1988 Johnson Evinrude "CC" 9.9 thru 30 Service Manual, P/N 507660, Page 50Get this manual
Propeller Selection Selecting the correct propeller for each engine and boat combination will ensure good engine service life and good boat performanceA propeller must be carefully selected to match the engineboat combination, the application, and the anticipated load in the boat
INote service life, affectwrong performance, or reduce serious Selection of the propeller could engine boat cause
damage to the powerhead OMC propellers available for these engines are listed in the Propeller and Steering Connector Guide and the OMC Parts and Accessories Dealer Catalog Procedure The propeller selection process is very important to the engine service life and to boat performanceProceed carefully and thoroughly while considering the following pointsDuring the engine break-in period, only run the engine at wide-open throttle for brief periods of time to verify full-throttle RPM You must use an accurate tachometer to determine the engine's full-throttle RPM as you test various propellers Select propeller that suits the customer 's application and allows the engine to run near the top limit of the full throttle operating range when the boat has light load in itRefer to Engine Specifications, this section Occasionally, one propeller will not cover wide range of boat applicationswater skiing to high speed performance boatingIn such cases, it might be necessary to have propeller for each situationIf the propeller blades have too much pitch, the engine is operating below its normal range at full throttlepower is being lost, and powerhead damage could occurIf the propeller blades have too little pitch, the engine is operating above its normal range at full throttle and damage from overspeeding could occur