Question 1111057
We translate "the square root of the length L in feet of the boat’s waterline" as
{{{sqrt(L)}}} .
 
If "K in knots is 1.35 times that,
{{{highlight(K=1.35*sqrt(L))}}} or {{{highlight(K=1.35sqrt(L))}}} .
 
NOTE:
I do not know what "the boat’s waterline" means,
but I know what  "the square root of" means.
{{{matrix(2,11,
L,18,20,22,24,26,28,30,32,34,36,
sqrt(L),4.243,4.472,"4.690",4.899,5.099,5.282,5.477,5.657,5.831,"6.000")}}}