Hydraulic pump on PTO engine

[powerabout]

I dont know how big your boat is but personaly I would take (serious) elec over hydraulic
You will get what you asked for from the gen versus power differences with a main engine hyd mounted pump.
(The engine maker should be able to give you power output at idle)
BUT I would assume the electric is going to cost more?
I mean commercial (stuff not vetus)
Think about the tunnel, prop and gearbox as one item and the power driving it another so could be either elec or hyd.
If hyd you will need to ( should ) run 2 pumps as the pump requirement for a bow thruster will be way over the top for all your other accessories.

BTDT with pleasure boats and hydraulics and dont like it..noise, heat, cooling problems due to engine idleing, oil tanks having to be mounted at a high point , huge mess on leaks, fire risk, lost space in engine room, hoses/pipes through the accomodation etc etc.
Bow thruster hose bursts and you have pumped the whole tank volume into the bilge before the oil tank level alarm has even gone off.
Will you carry enough spare oil to refill the system???

The chances of a small pleasure boat having an oily water separator...now what are you going to do (assuming your auto bilge pump was turned off?)

To me hydraulic is for a small fishing trawler as bigger they need electric when it comes to thrusters and the other hydraulics are usually run from power packs

If you send some vessel drawings to a bow thruster company they will do the current/wind calculation for you to select the horsepower/tunnel size/depth etc you need.
Then armed with your idle engine power see where you are.

[marshmat]

Why would you need two pumps? A single, variable-displacement pump with load sensing control can handle enormous swings in hydraulic power demand; size it for the full load (with thruster) and it'll just back itself off when not needed.

I do tend to agree that a properly engineered electric system would be preferable.... unfortunately, "properly engineered" in this case involves the big consumers (thruster, windlass, etc.) operating at 24 or 48 V (running 600 amps at 12 V the whole length of the boat through a 00-gauge cable is not good engineering, especially when the 12 V thruster motor has to be rated on a 10-second duty cycle to prevent it from getting cooked). So the battery bank becomes more elaborate, equalizers or DC/DC converters come into the picture....

[powerabout]

yes true
once we see how big the pump will need to be for the bow thruster and you think of the time spent driving (with just the steering for a load) versus docking, I would not want to be turning a pump that big continuously when jack shafted off the front of the main engine.


Yes large low voltage DC is ugly, I was thinking of AC thats why I said expensive ( in the short term)

17m powerboat without gen set?

[powerabout]

How about one of these on the front of the engine
http://www.raventechpower.com/
I like the idea of having this on your main engine so you can have a gen set as big as the main engine should you want?
This technology must be on the door step as it is needed in the windmill business.

I have an interest in this thread as I want to get an old 20m wooden fishing boat from around se Asia and convert to pleasure use.
They are all single engine so I would need a bow thruster for marinas.
Being both a pleasure and commercial user of boats, I lean toward the electric version, but variable speed AC is not as simple as hydraulic

[gonzo]

Hydraulic pumps and motors can be fairly cheap. Specially if you don't need a high efficiency system. For a bow thruster, the standard motors and pumps would be OK. Hydraulics, because they are internally lubricated fare well in the marine environment.

[bertho]

if can bring some experience....
talking about small boat..8/30 meters.
was working for years for fisherman,, everthing can be broken, they will ruine this thing, and hydraulic was the only items resisting to them !!!
so.., we install quantity of hydraulic systems , if properly do, it's the most relieable thing i know on a boat... elctricity will never be reliable on water/humid environment.. problems come mostly from the coupling/clutch, from temperature control, from rusting parts on the deck.
hydraulic power steering is simple, small gear pump, (10 CC ) with a good quality flow regulator, diectly on the engine, most of the time a PTO available somewhere in that all " industrial engine" but sometime the place is taken for sea water pump and you need to add a belt to drive this tiny pump, (do the support with external well sized bearing to avoid any stress on the pump)
sometime, you need to install two different flow regulator, to have quick control at low speed engine with the tiller ( 6 second port to sta.) , and another one for the autopilot ( 18/25 second port to sta.) , who like move slow reaction when sailing.
if you need more power, sometime, as bow thruster or winchs, or ?? , the most reliable is the pump on the gearbox PTO, standrad option with ZF/Masson/ twin disk..., they have 100% reliable hydraulic clutch for a very reasonnable price when you order with the gearbox, and you just engage this one when you need the "big power"
you can also have a mecanic cluth in the from engine, but .. often problems with the clutch...
for simple boats, other system like variable volume pump always running are much more expensive system if you need just a small power steering 90% of the time.. .
always have a large oil volume, good cooling/filter system for this oil , and do regular analyse to be sure is no pollution in like condensation water on the tank... .
unproper size diameter for hose is a common issue, running oil enjoy, cold, large and short way to go !
cheer's
(ps apologise for my "frenchglish" !!)