Originally Posted by
Pulsare2020
Usually, it works like you mentioned. A larger diameter prop has more blade area and can run with less slip. Of course if it does not have the right amount of cup and rake it might not be able to lift your bow, and then the drag increases and it does not work as well. Like you said, at one point, if you keep increasing the diameter past what is required for low slip, it just becomes harder to turn on your hull and will slow it down, but might not slow down a heavier boat. Still, like you said, some black magic. There was a post from someone that had a 27P Scorpion modified for more top speed. He said the prop shop measured it as 29.5". They actually cut the diameter down some from 15.125" because his light boat did not require all that diameter and he was able to turn it at higher rpm and gain speed. So, if that is true for most pitches of Scorpion, they appear to have more than the advertised pitch. I am no prop expert, but many props have progressive pitch which changes from the bottom to the top of the blade and the often the advertised pitch is the average pitch, but on a mercury Bravo type of prop, the average pitch is usually 0.75" - 1" less than the advertised pitch. So perhaps Scorpion measures the pitch in a certain place?? They have huge amount of cup and rake, which really helps to lift the bow, but are made out of very soft stainless steel. The Scorpion had low slip on my boat, but so did the Bravo 1, the Bravo FS, and the ProMax. I also used 24P to do the slip calculation on the Scorpion and that of course made it look very good. I did not really know what pitch it actually was, as it was sold as a 24P. If you do the slip calculation using 26P, then the slip is not as good. I have spent too much money on props, just like you did, and certainly would not tell you that the Scorpion will cure your issue, and which pitch you should buy, after what you have been through. All I could say, is if you can find a used Scorpion (new ones cost almost half of many merc props) you might want to roll the dice again??? I ran a 14.5" diameter, 24P, 4 blade, BBlades Blaster and it had 30% slip and only ran 65 mph at 6500 rpm. I recently ran a 14.5" diameter, 24P 4 blade ProMax and it ran 76 mph at 6348 rpm with less than 10% slip. The 24P Scorpion I could only turn to 6000 rpm at 71 mph but it had less than 10% slip if you used 24" for the pitch calculation. So it had more diameter at 15.125" but it did have one less blade. The ProMax probably had similar blade area to the BBlaster but it did not have as much cup or rake. So I have had a bit of a crapshoot with props as well as you. The ProMax was the first prop I have tried under 15.125" that actually worked very well.