How wide is a canal?

[Tony Dunkley]

 

 

 

Should not that be "e.g."? As in "for example". I thought that 1.34 was a constant that varied according to hull design.

 

 

 

 

It is, and it's also a fairly arbitrary figure for calculating hull speed in open water, not muddy ditches, for which there is no point in going to two decimal places.

Edited March 8, 2016 by Tony Dunkley

[Guest]

it seems to me that in everything you have either expounded or referred to so far you have ignored two very important and influential considerations applicable to narrowboats in the very small and very restricted English canals....

 

Secondly, and relevant to the pressure head loss influencing squat at the stern , I don't think you've given any consideration to the effects on pressure head under the stern of the differing wake percentages associated with the 'fineness' or otherwise of the run aft to the propeller, which in a narrow and shallow canal can bring all the the water that's rushing back along both sides of the boat to an abrupt standstill roughly level with the stern.

 

Tony, forgive me, but I'm struggling...

 

the calculation we mentioned previously is the flying equivalent of Mach, I'm (ex) ATPL/IR so I understand Mach, but the calculation for my hull shows this critical speed to be 10.3 knots, so I'm sure i can disregard it travelling at canal speed. Even if you decrease the factor to account for the higher Froude number of the displacement hull the number is still in excess of realistic canal speeds. There's no factor in this calculation that considers the wave refraction effects from the adjacent banks, so it can't be this that you're referring to because you referred to the effect as being significant.

 

There's reactionary effects at the boundaries between super and sub-critical flows, but at the shallow canal depths it doesn't make sense.

 

Unless others feel able to chip in here, I'll copy / paste the proposal into the boat design forum and see what the residential naval architects there have to say about the matter - I'd love to understand the reasons behind the phenomena you have observed, but I can't find anything that fits.

 

If it is the influential effect that you have implied then people will have undoubtedly studied and quantified it - it's just a case of finding the name of the resultant value.

[Tony Dunkley]

 

Tony, forgive me, but I'm struggling...

 

the calculation we mentioned previously is the flying equivalent of Mach, I'm (ex) ATPL/IR so I understand Mach, but the calculation for my hull shows this critical speed to be 10.3 knots, so I'm sure i can disregard it travelling at canal speed. Even if you decrease the factor to account for the higher Froude number of the displacement hull the number is still in excess of realistic canal speeds. There's no factor in this calculation that considers the wave refraction effects from the adjacent banks, so it can't be this that you're referring to because you referred to the effect as being significant.

 

There's reactionary effects at the boundaries between super and sub-critical flows, but at the shallow canal depths it doesn't make sense.

 

Unless others feel able to chip in here, I'll copy / paste the proposal into the boat design forum and see what the residential naval architects there have to say about the matter - I'd love to understand the reasons behind the phenomena you have observed, but I can't find anything that fits.

 

If it is the influential effect that you have implied then people will have undoubtedly studied and quantified it - it's just a case of finding the name of the resultant value.

 

I haven't got time just now to go into any more lengthy explanations. What I will do is to repeat the last paragraph of a previous post. The reason for the the relationship of squat to Cb on our very narrow and shallow canals being the inverse of how vessels behave in less restricted channels is within what I have already posted.

You will get to it and find it if you stop over complicating everything and simply do what I said here :~

"Don't concern yourself with calculating any precise values for anything from all this, . . . just consider what happens when the water flowing aft past the hull of a moving canalboat in a narrow canal meets up with the wake under the stern.

Concentrate on water flow velocities and the consequential effects on pressure head accompanying any changes in velocity."

Edited March 8, 2016 by Tony Dunkley

[Guest]

Thanks for the time you have dedicated to the cause Tony.

 

Until I find an alternative, I'll refer to the slender body paper I posted earlier, whose summary is repeated below. It covers all channel dimensions without specific mention of what you are describing, I suspect.

 

However, it does mention "The bow-down trim moment is found replacing B(k) by xB(k)" and if the bow lowers maybe the stern rises, but I need someone with a more advanced understanding of the principal than I have as a humble student.

 

 

I'm confident that the NAs on the other forum will kindly shed some light onto the matter.

Edited March 8, 2016 by dpaws

[bargemast]

 

 

I'm confident that the NAs on the other forum will kindly shed some light onto the matter.

 

I was going to ask if you could ask your highly qualified NA friends on the other forum, if they know much about Put-put boats.

 

I wonder if those were designed by NA's, Google hasn't been able to aswer this question.

 

Somehow I don't think they did, but I can assure you that my Put-put boat gave me several years of great enjoyment in the bathtub when I was a child.

 

It didn't create much wash, even at full speed, but there was plenty of water under her keel of course.

 

Simple things can give one lots of pleasure.

 

Peter.

[RLWP]

Simple things can give one lots of pleasure.

 

Peter.

 

I'm hoping we don't hear of any other things you were doing that gave you pleasure in the bath

 

Richard

[bargemast]

 

I'm hoping we don't hear of any other things you were doing that gave you pleasure in the bath

 

Richard

 

I never thought anything bad about you Richard, but after what you just wrote, I think that it's more likely that you are the one that must have done other things that gave you pleasure in the bath.

 

Myself I was only about 5 or 6 years old at the time, and perfectly happy with the simple pleasures I had from playing with my Put-put boat.

 

Don't worry, I'm not going to ask you to tell us more about your pleasures in the bathtub, and I won't tell anyone else about it either.

 

Peter.

[RLWP]

How is your eyesight?

 

Richard

[Paul C]

Do you have a bath with the taps at one end, or in the middle?

[Guest]

Well, it is the boat building forum...

 

http://www.steves-workshop.co.uk/toys/puttputt/puttputtboat.htm

[bargemast]

Well, it is the boat building forum...

 

http://www.steves-workshop.co.uk/toys/puttputt/puttputtboat.htm

 

Thank you very much dpaws, you made my day, I only owned one example, which was a very cheap thin metal one, but I didn't ask for more, and was very happy with it at the time.

 

This one of steves-workshop looks like a Rolls Royce of the Putt-putt boats, if I wouldn't so busy doing nothing, I could give it a try building something like that.

 

Thanks again,

 

Peter.

 

p.s. I wrote my (true) story, to make you see that one can have enjoyment with less than the best, and even straight away, by buying a nicely fitted out comfortable, good looking and fairly well performing boat.

 

But.......you want the very best, or in reality one that's even better, just the perfect boat, I think that it would be extremely sad that after all the hard brainwork and the millions of calculations you did, you have this boat (your dream) built, and then find out that it doesn't perform the way your calculations (and your NA friends) told you it would do.

 

You would certainly be most unhappy, while with a boat, just the nicest already existing one that you'd bought, and of which you knew right from the start that it wouldn't be the perfect boat you wouldn't be as unhappy, and you could enjoy the waterways much sooner too.

 

Of course this is just my view on the subjet, and you are free to do as you please, it's your time and your money and as long as it makes you happy, just do it.

[Guest]

Thank you for your sweet sentiments Peter, they're much appreciated. I can't wait to build one myself with my "little" Aurora, she'll be fascinated!

 

I've every confidence that our new build will be amazing, both inside and out. The final design will not be as maverick as many have assumed; above water it will be an aesthetically pleasing hybrid of traditional designs, underwater she'll be finer than some but not all.

 

I had considered a used hull, but I'd want to refit the interior anyway so it's easier to start afresh. Money isn't an issue and timing isn't an issue - if I bought used now I still have to honour my work commitments and we still have an 8yo in school in Italy so the boat would be moored in the UK but abandoned and corroding slowly but gracefully. I'd still have the stress of overseeing a refit and resolving the inevitable discoveries whilst trying maintain commitment to a senior position of work, all from 2000km away.

 

Personally it's important for me is I know why, so the the reason behind having a shallow V hull over a flat baseplate for example. I've seen that the boat builders don't like to deviate from what they've always done, so if I request a shallow V hull I feel it's important that I can explain as to why I would this feature and what benefits it gives me. BUT the final design will be a combination of some of my ideas and the builders significant experience.

 

My dear sister died at 34yo (cancer) - it's for the two young kids that she left behind too. I totally agree, life's short - just do it

 

Thank you again

Edited March 9, 2016 by dpaws

[colinwilks]

V hull has been done before. Have a look at

 

http://www.canalworld.net/forums/index.php?showtopic=82685&page=1

[Guest]

I'm familiar with the "Middle Northwich" boats and have the GA plans - I think Brinklow are working on a couple, or have had a couple in recently for maintenance.

 

I hadn't seen that thread though, thank you - I've always had a soft spot for nb Sickle, very pretty - both above and below the surface. It's often said that what looks right is right...

[Guest]

Personally it's important for me is I know why, so the the reason behind having a shallow V hull over a flat baseplate for example. I've seen that the boat builders don't like to deviate from what they've always done, so if I request a shallow V hull I feel it's important that I can explain as to why I would this feature and what benefits it gives me. BUT the final design will be a combination of some of my ideas and the builders significant experience.

 

A "trader" style shallow V hull, amongst other relevant sketches ** https://skfb.ly/M8xw

 

** Due to model ownership and potential liability exposure unfortunately I'm unable to facilitate the download of these models, even for personal use, sorry (A competent 3D modeller would be able to replicate these in about 20 mins)

Edited March 22, 2016 by dpaws

[bargemast]

With my slower than slow internet connection, it took a while to see these 3D models, all very clever, even more if you know that I can hardly draw a straight line.

 

Without any tank-testing, I'm pretty sure that the inspection style launch has the easiest arrival of water to the prop, and won't pull much water behind the boat.

 

The Dutch barge style one is a very close second, but of course not a very traditional style of narrowboat.

 

Good luck with your design progress.

 

Peter.

[Guest]

Thanks Peter, you're correct, in fact you can probably tell the two designs originated from the same initial sketch.

 

Unfortunately the correct profile bow that matches the stern is just too fine (nb Beech equivalent) for our interior - even with a bed over the swim incursion.

 

The re-design (WIP) is attached, here the bow and stern are in hydro-dynamic balance. The initial hydrostatic data is also most favourable, Cb = 0.68 (block co-efficient). A bow re-shaping above the waterline is underway.

 

For a comparison of fineness, a 61' Large Northwich, with the same draft has Cb=0.86 so with the historical hull in the same conditions, same speed etc the historic craft would have more squat, more forward resistance and increased disturbance for moored boats.

 

It could be better to have a finer hull and a more efficient interior layout, we're choosing this route with our build.

 

 

Design credit: Jùrgen Sass (www.sasssdesign.net)

Edited March 24, 2016 by dpaws