jddevel Posted February 16, 2017 Report Share Posted February 16, 2017 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? Link to comment Share on other sites More sharing options...
mross Posted February 16, 2017 Report Share Posted February 16, 2017 Is the tunnel seamless? there should be no sign of a horizontal weld. If seamless pipe has NOT been used this would concern me much more. Also, is there a steel bulkhead behind the thruster so that a leak could not sink your boat? Link to comment Share on other sites More sharing options...
David Mack Posted February 16, 2017 Report Share Posted February 16, 2017 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. Link to comment Share on other sites More sharing options...
lulu fish Posted February 16, 2017 Report Share Posted February 16, 2017 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. Link to comment Share on other sites More sharing options...
Murflynn Posted February 16, 2017 Report Share Posted February 16, 2017 I would think it was intended to reduce erosion, not corrosion. agree - erosion mainly caused by cavitation. Link to comment Share on other sites More sharing options...
Paringa Posted February 16, 2017 Report Share Posted February 16, 2017 Is erosion through cavitation a problem than with thrusters? What shows in a metal tunnel...pitting? Link to comment Share on other sites More sharing options...
Murflynn Posted February 16, 2017 Report Share Posted February 16, 2017 probably not, in practice. Link to comment Share on other sites More sharing options...
FadeToScarlet Posted February 16, 2017 Report Share Posted February 16, 2017 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 Link to comment Share on other sites More sharing options...
matty40s Posted February 17, 2017 Report Share Posted February 17, 2017 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. Link to comment Share on other sites More sharing options...
Sea Dog Posted February 17, 2017 Report Share Posted February 17, 2017 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. Link to comment Share on other sites More sharing options...
Murflynn Posted February 17, 2017 Report Share Posted February 17, 2017 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. yes but ................. that's not cavitation, it's mechanical impact erosion. Link to comment Share on other sites More sharing options...
matty40s Posted February 17, 2017 Report Share Posted February 17, 2017 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. Link to comment Share on other sites More sharing options...
jddevel Posted February 17, 2017 Author Report Share Posted February 17, 2017 Thank you all. Will consider further. Particularly reference concern over blade reduction. Link to comment Share on other sites More sharing options...
cuthound Posted February 17, 2017 Report Share Posted February 17, 2017 I guess it also depends on how often you use the bow thruster. Mine gets used for less than 10 minutes per year (mainly reversing and turning impacts strong winds), so I would expect cavitation or stone impact damage to occur slowly. Link to comment Share on other sites More sharing options...
Murflynn Posted February 17, 2017 Report Share Posted February 17, 2017 exactly. a much bigger issue is - how do you black the inside of a 4ft long 7" diameter tube effectively? Link to comment Share on other sites More sharing options...
Guest Posted February 17, 2017 Report Share Posted February 17, 2017 My bow thruster is 6ft 1in tall with a pole, I hope he doesn't get struck down with cavitation Link to comment Share on other sites More sharing options...
Sea Dog Posted February 17, 2017 Report Share Posted February 17, 2017 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. Link to comment Share on other sites More sharing options...
Guest Posted February 17, 2017 Report Share Posted February 17, 2017 Excellent, august advice that I shall follow to the letter! Link to comment Share on other sites More sharing options...
Machpoint005 Posted February 17, 2017 Report Share Posted February 17, 2017 (edited) 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 February 17, 2017 by Machpoint005 Link to comment Share on other sites More sharing options...
Sea Dog Posted February 17, 2017 Report Share Posted February 17, 2017 ...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!). 1 Link to comment Share on other sites More sharing options...
Machpoint005 Posted February 17, 2017 Report Share Posted February 17, 2017 (edited) 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 February 17, 2017 by Machpoint005 Link to comment Share on other sites More sharing options...
nb Innisfree Posted February 17, 2017 Report Share Posted February 17, 2017 exactly. a much bigger issue is - how do you black the inside of a 4ft long 7" diameter tube effectively? Get one of those long paint rollers, the ones with a wire bent at right angles, straighten it out and centre of tube can be reached from both ends. Link to comment Share on other sites More sharing options...
Murflynn Posted February 17, 2017 Report Share Posted February 17, 2017 (edited) but how do you prepare the surface before painting? Edited February 17, 2017 by Murflynn Link to comment Share on other sites More sharing options...
cuthound Posted February 17, 2017 Report Share Posted February 17, 2017 but hao do you prepare the surface before painting? Wire brush on a long stick? Link to comment Share on other sites More sharing options...
MtB Posted February 17, 2017 Report Share Posted February 17, 2017 My bow thruster is 6ft 1in tall with a pole, I hope he doesn't get struck down with cavitation Lol, greenie! I have an 18ft bow thruster Ok I did until someone nicked it off the roof.... Link to comment Share on other sites More sharing options...
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