Boston Whaler provides information about the engine power that will be suitable for their boats.
The propulsion engine power specified as the minimum power is the power that will get a very lightly loaded boat onto plane.
The powered specified as the maximum power is the power that should not be exceeded and is required to be specified by a boat builder according to federal regulations.
Choosing the minimum power is not often recommended, as a boat will be unlikely to ALWAYS be used with a very light load. About the only reasonable basis to choose the minimum power is perhaps to allow the boat to be used on a particular body of water where authorities have imposed a limit on the maximum horsepower for boats on that water.
Choosing the maximum rated power is more often recommended. The boat will be more versatile, and will be able to accelerate onto plane with heavy loads.
For your boat you are asking about, the OUTAGE 17 II, the specifications for power are:
Minimum HP = 90
Maximum HP = 150
Your inquiry seems to imply that an engine is about to be purchased for the OUTRAGE 17 II. Generally outboard engines are quite expensive when bought separately, that is, not as a bundle with a boat. For that reason, I do not recommend you buy a 90-HP engine. It won't be a good investment, as you may find that the boat is not particularly fun to operate at this power level. If you then decide to buy another engine, recovering most of your purchase costs of the 90-HP will probably be very unlikely.
Also, with a 90-HP engine, the rated horsepower will probably require the engine to be able to accelerate into the upper end of its engine speed range at which is is specified to produce the rated power. The propeller choice will need to allow the engine to reach that engine speed. When weight is added to the boat, the engine may no longer be able to accelerate into the engine speed range where it can produce its rated power, with the result that the boat will never be able to attain a speed that permits planing.
Regarding the 115-HP engine, while it is greater than the 90-HP, one should look closely at the configuration of the 115-HP model. If the 115-HP engine is a four-cylinder engine and part of a family of engines that includes models rated for more horsepower, then the 115-HP model may be a suitable engine on the basis that it is a conservatively rated engine. On the other hand, if the 115-HP engine is a three-cylinder or very small displacement four-cylinder engine that is from a family of lower-power engines, that 115-HP engine might not be particularly suitable on the basis that it is just a souped-up variant of a lower power design and may only develop its rated power output in a very narrow engine speed range.
Of course, to recommend that a 150-HP engine be purchased will be a good recommendation, but the added cost may be too much burden. But a 150-HP engine will typically have a wider engine speed range at which it will be able to develop its rated power or enough of its rated power to give excellent acceleration of the boat onto plane or to maintain the boat on plane at lower engine speeds. Being able to maintain a boat on plane at a lower engines speed and thus a lower boat speed is a very desirable characteristic of an engine, as it allows the boat speed to be chosen to suit the sea conditions, rather than having to choose a boat speed to suite the engine's power band, which often results in having to operate at too-high boat speeds in rough weather.
NOTE: the Boston Whaler specifications for engine power can be found in my compilation of data in the REFERENCE section at
Dimension and Production Informationhttps://continuouswave.com/whaler/refer ... tions.html