I had no idea there were so many different plates for the 21 ftrs. Especially on some of the Prosport's !!! I'm sure it's been a work in progress. Mine sticks out 4.1/2" is 19.1/8" wide-- it's straight across at the back with the outer edges turned down. It can be a handful to drive at higher speeds. Now I'm wondering how much of that can be from my plate ?? Would like to know what the dimensions are of the one shown in Allison's webpage. It appears in the picture that the trailing edge is far from being straight across like mine.
There seems to be a general consensus that the longer one is better for those who struggle with hole shot due to load and or elevation.
But there is some tradeoff in high speed handling and traversing BIG waves. I'm one who struggles with hole shot and has to run big open water. Some recent threads have me curious to find what works best for others especially with the handling and rough water. My rig is also prone to porpoise at slow speeds (some props) are worse than others.
I tried the Allison cavitation plate foil on my last Allison but did not like the way it caused the boat to act in big waves.. It does what it's designed to do (pushes the nose down) !! On a 2003 in big waves that will get you wet !!!
Would be real nice to know ALL the particulars of D.S. setup in those Columbia river videos ??