1.9 kts
2kW > 3.5 kts
3kW > 4 kts
4kW > 4.7 kts

[rabbi]

Impressive figures.

I overlooked the weight you stated, and obviously things are a bit different with these extremely leightweight builds compared to normal 50ft cats.

Now I just need to find 2 Million for this beauty so I can save a few hundred bucks on fuel.