Water Jet Bow Thruster

Thanks for the excellent info.
This one of the reasons I like this forum so much!
I have not had the opportunity to run a drop down but have inspected several and was not impressed...(in the yard for repair) The tube style works well.
I do like the quick response it gives. You make a good case Michael but I do enjoy the idea of using a deckie.
Frosty I will check out more sites on fairing.Thanks

 

I would like a similar thruster for my next boat but can I get the non hairy leg (split V) type drive

 

If you go Electric , use best practice when installing.

The electric units have a short life cycle if they are starved of DC power and if they get wet. No quick and dirty in the installation .... carefully follow the installation guide.

 

I never thought of that,---follow instructions,---carefully!!!!!

 

Yes the split V version would work very well!
Although sometimes the cost can run higher than a drop down or a tube and leave you with nothing to put it on...
I think electric powered hydraulic might be the way for me to go. I run a 75 Amp. alternator and a Balmar diesel 100 Amp.DC Gen-set/water-maker/scuba compressor and a 4-8 D battery bank. I think that might handle the short current draw. I seen several electric models fry from seal leaks.

 

One advantage to hydraulic is that on many models the motor is actually built into the leg, lower unit of the thruster. This saves space. I know nothing of electro Hydraulic , but straight Hydraulic, via engine driven pump is a very expensive system.

On a small boat, or a refit , Straight Electric is the way to go.

Might be worthwhile to visit the next major boat show and investigate what is on the market,

A good question to ask is ...How is the lower unit protected from monofilament fishing line building up between the prop hub and the lower unit oil seal. Monofilament fishing line or plastic bags is the killer of lower unit oil seals .

 

I agree with Michael, unless your DC has enough output to power a DC powerpack with hydraulic thruster motor, best option is DC electric thruster. Even a big frame Load master 175amp alternator with 1000 amp hr gel auxiliary house batteries would struggle to meet powerpack load for hydraulic thruster.

You could fit a belt drive hyd pump to your main engine or clutch PTO drive unit to transmission but then you have the expense of hoses, valves and thruster motor. DC powerpack for steering incl cylinders is about $6000.

A DC thruster is simple fit, (no hydraulic hose/valve/solenoid setting up) low purchase/set up cost and effecient but you need to ensure your DC unit meets thruster load, its the simple way if the DC genset kW output is enough.

Important issue is match thruster hp to your boat size - talk to a reputable manufacturer or dealer, most recreational boat chandlers don't have a clue about thruster selection.

 

Electric load is an issue. A typical bow thruster scenario has you pulling anchor in a tight harbor. You will be simulatnoiusly thrustering to stay on station and picking up your anchor with a poweful electric winch . This is a huge electric load. Over spec your energy storage system and use a dedicated charger...

 

I did some checking with a few of my past captain customers, (granted they run 90 to 140 foot vessels) and they do agree with Michael and watchkeeper.
The Amp. draw and space to run lines along with the pump and motor is really overkill for a 51'.
As Cap't. Dick said (your trying to build a better mouse trap and the one on the market works fine for my application.(ele. or one piece hydraulic)
As I said before, I've run her for 22 yeas with out one and had very little problem except once in a blue moon while docking in winds.
Never hurts to make things a little easier as the years go bye.

 

You get over that problem by placing a battery close to the unit and then only charge wires is necessary.

It does mean that you will have a battery sitting there with minimal use.

Doing without is a better idea

 

Frosty, I think you are right. Doing without saves a lot of problems when it is rarely needed anyway.

 

That won't work to well, a lead acid battery is designed for high load but very short cycling draw fast recharging suitable for starter motors.
A thruster requires deep cycle prolonged draw of high loads that a gel battery delivers but adding 60kg plus 30mm cable weight into bow area of a small cruiser wouldn't be clever.
The only way to power an electric thruster sucessfully is of a generating power supply or big bank of house batteries.

If your trying to get a boat along side against a heavy wind and tide you will use a lot of power.

 

In the end its best to interrogate the supplier when you visit a boat show. Might be some clever stuff around.

Generally a well conceived bowthruster increases the value of your boat. Even RIBs and center console boats have thrusters these days. Its what the market wants.

 

Did I say lead acid --- I cant seem to find that bit. A thruster needs no more than 10 second blasts.

There is no heavy cable --your site the battery near the motor . This is an accepted alternative. All you need is charging wires ---I said all this once.

If your boat is wieght critical over a bow thruster then the boat is not big enough in the first place.

 

If you opt for a thruster, a hydraulic unit need not cost that much more, especially if you can do the pipes and hoses yourself. Attached is the costs of the parts I bought in 2008 from Northern Tools.
I actually bought two new BCS BP-085 thrusters on Ebay for a total of over £600. The supplier was changing to another brand, Lewmar I think it was. It means I have a spare one but so far the one fitted works fine.

I calculated the flow required and selected a pump that would supply enough fluid at engine idle. If I rev to 1000rpm the bow litteraly throws itself sideways.

The engine manufacturer's engineer told me it was bad for the front of my engine to have the belt driven pump, but they sold me the multi-pulley from their spares list. He quoted that 4 HP was all he would be happy with drawing from the pulleys, so I would say I am just on the limit as long as I don't set the psv too high.

There is a clutch pump available that will sit in front of the engine crank pulley, but I did not have the room for that one. I think they are concerned about side thrust on the front bearing when drawing power on belt-pulleys, but as it only gets used for very short periods I don't think it's much of an issue,