Would this work?

S

Sybarite

Well-Known Member
Joined
7 Dec 2002
Messages
27,784
Location
France
Visit site
Single diesel engine charging batteries which drive two rotatable electric engine pods: one forward (suitably protected), one aft.

Think of the manouvrability.

John
 
losses on hydraulic motors and associated piping are higher than for comparable power from electric ones, which can be designed to be water proof.

http://www.hydraulic-motors.co.uk/application_of_hydraulic_motors.htm

The big advantage for oil would be in case of getting a rope round the prop, as the motor will stall and dump the supply through an overload valve.

EDIT efficiency.

It makes an intriguing concept: a ring hydraulic main powering propellor units, anchor winch, generator, sheet winches, bilge and fire-pumps - all from a constant-speed - economical - diesel engine
 
Last edited:
Sybarite said:
Single diesel engine charging batteries which drive two rotatable electric engine pods: one forward (suitably protected), one aft.

Think of the manouvrability.

John
Click to expand...

Why not? It's how a lot of commercial vessels work, if they require highly accurate placement (e.g. some kinds of diving and rig support vessels, cable layers, research vessels etc)
 
oldsaltoz said:
I suspect hydraulic units would br more efficient and last a lot longer in the high moisture.
Click to expand...
It's not uncommon on cats to have a single diesel powering two hydraulic motors. It works though there are some odd side-effects, e.g. you stop one and the other goes twice as fast.

You may have read 2 or 3 years ago that Nigel Calder was planning to sell his brand new Malo and replace it with an identical one using diesel-electric drive. Advantages include putting the engine's weight centrally, not needing a separate generator and the ability to run for short periods on battery alone.

Systems such as the OP is suggesting exist in some form already - a bow thruster is pretty similar and most outboard-powered sailing boats can turn the outboard for extra turning power (though few use it regularly).
 
this is effectively what the canting keel maxis like wild oats have. A single centrally located diesel runs a hydraulic pump and generator. Hydrualics run the sheet and halyard winches and the canting keel ram. Electrics run the computers, water makers, etc. Not sure what runs the prop.
 
Sybarite said:
Single diesel engine charging batteries which drive two rotatable electric engine pods: one forward (suitably protected), one aft.
Click to expand...

I drove a cat with this set up once, rather than having a prop per hull they were fitted in line with each other down the middle.

It took huge concentration to steer, the wheel turned both pods at the same time in opposite directions and then you had independent power and gear control for each.
 
Single diesel engine charging batteries which drive two rotatable electric engine pods
Click to expand...
Like one of the latest big cruise ships? QM2 or Queen Victoria? although all pods are aft IIRC
 
Variations on this system are common in the commercial shipping world.
Older systems such as on various jack up barges have constant speed electrically driven azimuthing thrusters fitted with controllable pitch propellors with the driving motors in the hull, but the latest systems as fitted to several cruise ships have the variable speed motors actually in the propellor pods driving fixed pitch propellors at infinitely variable speeds between full ahead and full astern. The advantages are many for commercial use but include the facts that you can have your prime mover(s) wherever you want and can run them at peak efficiency, also there's no need for lengthy prop shafts or separate steering gear.
I can easily imagine that a smaller system would be very advantageous in a smaller pleasure boat regarding maneouverability, although possibly less so in a yacht where you would have to consider the drag created and would still need a rudder for normal sailing...
If it's of any interest ROV's are manouvered with electrically driven propellor pods, but they run at high voltage in order to allow use of thinner wiring in the umbilicals which supply their power.
 
There is a diesel hydraulic drive being fitted to a classic yacht at Gweek, according to their newsletter.
We looked at it for commercial catamarans. Currently outboards are the norm for the lighter built ones, but as I posted on here, there are problems developing with picking up petrol, particularly in large quantities. As a fishing cat has a diesel donk for the hauler, why not use it to drive the props, particularly as one popular cat has not enough room in the hulls for diesels, and many users want to keep the hulls sealed as far as possible.
The hydraulic engineers say it will deliver only 65% of the engine power, and this is prohibitive for constant commercial use. OK for a yacht I would think, and consider the advantage of engine location.
 
Flat boats used by mussel fishermen in Brittany have diesel engine powered hydraulic system to operate crane to lift mussel baskets and to power hydraulic outboard leg rotatable for steering. Noise level and speed rushing home for market are horrendous. There is also a small diesel cum hydraulic powered passenger ferry across river in Concarneau. So efficiency must be acceptable.
 
Sybarite said:
Single diesel engine charging batteries which drive two rotatable electric engine pods: one forward (suitably protected), one aft.

Think of the manouvrability.

John
Click to expand...

I looked into this a year or so ago. There are benefits such as greater torque with the electric motors. However, problems come with sizing the engine/generator. You can't simply use a marine Yanmah GM30 or whatever with an alternator expecting it to charge your batteries ..... you'd never get adequate charging, and the crankshaft wouldn't take the eccentric loading for long. Essentially you are looking for a purpose built generator that can output say 10kw (20kw is roughly 30hp ..... but the extra torque with the electric motors should compensate for the lack of generating capacity ... and if you have large enough battery bank you will have reserve for a short run at high power).

Considering the weight of the batteries, the size of the generator, the lack of redundancy in the system (the generator electrical systems are vulnerable in a marine environment) I came to the conclusion that it wouldn't be worthwhile in anything less than a 60 foot boat.

However, I believe Lagoon has produced a hybrid .... see:
http://www.cata-lagoon.com/420_specs_uk.php
I haven't had time to check out it's performance ..... but it will be interesting to hear from owners.
 
Hydraulic drive is/was used by the RNLI. An ex Lifeboat from the 60s that was based at Dell Quay a few years back had twin Caterpillar diesels housed in a watertight (copper lined!) engine room, these drove hydraulic pumps and motors outside the engine room. In the event of capsize or flooding the engine room air intakes would close down automatically and the power units remained serviceable. Also, should either prop become fouled, the hydraulic motor would dump the power and the prop, shaft and power unit would remain undamaged. No idea what the power losses would be in such a system though!
 
You must log in or register to reply here.

Share this page

Top