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Rust in bilge


jenevers

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So you’ll have a bilge full of carbonic acid instead?  That’s assuming that you’re constantly replenishing the CO2 with a never ending supply of extinguishers of course...

 

Surely better to remove the other component - Water. 

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2 hours ago, WotEver said:

So you’ll have a bilge full of carbonic acid instead?  That’s assuming that you’re constantly replenishing the CO2 with a never ending supply of extinguishers of course...

 

Surely better to remove the other component - Water. 

How is carbonic acid created?  What's that acid in Vactan?

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Seriously folks...

 

I have often wondered about the wisdom of venting bilges, though it is accepted wisdom that creating some air flow through the bilge is a good idea, it also introduces fresh oxygen and if the air flow doesn't dispel what moisture is in the bilge might it actually make matters worse?  There's surely a case for sealing up the bilge entirely so once the oxygen has been used up (in the rusting process) no more can form.  

 

 

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11 minutes ago, Neil2 said:

Seriously folks...

 

I have often wondered about the wisdom of venting bilges, though it is accepted wisdom that creating some air flow through the bilge is a good idea, it also introduces fresh oxygen and if the air flow doesn't dispel what moisture is in the bilge might it actually make matters worse?  There's surely a case for sealing up the bilge entirely so once the oxygen has been used up (in the rusting process) no more can form.  

 

 

Or you could seal the bilge by treating and painting it, that would keep the oxygen at bay.

 

Keith

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2 hours ago, larryjc said:

Or do what I do and keep it dry!!

 

Some you can't keep dry. Our boat, Reeves hull, has a deep cratch. From the two side lockers pipes run the length of the boat to the engine room bilge. Although we have a cratch cover some water gets in, depends upon wind force and direction. This drains through to to the engine room bilge. Also when we drain the boat down for winter the calorifier also vents into the bilge, as it does on the odd occassion when the PRV blows. 

 

There is a separate sump beneath the engine, I can keep this dry.

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I guess I'm lucky with a pram over the hatch and only the stern gland to worry about.  However, previous owners weren't so careful and there has clearly been quite a lot of water in there in the past.  Which I why I have some fertran, bilge paint, wire brushes etc all ready for me to make the effort to paint it all out as soon as I can find the motivation!!!

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18 hours ago, jenevers said:

Here's an idea. Rust needs water and oxygen, so, how about depriving your bilge of oxygen by filling it with carbon dioxide by using a CO2 extinguisher?  Discuss ?

 

 

Unless you have gas tight bilges you'd have to keep filling until you filled the whole cabin with CO2 and it was coming out of the vents. By that stage you'd already be dead. 

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19 hours ago, Steilsteven said:

Or you could seal the bilge by treating and painting it, that would keep the oxygen at bay.

 

Keith

 

Which is almost my thinking too.

 

If painting seals out the oxygen, why does groupthink say is there a need to ‘treat’ the rust first with vactan or similar? Surely once painted the oxygen is sealed out, so further rusting is prevented whether or not existing rust has been ‘converted’ or ‘treated’.

 

I suspect it is simply because it sounds intuitively the right thing to do, so a whole industry has sprung up selling rust converters to a willing but misinformed market. 

Edited by Mike the Boilerman
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19 hours ago, Neil2 said:

Seriously folks...

 

............................ it also introduces fresh oxygen and if the air flow doesn't dispel what moisture is in the bilge might it actually make matters worse?  There's surely a case for sealing up the bilge entirely so once the oxygen has been used up (in the rusting process) no more can form.  

 

 

ahh .... the dreaded fresh oxygen.    dangerous stuff that - much better to have old and stale oxygen.   :banghead:

 

 

.............................. err, ..................... but ....................... how do you get fresh oxygen without air flow?

 

 

 

 

anyway, millenia of boat building experience has established that all spaces should be well ventilated - some narrowboat builders seem to have no knowledge of proper boatbuilding.

Edited by Murflynn
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1 hour ago, Mike the Boilerman said:

 

Which is almost my thinking too.

 

If painting seals out the oxygen, why does groupthink say is there a need to ‘treat’ the rust first with vactan or similar? Surely once painted the oxygen is sealed out, so further rusting is prevented whether or not existing rust has been ‘converted’ or ‘treated’.

 

I suspect it is simply because it sounds intuitively the right thing to do, so a whole industry has sprung up selling rust converters to a willing but misinformed market. 

If paint is permeable to water you can bet its also permeable to gasses like oxygen. The fact paint can micro-blister when water is trapped on the surface shows it is water permeable. I suspect the rust treatment is supposed to form a less permeable surface to be better at keeping oxygen away from the steel underneath.

 

I think International recommended (or did recommend) a minimum of five coats of Danbolin bilge paint.

 

Not sure ow permeable two pack is or water based paint. Maybe the duck keeper has some info on this.

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4 hours ago, Tony Brooks said:

If paint is permeable to water you can bet its also permeable to gasses like oxygen. The fact paint can micro-blister when water is trapped on the surface shows it is water permeable. I suspect the rust treatment is supposed to form a less permeable surface to be better at keeping oxygen away from the steel underneath.

 

I think International recommended (or did recommend) a minimum of five coats of Danbolin bilge paint.

 

Not sure ow permeable two pack is or water based paint. Maybe the duck keeper has some info on this.

It seems more logical to me that blistering occurs because the paint is impermeable, otherwise wouldn't whatever causes the blister be able to escape from under the paint?

 

The benefit of rust treatment is to provide a uniform surface to which paint will adhere. It shouldn't affect permeability of the finished paint system but it should help it to stay stuck to the boat. Rusted metal will have small voids within it because of the way rust forms and these will remain under the applied paint and potentially cause the system to fail. Best to treat rust by mechanical removal rather than by chemically converting if possible. Reality is that both are often necessary.

 

Let's see if Dr Duck concurs with either of our premises.

 

JP

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On 19/08/2018 at 13:29, Captain Pegg said:

It seems more logical to me that blistering occurs because the paint is impermeable, otherwise wouldn't whatever causes the blister be able to escape from under the paint?

 

The benefit of rust treatment is to provide a uniform surface to which paint will adhere. It shouldn't affect permeability of the finished paint system but it should help it to stay stuck to the boat. Rusted metal will have small voids within it because of the way rust forms and these will remain under the applied paint and potentially cause the system to fail. Best to treat rust by mechanical removal rather than by chemically converting if possible. Reality is that both are often necessary.

 

Let's see if Dr Duck concurs with either of our premises.

 

JP

 

Some years ago we had a bad winter where snow stayed on boats for many weeks and enough boats to cause notice had micro-blistered. Craftmaster paints got involved and we discussed in on this forum. Eventually Phill Speight  concluded that the water sitting on the paint, under the snow, had permeated the paint film causing the micro-blisters.

 

We also have a number of people periodically agreeing with the notion that you should not have things like mats laying on the paint because it causes paint breakdown and rust.

 

If paint was not permeable then how do you account for the above.

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