Page 27 of D-Day: The Darkest Day mentions the above as “reaching speeds of 22 knots…”
I think you’ll find that their top speed was nearer 42 knots; 22 knots is chugging along a lot slower than destroyers, cruisers and even battleships. I would suggest changing the Speed factor to 3 from 2…in addition I would think that the Higgins boat on p.29, which has a Speed factor of 3 should actually be 2…I had visions as the landing craft speeding past a chugging MTB !