6BY3-260 Joystick Solution
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Yanmar 6BY3-260 Joystick Solution Yanmar 6BY3-260 Joystick Solution
We think the Yanmar 260-hp diesel has a lot going for it both for new-boat installations and for re-powering. Because this 3 L engine is one of the lightest diesels on the market in class at 694 lbs. (315 kg.), bobtail, has overall dimensions to match, and can be harnessed to sterndrives in addition to being a conventional inboard, she has many applications. As a single-engine installation she is appropriate for boats in the mid-20 foot range (6 m). In twin-engine mode she can successfully power boats up to nearly the 40' (12 m) range, depending on application.

Yanmar 6BY3-260 Joystick Solution Captain's Report

Yanmar 6BY3-260

Pictured here is the installation of twin Yanmar 260-hp 6BY3 engines with Yanmar ZT370 sterndrives in a new MJM 36z Downeast cruising boat.

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.

Yanmar 6BY3-260

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.

Yanmar 6BY3-260

The 150 Amp alternator is one of the most powerful in class.

?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.

See BoatTEST.com's video on the 6BY series engine…

 Yanmar 6BY3-260

Each Yanmar lower unit has husky twin rams for trim. Note that the counter rotating props have the same diameter.

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.

Yanmar 6BY3-260

Because of its low profile of just 28.2" (712 mm), MJM is able to get twin 6BY3-260 engines below its cockpit deck enabling the MJM 36z to take advantage of the efficiencies offered by the Yanmar ZT370 sterndrive.

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.

See the BoatTEST.com video on the Yanmar ZT sterndrive…

 Yanmar 6BY3-260

In tandem with the typical joystick stalk is a digital LED screen called the CANtrak Display for messaging information about the system's status.

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.

Yanmar 6BY3-260

The Optimus 360 CANtrak screen.

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.

Yanmar 6BY3-260

Two 25' (7.62 m) sterndrive sisterships were tested on different days in different conditions. The sistership with the gas engine was 250 lbs. (113.6 kgs.) lighter and on test day was 14-degrees F cooler, both factors of which gave performance advantages to the gas engine-powered boat. Both boats used Bravo III sterndrive lower units.

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.

Yanmar 6BY3-260

Daily fluid checks can be easily made in the new MJM 36z because the huge hatch in the cockpit gives access to the outboard sides of the twin engines.


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.