You want to reach hull speed @80% of max rpm {1065.6rpm shaft}( for many reasons) and you want the boat to advance at the same rate as the prop .
So with a 13x11 prop at 1065.6 shaft rpms you are trying to push the boat at 11.1mph ( twice as fast as it should be ).

With a 13x11 prop turning at 1332 rpms (shaft) , you would be doing close to 15 mph or 14 knots + or - OR in order for you engine to max @ 3600 rpm with a reduction of 2.62 giving a shaft speed of 1332 rpms the boat would have to be going 14 to 15 mph .

I would say you need a 13x6 or 12x6 or 10x7 . You have too much diameter and too much pitch for 13.? HP which you only reach at 3600rpm , at 2100 it is much less. Your peak torque curve is near 2880 rpms ( engine ) and a 13x6 would put you in that ballpark .

Too much diameter is hard to turn over and too much pitch is just as bad.
I bet your rpm's drop radically when you put her in gear at idle , almost to a stall .

Will your tach read above 2100rpm when not in gear?

This is a 2 blade prop , right?

When you talk with anyone , make sure they understand it is 5000lbs you are trying to push to no more than 6 knots .

If your prop is too big and there is not enough 'tip' clearence , you will get vibration as the prop passes the hull . You need aprox. 18% dia. in clearence, 20% is better, so your tip should not come within 2.5" of the hull .

It is a big ballancing act to get the prop right .