Tether length Formula

[Gina McLauchlan]

This is one carried over from the old forum

If anybody happens to remember how to calculate approximate tether length by the diameter of the winch drum and the diameter of the tether, I could use some assistance.

Thanks

Mike

[DANFROV]

I do not kow if this makes sense.

Dan

NW = Number of Wraps 35 =Integer Drum Width divided by diameter of product
NL = Number of Layers 4 =Integer Flange Diameter less drum Diameter divided by 2 x Diameter of product
D = Diameter of Product 0.028 = Diameter of conduit/wire
d = Diameter of Drum 0.6 = Drum diameter

Maximum Total Length = π x NW (NL x d + (NL)² x D)

Maximum Total Length = 313.28

NOTE:
1 If NL is selected as an input it can be a fraction. (ie. 3.5 layers).
2 To determine product weight, multiply length by unit weight of conduit/wire.

[crusty]

if i new what lower case n was i would go look at winch and try it out

[Ray Shields]

Looking on the Web for a formula for a wire on a drum (same thing as tether) I found:-

L = pi(Do^2 – Di^2)W/(4Dw^2)

where
Do = drum outer diameter
Di = drum inner diameter
W = width of drum
Dw = diameter of wire or tether

Try both and see what you come up with!

[subseascott]

Surely there must be more variables to take into consideration than this?
Tether material, oil filled etc. with respect to wire on drum form. atmospheric deployment?
Don’t know as don’t design tethers but just an enitial thought……..

[truered]

when i first started my apprenticeship about 20yrs ago, we used this same method as part of stock control on umblical reels, it has depnedancy on neatness of spool etc… but was proved to be accurate to a couple of mtrs

[Barney]

The length can also be calculated through checking the resistance of a coax or twisted pair. The manufacturer of the umbilical/tether can give you the information.

You could use a TDR on the coax or twisted pair.

If you only have fibres then a OTDR can be used.

Regards,

BARNEY

[Author]

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