Every spring, as masts are plopped back on decks, I see folks out there with rig tension tools. I hear folks complain that the tool does not cover the size they need. As an engineer that has been responsible for tuning structural cables up to 1 1/2-inch in diameter, we don't need no toy tools. This method works for ALL sizes, since stretch is a steady function of % breaking load.
Yes. the tools are handy, particularly for fine tuning. For big wire, there are still other methods... but that is another chapter (hint: use a scale and pull to the side, using simple trig. On bridge wires we just use gravity and sighting.).
This specific wording is borrowed from Seldon Spars
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The following materials are
required:
- A 2 metre long measuring rod (a folding rule is recommended)
- Adhesive tape
- Vernier calipers
• Start with the cap shrouds only hand-tight. The rig is stayed with the lower shrouds and the
forestay and backstay.
• Tape the upper end of the folding rule to the starboard cap shroud. The lower end of the folding
rule must be approximately 5 mm above the upper end of
the wire terminal.Measure the distance between
terminal and folding rule exactly. This is index 0, let’s call
it point A.
• Tension the starboard cap shroud until the distance is A + 1.5 mm between the terminal and the
folding rule. Measure using the vernier callipers.
• Leave the folding rule attached to the starboard shroud, and move across to the port side and
tension the shroud rigging screw the equivalent amount.
• At intervals, check the starboard side to see how much
the folding rule has moved from the end
terminal. When there is a gap of A + 3 mm, the cap shrouds are
tensioned to 15% of the breaking load of the wire (3 x 5% =
15%).
If the mast is not straight, adjust
the lower shrouds, intermediate shrouds etc. There is more
information on this in the chapter dealing with your rig type.
The folding rule method can be used
on other stays, such as the backstay and forestay (without jib
furling system). It can also be used for Dyform- or rod rigging, but
please take the difference in stretch into account compared to 1 x
19 wire.
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Stretch per 2 meter at 5% of breaking load
1 x 19 wire Dyform Rod
1 mm 0.95 mm 0.7 mm
What is the stetch per meter of 7x19 wire at 5% of breaking load
ReplyDelete1x19 wire is most common for standing rigging. 7x19 is used for things where more flexibility is needed, such as wire halyards.
ReplyDeleteThe stretch of 7x19 is about double that of 1x19, or about 1 mm/M at 5% BS.
Why use a folding rule instead of a standard Tape Measure? They are both as as accurate, in fact the tape measure should be more accurate than a wodden folding rule. And you can make it as straight as the shrouds. I know this is what Selden also recommends, but not sure why.
ReplyDeleteCan you share some insights on this?
I'm planning to follow this method and I'm just wondering if I really should buy a folding rule or can I stick to my existing Tape Measure?
Thanks,
Rui
Re. Folding rule. Just a name someone gave it many years ago. Not me.
ReplyDeleteThis approach to setting pretension in construction predates common use of tape measures. It goes WAY back.
ReplyDelete