It depends. Your Bill Shaw designed P27 displaces approximately 5,800 lbs. Certainly, in calm and even moderate conditions, you can sustain hull speed for extended periods at less than WOT. It is certainly adequate to get you in and out of your slip, in relatively protected environment, in almost any conditions. The only area of concern would be extended motoring/motorsailing in adverse conditions, pounding into chop and waves, for hours at a time, because you may have to push the engine close to WOT. I would rather sail in those conditions, if at all possible, so I rarely motor into chop except to get out into the river. If it is an older engine, with older seals and less than optimal cooling, you may be stressing it at WOT for hours on end. You will also be burning much more fuel. My boat will cruise at 4 kts, burning a miserly half a gallon an hour; at 5 - 5.5 kts., it burns about 2/3 to 1 gallon per hour. That extra knot and a half requires a lot more energy.I'm going to look at a Pearson 27 with a 12 horse power Universal engine. I will sail the boat on Buzzards Bay, MA where there is considerable current and chop. Can this engine push the boat at or near hull speed?
Thanks for your help.