Bow Thruster Tunnel Leak - Repairs Macclesfield Canal Area

[blackrose]

29 minutes ago, ditchcrawler said:

As I said, I might be wrong. But you should be able to find stock steel pipe.

 

Just an example. This would work out to 152mm ID.

 

Edited January 3, 2021 by blackrose

[captain birdseye]

On 03/01/2021 at 21:15, Troyg said:

Thanks for your comments so far everyone. Interesting points about Kerridge, Bollington and Bullshead. I will certainly follow those up. I don’t recall a slipway or dry dock at Bollington though?

 

Bollington will however get a crane in to lift you out. Both Jason and Steve that work there are good welders. Both have done work for me

[blackrose]

On 03/01/2021 at 21:15, Troyg said:

The hull is a Liverpool boats build around 2002. As people have mentioned here the tube is thinner material than the hull. Unfortunately before I got the boat it had been neglected and obviously not blacked frequently. I have since blasted amd applied Jotun 2 pack a couple of years back. I got inside the tunnel with a brush on a broom handle to get as much blacking in as I could but could already see evidence of pitting so I am certain that is the cause for this issue now. The hole has appeared a few inches away from the propeller so this confirms that the pitting is most likely caused by aeration etc. of the thruster. 

 

Just resurrecting this old thread as my boat is out of the water now and I can't see any evidence of pitting in the BT tunnel which has never been painted since it was launched 17 years ago. 

 

I don't understand why your BT tunnel is made of thinner material than the hull? I guess it depends which part of the hull was being referred to in the thread? On my Liverpool Boat the BT tunnel is 8mm thick, so thinner than the 10mm baseplate but thicker then the 6mm sides.

 

The theory I heard from some on this forum of pitting caused by BT prop cavitation around the arc of the tips of the prop seems like nonsense to me. How long would you need to keep your finger on the button for that to happen? Anyway, there's no pitting around the prop on mine. I'll try to add a picture later.

[Bee]

So many variables in pitting and corrosion. Firstly painting, No idea why a steel tube should not be pitted and rusty with no paint on it - it should be horrible!, Thinner steel? I guess tube of the right dia. was ordered from the stockholders and wall thickness was a very secondary worry. As for prop cavitation, yes, I think this is a prop problem (I think) the prop tears holes in the water and the vacuum implodes eroding the surface of the prop, whether this would affect the tube I don't know, Do people fit anodes in tubes? I think the importance of anodes might be overstated (in fresh water on a painted hull) but near dissimilar metals it is almost certainly a real thing, Are BT props bronze? if so then an anode or two makes big sense. There is a lot of impressive science on this subject but as soon as you bung the whole assembly in grubby water full of fish poo and worse plus all sorts of other boats with dodgy electrics surrounded by galvanised sheet piling the science goes out the window,  Paint is the best protection - that and crossed fingers.

[blackrose]

It has still got some of the original red shop primer on the inside of the tunnel. Not sure what that was. This picture makes it look worse than it actually is. I think the BT leg is bronze but it's isolated from the tunnel with a thick plastic spacer. 

 

 

[ditchcrawler]

7 hours ago, blackrose said:

The theory I heard from some on this forum of pitting caused by BT prop cavitation around the arc of the tips of the prop seems like nonsense to me. How long would you need to keep your finger on the button for that to happen? Anyway, there's no pitting around the prop on mine. I'll try to add a picture later.

I have seen photos of that where the tube is eroded around the blade area. Grit in the water may also not help. 

[Troyg]

I’m not sure what is the exact cause but mine was badly pitted around the prop only. The was in ok condition. Objects going through, stirring up air. Remember oxygen feed corrosion. I ended up replacing the tune. Been fine since

[Alan de Enfield]

12 minutes ago, Troyg said:

I ended up replacing the tune.

 

"Sweet Caroline" seems a popular tune at the moment.

[blackrose]

I think anyone with pitting or corrosion around the prop tip area of their BT tunnel must have a very heavy finger! Seriously, you must be using it a lot. 

[ditchcrawler]

9 minutes ago, blackrose said:

I think anyone with pitting or corrosion around the prop tip area of their BT tunnel must have a very heavy finger! Seriously, you must be using it a lot. 

Some people do, getting into locks, trying to keep still in locks, even getting out of locks, mooring, casting off. picking up the crew between locks are just some examples 

[gatekrash]

Ours was like it when we bought the boat - pitted badly, to the point where the surveyor poked his screwdriver through it entirely. Again, only around the prop blade area. We had the whole tube replaced as part of our sale negotiations.

 

Surveyors view was it was caused by a combination of lack of maintenance (difficult to black in there) combined with mud and grit effectively scouring the tube in that area. Especially if someone has been using it to get the boat off the bank when moored where the shallow muddy water would be easily stirred up by the thruster.

 

When we came out for blacking last month which is now 2 years since we bought the boat the new tube was unmarked and still blacked. Probably because we keep forgetting we've got the BT and I've normally forgotten to turn the isolator off !