Prop Diameter RPM change

[cowlotter]

if i increase propeller by a 1/2 inch diameter how much wot RPM would i lose ?

sorry wrong thread not sure how to change it

 

[jbcurt00]

Moved to the Props sub-forum

 

[cowlotter]

if i increase propeller by a 1/2 inch diameter how much wot RPM would i lose ?

and is it possible to hook multi meter behind dash for accurate tach reading without having a second person in engine bay helping me reading off coil for WOT pulls? my tach is defenitly not 100 percent and need to use multimeter

 

[jimmbo]

How about replacing the tach in the dash, instead of creating some Rube Goldberg setup?

 

[tpenfield]

sort of depends on the current size of the prop . . .

but, if I assume a 14" prop w/ a 4" hub diameter, and doing some quick math . . . going to a 14.5" will add about 8% more ' effective area' to the prop.

You should expect about 92% of the original RPM or about 400 RPM less, depending on your current WOT RPM.

 

[Bondo]

if i increase propeller by a 1/2 inch diameter how much wot RPM would i lose ?

sorry wrong thread not sure how to change it

Ayuh,...... The odds are the rpm won't change much, if at all,......

Generally speakin', the engineers that design the props increase or decrease the diameter to match the blade area, so you shop for the Pitch you need, 'n the diameter works itself out,.....

 

[QBhoy]

Hi
a very very difficult question to answer. In reality if you take two exact same type and cut of prop of the same pitch, but one with 1/2” more diameter, you would likely see a slight drop in rpm.....but since this is a very unlikely of not impossible scenario...it’s not even a consideration.
Many many factors at play here.
The other extreme end of it is if you take a standard black max 19” pitch prop with its 14” (or close to) diameter....then compare it to a tempest 19” pitch with its much larger diameter (just under 15”)....on most boats with any average performance capability at all...the tempest will see you with more rpm...simply because it will lift the hull much further out the water with the cut of the prop being designed to do so.
Such a weird and wonderful science that can often see unpredictable results.
Just the difference between a well suited prop and not...can be a ridiculous difference. I’d hate to be the man that answers that question with any certainty

 

[Texasmark]

I agree with Bondo for a given blade type, the size remains relatively constant and the Rake and Pitch changes the overall diameter. You can shop props and for a given type/brand, upping the pitch reduces the diameter slightly.....like maybe ⅓" for a 4" pitch change sort of thing.

Also what Qboy said about performance changes as a result of the prop changes and it's ability to bow, stern, or not necessarily affect lift, then toss in trim positions, hull types and all make for a very slippery surface to predict.

I just bought a boat with reverse chines and talk about a game changer.