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An inboard motor is one with only a small portion of the drive shaft, along with the propeller, submerged in water. Typically, in such cases, the main portion of the inboard boat motor is located within the boat, usually near the center, especially in smaller crafts. Inboard boat motors have some advantages and disadvantages when it comes to cruising the water.
In most cases, inboard motors are preferred for water skiing and perhaps general cruising. They typically take less time to reach a plane and do not cause the bow to rise as much as an outboard when reaching that plane. This is also great for boaters who worry about those few seconds when they may not be able to see directly what is in front of them. The inboard motor makes this possible because it does not waste so much energy in raising the front of the boat.
Further, the inboard motor is popular for skiers because it keeps more of the boat in contact with the water. This can make for easier wakes and a smoother skiing experience. Still, some skiers may prefer the challenge that comes along with larger wakes and prefer them for activities such as wake jumping.
However, something is also given up with an inboard motor. The fact that it is in contact with the water so much, at least when compared to outboards, means there is substantially more drag experienced by the boats. This can slow the boat down when compared to outboard motors of similar horsepower. Therefore, the inboard motor may not be the best choice when speed is an important consideration.
This is just one reason why tournament fisherman, such as those who are going after bass or other gamefish species, prefer outboard motors. Also, the inboard motor boat has limited ability to tilt the drive shaft up to get into shallower waters where fish sometimes are. This is compared to outboard motors which can usually be lifted completely, or almost completely, out of the water for access to such areas.
Some claim that inboard motors tend to last longer than outboards. However, this may be explained away as a personal preference or a matter of luck. Two-stroke engines do tend to wear out more quickly than four-stroke engines and inboards are mainly four-stroke engines. However, modern outboards are nearly all four stroke as well, making this distinction no longer valid, at least for newer models. An inboard motor also tends to cost a little more than a comparable outboard motor, which may give some the perception the quality is just slightly better.