Need prop help right away please.

[Darin]

I can't remember the rule for going from 3 to 4 blade. If you are using a 19 3 blade, do you go to 18 or 20 4 blade?

Thanks.

[joedirt00]

What brand/pitch are you running now and what are you changing to?

From what I understand as long as you stay with the same design/series prop, they are pretty close to the normal prop change characteristics with a little better hole shot and handling and not too much effect to top speed. For instance, going from a 3 blade 19" Merc Black Max to a 4 blade 18" Merc Alpha 4, the 18 will pull a coulple hundred RPMs higher than the 19" like normal.

If you are switching to a completely different design/ manufacturer prop all that changes because now you are putting rake, cup, blade width, and surface area into the equation.

[bmartin]

Like piror post - A lot of things matter. If you want more or less same hole shot and top end, the 20pitch 4 blade is likely to be more similar to your 19pitch 3 blade though. All other things equal including pitch, you generally get more hole shot from a 4 blade and will run slighlty higher RPMs than a 3 blade for an I/O but this is a very general rule of thumb.

[joedirt00]

Since we are wakeboarding here, I would be tempted to go down to the 18" to get a little more ooomph.