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Bow Thruster


jddevel

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If I'd had a bow thruster (which clearly no self-respecting sailor has) I'd have painted my tube with so little issue last time around that I can't even remember whether I used a special bent brush or not. I'd imagine most folk could get their arm in, else coincide the blacking with bob-a-job week and send some disposable boy scouts in to do it. When I do the blacking again this year, I wouldn't be envisaging any issues prepping and painting inside the thruster tube again (if I had one, which clearly no self-respecting sailor has).

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I've had a BT on my boat for the past 12 years and the 8mm wall thickness tunnel is still painted in its original primer. After all this time and use there is zero evidence of any cavitation pitting or corrosion. Perhaps I've just been lucky. I don't have anything else to base my opinion on other than my boat and a couple of others, but for what it's worth I think the whole BT cavitation/corrosion issue is a myth peddled by the anti-BT brigade. Do you lot all have issues of cavitation corrosion at your stern ends? I don't.

 

Likewise, the idea that unless you have a full height bulkhead between your BT and the rest of the boat then it's going to sink is another myth. Lots of vessels of different types have underwater hull penetrations in various areas of the hull. They can't all go behind bulkheads. If a BT is properly installed there is no reason for it to leak. If a BT did leak it's not going to be like u-boat going down, it's more likely to be a drip or small seep. All I did was seal up both ends of the baseplate crossmember aft of the BT to make it watertight and installed a bilge pump forward of that just in case, but it's never leaked a drop.

Edited by blackrose
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I've had a BT on my boat for the past 12 years and the 8mm wall thickness tunnel is still painted in its original primer. After all this time and use there is zero evidence of any cavitation pitting or corrosion. Perhaps I've just been lucky. I don't have anything else to base my opinion on other than my boat and a couple of others, but for what it's worth I think the whole BT cavitation/corrosion issue is a myth peddled by the anti-BT brigade. Do you lot all have issues of cavitation corrosion at your stern ends? I don't.

 

Likewise, the idea that unless you have a full height bulkhead between your BT and the rest of the boat then it's going to sink is another myth. Lots of vessels of different types have underwater hull penetrations in various areas of the hull. They can't all go behind bulkheads. If a BT is properly installed there is no reason for it to leak. If a BT did leak it's not going to be like u-boat going down, it's more likely to be a drip or small seep. All I did was seal up both ends of the baseplate crossmember aft of the BT to make it watertight and installed a bilge pump forward of that just in case, but it's never leaked a drop.

 

There was a report in Waterways World (I think) a while ago about a boat which sank because its bowthruster tube had rusted through, and there was no separate bulkhead. In that case the inside of the tube had never been painted, and the outside of the tube was only painted on the visible bits - thetop and back, and the front and underside were unpainted. Rusting from both sides led to a hole sufficient to sink the boat. Proper maintenance would have prevented this, but it isn't the easiest of jobs.

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Poor design, shoddy build practices and neglect are far more of a threat to watertight integrity than a well-designed, properly fitted and effectively maintained bow thruster. Given the polarised views the bow thruster seems to generate, I think the most likely cause of sinking in a BT fitted boat is being torpedoed!

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Boats have sunk due to bow thruster tube failure. A bulkhead just seems sensible. And will help later when it comes to selling. Of course, a thick tube made of seamless tubing is going to last a very long time. But a seamed tube will be prone to corrosion on the weld and heat-affected zone (HAZ). If the boat is going to be unattended for weeks at a time.................................

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... But a seamed tube will be prone to corrosion on the weld and heat-affected zone (HAZ). If the boat is going to be unattended for weeks at a time.................................

That'll be poor design and shoddy build coming into play. Just add neglect...

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There was a report in Waterways World (I think) a while ago about a boat which sank because its bowthruster tube had rusted through, and there was no separate bulkhead. In that case the inside of the tube had never been painted, and the outside of the tube was only painted on the visible bits - thetop and back, and the front and underside were unpainted. Rusting from both sides led to a hole sufficient to sink the boat. Proper maintenance would have prevented this, but it isn't the easiest of jobs.

Well I'm sure there are reports of boats sinking because their stern tubes rusted through to and they had no separate bulkhead. Things do happen but that doesn't make it a general rule.

 

My tube has never been painted since it was new 12 years ago and last time it was out the water 18 months ago I couldn't see any pitting. Like most canal boat owners baseplate's never been painted at all and likewise it's fine.

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You have also had the luxury of being river based for the majority of your time, most of the problems are being found in boats on muddy ditches.

This IS a significant issue, not an anti bowthruster scam.

In the last 12 months we have sealed 2 up and inserted a re-enforcing tube in another. We have seen two brand new wide beams delivered with no blacking at all in the tube.

 

More electrical gadgets are going on boats to satisfy people's need for modern life aboard and I have no doubt that cases of severe electrolytic corrosion will become more prevalent as we go through the next few years.

  • Greenie 2
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Last year I spoke to a man who owns a boatyard and a hire company and he told me of three boats where the bow thruster tube had failed due to the use of a seamed pipe. If I had a bow thruster I would want to know if seamless pipe had been used or not. It's very hard to tell the condition by eye so the lack of visible pitting is not evidence that failure is unlikely.

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Torpedo tubes have outer doors, so could bow thrusters have them too?

What, torpedoes?

 

It's evacuating the water inside that would make doors impractical, and you'd still be left with a damp environment.

 

Bow thruster owners just have to accept that they're heading for disaster: if the torpedoes don't get them, catastrophic corrosion will. ;)

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