Prop selection.

[lrwashburn]

I have a 2000 202 Crownline 5.0 liter V8
What is the original prop for this boat and motor combination? WOT RPM should be 4400-4800. The current prop is a 3 blade stainless steel 14 x 23. WOT is 4050 rpm and 51 mph. I would like to try a 14.25 x 21 stainless steel 3 blade prop.

 

[porscheguy]

Mercruiser or Volvo Penta?
is your speed GPS or the dashboard speedo?

some will suggest you gown to a 19P, I’ll say you’re better off stepping down in increments like planning.

 

[lrwashburn]

It's a Mercruiser and speed was off ithe speedo. I will step down to a 21p next. Ty.

 

[Sea Rider]

If the rule of thumb applies here a 19 pitch prop should put engine right to 4400 wot revs as loaded, but will surely rev engine way higher. The speed measured one way is relative, it's a 2 run measured in opposite directions on straight water courses.

For the record, post whatever wot rpm was achieved with new prop loaded same as last run.

Happy Boating

 

[porscheguy]

I’ve been getting a lesson in prop pitch and rpm change the past few weeks. The old rule is a great guideline, especially when you’re flying blind. But very recently I’ve seen a 600 rpm drop after changing 2” in pitch. That’s when the science goes away and the voodoo kicks in.

 

[ahicks]

Agreed (voodoo). This past week I repowered a 16' bass boat with a Honda 50. Took a wild guess on a 15" prop. Boat was a little heavier than I was thinking (water logged foam likely), as that prop resulted in a total dog that would barely turn 4800. So I put a 11" (pontoon boat) prop on it to see what it would do. That prop resulted in 6200 or so, and was bumping into the rev limiter! Finally, a 13" prop gave me 5550 rpm, right on the sweet spot that I was looking for. So from the 11' to the 13" there was a change of 700rpm, and from the 15" to the 13" there was AT LEAST 700 rpm difference. That could have been more, because the rev limiter held it to 6200 (200 rpm past red line). All 3 of these props resulted in a speed difference of only about 4mph from top to bottom, with the 13" 5500 rpm prop going the fastest.

Lesson learned, though 200 rpm is often mentioned as the difference in rpm per inch of pitch, that may be the minimum. In the case above, it was more like 350 rpm - per inch of diameter. FYI, -Al

 

[SkiDad]

it depends on what you want to do - if just cruising the 21 would be OK. If you want to do water sports I would drop down to the 19. If it were my boat I would be running a 19. You will get the most predictable result if you stay with the same model of prop and just change pitch.

 

[Sea Rider]

Lesson learned : rule of thumb is way off from nearly cast on stone stated +,- 200 wot revs per one +,- pitch size, so be careful if going that route so not to dump big money into the deep blue buying too high or too low prop pitches sizes from current one. LOL!! Now imagine that same prop scenaio on a light or medium light boat

Happy Boating