Thrusters vs twins

Had a note from my sister, who lives up in North Carolina, and she said that they had a heck of a time docking their trawler over the weekend because there were high winds and the thrusters overheated while trying to maneuver the boat toward the dock (they have a Mainship 40) so that they were kind of stuck. They finally got it docked by throwing lines to people on the dock who helped bring it in.

My boat has twins, but I have always thought that a single-engine with thrusters would do just as well in docking situations. But perhaps not! Is this overheating of the thrusters a common problem? Or is there perhaps just something wrong with his?

John

Had a guy pull into my marina a couple weeks ago and he was on his bow thruster pretty hard. Understand, this is one long fairway with one smallish dogleg halfway down perhaps 500'. Wasn't down there to witness it but imagine from the yelling his went out when he tried to put into the slip.

The point is everything has a duty cycle and if you're using the thruster when the boats in a straight line you may need to switch to hydraulic.

No idea if this is what happened to your sister or not but it sounds plausable given your description of the winds.

If I just had to have a thruster, I'd get hydraulic as opposed to electric. Hydraulic is quieter and doesn't overheat like electric thrusters seem to do.

Giggitoni said:

If I just had to have a thruster, I'd get hydraulic as opposed to electric. Hydraulic is quieter and doesn't overheat like electric thrusters seem to do.

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Yep!... My hydraulic stern thruster can run for as long as you need it to. Of course, the fun is to always try and do without, but sometimes it's just nice to have when I'm feeling naughty.

Giggitoni said:

If I just had to have a thruster, I'd get hydraulic as opposed to electric. Hydraulic is quieter and doesn't overheat like electric thrusters seem to do.

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Hydraulic thruster is the answer. Spring lines are another answer. Have a single with no thruster. Had a single with a thruster. My main ride is twins with a thruster (electric & hardly used). I use the thruster mostly after getting into the slip to move the bow to lasso pilings.

I loved the boat with a single and a thruster. I could even move it sideways.

Haven't (on my single-engine boat) ever had an indication of overheating on my electric bow thruster. The longest I've used it continuously was for about 10 seconds to spin the boat 270 degrees. Normally use it in short bursts of one-half to three seconds. ... Some people may be overly and unnecessarily "leaning" on their thrusters.

markpierce said:

. ... Some people may be overly and unnecessarily "leaning" on their thrusters.

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I try to never pass judgement on how another person uses their equipment but in the case reported in my post that was my observation. Straight fairway, slack tide, no breeze and this guy had rocks in a blender in his bow in 1-2 second bursts pretending the fairway was a slalom course.

The screaming coming from down near his berth could be his SOP for all I know but my assumption was the thruster failed when the tell tale sound of multiple dock impacts could be heard. Had a nice looking boat though

I have a single with bow thruster, and make no apologies for using it often. When I do use it I usually do so in short bursts. I have never (that I know of) had it overheat or show any symptoms of overheating..

I have a single with a bow thruster and only once had an issue trying to pick up a mooring painter in Annapolis in a very tight mooring field in a 20 knot blow. it did not overheat but i think it came close. Too many oversize boats too close together and the way the field was layed out i had to come in 90 degrees to the wind. It was late at night and the admiral had a tough time grabbing the painter. That said, a guy came in with twins a little latter on and he had problems holding position as well; but obviously he could have held position a lot longer without the possibility of overheating.

John
MS390

Not again?

beachbum29 said:

Not again?

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I shouldn't have phrased it like that, since I only wanted the info about whether or not electric thrusters overheat (apparently they do unless used only in short bursts). So the "twins" being in there really had nothing at all to do with what I was asking. My humble apologies for appearing to raise an old issue like that again.

John

So what cause the short duty cycle? The motor overheating of the batteries or the wires?

jwnall said:

I shouldn't have phrased it like that, since I only wanted the info about whether or not electric thrusters overheat (apparently they do unless used only in short bursts). So the "twins" being in there really had nothing at all to do with what I was asking. My humble apologies for appearing to raise an old issue like that again.

John

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Hey Bro.

Never apologize to me. I'm just making silly comments.

CPseudonym said:

I try to never pass judgement on how another person uses their equipment but in the case reported in my post that was my observation. Straight fairway, slack tide, no breeze and this guy had rocks in a blender in his bow in 1-2 second bursts pretending the fairway was a slalom course.

The screaming coming from down near his berth could be his SOP for all I know but my assumption was the thruster failed when the tell tale sound of multiple dock impacts could be heard. Had a nice looking boat though

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OK, you could lose your engine as well..... Talk about screaming!

Or maybe one of the twins on your boat fails..... maybe you should think about getting a single so you don't rely on 2 engines?

As a trawler owner with a thruster, I WOULD NEVER have a trawler without one unless it had twins. The finite movement in docking situations is worth every penny spent. Don't forget that our boats are for pleasure, stern thrusters are for pleasure.

BTW, do you have a thruster?


As far as the OP question. I have an electric stern thruster that works excellent. Mine has a 30 second use with a 10 second cool down. As other posters have stated, most generally use quick bursts, never getting anywhere near the 30 second maximum.

Adelaide said:

Or maybe one of the twins on your boat fails..... maybe you should think about getting a single so you don't rely on 2 engines?
<snip>
BTW, do you have a thruster?

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I have a single.

No, I do not have a thruster.

Assuming those questions where for me to answer, not really sure I get your point. Whether someone wants 3 engines a sail and 4 thrusters or just a simple set of Viking oars I can care less, though I do wish them well and trust it provides them great joy.

If I had my druthers my next boat would have twin pod drives with joystick controls along with bow and stern thrusters if so equipped. But for the foreseeable future we are quite satisfied with what we have now.

Twins no bow thruster. Would not mind if I had them.
I often see people use thrusters in easy conditions when they are not needed at all. I expect after a while they become reliant on them, losing skills they possibly had. Our Maritime authority has warned against over reliance. I`d still be happy to have them for those tough times, so far cost outweighs need.
A set up per Craig`s druthers would be great, but not likely to happen.

Wonder why our small-boat electric thrusters are subject to overheating. I've observed the "big boy" thrusters run for many, many minutes continuously.



(That isn't the Golden Gate Bridge.)

markpierce said:

Wonder why our small-boat electric thrusters are subject to overheating. I've observed the "big boy" thrusters run for many, many minutes continuously.

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Because little boats typically use a DC series wound starter motor that produces a great deal of power from a small package with no provision for cooling.

Your cruise ship has 3 bow thrusters, they are variable speed AC powered and are air/water cooled and are rated for continuous operation. They cost more than your bow thruster.

Note the two gray pipes attached to the header on the right side of the photo. The motor housing contains fans that circulate cooling air across the fins of that water cooled heat exchanger.

Wow! a stand-up, multi-level thruster room!

Rick B

Thanks for the photos of a cruise ship's thrusters. Where did you get the photos?

Marty

usually thrusters that are overheating are because of...

1. You are in environmental conditions nearing the worst case scenario for the boat or crew or both.

2. The thruster is too small for the situation you are asking it to perform in.

3. The wiring might not be up to the thrusters requirements and dropping too much voltage.

4. Inefficient use of the thruster...(a little harder to determine).

Something that might be a quick fix...check to see if the wiring gets hot or the voltage with a meter...if hot/low voltage....install a battery right near the thruster...

I took them on an NCL cruise ship in Hawaii. I was onboard to deliver some crew training, otherwise I avoid cruise ships as they carry plagues of all sorts.

psneeld said:

usually thrusters that are overheating are because of...

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...very high power output from a small motor with no cooling. That is why they are placarded against using for more than a couple of minutes and why the better ones have a protective circuit that shuts them down after 2 or 3 minutes continuous use.

Commutator and brush rigging failure is nearly certain if they are overheated by normal operation beyond the manufacturer's time limitation. Overheating is a "feature" of those units and is not normally a fault caused by other issues.

RickB said:

...very high power output from a small motor with no cooling. That is why they are placarded against using for more than a couple of minutes and why the better ones have a protective circuit that shuts them down after 2 or 3 minutes continuous use.

Commutator and brush rigging failure is nearly certain if they are overheated by normal operation beyond the manufacturer's time limitation. Overheating is a "feature" of those units and is not normally a fault caused by other issues.

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On the many Sea Rays I ran...many did trip the CB on the main panel....undersized wiring? or the unit becoming hot needing more amps? or the protective circuit built into the motor itself? Not familiar enough whether the unit itself would cause the demand more amps.

The fix in many cases for after manufacture installed thrusters that kept popping CBs was a closer battery.... so I was always thinking wiring on the units.....

RickB said:

Because little boats typically use a DC series wound starter motor that produces a great deal of power from a small package with no provision for cooling. .

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That's true for most DC thrusters but not all. WESMAR'S DC Pro series solves those problems but is really expensive.

jwnall said:

Had a note from my sister, who lives up in North Carolina, and she said that they had a heck of a time docking their trawler over the weekend because there were high winds and the thrusters overheated while trying to maneuver the boat toward the dock (they have a Mainship 40) so that they were kind of stuck. They finally got it docked by throwing lines to people on the dock who helped bring it in.

My boat has twins, but I have always thought that a single-engine with thrusters would do just as well in docking situations. But perhaps not! Is this overheating of the thrusters a common problem? Or is there perhaps just something wrong with his?

John

Click to expand...

There are thrusters, and then there are thrusters. A small 12v unit could easily be overheated if used beyond it's rated duty cycle... where a larger 12v or a 24v unit may have a longer duty cycle... and then you've seen about the hydraulic units. I've heard some of the thrusters that are factory installed are usually selected by price point...

And then there's the way it's used. Leaning on it through a slalom course is different from a few minor tweaks once the helmsman has brought the boat 95% home. IOW, one doesn't exactly "maneuver the boat toward the dock" with the thruster; that's usually main engine work (without having seen the particular situation they faced).

Given a combination of good hardware and good technique, I'd take a single with thruster over a twin... because it's probably less expensive to run, easier and cheaper to maintain

-Chris

Here is one of the auxiliary helm control stations of a modern cruise ship (one each at the starboard and port ends of the bridge) used when docking. The throttles/controls for the two main propulsion engines are at the bottom. Which handle(s) control forward thruster power? The one next to the meters?

markpierce said:

The one next to the meters?

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Yes, the old fashioned looking one with the round knob and white pointer showing "0".

The lower units with the azimuth ring are azipod controls, power ahead and astern with the lever and azimuth by rotating the whole assembly. The single lever in the center just above and between them is a "jog steering" lever with rotates both pods the same direction and azimuth. That would be used while steering in open water while the separate controls provide near infinite thrust vectoring.

The same type of control is used for jet drives and many of the most recently built yachts.

usually thrusters that are overheating are because of..


.Someone read Da Book and is using the TIME limits the unit mfg suggests?

I have a single and a Vetus 12 volt stern thruster. Manual indicates I can get 2 minutes of use per hour. I have never overheated it to the point of shut down. Two minutes is a lot of thruster use.

I can dock the boat without it but use it regularly. It is just another tool albeit a very useful one.

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