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Canopus and Sculptor


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ah, erm... yes maybe not sure about these force thingies, just know when people mention channel sides and the parallel slab hull there are a only few things you need to know, that effect being one. We have ice now, come back and break some, see how your steerage performs then. Not sure if bowthrusters like it though.

 

edit: IanM & IanD sounds good to me.

Edited by JohnO
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Lots of work -- both theoretical and backed up by experiments -- has been done over the last couple of hundred years on how to optimise hull design, even for unusual cases like narrowboats in a relatively shallow canal, though most of the effort has been deep sea ships for obvious reasons

 

And while there is an obvious commercial motive for seagoing freight operators to optimise their hull designs, there is virtually none for narrowboat builders.Most narrowboats are built by steel fabricators with little or no interest in the finer points of hydrodynamics, and are selling their boats to an uninformed and largely uninterested buying public. So shells are designed for ease of fabrication, minimum cost, provision of usable internal space and general good looks, which for the middle market means looking like every other clonecraft, and at the top end means looking like a working boat. The boatbuilder has no incentive to refine the underwater hull shape for better performance. Edited by David Mack
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The boatbuilder has no incentive to refine the underwater hull shape for better performance.

 

I absolutely agree. Engine horse power is cheap, 43 being the norm, so who cares. When the tide turns for diesel-electric I think the mentality will change as batteries cost a load and take up valuable space. My boat goes further than your boat will be the subject of much debate in the future, I'm sure. We just need recharging points at the 48hrs mooring points and then the scene will take off IMHO.

 

Technology's making the prospect of complex shaped hulls much easier with precision laser cut kits, only a couple of clicks once you've got a 3D model. Put them together in Eastern Europe and ship them over in standard containers to weld shut here and add whatever fancy superstructure the customer asks for.

 

When you leave the hull structure to "fabricators" rather than boat builders then a whole new world of equipment opens up. My potential hull fabricators have a gantry 3D scanner with mm precision and 20mm sheet rollers. Even their "apprentice" welders are multi-coded; it's a different world to that on the cut. If you request their apprentices and forgo official engineering certification then you can find nuclear industry build quality at canal-side prices. The difference is being able to the slacken the build tolerances to mere whole millimetres!!

Edited by dpaws
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I absolutely agree. Engine horse power is cheap, 43 being the norm, so who cares. When the tide turns for diesel-electric I think the mentality will change as batteries cost a load and take up valuable space. My boat goes further than your boat will be the subject of much debate in the future, I'm sure. We just need recharging points at the 48hrs mooring points and then the scene will take off IMHO.

 

Technology's making the prospect of complex shaped hulls much easier with precision laser cut kits, only a couple of clicks once you've got a 3D model. Put them together in Eastern Europe and ship them over in standard containers to weld shut here and add whatever fancy superstructure the customer asks for.

 

When you leave the hull structure to "fabricators" rather than boat builders then a whole new world of equipment opens up. My potential hull fabricators have a gantry 3D scanner with mm precision and 20mm sheet rollers. Even their "apprentice" welders are multi-coded; it's a different world to that on the cut. If you request their apprentices and forgo official engineering certification then you can find nuclear industry build quality at canal-side prices. The difference is being able to the slacken the build tolerances to mere whole millimetres!!

The extreme case of having a real *need* to minimise required power was Keith Jones's steam-powered "Firefly", which IIRC had about 3SHP at 200rpm flat-out. Also had a very well-shaped hull with long swims, a relatively big prop (26"?) and deep draft (32"?). On most canals it just glided along with hardly a ripple, but you couldn't keep up easily walking. On shallow canals it slowed down quite a lot, but didn't have enough power to make the stern squat so still wafted along, just more slowly. For stopping however you'd be quicker throwing out an old boot on a rope...

 

It meant you had to think more like a supertanker captain, planning both acceleration and stopping much more in advance than with a nice big 43HP diesel, but there was something satisfying about timing it just right and going astern before the bows had even entered a lock so that you just came to a silent halt before touching the gate :-)

 

For cases like this (power-efficient battery-electric) it would be interesting to really put modern CFD and double-curved hull fabrication to the test and see just how low-drag such a hull could be made in a modern canal. My guess is that typical cruising power requirement could be kept down to something around 3kW/4HP which would give a pretty big range (several days) between recharges with a typical 48V/800AH traction battery bank.

Edited by IanD
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Why not just make it lighter using wood or glass fibre and dump the steel, come in at 10 ton and not 20.

 

If you want the same draft then you'll need the same displacement - you could make it out of paper but you'd need to fill it with ballast just the same... and besides, you'd look like a Broad's bathtub... wink.png

Edited by dpaws
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If you want the same draft then you'll need the same displacement - you could make it out of paper but you'd need to fill it with ballast just the same... and besides, you'd look like a Broad's bathtub... wink.png

But why have a 3 foot draft if you want maximum propulsion efficiency

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and besides, you'd look like a Broad's bathtub... wink.png

 

 

Some of the early GRP hull broads boats are actually rather handsome boats. I'm thinking of some of those with the mahogany superstructures.

There is a very sad and neglected one on the Moon Boat moorings at Honeystreet.

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But why have a 3 foot draft if you want maximum propulsion efficiency

 

Have a look at a Peter Nichols build, it depends on your aesthetic tastes. Springers too I suppose to be fair.

 

We all need 6ft+ headroom interior, so if there's less underneath then there's more sticking out the top. But you're right of course.

 

You've two choices - get sucked off course with a deeper hull or get blown off course with a higher superstructure :)

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You've two choices - get sucked off course with a deeper hull or get blown off course with a higher superstructure smile.png

 

 

Three actually.

 

The third being buy a motor home...

Which brings me onto a subject swerve. I keep noticing scruffy liveaboard motorhomes parked up (sometimes for months at a time) in CRT VM car parks.

 

I think this is a new and generally unrecognised use of CRT facilities. I noticed one back in the summer using a CRT key to empty their cassette...

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Three actually.

 

The third being buy a motor home...

 

Which brings me onto a subject swerve. I keep noticing scruffy liveaboard motorhomes parked up (sometimes for months at a time) in CRT VM car parks.

 

I think this is a new and generally unrecognised abuse of CRT facilities. I noticed one back in the summer using a CRT key to empty their cassette...

Let me fix that for you Edited by Loddon
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"Rudder forces aren't consistent and change with speed. Typically the right arm aches a lot more than the left on an evening after cruising. At close to 90kg I'm not lightly built and it takes my full strength and full rudder deflection at times with very little effect."

 

 

My antennae pricked up at this earlier and since nobody else has bitten I will: When I'm steering the tiller doesn't swing outside the slide runners much, and very rarely outside the handrails. Full rudder deflection? Never, it's a waste of time and effort.

 

A group* of us were in The Folly last night & this thread came up several times with varying degrees of incredulity/head shaking/nodding sagely/choose your own reaction. At risk of causing offense, here's one summary, related to me by Ian Sly a long time ago:

 

"So Ian, what makes your boat go so well?"

 

"There's four things make a boat go well."

"There's the right engine; the right blade; the right hull shape and then there's the most important thing of all..."

(Leaning inwards to catch this pearl of wisdom)

"Ooh, what's that Ian?"

 

"The twat with his hand on the speedwheel"

 

*collective boat owning/steering/building experience approaching the age of the universe

Edited by davidg
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Rudder forces aren't consistent and change with speed. Typically the right arm aches a lot more than the left on an evening after cruising. At close to 90kg I'm not lightly built and it takes my full strength and full rudder deflection at times with very little effect.

 

Have you been moonlighting on Canopus? I genuinely double-taked to see if that was one of my old posts!

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what airfoil did you use on the propeller? and water temp?

 

I'm sure it was one that you sent me! 60°F naturally, as it was an American that developed and published the Schilling section, full CFD analysis by XFOIL tongue.png

Edited by dpaws
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Just need Cart to dredge and construct the canal profile according to Schilling, drop in a few waterbath heaters to maintain 60f and the job is done. wink.png

 

I'll start preparing the risk assessment....

 

...yip, it's risky; there's a chance it could actually work... wink.png

Edited by dpaws
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Schilling is a rudder profile, comes in different refinements, it works, it works a lot better then a flat plate rudder does, a thick Schilling works better then a Thick NACA 00xx profile. Dalslandia have a Schilling of my own design, it was a WOW factor when first tested it.

 

Dalslandia have a 400 mm diameter bow thruster, it works very well too.

 

Non of the Schilling or bow thruster replace the other. they are there to be used.

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Unlike some of the other (marine) hull refinements, there's absolutely no reason a Schilling rudder shouldn't have all the advantages over a flat plate one that numerous tests (and simulations) have shown, and which have been borne out by those few intrepid narrowboaters open-minded enough to try one -- better rudder response and working effectively to much bigger rudder angles, which is if anything even more valuable on the canals than at sea.

 

The only reasons for not using one are probably increased cost, the fact that most (all?) boatbuilders don't offer it as an option, and entrenched disbelief that improvements in a hundred-year old motor hull design are possible because the old guys knew everything ;-)

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For people that are stuck to (their) old ideas, all the changes that have been done over the years, and that took a lot of time to be accepted i.e.:

 

The change from wooden to steel (iron) boats, with some hesitation at first still using a wooden bottom.

 

Welded instead of rivetted construction, welds were something that many boat people had difficulities with too.

 

In the future we may see more "Shilling" rudders being installed on narrowboats, for the time being, I only know of one.

 

It all takes time, but maybe one day we will see a new kind of narrowboat arriving, with less draft and better underwater shape, as they don't have to carry cargo anymore for which the traditional shape was developped.

 

Peter.

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Meanwhile if you have no concept of where the channel is likely to be and can't read the clues the boat constantly gives you regarding your speed and position, you'll still struggle.

 

Bottom line, your boat's a moving hole in the water. If there's not enough space around you for the water to get past and refill it, all calculation and theory is irrelevant.

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