Safe to seal a bow thruster tube with sealant?!

[Poppin]

Hello,

 

I am hoping someone can put my mind at rest. Our new boat has an enclosed bow and a bow thruster tube running through the cabin. This tube was installed by mistake, as we are not having a bow thruster, but we decided to keep it incase we ever decided to have one installed later. 

 

The builder is very well known and respected. They said they would seal it off, and I thought this meant welded shut. However they have just sent me this picture (attached) which shows a clamp with sealant. Now, I'm no expert and I don't know best practice, but this concerns me. Should it? It is below the water line and there is nowhere for water to go but inside the cabin should the seal ever fail. If this did occur, the boat would need to come out of the water quickly to have it welded. Am I wrong? Or is this commonly done? Surely all sealants eventually fail.

 

Any advice much appreciated.

 

 

[IanD]

2 minutes ago, Poppin said:

Hello,

 

I am hoping someone can put my mind at rest. Our new boat has an enclosed bow and a bow thruster tube running through the cabin. This tube was installed by mistake, as we are not having a bow thruster, but we decided to keep it incase we ever decided to have one installed later. 

 

The builder is very well known and respected. They said they would seal it off, and I thought this meant welded shut. However they have just sent me this picture (attached) which shows a clamp with sealant. Now, I'm no expert and I don't know best practice, but this concerns me. Should it? It is below the water line and there is nowhere for water to go but inside the cabin should the seal ever fail. If this did occur, the boat would need to come out of the water quickly to have it welded. Am I wrong? Or is this commonly done? Surely all sealants eventually fail.

 

Any advice much appreciated.

 

 

 

I assume that's on top of the BT tube where the thruster itself would be mounted?

 

If so there's normally a circular hole cut into the BT tube with a short length of pipe welded into this and then a flat flange on top which the BT is bolted/sealed down to. It looks like all they've done is bolt a cover plate down onto this with some sealant -- not as good in the long term as a welded plate but easier to do and reversible, and no riskier for leaks than having a BT bolted to it -- and if a plate was welded on (and later cut off, not easy) you wouldn't have a flat surface to mount a BT on in future if you wanted to.

[David Mack]

Is that a flat plate bolted onto a curved BT tube with a varying thickness of sealant below?

And what's on the other end of that bolt holding it down? Some sort of spreader bar which could quietly rust away with you none the wiser?

As a temporary fix it may be OK, but I wouldn't like to live with it long term. A better solution would be to weld a plate on the outside over each end of the BT tunnel and keep the inside dry. The plates could always be cut off if you ever wanted to install a BT.

[matty40s]

57 minutes ago, Poppin said:

 

The builder is very well known and respected. They said they would seal it off, and I thought this meant welded shut. However they have just sent me this picture (attached) which shows a clamp with sealant. Now, I'm no expert and I don't know best practice, but this concerns me. Should it? It is below the water line and there is nowhere for water to go but inside the cabin should the seal ever fail. If this did occur, the boat would need to come out of the water quickly to have it welded. Am I wrong? Or is this commonly done? Surely all sealants eventually fail.

 

Any advice much appreciated.

 

 

That is commonly known as a bodge.

It looks like a flat plate on a bed of grip fill or bond and seal. The tube has a round profile. You need to see what they have done on the inside of the tube to bolt to, and also make sure that bolt is stainless steel, not mild steel, as the other end will deteriorate. 

 

[blackrose]

When my widebeam was built Liverpool boats installed the BT motor right in the middle of a 10ft tunnel. I questioned this on the basis there's no weed hatch and how would I clear a fouled BT prop as my arm is only 2.5ft long.

 

They moved the motor to one side under warranty and fitted a curved cover made from a section of steel tunnel of the same diameter over the old holes. They tapped two of the holes and used some vetus gasket material and Marineflex sealant, bolting it up with two M10 stainless bolts.

 

When I asked them why they weren't welding the repair they said they couldn't weld it from the inside and if they just welded the cover on from the outside it would leave a crevice and a corrosion trap on the inside. They said what they were doing was at least serviceable. I ended up agreeing with them although I've never actually taken that cover off while in dry dock to check it, and that was 18 years ago.

 

However, having said all that, I don't like the look of your repair. If you're not fitting a BT I think they should weld the tunnel ends over.

Edited March 30, 2023 by blackrose

[Annie cariad]

Well known/respected builders do NOT bodge like that . Boat out tube removed and welded closed only way 

[blackrose]

3 minutes ago, Annie cariad said:

Well known/respected builders do NOT bodge like that . Boat out tube removed and welded closed only way 

 

There's no need to remove the tunnel. Just get the tunnel ends welded over.

[magnetman]

Definitely wants taking off and a curved matching piece welded over the hole. 

 

What does a very well known and respected boat builder mean?

 

I think I would ask for the holes on the outside to be plated over. They could always be plasma cut open again later if needed. Then you could just keep that hole open and use the tube as a beer cooler. 

 

 

ETA cross posted with Mike. Great minds like a think. And fools seldom differ. 

 

 

 

Edited March 30, 2023 by magnetman

[Guest]

16 minutes ago, blackrose said:

 

There's no need to remove the tunnel. Just get the tunnel ends welded over.

 

Or bite the bullet and fit a bow thruster...

[Jon57]

54 minutes ago, M_JG said:

 

Or bite the bullet and fit a bow thruster...

Or put drain bungs in the tube like they use to test domestic drainage. The rubber ones that compress to fit the right diameter. Someone will put a link to what I mean. Welding plates over is the best way but the bungs will be ok if you change your mind in the future you don’t have the hassle of having to dry dock the boat to retro fit bowthruster.

[blackrose]

I'm not sure how those bungs work exactly. Wouldn't bungs just get knocked out as soon as the bow hit something?

 

If you can remove the bungs with the boat in the water as you suggest, I can't see how they would be reliable enough to stop a boat from sinking.

 

The OP needs to get the job done properly in my opinion 

Edited March 30, 2023 by blackrose

[magnetman]

two metal plates pulled onto a heavy rubber diaphragm by tightening a nut down a threaded post in the middle. 

I think that is how they work but never used one.

 

 

 

 

I think welding over the end holes is the way to go as it also protects the inside of the tube from corrosion and biological attack. 

[Jon57]

22 minutes ago, blackrose said:

I'm not sure how those bungs work exactly. Wouldn't bungs just get knocked out as soon as the bow hit something?

 

If you can remove the bungs with the boat in the water as you suggest, I can't see how they would be reliable enough to stop a boat from sinking.

 

The OP needs to get the job done properly in my opinion 

 

[Bee]

Its not good enough.

[blackrose]

No you definitely wouldn't want to rely on those bungs - even if you could find them at the correct diameter.

Edited March 30, 2023 by blackrose

[Jon57]

1 minute ago, blackrose said:

No you definitely wouldn't want to rely on those bungs - even if you could find them at the correct diameter.

They are proper bungs available. The picture was just an example of how they work.

[Slim]

At the very least plates welded over the tube at each end. Maybe also have them remove the redundant tube itself. An alternative may be for them to make a hefty contribution to a thruster. 

[matty40s]

"The builder is very well known and respected. They said they would seal it off, and I thought this meant welded shut. However...."

 

This is the crunch.

This is not the practice of a respected boat builder,  although probably IS the practice of a couple of very well known builders.

You are probably paying a lot of money for your new boat. 

Get this fixed satisfactorily for you, as a proper fix. Not a bodge....before it gets launched, as afterwards, you will find it almost impossible to get it sorted properly.

 

 

Edited March 30, 2023 by matty40s

[MtB]

6 hours ago, Poppin said:

Any advice much appreciated.

 

 

That is one MONUMENTAL bodge. 

 

Name them on here and they won't be "respected" any longer.

 

Collingwood is my guess.

 

 

That foam insulation looks a right mess too, if I may say...

 

 

[Tonka]

8 hours ago, MtB said:

 

 

That is one MONUMENTAL bodge. 

 

Name them on here and they won't be "respected" any longer.

 

Collingwood is my guess.

 

 

That foam insulation looks a right mess too, if I may say...

 

 

If that is in the area that just houses the bow thruster then why is it spray foamed

[Hudds Lad]

5 minutes ago, Tonka said:

If that is in the area that just houses the bow thruster then why is it spray foamed

The OP says it's an enclosed bow, so it'll be in the cabin (probs bedroom) rather than the well deck?

[Tonka]

9 minutes ago, Hudds Lad said:

The OP says it's an enclosed bow, so it'll be in the cabin (probs bedroom) rather than the well deck?

But are they not sealed apart from where the wire goes through to the motor. So as if the tube does leak it does not sink the boat

[magnetman]

edit as did not look at picture properly. 

Edited March 31, 2023 by magnetman

[MtB]

Surely a bow thruster goes under the waterline at the bow, two or three feet back from the stempost. 

 

You can call the accommodation built around it later anything you like. the thruster tube will always be in the same place. 

 

And saying it won't sink the boat if it leaks, is no excuse for the total and utter amateur bodgery in the OP's photo. 

What's more worrying is if the builders are willing to do this where it can be seen, what horrors might they have they committed elsewhere in this boat that are hidden from view?

 

 

[magnetman]

5 minutes ago, MtB said:

Surely a bow thruster goes under the waterline at the bow, two or three feet back from the stempost. 

 

You can call the accommodation built around it later anything you like. the thruster tube will always be in the same place. 

 

And saying it won't sink the boat if it leaks, is no excuse for the total and utter amateur bodgery in the OP's photo. 

What's more worrying is if the builders are willing to do this where it can be seen, what horrors might they have they committed elsewhere in this boat that are hidden from view?

 

 

I wonder if this boat has a 6mm uxter plate and a 10mm base plate.