I made the Horse Knotting Fixture after a few attempts to tie evenly spaced knots under the jib boom(s) failed.
I did not like the results, So the Fixture was born.
I took a piece of maple wood.

Made it 3/8" wide by 3/4" high by 5 11/16" long.
A couple of books I have, mentioned the knots as being between two or three feet apart, to provide a foothold for the seamen.
I am working on the Victory by Corel, which is 1:98 scale. Three feet works out to .367".
I modified that slightly and my spacing is .350", which is 34.3", close enough, because that enabled me to cut the grooves in my Sherline Milling machine. One turn of the handle is .050". So seven turns works out fine.
I used a 1/32" (.031" ball end mill, which gave me a nice radius at the bottom of the groove for the line.

First I set up the piece in the vise on the Milling machine. Then, I cut a slot the entire length of the piece, which is 5 11/16" long.
that slot is central to the 3/8" width and 3/32" deep.(.094").

Then, I cut slots at right angles to the central slot across the 3/8" width, starting at 10 MM (.394") from one end, hereafter known as the reference end. You can mark it if you wish.
The slots should be at the same depth (.094") as the central slot.

So, the result was a total of 15 slots in the piece.
I drilled for, and installed two eyebolts in each end of the Fixture. Central to the 3/8" width, and 3/16" from the bottom., opposite from the slots, which are on the top of the Fixture.
The eye bolts were cemented in and they are there to secure the ends of the main line that runs down the length of the Fixture.
OK, So now, we put the Fixture in a vise.
By experimenting, determine what is the shortest piece of line you can use to tie the knot you want to work with.

After you know what you want to use, cut a number of pieces, and put them into the cross slots. Adjust the number to what suits your particular model, and or jib boom(s).
Now, put a line in the central slot. It should be a snug fit. Secure the ends in the eyebolts at the ends of the Fixture.

Then you start at one end, tie a knot , pull it tight, add a very small amount of diluted white glue to the knot. Keep going until all the knots are tied and glued.

Unfasten the main line from the eyebolts.
Now, carefully strip the knotted assembly from the Fixture. Only pull straight up on the knots and line so as not to provide any lateral force to disturb the spacing the Fixture gave you.
You may need to use a pair of tweezers to do this.

Put the assembly on the side to dry.
Clear the Fixture of any excess glue.
This Fixture can also be made in a precision circular table saw, like the Preac,
if you make a little fixture for the spacing of the slots.

Make as many assemblies as you need. Install them on the jib boom(s) when you are ready.
And, as a great gentleman, named Franz Luber (who took the time to teach me a lot of tricks) said, when I goofed, "make a newie one" (not a typo, just the way he spoke!)