Thames Sailing barge

[Bob Abell 2Participant @bobabell2]

Shop floor to Drawing Office

Thank you for your explanation….But……

Don`t think you have understood my latest post

The model is now as a normally built model but with water ballast

Bob

[lnvisiblemanParticipant @lnvisibleman]

I could have sworn that I suggested that earlier !

I must be going senile.

[Paul TParticipant @pault84577]

Hi Bob
I understood what you meant. A hull filled with water in the method that you propose will act in exactly the same way as a plank type hull. Even water contained within ballast tanks wouldnt provide sufficient mass to act as ballast.
Paul

[Dave MilbournParticipant @davemilbourn48782]

Posted by lnvisibleman on 02/05/2014 08:08:26:

I could have sworn that I suggested that earlier !

I must be going senile.

This thread does that to me, too!

[Bob Abell 2Participant @bobabell2]

Hello Paul

I feel sure you still not understanding my latest suggestion……..With the greatest respect of course

Imagine we have a normal model boat with a drop keel at the waters edge

Then we add umpteen bottles of water for the ballast

The model sinks down to the correct depth

Would you be happy with that?

Yes

Well, that`s what we have with my latest idea!

Bob

[lnvisiblemanParticipant @lnvisibleman]

Do you mean something like this ?

[Amy jane SeptemberParticipant @amyjaneseptember49770]

Hi Bob.

Think of it this way,

Load your water bottles in you hull and they will act as ballest, (All be it not very effective ballest) The bottles are surounded by air, water is heavier than air. Put the same hull in the water, and pour water in untill she sits down to her water line. She will still need to have a ballest keel of some sort, to keep her up right, and the water in her will have no righting moment, as water, surounded by water, weighs nothing.

If you want a light displacement flat bottom hull, google "New Haven Sharpie" for inspiration

All the best

Aj

[Bob Abell 2Participant @bobabell2]

Thank you, Amy

I understand what you are saying

But for some reason, you and Paul and the readers are missing the point!

I'll have one more go at presenting my case then I'll call it a day

We decided that a plank and keel weight would probably work……Agreed Paul

Then Paul had a rethink last night and said it wouldn't …..because because because etc

I then had an idea……Make a normal model boat….He can't argue with that!

Fit a normal keel and weight….Still OK?

Place in the pond……..Model floats high in the water…..Obviously!

Drill a few holes in the hull………..What?…..Just do it!

What happens?…….The boat sinks down to the waterline…….Oh! my poor boat!

Don't worry!…..Switch on the radio and sail away!……Ha! Ha! Ha!

What's up with that then?

Questions or comments please……..Posted with a smile…..lol

Bob about to call it a day

[Paul TParticipant @pault84577]

Bob
I understand exactly what you are proposing.
Putting water in bottles within the hull will only lower the waterline slightly, you would have to fill the hull with water to reach the required depth. For ballast to be effective its mass must be concentrated at the keel level, which is why we use a denser material such as lead.
Drilling holes in the hull will only make the boat sink down to deck level the water won’t act as ballast because its part of the wider lake system (a hull is a closed system and can be raised and lowered in the water by adding or removing ballast whereas a hull full of holes becomes part of the greater water system ) a hull full of holes will just roll around in the water.
I propose that you try the experiment with an empty pop bottle and see what results you get.

I agree that a plank and keel will work but not if the plank has a large superstructure or huge sail area above it, its basic hydrodynamics.
Paul

Edited By Paul T on 02/05/2014 09:48:26

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Bob,

I see your idea perfectly, and think with a 2 – 3" "hull" it would work. You require some depth to put a couple of servos, battery and, if wanted, a motor. [One of the barges with a wheelhouse would supply that requirement.]

If you proceed, I'll make the sails for you – how's that for an offer? Maybe destroy was a bit harsh, that big box hull is part of the charm of them, but I really have a strong affection for these grand old ladies, and fully agree with you, under a "full and bye" wind there's nothing that can compare [except a J class from the 1900's goose winging down wind with everything hanging out!]

Did you know that in racing trim these big boats could make 12 knots, and even 8 knots loaded. That was better than the steam engined coasters that eventually took over from them.

I've tried water bottles, not good, but an open bottomed flooded hull, that works.

Kimmo

[Bob Abell 2Participant @bobabell2]

Paul

Ref…Your last posting

I've not mentioned water in bottles

I've not mentioned ballast

I want to sink the boat to deck level…..The deck is a hollow 2" box

You keep saying I must have a hull at least 6" deep……I've got one!

Has this changed your thinking?

Don't get upset, we are only talking on crossed purposes

Kimmo….Thanks for your comments and thanks for the sails offer, but I don't we'll be going much further at the moment

Please explain why you say a bottomless flooded boat works!

Because that is what I am suggesting

I think Paul is being guided by calculations and he would say that a bumble bee can't fly!……lol

Bob

Bob

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Bob,

I've sailed a yacht that flooded but stayed afloat. Sure it was lumbering and wallowing about because water tends to slosh about, and we had to shorten sail because we were low in the water, but sail she did.

Earlier in the thread you noted that these barges have no waterline, yes they were sailed with decks awash, and were sailed very well. I have heard a nautical architect state that the thames barge design should not be able to maintain an upright position as it is an empty box with weight on and the mast and rigging should cause at least a list to one side, but they do float upright with no list.

If you still keep the hull shape, and have the keel (and ballast weight at its end), but allow the hull to flood to a defined level (a flooding chamber or two) then why should it not stay upright and be sailable. There are many models that use this technique to lower the boat to the water line without adding lead etc. Several of the RTR tugs from China have this "flooding" chamber to decrease buoyancy and lower the boat in the water.

Lifting the boat out empties the chambers.

Kimmo

PS in fact I'll build some into a pushing barge I'm about to build, as it needs weight, so why not use water! I'll post on it later when done.

[Bob Abell 2Participant @bobabell2]

Thank you, Kimmo

You understand the idea right enough!….A man after my own heart!

A picture is worth a thousand words!…….And we`ve used them all up already! ……..So let`s have a few pictures

Here is the barge

Full hull……20lb keel weight………The top deck is a plank, hollow, with space for the gear

The barge floating on top of the water……Hull not punctured yet, just to demo the floatation

The plank has dropped down slightly

The hull has been punctured and is settling down

The barge has settled down to the plank level……..About 2"

That`s all there is, folks!

Hope this helps?……..Capt Bob

[Colin BishopModerator @colinbishop34627]

One disadvantage with a free flooding hull is that you have to lift the weight of the onboard water when you take it out of the pond. Removing it slowly will allow the water to drain out at the 'same' rate as the hull rises, thus lessening the load, but the time taken will depend on the ration of hole size to volume of water on board. (and also upon the ability of your knees and back to take the strain!)

In that sense, Bob's idea of a shallow plank but with full depth sides does avoid the problem but the are underneath the plank and constrained by the sides must be able to vent easily.

Of course, as already pointed out, that also introduces further effects in that the water within the space between the side 'skirts' is directly connected to the pond water across the whole footprint of the deck shape and there is bound to be interaction when you are dragging along one volume of water within another. You might find that it creates a low pressure area under the bow for example.

I'm rather inclined to agree with Kim, just build a proper barge and fit it with removable ballast and perhaps a weighted and removable false keel.

Colin

[Bob Abell 2Participant @bobabell2]

Thank you, Colin

Water entry holes will be in the bottom and large for rapid fill and empty

I think this idea will, one day, become the adopted method for all giant models in the future?

Bob

[Paul TParticipant @pault84577]

Bob

I built a 6ft TID with a free flooding hull some years ago

It floated as expected but was very sluggish in the water and required a larger than normal motor to drive it.

Paul

[Bob Abell 2Participant @bobabell2]

Well!……You're a dark horse!

You never said!

I'm sure something could have been done about the sluggishness, but it's a bit too late now

Bob

[Paul TParticipant @pault84577]

Bob

I built it to test our theory about free flooding hulls.

It filled through the large holes on the base and the air was released through a valve in the funnel, I maintained the water level within the hull by closing the air release valve which stopped the water sloshing about inside when the boat rolled.

The down side apart from the sluggishness was that it rolled a great deal in even a slight swell, as an experiment it worked quite well but as a tug it was useless.

Paul

[Bob Abell 2Participant @bobabell2]

I'm surprised you didn't show your experiment before now. Paul…….It would have a lot of aggro all round

If you hadn't gone the water route, how much ballast would have been required for the six foot Tid?

I would have guessed about 50lb?

I think we can call it a day now?

We've had an interesting debate and somebody may take up the baton in the future

Many thanks to all concerned

Paul and Bob

[Paul TParticipant @pault84577]

Hi Bob

I didn't mention the TID as our discussion had related to a plank sailing boat and my comments were concerned with counterbalancing the huge 70sq foot sail area. Besides I was enjoying trying to impart some basic physics and enlightening people about the Archimedes principal.

But now that the elementary maths lessons have ended have you decided what kind of hull your barge will have?

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

I prefer to just to talk at the moment

I'm a bit surprised at the figure of 70 sq ft?…..That's 10 ft x 7 ft of assorted sails?

How tall is the main mast?

At a wind speed of 25 mph……What's that in p.s.i.?

Just for interest

Bob

[Bob Abell 2Participant @bobabell2]

Message for Kimmosubby

My brother Geoff, sold his model barge, Lady Daphne, to a member of your gang, he was a member of the Malden club and he was called Doug Tearall

How is he getting on and is he still sailing the model?

Bob

[Paul TParticipant @pault84577]

Bob

The main mast stands just shy of 9ft above the deck.

As a matter of interest why do you want the wind load in psi?

Paul

[Bob Abell 2Participant @bobabell2]

9 feet!………I didn't realise it would be so tall…..That's higher than our ceiling,

To be honest……That puts it in perspective and have to admit, the project is out of the question now!

Sorry Paul

I only wanted to estimate the side load on the sails, using the psi figure

Bob

[Paul TParticipant @pault84577]

Bob

The side load on the sails would be 290lbs but working out the load in relation to pounds per square inch wouldn't really help as the load has to be calculated in totals of individual sail areas.

The wind side load would actually be slightly higher due to the unmeasured effect acting upon the masts and rigging.

Re the mast, for a boat 8ft long the shortest (effective) mast height would be 8ft as a matter of interest how tall was the mast on the 4ft version that you built?

Paul

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