12/2/2023 0 Comments Inboard vs sterndrive![]() ![]() A sterndrive engine, or an inboard/outboard (I/O) engine, combines an inboard engine with an outboard drive unit, making it the best of both worlds. What does stern mean, though? The stern is the outside rearmost part of the boat, as opposed to the bow. Since the outdrive is placed at the stern of a boat, it is also called a sterndrive. The outdrive is either hooked with the inboard engine or an outboard motor mounted on the rear end of the boat. This drive unit transfers power to the propeller on the outboard unit, propelling the boat through the water. The outdrive includes a drive shaft, a propeller, and a gearbox. It converts engine power into movement via a combination of an inboard engine and an outboard drive unit that is mounted to the transom of the boat. An outdrive is a propulsion system used on boats. ![]() Is It Better to Have an Inboard or Outboard Motor?.This may matter less on a displacement boat with a 50HP engine, but a recent trip on a friend's displacement boat with a single engine on a shaft showed just how tiring and irritating the noise level on such an installation can be - and at 8kts it goes on for a good while too. To give you an example, our boat, which has a 350Hp diesel on an outdrive and an enclosed centere wheelhouse is quieter inside at 30kts than my car is on the motorway. Indeed if you have a bow thruster a bit of practice will allow you to move a single engined OJ equipped boat more or less directly sideways with minimal fore and aft movementĢ) The ability to trim the leg means that you can get access to a fouled prop without swimming.ģ) The geometry of the installation means that the engine is under the stern-deck and is thus easy to insulate accousticaly from the wheelhouse/accommodation, whereas a shaft boat typically has the engine underneath a centre wheelhouse - which pretty much guarantees high noise levels. These factors combine to imply that most boats with OJ's qre quite "wandery" at displacement speed - that is they require constant attention to maintain a respectable course and larger steering inputs than you would expect to restore direction once lost.ġ) You have vectored thrust at the stern which means that steering at berthing speeds is much better than a single engined shaft boat (which usually uses prop-walk to achieve the same effect - less well and only in one direction). The pseudo rudder provided by the leg is quite small so steering while moving with the power off, while not absent, is further restricted. More of the routine maintenance items are below the waterline and can only be accessed during liftout.Ģ) The boat steers by turning the outdrive and so max steering angle is usually quite small - this doesn't matter at 30kts but certainly does at 8. Its watertight integrity is determined by one or more rubber belows which prudence dictates should be replaced well before any possibility of failure. The outdrive is a complicated bit of kit which has to turn many HP through 90 degrees twice. ![]() However, I can see some possible utility in them for displacement use, so here is my list of pos and neg pointsġ) Maintenance costs are way higher than shafts. An outdrive is an odd choice for a displacementboat, because their real payoff comes with the ability to trim the drive angle of the leg.
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