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Bow thruster tube replacement


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Hi, we have just had a survey done on a boat were the surveyor has managed to sound test the inside of the bowthruster tube and found the thickness to be down to 2.5mm ( originaly 5mm ) were theres erosion around the bowthruster prop. Sounds horrific but I guess this is very common and we're prob lucky the tubes big enough to get in to test and the grilles are removable. So question is should I be panicking and imediatly getting the welders in or are we kicking at a problem for future me to deal with.

Also has anyone had a tube replaced did it take long / go well and any ideas on cost so I can have an idea where to start for negotiation purposes.

Thanks in advance 

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35 minutes ago, calon said:

Also has anyone had a tube replaced did it take long / go well and any ideas on cost so I can have an idea where to start for negotiation purposes.

Negotiate for £1500 off the purchase price, then just have the tunnel-holes plated over and learn to steer the boat.

Its not called a 'cissy button' for nothing.

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Oddly enough just discussing the same issue at the weekend .  Therefore I  assume corrosion of steel bow thruster tunnel is a recognised  issue . 

GRP cruisers don't have issue with erosion of the bow thruster tunnel (as far as I know) so I am wondering if a plastic  bow tunnel tube could be fitted in a  steel hulled boat?

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16 hours ago, MartynG said:

Oddly enough just discussing the same issue at the weekend .  Therefore I  assume corrosion of steel bow thruster tunnel is a recognised  issue . 

GRP cruisers don't have issue with erosion of the bow thruster tunnel (as far as I know) so I am wondering if a plastic  bow tunnel tube could be fitted in a  steel hulled boat?

The difficulty would be keeping the plastic to steel joint waterproof over time. It is underwater, so a failure would be bad to catastrophic, depending on how serious it was. Any idea why the pitting happened there? Might be cavitation from a too strong bow thruster prop, but I have no idea if that is a risk or not for something so small. As others have said, get the ends welded over and sell the thruster.

 

Jen

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17 hours ago, mrsmelly said:

They are a nonsense. Weld over the ends and job done. The bar at the back end attached to the rudder moves and steers the boat it REALY is that simple. Bowthrusters are for incompetents much the same as reversing sensors on cars.

Having recently had to reverse 2 miles single handed, I would argue that they do have their uses.

 

Any pitting which occurs does tend to happen in line with the blades - possibly due to a degree of erosion from bowthruster use.

 

A well designed boat will have a bulkhead behind the thruster to ensure that any flooding won't sink the boat.

Edited by billS
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35 minutes ago, Jen-in-Wellies said:

 Any idea why the pitting happened there? Might be cavitation from a too strong bow thruster prop, but I have no idea if that is a risk or not for something so small.

 

 

from what I have read relating to bow thrusters on larger vessels there is some damage from cavitation but a lot more occurs from scouring when a thruster pulls silty water through the blade, effectively you end up with a very wet sandblaster close to the tips of the blades.

Edited by Jess--
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16 minutes ago, billS said:

Having recently had to reverse 2 miles single handed, I would argue that they do have their uses.

 

Any pitting which occurs does tend to happen in line with the blades - possibly due to a degree of erosion from bowthruster use.

 

A well designed boat will have a bulkhead behind the thruster to ensure that any flooding won't sink the boat.

I agree with all of this. I've just had my thruster tube 2-packed but if it ever should fail it's within its own compartment so won't sink the boat. If the boat has one there are times it is useful no matter how competent a steerer you are, although you do reach a higher level of competence being without one for a while!  

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Perhaps you could get a welder to put 2 larger half tubes around the tube effectively creating a thicker pipe around the blades, a bit like overplating but inside the boat. My tube was built like that with a double thickness section about a foot long.

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25 minutes ago, Jess-- said:

from what I have read relating to bow thrusters on larger vessels there is some damage from cavitation but a lot more occurs from scouring when a thruster pulls silty water through the blade, effectively you end up with a very wet sandblaster close to the tips of the blades.

Yes this apears to be the cause of the errosion the boat is not old 2009 with low engine hours so I was surprised at the wear but I guess low engine hours doesnt mean low thruster usage. 

I'm trying to find out if it's behind it's own bulkhead but the access is under a bolted down plate on the front deck which has very recently been painted so didn't want to go chipping away at it just yet .

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2 hours ago, calon said:

Yes this apears to be the cause of the errosion the boat is not old 2009 with low engine hours so I was surprised at the wear but I guess low engine hours doesnt mean low thruster usage. 

I would suggest quite the reverse - low engine hours probably means the owner never got experienced in actually steering the boat. I have seen boats going along 'the straight' with the cissy-button in continuous use, first one side and then the other, zig-zagging along so the bow thruster probably did as many hours as the engine.

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38 minutes ago, Alan de Enfield said:

I would suggest quite the reverse - low engine hours probably means the owner never got experienced in actually steering the boat. I have seen boats going along 'the straight' with the cissy-button in continuous use, first one side and then the other, zig-zagging along so the bow thruster probably did as many hours as the engine.

I think you are absolutely spot on. I am on the Thames at the moment and most boats just hold their steering wheels in the ahead position and press the incompetence switch to move the pointy end :banghead:  I am at present typing from a mooring at Maidenhead and a medium size yoghurt pot just went about only using the incompetent button when their is enough space here to turn the Titanic. ? I reckon they think it looks cool like those numpties that use them vapour jobbies instead of proper fags!!

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On 22/05/2018 at 17:57, calon said:

Hi, we have just had a survey done on a boat were the surveyor has managed to sound test the inside of the bowthruster tube and found the thickness to be down to 2.5mm ( originaly 5mm ) were theres erosion around the bowthruster prop. Sounds horrific but I guess this is very common and we're prob lucky the tubes big enough to get in to test and the grilles are removable. So question is should I be panicking and imediatly getting the welders in or are we kicking at a problem for future me to deal with.

Also has anyone had a tube replaced did it take long / go well and any ideas on cost so I can have an idea where to start for negotiation purposes.

Thanks in advance 

If you have a limited area of corrosion and 2.5 mm was thickness remaining then I suggest you should not panic. Its quite unlikely to perforate for quite some time with that wall thickness and even if it does it will initially leak rather than catastrophically fail (so inspect it routinely). This gives you time to consider options and plan remedial work.

 

Over the years I have been involved in many instances of pipework where wall thickness has degraded from the original.   There are options other than tube replacement. One approach that is commonly used in industry is to clean the external wall of the tube and wrap in an engineered composite (similar to fibreglass). The wrap provides a leak tight pressure boundary with equivalent strength to the original tube. Done properly this will withstand vey high pressures (and temperatures) many orders of magnitude greater than required for a bow thruster tube. Whilst I am not suggesting you contact these people (the cost would not be insignificant) the following people would do a good job and you will see that they can do this tube of repair on 12" diameter lines and up to 250Barg.

 

http://icr-world.com/products-and-services/technowrap-engineered-composite-solutions/piping-systems

 

My advice would be to get the tube inspected properly. Ensure its got 2.5 mm wall thickness (ask whoever does the thickness checks for the minimum thickness and the tolerance on the measurements). If this value is correct get the tube cleaned inside and out and properly recoated to prevent further corrosion and to resist internal erosion. If the corrosion is worse, e.g thinner and or more extension, then it is time to consider blanking off or tube replacement.

 

Oh, and ignore the comments about sissy buttons etc. You can decide for yourself if you want to keep and or use the bow thruster.  (I will now head for the bunker......)

 

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The erosion of the steel is known as "explosive pitting" caused as previously mentioned by the speed of the propeller and the proximity of the pipe steel. We used to see it a lot in the enclosed prepellers on ghe ships. 

 

I would not call bow thrusters on ships "cissy buttons" they help to control the vessel. I will agree that too many boaters mis-use them as they do not understand how to get the best from them. A lot of bank erosion is down to inexperinced boaters using them to push off the bow having unmoored. Just walk forward and give a good shove, however in the middle of the canal or river when manoeuvering that is not so easy. In the same disparaging vein I suppose hot water tanks could be classed as a bit cissy. Old sea dogs and canal boaters used to get bathed  from a kettle of hot water off the stove. Some things just make life easier and better.

 

Now that's going to be fun . . . . 

 

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1 hour ago, DaveR said:

 Some things just make life easier and better.

 

Now that's going to be fun . . . . 

 

My bow thruster certainly  makes life easier in certain situations .

I nudge from the thruster can be very helpful.

Even when not needed it presence and availability adds confidence when maneuvering in a tight situation .

 

I watched a narrowboat take half an hour to reverse into a mooring at the weekend. The skipper seemed adequately experienced and it was his home mooring. There was a light wind and that didn't help.  However a bow thruster would have made it a much quicker / easier job.

 

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On 22/05/2018 at 17:57, calon said:

Hi, we have just had a survey done on a boat were the surveyor has managed to sound test the inside of the bowthruster tube and found the thickness to be down to 2.5mm ( originaly 5mm ) were theres erosion around the bowthruster prop. Sounds horrific but I guess this is very common and we're prob lucky the tubes big enough to get in to test and the grilles are removable. So question is should I be panicking and imediatly getting the welders in or are we kicking at a problem for future me to deal with.

Also has anyone had a tube replaced did it take long / go well and any ideas on cost so I can have an idea where to start for negotiation purposes.

Thanks in advance 

Did the surveyor check the rudder tube and weed hatch for thickness as well ? I suspect they are often ignored when a boat is surveyed. 

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1 hour ago, DaveR said:

The erosion of the steel is known as "explosive pitting" caused as previously mentioned by the speed of the propeller and the proximity of the pipe steel. We used to see it a lot in the enclosed prepellers on ghe ships. 

 

I would not call bow thrusters on ships "cissy buttons" they help to control the vessel. I will agree that too many boaters mis-use them as they do not understand how to get the best from them. A lot of bank erosion is down to inexperinced boaters using them to push off the bow having unmoored. Just walk forward and give a good shove, however in the middle of the canal or river when manoeuvering that is not so easy. In the same disparaging vein I suppose hot water tanks could be classed as a bit cissy. Old sea dogs and canal boaters used to get bathed  from a kettle of hot water off the stove. Some things just make life easier and better.

 

Now that's going to be fun . . . . 

 

I think you have hit nail on head. Yes they are needed on ships but no way on a tiny a boat as a narrowboat. Also I practicaly never have the the pointy end pushed off when " un mooring "

When leaving a berth the propeller needs to be in deep water not the pointy end. I always gently push the stern off and reverse a small amount and with correct use of tiller and engine controls away I go. If its awkward to push the stern off which it oft is I usualy just use power to get back end off then resume the rest of the procedure. I am still astonished to this day when daily I see people pushing the front end of their boats off the side then rattling for many a yard along the bank/moorings with the prop stuck in the shallow water churning the silt up and getting nowhere.

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14 hours ago, mrsmelly said:

I think you are absolutely spot on. I am on the Thames at the moment and most boats just hold their steering wheels in the ahead position and press the incompetence switch to move the pointy end :banghead:  I am at present typing from a mooring at Maidenhead and a medium size yoghurt pot just went about only using the incompetent button when their is enough space here to turn the Titanic. ? I reckon they think it looks cool like those numpties that use them vapour jobbies instead of proper fags!!

I saw a similar thing at Shepperton lock a few years ago. A medium sized gin palace had the lock all to itself and when the gates opened set off steering with the bow thruster. It zig zagged out of the lock managing to hit both sides quite hard. The lock must be about 30 ft wide. The lock keeper said it was not an unusual occurrence.

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the only time I have seen a smaller boat make effective use of a bowthruster was while waiting in a lock channel on the thames while some work was being carried out (unexpected 30 mins of work).
all available positions on the fairly short landing were taken (narrowboats 2 & 3 abreast)

a dutch barge (probably a piper replica) of around 60x12 came down the channel and then held position mid channel for about 20 minutes.
Watching how they were handling it they had it in gear astern (very slow / just enough to hold against the current) and were using the bowthruster roughly once every minute, with each burst being less than half a second (just enough to give the bow the tiniest nudge)

over the 20 minutes I would say the boat moved less than 6 feet forward & back and around 2 feet side to side which I thought was pretty good considering that working against the current they were effectively reversing continuously for those 20 minutes

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Perhaps morse controls should be called a "cissy levers"? Real boaters should be using horses to pull the boat, shouldn't they?  

 

I've had a BT on my widebeam for the past 13 years. I don't overuse it but it's certainly useful for reversing any distance and I'd love to see some of the less experienced boaters on here try to steer my 30 tonne boat single handed. Even with the BT I don't think many would be able to take it through a canal lock or manage a Thames lock by themselves without assistance. If some boaters don't know how to steer their boats because they overuse their BTs that's another story of course and I do understand the frustrations, but there are plenty of boats out there with BTs which you will be completely unaware of because the owners don't overuse the BT. 


So now that we know that having a BT and knowing how to steer a boat aren't mutually exclusive, perhaps some people might want to think about stopping all the disparaging, judgemental nonsense. I don't get angry because someone else's boat has wheel steering and mine has a tiller, or they have a combi battery charger/inverter and I don't. These are just bits of equipment and slagging off someone else's boat or choice of equipment is frankly a bit childish. If you want a BT get one, if you don't want one then don't have one. Simples!

 

 

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