Bow thruster tube replacement

[yabasayo]

Most small seagoing boats are GRP so they wouldn't fit a steel tube.

[blackrose]

19 hours ago, yabasayo said:

Possibly not. However it is more likely that soft protective coating in the blade tip area has been eroded leaving bare metal to quietly corrode away unseen.

It takes a lot of high velocity water over a substantial period to erode steel.

Never seen any corrosion on the blade tip area of mine.

[blackrose]

15 hours ago, Boater Sam said:

Not got one, don't want one, no need of one.

But I have seen the advantage for some folk in having one.

They do a grand job of removing poly bags but rubbish, mussels and stones going through must inevitably mark the blades and the inside of the tube leading to rapid corrosion.

 

Not inevitable and no corrosion after 14 years. The tunnel is made of steel, not cheese! As I mentioned earlier I've never removed and bags from the water.

 

I did replace the plastic BT prop after about 6 years. One of the blades was slightly damaged, but the last time the boat came out of the water 3 years ago the internal coating of red primer was still visible inside the tunnel. That was after more than 10 years.

[blackrose]

10 hours ago, matty40s said:

It isn't the water thst erodes it, it is the silt, small stones and other debris which is prevalent in the shallow ditches...especially at the bankside.

All the failed or very thin ones I have seen have had the worst wear at the propeller area.

 

I wonder why that hasn't happened to mine?

 

If this phenomenon it's really so prevalent then wouldn't we also see it on the skegs and uxter plates of steel canal boats, in areas in proximity to the prop tips? On mine these areas are only a couple of inches away and I've seen prop tips a lot closer to the steel on other boats when I've seen them out of the water.

 

Edited March 11, 2019 by blackrose

[matty40s]

You treated your boat properly from Day1 of your ownership, you have always looked after it.

Most of your time has been on deeper rivers rather than on 2 foot deep mud trenches.

As most Liverpool and now Collingwoods are observed at launch to have no blacking at all in the tubes, they start on the backfoot straight away.

A lot of boat owners seem to think they need to use the bowthruster to move the front end onto and off the bank....this introduces small stones, silt and other debris into their tube.....thus accelerating wear in a small area...which is already vulnerable having no coating...

Edited March 11, 2019 by matty40s

[blackrose]

39 minutes ago, matty40s said:

You treated your boat properly from Day1 of your ownership, you have always looked after it.

Most of your time has been on deeper rivers rather than on 2 foot deep mud trenches.

As most Liverpool and now Collingwoods are observed at launch to have no blacking at all in the tubes, they start on the backfoot straight away.

A lot of boat owners seem to think they need to use the bowthruster to move the front end onto and off the bank....this introduces small stones, silt and other debris into their tube.....thus accelerating wear in a small area...which is already vulnerable having no coating...

Mine is a Liverpool boat. The inside of the tunnel has never been painted but I have done the bits I could get to at the ends. But if silt and debris is going to erode steel then one would imagine it would do the same to paint? I think cavitation from the blade tips might actually be more damaging to steel than silt, though I haven't seen any cavitation damage on my boat.

 

I used to be on the GU (actually river Brent) for the first 5 years but admittedly spent more time going out onto the tidal Thames. However I took the boat up to the Tring summit a few times and down the Paddington arm to Limehouse. I also did the entire length of the K&A from Reading to Bristol. I think those are the only bits of canal I've navigated on this boat, apart from the G&S and I guess a ship canal isn't a muddy ditch. But I think there's plenty of silt on rivers too. 

Edited March 11, 2019 by blackrose

[Movin' on]

I seem to remember a few boats/years back I had a survey fail a boat on its BT tube and this was not wear but Electrolytic corrosion between the blade/motor and the tube as it was very localized to prop pitch/width. 

[PeterF]

14 hours ago, matty40s said:

It isn't the water thst erodes it, it is the silt, small stones and other debris which is prevalent in the shallow ditches...especially at the bankside.

All the failed or very thin ones I have seen have had the worst wear at the propeller area.

Most likely a coupling of erosion and corrosion, the erosion removes the corrosion products which normally act as a bit of a barrier slowing down corrosion, revealing fresh steel to rapidly corrode. Seen it a lot in the chemical industry in pumps and high velocity / turbulent pipework if there are solids in the fluid.

[blackrose]

1 hour ago, Halsey said:

I seem to remember a few boats/years back I had a survey fail a boat on its BT tube and this was not wear but Electrolytic corrosion between the blade/motor and the tube as it was very localized to prop pitch/width. 

Maybe that's why the prop on mine is made of plastic? 

Edited March 11, 2019 by blackrose