See full version: Twin Outboards on Small Boat Key Facts
If you’re looking to repower your boat, understand that many factors go into the decision. The engine manufacturers provide a lot of information on their websites. For example, on the Yamaha website you can browse performance reports for many different hull and engine combinations. It’s relatively easy to find a boat like yours and gauge the difference that possible engine size and configurations could make. [links]
The cost of purchasing two engines is rarely less than the cost of buying one big engine. In other words, bigger engines are more expensive than smaller ones, but they are seldom twice the price. From the start of your project, buying two motors is going to cost more. more
The most common problems that affect outboard motors today are fuel related. Water contamination or low-quality ethanol fuels are common culprits. But unless your boat has two completely independent fuel systems with two separate tanks, any fuel issue is likely to affect both of your engines at the same time. And even if you do have two tanks, it’s possible that the problem would affect them both. Whether you have one outboard or two, keeping your fuel tanks clean and using high-quality fuel-water separators are vital to engine reliability. [links]
The setup and rigging of an outboard engine are relatively straight-forward and uncomplicated, but the thought and planning that goes into a proper repower job are pretty incredible. Every hull design is slightly different, and it might not be as easy as it appears to go from one engine to two or vise versa. Before you dive into any big project on your boat, you need to run through the hows and whys to ensure there will be no costly surprises. [links]
The decision of twin versus single outboards is a common one. When shopping for a new boat or repowering an older hull, you might find yourself wondering about the differences between having one large outboard versus two smaller ones.
Here’s a look at some of the differences between single and twin outboard boats, as well as some of the advantages and disadvantages of having two motors. Are two outboards better than one? The short answer is that it depends.
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Force never made a counter rotating engine. All force engines rotate clockwise at the flywheel and clockwise at the prop. Even if both engines had been mounted on a twin engine installation, they would have been both exactly the same. So choose to use whichever you wish. here
I think what the person ment was if the motors were set up for opposite rotation. One rotates to the right, one rotates to the left. This is usually the case if they came off the same boat. Check and see if the props are the same.
Counter-Rotation
Steering can be a real chore with a dual engine power setup. When the props turn in the same direction, the boat tends to list and steer off course. Keeping an even keel and true course requires constant attention, especially in choppy water and high winds. Much of that problem can be solved by having two props turn in opposite directions. In other words, counter-rotation. The major advantage of counter-rotation is its ability to enhance performance by reducing steering effort in all RPM ranges.
Most single engine boat setups normally operate in forward motion using clockwise rotation of the engine and gearcase. Although counterclockwise rotation setups have been used since the creation of the outboard engine, the use of counter- rotation has become more prevalent in the last decade. This increase is largely due to the manufacturing increase of larger twin engine recreational boats and performance boats. [links]
I plan on using only 1 of these motors for a ski boat, somebody ask me if one has a reverse prop on it.
Just purchased a pair of 1992 Force 120 HP motor, the guy stated that one works great and the other had a gasket leak.
Re: 120 Twin Force Engines [links]
If your boat has twin engines, counter rotating engines have long been used to neutralize propeller torque which improves vessel handling and performance. The port, left side engine, is the standard rotation engine. The starboard, right side engine, is a reverse or counter rotation engine. Sometimes it is not possible to view the flywheel so engine rotation will have to be viewed from the front of the engine. Just remember to reverse what you see at the front of the engine so it agrees with flywheel rotation. These are the guidelines for engines mounted in the normal fore and aft position with the flywheel closer to the stern of the boat. Some older boats used a flywheel forward configuration that can change the rules. Also, some ski boats with single engines, mostly Ford 302/351 power plants, used reverse rotation engines so it is a good idea to determine your engine’s rotation before visiting the parts department to avoid error.
Post by Tony Meola » Mar 5th, '13, 22:32 here
Post by In Memory Walter K » Mar 5th, '13, 19:53 more
Post by bob lico » Mar 5th, '13, 20:15 more
Rotation is always determined by looking at the flywheel end of an inboard engine. The flywheel of a standard rotation engine turns left, or counter-clockwise, when viewed from the flywheel. The flywheel of a reverse rotation engine turns right, or clockwise, when viewed from the flywheel. Most single engine inboard and I/O boats use a standard rotation (L.H.) counter-clockwise engine. Use the illustration to the right, courtesy of API MARINE, to help understand engine rotation.
Post by Tony Meola » Mar 4th, '13, 23:02