Thames Sailing barge

[Bob Abell 2Participant @bobabell2]

Paul……What is the "Issue with displacement" you are on about?

Bob

[Dave MilbournParticipant @davemilbourn48782]

Posted by Bob Abell on 01/05/2014 11:01:03:

You chaps know exactly what I mean!

Bob

No, Bob; I wish I did. I know I'm not having a 'senior' morning because I've just fixed a very complicated electronic boat installation for a customer.
Your post about removing unwanted air pockets was not at all clear to me. What is it that you are trying to achieve? Is it to reduce the amount of removable ballast you need to carry? That would make sense, but the total weight of hull plus ballast would have to remain the same. Conversely if the process is intended to reduce the total displacement of the model then that could well have an adverse effect on the handling and how much sail it can carry – but I'm sure you know that already.
Please would you clarify things for us dumb animals who know only about motor vessels?

Dave M

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

I was only away for a weekend and find all this when I get back. There is a 1/18 barge on the circuits, I'm sure a 1/12 is achievable but quite how tender she'd be?

Some quick answers to questions raised along the thread. Bob, yes, for a first barge I'd put in a motor, in my first barge, the Celia Jane [original Metcalf model] I installed a 6V decaperm with the intention that lead acid batteries would supply the ballast. I made the sails but had no knowledge how they were used, so I over did it all. BUT the engine is superb – the shaft is on the port side and has a large 4 blade prop. I've used this barge in steering competitions very successfully as she has tremendous bias in steering.

Ballast – as little as possible, the lads race light as do the real barges. I use half IOM lead keel weight (about 2.4lb) on a wide flat keel positioned? (look on the website!) Almost all use a removable keel. The leeboards are for show, at 1/24 scale they do not have sufficient area in the water below the hull to actually do much. Its the problem of scale and the relationship between volume:area:length.

Sails – unique mixture for a barge. R/c controls usually only the main and the sprit vang (same servo) and rudder. The foresail is on a running chain on the fore horse, the top sail sets with the main, and the stay sail is sheeted to the mast hounds area.

Yes there are rules for construction, on the website. Basically the barge must be representative of a sailing barge and most (I think all) are based on real barges. The problem is that ALL barges were built differently according to their builders whims, owners wishes and areas of use. The biggest barges were over 100feet, smaller barges for river work were maybe only 40feet. Pudge, I think being the smallest built for a farmer who lived "up a creek".

Many attempts have been made by model builders to achieve the best, but it all depends on the weather on the day, and the depth of water too. It is impossible to replicate accurately the true sailing technique of sailing a barge. For instance, tacking is done by holding the foresail to the windward shrouds when well after the bow has passed through the wind, so that the sail assists in pushing the bow round. The mizzen sail can also be set to assist.

Aye Kim

[Paul TParticipant @pault84577]

Hi Bob

Yes I did know what you were getting at but I was going along with your discussion as you were making a very good point about the difference between buoyancy and displacement.

But to those readers who don't understand the technical differences between buoyancy and displacement I will expand upon your analogy of the solid plank and hollow box:

Both the plank and box will float because they are made from wood but whilst the plank floats simply because it is buoyant (most timbers float) the box floats because it is both buoyant and creates displacement. An explanation of displacement is at the bottom of this piece.

But if we substitute the wooden plank for a steel bar and the wooden box for a metal box…….the bar will sink because it is not buoyant however the metal box will float…….it becomes buoyant because of the displacement it creates.

If we apply the same principals of fluid dynamics to the barge:

If the barge were made from solid wood it would float much lower in the water than a conventional hull because of its extra mass, but we all know that boats aren't solid structures, they contain an empty void and no amount of solidity to the construction of the hull will alter the fact that the hull will float high in the water until an internal load (ballast) is added.

I apologise to the technically gifted for this somewhat simplistic explanation and to Bob for invading his train of thought.

Paul

In fluid mechanics, displacement occurs when an object is immersed in a fluid pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this the volume of the immersed object can be deduced (the volume of the immersed object will be exactly equal to the volume of the displaced fluid).

An object that sinks displaces an amount of fluid equal to the object's volume. Thus buoyancy is expressed through Archimedes' principle, which states that the weight of the object is reduced by its volume multiplied by the density of the fluid. If the weight of the object is less than this displaced quantity, the object floats; if more, it sinks. The amount of fluid displaced is directly related (via Archimedes' Principle) to its weight.

In the case of an object that sinks (is totally submerged), the volume of the object is displaced. In the case of an object that floats, the amount of fluid displaced will be equal in weight to the displacing object.

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Hi All,

interesting stuff Paul, and grateful for the explanation.

I forgot to add to my piece above – Richard Chesney's barge at the Sandown model engineering show gained a bronze medal, and that barge is also used as displayed as one of his racing fleet. So our barges are built to scale and a standard worthy of exhibition. Our construction methods are also very similar to the "old way".

Kim

Edited By Kimosubby Shipyards on 01/05/2014 13:52:19

[Bob Abell 2Participant @bobabell2]

Dave M

You say…" Is it to remove the amount of removeable ballast you need to carry"…………Yes

"but the total weight of the hull and ballast will weigh the same"………. Why do you say that?

Etc etc

Let's start again

A normal model barge with a length of 96" will require about 60 to 80 lb of ballast to get it down to the correct waterline…..About 2" below the handrail

A plank 96" long x 20" wide wouldn't even need any ballast! It would probably need to be a hollow box about 2" deep to get the same effect…..ie No weight required!

To counteract the forces of the wind on the sails, where the model rotates about the waterline, we need a counterbalance……….A weight on a keel.

The keel weight would be about the same for either the box or the plank versions and I would guess 20lb would be OK

Since the model is 20" wide there would be less tendency to heel over and may act more like a full size boat

The point of the exercise is to make the model more portable and easier to handle

My Idea has saved about 60lb

While I've been typing this post the email in post has rung about ten times!

So this subject is attracting plenty of attention

Bob with his back against the wall!

[Dave MilbournParticipant @davemilbourn48782]

So you ARE intending to reduce the volume of the hull below the water. So it won't be a scale sailing barge any more. It will be a plank with sails. Yes? No?
DM (slowly losing the will to live……)

[Bob Abell 2Participant @bobabell2]

Chaps

My original idea a few years ago, was for a large barge of 96" hull length with the big blousey sails etc

Paul got wind of it and wondered why I didn't go ahead and just make one

I am now 77 years of age and find it too much to handle such a heavy clumsy model….Thor was bad enough!

My latest thoughts now are for a same size large boat that is easy to handle

My idea of a plank type boat would look identical to a normal model boat when sailing on the water

Has this put things in perspective?

Bob

[Paul TParticipant @pault84577]

Captain Bob

Now I understand

We have been talking at cross purposes.

I do remember constructing a model some years ago to test the plank theory and essentially it looked exactly as Bob describes …a long, thin and shallow hull that sat on the water rather than in it. The test model had a weighted keel to counter the capsizing effect of the superstructure………but the model I tested was a motor cruiser which didn't have any sails.

I will look up the calcs that I did at the time but I'm not sure that such a design will work with a large sail area.

Paul

[Bob Abell 2Participant @bobabell2]

Chaps I've just emerged from the ravages of World War Three!…..Been up to me neck in muck and bullets!

I've fought off verbal assaults from all directions….Phone call, Emails, PM's and Thread postings

But now the war is over…..No harm done, no offence taken and has all been a battle of wits and a bit of fun,

Capt Bob reporting for duty

[Colin BishopModerator @colinbishop34627]

Sounds like a sailing waterline model then! But, as Dave points out, it will not be a true scale type model and the handling is likely to be problematical to say the least due to the shallow draught. Also, when the wind blows, it will only take a small amount of heel before one side goes under at the deck edge and the other comes out of the water and that really will play merry hell with the hydrodynamics!

Bob, basically, what you are suggesting would appear to be little more than a raft with a barge deck and sailplan attached. (and probably something hanging underneath in an attempt to stop it blowing over….)

Colin

[Bob Abell 2Participant @bobabell2]

Thank you, Colin

Nice to see you adding your two pen'th

You are mainly correct in what you are saying, but don't forget, the plank is 20" wide.

The edge will go under water during the heel, but a fully laden barge would do the same?

I think my idea may behave like a surfboard?

In strong winds they reef the sails…..I could do that too?

Bob

Edited By Bob Abell on 01/05/2014 15:04:04

[Paul TParticipant @pault84577]

Aye Aye Captain

All of this has inspired me to revisit the 'plank' design that we played about with and I have to say there is some merit in Bobs surfboard idea.

Whilst a standard box shaped 'plank' hull has obvious limitations there is a distinct advantage to having a shallow hull coupled with a dynamic keel and ballast system.

The drawing office is ready for the Captains orders.

Paul

 

Edited By Paul T on 01/05/2014 15:00:47

[Bob Abell 2Participant @bobabell2]

Perhaps, Paul, a nice cross section would not go amiss at this stage?

Colin, when the plank heels over, the plank has side walls to disguise the fact!

Bob

[Colin BishopModerator @colinbishop34627]

Bob, I see, just like those yoghurt pots that look quite big on the outside until you discover that the bottom is halfway up the inside!

Colin

[Dave MilbournParticipant @davemilbourn48782]

"Goodbye, cruel world!!" (Photo: Martin Davis, Modelboat Mayhem)

Edited By Dave Milbourn on 01/05/2014 17:56:12

[Bob Abell 2Participant @bobabell2]

I don't think Dave has twigged it yet?

Colin……Something like that!

Do you think it will work?

Bob

[ashley needhamParticipant @ashleyneedham69188]

I have only built one sailing…thing.. the triumph Herald.

This is a shoe box , and it does not sail at all well. There is no length of hull pointyness to keep it in a straight line at all, a flat sailboard hull would simply crab sideways all the time unless it had a really really long flat keel, negating any possible saving in simplified construction and indeed aesthetically speaking would be a disaster,

Kimmo. I like it…"I have only been away a week end and…" yes, made me LARF.

No mention of ducks plse …I know where you live.

Can I get DM any ammo for that??

Ashley (sorry to use such technical terms)

[Bob Abell 2Participant @bobabell2]

How's this for another Crazy Bob idea?……..Groan! Not another?

Imagine a yacht with a drop down keel, with no ballast!……What!…No ballast?….Yep! No ballast….Impossible!

Impossible?……Don't let Bob hear you say that!

Suppose it had a thickish keel to house two Bow Thrusters!….Wow! Now yer talkin'!

With a tilt sensor on deck, it could switch on either thruster to remain upright!

What do we think of that one?

Bob does it again

[Paul TParticipant @pault84577]

Bob

Sorry to burst your balloon but thrusters can't produce enough power or react fast enough to resist the force of gusting wind.

Paul

[Bob Abell 2Participant @bobabell2]

Thanks for that Paul

It was just an idea that occurred to me

Back to sleep, Bob

[Bob Abell 2Participant @bobabell2]

I was just about to announce that the plank barge idea is dead and buried, when I had another blinkin' idea!

Paul came up with some cock and bull story this afternoon as to why it wouldn't work etc…..Sorry Paul

New idea……

Supposing we had a normal barge hull……OK….Now you're talking

With a 2" thick hollow deck!…….Here we go again!

The hull has water vent holes…. so the hull is now full of water!…..eh?

Still no ballast required………… We are back to the plank idea again and the hull is as the official layout drawing

This was our original idea, way back in 2006 or there abouts!

Over to you Paul……Groan

Let's be honest, if you don't like the project, we can call it a day, if you like?

So as not to waste your time, I may have a dabble on my own?

Let's call a Board Meeting tomorrow and have an Email conference?

Bob

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Hi Bob, here's an Italian idea from during WW2 that I spotted in the Nautical museum in Venice. You'll require someone who can speak Italian to translate the document, but basically it's a bomb, design to float just, and it was to be directed at "enemy" ships and the helm dropped off when the target had been selected and the device aimed.

It has some curious wings on the keel plus a very unusual stem rudder, plus a push-me pull-me propeller system.

How do like that for a project, instead of trying to destroy those lovely barges.

Kim

[Bob Abell 2Participant @bobabell2]

Thank you, Kimmo

Not got any spare time at the moment for new projects, but thank you, for your suggestion

But I must take you to task about me destroying those lovely barges?

My idea does nothing of the sort…..So why do you think I do?…..lol

Bob

[Paul TParticipant @pault84577]

Bob
The idea will work for a canal barge but won’t work for a sail powered Thames barge.
There are very few forces acting on a canal barge and consequently its attitude to the water surface remains fairly constant however the forces acting on a sailing barge are far more unpredictable with the resulting constant and excessive changes in attude relative to the waters surface.
In layman’s terms it will slide sideways across the water instead of heading forward and with a full set of sails it will capsize in any gust greater than 12mph.

Sorry Bob but the minimum depth of hull for an 8ft sailing barge is 6in and this would be a very skittish and difficult to control boat.
Paul

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