Lock gates are a real problem because when they get manufactured incorrectly for what ever reason, the new design "feature" then stays for the next however long, till the gates have to be replaced, then there can be an argument about what is historic! This has been happening since the canals were built, and has created all sort of anomalies, all over the places. In recent times this has been exasperated by the closure of lock gate workshops, we now only have two left, most canals had at least one workshop if not more, and they built the gates, as they saw fit, with rules caulked on the walls in some cases.
This has lead to all sorts of messes with look and feel of a canal. For a classic example of how it can go wrong, take a look at the Rochdale canal, which has Northwich style gates as per the Chester canal, L&L style gates as per the Appleby, LL style Northwich gates. Carris Mill style gates, and others! There are no Rochdale gates left as I remember them, however when I started to attempt to justify returning to that design I discovered they where not the original design either. This raises the question of just what is right historically. Should the Ashton gates still be painted Brown & White as I remember them from when I was a kid, or was there another colour scheme before that?. On top of that the listing of the Manchester locks on the Ashton happened so late - 1997 that the listing says they should have steel balance beams, hydraulic paddle gearing and black and white colour scheme. It will take a major shift to get the listing change and the new gate had to have its steel beam repaired and refitted, even though historically its totally wrong in my book.
In an attempt to stop this C&RT are attempting to capture what a canals standard gate should be and record it in their CAD system. I am attempting to get these drawing made public. They require this given that they are moving to CNC manufacture of lock gates. The new head gate which have just been install this winter on 'hampton were machined in 47 minutes on a CNC machine, rather than taking 3days to do on the machines currently installed at Bradley.
It then took the same 2 days to assemble the gate.
Given this the BCNS and the NAG have agreed with C&RT what a standard BCN gate should be, and a set of drawing have been produced. If you would like a copy I will attempt to procure you a set.
The best place I think to go for a set of drawing for a new lock chamber would be Tameside Planning Department. They specified what the new locks on the HVNC should be. In particular lock 4W & 6W which are totally new locks built in 1999. They were responsible for specifying the new chambers and having a contractor build them. being a council these drawing will still exist somewhere! They are not as clever as the Perry Bar locks or the original locks on the Droitwich Junction canal which were probably the peak of narrow lock design. Followed by the new locks on the Warwick canals when the GU modernised, however they are broad locks and have some significant differences. I attach a few images of Lock4W Not both top paddle are lineside.
The next thing you will need to wrestle with, is from what are you going to make your lock gates. Follow current C&RT convention and build them of crappy French Oak with a life expectancy of about 25 years plus or minus 5 years. Or do as the River Avon Trust had done and make them of steel with a life expectancy of 50 years followed by a refurbish and then another 50 years. C&RT also have steel gates made in the late 1960's / early seventies which are currently being refurbished.
There is a pilot project underway within C&RT to investigate swapping to all(well mostly all) steel gates, two locks have already been done one set on the K&A and another set on the River Lee. Even after having people sit by the gates on the K&A there has been very little negative feedback other than the balancing is incorrect, which is due to the wrong Balance beams being fitted ie the old one rather than having new ones which were made to go with the gates, a cost/time decision taken when the two sides of the coin forgot they are connected, a problem all organisations have.
Marple locks were originally a great piece of design. When the weir crests were set correctly the locks would self fill before the bywashes kicked in. They had spill weirs for both top and bottom gates, All the gearing was ergonomically laid out, one top ground paddle , which was bigger than those now fitted and then two danny paddles driven off one spindle in the top gate. At the bottom end were a highly gear ground paddle attached to a very small paddle, then a large ground paddle, and lastly a large gate paddle on the far gate. The bottom ground paddles were removed during and post restoration in the mid 70's, the culverts bricked up and two gate paddles installed, made the locks a lot slower. I attach a few images of Marple as it was in the late sixties. The last image 7775 you can just see the three paddle posts at the bottom end right at the bottom of the image.