Originally Posted by MarkJ
Would 3/4 inch Dyneema have a higher SWL than a SS keel bolt? Gotta be close.
I believe the SS keel bolts in this case are M28. So, taking a standard material factor of 1.15, and a 0.2% offset yield for the AISI316 as 355MPa.
Then the permissible yield strength (not ultimate tensile strength) of a single
M28 bolt would be:
(PI/4)*(28^2)*(355/1.15) = 189555N... 19322Kg
However, we cannot compare yield strengths directly as Dyneema doesn't have one (too stretchy) so we cam compare Ultimate tensile strengths (break point).
A typical AISI316 stainless would have a UTS of 550MPa. The best Dyneema is up in 2800MPa.
The breaking load require for the M28 would be:
The breaking load of the 3/4" dyneema would be:
It looks like Dyneema has it, but remember that this is comparing one dyneema line to only one keel bolt. Obviously there's more than one keel bolt.
Another thing not considered here is that the yield strength of the cast iron in the keel is only around 130MPa as opposed to the 355Mpa of the SS. It's more likely that the threads in the keel.would shear before the SS bolts.
This calculation is also straight tensile and doesn't account for moments, shear etc on the keel bolts nor directionality of the dyneema line.
Just thought somebody might be interested!