Which would be the most fuel efficient assuming each powerplant having the same HP and was installed on the same boat in a planning hull boat of 21' I believe both the straight inboard and the OB would be faster but by aprox. how much percentage?Also the same question for fuel. If this has been answered before please point me in the right direction as I am new to the forum, and learnin the format and system.Thanks,Scott
Scott, In my opinion.An true inboard is a very efficient machine for a center console type fisherman for the following reasons.1. With a closed cooling system, the maintenance is simple. Not much different than a car.2. The weight of the engine is in the center of the boat and the center of gravity is low. This is important in controlling rocking in a deep V hull.One of the finest fishing machines I have ever been aboard was a Shamrock Center.Disadvantages:1. Inboards need plenty of water underneath them. They are not necessarily a "skinny water" craft. 2. They can be a handfull to control around docks and so forth for a novice.3. They represent challenges in trailer design if they are to be trailered.I/O'sI/O's are the most complicated of the lot-in my opinion. True, the engine is automotive based yet the outdrive is complex. They also have an engine box at the transom which clutters the fishing cockpit. The only way around this is the use of a jackshaft system.OutboardOutboards are by far the choice of center console fisherman. 1. Most are designed to live well in salt water.2. They offer good shallow water ability.3. The new four strokes and direct injection models offer fuel economy rivaling that of I/O's and Inboards with half the weight.The only real disadvantage is the engine hanging out the back of the boat cluttering the fishing area a bit.
Each boat has its own characteristics, so it really depends on the type and brand of boat. The weight and hull are very important factors. As an example, a boat that weighs 3,000 lbs vs. a boat that weighs 6,000 could use half the horsepower.It looks like you want everything.....best speed, best fuel economy, and best ease of maintenance. It's hard to get everything, but I'm sure there is a best combination. Usually the boat manufacturers set the boat up using the best combination for its specific use.With that said, it's my opinion that the inboard and the inboard/outboard would perform about the same. If the inboard boat was a "keel" type, then it would be slower and require yearly maintenance of the propeller shaft. The I/O would probably be a little faster, but require more maintenance of the outdrive. Fuel consumption difference between the two would be close and would probably come down to prop. Again in my opinion, the outboards would be less costly to maintain. But you inquired about 2-strokes, not 4-strokes, so fuel economy would probably be worse witht he 2-strokes. Not with the 4-strokes.Horsepower is horsepower, whether its inboard, outboard or inboard/outboard.