nb Beech

[Jay4424]

 

I always liked Jasons Bow too.

 

 

 

that'll be because "Jason's Trip Boat" is a real Josher!!

 

 

"Consensus seems to be that she is Portugal, built at Saltley in 1906 as a horseboat." from a topic about JAson's trip boat on this forum from 2008

[Guest]

It's strange that she's so old and yet I'm sure I can see rivets, I'd first assumed that she was all wood just from the fineness of her bow.

 

EDIT : Ahh I see 1896 production changed to the composite construction

Edited January 11, 2016 by dpaws

[Laurence Hogg]

Ahh, have I confused again? They rolled more, not less, and apparently were unpopular with the crews - or so I've read on this forum. More roll when turning too, (less grip on the water I suppose, if that makes sense in simplistic terms) - more roll means more weight transfer about the roll centre.

Having owned a middle boat I found it more or less the same as any other craft in handling, there was a little more roll but virtually unnoticeable, that boat is now a floating class room.

[Laurence Hogg]

You are correct indeed Sir... though the original boats changed from slab sided in wood to a bottom favoured profile with their shaped swims in steel. Conversely of course it won't draw in so much from the surface - is it a rock and a hard place thing?

 

Stern 1 is probably as fine an aft profile as I can achieve with the engine in it's present position in the hull. Stern 2 is more of a refined slipper stern type ( as in XR&D slipper, not Thames) with a flared central "pod" to accommodate the engine bulge.

With both of those sterns I would incorporate a very large weedhatch if you intend to do urban cruising, both will be traps for bottom rubbish to be sucked up and foul the prop. Theres a good reason why working boat stern swims developed as they did, I think you need to appreciate that.

The only boats ever built with hydrodynamics at the fore were the "Admiral" class where the spec was to achieve a full load on a silted, badly maintained waterway with little wash, they worked very well, the counter profile and uxter plate shape is worth studying.

It's strange that she's so old and yet I'm sure I can see rivets, I'd first assumed that she was all wood just from the fineness of her bow.

 

EDIT : Ahh I see 1896 production changed to the composite construction

Composite boats were long about before 1896, ie Bantocks where the side was composite.

[Guest]

With both of those sterns I would incorporate a very large weedhatch if you intend to do urban cruising, both will be traps for bottom rubbish to be sucked up and foul the prop. Theres a good reason why working boat stern swims developed as they did, I think you need to appreciate that.

The only boats ever built with hydrodynamics at the fore were the "Admiral" class where the spec was to achieve a full load on a silted, badly maintained waterway with little wash, they worked very well, the counter profile and uxter plate shape is worth studying.

 

I hear you and I get the theory but are these concerns borne out in practice - do any XR&D slipper sterners hang around here? I don't remember such comments linked to this swim profile, or do users suffer in silent shame for having deviated from the norm?

 

Admiral: I've got the side view from Brinklow's replica, does anyone have any pics that can shed light on the uxter and counter profiles? Does the water still slap the counter when she's running light? I can't be having that - there's often sufficient incessant noise coming from the galley...

Edited January 11, 2016 by dpaws

[Guest]

With both of those sterns I would incorporate a very large weedhatch if you intend to do urban cruising, both will be traps for bottom rubbish to be sucked up and foul the prop. Theres a good reason why working boat stern swims developed as they did, I think you need to appreciate that.

 

Just had a look at the Town Class Woolwich plan (thanks Laurence!) and I see that the aft swim starts at the base plate some 17'1" fwd of the stern, but the swim at counter stern height starts much later along the hull, around 7' later, approximately 10' from the stern.

 

By my reckoning the swim will initially be fed primarily from the bottom layers, allowing a Bernoulli effect to supliment the flow from the sides once an area of sufficient low pressure had been induced by the primary flow boundary layer. Does this secondary action limit the suction from the canal bottom?

 

My "Stern2" XR&D inspired profile starts to feed water into the swim from the sides AND from the bottom some 17' forward of the stern, so with my profile I'm feeding LESS water from the bottom of the canal than a Town Class... but I'm not convinced that the two swims will act so differently. If the sides were skirted allowing feed from below only then I'd share the concerns, but flow from the sides is fed in in the same way....

 

The change in swim displaced volume/cm length of hull (I'm sure there's a posh name for that) should be about the same, in that for both we're starting from more or less the same profile and we're tapering down to a stern post the same distance away. if anything, and by eye only against a 45° approximation then I'd say the XR&D is a little finer, at the cost of some space and buoyancy aft.

 

Does anyone see it differently? Any closet Naval Architects out there on the canals forum?

Edited January 11, 2016 by dpaws

[Laurence Hogg]

The stern lines and fore end design of the "Admiral" class were designed by the Docks & Inland Waterways research team at Bulls Bridge. They had a test tank there with various "channels" to represent the canal. When Bulls Bridge closed down this facility went to Southampton university, I have no idea if anything of it remains today.

 

 

The Docks and Inland Waterways Executive research facility at Bull Bridge. A "jebus" design under test. Note Sir Frank Price looking on second from the left.

[Guest]

It may just be me, but has anyone else noted the similarities between the profile of the eco-hull bow and the Admiral Class bow, the wet areas I mean...

[Guest]

Could be worth printing out a copy for those Sunday mornings on the throne...

 

https://www.dropbox.com/s/b04jcebyvope4j6/Analysis_of_hull_resistance_of_pushed_ba.pdf?dl=0

[Derek R.]

We have come away from regarding BEECH as a beautiful boat, however -

 

The Polish data seems to show that any kind of sloping section fore and aft is better than a vertical stem section.

 

Regarding Bernoulli's principle on canal bottom detritus;

In relation to a shallow canal with detritus laying on the bottom, the oncoming bow wave caused by a vessel moving along the canal will create a higher pressure than when static. This will produce a movement that will lift the lighter detritus. When the vessels bows move over the bottom, the fluid speeds up and travels aft, taking the detritus with it. Upon reaching the swim area aft, the detritus is met with a greater pressure of the slowing fluid and tumbles about whereupon the rotating blades of the propeller draw it in.

 

Whether or not a long swim aft with vertical sides and a square chine is less efficient than a long swim aft with sloping and rounded chines, I cannot scientifically show. But I would guess from personal experience from looking over the sides and observing, also the number of times I have had to clear the blade, there is not a great deal in it regarding a fouled blade, though with regard to a smoother flow of water of the rounded version - I think the rounded section wins.

 

And as Dave Harris alludes - they are far more beautiful when on dock . . .

 

 

Hope Speedwheel doesn't mind me nicking his image!

 

 

[mark99]

I would have thought displacement, water flow and turbulence are the actual forces causing crap to lift off the bottom rather than Bernoulli (the Bernoulli effect from a boat prop being a forward "lift" or thrust created by the prop - which then creates the displacement, water movement and turbulence).

 

If you decrease the pressure or depth of a canal, the stuff just does not lift off the bottom because the pressures have decreased (water being largely in-compressible the pressure below the crap on bottom equals the pressure on top of the crap so no lift off).

 

I'm no hyro engineer however.

Edited January 12, 2016 by mark99

[Guest]

It's maybe a tad early in the morning... but in my mind I'm thinking about the Dyson fan. The jetted flow of the fan is the equivalent of the boundary layer acceleration over the swim's surface, pulling additional water along with it in the same way the fan pulls additional air along with the jetted flow. The sediments are lifted as Derek described (thanks), and become part of this extended flow.

 

I think what is concerning people is that the XR&D slipper stern would cause a sudden low pressure over the bottom specifically, causing water to flow to equalise that pressure and that water having sufficient force to lift lying debris larger than sediments, old tyres and pairs of tights etc.- more so than a conventionally shaped narrowboat swim.

 

To be fair my preference is for the less conventional STERN1, simply because all of the profiles are smoother. Forgive me, but my father always suggested that naval architects were simply failed aeronautical engineers (of which he was one, amongst many other things!). His logic was that if you wouldn't see that shape on an aeroplane then it didn't belong in the water.

 

Thinking aloud I'm not a fan of the square section side on to the water on the slipper stern. Not that you don't get square sections on planes of course, (our old Bolkow 108 was hideously square - and flew like a bitch) but never where there's a significant pressure differential between the tangental surfaces as the equalising flow between them will become turbulent as it crosses the 90° edge.

 

Flows into any screw benefit from being as stable and controlled as possible, leading the industry to fit pre propellor flow stabilisers with fuel savings off about 10% on offer for a medium sized oil tanker, RTI about 18 months.

 

Sorry, I get far too tangential myself!

 

Ahh yes Beech! I have two excited builders who are very keen to arrange a trip out to measure her up. Her owner will join them on site, as, I'm hoping, will the local wooden boat building guy who has done work on her before. As others have pointed out though, measuring up and tempting is one thing, getting the steel to flow around compound curves is quite another!

 

With regard to Beech, whilst I haven't spoken to the chap who surveyed her, I understand from the owner that she needs 12' of new bottoms and a port side plank replacing. I didn't want to enquire further, it was obviously a painful subject...

Edited January 12, 2016 by dpaws

[Tony Dunkley]

 

Ahh yes Beech! I have two excited builders who are very keen to arrange a trip out to measure her up. Her owner will join them on site, as, I'm hoping, will the local wooden boat building guy who has done work on her before. As others have pointed out though, measuring up and tempting is one thing, getting the steel to flow around compound curves is quite another!

 

 

What compound curves, . . . there aren't any in the hull of a wooden narrowboat.

[Guest]

 

What compound curves, . . . there aren't any in the hull of a wooden narrowboat.

 

Before or after you've sanded it?

[gazza]

dpaws.

 

With regard the R&D stern, are you aware the TNC have covered pretty much all the navigable waterways in an R&D boat, one of the TNC posts on here now and again, perhaps drop him a line and ask his experience with that boat?

 

http://www.tuesdaynightclub.co.uk/

[Derek R.]

I would have thought displacement, water flow and turbulence are the actual forces causing crap to lift off the bottom rather than Bernoulli (the Bernoulli effect from a boat prop being a forward "lift" or thrust created by the prop - which then creates the displacement, water movement and turbulence).

 

If you decrease the pressure or depth of a canal, the stuff just does not lift off the bottom because the pressures have decreased (water being largely in-compressible the pressure below the crap on bottom equals the pressure on top of the crap so no lift off).

 

I'm no hyro engineer however.

 

The first bit sounds right.

 

Bernoulli's principle simply states that water forced through a narrow space will increase in speed, and drop in pressure.

 

Let's look at that another way. The prop pushes the hull through the water. In a canal with a cross section limited by depth and breadth, the displacement of the hull as it is pushed forward, forces water ahead of it raising the level ahead. Gravity demands that water remain level, but the water ahead has been raised in comparison to the water alongside which is falling as it speeds up, both alongside the hull and if there is sufficient room, beneath also, this is the Bernoulli effect. The pressure of the faster moving water is less, so a drop in water level is seen at the surface beside the boat (clearly visible when going through bridgeholes). This faster moving water creates turbulence, and is well capable of moving tights and tarpaulin from their previous dormant position in relatively high pressure static water. So yes - it's the turbulence created by movement that stirs up the crap.

 

As water is not compressible it moves faster through the introduction of a moving displaced body - the hull - along the narrow canal. The drop in water level either side of the boat is caused by the atmospheric pressure acting on the lower pressure of the faster moving water in comparison to the relatively higher pressure of static water ahead - which in turn has been increased by the forward hull movement. The action of the prop is also that of a pump, dragging the water from around and beneath to be forced aft. The faster one tries to go along a shallow canal, the less efficient is progress as more fuel is spent forcing water from ahead to aft creating more turbulence. It also pushes the back end of the hull closer to the bottom leaving even less room for water to flow past the hull, and at the same time increasing the turbulence.

 

No, nor I. But don't tell anyone . . .

[Tony Dunkley]

 

Before or after you've sanded it?

 

I'm unsure whether or not to take that response seriously. Do you really think that a wooden working boat hull would be sanded down after completion?

All that was done was to trim off the edges of any bends or planks that weren't quite flush with the next one to it with an adze. What you think is a curve from the fore-end top guard downwards is in reality four straight lines of around 7'' in length, with the 2.5'' wide guards disguising the knuckle at each seam.

[mark99]

I'm reading Dpaws "compound curve" in this instance as the <more than 1> bending planes of the bow form/planks. IE the planks are bending upwards and curving or twisting outwards. When proportioned correctly, a very pleasing effect.

 

*Probably not the correct terminology.

Edited January 12, 2016 by mark99

[mark99]

 

 

As water is not compressible it moves faster through the introduction of a moving displaced body - the hull - along the narrow canal. The drop in water level either side of the boat is caused by the atmospheric pressure acting on the lower pressure of the faster moving water in comparison to the relatively higher pressure of static water ahead - which in turn has been increased by the forward hull movement.

 

Is there not more than that happening?

 

The boat pushes up a wall of water ahead (displaces) - water has no resistance to shear so it has, by gravity to find it's own uniform level so water flows from uphill to downhill pushing down side of hull. This is continuous whilst you continuously move forward.

 

Speed up in shallow water and all that happens is the rear end as you say digs down - because the prop has removed (grabbed) a bigger volume of water from under boat which drops the boat locally.

 

Maybe reversing a boat fast in shallow water (notwithstanding you can't steer) will test what's happening (IE demonstrate crudely which major forces are in play) as you are shoving a big volume of water under the boat not removing it <from under the boat> whilst still displacing water up front (in this case stern).

 

I don't think atmospheric pressure is significant variable. After all 2" of height in hydraulic head is significantly more than 2" increase in pneumatic (barometric) head (> 1000 times). What we are seeing is the prop has removed a big chunk of water and the water upstream is flowing down the hydraulic gradient and trying to "backfill" it. Barometrics are a sideshow?

Edited January 12, 2016 by mark99

[Derek R.]

Forwards or backwards, the hull displacement is still the dominant factor in forcing water ahead or astern with the same theoretical effect. The only difference is that the pulling effect of the prop in astern has less effect on drawing the stern down due mainly to it's inefficiencies in blade contours astern, though if you could get enough speed up without losing control I think you would find the counter pulling down. It certainly wouldn't be trying to 'climb' out of the water. If in astern the prop was pushing water under or around the boat towards the bow, Bernoulli's effect still stands as the water is speeding up. Need some tank experiments to show results.

[mark99]

Forwards or backwards, the hull displacement is still the dominant factor in forcing water ahead or astern with the same theoretical effect. The only difference is that the pulling effect of the prop in astern has less effect on drawing the stern down due mainly to it's inefficiencies in blade contours astern, though if you could get enough speed up without losing control I think you would find the counter pulling down. It certainly wouldn't be trying to 'climb' out of the water. If in astern the prop was pushing water under or around the boat towards the bow, Bernoulli's effect still stands as the water is speeding up. Need some tank experiments to show results.

 

 

I tend to agree but I don't buy the atmospheric (baromoteric) is a significant. It's the hydraulic gradient imo.

Edited January 12, 2016 by mark99

[Guest]

This could get confused even further...

 

What's the squat on a canal at cruise speed? 2 inches? About 2 tonnes of force, assuming 1 tonnes displaces one inch.

 

How high and long is the bow wave across say a 5m canal?

 

What is the weight of the displaced water, 1m3 = 1 tonne. (tonne = metric ton = 1000kg = 1000litres of water...

 

 

Who started this?

[Derek R.]

Hydrodynamics is a fascinating subject. Against the 'squat' of the stern under way, there is some compensation in a rise at the bow. The drop of one inch per ton depends on the length (often one inch on a seventy footer), and that the craft drops one inch for its entire length. Some craft are known to 'submarine' when under full power on deep water, PENSAX did that in the Manchester Ship canal - a bit scary! Both our narrow boats would pull down a good four inches under way at the stern. Didn't make them any heavier though.

 

Hydraulic gradient. Quite likely a factor, I'm just not clued up enough to comment accurately enough not being of a scientific education, though I try. And maybe fail?

 

Bow waves. Well they can be observed, and horse drawn packet boats rode them, blessed if I know the calculations required to measure one!

Edited January 13, 2016 by Derek R.

[MtB]

This could get confused even further...

 

What's the squat on a canal at cruise speed? 2 inches? About 2 tonnes of force, assuming 1 tonnes displaces one inch.

 

How high and long is the bow wave across say a 5m canal?

 

What is the weight of the displaced water, 1m3 = 1 tonne. (tonne = metric ton = 1000kg = 1000litres of water...

 

 

Who started this?

 

 

I'd have thought the squat effect was due to the blade sucking the water out from under the boat and simply lowering the average water level its floating in.

 

The water level at bankside drops by 3" in line with my boat as I cruise along, even at only 2.5 mph. I suspect the level drops more if it could be measured right by the boat.

Edited January 13, 2016 by Mike the Boilerman

[Guest]

"The squat effect is the hydrodynamic phenomenon by which a vessel moving quickly through shallow water creates an area of lowered pressure that causes the ship to be closer to the seabed than would otherwise be expected."

 

It's certainly not limited to only the aft of the hull, the propellor can't suck a hole out of the water into which the stern falls, because that would require the water to be stretched, or uncompressed, which you can't do...

 

This is the same force as felt when you hold the back of a spoon against the stream of water from a tap, it's lift, like a spoiler on a car boot, it's a lift force that happens to be downwards.

Edited January 13, 2016 by dpaws