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Old Aug 24th 2019, 04:34 PM   #1
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Capstan Equation

I need help please, as this math is beyond me
For capstan , bollard frictions.
I even have trusted document that has let me make sense and understand many things of knots and bollard frictions.
.
Jrre.org/att_frict.pdf
gives .25 coefficient for nylon rope on aluminum pipe for brake force.
.
I have made this chart, the paper shows brake force same on larger pipe, friction by degrees of contact.

.
I am seeking to mostly fill in 180 on to table assuming same coefficient to show pattern.
But , would also like to show 90, 360, 720 please.
Wouldn't mind knowing how to calc or some tool even.
This would help immensely to define more about working knots and rigging, thank-you!
.
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Old Aug 28th 2019, 05:51 AM   #2
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If you have Microsoft Excel available to you,
try placing the data into a graph and fitting an exponential trend-line through the data.
This will give you an equation fitting the data.

However I doubt that, in practice, the actual friction is as precisely matched to the theoretical friction, as this table suggests.

For a practical estimate of the friction, I would suggest that a simple linear interpolation (straight line between the adjacent points in the table) will suffice.

Having said that, the gap between 5pi and 7pi is a bit large,
which will result in a simple linear estimate being less than ideally accurate.
If data in this region is vital, then the more accurate exponential fit is indicated.
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