prop question

[Destroyer]

Originally Posted by smokeonthewater

I disagree..... a 4 blade 17 would replace a 3 blade 18 or 19 (rule of thumb) but stainless to alum there is no automatic pitch change.... I had a 19 stainless and a 19 alum for the same boat... I got about the same holeshot with each but I got about 100 more rpm and 2-3 more mph with the stainless

Perhaps, but a 4 blade prop is not the same as a 3 blade prop. I said twice in my post all other things being equal. 4 blade props will give you a much better hole shot since there is 1/4 more blade area in the water...but 4 blade props will also result in more drag and a slower top end. They're great for tubing and water sports, but generally not recommended for racing or going fast..

As for an automatic pitch change, that's true, there is no such thing, because there are so many diferent variables, even between two props from the same manufacture. BUT, as a general rule of thumb, I've always found that when you switch from an Alum to a SS prop you wind up dropping 2 inches of pitch and usually get better preformance. Not all the time, not always, but generally speaking.

The reason you were getting more RPM and 2-3 more mph with your stainless is probably because at top end your aluminum prop was actually flexing slightly and you wound up running a prop with about an 18P at WOT. Stainless props don't flex like that so it was performing better.