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Bow Thruster


jddevel

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Now I know this subject irritates some owners but please bear with me because I`ve had one fitted being my choice. However after fitting I was advised by the yard engineer

that when the final coats were applied to the hull blacking (it`s a sailaway with basic cover) that it would possibly be prudent to reduce the ends of the propeller blades

slightly and put a "good" coating of blacking in the blades vicinity due to cavitation.

Well I must admit that I`ve as yet to remove the covering grill and inspect the tube in detail ( weather not suitable and too much else to do) but I did wonder whether it was

feasible to insert a sacrificial liner -say in plastic- to help alleviate the problem. I don`t anticipate excessive use of the thruster but then at my age who knows. Anyone out there thought about this in the past?

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Unless your liner is somehow securely bonded to a clean steel surface I don't see how if will reduce corrosion of the tube from the inside. You also need to keep the outside of the tube painted - including the underside which is hard to reach or see.

I would think it was intended to reduce erosion, not corrosion.

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Is erosion through cavitation a problem than with thrusters? What shows in a metal tunnel...pitting?

Yes, it's called "cavitation attack" and is certainly known about and protected against with the big seagoing stuff:

 

http://www.canalworld.net/forums/index.php?showtopic=85565&p=1840098

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Is erosion through cavitation a problem than with thrusters? What shows in a metal tunnel...pitting?

Yes, more so on muddy canal ditches than seagoing stuff as owners are usually using the thruster close to the bank with silt and small pebbles thrown around.
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I was advised by the yard engineerthat when the final coats were applied to the hull blacking (it`s a sailaway with basic cover) that it would possibly be prudent to reduce the ends of the propeller bladesslightly and put a "good" coating of blacking in the blades vicinity due to cavitation.

I wouldn't disagree with making sure the tube is effectively blacked, but I'd not be buggering about with the carefully designed blades. If you take the blade tips off (which I can't see being an easy job!), you could make cavitation more likely.

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yes but ................. that's not cavitation, it's mechanical impact erosion.

I didn't say it was, an engineer told the OP it was....and yes, you are correct with your second bit, it does happen, and yes, a sacrificial plate within the bowthruster tube would help prevent this.
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My bow thruster is 6ft 1in tall with a pole, I hope he doesn't get struck down with cavitation

As long as you give his tube a wire brushing and a few coats of bitumen every couple of years he'll be fine. Again, I'd caution against cutting the tip off his whizzer.

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exactly.

 

a much bigger issue is - how do you black the inside of a 4ft long 7" diameter tube effectively?

 

With a 2ft long brush less than 6" wide?

 

On the cavitation issue, isn't the damage directly proportional to the time for which the propeller rotates? I can't imagine that a girly button bow thruster would be used for more than ten minutes a day on aggregate, and what makes anyone think it it will cavitate seriously anyway?

Edited by Machpoint005
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...and what makes anyone think it it will cavitate seriously anyway?

Saw the blade tips off and it might! I'm tempted to dig up the old chestnut about the advice the OP received being from an "Engineer", but I'll resist (he wasn't one though - oh bum, I did it anyway!).

  • Greenie 1
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Saw the blade tips off and it might! I'm tempted to dig up the old chestnut about the advice the OP received being from an "Engineer", but I'll resist (he wasn't one though - oh bum, I did it anyway!).

 

Greenie for highlighting the improper use of 'engineer' .

Edited by Machpoint005
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