When fabricating your synthetic standing rigging, you may wonder what length you should cut your section of rope for the stay. The trick is to measure and mark everything before you begin working the line.
The moment you open the weave to perform a splice, you will lose your ability to estimate the accurate length of the finished stay. The length of the stay needs to take into account the amount of line that will be buried back into the line, as well as the amount of line that will be consumed in passing around the eye, and the length of the stay that will be composed of the lashing and deadeye.
The simple method to calculate this is:
Length of the stay + Perimeter of Thimble + Amount buried - Length of deadeye - Length of lashing
The length of the stay is the distance from the mast tang down to the chain plate.
The perimeter of the thimble is easiest to calculate by wrapping the line around the thimble and measuring the length involved.
The amount buried is 72 times the diameter of the line in millimeters. You will also want to taper the end of the tail that gets buried, so it is wise to give yourself the minimum amount of bury before the taper begins. This will ensure that you are not going to end up with insufficient bury on such an important splice.
The length of the deadeye tends to be around 1 foot.
The length of the lashing is up to you, but I recommend planning it to be around 3 feet. This distance gives you plenty of leeway in case your stay comes out a bit long, and it places the lashing in harms way of the lazy sheet. This means that most of the chafe will occur on a disposable lashing instead of an expensive stay.
Once you have all of these numbers calculated, it is time to mark it on the line before you cut it off the spool. When you mark your points, you can then make sure that everything is correct before you cut the line. If you cut the line too short, you will not be able to make the stay the correct length. If you cut the stay too long, you can always trim it shorter. This is why I like to cut a few extra inches of leeway on each end just in case I find that I need a bit more length.
When you stretch out the line to cut, you will start at the bitter end. For this example, we will do the math using 9mm line.
The first point in will be the tapered length. To taper the end gradually, it is best to do this over 2 feet, where the taper runs 1 strand every few weaves.
The next point to measure is the amount that will be buried. For 9mm line, that would be 9mm x 72 = 648mm or 25.5 inches. After the 2 feet of taper, you then need 25.5 inches of bury. This comes out to be 4 feet, 1.5 inches of tail to be buried on one splice.
At this point, you have the taper and the bury marked on the line. Now you will need to measure and mark the thimble section. Simply place the throat of the thimble at the tail mark and work the line around the thimble, then mark it again. You want to make the eye that goes around the thimble loose that way you can easily replace the thimble if it fails. The looseness of the eye can be closed by a small seizing knot to hold everything in place.
All this length is what will lay outside of the length of the actual stay. Now that the tail portion is calculated, measured, and marked, it is time to measure out the length for the actual stay.
The length of the stay is the span from mast tang to chain plate minus the four feet of the lashing and deadeye. For the sake of the example, let's assume that the distance is 50 feet. If you are going to have 3 feet of lashing and 1 foot in the deadeye, this would mean that 50 - 3 - 1 = 46 feet of length.
Your length of line would be as follows:
2 feet for taper
2 feet for bury
8 inches for thimble
46 feet for stay
8 inches for thimble
2 feet for bury
2 feet for taper
As you can see, the cut length of 51 feet and 4 inches long.
When you finish fabricating the stay, you will notice that it will be much shorter than 46 feet long that you were trying to achieve. This shortness is due to the constructional stretch, which at this time can be thought of as potential constructional stretch.
The more weave you opened to perform the splice, the shorter the stay will appear to be. Upon initial tensioning, this stretch will be removed and it will nearly approach the ideal 46 feet of our example. After a bit of creep during Phase I of the dyneema lifecycle, you will find that it will reach closer and closer to the ideal 46 feet desired.
This is very important when working with headstays, where you want the eye splice to sit as low to the deck as possible, allowing you to have your first hank attach to the stay as soon as possible. Proper measuring can safely place this eye 24 inches above the stem, where the deadeye is 12 inches, and the other 12 inches is the lashing.
If you have to err, it is best to err on the short side. If your stay is too short, the stay will have a longer lashing and will still achieve the same amount of proper tension. If your stay is too long, you will end up two-blocked and you will need to redo your splice and tension it all again.
