electric motors for power cat

[auzie]

hi i am trying to work out if its feasible to have two gen sets running two 9000 thoosa motors which should be big enough for the 6 ton cat i am building .being power only and having two motors ,takes away any possible break down problems .and with two gen sets to run continuasly if necessary the need for a large battery bank is avoided, so less bats -less fuel ,less weight ,or am i missing something but what i dont know is what size these gen sets have to be? any ideas very welcome .

[FAST FRED]

The use of gensets to produce electric to move the boat will result in MUCH higher fuel consumption compared to the usual gear box and shaft.

What is the purpose of the exercise?

FF

[Rick Willoughby]

I cannot figure out how you can get less weight if you connect alternators to diesel engines then connect those alternators to a battery charger then the charger to batteries then the batteries to controllers then the controllers to electric motors then the electric motors to belt reductions that connect to a prop compared with just connecting the diesels to the prop through a small reversing box.

You would need large incentive like a diesel prohibited zone of operation to justify all the added expense and complexity.

Rick W.

[xsboats]

Not having your diesels directly connected to the shafts allows for their placement in the hull to be advantageous to trim needs. Diesel/electric allows you to run your diesels at a constant efficient rpm .This comes with a 15%+ loss of efficiency to heat,etc...on the electric side. The traction motors I have used were quite heavy , which somewhat offset the trim benefits. I have had moderate success converting a twin gas engine displacement vessel to diesel on one screw and electric on the other.This allowed for cruising on the diesel screw, docking on both, and harbor cruising on the electric via the genset. I am currently working on a diesel/hydraulic boat. Anyone have input or experience in that setup?

[Rick Willoughby]

Originally Posted by xsboats

Not having your diesels directly connected to the shafts allows for their placement in the hull to be advantageous to trim needs. Diesel/electric allows you to run your diesels at a constant efficient rpm .This comes with a 15%+ loss of efficiency to heat,etc...on the electric side. The traction motors I have used were quite heavy , which somewhat offset the trim benefits. I have had moderate success converting a twin gas engine displacement vessel to diesel on one screw and electric on the other.This allowed for cruising on the diesel screw, docking on both, and harbor cruising on the electric via the genset. I am currently working on a diesel/hydraulic boat. Anyone have input or experience in that setup?

Why not design the diesel system to cruise at optimum efficiency in the first place. Saves lots of money initially and less fuel in the long run. Agreed if there are location rules that prohibit diesel then the diesel/electric offers a possibility.

There are many ways to adjust trim with a 6 tonne boat rather than buying all the expensive electric to allow flexibility in placement of components. A chunk of lead is used in sailing boats. However getting the trim wrong is poor design.

The losses will be much worse than 15% by the time you add in all the extra weight that has to be dragged around.

Hydraulic has potential to be lighter than electric but losses of the order of twice electric. Expect losses of 30 to 40%. A close coupled system might do slightly better. However there will be very limited ability to store energy to operate on hydraulic alone.

There are others who have the same idea believing the because hybrid has advantage on the road it will magically have advantage in a boat. It would be helpful if you could provide some numbers on the results you achieved with your partial conversion. I am figuring you are not entirely happy with it given the intention now to try hydraulic.

Rick W

[auzie]

I have seen two people with hydraulic motors on their catamarans and they took them off because it was too noisy,

[ASM]

Auzie

The hydraulics noise problem is just a case of bad engineering. Hydraulics can be a pain and even the biggest shipyards make mistakes with them. ALL components need to be resiliently mounted, use flexible hozes and the lowest pressure possible, use pressure pulse dampers and use resilient connections for the lines running the the hydraulics. Forget one connection, then the whole thing will be noisy, hydraulic whining noise in the construction is the result.

[Jack Daniels Eq]

I am working toward that solution, and will avoid the entire diesel bit.
Use wind, motion, solar for recharging if nowhere near replenishing diesel. I simply dont want it on board. Plus when ya run out of it, its all over.
There is tons of very good, relevant data avail.
Li-on has about 100,000hr life nowadays, packs massive punch, its very lite. I would simply go down that road, period. My situation will be sail assisted, but the concept will be identical.
BR>Jack

[StianM]

Originally Posted by xsboats

This comes with a 15%+ loss of efficiency to heat,etc...on the electric side.

Ever heard about permanent magnet motor? the cos on them is about 1. no reactive power causing heat, but they are quite expensive.

[Jack Daniels Eq]

Hi - thanks for the reply - I must say - it has gone very quiet here - most of the other forums are pretty active, by comp.
None of my theories or solutions are cast in stone. I have looked at real-life situations from Tesla - 380vac, 3phase to 110vdc, 1phase, to egg-beaters.
About 15 years back I was doing some pretty serious model boat racing - I built a 5 foot Kevlar copy of my real 48 foot Scarab. My baby Scarab had 3 x K&B gas outboards on it that developed some real serious horsepower for a plank. Next to me were some kids playing with a toy electric boat. In a drag race, they could whip me. Already then I knew it to be the future ... look at Tesla autos.
I am open to any/all ideas.
BR>Jack