Does rust ever sleep?

[OldGoldy]

Hi Dave

 

This is an interesting idea. Two questions:

 

1) Do you actually need the two computer fans, or would two holes, say 3" diameter (with a suitable grille or mesh over them) at either end of the boat do the trick? I mean, could there be some kind of natural air flow without the fans?

 

2) If you use the fans, are they powerful enough to move the air through the bilges?

 

I think that (1) would only work if you have a deep-draughted boat which has full length clearance under the cabin floor ie you have the steel angle on the bottom plate and you have floor bearers a few inches above that. (Like in a house)

 

In my boat there is no underfloor gap, save that at the junction of baseplate and sides, which happens to be an approx 2in triangle.

 

(2) The short answer is - I don't know - I am currently refitting after having the bottom overplated, but anything that encourages airflow has to be worth a try. There are, of course, a variety of fans available with different airflow ratings, so I think - worth trying. Surely any air movement will have a drying effect?

 

Good idea? Anyone care to comment? Will I be wasting my time?

[nb Innisfree]

I think that (1) would only work if you have a deep-draughted boat which has full length clearance under the cabin floor ie you have the steel angle on the bottom plate and you have floor bearers a few inches above that. (Like in a house)

 

In my boat there is no underfloor gap, save that at the junction of baseplate and sides, which happens to be an approx 2in triangle.

 

(2) The short answer is - I don't know - I am currently refitting after having the bottom overplated, but anything that encourages airflow has to be worth a try. There are, of course, a variety of fans available with different airflow ratings, so I think - worth trying. Surely any air movement will have a drying effect?

 

Good idea? Anyone care to comment? Will I be wasting my time?

 

As condensation usually only occurs in winter I would think it better to blow cold air through bilges to reduce temp differential on bottom plate, any warm air would just increase condensation.

[Hairy-Neil]

So you have seen my locking techniques then...

 

Richard

 

Yes...

 

I'm sure Alvechurch get lots of phome calls about the antics Tawny Owl gets up to....

[Jim Batty]

I think that (1) would only work if you have a deep-draughted boat which has full length clearance under the cabin floor ie you have the steel angle on the bottom plate and you have floor bearers a few inches above that. (Like in a house)

 

In my boat there is no underfloor gap, save that at the junction of baseplate and sides, which happens to be an approx 2in triangle.

 

(2) The short answer is - I don't know - I am currently refitting after having the bottom overplated, but anything that encourages airflow has to be worth a try. There are, of course, a variety of fans available with different airflow ratings, so I think - worth trying. Surely any air movement will have a drying effect?

 

Good idea? Anyone care to comment? Will I be wasting my time?

 

Re 1) This boat we're looking at has about 3" underfloor gap from the base plate, so yes I suppose some type of forced air would be best. I wonder if those curved horn shaped air vents you see on small ships could be used on narrowboats in some way. Shafted down into the bilges.

[MarkAdrian]

Sounds like a nice recipe. The turps evaporates ... a hint of beeswax in the air ... but do you smell the machine oil?

 

Like waxoyl there is a smell for a week or so after application, but it soon goes.

 

I like the idea of the computer fans, small enough to be driven by a small cheap solar panel too. Though I wonder if you would need two? i.e. one pushing the air and the other pulling it? Could they not both be set to "extract" at one end of the boat and just have two vents at the other, which would then draw air through? Just a thought.

[ChrisPy]

I'd be very surprised if any boat floor extended to the hull sides and made a seal against draughts. I don't think through ventilation will ever work, but cross ventilation in each 2ft wide bilge section probably exists already, to a degree.

[nb Innisfree]

I'd be very surprised if any boat floor extended to the hull sides and made a seal against draughts. I don't think through ventilation will ever work, but cross ventilation in each 2ft wide bilge section probably exists already, to a degree.

 

To be effective I think air would need to be forced in from the centre of each section, and then air needs to come from outside, impractical really.

[MarkAdrian]

I'd be very surprised if any boat floor extended to the hull sides and made a seal against draughts. I don't think through ventilation will ever work, but cross ventilation in each 2ft wide bilge section probably exists already, to a degree.

 

Very true.

[Phil Speight]

A boat we're hoping to buy (first one) has had about 3 inches of water under the floor — possibly over the winter or for the last year. It's just been sucked out and is now drying out but is very rusty, but not flakey. This is seen under the cabin floor inspection hatch right at the back of the boat. There is no balast (it has very high ceilings) and the steel plate hasn't been treated.

 

Will this rust continue to corrode the interior plate, even if it can be kept dry, and pose a problem to the integrity of the hull some years down the line? Or will it just remain 'dusty rusty' and isn't really worth worrying about?

Consider yourself lucky. You have a boat - I have a boat and two old Alfa Romeos!

Phil

[RLWP]

Consider yourself lucky. You have a boat - I have a boat and two old Alfa Romeos!

Phil

 

Which is worse - Alfa Romeo rust or MG rust?

 

Richard

[OldGoldy]

To be effective I think air would need to be forced in from the centre of each section, and then air needs to come from outside, impractical really.

 

But air from outside *could* have a greater moisture content than inside.

 

Best I think to extract to outside, or to the engine 'ole (cruiser stern), using maybe upvc ducting, but have the intake from within the cabin, in my case in a forward locker (inside) as I don't have a forward well deck (stern access only)

 

Having an extra 1 ton+ with new bottom plate means I can lose much of the existing ballast, decreasing the air resistance under the floor. I will be waxoyl-ing that steel that I can get at (2ft width of floor removed along centre line of boat to enable 'slashing' of existing baseplate and enable it to be welded to new, plus areas where plywood has rotted)

 

I like the solar panel option (will note that in the old grey matter) and I guess two fans one end with vent at t'other would be just as effective - Thank you, Mark.

 

I think cross ventilation may exist, but would be minimal. I always remember, when planning equipment rooms for telecomms gear, that so many air changes per hour was necessary (to remove heat and any battery fumes) and that if not forced ventilation, should have vents at high and low levels at opposite ends of the room for it to work (natural convection). This differential cannot be achieved (I don't think) across the width of a boat.

[ChrisPy]

I think cross ventilation may exist, but would be minimal. I always remember, when planning equipment rooms for telecomms gear, that so many air changes per hour was necessary (to remove heat and any battery fumes) and that if not forced ventilation, should have vents at high and low levels at opposite ends of the room for it to work (natural convection). This differential cannot be achieved (I don't think) across the width of a boat.

The point is that most boats do not have a continuous and substantial air path from front to back.

The steel frames support the floor directly or with full width battens, and the only holes are small 'limber holes' cut at the outer ends of each bottom frame. Mine were well blocked with bitumen felt, dust, rubbish and sprayfoam offcuts when I lifted the floors during fit-out. There would have been little or no ventilation in that direction.

And in view there is an air path from below the floor into the cabin (actually behind the panelling) at either edge of the floor, there will be no significant air movement from front to back.

[Max Sinclair]

put a few handfuls of cement powder in the water and let it swill around, it will inhibit corrosion. an old traction engine drivers tip.

[nb Innisfree]

But air from outside *could* have a greater moisture content than inside.

 

Yes it may but if if air is close to temp of bottom plate then it won't condense. Inside air will condense on BT in cold weather

[OldGoldy]

The point is that most boats do not have a continuous and substantial air path from front to back.

The steel frames support the floor directly or with full width battens, and the only holes are small 'limber holes' cut at the outer ends of each bottom frame. Mine were well blocked with bitumen felt, dust, rubbish and sprayfoam offcuts when I lifted the floors during fit-out. There would have been little or no ventilation in that direction.

And in view there is an air path from below the floor into the cabin (actually behind the panelling) at either edge of the floor, there will be no significant air movement from front to back.

 

Point taken - I can only comment on my own boat, where the limber holes are clear. She was built with

no insulation to the hull sides (but now has 2in polystyrene) and no felt under the ballast.

 

Yes it may but if if air is close to temp of bottom plate then it won't condense. Inside air will condense on BT in cold weather

Ah, assuming the boat is in use.

 

The upper cabin sides are thin GRP - and doesn't hold any heat. As a '70s ex-hire boat, it was built for, IMHO, fair weather boating.

[koukouvagia]

Condensation on the bottom plate can be a real problem. I have no ballast and the air circulation is not impeded by continuous cross-bearers. (There are triangular gaps over the chine angles). The floor boards consist of one and a half inch thick boards and the under-floor gap along the length cabin is about three inches.

A couple of winters ago I left some of the inspection panels open in the floor to encourage better air circulation. I was amazed to find that in a weekend a couple of buckets of water had collected in the bilges which hitherto had been bone dry. I was convinced that I had a water tank leak, or worse, that one of the rivets had failed. After wracking my brains and lots of grovelling about looking for leaks, I realised that the problem was the condensation formed by allowing the warm cabin air to come into contact with the cold base plate via the open inspection panels.

I now keep these panels firmly closed during the winter and the problem has disappeared.

[Morphyous]

So you have seen my locking techniques then...

 

Richard

 

No! but as long as you stick to the rule, short rope well knotted to a

cleat when you're going down a lock, you'll be ok!

[blackrose]

Which means - take out all of the interior structure of the boat, remove the floor coverings, lift the floorboards, remove the ballast, carry out the instructions as described above, rebuild boat.

 

Forget it, go and worry about something else.

 

Richard

 

Exactamente! If any mild steel which has previously been exposed to water is going to rust in perpetuity we're all doomed!

 

I don't know how that theory would explain the condition of areas of my bilges which got wet a few years ago and were dried out, but now show no signs of further corrosion?

If it happens at all it must be a very slow process so not worth worrying about.

Edited August 21, 2009 by blackrose

[nb Innisfree]

Exactamente! If any mild steel which has previously been exposed to water is going to rust in perpetuity we're all doomed!

 

I don't know how that theory would explain the condition of areas of my bilges which got wet a few years ago and were dried out, but now show no signs of further corrosion?

If it happens at all it must be a very slow process so not worth worrying about.

 

Was it occupied in the winter, was the underfloor insulated from the cabin, was the Bottom plate blacked/protected inside?

[blackrose]

Was it occupied in the winter, was the underfloor insulated from the cabin, was the Bottom plate blacked/protected inside?

Yes, no & yes (I've been fitting it out during that time), originally yes it was protected with bitumen soaked cloth but I ripped that out in order to dry the water out which had got underneath.

 

This last point also raises two other issues: Firstly water gets trapped under ballast which is lying directly on the baseplate and can be difficult to properly dry out without removing the ballast - this also applies to bitumen soaked cloth. Secondly those who recommend simply pouring waxoil or Vactan into the bilges on the basis that it will go where the water goes should remember that water, waxoil and Vactan are all different viscosities. 6or example water will find its way under ballast lying directly on the baseplate, whereas Vactan and waxoil will not.

Edited August 21, 2009 by blackrose

[nb Innisfree]

Yes, no & yes (I've been fitting it out during that time), originally yes it was protected with bitumen soaked cloth but I ripped that out in order to dry the water out which had got underneath.

 

This last point also raises two other issues: Firstly water gets trapped under ballast which is lying directly on the baseplate and can be difficult to properly dry out without removing the ballast - this also applies to bitumen soaked cloth. Secondly those who recommend simply pouring waxoil or Vactan into the bilges on the basis that it will go where the water goes should remember that water, waxoil and Vactan are all different viscosities. 6or example water will find its way under ballast lying directly on the baseplate, whereas Vactan and waxoil will not.

 

The point I was making was that your plate didn't rust because it was either not getting wet or it was , as in your case, blacked.

 

When I ballasted our boat I raised slabs on squares of roofing felt to give drainage room and some ventilation, something that is quite easy to do.

 

True Waxoyl is thicker than water but can be made almost as runny with white spirit which is what manufacturers recommend anyway, but better done in warm weather and even better with ballast removed

[ChrisPy]

When I ballasted our boat I raised slabs on squares of roofing felt to give drainage room and some ventilation, something that is quite easy to do.

Do you mean separate little stacks of felt?

 

Checking my LB widebeam, which I assume is the same as Mike's, the bottom is covered by a continuous layer of bitumen felt and the ballast is laid on top. Unfortunately the buyer of a sailaway never gets a chance to check what is below the bit felt, unless he removes the floorboards and the ballast. I did the former, and found loads of rubbish which inhibited air circulation, but I baulked at lifting the slabs to check what was below the bit felt. Bare steel? Who knows. Any water will get trapped under the bit felt and needs good ventilation to ensure that, over time, it evaporates.

 

The practice of laying slabs on bit felt seems questionable. If you want to raise the slabs off the bottom, better to use loops of electric cable which will not inhibit free air movement.

[blackrose]

The point I was making was that your plate didn't rust because it was either not getting wet or it was , as in your case, blacked.

 

When I ballasted our boat I raised slabs on squares of roofing felt to give drainage room and some ventilation, something that is quite easy to do.

 

True Waxoyl is thicker than water but can be made almost as runny with white spirit which is what manufacturers recommend anyway, but better done in warm weather and even better with ballast removed

Yes, I understood your first point and agree.

My point however was questioning the poster of the original thesis which said that rust will continue to corrode steel even without the presence of water.

 

Ideally I would have liked a drainage gap under my ballast, but as Chris says, lifting the floorboards on many sailaways, part-fitted and fully fitted baots is not easy.

Edited August 22, 2009 by blackrose

[RLWP]

No! but as long as you stick to the rule, short rope well knotted to a

cleat when you're going down a lock, you'll be ok!

 

I see that you are in need of some training. I'll put you on the reserve list for Team Tawny Owl BCN challenge 2010.

 

Richard

 

24 hours before the mast should sort you...

[blackrose]

The ultimate solution has to be a boat with a 1" thick baseplate. No need for any ballast so you could have a nice airy bilges which are easy to drain and dry - and you'd never need to worry about corrosion. The other advantage would be increased headroom.

Anyone know roughly how much this would add to the cost of a new NB? (Say 60')