Several years ago I speculated that
use of twin engines of 150-HP or less might become less common as there were 300-HP single engines being produced. Twin 115-HP engines on an OUTRAGE 22 would be an interesting rig. The concern will be with the total transom weight, which should be quite heavy, and if the boat can be pushed onto plane by one engine.
Boston Whaler did not publish any specification for maximum transom weight for an OUTRAGE 22, but they did for the equivalent commercial and government hull, the 22 GUARDIAN. The maximum transom weight was 720-lbs. See
http://continuouswave.com/ubb/Forum4/HTML/002449.htmlfor more discussion on maximum transom weight for older classic Boston Whaler hulls.
According to Yamaha, their
F115 outboard engine weighs 377-lbs. Two of them would weigh 754-lbs, just slightly over the recommended maximum transom weight. The 377-lbs figure is for the long-shaft (20-inch) model, which would be appropriate for use on the 22-foot hull in twin engine configuration. Compare at
http://continuouswave.com/whaler/reference/specifications.html#hulls20-22.
To the 754-lbs total weight you should add the two propeller weights, the two hydraulic steering rigging weights, and a few more pounds for the lubricants in the engines. (The manufacturers like to quote the lowest possible weight in their specifications and usually exclude a propeller and lubricants.) I would expect that the total transom weight will be over 800-lbs.
The best indicator of the transom weight load on the hull is perhaps inferred from the position of the engine splashwell drains. The drains in the engine splash well ought to be just at the static water line or just above the static waterline. Otherwise those through-hull openings are not working as drains but as inlets for water to come aboard. I base this analysis on the notion that the designer of the hull must have located the engine splashwell drains on the transom to work as drains, which requires that their outlet not be underwater. That said, however, seeing Boston Whaler classic hulls carrying so much weight on their transom that the engine splashwell drains are submerged at static trim is fairly common.
If you have a twin engine rig on a planing hull boat, and the hull won't plane with just one engine, the utility of twin engines is reduced somewhat. I had a set-up on my 20-foot hull, a REVENGE 20, with twin 70-HP engines. (I bought the boat used and rigged that way.) With a single 70-HP the boat just could not overcome its bow wave and get onto plane. It was close, but a plane was never achieved. With a 22-foot hull and twin 115-HP engines, I suspect that it may be possible to get on plane, but it may require careful selection of the propeller pitch. To get on plane with one engine, the pitch of the propellers might need to be a bit smaller than optimum for two engine operation, if you don't want to change propellers for running on a single engine.
I did run for a short while on another REVENGE--I can't recall if it was a 20 or 22-foot--with twin 90-HP Honda engines. What I remember from that ride along was how quietly the engines ran. They sounded more like electric motors than outboard engines, at least compared to my twin 70-HP classic Yamaha two-stroke-power-cycle outboard engines that made a lot more noise when running. I don't recall if we tried to plane on one engine.