Hydraulic Bow Thruster

[blackrose]

My neighbour has just bought a 70' x 12' boat. Being a novice with such a big first boat I advised him to move it very slowly. The problem with this is that his hydraulic system gets it's power from the engine, so when moving slowly the bow thruster doesn't seem to work and he has to rev the engine in gear to get any power from it.

 

He managed ok without it but I wondered whether this was the normal state of affairs for hydraulic systems? It seems a bit odd to me, since it's when you are moving slowly or holding a stationary position that a bow thruster comes into its own and then you really don't want to have to start revving the engine. Or is there something wrong with his system like low fluid pressure or something?

 

I've heard so much about the superiority of hydraulic systems over electric bowthrusters but this isn't backed up by the experience of those around me - a big replica Dutch barge on the mooring lost his hydraulic system completely a few weeks ago.

 

No replies from the anti-bowthruster lobby please - we've already done that.

Edited August 14, 2006 by blackrose

[DHutch]

I could see how you could get the problem you have decribed, but you are right, its unsatifactory in my option also.

 

- Dont know what to suggest tho?

 

 

Daniel

[BGA]

This looks like a miss-match of systems, hydraulic systems require the pump to be running at optimum speed whenever the hydraulic motor is required. Therefore if a hydraulic bowthruster is fitted the pump should be electrically powered. If the boat has a hydraulic main drive then the bow thruster could be operated using the same power unit, because the diesel powered pump will be running at optimum speed whether or not the drives are engaged.

Edited August 14, 2006 by BGA

[blackrose]

This looks like a miss-match of systems, hydraulic systems require the pump to be running at optimum speed whenever the hydraulic motor is required. Therefore if a hydraulic bowthruster is fitted the pump should be electrically powered. If the boat has a hydraulic main drive then the bow thruster could be operated using the same power unit, because the diesel powered pump will be running at optimum speed whether or not the drives are engaged.

 

I think I understand... but an electrically powered pump on a hydraulic bow thruster sounds overly complicated - if you're relying on electrics why not just have an electric bow thruster?

 

I thought the very reason for hydraulics was to avoid "unreliable" electric motors & batteries.

[len]

My neighbour has just bought a 70' x 12' boat. Being a novice with such a big first boat I advised him to move it very slowly. The problem with this is that his hydraulic system gets it's power from the engine, so when moving slowly the bow thruster doesn't seem to work and he has to rev the engine in gear to get any power from it.

 

Hi,

The hydraulic system on our share boat works in the same way. While it can be disconcerting at first it is possible to balance the outputs by judicious use of the power.

 

I haven't {yet} found a situation where I want full power forward or reverse while using the bowthruster to manouver the front end - I try to plan it so there is way on the boat and use the b/t to push the front where I want it - or to hold me where I want to be while waiting for a lock, for example.

 

An electrical pump pressurises the hydraulic system without the need for extra batteries and long runs of heavy cabling - hydraulic lines make the run to the thruster. It's a standard way of doing it as I understand it.

 

Len

Edited August 14, 2006 by len

[John Orentas]

The only problem with hydraulic systems is the cost, they use positive displacement pumps and motors which means that the speed of the engine is directly proportional to the speed of the thruster. Of course you will need to rev the engine to get the speed, that is the point. You certainly don't need to 'Engage a gear'.

 

Hydraulic system have proved themselves to be very efficient and reliable in industry over the years, look at telescopic cranes, concrete mixer trucks and fork lifts.

[blackrose]

Hi,

The hydraulic system on our share boat works in the same way. While it can be disconcerting at first it is possible to balance the outputs by judicious use of the power.

 

I haven't {yet} found a situation where I want full power forward or reverse while using the bowthruster to manouver the front end

 

This is exactly my point - perhaps you have misunderstood my earlier message. Use of the thruster while motoring forward with medium to high engine revs is hardly ever done, because you have plenty of control due to lots of water passing over the rudder. Its the opposite that's more useful & is what we're having trouble with - moving on tickover & using the thruster at the same time.

[blackrose]

You certainly don't need to 'Engage a gear'.

 

Hydraulic system have proved themselves to be very efficient and reliable in industry over the years, look at telescopic cranes, concrete mixer trucks and fork lifts.

 

Ok, he seemed to think revving in neutral wouldn't work when I suggested it so perhaps he didn't know.

 

Still, having to take the engine out of gear in order to use the thruster seems a bit of a disadvantage. Ironic that the thruster's there to help you with tight manouvres but you have to mess about going in & out of neutral & so risk losing control that way! I guess there's a knack to it.

 

In general I agree that hydraulics are more robust than battery/alternator powered electrics, but for this particular application hydraulics seem impractical.

[John Orentas]

The hydraulics are driven from a pump that is usually fitted to the front of the engine, completely independant of the gearbox so it can be used whether in or out of gear, forward or reverse.

[blackrose]

The hydraulics are driven from a pump that is usually fitted to the front of the engine, completely independant of the gearbox so it can be used whether in or out of gear, forward or reverse.

 

Yes, it may be independant of the gearbox but not from the engine. To get any power from a hydraulic thruster it seems you have to rev the engine, which in many situations may not be what you want to do. In such cases it might mean taking the engine out of gear which in itself presents handling issues.

[Yoda]

Yes, it may be independant of the gearbox but not from the engine. To get any power from a hydraulic thruster it seems you have to rev the engine, which in many situations may not be what you want to do. In such cases it might mean taking the engine out of gear which in itself presents handling issues.

 

It sounds like a vital component is missing from the system. The pump is driven directly from the engine all of the time but does not have enough pressure to operate the thruster except when reved. This means that there is no hydraulic accumulater that the pump should be charging when the bow thruster is not in use. So the situation is to take the engine out of gear, or rev in gear whilst manuevering. Not a good situation. Take it back and ask for the rest of the system to be fitted.

[len]

Its the opposite that's more useful & is what we're having trouble with - moving on tickover & using the thruster at the same time.

 

Sorry, wasn't very clear

 

Yes you may be in tickover, and as you engage the b/t the engine revs drop so you gently increase the power to the engine to pick up the drop caused by engaging the b/t.

 

Maybe I should have said it's a balance between the two you are trying to reach - it's certainly possible with our arrangement to maintain a tick over speed and use the b/t - takes a bit of practice though. On a good day I can get ours moving sideways!!!

 

Len

[Golden Duck]

Yes we have a hydraulic bow thruster and the same thing happens.

The thruster works when the engine is in gear at slow speeds, but we find we get a much

better thrust when the engine is revved in neutral.

We know why it does this and it is explained by subsequent posters in detail.

 

It doesn't really cause us a problem.

 

We haven't had any technical problems with the system since the boat was new.

 

Our engine has a lot of other demands on its power - we have two alternators and a travel power

as well.

 

My neighbour has just bought a 70' x 12' boat. Being a novice with such a big first boat I advised him to move it very slowly. The problem with this is that his hydraulic system gets it's power from the engine, so when moving slowly the bow thruster doesn't seem to work and he has to rev the engine in gear to get any power from it.

 

He managed ok without it but I wondered whether this was the normal state of affairs for hydraulic systems? It seems a bit odd to me, since it's when you are moving slowly or holding a stationary position that a bow thruster comes into its own and then you really don't want to have to start revving the engine. Or is there something wrong with his system like low fluid pressure or something?

 

I've heard so much about the superiority of hydraulic systems over electric bowthrusters but this isn't backed up by the experience of those around me - a big replica Dutch barge on the mooring lost his hydraulic system completely a few weeks ago.

 

No replies from the anti-bowthruster lobby please - we've already done that.

[blackrose]

It sounds like a vital component is missing from the system. The pump is driven directly from the engine all of the time but does not have enough pressure to operate the thruster except when reved. This means that there is no hydraulic accumulater that the pump should be charging when the bow thruster is not in use. So the situation is to take the engine out of gear, or rev in gear whilst manuevering. Not a good situation. Take it back and ask for the rest of the system to be fitted.

 

Accumulator eh? That sounds like it might work!

[len]

Accumulator eh? That sounds like it might work!

 

Well, it will but ....

 

In hydraulic systems accumulators are most commonly used as safety devices where an object needs to be held - when constant motion is required they are generally not used because using an accumulator as an energy storage device effectively reduces the required flow rate capacity of the hydraulic pump, this results in a reduction of the installed power.

 

So, the energy stored in an accumulator is used to avoid the accidental interruption of the working of the power generator by guaranteeing continuity of the safety function for a specific time.

 

So you are back to one of the drawbacks of the electric b/t, flat battery - or empty accumulator in this case. You will then experience the same problem you are trying to avoid as the hydraulic pump kicks in to repressurise the accumulator, leaving you with no b/t and a loss of power to your prop.

 

This is why the hydraulic pump is run directly from your engine - to maintain a constant pressure in the hydraulic system to drive the b/t constantly and at its optimum power output.

 

It's like driving uphill in your car - you either have to drop a gear, or apply more power to maintain a steady speed - certainly on our boat we don't have the option of dropping a gear so we apply more power...

 

Len

[Gary Peacock]

We have done quite a lot of hydraulic stuff and in all honesty I would not go down that route without the design dictated an hydraulic drive to the prop, in which case you have already paid for quite a lot of the equipment needed for an hydraulic bow thruster.

 

The engine manufacturers like selling hydraulic kit because they don't actually do it themselves!

[len]

We have done quite a lot of hydraulic stuff and in all honesty I would not go down that route without the design dictated an hydraulic drive to the prop, in which case you have already paid for quite a lot of the equipment needed for an hydraulic bow thruster.

 

Agreed,

 

but some people just can't be convinced....

 

Len

[blackrose]

I'll stick to me electric BT!

[speejo]

Just to add to the views.

 

Our previous boat had a Vetus electric bow thruster and while it was fine we always had problems with keeping the batteries charged, the bow thruster was fine for 30 seconds but then started to run down.

 

Our current boat came with a Cramm hydraulic system and it is fantastic. Yes at tickover the thrust is less than when running the engine, but to be fair the thrust at tickover is not far off the best the electric bow thruster had.

 

I find the ability when turning around in a strong wind to simple disengage gear and rev the engine and get the resultant extra turn truly impressive.

 

I accept this is only my experience but I wouldn't go back to an electric unit after experiencing this unit. The difference is quite something. You get used to the changing thrust very quickly, it simply gives you more options when you need it.

 

Of course I didn't spec our current boat from new - so cost might be a consideration.

 

As always a matter of personal choice but I have owned both.

 

John

NB Mugwump

[Liam]

Thing is though, that I think the majority of people use their bow thruster to get them out of sticky situations, fast and probably usually within seconds... so getting the revs on first, and then engaging the thruster takes up valuable time. How's it go on then?

[blackrose]

Just to add to the views.

 

Our previous boat had a Vetus electric bow thruster and while it was fine we always had problems with keeping the batteries charged, the bow thruster was fine for 30 seconds but then started to run down.

 

John

NB Mugwump

 

I don't think you're supposed to keep you finger on the button of an electric bowthruster for 30 secs - perhaps that's why you had problems with it. Not only will you run the batteries down but you'll probably burn the motor out too! Perhaps your old electric BT wasn't powerful enough for the size of boat?

 

Unlimited use is the main benefit of a hydraulic thruster (the only one as far as I can see, which the disadvantages outlined in previous posts seems to outweigh). I only ever use my electric thruster for a few seconds in short blips when neccessary - that's all it's really designed for. You're not supposed to turn the bow through 180 degrees with an electric BT for example, whereas you can do that with a hydraulic. I guess one's choice of system depends in part on the how it's to be used - as an aid to handling or as a means of propulsion.

 

I think I'm limited to a total use of about 3 or 4 mins/hour without running the batteries down, but that's plenty of little blips and I've had no charging problems yet. The thruster batteries (2 x 110a/h) are charged from an auxilliary 70amp alternator via a voltage sensitive relay (the same alternator also charges my starter battery). I do wonder how voltage drop is overcome though, since the cables from the alternator run right down the length of the boat (57ft) and are probably only about 25mm2.

Edited August 17, 2006 by blackrose

[blackrose]

Thing is though, that I think the majority of people use their bow thruster to get them out of sticky situations, fast and probably usually within seconds... so getting the revs on first, and then engaging the thruster takes up valuable time.

 

Agreed, and you missed the bit about taking it out of gear before you put the revs on - mustn't forget that while you're trying not to panic!

 

To be fair, thrusters are predominantly used in less stressful low-speed or holding station situations, especially useful when you're single handed on a big boat like myself. So I guess once you've got the knack of a hydraulic system it's fine.

[speejo]

I was simply trying to give a real life experience having had two boats built from scratch and now having a third I didn't spec and having used both systems. To many opinionated postings on any forum come from people who have actually never experienced the item being discussed, this is one of those occasions when I have.

 

30 seconds was meant to be total usage in a day rather than one blip (30 seconds with this unit would have you doing cartwheels), if you have had a 62ft boat on a very windy winters day on the Trent & Mersey you'll know 30 seconds is quite possible. I agree 9 days out of 10 I wouldnt touch the bow thruster (its a point of principle ) but its great to know its there when you are going sideways in a marina near everyone else's boat.

 

I am not sure why reving the engine is such a time delay, the thruster works fine in neutral and in split second I can( if I need ) have additional power an electric system simply cannot provide. It simply gives you more options - it still works in neutral!

 

I personally would not have selected a hydraulic system had I built this boat but having now experienced its advantages in terms of what it is designed to do outweigh any disadvantages. The Vetus (and one owned by friends) are also prone to shear pins at inconvenient times.

 

As always each to their own - but try it some time, you might be pleasantly suprised - I was

 

John

NB Mugwump

[blackrose]

I was simply trying to give a real life experience having had two boats built from scratch and now having a third I didn't spec and having used both systems. To many opinionated postings on any forum come from people who have actually never experienced the item being discussed, this is one of those occasions when I have.

 

30 seconds was meant to be total usage in a day rather than one blip (30 seconds with this unit would have you doing cartwheels), if you have had a 62ft boat on a very windy winters day on the Trent & Mersey you'll know 30 seconds is quite possible. I agree 9 days out of 10 I wouldnt touch the bow thruster (its a point of principle ) but its great to know its there when you are going sideways in a marina near everyone else's boat.

 

I am not sure why reving the engine is such a time delay, the thruster works fine in neutral and in split second I can( if I need ) have additional power an electric system simply cannot provide. It simply gives you more options - it still works in neutral!

 

I personally would not have selected a hydraulic system had I built this boat but having now experienced its advantages in terms of what it is designed to do outweigh any disadvantages. The Vetus (and one owned by friends) are also prone to shear pins at inconvenient times.

 

As always each to their own - but try it some time, you might be pleasantly suprised - I was

 

John

NB Mugwump

 

I'm always interested to read anyone's experiences with their equipment, but what makes you think my experience isn't "real life" too? I have tried a hydraulic bow thruster on my neighbours boat and I wasn't impressed. If your old Vetus unit only allowed you 30 secs/day then there was obviously something wrong with the setup - you should have been getting at least 3-4 mins/hour.

Edited August 18, 2006 by blackrose

[speejo]

Thing is though, that I think the majority of people use their bow thruster to get them out of sticky situations, fast and probably usually within seconds... so getting the revs on first, and then engaging the thruster takes up valuable time. How's it go on then?

 

For me I can press the bow thruster button and it works well immediately, if I am in a really tricky situation (and we had one in the storms a couple of weeks ago) I can simply move the throttle forward either in gear or out of gear and the thruster power increases proportionally.

 

There are no seconds delay, pushing the disengage button and moving the throttle takes less than half a second and you can have the thruster working at the same time if you wish. In the instance above I was quite happy to remain in gear - I actually managed to move the boat rapidly sideways using the tiller and thruster to get out of the way of a fast moving, completely out of control hire boat, who thought they could counter the wind by simply going faster straight at me and hoping for the best and with no chance of stopping.

 

It really is quite clever (albeit obvious I guess) but perhaps it needs to be tried to be believed.

 

John

NB Mugwump

Edited August 20, 2006 by speejo