How to Thrust - Electric or Hydraulic

Gludy

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Up until now and having experienced both types of thrusters I am of the strong opinion that hydraulic ones with no time limit are better than electric.

Hydraulic ones can also be used in a very powerful mode by revving the engines a bit and so get of sand banks etc without the problem of overheating and cut out inherent in electric thrusters.

So I was surprised yesterday to learn that a very respected boat designer prefers electric because hydraulic can cause the engines to stall!!! This has never happened to me but I would be interested if anyone out there can shed more light on the subject. Also which type of hydraulic - power variable depending on joystick displacement or simple power on/off which is the only type I have experienced?
 

Chris_d

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Thats like saying you shouldn't fly because the plane might crash, hydraulic must be better for all the reasons you quoted. Its just a question of managing the failure mode, which with hydraulic thrusters must be less likely than overloaded electric ones.
 

Gludy

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Apparantly its the engines that may stop because of the sudden load of the thrusters - but I have never had anything like that happen. I am trying to find out if antyone has had that happen.
 

BSJ2

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hydraulic is more powerful and therefore potentially more useful in strong winds and they will not trip out at the critical moment? but then the electric ones can be used with no engines on? which can be useful for adjusting lines etc? difficult call i suppose, but all in all an independent thruster to engines maybe safer for all occasions?if engines were stalled for any reason? or unsafe to use electric could save the day!
 

acbruce

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No experience but I have heard that you have to rev the engines to get some hydraulics to work. I thought i read of one that had overcome this.

Why not power the hydraulics from the generator?
 

Nautorius

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Paul,

I was surprised to see that a majority of Barges (60ft widebeam) have hydraulic thrusters. Seems far better and they are more 'buletproof' than electric!

Out of choice on a big Heavy boat (50ft +) I would go Hydraulic.

Cheers

Paul /forums/images/graemlins/smile.gif
 

jfm

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There isn't an answer to your question Gludy. Good electric is better than crap hydraulic, and vice versa. People often say hydraulic is more powerful, including a poster on this thread, but that is of course nonsense

Personally I'd chose electric on sub 80 foot boats where you are looking at sub 20hp thrusters. Much simpler, less weight, etc and plenty of good units on the market. It would need to be a properly specced electric job of course. when go go above that size I think hydraulic may be better simply becuase there are better/more reliable units on the market in hydraulic than electric. The cutting out problem sounds like it was an old/manky engine - that shouldn't happen with a modern electronically controlled diesel - the computer will just squirt some more fuel in to keep it running at same rpm when the extra hydraulics load kicks in

But we need to get away from this nonsense about hydraulic being intrinsically better and electric being always non-continuously rated etc. As you know the Queen Mary runs on electric motors. So did the Canberra. So does Ice. They're (obviously) continuously rated.
 

Gludy

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I had planned hydraulic having used both types - it was just that a very respected boat designer has favoured electric because of the engine cut out problem that I have never encountered.

The new boat is 77 foot long with a 20 foot beam and there will be just two of us handling her and SWMBO is only 5 foot high!! So I have to ensure its easy to handle. The last thing I want is thrusters cutting engines.
 

Divemaster1

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Personally I'd go good quality hydraulic ... no practical limitation of how long you can run them.... pinning the boat to the quay/pontoon whilst leisurely tying her up ... (the boat that is). The boat you are looking at will have proper engines with good governors, which will pick up the extra strain of a hydraulic pump with no more than 50 RPM drop, before bringing her up again. would even consider hydraulic waterjets as a serious alternative, to having "normal" thrusters.
 

jfm

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Are you saying David Marlow recommends electric? Good call. He'll be installing decent electric ones of course, not the poxy 30 second-rated food mixers that other builders fit. So yes, if Marlow has found a source of good electrics, install those imho.

Intrinsically, an electric motor+wires+switch+solenoid+battery combo is a much more reliable/easier thing to maintain than a hydraulic motor+valves+hoses+valve controllers+pump combo.
 

Gludy

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Yes it is David saying that, although i have not yet discussed it with him.
They fit powerful SidePower ones and I have already used those on Drumbeat but they can cut out.

I was once waiting for the lock at Swansea and all the messing about with the smaller boats creeping in here and there sort of boxed me in - I was using my thrusters off an on to stop collof=ding and then .... they stopped working.
Currently I still lean towards hydraulic and this is so far the only thing I disagree with david on.
 

andyball

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my vetus 24V is rated 5mins continuous afaik - also err 5mins an hour, which doesn't sound so amazing, but it really is needed for just seconds at a time; & yep, still great in a F6+

This is a 250mm tunnel 8hp'ish, on a 38' . Vetus now do a better prop, with claimed much more thrust & loads quieter too.

Umm, no way a hydraulic setup should stall a modern motor with elect control imo.; but as you found with Trader, the huge available power of hydr's isn't necessarily available at tickover anyhow - and juggling engine speeds likely is not something to be doing in a tight spot.

Do the sums on windage etc at Vetus - should give an idea of what'll work well.
 

rickp

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[ QUOTE ]
Vetus now do a better prop, with claimed much more thrust & loads quieter too.

[/ QUOTE ]

Meant to tell you last time I saw you Andy - I have the new props for my vetus thrusters and will fit at the next lift out/scrub.

Rick
 

jfm

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Hmmm, i wonder then if electrics have just got better in recent years? I have 11hp Sidepower in the Sq58, which is 2004, and have never had it cut out. I have deliberately tried to make it cut out by running it for ages, but it wont! Worth talking to DM about - can't believe he would fit junk for something as important/not-easy-to-replace as a bow thruster, so he must have got to the bottom of this whole issue?

Has anyone here experienced cut out on a Sidepower unit that is 4-5yrs old, or newer?
 

jfm

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In general, Vetus stuff is standard catalogue stuff made by others and badged Vetus. Do you know the underlying manufacturer of Vetus bow thrusters?
 

Bilgediver

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Hi Paul

If you have hydraulic thrusters of a high power then you have to look at what the engine is doing when you apply the thrust.

If you have a smallish diesel say 100 hp and 35 hp of thruster and you are running at slow ahead then applying full thruster will place an abnormal load on the engine in relation to the governed speed being demanded for the prop. You would have to declutch and rev the engine up to a speed where the thruster power was within the engine envelope.

I think you are buying a supadupa boat with supadupa big big engines and it is quite posssible that these could quite happily take the thruster loads at fast tickover.

The only way to comment further is to tell us what engines they are and how much power do the thrusters take at full load. Then maybe we can find the load charts for the engines on the web.

You probably have 2 1000 + ?????? So possibly no problem.

I played with one of the first north sea life boats fitted with 35 HP hydraulic thruster and 100 HP engine and it was easy to stall the engine unless it was gunned as you applied full thrust.

The boat could turn on a sixpence /forums/images/graemlins/smile.gif


John
 

Gludy

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Well it seems the meassage was conveyed to me slightly wrongly - its the danger of the thruster stalling not the engines.

I will have two CAT18s rated at over 1000hp each.

I will probably have about a 30 hp thruster at the bow and about 20 hp at the stern - say a total of 50 hp.
 
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