[Fr. Frank]

Dunk is right, and so is Strick. It depends upon the hull, and especially on the amount of rocker in the hull. In a previous life, I spent some time as a test pilot (strange name, that) for Wellcraft, testing engine and propeller combinations for new boats, or new factory power set-ups for renewed models.
For instance, Wellcraft chose NOT to make a 19' bracketed OB version of the Scarab hull after testing showed that that configuration porpoised continually without putting K-planes down in the water at 10+ degrees at all times - not enough hull length to rocker.
Here's a rule of thumb we came up with, which Wellcraft follows to this day. If you set the hull on the ground, balanced from side to side with the keel line at the transom touching the ground, at 45% of the vessel LOA the hull must be in contact with the ground. In other words, there must be no appreciable hull rocker in the aft 45% of the boat in order to put a bracket on the hull.
The last Wellcraft production hull to violate this rule was the 1990 26' Scarab OB center console. Rigged with a B-bracket for twins, it came factory equipped with either twin Yam 130's, or twin Merc 115's. On plane, the boat porpoised, always. Testing w/ V6 OB engines showed the aft CG made it worse. When we tested the same hull with transom mounted engines, the problem was greatly reduced. The hull had a 37% rocker point.
I have seen many 20 SeaCrafts with bracketed OB's, and all seem to run fine. A 20' Seacraft has a rocker point GREATER than 60%. So does a 23".
On the other hand, my 20' Seafari seems to like it's transom mounted V6 Merc [img]/images/graemlins/cool.gif[/img]