Maths for ballast in a listing hull

[akuaku]

My 14m x 3.5m rectangular steel hull is listing in one corner such that the waterline is 28cm out in opposite corners.  I have found some suitable pig iron ballast online which I want to put in the high corner.

 

Having passed GCSE maths many years ago I feel I ought to be able to work out how much ballast I need, but I'm struggling and would very much appreciate some help.

[Tony Brooks]

28mm or over 8 inches is one hell of a list so do you have a reason for it? If not I suggest a very close inspection of the lowest end/side to ensure you don't have a build up of water in the bilge. As you talk about one corner are you including the fore-aft trim in the 28cm? If so most boasts trim down by the stern to a degree so the actual list may be far less. Altering the fore-at trim usually alters the boat's pivot point when turning.

Edited January 18, 2019 by Tony Brooks

[Sea Dog]

6 hours ago, akuaku said:

My 14m x 3.5m rectangular steel hull 

This doesn't sound like a boat - is it static?  I ask, because correcting trim isn't about how much ballast but rather about evening up the weight distribution.  For a proper boat creating the right draught is also important for stability and hydrodynamic reasons, so this takes a lot more calculation or experience to get right. If you explain what the "hull" is, you'll get better targeted advice.

 

 

 

 

 

 

[Murflynn]

google boat hull stability calculations and work it out from there.  without a shed-load of data that is available to you, but not us, no-one can give you the proper answer.

 

it's all about getting the centre of gravity to coincide with the preferred centre of buoyancy.

Edited January 18, 2019 by Murflynn

[cuthound]

Moths don't weigh very much, so you would need lots of them for effective ballast. Do you have the space for them in the bilge? ??

 

 

 

 

 

 

 

Whoops re-read the title. I should have gone to Specsavers.

[Alan de Enfield]

20 minutes ago, cuthound said:

Moths don't weigh very much, so you would need lots of them for effective ballast. Do you have the space for them in the bilge? ??

But if you put a light in the 'high corner' they would all flock to that corner and the down-draught from their wings (if there were sufficient numbers) would 'blow' that corner downwards and level up the boat.

 

It may, however, only be a temporary measure (until the moths died) but could be used to secure (say) a sale and then buy one more boat-shaped that doesn't lean.

 

Reminds me - I went into the local Butchers yesterday and asked for some Pork Chops and said 'make them lean', he said "certainly Sir, in which direction ?"

Edited January 18, 2019 by Alan de Enfield

[BWM]

8 hours ago, akuaku said:

My 14m x 3.5m rectangular steel hull is listing in one corner such that the waterline is 28cm out in opposite corners.  I have found some suitable pig iron ballast online which I want to put in the high corner.

 

Having passed GCSE maths many years ago I feel I ought to be able to work out how much ballast I need, but I'm struggling and would very much appreciate some help.

You could place some plastic dustbins or similar containers in that area, then calculate weight by volume of water used to counterbalance. If you have enough access, known volume containers such as water butt, 205 litre drum, etc would make it easier. 

Edited January 18, 2019 by BWM

[howardang]

8 hours ago, akuaku said:

My 14m x 3.5m rectangular steel hull is listing in one corner such that the waterline is 28cm out in opposite corners.  I have found some suitable pig iron ballast online which I want to put in the high corner.

 

Having passed GCSE maths many years ago I feel I ought to be able to work out how much ballast I need, but I'm struggling and would very much appreciate some help.

Your first priority is to find out what has caused such a list - a pipe burst, hole in the hull, rain water ingress etc -  and correct that. If the boat  floated at the correct trim before the list developed then if you can correct the list you don't need any ballast. Did the list develop suddenly, or did it develop gradually, and what type of craft are you speaking about?

 

Trying to understand stability  calculations is not your first priority, although a basic understanding of the subject is always useful with any boating scenario. |Although it is possible to calculate how much ballast is need to correct any particular list, I suspect that most people on the inland waterways will use common sense, combined with a degree of trial & error to do the job. 

 

Howard

[Mad Harold]

8 hours ago, akuaku said:

My 14m x 3.5m rectangular steel hull is listing in one corner such that the waterline is 28cm out in opposite corners.  I have found some suitable pig iron ballast online which I want to put in the high corner.

 

Having passed GCSE maths many years ago I feel I ought to be able to work out how much ballast I need, but I'm struggling and would very much appreciate some help.

It'll make your brain hurt trying to work it out. My boat was a bit tail down,and i worked out the amount of forward ballast needed by inviting a couple of fellow boaters aboard for coffee.Sitting them in cratch on the benches the trim was about right, I would guess that most boaters work out the ballast needed by trial and error.

Your boat seems an odd size and shape. Are you converting a skip?

[GUMPY]

When Parglena was lengthened the counter was 6" out of the water.

I calculated the volume of the extension that was going to be below the waterline in cubic metres(=metric tons displacement), subtracted the weight of the new steel and ordered ballast of the same weight that was exactly right to get the boat home but once the fit out and extra water tank were fitted I did have to remove some.

 

[Tacet]

28 minutes ago, BWM said:

You could place some plastic dustbins or similar containers in that area, then calculate weight by volume of water used to counterbalance. If you have enough access, known volume containers such as water butt, 205 litre drum, etc would make it easier. 

People are usually easier than dustbins.  Stand them about where the ballast will go, and you will get a reasonable idea, assuming they will each disclose their weight.  In they are initially reticent,  add two stone.

 

[GUMPY]

on reflection maths was wrong

Edited January 18, 2019 by Loddon

[pete.i]

45 minutes ago, howardang said:

Your first priority is to find out what has caused such a list - a pipe burst, hole in the hull, rain water ingress etc -  and correct that. If the boat  floated at the correct trim before the list developed then if you can correct the list you don't need any ballast. Did the list develop suddenly, or did it develop gradually, and what type of craft are you speaking about?

 

Trying to understand stability  calculations is not your first priority, although a basic understanding of the subject is always useful with any boating scenario. |Although it is possible to calculate how much ballast is need to correct any particular list, I suspect that most people on the inland waterways will use common sense, combined with a degree of trial & error to do the job. 

 

Howard

Otherwise known as "chuck it in and see what happens." If straightens up you have put enough in if it doesn't then you have too much or too little in.

[Tony Brooks]

If this list does turn out to be water in the bilge the OP had better think about what happens if he ballasts the other side to level it up and then the water transfers  to the now heavier side. The list would be more than 28cm then, possibly 56 cm. He rally needs to be sure why its listing as has been pointed out before. Only then worry about ballast. In fact if its caused by something heavy on one corner a better way may be to remove ballast from that corner rather add it to the other. Adding it is likely to upset the fore-aft trim.

[howardang]

17 minutes ago, Tony Brooks said:

If this list does turn out to be water in the bilge the OP had better think about what happens if he ballasts the other side to level it up and then the water transfers  to the now heavier side. The list would be more than 28cm then, possibly 56 cm. He rally needs to be sure why its listing as has been pointed out before. Only then worry about ballast. In fact if its caused by something heavy on one corner a better way may be to remove ballast from that corner rather add it to the other. Adding it is likely to upset the fore-aft trim.

He hasn't actually confirmed whether this is a new build which has listed as soon as it was launched or whether it is a developing list after being in the water for some time.

 

For example, which you have touched on, in some circumstances the worst thing you can do is to attempt to correct a list by adding weight to the high side, which is one of the many reasons why, with the subject of stability, a little knowledge can occasionally cause more problems than it solves!

 

Cue the "experts"!

 

Howard

 

 

 

 

[ditchcrawler]

When I launched Harnser we were a long way down at the bum and leaning to port so after 2 days we had a coffee table made of paving slabs in the lounge on the starboard side with everything I could get out aft of the toilet and on the port side. In the end I removed all the slabs under the floor at the bows as well and replaced it with pig iron, we are still to deep at the bum.

[WotEver]

14 minutes ago, ditchcrawler said:

When I launched Harnser we were a long way down at the bum and leaning to port so after 2 days we had a coffee table made of paving slabs in the lounge on the starboard side with everything I could get out aft of the toilet and on the port side. In the end I removed all the slabs under the floor at the bows as well and replaced it with pig iron, we are still to deep at the bum.

You need a nice lightweight Japanese engine

[BWM]

48 minutes ago, Tony Brooks said:

If this list does turn out to be water in the bilge the OP had better think about what happens if he ballasts the other side to level it up and then the water transfers  to the now heavier side. The list would be more than 28cm then, possibly 56 cm. He rally needs to be sure why its listing as has been pointed out before. Only then worry about ballast. In fact if its caused by something heavy on one corner a better way may be to remove ballast from that corner rather add it to the other. Adding it is likely to upset the fore-aft trim.

With that amount of list, any water present should be visible by now, particularly on corner to corner. 

[akuaku]

Thanks so much all for your thoughts. I realise I should have given more info. This relates to my home, one of those 2 storey garden-shed-on-a-skip type static houseboats. It's about 14ft tall and has always listed somewhat due to large cold and hot water cylinders sitting to one side. She's been listing a lot more for the last year or so, I think since I laid down a reclaimed solid beech floor upstairs altho I didn't seem to notice the extra list at first. No water in the bilges thankfully which was my initial fear. 

 

Googling for the formulas brings up lots of confusing stuff for setting keels on sailboats which is why I thought I'd sound out you guys, really appreciate all your help. I like the idea of weighing some mates, making them huddle in the corner and then measuring how much the list has changed. Then it's just a matter of adding up the Bobs and Janes. The way the ballast is being sold means I'm much better off making one order so I need to get it right from the start.  

 

 

[alan_fincher]

Until the OP confirms otherwise, from the description " 14m x 3.5m rectangular steel hull ", I think we need to assume this is a floating brick, rather than a canal or river boat shaped cruising boat.

EDIT:

Strike that - I missed the answer above!

I would have thought enough water inside to be down by 11 inches (28 cms) at one corner, (not 8 inches as Tony converted it), would be entirely obvious.  It would be well over any flooring at the corner, surely?

Edited January 18, 2019 by alan_fincher

[bizzard]

It might be aground, resting on a hidden pile under one corner. If so a suppository might help.

Edited January 18, 2019 by bizzard

[Guest]

29 minutes ago, bizzard said:

It might be aground, resting on a hidden pile under one corner. If so a suppository might help.

My first thoughts. I have seen many boats listing that were obviously aground. Hppaens on the time on the L&L canal. As the OP has added weight (floors etc) this is possible. All depends what kind of water/mooring the boat is on, depth etc.
ps suppositories aren't all they are cracked up to be. The quack gave me some, and I might as well have shoved them where the sun don't shine for what good they did.

Edited January 18, 2019 by Guest

[BWM]

55 minutes ago, akuaku said:

Thanks so much all for your thoughts. I realise I should have given more info. This relates to my home, one of those 2 storey garden-shed-on-a-skip type static houseboats. It's about 14ft tall and has always listed somewhat due to large cold and hot water cylinders sitting to one side. She's been listing a lot more for the last year or so, I think since I laid down a reclaimed solid beech floor upstairs altho I didn't seem to notice the extra list at first. No water in the bilges thankfully which was my initial fear. 

 

Googling for the formulas brings up lots of confusing stuff for setting keels on sailboats which is why I thought I'd sound out you guys, really appreciate all your help. I like the idea of weighing some mates, making them huddle in the corner and then measuring how much the list has changed. Then it's just a matter of adding up the Bobs and Janes. The way the ballast is being sold means I'm much better off making one order so I need to get it right from the start.  

 

 

Being taller will exacerbate any imbalance so you may not need as much ballast to correct it. As others have said, are you sure nothing has drifted underneath?

[bizzard]

There are hidden pile warnings dotted about like on the upper Thames and Broads, like, ''Beware hidden piles ! and keep clear hidden piles !'', usually old rotted posts from old landind stages and the like lurking just below the surface. I once moored opposite the Ferry Inn Stokesby with an old hired from Marthom Boats traditional wooden Broads sailing cruiser, I was towing a small sailing dinghy. Woke up next marning, 'thats how they say morning up there' and the dinghy wasn't in sight, looked down and there were its gunnels  just showing. As the tide ebbed it had become impaled upon a sharp bit of old piling which punctured it.

Edited January 18, 2019 by bizzard

[howardang]

2 hours ago, akuaku said:

Thanks so much all for your thoughts. I realise I should have given more info. This relates to my home, one of those 2 storey garden-shed-on-a-skip type static houseboats. It's about 14ft tall and has always listed somewhat due to large cold and hot water cylinders sitting to one side. She's been listing a lot more for the last year or so, I think since I laid down a reclaimed solid beech floor upstairs altho I didn't seem to notice the extra list at first. No water in the bilges thankfully which was my initial fear. 

 

Googling for the formulas brings up lots of confusing stuff for setting keels on sailboats which is why I thought I'd sound out you guys, really appreciate all your help. I like the idea of weighing some mates, making them huddle in the corner and then measuring how much the list has changed. Then it's just a matter of adding up the Bobs and Janes. The way the ballast is being sold means I'm much better off making one order so I need to get it right from the start.  

 

 

Just a note of caution. I did say on my earlier post that it is not always a good idea to correct a list by adding weight . To amplify this, if the weight at fault is high up in the boat, putting even more weight high up on the opposite side can seriously diminish the stability of the boat. Further to this, if you had forgotten about the flooring, are there any other things you have installed you may have forgotten about - marble work surfaces, stove, cabin lining etc etc etc which may have also contributed to the list? Are there any tanks - oil or water - high up in the boat that contain liquid,  especially ones that are not completely full or empty, that can cause a reduction in stability due to  "free surface effect"?

 

Howard