Choosing Shaft Length For Your Transom

Get shaft length wrong and the motor either ventilates at the surface or drags the lower unit through the bottom. Hightime publishes two shaft lengths across the range, so the decision is straightforward once you measure.

The Two Lengths

The S Series shaft length was not published on the previous site; confirm it with sales before ordering.

How To Measure The Transom

1. Load the boat as it will be used, with battery and crew aboard
2. Measure vertically from the top of the transom where the bracket clamps down to the waterline
3. Add the depth you want the propeller below the surface, normally 300 mm or more so it stays submerged in chop
4. The result is the working shaft length you need

What Happens If It Is Too Short

The propeller sucks air at the surface, thrust falls away and the motor whines instead of pushing. It is worst in chop, exactly when you need the thrust. A short shaft cannot be fixed by lowering the bracket beyond its stop.

What Happens If It Is Too Long

The lower unit sits deeper than it needs to, adds drag, and in shallow venues it hits the bottom. The 7-level lock bracket gives useful adjustment here, so a slightly long shaft is the safer error of the two.

Adjustment Range

All series use a 7-level lock bracket at the transom, reinforced nylon on the brush series and aluminium on the brushless series. Set the height so that the propeller is fully submerged at rest and stays submerged when the bow lifts. See the mounting guide for the fitting sequence.