Theorertical Prop Configuration By Walleyehed's Sticky

[sianyde9]

ok, ive read walleyehed's post in the FAQ and i'd like to see if i'm understanding it correctly. I have a mercruiser 470 in an 84 century 4000. The WOT rating stamped on the engine is 3800-4200 rpm. i gathered i should run around the top of this range, so that would obviously be 4200 rpm. ive read that a degree of prop pitch is roughly equal to 175-200 rpm. therefore, i should be using a 21 degree pitch, correct? ive also read externally that more blades are for heavier loads and fewer blades go faster. is this correct? should i use a 3 blade for when i have close to the max load on board, and 2 blades for say, a long run i want to cover quickly w/ just myself or 2 persons on board? i also understand from another forum post that you should try to match the load with the WOT... does that mean i should set up so that when the throttle is physically open as far as it goes, the engine is doing 4200 rpm? thank to anyone who reads and replies...

 

[Bondo]

Re: Theorertical Prop Configuration By Walleyehed's Sticky

does that mean i should set up so that when the throttle is physically open as far as it goes, the engine is doing 4200 rpm?

Ayuh,......You've got that much Correct......

Props are measured in Inches,.... Not degrees......

Most props today are 3 bladed,.....
2 bladed props are a real Rarity.... 4 blades are somewhat common,+ 5 blades are only slightly popular.....

 

[steelespike]

Re: Theorertical Prop Configuration By Walleyehed's Sticky

Not figured that way. That 200 rpm figure is only for figuring pitch changes.
Usually a prop selection is based on present prop,max rpm and speed.Sometime the boat company has prop size info.
In desperate times the experts here may have a starting point and some dealers will let you test props if you intend to buy.
If you have your present prop size and max rpm and speed that would be a start.