Starting thrusters when vessel is moving at a high speed


#1

Will starting bow and stern thrusters when at a speed of say 10 knots cause any damage to them?

Some people I have spoken to have said that it does cause damage, but others say it causes no damage whatsoever and is perfectly fine to do, what is the right answer?

Obviously they won’t have much effect on vessel movement until at a lower speed, but its just whether is causes damage that I am confused about.


#2

They won’t be effective so I font see why you just don’t wait for it to drop a few kts. It probably depends on the vessel but I’ve never heard of them being damaged. I really wouldn’t start them above 12kts though.


#3

My controls are marked “DO NOT USE OVER 6 KTS”… I have always assumed it’s because the loads on the blades would be unbalanced but I’ve never seen or heard an explanation. There is also a graph in the plans showing effectiveness at difference speeds. The effective side thrust drops off very rapidly as speed increases.


#4

Some systems like the one on the vessel I am one, Ulstien Helicon X, have the operation of the bow thruster integrated into the main propulsion. If the thruster is started it initiates a pitch limitation, lots of scenarios where that would not be so good.


#5

Is it possible that at such a high vessel speed, there is a possibility that air cavitations could be created in the bow thruster tunnel, to the extent that the propeller blades could race into an environment of not sufficient hydrostatic density. Would it be a good idea to use a bow thruster when the tunnel is out of the water ? Blades would race and vibrate to overheating or such. Have you ever heard the scary noise coming out from the engine room when the propeller goes out of the water in rough seas … does not feel too good either !


#6

On some type of vessels, smaller than bigger, equipped with a powerful bow thrust, at a certain speed of let’s say 4 knots, if you set the thruster full to starboard the bow will swing in the opposite direction to port ! The water depression created in the area of the tunnel combined with acceleration of the water flow create a Venturi effect that can suck the bow toward that direction. Amazing !


#7

In the thruster manual it will tell you, most transverse thrusters are not started above 5 knots, look on the specification page in the manual for your particular thruster.


#8

What kind of thruster?

Tunnel? FPP? CPP? Shaft brakes? More info needed


#9

[QUOTE=JW-Oceans;131843]What kind of thruster?

Tunnel? FPP? CPP? Shaft brakes? More info needed[/QUOTE]

Holy cow, I was amazed at the number of responses given before someone asked for any details… Scary!

I guess if you were in a collision an equal or greater number would be providing legal counsel.

This might be a good thread…


#10

if a thruster is connected but is being “driven” by high hull speed, then it will backfeed into the switchboard and we all know what happens then!

POP GOES THE WEASEL!


#11

[QUOTE=Ea$y Money;131846]Holy cow, I was amazed at the number of responses given before someone asked for any details… Scary! [/QUOTE]

Not half as amazing as missing the word TUNNEL in the first post.


#12

[QUOTE=Topsail;131779]On some type of vessels, smaller than bigger, equipped with a powerful bow thrust, at a certain speed of let’s say 4 knots, if you set the thruster full to starboard the bow will swing in the opposite direction to port ! The water depression created in the area of the tunnel combined with acceleration of the water flow create a Venturi effect that can suck the bow toward that direction. Amazing ![/QUOTE]

Humor me and provide a bit more information about the physics of that phenomenon.


#13

I am not sure about this either. Pushing on one side and sucking on the other would both seem to move the bow the same direction :confused:

In other news, fresh out of the yard is a good time to test the thruster NOT near a dock. If they get wired backwards and you call for port and get starboard it isn’t good. Don’t ask me how I know that…


#14

[QUOTE=Steamer;131863]Humor me and provide a bit more information about the physics of that phenomenon.[/QUOTE]

In my previous contribution, I alleged that; “The water depression created in the area of the bow thruster tunnel combined with acceleration of the water flow create a Venturi effect that can suck the bow toward that direction.” Thus, if you knew barely about physics or be able to read a phrase without acetaminophen needs (only to humor you), you would realized that I proposed a few combined physics phenomenon … “Water Depression + Water Acceleration = Venturi Pressure Differential or Vacuum”. These physics can be understood by an average ordinary seaman or by a Chief (again to humor you), but in reality it is more complicated than that.

In fact there is another very important phenomenon which has just been exposed, tested and currently lectured in manned model ship’s handling facilities. It is called the peripatetic pivot point produced by ship’s hull Lateral Resistance. As a bow thruster, the head of a vessel could be altered in a direction “opposite” to a pushing tug. Theses phenomenon’s are labeled “Unpredictable Behavior” to unaware navigators and thus, the reason to reconsider some deep anchored myth into the mariners community.

p.s. Chief, please have a look to the attached pdf file from p.10 to p.13 and take a special attention to fig. 20,21,22,23 & 24. There is also some videos on the web describing that phenomenon.

http://www.cpslc.ca/media/a_understanding_pivot__049144700_1201_28102010.pdf

Keep the propeller and rudder turning …


#15

[QUOTE=Topsail;131911] “Water Depression + Water Acceleration = Venturi Pressure Differential or Vacuum”. These physics can be understood by an average ordinary seaman or by a Chief (again to humor you), but in reality it is more complicated than that…[/QUOTE]

Not sure where you are finding these ordinary seaman… Most of my guys are still working on Bow = pointy end… I will see what they make of your reference materials… This could be the epiphany that transforms them to gentlemen of the sea.


#16

If the famous Engine Room Pilot would’ve asked; “Could you provide a bit more information about the physics of that phenomenon” instead of “Humor me and provide a bit more information about the physics of that phenomenon.” I would’ve been as well transformed into a Gentlemen of the Sea. Respect or disrespect is a two way channel.


#17

[QUOTE=JW-Oceans;131843]What kind of thruster?

Tunnel? FPP? CPP? Shaft brakes? More info needed[/QUOTE]

Sorry I meant to say tunnel thrusters.

Of any type, as who knows what our next ship will have.

So which thrusters are ok to start at 10 knots then?


#18

Drop your swing down thruster at 10 knots and let us know what happens?

:wink:


#19

[QUOTE=Topsail;131911] These physics can be understood by an average ordinary seaman or by a Chief (again to humor you), but in reality it is more complicated than that.

.

p.s. Chief, please have a look to the attached pdf file from p.10 to p.13 and take a special attention to fig. 20,21,22,23 & 24. There is also some videos on the web describing that phenomenon.

http://www.cpslc.ca/media/a_understanding_pivot__049144700_1201_28102010.pdf

QUOTE]

Before you get too lightheaded, review your links. In no place does it state that there is a region of what airplane drivers call a “region of reversed command.”

Yes, there is a low pressure area on one side between the hull and the thruster discharge, but as the document, and several other scholarly tomes on the subject clearly state, the location and degree of low and high pressure near the tunnel are responsible for the loss of effectivity as water moves across the opening but have no effect on the direction of thrust. If your link is the best you can do, you have failed completely. Trying to smokescreen the issue with pivot point diagrams and propeller thrust vectors only shows that you cannot provide any citation or description of the physics that will confirm your fictitious statement that at 4 knots a bow tunnel thruster will move the bow opposite the desired direction of movement.

There are several studies available on the subject that, if such a phenomenon existed, would have stated so and described the physics and mathematical model to prove it. When you get off your pedestal, review the literature, you found one that shows you are wrong, find a few more.

Like the yachtie wrote … “pushing on one side and sucking on the other” moves the bow the same direction … in my world anyway.


#20

No wonder why you work in the engine room. Keep the propeller and the rudder turning and will manage the rest. Unpredictable Behavior is enigmatic by most navigators, so can you imagine by motor mans. Reconsidering deep anchored myth needs mind openness …

In the area of the discharge mouth of a bow thruster, a pushing force and a water acceleration create a pressure differential or a vacuum that combined by the lateral resistance of a vessel moving ahead, could divert the bow in the opposite selected direction. The same phenomenon can occur with a pushing tug.

But just forget it if it seems for you coming from outer space.