Fast narrow boats

[Paul H]

Allan,

 

We also have experienced this effect - in fact the previous owner warned us of this in relation to low bridges - he said 'if you approach a narrow bridge 'ole too fast to the extent that you have been making a wash and then slow for the bridge, a rush water from behind can surge foward and lift the stern high enough to damage the back cabin chimney against the arch of the bridge.'

 

Of course we always endeavour to limit our speed so as to avoid damaging either the boat or its surroundings.

This is something working boats take advantage of. Slow down at the right time and it lifts your deep-draughted stern over any rubbish in the bridgehole. Get the timing wrong and your stern will come down again right on top of the rubbish!

 

Paul H

[Keeping Up]

I think the soliton wave effect can be used to open lock gates. Yesterday i was approaching a lock near Leighton Buzzard. the top gates were closed but a small gap was there. I gave the boat a bit of throttle until i got a wave going then slowed down. The gates opened a bit. Then they shut. Perhaps with timing the gates could be made to open and not shut again, or a pulse of two waves maybe?

It's got to be worth a try. I can vaguely remember hearing about someone who used to do exactly that with the top lock of Braunston flight, having built up a good wave while coming through the tunnel, but I've always assumed it to be just a story. I can imagine though that until you get it right, you'll have a lot of collisions with gates that shut in front of you just as you are about to enter a lock.

 

This is something working boats take advantage of. Slow down at the right time and it lifts your deep-draughted stern over any rubbish in the bridgehole. Get the timing wrong and your stern will come down again right on top of the rubbish!

 

Paul H

I like that one. On similar lines I've found that shutting off the throttle at just the right moment when going through a narrow (ie 7ft) bridge-hole, can surf-ride you through faster than if you had kept the throttle open.

[magnetman]

I'm going to try that at Braunston. If anyone else is coming through braunston on friday 21st beware of 'issues around visibility and respiration', my engine smokes like a damp bonfire - i think its bored and glazed not doing enough work . Hope the vents work well

[Sue]

We went through Gainsborough once on our last boat. We were with the tide and the guy in front on his cruiser said we were doing 12 knots, whatever that means.

 

Yeah thats almost 14 mph.. we went through the same stretch at Gainsborough on an incoming spring tide at a hairy 24.5 mph.. it was soooooo scarey, and going round those bends the tide was almost faster than No Problem! I needed camber, and we were moving from one side to another trying to lay some weight down!

 

I still can't make my mind up whether I enjoyed that or not.. for sure it gave me a real buzz.. and I had full throttle too, but the river was even faster than I was going at times!

 

[bouy]

Yeah thats almost 14 mph.. we went through the same stretch at Gainsborough on an incoming spring tide at a hairy 24.5 mph.. it was soooooo scarey, and going round those bends the tide was almost faster than No Problem! I needed camber, and we were moving from one side to another trying to lay some weight down!

 

I still can't make my mind up whether I enjoyed that or not.. for sure it gave me a real buzz.. and I had full throttle too, but the river was even faster than I was going at times!

 

Yes the tidal Trent is a mans water for sure and the bends can be frightening, last time i came up the Trent with a few other boats out of west Stockwith "Little Mester "unfortunatley got a fertilizer bag round his prop now that would not bear thinking about under the above conditions

[NB Alnwick]

On similar lines I've found that shutting off the throttle at just the right moment when going through a narrow (ie 7ft) bridge-hole, can surf-ride you through faster than if you had kept the throttle open.

 

That's alright until you meet someone with a bigger boat doing the same thing and coming from the opposite direction.

[mykaskin]

I always worry about the accuracy of speeds given in these sorts of things. On water, speeds always seem higher than they really are. I've been using an accurate GPS (give speeds to better than 0.3 mph accuracy) for many years on many canals, and rivers. Here, mostly from memory are the speeds we have seen:

 

Flat out, on still open water, 50 ft 'holiday' narrowboat, Isuzu 1.7l 42 HP @ 3000 RPM. Makes about 2400 RPM with our prop (2:1) reduction. 6.5 mph.

 

Float out, on still open water, 60 ft residental narrowboat, SR3, 5.4

mph (and lots of smoke, I think it's a little over prop'd)

 

Rest of the figures are for the 50ft boat unless noted:

 

Bridgewater Canal near Manchester, 5.5 mph (not flat out) - no wash

 

Most large canals (e.g the deeper parts of the Grand Union), 4.7 mph - no wash (and piled)

 

Slowest part of the GU, 3.2 mph, 60 ft narrowboat - no wash (slowed down more for moored boats mind).

 

Chesterfield canal, 50ft boat, 2.5-3 mph in shallow sections

 

River Severn, in flood last year, we topped 8.75 (going with the flow) at Norton Hill - we weren't flat out. At Tewksbury we measured the flow at only 2.75 mph but it still looked impressive. This was 16/7/07, 3 days before the big one. I'd say even at peek flow it never got over 6 mph at that point, as it then starts to go over the banks instead.

 

We pushed the flood of the Trent, this was during the first flood event, 3/7/08. Our slowest points were just below Newark where Newark Dyke splits off from the main river, which slowed us to 2.6 mph, and at Thrumpton which slowed us to 1.8mph. We were flat out at both points, and so gave the river a flow of 3.9mph and 4.7 mph respectively. We had to wait until the follow day to get through Newark as the flood gates were shut, and the following week at Cranfleet!

 

Once you are on the tide way things start to get a little faster at times. Bottom of a spring tide at Susworth near Keadby, 8.7 mph, giving it a flow of only 2.2 mph! After the tide turned I slowed down to about 2,000 RPM approx 5.5 mph, and we slowed to about 3 mph in the main flow, so the tide was making 2.5 mph. It didn't slow a coaster who left Grove wharf soon after low water. We must have dropped about 1 foot as he passed. Leaving Keadby just before the top of a spring tide slowed us a bit more, but on the outside of the corner just after Keadby was still not more than 4 mph.

 

The fastest we've ever managed (in water) was 12 mph on the Humber near Reeds Island getting towards the bottom of a spring tide. We would have been doing about 6.2 mph at the time, making it a 5.8 mph stream speed.

 

So, the point I'm making is that water moves a lot more slowly than people think. Narrowboats can vary enormously, I've seen boats struggle to get to 3 mph, and others go fast enough to push water over the bow! It was a tug style boat though :-) I think there are few narrowboat capable over going over 8 mph, even Ocean Princess doesn't manage much more than this with a 75 hp engine, and a very big prop - wins any tug of wars even with working boats!

 

Re solitons: I don't think you could use the wave to push an engined boat alone as the speed is to high (6 mph?) on a canal. I've had lock gates open thanks to the boat wash travelling ahead, but I've had many more slam in my face! I like the idea of using a wave to get through a bridge, I'll have to try that one!

 

Alnwick looks great travelling at speed, and I'm sure the engine would thank you for opening it full up, most diesels do better after a good run - important note however, is to ensure the cooling is good enough!

 

Cheers,

 

Mike

 

ps. A lockie on the Avon said the flow of water around Norton? corner was 12 knots! It was less than 1.5 mph when we reached it, and we actually went slower just below the corner. He was using it as an excuse not to let us go further up the river after the floods. It was about 3 foot into the red further up, but even then the flow never got above 4 mph! At Marlcliff just above the look we were slowed to 2.5 mph flat out, which is a flow of 4 mph. The peak flow on the Avon during the flood at Tewksbury I estimated to be below 6 mph.