Mission of the Yanmar 6BY3-260
The 6BY3 in-line 6-cylinder block is rated from 220-hp to 260-hp and fills in the top of the lower tier of Yanmar's horsepower range. She performs equally well in sportboat, cruising boat and fishboat applications. Her strong suits are her lightweight, one of the lightest on the market, quiet operation, and the ability to mate with the Yanmar ZT370 sterndrive which provides superior performance to conventional inboard systems.
For these reasons, the 6BY3-260 is as versatile as any diesel engine in class.With the protective covering removed from the top of the 6BY3 diesel we can see the aluminum intake manifold of this in-line 6 design.
Major Features of the Yanmar 6BY3-260
?Lightweight. At 694 lbs. (315 kg) it is one of the lightest diesel engines in class on the market. Yanmar has been able to accomplish this weight savings by using aluminum in the pistons, oil pan, heat exchanger, raw water air cooler and elsewhere. She also has a hollow, heat-treated cam shaft, employs plastic for its valve covers and raw water plumbing among other things.
?Smooth Running and Relatively Quiet. Because she is a relatively high rpm diesel (rated at 260-hp at 4000 rpm) 6-cylinder in-line engine she runs smoothly and as a result is relatively quiet for a diesel. Her common rail and pre-injection system also reduces both noise and emissions.
?150 Amp Alternator. Yanmar is aware of the power requirement that modern boats have and has stepped up to the plate by equipping the 6BY3-260 engine with one of the highest output alternators in class.
?CAN Bus Output. Yanmar uses the NMEA 2000 Protocol that standardizes digital communications among a wide variety of electrical equipment including data display units. This means when re-powering, the 6BY3-260 can be plugged into existing displays if they are NMEA 200 compatible.
?High-Quality Paint. Yanmar uses a high-quality two-part polyurethane paint to protect the engine's surface from rust.
Yanmar ZT350 Sterndrive
The 6BY3-260 diesel can be used in a conventional inboard configuration or be connected to Yanmar's own sterndrive, the ZT350. Yanmar's lower units are the only ones currently on the market that was designed specifically for exclusive use with diesel applications, and as a result is built with robust shafts and pinion gears to take the tremendous torque exerted by diesel engines.
Sterndrive propulsion has several advantages over conventional inboard straight shaft systems--
1) Sterndrives give up to 30% better fuel economy at cruising speeds.
2) They usually provide as much as 15% higher top speed.
3) They usually draw less water.
4) They permit the engine to be located in the stern of the boat, and fairly low, which opens up the mid sections of the boat for other uses.
Hydraulic Clutch. The Yanmar ZT370 uses a hydraulic clutch instead of a cone clutch. The result is the complete elimination of the "clunk" that one hears, and the slight jolt that is sometimes felt, when a cone-clutch lower unit is put into gear. The ZT370 goes into gear smoothly and quietly because it is hydraulic.
Other Features. The ZT370 also has two counter rotating props. These props keep the boat going straight in single-engine applications as well as helping the boat get on plane faster. The lower unit's gears are robust and precision-forged for longer life. The unit has through-the-hub exhaust for lower back pressure, provides power steering and power trim, as well as being the same size for transom mounting as other brands.
Joystick Control for the 6BY3-ZT260
At the date of the publication of this report Yanmar does not have a proprietary joystick control system for the 6BY3-ZT260 as it has for its larger engines. What is used instead is an Optimus 360-degree joystick made by SeaStar.
Joystick Operation. SeaStar makes a full line of joystick products along with many other types of control systems for marine applications. The Optimus 360 is a three-axis unit with a guided feel that has both a "boost" and a "take command" mode for simple, intuitive operation.
Typically, the joystick control is limited to rpms of 1200 and less as the unit is intended strictly for close quarter maneuvering and station-keeping.
Diagnostics And Adjustments. The CANtrak digital display is part of the Optimus 360 package. In addition to the system diagnostics, it can also adjust the number of turns lock-to-lock of the steering, adjust the effort of the steering, and modify the amount of tow in/out of the inboard engine when placed in a hard-over turn. It also shows the direction of the lower units like a rudder indicator.
Gas vs. Diesel
It is not often that we are able to compare the performance of gas engines with a diesel engine, but the Yanmar 6BY3-260 is one happy case in point. The image above is a frame from a video comparing two tests we did in the same 25' (7.62 m) model boat with one powered by the Yanmar 6BY3-260 diesel and a sistership powered by a 300-hp MerCruiser gas engine.
Gas is Fast. As one might expect the gas-powered boat with 40 more horsepower had the highest WOT speed, helped to some degree by the cooler day and slightly lighter load. The gas vessel also was quicker out of the hole. This was a good apples-to-apples gas vs. diesel test as even the lower units were the same -- Mercury Bravo III units. The test was done before the introduction of the Yanmar sterndrive lower unit.
The Long Ranger. But there was one characteristic in which the Yanmar 6BY3-260 excelled -- and that was range. The diesel powered boat got exactly 50 miles more on a tank of fuel (with a 10% reserve) which means that its range was 30% greater. Add to that the fact that in Europe diesel fuel is typically these days about 10% less expensive than gasoline, and it becomes obvious why Europeans have long preferred diesel engines to gas-powered ones.
The gas vs. diesel debate will always be with us and both have their advantages. But a system that is not so debatable is conventional inboard, straight-shaft propulsion vs. a sterndrive system. Because of its location, angle of attack, twin counter-rotating props, and drag coefficients, sterndrives are simply more efficient than straight inboards no matter what kind of fuel the engines burn.
Add to that the ability to dock with a joystick, and the Yanmar 6BY3-260 becomes a compelling system in our opinion.