Tohatsu Prop Troubleshooting: Lost Top Speed, Over-Revving + Prop Size Guide
If your Tohatsu feels slower than usual or starts over-revving at wide open throttle, the propeller is often the culprit. Here is a quick checklist and how to read your prop size so you can order the correct replacement.
A propeller is effectively your Tohatsu’s “gear ratio” in the water. When the prop is wrong, damaged, or slipping, you will often see either lost top speed or over-revving.
Lost top speed (but RPM seems normal):
Check for bent blades, nicks, or heavy fouling. Even small damage can reduce efficiency. Inspect the prop hub for slip (a spun hub can let the engine rev but not push properly). Confirm the prop nut, thrust washer, tab washer, and split pin are fitted correctly and torqued. Also check the engine is trimming correctly and the boat bottom is clean.
Over-revving (RPM climbs too easily, speed does not follow):
This usually points to a prop with too little pitch, ventilation (air getting to the blades), or a spun hub. Make sure the outboard is mounted at the correct height and that the anti-ventilation plate sits roughly level with the hull bottom on many setups. If you changed load, fuel, or layout, the previous prop may no longer suit.
How to find your prop size for a direct Tohatsu replacement:
Remove the prop and look for markings stamped on the hub, such as Diameter x Pitch (example: 9 1/4 x 10). Note the number of splines, rotation (normally right-hand), and any part number on the hub. Match these details to order the correct Tohatsu-compatible prop and the right hardware kit.
