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Old 04-22-2015, 12:52 AM   #1
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Hydraulic Bow Thruster Problem

My boat has a 27HP Wesmar hydraulic bow thruster. It's a two speed unit (Hi/Lo in each direction) from around 2001 I believe. The hydraulics are shared with Wesmar active fin stabilizers and run off the main engine.

The last time I used it I found I was getting low power from the thruster at times. On one occasion it caused the bow to be driven into a piling by the wind, causing my first gel coat damage. No big deal - way less concerning that many other things that could happen.

I reproduced the problem at the dock today. For a while it would sometimes operate at much lower power (still at two speeds - just lower power) and at other times it would operate at much higher power. I could hear it and see the difference in turbulence being kicked up around the boat. After a while I could not get the low power problem to recur. I will try again another day.

So - does anyone have any experience and suggestions where to look for possible causes? I should probably get the whole system serviced and inspected in detail. However, I'm curious where I might start to look.

Thanks

Richard
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Old 04-22-2015, 01:52 AM   #2
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Are you able to have a buddy watch the hydraulic pressure gauge while activating thruster. This will allow you to know minimum engine RPM necessary to keep pressure in stable operating range specified in Wesmars manual. On older systems lower RPM can be problematic for thruster operation.

Vickers pump? No leaks or drips in system especially hard to see places where hoses run forward?
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Old 04-22-2015, 01:59 AM   #3
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Are you able to have a buddy watch the hydraulic pressure gauge while activating thruster. This will allow you to know minimum engine RPM necessary to keep pressure in stable operating range specified in Wesmars manual. On older systems lower RPM can be problematic for thruster operation.

Vickers pump? No leaks or drips in system especially hard to see places where hoses run forward?
I didn't have a buddy today. I did take a look at the pressure gauges to try and see if I could learn something but didn't come to any conclusion. I either need to set up a video camera or have a buddy as you suggest. I will report back my findings. I did try higher RPMs and that didn't help when I encountered the problem. In practice that would be a problem since I often use the thruster with the engine in gear at idle to maneuver. Higher RPMs wouldn't be an option.

It's a Parker variable volume pump. I have observed no leaks, but much of the system is hidden from casual observation.

The problem is intermittent.

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Old 04-22-2015, 06:47 AM   #4
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It's just guessing without seeing a schematic. You don't have one, do you? This boat is brand new to you, right?

Is the main engine the only source of hydraulic power on the boat? On hydraulic Nordhavns there is almost always a second power source; either the wing engine or generator. The reason is that the thrusters require a huge about of fluid flow, and you run them when the engine is idling and producing it's minimum fluid output. A generator running at 1800 RPM or a wing engine revved up can much more easily produce the required flow.

So the first question is whether one of these other two engines has a pump, and if so, I think you need to run it when you are performing docking maneuvers. Mine is on my generator, so I run that. And I need to remember to NOT turn on it's breaker to ensure there is no AC load, otherwise it gets overloaded and stalls.

If there isn't a second pump somewhere, then the issue is elsewhere in the hydraulics. Your main engine pump is surely a variable displacement pump. It could be sticking, but I'd put that low on the probability list. There is also a feedback hose that controls the displacement and maintains a constant pressure. On mine there is something like a 200psi regulator that feeds the hose back to the pump. When that's at 200 PSI, the rest of the system is at 3500. Maybe that regulator is sticking.

Speed control is done either by regulating pressure or by regulating flow. My thruster speed control is done by regulating pressure. That's another possibility.

I think the fist step is to monitor the system pressure while this is happening. If you can't get a helper, then perhaps you can set up you phone to video the pressure gauge while you go operate the controls. If you have a system pressure problem, then it will narrow down the possible causes.

If the system pressure is OK, then you will need to get a gauge on the thruster control block to see what its pressure is doing.

I think you have already discovered the hardest part - being in two places at once.
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Old 04-22-2015, 07:21 AM   #5
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Another piece of data to have is reliable and accurate engine RPM. An Aetna tach is worth considering. This way you can have transmission safety shifting RPM at your disposal while maintaining thruster pressure. First things first though, chase the system down as Twistedtree suggests.

The popularity of electric thrusters is not without reason. The cost to convert to electric would be a nice back pocket item. Twistedtree is an expert in this regard given his well documented install on his GB. Knowing options is one thing, exercising quite another.
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Old 04-22-2015, 07:35 AM   #6
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I would check all the electrical connections to make sure they are tight and corrosion free. Switches, clutch, solenoids, etc.
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Old 04-22-2015, 07:39 AM   #7
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In a properly sized system you should not have to run another engine to achieve proper fluid flow to run your thruster. It's possible a bypass valve is sticking open a bit and you are not getting proper flow at all times.
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Old 04-22-2015, 07:43 AM   #8
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In a properly sized system you should not have to run another engine to achieve proper fluid flow to run your thruster. It's possible a bypass valve is sticking open a bit and you are not getting proper flow at all times.

Not with Nordhavns, I have multiple friends that either have to use they're second engine, generator or wing.
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Old 04-22-2015, 07:47 AM   #9
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Most docking is done at or near idle , and hyd pump output is RPM driven.

That's why some mfg will add a hyd pump to the noisemaker or get home engine or both.

After cleaning the electrics , it would be easy to raise the main engine RPM and see if you get the higher thrust.
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Old 04-22-2015, 08:22 AM   #10
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The popularity of electric thrusters is not without reason. The cost to convert to electric would be a nice back pocket item.
For what it's worth, I would never convert from a hydraulic thruster to an electric one. Hydraulic thrusters are generally more powerful, and best of all they never timeout due to thermal overload. To me, that's the Achilles' Heal of electric thrusters. If you use them too hard and too long, they overheat and shut down. But if you are using them long and hard, it's because you REALLY need them, yet that's exactly when they shut down and set you adrift.

Whether it's worth the extra cost for hydraulic thrusters depends on lots of factors, but if you have then, keep them. At least that's my view.
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Old 04-22-2015, 08:30 AM   #11
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Not with Nordhavns, I have multiple friends that either have to use they're second engine, generator or wing.
Ditto here. I went through all this with ABT engineering when we were specifying our boat's hydraulics. With just the main engine pump, which is huge by the way, I can get most of the power from one thruster, but not full power. And running both thrusters pretty much doesn't work. You need to alternate back and forth. So we have a second pump on the gen set. Interestingly, the gen set pump is 1/2 the displacement of the main engine pump. The greater RPMs of the gen set makes a huge difference and allows for the smaller pump.

Now if you had twin engines with pumps on both, then powering both thrusters might be possible.

It sounds like Britannia has a single thruster, so it's possible he has just one pump. It will be interesting to see. But either way, even with one or two pumps, it doesn't explain his come-and-go performance.
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Old 04-22-2015, 10:10 AM   #12
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It sounds like Britannia has a single thruster, so it's possible he has just one pump. It will be interesting to see. But either way, even with one or two pumps, it doesn't explain his come-and-go performance.
Lots of great responses - thanks. Yes I have a single thruster with single pump off the main. The problem is indeed intermittent, which is why RPMs aren't the issue - and as I mentioned before, raising the RPMs did not help when the problem occurred.

Electrical could be an issue for sure - I will try to track this down. A stuck regulator valve affecting pressure also sounds like a possible candidate. Either of these could be intermittent.

I will try to replicate myself and get some accurate pressure readings when I reproduce the problem at the dock again this week.

I intend to stick with hydraulics - the thruster can run at 27HP all day long without any overheating.

Thanks again

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Old 04-22-2015, 10:23 AM   #13
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I think that Wesmar uses a load sensing circuit that allows the pump to deliver max flow at any rpm so perhaps a bad sensor in the circuit.

Peter my brother in Bellingham may cross paths with you this summer and probably would be interested in seeing that new dome furuno you installed.


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Old 04-22-2015, 11:00 AM   #14
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Not with Nordhavns, I have multiple friends that either have to use they're second engine, generator or wing.

That might be. But I'd like to hear their reasoning behind setting it up like that. If the pump is sized right you shouldn't have to do that.

Having two pumps where one is a back up makes sense. But having to run two engines all or most of the time just to make the system work right does not. At least in my mind. Especially on a single screw boat.
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Old 04-22-2015, 11:35 AM   #15
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That might be. But I'd like to hear their reasoning behind setting it up like that. If the pump is sized right you shouldn't have to do that.
Hi Bill,

I think the reasoning is along the lines that Wing Engines get little use and the main engine is typically at idle when docking. Getting enough hydraulic pressure from the main would require a much larger, more expensive pump.

The hydraulic pump for the stabilizers is small and they are only used when the boat is at cruising speed. Also, most of the commercial boats that I have worked on had an axillary motor that ran the boat's hydraulics, so it seems like a common practice.
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Old 04-22-2015, 12:39 PM   #16
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Silly question, but is pump belt drive off engine? 27hp is lots for belts, but gots to ask.
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Old 04-22-2015, 12:42 PM   #17
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I will try to replicate myself and get some accurate pressure readings when I reproduce the problem at the dock again this week.
You're really lucky that you can reproduce it. With that, tracking it down shouldn't be too hard as long as you already have or can attach gauges in the right places.

Keep us posted. I'd be interested to hear what you find.
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Old 04-22-2015, 12:47 PM   #18
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Silly question, but is pump belt drive off engine? 27hp is lots for belts, but gots to ask.
Not a silly question. Yes - belt drive - a pair of them. You're wondering if the belts are slipping? I guess I'd have to somehow check the rpm of the pump to figure that out. Or the pressure of course - but that might be due to another cause.

Thanks

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Old 04-22-2015, 12:49 PM   #19
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You're really lucky that you can reproduce it. With that, tracking it down shouldn't be too hard as long as you already have or can attach gauges in the right places.

Keep us posted. I'd be interested to hear what you find.
Yes - reproducible for a while yesterday then went away. We'll see how it fairs today. I'll update the thread on what I find.

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Old 04-22-2015, 12:55 PM   #20
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I think that Wesmar uses a load sensing circuit that allows the pump to deliver max flow at any rpm so perhaps a bad sensor in the circuit.

Peter my brother in Bellingham may cross paths with you this summer and probably would be interested in seeing that new dome furuno you installed.


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That's mostly right. The load sense controls the pump displacement. When there is a large call for fluid like from the thruster, the sense pressure drops and the pump displacement increases to meet the demand.

But a pump's output is the displacement x RPM. So even at full displacement, an engine turning at 600-700 RPM can only deliver so much fluid. Crank it up to 1800 RPM, and you get 3x the flow which translates into 3x the available hydraulic power.

As I recall from when we were specifying my boat's hydraulics, the limiting factor on the engine pump was the 1) the class of PTO mount (SAE A, B, or C), and the available physical space. My engine PTO is SAE B, but the transmission PTO is SAE C, so we used that one because it allowed for a larger pump. But even with the largest pump that would fit, it can only run one thruster at a time with the engine idling at 650 RPM. The other consideration is that you are limited by the engine manufacturer in how much power you can draw off the main via the PTO when idling. I recall that we were pushing the limit. Asking an idling engine to put out 30hp is a lot. The generator pump is 1/2 the displacement of the main engine pump, but does more than half the work since it runs at 1800 RPM.
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