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Under the Subfloor . . but why!


Keajre

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Dear Friends,

 

I am replacing the floor soon and wanted to inspect the sub floor and bilges. Not sure why someone has filled the bilges with paving slabs. If it was for ballast then they would be spread unevenly to say balance the boat if it was listing to one side. These appears to be under the floor from one side to the other.

 

Anyone got any thoughts?

 

Also, what the heck is the steel raised floor for? Wasn't expecting to see that. That is not the bottom of the boat, its a steel platform which doesn't seem to be serving a purpose, though it must be of course, which is why I thought I would ask you clever people.

 

This is a south west duram steel boat built in 2000, they used to build hulls for hire boats before the went bust.

 

Many Thanks

 

Stuart

 

 

post-24573-0-96723200-1474302591_thumb.jpg

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Looks like a pretty standard setup. The steel plate under the slabs is the base plate. Ah, but it looks as though the steel sheet is higher - probably put in as extra ballast over the slabs (steel is much denser that concrete). The slabs are ballast which would have been put in to trim the boat, both for list and for fore and aft trim. Often done by guesswork/experience as it is usually put in before the boat is fitted out.

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I see, well the boat is much lower at the back because of the engine, so I guess without the lovely paving slabs it would be even worse. Shame, i wanted to make some under floor storage!

 

The raised steel thing, I mean really, just ballast? wow seems odd. I cant see what is under it, probably more paving slabs!

 

If I wanted to put celotex down, just lay it onto of the paving slabs or is it a waste of time? Going to put a floating floor in, with a nice quality underlay, but I read that most ppl put the insulation under the subfloor. Is that best?

 

Cheers


ps that stove is for sale if anyone wants it!

 

http://www.ebay.co.uk/itm/282182345505?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1558.l2649

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Also, what the heck is the steel raised floor for? Wasn't expecting to see that. That is not the bottom of the boat, its a steel platform which doesn't seem to be serving a purpose, though it must be of course, which is why I thought I would ask you clever people.

 

Is that a steel plate (in which case it is just another form of ballast) or does that slab have sides and ends going down to the base plate? If the latter perhaps it's a holding tank (disused?). Any evidence on the hull or roof of disused pump out fittings?

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ahhhhh there used to be a toilet there, omg I think its a holding tank!! The only thing is, the toilet was on the other side, would have been a drop through style tank. Doubt it would stretch under the whole floor. That would be one huge tank!

 

I could get my hole saw out . . . . temping!


It connects to the floor strut, so cant see the sides might be connected to the base plate I will investigate

Edited by Keajre
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ahhhhh there used to be a toilet there, omg I think its a holding tank!! The only thing is, the toilet was on the other side, would have been a drop through style tank. Doubt it would stretch under the whole floor. That would be one huge tank!

 

I could get my hole saw out . . . . temping!

It connects to the floor strut, so cant see the sides might be connected to the base plate I will investigate

 

The concrete ballast is to get the boat low enough down in the water to keep the counter at around water level, the prop under water, and to keep the airdraft down. Without it the boat will sit higher in the water.

 

The poo tank (if that is what it is) will almost certainly extend the full width of the boat, under the floor panels you haven't lifted. Otherwise the side-to-side trim of the boat would change significantly between empty and full. It could also be your fresh water tank, although this is an unusual location, so check before you start cutting into it.

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Paving slabs are fairly standard for use as ballast. It not only levels the boat from side to side and trims it down towards the propeller, the weight of the ballast also helps the boat sit down in the water rather than bobbing around on the surface. Imagine trying to get your boat under a bridge while still having enough head room to stand up inside the boat otherwise.

 

Also a boat sitting down in the water is more stable than one on the surface like a raft. So it's normal to have ballast throughout not just on one side.

 

The slab of extra steel is interesting. Presumably also for ballast (seems shallow to be a tank?) but I'm curious as to why it's not paving slabs throughout

Edited by BlueStringPudding
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The poo tank (if that is what it is) will almost certainly extend the full width of the boat, under the floor panels you haven't lifted.

 

Think the mystery is solved. I have removed another board, and yes its the former poo tank (water tank is at the bow end). Makes sense it would traverse the width of the boat like you said, otherwise would cause uneven ballast depending on how full it was. Its been welded up, I can see where the drop through hole was. I actually want to replace my live and used poo tank for a compost loo. Was thinking about if I would remove the old tank or just weld it up. Having looked at this tank, would be a nightmare to try and remove. So understand why the previous owner just sealed it and left it there.

 

Is that an ok practice? Sealing and leaving (after emptying and clean) vs welding? Could leaving it catalyze the rusting process of the base plate?

 

 

Paving slabs are fairly standard for use as ballast. It not only levels the boat from side to side and trims it down towards the propeller, the weight of the ballast also helps the boat sit down in the water rather than bobbing around on the surface. Imagine trying to get your boat under a bridge while still having enough head room to stand up inside the boat otherwise.

 

Also a boat sitting down in the water is more stable than one on the surface like a raft. So it's normal to have ballast throughout not just on one side.

 

The slab of extra steel is interesting. Presumably also for ballast (seems shallow to be a tank?) but I'm curious as to why it's not paving slabs throughout

 

Makes sense, thanks for the explanation!

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Also a boat sitting down in the water is more stable than one on the surface like a raft

 

smiley_offtopic.gif We have been running with the water tank and diesel tanks almost empty for a while now, and have just filled up again. It's nice to feel the boat sat down in the water again

 

Richard

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To be honest I cannot see a raised steel plate in that picture. I can see the basplate of your boat and if that is what it is then drilling into it will sink your boat so I would be very careful what you do with any drills and hole saws.

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No this is 100% an old poo tank, its six inches deep. It spans the entire width of the bilges. I have also spoken to the previous owner who confirms this. Just glad I didn't drill into it!

 

Going to leave it there to rust all it wants. Question is, will a rusting poo tank act as a catalyst for corroding the base plate?

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No this is 100% an old poo tank, its six inches deep. It spans the entire width of the bilges. I have also spoken to the previous owner who confirms this. Just glad I didn't drill into it!

 

Going to leave it there to rust all it wants. Question is, will a rusting poo tank act as a catalyst for corroding the base plate?

I would think that if it is rusting then that certainly will spread rust elsewhere. I blacked my baseplate on the inside of my boat because, bottom line, water will inevitably get there through condensation, domestic water leaks, etc etc. I found that my shower base had leaked quite badly when I bought my boat (now sold) and the baseplate beneath the floor was quite badly rusted. Flakey rust does look a lot worse than it actually is even so, eventually, the rust will eat it's way all the way through the baseplate. I stopped the leak, cleaned the rust out then put Vactan down and then blacked over that. That sounds a hell of a lot of easier than it actually was to do. I think your problem is that if that is an unused poo tank then you do not know what is going on inside it or if the bottom of the tank is actually your base plate. So whilst I did say be careful with drills and hole saws, in my opinion you do need to envestigate the inside of that tank somehow safely.

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rust is not an infectious disease - it 'spreads' only if the conditions are appropriate for rusting.

 

understandably you are worried about the inside of the tank rusting away. I would fill it with an inert material - could be a cement grout that will flow and find its own level, helps with ballast. Alternatively you could fill it with polyurethane foam, will need several access holes cutting in the top in either case.

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rust is not an infectious disease - it 'spreads' only if the conditions are appropriate for rusting.

 

understandably you are worried about the inside of the tank rusting away. I would fill it with an inert material - could be a cement grout that will flow and find its own level, helps with ballast. Alternatively you could fill it with polyurethane foam, will need several access holes cutting in the top in either case.

 

 

Well that's a pretty obvious thing to say. Any infectious disease spreads when the "conditions are right" and the conditions are very right in most steel boat's bilges for rust to spread. I say again to the OP it needs investigating carefully and treating properly. I'm out of here now

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Well that's a pretty obvious thing to say. Any infectious disease spreads when the "conditions are right" and the conditions are very right in most steel boat's bilges for rust to spread. I say again to the OP it needs investigating carefully and treating properly. I'm out of here now

Yeah but the rust spreads because of the conditions, not because it's infectious. It would still rust in rust-inducing conditions even if there wasn't any rust there already.

 

Could you get Waxoyl under the tank? That's what we put between our old baseplate and the overplating.

 

Ah, or is the bottom of the tank also the baseplate?

Edited by Chertsey
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I'd squirt PU foam into it, reaching only as far in as was easy from the orifices, and then forget about it. I believe the voids left inside will not corrode much without an airflow. I have precisely no supporting information for this belief. Its based on how the PU foam I've used elsewhere in the boat has behaved over the years. ie brilliantly.

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Is the tank likely to have been sealed so that it is air tight? If so surely only a limited amount of rusting will take place inaise as oxygen is needed for ruts to form.

 

Yes, that's what I thought. You need oxygen to cause rust (it's iron oxide, and that's a clue) so if there isn't any free oxygen the steel won't rust. Is there a chance a previous owner squirted some Waxoyl in before sealing the tank up? If so, opening it up again might make matters worse.

 

If there is any water (grey or black) inside the tank, the bottom will rust last. Did anyone ever do the nail-in-a jam-jar experiment at school? The totally immersed nail was the shiniest,

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