First ...This is only my opinion and the way I break my engines in. Its basically as per the manual but adding the smooth short 2-3 second wot full rpm bursts with only a driver in the boat.
There is a lot of controversy on this subject. A couple that are most important are not to overload the engine, ie with a lot of people or ballast in the boat, or by performing hard accelerations.
Personally I feel that smooth acceleration to wot and letting it sit there for 2 - 3 seconds during the break in procedure (every so often, once per 5- 10mins or so) will help the rings seat better as the combustion gases will force the rings out to their maximum tolerance as well as give it a better break in over all. Also, after break in, do not go crazy with immediate long wot runs. Work your way up to them.
Again , there will be some who disagree, this is my opinion only, so take a pill if you do.