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Removing Ballast


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Ok, so our 70ft narrowboat boat has survived the surveyors hammer this time round. He will look again in six years.

In the meantime, he suggested I turn my thoughts to ballast removal, should overplating be required  in the future. 

Our ballast is engineering bricks in separate compartments, seperated by a longitudinal central  keelson. 

There are some inspection hatches, but probably not big enough to remove a whole brick. 

So cut lots of hatches each side of the keelson the entire length (where possible), or a central hatch that spans the keelson (where possible)? 

Secondly, are there any tools that would make the job easier. 

Finally, am i likely to need to remove ALL ballast if a new 8mm baseplate is required? (currently 6mm)

Thanks. 

 

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A mini circular saw and multi tool would make short work to make bigger hatches.  

my guess is that you will need to remove as much ballast as the new baseplate weighs if you want to keep the same draft.

Edited by Robbo
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A reciprocating saw makes that job easier however there is/was a hole cutter I remember years ago which allowed for the removal of the piece cut which due to its shape could then be replaced back in the hole without gluing or nailing etc. It would allow certainly for inspection holes which are readily accessible and then if necessary take more drastic action. If I remember correctly it was associated with plaster board cutting.

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29 minutes ago, rusty69 said:

Finally, am i likely to need to remove ALL ballast if a new 8mm baseplate is required? (currently 6mm

Are you talking about reducing the amount the boat draws with the extra steel, or the actual practicalities of rebottoming a boat that has ballast piled on the current baseplate?

I would say that the norm for most "modern" boats is to overplate, rather than to cut old bottoms out and replace.  It is a very much bigger job to replace than overplate, (otherwise it would always be done that way), and clearly to do that you couldn't have bricks cascading down on you as you cut the old bottoms out.

However if overplating, I can't see the bottom increasing from 6mm to just 8mm - you wouldn't realistically overplate in less than 4mm, and the problem with 4mm is that once that starts to erode or pit, yuou then effectively quickly have less than this so called insurable minimum.

I would think overplating in 5mm or 6mm makes more sense, so that is actually what you need to allow for.

We don't know how many bricks you have, so impossible to say how many ideally would need removing.  It is not however hard to estimatethe weight of  an extra layer of 5mm or 6mm of steel added to your boats baseplate.

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7 minutes ago, alan_fincher said:

Are you talking about reducing the amount the boat draws with the extra steel, or the actual practicalities of rebottoming a boat that has ballast piled on the current baseplate?

I would say that the norm for most "modern" boats is to overplate, rather than to cut old bottoms out and replace.  It is a very much bigger job to replace than overplate, (otherwise it would always be done that way), and clearly to do that you couldn't have bricks cascading down on you as you cut the old bottoms out.

However if overplating, I can't see the bottom increasing from 6mm to just 8mm - you wouldn't realistically overplate in less than 4mm, and the problem with 4mm is that once that starts to erode or pit, yuou then effectively quickly have less than this so called insurable minimum.

I would think overplating in 5mm or 6mm makes more sense, so that is actually what you need to allow for.

We don't know how many bricks you have, so impossible to say how many ideally would need removing.  It is not however hard to estimatethe weight of  an extra layer of 5mm or 6mm of steel added to your boats baseplate.

Overplating, keeping current waterline. Surveyor mentioned 8mm.

9 minutes ago, alan_fincher said:

We don't know how many bricks you have, so impossible to say how many ideally would need removing.  It is not however hard to estimatethe weight of  an extra layer of 5mm or 6mm of steel added to your boats baseplate

True, i don't either, probably one layer the entire cabin length minus engine room(trad stern) 

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2 minutes ago, rusty69 said:

Overplating, keeping current waterline. Surveyor mentioned 8mm.

Don't understand that.  If it is 6mm currently, it can't end up less than 10mm, as 4mm overplate would surely be a minimum.

I think you need to recheck with surveyor what he would actually be recommending.

If you take out enough ballast to cope with a new bottom you don't know if you'll actually be needing in 6 years, surely you will then spend at least 6 years with a potentially unstable poorly handling boat. This would seem a very odd thing to do.  You really only should adjust the ballast at such time as the boat might actually be made heavier?

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2 minutes ago, alan_fincher said:

Don't understand that.  If it is 6mm currently, it can't end up less than 10mm, as 4mm overplate would surely be a minimum.

I think you need to recheck with surveyor what he would actually be recommending.

If you take out enough ballast to cope with a new bottom you don't know if you'll actually be needing in 6 years, surely you will then spend at least 6 years with a potentially unstable poorly handling boat. This would seem a very odd thing to do.  You really only should adjust the ballast at such time as the boat might actually be made heavier?

I think the surveyor suggested 8mm overplating on whatever will be there when it requires doing. 

I doubt he was suggesting removing anything at this stage, just preparing for it, as it will be quite a big job. 

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1 minute ago, rusty69 said:

I think the surveyor suggested 8mm overplating on whatever will be there when it requires doing. 

I doubt he was suggesting removing anything at this stage, just preparing for it, as it will be quite a big job. 

I'm no expert but I would have thought overplating in 8mm "challenging" to say the very  least.  I would have thought trying to attach that thickness adequately  to existing thinner bottoms  might be impractical, but I guess we probably need the views of people with hands on experience of this type of work

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48 minutes ago, jddevel said:

A reciprocating saw makes that job easier however there is/was a hole cutter I remember years ago which allowed for the removal of the piece cut which due to its shape could then be replaced back in the hole without gluing or nailing etc. It would allow certainly for inspection holes which are readily accessible and then if necessary take more drastic action. If I remember correctly it was associated with plaster board cutting.

I guess you're talking about this kind of thing? There are many about, this was just the first link I clicked on. 

http://www.screwfix.com/p/super-rod-cavity-master-kit/85585?kpid=85585&gclid=CjwKCAjw5uTMBRAYEiwA5HxQNrXDXlhwv9sdHszYUzMf9mKH9NyCXwr4WnIMIcnTZkTcAGttp3xJmhoCPf8QAvD_BwE&gclsrc=aw.ds&dclid=CNyP7qCx5dUCFVYh0wodaJYNFQ

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11 minutes ago, WotEver said:

There's something like that on the YouTube offerings on the homepage today 

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I'd suggest you talk to someone who actually does overplating rather than going by what a surveyor says.  

A 70 foot boat will stand a lot of extra weight compared to a "short" vessel I wouldn't worry about removing ballast until the work's done and she's back in the water.  Unless of course you're contemplating replating which is a mammoth job especially on a boat with ballast laying direct on the baseplate.  

I've removed ballast from our boat which admittedly did have 2' square concrete slabs so I didn't have the option of the sort of keyhole surgery you're thinking of, but the idea of cutting holes here and there in the floor to try and extract bricks sounds nightmarish to me. You are effectively constructing an inspection hatch with all the carpentry that involves every time you take a saw to the floor.  Taking the whole floor up (in sections) might sound more disruptive but it's the best way IMHO.  If you're lucky the fitter out put the floor down after the partitions/bulkheads but It's probably not that straightforward.

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Ok, some here seem capable of making this incredibly complicated when it isn't.

If you add an 8mm baseplate you'll need to remove the exact same weight of ballast as the steel you're adding, to keep the same displacement and waterline.

Mild steel weighs 8 tonnes per cubic metre near as dammit, so a new 8mm baseplate will weigh approx 2.5 tonnes. So you'll need to remove 2.5 tonnes of ballast. Engineering bricks are usually around 3kg each (weigh one of yours to check), so that means taking out 833 bricks. 

Do you actually have than many under there?

  • Greenie 1
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Trend used to do a jig that let you make circular holes with a router with a lip for which you could get standard "lids" but whilst anything made by Trend is high quality it is also expensive. I haven't checked to see if they still do. (Search Trend & router as there is another company called Trend.)

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An additional 2.5 tonnes of steel would sit you no more than 6cm lower in the water. Possibly critical on a narrowboat given the limited freeboard and engine air vents etc, but it would probably improve the sea keeping abilities of my Luxmotor.

For the bit of extra cost at the point of the original build (lest additional cost than for an 8mm over-plate job later on), far better I would think to just specify the base plate thickness to avoid the need of blasting at all, apart from a little trim blast perhaps: No bricks/slabs to absorb moisture and encourage condensation due to 'dead air' pockets, no need to worry about what is going on beneath the slabs, much easier to clean and re-paint if it is true that often steel boats rust more seriously from the inside out, thicker steel base will last longer and preserve the boat's resale value better, all the weight is as low as possible improving stability marginally.

You do see advertised narrowboats with 15mm base plates and 10mm sides, my neighbour has one, but I assume that they are rare.

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2 minutes ago, cuthound said:

ou could use a multitool held at 45° to cut the access holes. That way the cut out will go back in without falling through.

I've tried that, and you'd be surprised how low the lid sits once re-inserted, due to the material lost as part of the cutting process: You could certainly feel it through carpet.

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2 minutes ago, Bargebuilder said:

I've tried that, and you'd be surprised how low the lid sits once re-inserted, due to the material lost as part of the cutting process: You could certainly feel it through carpet.

 

2 minutes ago, WotEver said:

But sit lower...

True, I suppose you could always glue a batten to the underside of the floor around the hole to stop it slipping down.

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14 minutes ago, cuthound said:

True, I suppose you could always glue a batten to the underside of the floor around the hole to stop it slipping down.

In which case, no point struggling to get sloping sides, no?

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2 minutes ago, WotEver said:
18 minutes ago, cuthound said:

True, I suppose you could always glue a batten to the underside of the floor around the hole to stop it slipping down.

In which case, no point struggling to get sloping sides, no?

Excellent point, but glueing/screwing battens up from underneath is a pain. With sloping edges, one could very simply glue onto the upward facing edge a veneer of the same thickness of the material lost: Very easy to do if you have some veneer hanging around or even better an accurate table saw to make your own.

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