Prop functions and measurements help

[jlutsey]

I am about to be in the process of chaging props for my 175 optimax and just curios to see if anybody can put some mathmatical stats to the difference in props. I know that raising/lower 2degrees of pitch will usually change about 200 rpmsup or down, but what effect does changing the diameter have? abviously the same thing but how? what if you change the diameter but not the pitch? pitch but not the diameter? more cup, less cup? surely we've got a few Naval engineers on here.

go to iboats.com. They were a big help to me for sizing my prop.

[Gary1911]

jlutsey - 8/20/2005 8:00 PM

I am about to be in the process of chaging props for my 175 optimax and just curios to see if anybody can put some mathmatical stats to the difference in props. I know that raising/lower 2degrees of pitch will usually change about 200 rpmsup or down, but what effect does changing the diameter have? abviously the same thing but how? what if you change the diameter but not the pitch? pitch but not the diameter? more cup, less cup? surely we've got a few Naval engineers on here.

No naval Eng. but a couple of years with props under my belt

1"P=200+/- rpms
1" D=2"p

Cup= +/- 50-150 rpms +/-


Gary

[shep70057]

I'm one that believes diameter affects R's but there are a lot of people who will argue that. That jives with what I've been told and learned.

1/4" Diameter=75 or so R's