can anyone explain what this means?

[allybsc]

The "Swim" of a boat is that portion underwater "Aft" where the Hull tapers in to the propeller. ...

 

Edit: I was accidentally shouting

 

Thanks, Like most people even tho' I have my lovely boat I still look at appolloduck etc. I've seen boats advertising the length of their swims as a selling point! just wondered what they were and also what effect they had

[Matthew Dowson]

I read an article some years ago on "Fly Boats" The boats were built with a long swim so as to reduce wash and the horses used to trot, sometimes as fast as 10mph. The horses were "staged" like the old "stage coaches"

 

Cant remember where I read the article

 

Pick up a copy of CS Forester, Hornblower and the Atropos, Chapts 1 & 2 are a brilliant fictional account of a trip by flyboat from Gloucester to London in the 1790s, particularly on stretch with ''staunches" used instead of locks, involving partial damning of the river with a gap in the middle, sort of like rapids, sounds wild! Also includes legging, lots of detail about how things were done, the social aspect of travelling over long distances as a passenger etc.

[bottle]

Thanks, Like most people even tho' I have my lovely boat I still look at appolloduck etc. I've seen boats advertising the length of their swims as a selling point! just wondered what they were and also what effect they had

 

Hi Ally

 

As I understand it the 'finer' (longer) the swims the better the boat moves through the water.

 

I am sure a marine engineer will pop up and give a better explanation

[Teadaemon]

Hi Ally

 

As I understand it the 'finer' (longer) the swims the better the boat moves through the water.

 

I am sure a marine engineer will pop up and give a better explanation

 

well I'm not a marine engineer, but from my limited knowledge of such matters I'd suggest it's unlikely that particularly long swims would make a noticable difference to top speed (for our purposes defined as the speed at which you create a breaking wash) or to fuel consumption. OTOH, have no swims at all or very short swims will result in increased drag, and create lots of turbulence at the stern. This will make steering the boat more difficult, cause it to make more wash than a better-designed narrowboat, and increase fuel consumption.

[allybsc]

well I'm not a marine engineer, but from my limited knowledge of such matters I'd suggest it's unlikely that particularly long swims would make a noticable difference to top speed (for our purposes defined as the speed at which you create a breaking wash) or to fuel consumption. OTOH, have no swims at all or very short swims will result in increased drag, and create lots of turbulence at the stern. This will make steering the boat more difficult, cause it to make more wash than a better-designed narrowboat, and increase fuel consumption.

 

Thanks, now I know. I'm off to the boat in the morning so I'll inspect our swims, still havn't got round to measuring the draught so I'll prolly do both to while away the time.

[Phil Speight]

and how often did these horses exceed 2mph? On the downhill stretches maybe?

I have heard that the "Shroppie" fly boats AVERAGED between 7 and 9 miles per hour over an entire trip. I actually believe it.They were the ultimate development of the horse drawn carrying boat ( although they carried less than others ) and they had priority passage everywhere. The boatmen would I suppose be riding - either a horse or the boat. They also had a whole system of operation designed purely to achieve the the quickest journey times. It wasn`t remotely haphazard. The canal then was a highly profitable and well organized national transport system - most of the techniques used are lost to us now and while we don`t really need most of them anymore I wish we new more about them.CheersPhil Edited August 7, 2007 by Phil Speight

[bargeeboy]

most of the techniques used are lost to us now and while we don`t really need most of them anymore I wish we new more about them.CheersPhil

 

I think you mean knew. Unfortunately the modern world has no wish to understand them. If only boaters would understand the basics. Let the water do the work!!

[DHutch]

Well, the majority anyway, which as you say, is a shame.

 

Joe often refers back to an a time the left a lock, putting on a bit of a spurt to get cracking on, and to help draw out the waiting boat.

- Said boat then used all the might to frantical hold the boat into the side, shouting muttings of discontent at the affect of there speed.

- Then, without a pause, used equall force to push there boat out again, ready to enter the lock that had just been left for them.

 

The only way that could have been beter is if the boat had had an name along the lines of "Think before you jump" or somthing.

 

 

 

Daniel

[dacaB]

A swim allows the water to flow easily around the back of the boat directly to the propeller, the propeller can do it's stuff, thus the boat can flow easily thru the water.

 

On a narrow boat another huge advantage of a swim is that it allows the propeller to be mounted above the keel line ( the bottom of the boat ) Canals are shallow. The swim 'keeps' the propeller and the rudder off the bottom of the canal and out of harms way.

 

Most builders build the swim as a single convex curve from the sides to the prop. Others build-in a double curve, convex from the side then concave to the prop, very sexy The latter say that this arrangement causes the boat to steer and 'flow' more eficiently.

 

At the front the swim is the tapering lines in the side and bottom plates that create the bow shape.

[Gary Peacock]

A swim allows the water to flow easily around the back of the boat directly to the propeller, the propeller can do it's stuff, thus the boat can flow easily thru the water.

 

On a narrow boat another huge advantage of a swim is that it allows the propeller to be mounted above the keel line ( the bottom of the boat ) Canals are shallow. The swim 'keeps' the propeller and the rudder off the bottom of the canal and out of harms way.

 

Most builders build the swim as a single convex curve from the sides to the prop. Others build-in a double curve, convex from the side then concave to the prop, very sexy The latter say that this arrangement causes the boat to steer and 'flow' more eficiently.

 

At the front the swim is the tapering lines in the side and bottom plates that create the bow shape.

 

Yup the "S" swim makes us builders very happy easy and cheap to do easy to sell for good money, every exspensive boat can't be without one!

[barroca grande]

I used to do endurance riding and the best speed is trotting and it is 7mph on average. I only did the short distances such as 25miles. But my 70yo aunt did a 100mile one in a day on her 25yo horse. I believe that the fly boats also caught 'the wave' not sure what it's technical term is and basically surfed along.

[carlt]

I believe that the fly boats also caught 'the wave' not sure what it's technical term is and basically surfed along.

If you mean they got up on the plane then the laws of physics would have to be rewritten.

No narrowboat has or ever had the necessary hull design and streamlining to aquaplane.

[barroca grande]

Ha,

 

I feel better now that I have found an article that shows what I was thinking of - even if I might have misremembered it a little.

 

look at http://www.newscientist.com/article/mg13217974.800.html

 

solitary wave

 

not aquaplaning

[carlt]

Ha,

 

I feel better now that I have found an article that shows what I was thinking of - even if I might have misremembered it a little.

 

look at http://www.newscientist.com/article/mg13217974.800.html

 

solitary wave

 

not aquaplaning

All narrow boats create this effect.

 

If you go along, emptying the cut ahead of you and creating a bow wave behind, then slow down quickly, the wave 'catching up and overtaking' is actually the water behind attempting to fill the 'hole' you've created in front.

[Radiomariner]

All narrow boats create this effect.

 

If you go along, emptying the cut ahead of you and creating a bow wave behind, then slow down quickly, the wave 'catching up and overtaking' is actually the water behind attempting to fill the 'hole' you've created in front.

 

I don't think "catching the wave" is the same as planing (like hydro-foils).

My understanding is this:-

Horse drawn (or sail boats for that matter) do not draw (displace) water from under and around the sides of the boat as do powered boats. The wave or wash in their case is caused only by the displacement of water pushed away by the hull. In a channel (canal) this builds up behind the boat causing a rise in water level which rolls forward to fill the space after the boat has passed. On a non powered boat with a well designed swim, this wave can catch up with the boat and lift the stern, gravity then adds to the boats momentum. It is a bit like 'squat' in reverse! The 'wave' formed by a powered boat with the propellor at the stern is unlikely to catch up unless the boat stops or slows down. Occasionally the guy going far to fast down the cut when finding himself in an emergency situation, slams into reverse only to find that his boat momentarily speed up while his wash catches up with him.

[carlt]

I don't think "catching the wave" is the same as planing (like hydro-foils).

I know....

 

If you mean they got up on the plane then the laws of physics would have to be rewritten.

No narrowboat has or ever had the necessary hull design and streamlining to aquaplane.

[barroca grande]

On a non powered boat with a well designed swim, this wave can catch up with the boat and lift the stern, gravity then adds to the boats momentum. It is a bit like 'squat' in reverse!

 

 

Thank you,

 

My case is rested.

[chris w]

On a non powered boat with a well designed swim, this wave can catch up with the boat and lift the stern, gravity then adds to the boats momentum.

 

These two parameters are dimensionally very different and cannot be "added". Further, as the wave travels along the boat, first lifting the stern, then momentarily later lifting the bow, the effect (if it even existed) would cancel out from stern to bow.

 

Chris

[carlt]

It can also be observed with powered boats and, as it is the wake catching the boat up, would probably be more apparent on a boat with an inefficient swim.

[Radiomariner]

These two parameters are dimensionally very different and cannot be "added". Further, as the wave travels along the boat, first lifting the stern, then momentarily later lifting the bow, the effect (if it even existed) would cancel out from stern to bow.

 

Chris

 

I am not sure, as I said it was only my 'understanding' of an article I read many years ago about fly boat design and test tanks. When most of the science in an article is above my head I jump to the end of the article to read the 'conclusion. This article in a marine engineering publication, definately said that it was possible for a horse drawn boat to "catch the wave"

Perhaps my reference to "squat in reverse" was a bad analagy. It would be more like 'surfing" (Not planeing thats different) The two parameters do add up. As an electrician you should know all about vector calculations. After all, surfers use gravity to propel themselves forward, the water itself does not move forward it only rises. I have seen quite large fishing boats(bigger than canal boats) enter through the breakwater of the harbour at Abidjan at phenonamal speed surfing the slope of waves channeled by the breakwater and heightened by the shallowing waters. (I've seen one sink too)

 

On your second point, the wave is not allowed to travel the length of the boat, the horse is pulling the boat so as to maintain the wave under the poop. The resultant action I believe will not increase the speed of the boat but it will take some of the strain from the horse by counteracting the drag. It iwill be nowhere near as dramatic as surfboarding or those boats at Abidjan.

Of course this could only happens in canals where the water displaced by the passage of the boat has no option but to form a wave.

 

I can not remember clearly if it was the same article but I also read that these boats had a very fine fore swim and a wide counter, I dont know if that is true, I have never seen one.

 

In the case of the powered boat stopping, I agree, the wave (if it existed) will eventually lift the bow of the boat nulifying most of any effect on lifting the stern. But that takes time, the boat is still travelling forward as well as the wave. The wave will also be losing energy reducing the effect on the bow. The boat of course would never travel faster than the wave, thats impossible but it would not slow down as fast as would be possible were there not a wave travelling up its backside.

 

This has for a long time been the way I thought this worked. If someone else can tell me how it works, I will be happily enlightened.

 

I am not the sharpest pencil in the box. It took me a half a sleepless night to understand why two boats in a wide lock use exactly the same amount of water as one! Yet The penny did eventually drop. A lot of people I talk to on the cut do not believe this to be true, so I am not the bluntest in the box either!

 

regards

[AllanW]

Wow.... A down hill canal! Where's my skis

 

Dunno about around your way, but the canal around Chester has been going downhill for years

 

Allan

[carlt]

I am not sure, as I said it was only my 'understanding' of an article I read many years ago about fly boat design and test tanks. When most of the science in an article is above my head I jump to the end of the article to read the 'conclusion. This article in a marine engineering publication, definately said that it was possible for a horse drawn boat to "catch the wave"

Perhaps my reference to "squat in reverse" was a bad analagy. It would be more like 'surfing" (Not planeing thats different) The two parameters do add up. As an electrician you should know all about vector calculations. After all, surfers use gravity to propel themselves forward, the water itself does not move forward it only rises. I have seen quite large fishing boats(bigger than canal boats) enter through the breakwater of the harbour at Abidjan at phenonamal speed surfing the slope of waves channeled by the breakwater and heightened by the shallowing waters. (I've seen one sink too)

 

On your second point, the wave is not allowed to travel the length of the boat, the horse is pulling the boat so as to maintain the wave under the poop. The resultant action I believe will not increase the speed of the boat but it will take some of the strain from the horse by counteracting the drag. It iwill be nowhere near as dramatic as surfboarding or those boats at Abidjan.

Of course this could only happens in canals where the water displaced by the passage of the boat has no option but to form a wave.

 

I can not remember clearly if it was the same article but I also read that these boats had a very fine fore swim and a wide counter, I dont know if that is true, I have never seen one.

 

In the case of the powered boat stopping, I agree, the wave (if it existed) will eventually lift the bow of the boat nulifying most of any effect on lifting the stern. But that takes time, the boat is still travelling forward as well as the wave. The wave will also be losing energy reducing the effect on the bow. The boat of course would never travel faster than the wave, thats impossible but it would not slow down as fast as would be possible were there not a wave travelling up its backside.

 

This has for a long time been the way I thought this worked. If someone else can tell me how it works, I will be happily enlightened.

 

I am not the sharpest pencil in the box. It took me a half a sleepless night to understand why two boats in a wide lock use exactly the same amount of water as one! Yet The penny did eventually drop. A lot of people I talk to on the cut do not believe this to be true, so I am not the bluntest in the box either!

 

regards

Sorry but a loaded narrowboat, drawing over 3', with less than 6" of freeboard, is not capable of 'catching the wave'. Even unloaded, the amount of draught, lack of streamlining and the restrictive dimensions of the trough it's travelling in make the difference between a shroppy fly and a BCN Joey negligible.

 

The reasons the fly boats outperformed the rest were:

They had the best horses, changing regularly,

The crews worked shifts, round the clock,

They carried smaller loads and

They had, and asserted, right of way over the other boats.

 

They were still wooden tubes being dragged along a narrow, shallow trough.

[chris w]

I am not sure, as I said it was only my 'understanding' of an article I read many years ago about fly boat design and test tanks.

 

Gravity is an acceleration (metres per second squared) and has the dimensions of ms^-2 and momentum is mass x velocity and therefore has the dimensions of kg.ms^-1

Clearly adding these two is not possible - like adding 2 apples and 3 oranges to get 5 apples!

 

Chris

[Scotty]

gravity then adds to the boats momentum

Chris, I think you're being very picky. I don't see a problem with the sentence. Perhaps he should have said 'increases' instead of 'adds to'

 

 

Lets say I am on a bicycle freewheeling along a level road, using just momentum.

If the road then goes downhill gravity will increase (add to) my velocity and surely increase (add) momentum for when the road levels out again?

[Radiomariner]

Thank you Scotty.

Chris have you got a nice dark coloured felt tip pen handy, or perhaps a very free flowing ball point pen?

With the pen point facing towards you, supported it with a finger of the left hand near the pen point and a finger of the right hand about an inch and a half further away from you.

Keeping the left hand steady, very slowly raise the right hand until something happens.

Get an ink stain down your shirt? Gravity was the prime mover.

 

On the subject of "catching the wave" I personally do not believe a word of it. The thread is only about 'what does it mean?'

However I once sincerely believed until recently that two boats in a lock used less water than one!

(Meaning, I will believe if given sufficient proof)

 

Interesting thread, regards to all

Edited September 22, 2007 by Radiomariner