Apparently there's a race on

[Guest]

10 minutes ago, RLWP said:

That's Mr Bernoulli causing trouble again, curse him

I never knew it was called thus, every day is a school day. I will be telling everybody that in the pub tonight 
Happened to me in Braunston tunnel once when one boat was seriously tailgaiting another coming towards me. The first boat dragged our boat away from the tunnel wall but as the second boat was so close (almost touching the first, I thought he was towing it but turned out he wasn't) that I couldn't get back in line quickly enough and hit the second boat quite hard. Of course it was all my fault, rather than the laws of physics....

Edited July 8, 2019 by Guest

[magictime]

1 hour ago, noddyboater said:

I’m always amused by the growing number of boaters who use their tacho as a speedometer. “I cruise at 2,500 rpm and pass moored boats at 1,800..”

Irrespective  of the canal depth/width etc. 

I confess, I use mine as a guide cos I don't have any other guide other than my own fallible sense of how my speed relates to 'walking speed'. So 800 revs (tickover) is 'moored boats' speed, 1000 revs is 'tunnel speed', and 1200 revs is 'cruising speed' - with tweaks according to breaking wash, width of canal etc. 

[noddyboater]

25 minutes ago, magictime said:

I confess, I use mine as a guide cos I don't have any other guide other than my own fallible sense of how my speed relates to 'walking speed'. So 800 revs (tickover) is 'moored boats' speed, 1000 revs is 'tunnel speed', and 1200 revs is 'cruising speed' - with tweaks according to breaking wash, width of canal etc. 

But passing moored boats is variable, how are they moored? How much water is under them?etc etc. Tunnels can be wide and deep or narrow and shallow, totally different revs needed to maintain a decent speed. Try covering up your tacho and enjoy the view a bit more, but be aware that someone may want to go a little faster than you are comfortable with. 

[blackrose]

1 hour ago, magictime said:

 

As above, yes of course with hindsight I should have slowed down.

 

It's very easy to look at this only from one's own perspective. From your point of view the overtaking boat was being unnecessarily aggressive, and maybe you have a point, but perhaps from his perspective he was expecting you to slow down to let him pass and by the time his bows were level with your stern he felt like the safest thing to do was complete the manouvre even though you weren't slowing. You're probably both at fault to some degree so we should always try to avoid perceiving negative intent on the part of other boaters. 

Edited July 8, 2019 by blackrose

[Machpoint005]

1 hour ago, RLWP said:

That's Mr Bernoulli causing trouble again, curse him

 

PTHPTHTHPTHPTHPHTHTPHTHPTPHTPHTPHPTHPTPHTPH! 

 

(visual rendition of a blown raspberry)

[Alan de Enfield]

1 hour ago, mrsmelly said:

I take it thats not a narrowboat with a diesel engine? If I were using those revs I would be on the plane at 1800 revs, I pass moored boats at about 700 revs in my van engined boat.

At 1800rpm I'm doing 7.7mph

At 2500 rpm I'm doing 7.8mph and using 40 litres per hour.

[Machpoint005]

22 minutes ago, noddyboater said:

be aware that someone may want to go a little faster than you are comfortable with. 

 

You could acknowledge your awareness of the steerer behind you by waving or even shouting to (not at) them?

[noddyboater]

1 minute ago, Machpoint005 said:

 

You could acknowledge your awareness of the steerer behind you by waving or even shouting to (not at) them?

I’ve found that if you’re following someone who is oblivious to your existence, and dawdling to the point where I need to keep knocking it of gear..

Get as close as you can, leave it gear at tickover and go and stand on the bow of your boat. Shout “EXCUSE ME! Is there any chance of getting past?” 

It doesn’t half make them jump. 

[magictime]

1 hour ago, blackrose said:

 

It's very easy to look at this only from one's own perspective. From your point of view the overtaking boat was being unnecessarily aggressive, and maybe you have a point, but perhaps from his perspective he was expecting you to slow down to let him pass and by the time his bows were level with your stern he felt like the safest thing to do was complete the manouvre even though you weren't slowing. You're probably both at fault to some degree so we should always try to avoid perceiving negative intent on the part of other boaters. 

A fair point and a laudable attitude. But I still think it was a strange place to attempt to overtake, even if I had slowed down. We'd still have been alongside one another for maybe 30 seconds, on a blind bend, with (as it turned out) a boat coming the other way.

 

1 hour ago, Machpoint005 said:

 

You could acknowledge your awareness of the steerer behind you by waving or even shouting to (not at) them?

I think part of the other boat's beef with us was that he knew we were aware of him, because he'd seen us turn round, but we hadn't acknowledged him in the sense of actually waving him on (or similar). But I just felt it would have been 'off' of us to actually invite him to pass by waving, given the risk of meeting an oncoming boat on a bend with poor visibility; to my mind it would then have been partly 'our' mistake. 

 

And I must admit, I still have my doubts about when we should have slowed down. If we'd done so as soon as we became aware of him very close behind us, that would have pretty much forced him to pass us on a blind bend - which is fine if he was definitely going to overtake anyway, but we weren't really sure of that until his bow came alongside a couple of minutes later. At that point, yes, I should have slowed.

 

I should maybe clarify that because we'd stopped for the trip boat and then slowed for a moored boat, it seemed quite possible that he'd caught up to us by a hundred yards or so just because we were only just coming up to cruising speed. This whole thing took a very few minutes, so when he first got close I was probably expecting that, now I was cruising at a normal speed, he'd settle in a little way back.

[Machpoint005]

49 minutes ago, magictime said:

But I just felt it would have been 'off' of us to actually invite him to pass by waving,

 

Hold you hand up and yell "hang on a minute!"??

[magictime]

35 minutes ago, Machpoint005 said:

 

Hold you hand up and yell "hang on a minute!"??

I think some people might receive that better than others. Not sure Mr. "You don't tell me what to do" would have appreciated it. But yes, again, with hindsight, maybe "Do you mind if we get wait for a straighter stretch?"

[Arthur Marshall]

1 minute ago, magictime said:

I think some people might receive that better than others. Not sure Mr. "You don't tell me what to do" would have appreciated it. But yes, again, with hindsight, maybe "Do you mind if we get wait for a straighter stretch?"

I can't even hear what someone standing next to me is saying half the time - I wouldn't have a chance of hearing someone on another boat asking me politely to hang on a bit.

[RLWP]

Just now, Arthur Marshall said:

I can't even hear what someone standing next to me is saying half the time - I wouldn't have a chance of hearing someone on another boat asking me politely to hang on a bit.

All those years of trombone playing?

[magictime]

10 minutes ago, Arthur Marshall said:

I can't even hear what someone standing next to me is saying half the time - I wouldn't have a chance of hearing someone on another boat asking me politely to hang on a bit.

Pardon?

[GUMPY]

Surely if a boat is wanting to pass, you indicate its fine to do so at the most unsuitable place (blind bridge, twisty bends etc) stop your own boat and pray  a loaded pair or a widebeam  is coming in the other way.

[RLWP]

4 minutes ago, Loddon said:

Surely if a boat is wanting to pass, you indicate its fine to do so at the most unsuitable place (blind bridge, twisty bends etc) stop your own boat and pray  a loaded pair or a widebeam  is coming in the other way.

On the one hand, you get a good half-hours entertainment, on the other, you get held up while they disentangle themselves

 

Swings and roundabouts on that one

 

Mind you, you could put the kettle on and nip inside for a wee while you wait

 

Richard

[system 4-50]

51 minutes ago, RLWP said:

Mind you, you could put the kettle on or nip inside for a wee dram while you wait

corrected that for you.

[RLWP]

2 minutes ago, system 4-50 said:

corrected that for you.

 

could you insert 'wee and a' into that sentence?

[system 4-50]

Just now, RLWP said:

 

could you insert 'wee and a' into that sentence?

this could go on for some time...

[RLWP]

1 minute ago, system 4-50 said:

this could go on for some time...

Depends how tangled up the boats are

[ditchcrawler]

9 hours ago, RLWP said:

 

Bet you get a really big number when you come out of the tunnel!

 

Richard

No

 

[RLWP]

5 minutes ago, ditchcrawler said:

No

 

Hmm, the ancient Garmin GPS we have had used to suddenly find the boat had leaped forwards at enormous speed

 

They must have changed the algorithm

 

Richard

[ditchcrawler]

28 minutes ago, RLWP said:

Hmm, the ancient Garmin GPS we have had used to suddenly find the boat had leaped forwards at enormous speed

 

They must have changed the algorithm

 

Richard

I use an Ipad

[BilgePump]

Top tech suggestion, lump of lead, a rope and knots in it. You know, it could measure things like....

 

eta:  obviously only works in shallow saucer shaped ditches. For owt else try looking for trailing log., but then if you're in deep water, you know already

 

eta:  Please realise this is all said in jest. Don't put a hundred yards of line out behind a canal boat. Think how many trolleys you will catch, even if the rope misses the prop.

Edited July 8, 2019 by BilgePump

[nicknorman]

46 minutes ago, RLWP said:

Hmm, the ancient Garmin GPS we have had used to suddenly find the boat had leaped forwards at enormous speed

 

They must have changed the algorithm

 

Richard

There are two ways to measure gps speed. One involves measuring the distance between consecutive fixes and dividing by the time. This doesn’t work well!

 

The better way is to use the satellite frequency offset. The satellites operate on a very high frequency and an extremely low bandwidth. So precise tuning is essential and Doppler shift caused by satellite velocity relative to the receiver has to be taken into account. The satellite’s known precise transmission frequency has to be tweaked / offset to allow for the Doppler shift. Satellite relative velocities are known from the ephemeris data and so the receiver velocity can be deduced with great accuracy, without needing successive fixes.

 

If you look at the spec for GPS receivers they often describe not only maximum velocity limits, but also maximum g (acceleration) limits. These relate to the maximum frequency offset and the maximum rate at which the offset can change (limited by filtering).