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[El Neave]

Apologies for any howlers-  This is my first posting and my first howl.  Advice from "those who know better" would be welcome indeed.
I have been building a 1/96 Ticonderoga for the past 20 months.  I have reached the point where without the knowledge from others, ambition
risks being thwarted!  Amazingly so.  Question; how much lead or lead shot would one have to put along the centre line to prevent
the wretched vessel capsizing due to its inordinate top hamper?  If anyone has any idea, or has built this ship, say how many pounds
or better still kilogrammes since I live in France, should I align on the centre line to avoid ignominy and the scoffing of the locals,
in the event of trying to sail it in say a 10 knot wind? 

Any advice welcomed with a gratitude born of desperation!

El Neave.

[DickyD]

The only real way to do this is to put the completed boat in water along with installed batteries and then ballast it down to the waterline.

The ballast should be kept low and if possible fixed to the hull sides rather than keel. This will help to prevent roll. Weight in the middle of the hull acts like a yacht keel and your boat will rock and roll.

[derekwarner]

El Neave ...please re-read the experienced words provided by DickyD  .......the second sentence is of particular importance  ....

So simple.......but if you have any question....just ask.....Derek

[El Neave]

Much tugging of forelock for the advice and much note taken of your second sentence, DickyD.  Since Rocking and Rolling is highly unfashionable in these latter days, I will do my best to avoid it. When
you suggest aligning the ballast along the sides of the hull, I take you to mean aligned on the inner side of the hull.  Such an asinine remark is a further revelation of bestial ignorance, to be sure.  But in these matters it is always better to admit such virtues if only to avoid the consequences if one misinterprets excellent advice. 

Your empirical suggestion, to "get thee to a pond" is more than sound.  I dread it however, since the nearest pond is in front of a very well known Château which brings with it the not inconsiderable disadvantage of the event being attended by a cast of thousands of onlookers from 5 to 555 years old.  Thus, the risk of parts suddenly disappearing or - worse still - being trodden under the foot of Man, Beast, Child or insect is so great that no insurance company would even give you quotes! 

One other question:  which, in your opinion, is better -  shot in specially built silos as low as possible along the inner hull or lead plates?

El Neave, a little wiser but still a long way to go!

[DickyD]

Much tugging of forelock for the advice and much note taken of your second sentence, DickyD.  Since Rocking and Rolling is highly unfashionable in these latter days, I will do my best to avoid it. When
you suggest aligning the ballast along the sides of the hull, I take you to mean aligned on the inner side of the hull.  Such an asinine remark is a further revelation of bestial ignorance, to be sure.  But in these matters it is always better to admit such virtues if only to avoid the consequences if one misinterprets excellent advice. 

Your empirical suggestion, to "get thee to a pond" is more than sound.  I dread it however, since the nearest pond is in front of a very well known Château which brings with it the not inconsiderable disadvantage of the event being attended by a cast of thousands of onlookers from 5 to 555 years old.  Thus, the risk of parts suddenly disappearing or - worse still - being trodden under the foot of Man, Beast, Child or insect is so great that no insurance company would even give you quotes! 

One other question:  which, in your opinion, is better -  shot in specially built silos as low as possible along the inner hull or lead plates?

El Neave, a little wiser but still a long way to go!

Ballast inside hull is best idea.

I use lead plates stuck in with silicone.

For testing tank, if boat to big for bath I use white melamine screwed together to form box with joints sealed with silicone. Empty after use and keep dry for next time.

[derekwarner]

El Neave ...surely in modern France someone must have a bathtub long enough to trail ballast your 1/96 Ticonderoga 

An alternate method of trial and error is to take a set of bathroom scales....lay flat on your vessel  & add downwards force until the correct waterline is achieved.....

  ...at that point memorise the mass/weight displayed....this then provides you with the known mass of ballast required 

Lead shot is OK.....could have advantages in spreading the ballast evenly........then add some epoxy resin to set the ballast........Derek

[Mankster]

Why is there a differeance between laying lead weight along the inner sides and laying in flat on the bottom of the hull? I would have thought it would make no differance.

[unbuiltnautilus]

Why is there a differeance between laying lead weight along the inner sides and laying in flat on the bottom of the hull? I would have thought it would make no differance.

One for the yachties I feel Centre of mass??

[Colin Bishop]

Why is there a difference between laying lead weight along the inner sides and laying in flat on the bottom of the hull? I would have thought it would make no difference.

It can affect the righting moment as the hull heels. If the weight is at the sides then it takes more effort to move the side of the hull out of the water than if it was pivoting around the weight at the centre of the hull. The same thing applies in a fore and aft direction.  The turning characteristics will be different if you have the weight at the ends of the hull rather than concentrating it in the middle. In the former case the model will be more directionally stable but harder to turn, in the latter it will be more agile abut also more sensitive to the rudder and may need constant correcting to steer in a straight line.

It all comes down to the basic laws of physics with particular reference to leverage.

Colin

[Mankster]

But doesn't the centre of Gravity always act through 1 point of the hull? If so then placing the lead on the sides or in on the bottom wont affect the centre of gravity - it should act through the same point.
I can understand a yatch with weight in the keel to lower the centre of gravity and I can understand the centre of gravity moving fore and aft affting how a boat steers.

[DickyD]

Try thinking counter balances.

      _V___________________________V_                             
                               I

Does that help ?

[Colin Bishop]

It's to do with the pendulum effect. Imagine you have a see saw with equal weights on each end. It will go up and down relatively slowly as there is a mass at the end of each arm. If you put both weights over the pivot you can flick it up and down with hardly any effort at all because you have more leverage. So in a model it will roll more slowly if the weights are placed at the sides.

The analogy of a yacht is not quite right as in effect you have a vertical see saw here with the weight of the keel being balanced by the weight of the mast, rigging, sails and wind strength and pivoting around a point somewhere in the middle of the hull. It's also complicated by the fact that as the yacht moves forward the foil cross section of the keel also exerts a force towards keeping the vessel upright.

The forthcoming Model Boats Construction Special, due for publication at the beginning of May, will feature a comprehensive article on model boat stability along with other items on the questions which commonly crop up on the model boating forums.

Colin

[DickyD]

Another free ad Colin.

[Mankster]

It's to do with the pendulum effect. Imagine you have a see saw with equal weights on each end. It will go up and down relatively slowly as there is a mass at the end of each arm. If you put both weights over the pivot you can flick it up and down with hardly any effort at all because you have more leverage. So in a model it will roll more slowly if the weights are placed at the sides.

Thanks. But if there was a see saw with the same weight distributed evenly across its entire lenght - wouldn't that be just as easy to to flick up and down and move relatively easily? An empty see saw still has the weight of the plank and that moves easily with a flick, no harder than if you place equal weights at either end.

If a boat is more stable with weight on its sides rather than laid out evenly on its bottom, there must be another explantion beccause the math only require centre of gravity, centre of buoyancy and the differance in the vertical height between them to determine the stability of of a static body in water.

[pugwash]

In the book "Warships and Warship Modelling by Dave Wooley there is a section on ballasting model hulls - particularly the narrower warship hull
in which it describes where to put the weight  
                                                      M  - metacentre

                                                      G  - centre of gravity

                                                      B  - centre of buoyancy

                                                      K  - keel
states the weight is best placed below the centre of gravity but above the centre of buoyancy
and goes on to say this is best placed on the side of the hull.

it also states if you place it in the centre the ship will be very stiff and will look unnatural when righting from a heel
This is just another way of saying what colin and Dickie have already said
Geoff

[Talisman]

I'm interested in this discussion.

First of all, are we talking about this type of ship?
http://en.wikipedia.org/wiki/File:Spruance_and_Ticonderoga_lead_ships_in_class.jpg

If so then...

I agree that weight either side will dampen roll and improve initial stability.

But should we not be concerned with keeping the centre of gravity central and low given the upper weight.

Just thoughts at the moment.
Regards,
Kim

[unbuiltnautilus]

Trying to explain in a term I understand ( call it idiotspeak ) imagine a destroyer model with the weight placed in the bow and stern, down to its waterline, in a chop the model would be prone to pitch into waves rather than ride easily over them if it had all its weight concentrated midships. Now turn the concept 90 degrees, so that the effect is acting across the vessel rather than fore and aft, I think that makes sense....

[Mankster]

In the book "Warships and Warship Modelling by Dave Wooley there is a section on ballasting model hulls - particularly the narrower warship hull
in which it describes where to put the weight  
                                                      M  - metacentre

                                                      G  - centre of gravity

                                                      B  - centre of buoyancy

                                                      K  - keel
states the weight is best placed below the centre of gravity but above the centre of buoyancy
and goes on to say this is best placed on the side of the hull.

it also states if you place it in the centre the ship will be very stiff and will look unnatural when righting from a heel
This is just another way of saying what colin and Dickie have already said
Geoff

M, G, B.  I can understand centre of gravity (you want this to be as low as possible to increase stability - so add weight to the lowest point in the hull), I can understand centre of Buoyancy (you cant change this as it is a function of the hull design of a ship, a sub is another matter entirely) and the you want the metacentric height to be as great as possible to increase stability.
What I don't understand is why weight on the sides of the hull will make any difference when it does not alter the centre of Gravity.

[Mankster]

Trying to explain in a term I understand ( call it idiotspeak ) imagine a destroyer model with the weight placed in the bow and stern, down to its waterline, in a chop the model would be prone to pitch into waves rather than ride easily over them if it had all its weight concentrated midships. Now turn the concept 90 degrees, so that the effect is acting across the vessel rather than fore and aft, I think that makes sense....

No it wont, if the centre of gravity of the destroyer the with weight either end is the same as the destroyer with the weight dead in the centre then both destroyers should behave in the same way.  And both destroyers will ballance about their mid point. (same as the see saw analogy - doest matter if you have 2 equal weights either end or spread evenly across the the see saw, if the centre of gravity passes through the pivot of the see saw the see saw will balance)

[Colin Bishop]

Are we not mixing up different things here? Where you place the weights on the see saw will affect the inertia entailed in moving the arms. The centre of gravity will remain exactly where it is. The overall stability will also remain the same but the way in which it manifests itself, i.e. quick or slow roll will change.

Colin

[Mankster]

Are we not mixing up different things here? Where you place the weights on the see saw will affect the inertia entailed in moving the arms. The centre of gravity will remain exactly where it is. The overall stability will also remain the same but the way in which it manifests itself, i.e. quick or slow roll will change.

Colin

Ahh... ok we migt be tying it down. So how you do you work out the initeria roll of a ship? 

[gingyer]

Hi all,
I have seen 1:1, 1:72 and 1:96 scale Ticoderoga class cruisers and they all ROLL about and I mean ROLL

El Neave, what my friends who have built models of them have done is put the model in the water and place in your batterries
then some extra weight to finish the ballasting as far down in side the hull as possible ballast the model so the top of the waterline is at the water level.
then you should be ok to sail, watch out for strong side wind though

also what did you make your mast out of ? please say plastic tubing and not brass 

here is a video clip of a 1:72 scale Tico I took http://www.youtube.com/user/gingyer#p/u/6/U1Etw17HGX4
I hope it helps see what I was saying about the ballasting to the waterline
Colin

[bat44]

the amount of ballast depends on how you have built your upper works and what materials you have used and what type of electrics and what type of batterers you are using.
All i can say is ballast your boat to the water line and see what happens ,if that doesn't work then maybe you will have to hang some weight from a small Kiel about 2in long witch will lower the center of gravity and act like yacht to keep it up right but make it removable for showing  the model at shows.

                                           bat44

[Mankster]

Are we not mixing up different things here? Where you place the weights on the see saw will affect the inertia entailed in moving the arms. The centre of gravity will remain exactly where it is. The overall stability will also remain the same but the way in which it manifests itself, i.e. quick or slow roll will change.

Colin

I been doing a bit of reading and everything I've seen so far suggest the roll inertial of a ship is related to the Metacentric height and the mass of the ship, and NOT related to if weight is placed on the sides of the ship or laid flat on the bottom of the hulll. This matches my experience balasting and trimming countless submabarines that love roll by virtue of their shape, and unlike a ship, varing metacentric height as the sub progresses from surfaced to submerged trim.


This Wiki article simplipies it http://en.wikipedia.org/wiki/Metacentric_height

 May be a rewrite of that forthcomming article is in order???

[Colin Bishop]

Well, the guy who wrote it is chief engineer on a very large ship and a qualified marine engineer so I am prepared to defer to his expertise...

Colin