Scholar Gypsy

Very good. Any photos please ?

This chart (dating from the 1970s) deludes me into thinking I understand what is going on...

There's a nice video (can't find it just now on youtube) of a narrowboat moored at Gainsbourgh when the aegir/bore went past. The owner looked a little surprised.

I think this is a surface wave effect - ie the kayak/speedboat makes waves on the surface which cause you to bounce up and down a bit vertically, but are unlikely to move you much in a horizontal direction. The water moves up and down only (in the main). By contrast a passing heavy boat on tickover (see this thread) is unlikely to generate any significant surface waves. But the effect of moving X tonnes of water from in front of you to behind you, and the propellor drawing water in from the sides, is actually moving quite a lot of water around from one place to another. So this is quite likely to move you in a horizontal direction (normally forwards/backwards) which can cause problems with mooring pins etc.

On a RH bend, if the oncoming boat loses control then that's not really an issue. They plough into the trees on the outside of the bend and I just slide through on their inside. On a LH bend, to do that I need to pass stbd to stbd.

I agree - my point was that in some circs plan A (which is to keep well to the outside going around a left hand bend) needs to be abandoned if the boat coming towards you is losing control and is going to either hit, or get too close to, the outside of the bend.

I find this can be particularly tricky if you are going slowly around a blind left hand bend and see an oncoming boat. Do you keep to the right, which can be risky? Or do you judge that the oncoming boat has lost control a bit, and is going to get too close to the outside of the bend. In that case one might apply some power to steer hard left and pass stbd to stbd, the "wrong" side. (No point in sounding your 2 hoots of course...). On some parts of the Oxford - esp the summit - you can sometimes feel the bow wave that an oncoming boat is pushing in front. But I wouldn't rely on that.

I think the confusion between us is: i) in all the examples I am talking about above, the boat is in a "normal" canal, ie with a negligible flow when there are no boats around. That zero flow changes when a boat passes a given point, as 15 tonnes or whatever of water moves from one side of that point (in front of the boat) to the other (behind the boat) The point I was making is that if one runs aground - perhaps because one is over-revving the prop - then the net flow past the boat will be zero. ii) I was only making a statement about the average speed of the water that flows past the boat as it moves along the canal. As I said earlier, the actual flow of water is much more complex than that - that's the point you are making.

I really would doubt it was as much as 30 degrees. The issue is indeed the hydrodynamic effects as the boats pass each other, and will be affected by the shape of the canal bottom and how much of the cross section the two boats occupy. I'd be surprised if fiddling around with tanks etc would make much difference. Have you tried steering closer to the boat coming the other way - that may also encourage them to slow down a bit...

Um, I think you are trying to change the laws of physics (conservation of mass), but never mind! The earlier result (for average flow) assumes one is on a canal (with no ambient current, and a reasonably constant cross section) not a river. If you are not moving over the ground then the net flow past the boat is (or will stabilise at) nil - ie all the water that your prop is pushing backwards is offset by flows (weaker, as less concentrated) in the opposite direction. Of course, as you say and especially in shallow water, the moored boats would certainly notice your presence if you rev the engine.

I have been slowing upgrading my 2D fluorescents by removing all the innards, and then putting in three LED lights, with a bit of soldering and some cable ties to hold the connectors in place. I can post a photo in about a week if you like. So far they have worked very well. From Ultraleds: http://www.ultraleds.co.uk/catalogsearch/result/?q=UG412WW. A much nicer/warmer light.

I wouldn't like to cruise past this boat (photo from https://twitter.com/Fo_RegentsCanal). Still the alternative is driving mooring pins into the 400 KV cables in the towpath.

Thanks - good to know, I will be travelling along there in a couple of weeks!

Indeed so. The average speed of the water, moving backwards over the ground as a boat goes past forwards, is equal to the speed of the boat divided by: (cross section of boat)/(cross section of canal) - 1. This speed will be negligible on wide rivers (where wash ie surface waves is more of a factor) but will be significant on narrow & shallow canals. This result follows from the fact that as the boat moves forward, water moves from in front of it (to create a hole that the hull then moves into, if you like) to behind the boat (to fill the hole that it vacates). The actual pattern of flow will be much more complex of course - this just gives the average speed across the entire cross section of the canal. The action of the prop will have an impact - but the water it moves from in front of the boat to behind is just part of the overall flow described above,

Sounds fun. I helped Joel when he took his boat up the tideway a few years ago - see video. Some of my favourite charts and graphs are in this talk.

I think you need another dimension namely the number of miles travelled per day. The boater will be happier if this is a larger number, as they will have less far to go to the next water or pump out point. And then a fourth dimension depending on whether you are a tank or a cassette boat?

I very much agree. Much more alarming are the people who don't do preparation, and don't ask questions beforehand - and forums like this are of course very good for that, compared with pre-internet days. Much better to ask a stupid question beforehand (I would nominate this thread - I am still waiting for my game of cricket) than find yourself in a situation on the day, and not have much of a clue what to do.

Thanks - not an acronym I'd heard before but acronymfinder.com came to the rescue. I think you mean #3? I rather agree with you to be honest (but not on a narrow canal).

I would also add that I regularly use biggish squashy fenders when mooring up, on rivers and canals. I find that this means that any movement that does occur (even after using springs etc etc) creates much less grinding and bumping. PS you do need to remember to lift your fenders when cruising. (source)

I've done quite a bit of crewing on others' boats - as mine is not in London at the moment. I might be able to come along with you in September, if you do want to do the run down to Limehouse.

Good point. I have already clocked that I will need to watch my behaviour on the Chesterfield this summer - my first narrow canal for well over a year....

Here we are going under Br 35 (nominally 1.96m), the lowest point on the main transit route. As you can see there was still quite a bit of stuff that could have come off the roof if necessary. I got under a bridge near Ramsey that is nominally 7 cm lower, with the plants just brushing the bridge.

This was all very sociable (Limehouse)

See here. Note the Bridge heights are relative to the nominal water level - can be higher, can be lower. http://www.middlelevel.gov.uk/docs/Navigation/NavBridges2013.pdf extracted from here: http://www.middlelevel.gov.uk/docs/Navigation/NavNotes15-web.pdf You could always go via the Wash, of course ....

That depends on the size of the boat. If you are 57' x 7' or smaller then you can go everywhere (with one trivial exception). If you are wider than 7' then you are confined to a number of wide navigations - in four groups North, South, West, East. You can make some connections (South to West, East to North) if you are prepared to tackle short stretches of sea/estuary. There are then a number of interconnecting narrow canals that you can't reach. If your boat is longer than about 58' then progressively there are various waterways in the North that you are excluded from! Road transport is feasible.