I ordered my net from the Memphis Net & Twine Company. If you have your own favorite gill net vendor, you can probably order an identical item from them. I have NO financial ties to MN&T other than being a satisfied purchaser of their retail products.
Here is the link to the product page on the MN&T website. Below is the exact info from my order information page, shipping is not included in the price. One pound of this net (minimum order) will make 7 or possibly 8, 9-1/2 foot square nets.
Description: 3 in. sq. mesh, 12 ft. deep
If you would like to try an alternate net part number please read the Alternate Net Substitution section below.
Optional Net Math Section
You may have noticed that the catalog description lists the net as 12 feet deep while I have claimed it is 9-1/2 feet square, why the difference? Let us first deal with a hypothetical net that has 3" mesh and is 3 meshes deep. You might think 3 x 3 equals a 9 inch deep net, but that would be incorrect. Visualize the meshes as diamonds stacked point to point and NOT squares stacked like bricks. Reference Fig 1 and it becomes apparent that the depth of our hypothetical net is nearly 12-3/4 inches. To extend this example to MN&T sku# 263, 27 x 4.24 equals 114.48 inches, divide by 12 and we get 9.55 feet deep. So where does MN&T get the 12 foot depth figure? They are building a certain amount of droop, when used in a fishing application the diamonds will be longer vertically than they are wide.
I have included a spreadsheet that will allow you to enter different figures to see what size net you will end up with, and how many nets you will get from a pound of that particular net. If the spreadsheet returns a zero for waste material, you may want to subtract one net from the total expected. The default numbers in the spreadsheet are for MN&T sku #272.
Alternate Net Substitution
I will use MN&T catalog and part numbers in this example, but as long as you know the correct variables, any net vendor should work. Using the spreadsheet is important, if you don't own MS excel, consider downloading OpenOffice. An excellent free MS office replacement that will allow you to view and edit the Net Math spreadsheet.
Please consult Fig 2 or have the spreadsheet open for this example. The top section of the spreadsheet contains a section called Mesh Count Estimator. This will help you calculate the mesh count you need to reach a desired net size. In this example I have entered 3.5 (3-1/2" mesh) in the Mesh size cell and 9.5 in the Desired depth cell. This should closely match the sku #263 net's overall size but with a 3-1/2" mesh instead of 3". The computed result, 23.03 appears in the mesh count cell. As fractional net meshes don't exist, just round to the closest integer, 23 in this case. Next, we will browse through the MN&T catalog for a 3-1/2" mesh net 23 meshes deep.
Go to the multifilament net section of the MN&T web catalog, then select #208 twine size and browse through the 3-1/2" mesh part numbers to find a net closest to the 23 mesh count. Part number 272 fits our specification perfectly.
Now enter all the information from the 272 page into the yellow cells on the Enter line of the net properties section of the spreadsheet. The Square depth cell tells us this net will be 9.43' square. This is also the spacing for the knots of your spreader string in step 9. The Knot cut point shows we need to count 46 knots and then cut between knot 46 and 47, the Cut length cell tells us knot 46 should fall at 161" on stretched netting. We can also assume that because the overall weight of the 272 net is slightly less than the 263 net, it should fit fine in the net holder.
I would advise waiting to build the net holder part of the launcher section if you try any radically different mesh, twine, or overall net sizes. Once you have the net constructed, fold it up and make sure you have the correct size PVC holder.