---

Dick Fisher, President of the Fisher-Pierce Company, wrote in a letter dated 6/10/1970, entitled: Advance Information on Boston Whaler "Outrage"

Outrage is a rugged, seaworthy, fast twenty-one footer, made for any single large outboard motor, or twins totaling up to 200 horsepower.

Looking through photographs on this site and elsewhere on the net, revealed single outboard power ranging from a 55 HP 4 stroke Bearcat to an Evinrude E-Tec 250 HO.
Yes, there is the occasional twin-outboard rig, e.g, Mark Sr's personal page showing an O-21 rib-side rigged with Johnson 70 hp outboards.

I recommend a thorough inspection of your 1973 hull prior to making a repower decision. While I have never seen a transom failure on an O-21, I have seen a few bottom catastrophic failures of the hull on O-21 ribside and smoothside models. Specifically, a simple hammer tap on the bottom in the area of the planing strakes, located 3-4 feet forward of the transom bottom will determine if you have any potential delamination/separation of the foam from the hull.

I also recommend weighing your hull, when the old engine is removed and compare the weight to the factory specs.

I personally consider a single outboard in the 115-150 hp range as being more than sufficient horsepower for teenager-related water sports.