Question for solo narrowboaters on the Thames

[Scholar Gypsy]

8 minutes ago, Neil2 said:

Yes I was thinking how much would the boat move fore or aft as the water falls/rises, also isn't there still a chance the bow might get hung up when descending?  How do you know how much bow line to attach?

Pythagoras can help you. For example if you use a 20' fixed line and the lock rise is 4' which is quite typical, then the boat will move forwards or backwards 5 inches.

[Neil2]

16 minutes ago, Scholar Gypsy said:

Pythagoras can help you. For example if you use a 20' fixed line and the lock rise is 4' which is quite typical, then the boat will move forwards or backwards 5 inches.

Ah yes I see, the bow line forms one side of a right angle triangle and if you assume the line is level before or after the exercise once you know the rise/fall you can calculate the other side of the triangle - thanks!  

 

 

[Scholar Gypsy]

10 minutes ago, Neil2 said:

Ah yes I see, the bow line forms one side of a right angle triangle and if you assume the line is level before or after the exercise once you know the rise/fall you can calculate the other side of the triangle - thanks!  

 

 

I have not allowed for the line stretching under tension. 

[ditchcrawler]

On 16/08/2018 at 13:01, Dave123 said:

This has worked for me so far - although I haven't been up hill in any of the deeper Thames locks.

That's how I do it on self service

[blackrose]

14 hours ago, Neil2 said:

 

Edited August 19, 2018 by blackrose

[blackrose]

14 hours ago, Neil2 said:

... also isn't there still a chance the bow might get hung up when descending?  How do you know how much bow line to attach?

I tend to overestimate how much bow rope I need for this reason. But if you've taken the rope forward there's no chance of getting hung up until that bow rope is vertical. That would be a long drop. 

Edited August 19, 2018 by blackrose

[LadyG]

I struggle with that, esp as Pythagarus might have had 16 digits per Greek foot, help me out here, which is the hypotenuse?

EDIT yes, h must be the longest measurement, so is that the length of the boat or the length of the bow rope to bollard when in the bottom of the lock?

EDIT x 2~       20 x 2 = 400 , 4 x 4 = 16,  what now ,  assuming no calculator .............

5 x 5 = 25

25/12=2.08, ??????

Edited August 19, 2018 by LadyG

[Scholar Gypsy]

20^2 = 400

4 ^ 2 = 16

400 - 16 = 384

Sqrt(384) = 19.6 (approx) - if you don't have a calculator you have to guess this by trial and error. 

 

So the horizontal distance from bollard to boat reduces from 20 (lock full) to 19.6 (empty) , a difference of 0.4 feet or about 5 inches. 

 

[There is a whole page on Wikipedia on computing square roots.  Not something I have ever needed to do.  https://en.m.wikipedia.org/wiki/Methods_of_computing_square_roots ]