Propeller & engine shaft

Propeller – usually, all outboard motors come in a package with a standard propeller, but some engine suppliers sell them separately, or you may just want to have a different one. Either way, the truth is that it’s nearly impossible to give one and real advice on the best propeller, because it depends on a lot of different things. In fact, as this is considered to be a boat tuning, it’s better to ask your engine-inflatable boat dealer on what he thinks will fit you and your targeted use.

If you still decide to try it yourself, after installation and 10-12 hours of first run, put your RIB boat under the conditions of your target use(load and passengers) and check the RPM at the full throttle at the top speed, then consider these tips:

• If the max RPM you’ve reached is less than max RPM set for your engine – change the propeller into one with one-step smaller pitch and check your RPM again.
• If you easily reach the max RPM even when not at 100% throttle – change the propeller into one with one-step bigger pitch and check your RPM again.
• Play around with the propellers in order to get the best performance at full throttle, but in any case try not to overload your engine with an extremely speedy propeller (too big pitch).
• Out of practicality considerations, it’s OK to have two propellers for your engine: one – for heavy load (with short pitch), and one – for boating light (with long pitch).

Engine shaft – usually the required engine shaft length would be clearly stated on the User’s Manual of every rigid inflatable boat. Well, at least at Grand Boats, we have that written down. After the engine has been installed, have a final check and make sure that anti-cavitation engine plate is 25-50 mm (1-2inch) lower than the lowest transom point.