how much ballast?

[Gary Stacey]

How much ballast would you normally expect to put in a broad beam flat bottomed boat such as a broadbeam narrowboat? Are they usually double slabbed?

 

Gary

[Richard Bustens]

I suspect it would depend on the size.

On my 70' narrow it workes out about 1 ton per inch you need to drop, with engine and generator fitted with 1 row of bricks accross the base plate i'me still about 8 inches high, but this will come down as fitting out progresses.

[Gary Stacey]

Richard are you going to add any more ballast or do you extpect the out to take it down 8 inches?

 

Gary Peacock how much ballast do you normally put in broadbeams?

 

Gary

[NB Willawaw]

If you want to be scientific about it, calculate the cross sectional area of the bottom plate and multiply by the required draught to get the final volume of the boat under the waterline (displacement).

1 cu ft of fresh water weighs 28.35Kg. If you multiply the displacement in cu ft by 28.35Kg, this will give you the boats approx final displacement tonnage in metric tonnes.

If you then subtract the weight of the bare shell obtained from your shellbuilder, the weight of the engine, weights of full fuel and water tanks (1 gallon fuel = 4Kg, 1 gallon water = 4.5Kg) and the estimated weights of the lining boards and major fixtures and fittings used, this will leave you with the weight of the ballast needed to pull her down to her marks (i.e. required draught).

 

Mark

 

NB Willawaw - Stoke Bruerne (GU Northbound)

[DHutch]

In our narrow boat we have double slabs over every avalable area, except the engine room.

[Big COL]

I suspect it would depend on the size.

On my 70' narrow it workes out about 1 ton per inch you need to drop, with engine and generator fitted with 1 row of bricks accross the base plate i'me still about 8 inches high, but this will come down as fitting out progresses.

<{POST_SNAPBACK}>

 

Hi Richard

 

Dream on.

 

My 70' sailaway came with 75, 2'x2'x2''paving slabs and she was 7'' high.

After adding 2 ton of ingots 3packs of 18''x18''x2''paving slabs and the fitout which included freezer and washing m/c, she was just about right we had to remove a few ingots on one side to get rid of a slight listing. So unless you are using green oak panels 6'' thick, based on my experience, I would suggest you have a rethink as its a real b*****d to add under floor ballast when the fit out is complete.

[Glennbrown]

Final stages of a 55ft 10ft wide NB

 

I put concrete Blocks across the whole 40ft cabin with gray commons between

the gaps and foamed in. The purists would say since they are very porous you should use concrete flags ( 2ft x 2ft two layers thick) but dont imagine i shall have any leaks!!!

 

The boat sits perfect

 

Glenn

 

Ps the pics is of the girlfriend doing the hard bit at the locks!!!!

Edited February 17, 2005 by Glennbrown

[John Orentas]

Mark

 

Easier said than done all that, there is so much margin for error that you may as well put in a single layer of concrete flags and anticipate adding more or taking some out which means much of the floor must be removable, until the final stages anyway.

 

Different boats can vary enormously, I had to take a ton out of mine as I didn't fully calculate the reduced buoyancy of long swims, bow and stern.

 

Richards 'rule of thumb' for larger boats, one inch per ton is quite useful. i.e. 20 tons = 20 inches. I would guess a broad beam boat would need a full two layers of flag-stones.

[ChrisPy]

Final stages of a 55ft  10ft wide NB

 

I put concrete Blocks across the whole 40ft cabin with gray commons between

the gaps and foamed in. The purists would say since they are very porous you should use concrete flags ( 2ft x 2ft two layers thick) but dont imagine i shall have any leaks!!!

 

The boat sits perfect

 

Glenn

 

Ps the pics is of the girlfriend doing the hard bit at the locks!!!!

<{POST_SNAPBACK}>

how thick is a 'concrete block' ??

 

PS who are you kidding?

 

PPS do you have green knees?

[Richard Bustens]

Hi Col

It has got to be easer to put more in then take them out later and i think the fit out will be in the region of about 6-7 tons.

Oak is about 2cu ' = 1cwt So there will be about 2 tons of oak + water,fuel and all the other bits and bobs i dont think there will be a lot to add in the end.

[Big COL]

Hi Col

It has got to be easer to put more in then take them out later and i think the fit out will be in the region of about 6-7 tons.

Oak is about 2cu ' = 1cwt So there will be about 2 tons of oak + water,fuel and all the other bits and bobs i dont think there will be a lot to add in the end.

<{POST_SNAPBACK}>

 

Hi Richard.

 

Not much to choose between the two, either taking it out or putting more in, its still a b*****d of a job on a fully fitted boat. I would suggest that you design your floor plan to incorporate removable sections in the corridors, this will only help if you have a cross over and have corridors on both sides of the boat. By your own calculations using 1ton to be equal to 1'' and being 8'' high with the engine fitted you could still be 2'' high on completion.

I wouldn't like to try and get 1 ton of extra ballast into a fully fitted boat let alone 2tons. You can do it but it will take up all the space that you wanted to use for something else, plus you may finish up with boxes of ingots in the engine room.

You can spoil a nice boat by trying to hide extra ballast. You should only half fill your tanks with water and fuel and don't forget to half fill the waste tank, and this will give you an average on the liquid ballast.

Its very important to get this as near as you can at this stage, ask a few boat builders for their views and advice, and I bet they could tell you a few horror stories as well. One way round this or one way that takes a lot of the need to worry about ballast is to go for a 20mm base plate, to late for that now. I really struggled to get my 70' right, couldn't believe just how much ballast went into it.

[David Schweizer]

This is not really helpful but my boat only has two inches between the bottom plate and the timber floor, and whilst I haven't had all the floor up, I have yet to find any ballast in it at all. I added some cast steel lift weights (under the galley units) a few years ago to compensate for some heavy bulkheads and fixed furniture that was removed during a re fit, and there are quite a few 56lb weights inside the rear counter plus a few more in the front well sump, but that's about it. At most there could only be one layer of slabs in the bottom of the boat, but the strange thing is that I have a draft of over 2ft 6ins, so it must just be a very heavy boat.

[Amicus]

One way round this or one way that takes a lot of the need to worry about ballast is to go for a 20mm base plate,

<{POST_SNAPBACK}>

Is it possible to get a builder to do this, without crossing his palm with a very serious wedge?

[John Orentas]

Many builders will be happy to supply a heavy base-plate. I had a 12mm thick base, the standard being 8mm at the time, I was charged an extra £300 for a 50 foot boat, but that was 12 years ago, probably would be £500 now but that is not much on the price of a shell (it would probably cost £150 for the equivalent weight of concrete flags).

 

If I did it again I would go for a 20mm base-plate. There are other advantages other than overcoming the ballast issue, it will take 200 years to rust through and the heavy base gives the boat a very solid, non-resonant feel.

[Amicus]

Very interesting, if a little scary. I think a 20mm plate for a 60’ boat is going to be, say 5.5ish tonnes? Any chance of over cooking it, so that the finished boat settles above her marks, be a bummer trying to lighten it,

 

ps. it'll put an end to the bottom blacking quandary, thats for sure

Edited February 18, 2005 by Amicus