Free Flooding Hulls

[Paul TParticipant @pault84577]

Bob

After our discussion about free flooding hulls and my adamant stance that they would be to top heavy I decided to carry out some experiments with a 6ft tug hull.

I put in a false bottom at the waterline level and made sure that it was watertight through which I inserted 2 plastic battery boxes so that they protruded below the false bottom and into the free flooding area (to keep the centre of gravity as low as possible) a couple of holes next to the keel to let the water in and an air release tube sealed into the false bottom to let the air out completed the work.

The hull had been stripped of its ballast and engine for the experiment so without the free flooding void it would have bobbed about like a cork.

Without the ballast etc the hull is very light but when put into the water it settled right down to the waterline without any tendency to roll.

The experiment is a great success and I have to apologise to Bob for doubting his “plank” idea.

SORRY BOB

Paul

[Revell WalkerParticipant @revellwalker82816]

Yeah, I like this idea, because it saves weight and your back (remember folks, bend  down with your KNEES, not your back, when picking heavy objects up!). The Dickie tug uses this method, works pretty  good. I’ll try this on my next project.

[Bob Abell 2Participant @bobabell2]

Well!……….Thank you Paul!………Your`re a real gentleman!

I`m pleased that the idea worked out ok……..what made you test the idea out?

There`s a chap in our club with a big bulbous boat and he has to load it with 65lb of lead…and that was when I first thought of the plank idea.

Why don`t you submit the idea to the Modelboats Magazine?

 The finest regards to your goodself………Bob the Plank

[Paul TParticipant @pault84577]

Hi Bob

After our last exchange of views on this subject I began to ponder about what had been discussed and I became convinced that the principal of "free flooding" actually had quite a sound basis so I decided to physically test the theory.

It would have been no use testing on a small hull as the ballest load is light so I adapted a 6ft hull and the test worked a treat so it proved that you were 100% correct.

So I take my hat off to you and admit to being very happy to have been wrong.

I can’t imagine that the guys at the magazine would think that this is news worthy as they probably know all about free flooding and would think me foolish to have questioned the idea.

Thanks for the kind comments

Paul

[ashley needhamParticipant @ashleyneedham69188]

Paul.very magnanamou..magnanomo..   good   of you to realise the errors of your ways there,,,but free flooding "ballast" has been around for a bit in RTR types, and so needed no proof-of-concept jiggery pokery (in my eyes) to validify this concept, BUT I though we were grappling with the idea of a plank type hull/botton a free flooding compartment/hull extension underneath, or do I have it wrong again?, which is slightly different I think. Needless to say mt Titanic is sticking to lead ballast, there having been too much of the free flooding bit a while ago…

HOWEVER while on the plank subject, I intend to make a plank hull to test the hydrodynamics of an HMS Glorious Battlecruiser wot may be my next project (about 1;200, 48" long ). This class of ship had a very shallow draught so a 1/2" or 3/4" plank with some hardboard sides may well serve as a test hull. Reason being is my Titanic rushed up to a good maximum scale 25kts speed and then, at about 30 knots  (scale) topped out with massive propellor cavitation before max power had been applied.  Must be the rear hull shape, Dont want that happening to me Glorious as its supposed to be jolly fast.   Ashley

PS…. B&Q or Homebase best for a marine grade plank??

[Paul TParticipant @pault84577]

Hi Ashley

I was to fast to dismiss Bobs idea regardless of the hull type and whilst I did carry out a test on an adapted hull, i.e. free flooding system I am now convinced that the "plank" will also work provided the centre of gravity is kept below the C/L of the plank.

What the experiment proved to me was that the principal of using a free flooding compartment on a large model was feasible and with this I will be able to redesign the 8ft TID Tug that I am going to build this summer and save myself a lot of backache.

The Titanic should be a perfect subject for this principal as it was designed with a floodable tank deck or double bottom .

Cheers

Paul

[Bob Abell 2Participant @bobabell2]

Hello Boys

I was in New Brighton recently and was marvelling at the stability of a crazily piled high container ship.

A chap nearby, who was a nautical fellow  told me that the ships take in massive amounts of sea water ballast………once they clear the Mersey…….and vice versa on entering the River.

A big bulbous model ought to be abell to incorporate this feature?

Bob the Bulbous model

[Bob Abell 2Participant @bobabell2]

I once read somewhere that all plywood is water resistant……….as it was pointless not making it waterproof

Bob the Plywood expert

[Paul TParticipant @pault84577]

Hi Bob

Sorry to rain on your parade but I am afraid to say that its a popular myth that all plywood is waterproof or water resistant.

Whilst it is true to say that most plys will resist a very small amount of moisture only one can be said to be waterproof and even that one (marine ply) needs any cut edges to be sealed before putting it into water.

Most sea going ships have the ability to pump in water to make themselves more stable and it would be quite easy to construct a model with the same facility but this is different to the principal of free flooding hulls as we were discussing.

Paul

[Paul TParticipant @pault84577]

Bob

The plank idea doe’s work…..I tried fitting a few basic bits to a 4ft shaped floor board and by keeping the main weight i.e. the batteries below the waterline I managed to keep the center of gravity low so the plank remained stable even in the choppy waters of the Bridgewater canal.

Respect to you my friend.

p.s are you going to Birchwood this year?

Paul

[Bob Abell 2Participant @bobabell2]

Paul

What about the motor bit underneath?…………Suppose a watertight box, sunk in would do the trick?

I`ll be going to Birchwood and Ellesmere shows without a doubt……I remember in the 80`s they used to hold a model aircraft show called the Kings Cup air races at Birchwood…..I was next to a young land when he was dive bombed on with great ferocity…and that was that!……could have killed him!……..end of the shows!

Our club has got a show on at  Lyme Park again this year…….July 5th and 6th………a nice venue…nice park…nice cafe….nice hall….comin`?

Bob

[Paul TParticipant @pault84577]

Hi Bob

Yes a watertight plastic box with the prop shaft going through the wall, it worked a treat.

Looking forward to maybe seeing you at Birchwood, you should find me near the lifeboat stand as my Trent is planned to be part of the display.

Meanwhile I will do my best to get to Lyme Park (is there a pub?)

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

There`s a nice cafe close by………not sure about the beer though

For more info look at…..this

Bob

[Len OchiltreeParticipant @lenochiltree67043]

The Fat Controller wrote (see)

Meanwhile I will do my best to get to Lyme Park (is there a pub?)

Paul

If you take in lotsof liquid will that make you more or less stable?.

Len.

ps, have a nice time guys and one for me.

[Paul TParticipant @pault84577]

Len

My capacity for taking on board liquid ballast whilst remaining totally stable used to be well known in these parts but, alas, not these days as there are younger, sleeker and faster models available.

Hic

[JC Uknz 1Participant @jcuknz1]

If you get a book on yacht design, there are numerous writers books at your public library I’m sure, you will learn all about stability and centre of weight and centre of bouyancy and so on.  There is no reason why if in doubt you not should apply these subjects to model boats bearing in mind that you cannot scale nature.  There is a yacht designer [Young] who ‘thing’ is water ballast for his trailer yachts.   My only thought on the subject would be the agonising wait as the water drains out of small holes with you holding the boat at arms length over the pond

[Paul TParticipant @pault84577]

Hi JC

The plan would be to use 50mm dia holes in the 8ft TID so as the model was raised out of the water it drained simultaneously.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

I always had the idea of no bottom at all!

Bob

[Paul TParticipant @pault84577]

Morning Bob

I want the model to be as exact as possible but I want to avoid the problem of excess weight in traditional ballast so this free flooding hull is a compromise between a normal model and your proposal to build on a "plank".

I am looking forward to building it.

Thanks for your help in pointing me in the right direction.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

Keep posting progress pictures…….I find your project quite interesting!

Bob

[Len OchiltreeParticipant @lenochiltree67043]

Hi Bob,

Where is "the plank" article that set off this thread?,

And if I had no bottom, well that would solve a lot of problems.

            Len         

[Bob Abell 2Participant @bobabell2]

Hello Len

I`ve had a look in the archives…..and I can`t find the original thread either….

……….but I know a man who probably does………………..Paul!

Help us out Paul please

Bob

[Paul TParticipant @pault84577]

Hi Len and Bob

I can’t remember what started it off all I can recall is that Bob floated the idea of a plank as a hull (waterline type model) and I pooh poohed the idea on the basis of the model being top heavy and therefore unstable.

Subsequently I have been very happy to prove myself wrong. 

I think it was a thread that Bob started.

Paul

[Bob Abell 2Participant @bobabell2]

I`ve looked high and low……………..no sign of what started the original thread off……having a Senior moment I fear!

But ………Brought this thread to the top of the page for the simple plank yacht project……for Martin

Bob

[Paul TParticipant @pault84577]

Hi Bob

I tried the simple plank yacht as per your sketch and have to say that it is a perfect beginner’s boat for introducing children to the art of sailing.

Whilst it clearly would not perform anything like a traditional hull the plank offers stability and ease of use and is very forgiving when you fluff the turn at the end of a reach.

Perhaps you should market the idea to schools.

Paul

[Author]

Posts