Teague On Tech: Q & A with Bob Teague April 2024

As seen in Speedboat Magazine’s
April 2024 Issue.


Dear Bob:
Can you explain the correct procedure for setting the alignment of the drives on a twin-engine boat? I would think that if it is not in correct alignment, you could be scrubbing off speed. On a car, there is a certain amount of toe-in, when the car starts moving, that position likely will change slightly. Is a boat the same? Does the procedure change with regard to the direction the props are turning?

Randy Hallman
Page, AZ

Traditionally, the front suspension on an automobile is set up so the wheels have a slight amount of toe-in. Being that there is (probably more in the old days) a certain amount of slop or play in the suspension or steering components such as ball joints, drag links, bushings and so on, if the front wheels were not set slightly toe-in to keep a constant load in one direction, the result would be what is commonly called a shimmy. The shimmy can result in a violent shaking of the front wheels and steering wheel.

The amount the drives should be toe-in or out on a boat depends on a number of factors. The most common considerations are hull type, drive type, propeller shaft depth, and propeller rotation.

Generally speaking, twin-engine vee-bottom boats with the propellers spinning out are usually set up with the drives toe-in slightly. It is common to set the nose of the drives about a total of 1/8 inch closer together than the aft end of the propshafts. The theory is that water exiting from the back of the hull is being parted slightly by the keel, so setting the drives at a slightly toe-in angle would result in them running more aligned with the water flow. That is only a theory. What we do know is that certain boats handle better with varying degrees of drive toe-in or toe-out.

If the propeller shafts are high enough so the propellers are surfacing, the side load created by the propeller blades seeing cleaner water in the lower sweep of their rotation will tend to push the drive in one direction. Similar to an automobile suspension, there is a slight amount of play in the gimbal ring and transom assembly pins and attachments. The side force created by a surfacing propeller will load the drive and transom assembly in the opposite direction of the propeller rotation. In other words, if the propeller is a right hand rotation (clockwise from the rear), the result will be that the force will be the same as turning (or flexing) the drive to the right, and vice versa. So, if your propellers are surfacing and turning out, the toe-in (nose cones closer together) will increase under load. And, if the propellers are rotating inward (port clockwise and starboard counter-clockwise), the force will tend to pull the propshafts closer together resulting in toeing the drives outward. The magnitude of the deviation is related to the type and condition of the gimbals and transom assemblies, and how high the propeller shafts are when the boat is under way. The result of the movement under load should be considered when deciding what the ultimate perfect set up is relative to drive toe-in or out.

Catamaran hulls that are running a high “X” dimension with the drive placement very close to the tunnel present additional criteria to consider. If the drives are close enough to the tunnel wall so that the sweep of the propeller blade is “seeing” clean water exiting from inside the tunnel, there is a tendency to neutralize the effect on the propeller created by water exiting from the angle of the running surface of the sponson.

The bottom line is to get some advice from the manufacturer or someone who knows a lot about your particular type of boat and set up. Then start from a setting and make minor adjustments testing the boat each time to gauge the effect on the handling and efficiency.

Always measure the toe-in or out with the drives trimmed to a neutral position and steering straight. With an assistant, measure from the front of the center of the nose cones or bullets compared to the center of the aft end of the propshafts. If you run the boat and discover that the toe-in measurement has changed all by itself, the indication is that there is significant slop in your transom assemblies, tie bar, or steering. A change in the measurement could also be due to the transom assemblies themselves moving on the boat’s transom and needing to be re-torqued.

Changing toe-in measurements could also be caused by a transom that is deteriorating from water intrusion or dry rot. It is always a good idea to occasionally re-torque the transom attachment nuts on the inside.

For your chance to be featured in Teague On Tech, email your questions for Bob Teague to AskBobTeague@gmail.com.

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