age old question.... PROPS and their mystery. will it ever be solved?

floater212

here's a question about props.... I had a 21" high five prop, hit a rock or submerged barge, now I have a 4 blade 19" aluminum prop, shouldn't the hole shot be better than the 21"? not for me. so here goes.... the high five was 13 3/8" dia. and the 19" 4 blade is 14 1/4" does the diameter make a big difference or not ? smaller prop would spool up faster that larger? my drive has clearance for about  15" diameter prop, should I go for a bigger dia. prop or stick with the smaller high five for the performance I had? some say pitch is pitch no matter what diameter or materials. my 21" had a good hole shot and nice cruising speed, the 19" is slower out of the hole and speed is down too. I'm looking into ron hill signature 5 blade, they are fatter blades so I'm thinking, pushes more water, he says their slippage is lower than most others so more bite. let me know your thoughts. thanks 

212rowboat

Props are so fascinating to me that I bought an ebook some time back to get a grip on them..

Re: your high five... Toss everything you know about props out the window.. the high five plays by its own rules, and adjusting material, blades, pitch, geometry, and venting based on what the high five did to a non high five is an exercise in futility.. and a lot of prop swapping to find a performance equivalent..

I think the high five is vented, which likely accounts for a better hole shot.. those vents offer a controlled cavitation as the exhaust spews across the face of the blade, but as it redirects more fully through the hub alone, the bite and speed increases.. a vented prop has hole shot comparison to a prop one or two pitches less, depending on the size of the vents..

Bigger diameter is going to require more torque, as it saps it quicker with the added pressure of water forcing off them.. bigger ain't always better, but its not a bad thing if the drive and motor can handle it.

What engine do you have in your 212?

Mine has a carb'd 4.3... Alpha drive, 1.6:1.. after playing swap all last summer, I found that a precision performance turbo one in stainless steel, 22p 14.25" works great.. its vented.. if I had my choice again, though, I'd go with a pitch less but keep same geometry and diameter.. I hit around 4600rpm tops and though that's in the middle of the requested range, I'd like to hit 4800..

floater212

it has the 350mpi 300hp alpha1 with a 2.0 ratio the rpm range is around 4400rpm, but I've changed out tach twice because they bounce WAY too much. the high five has vents but they are all closed up. the 21" high five ran great but the guy from hill marine says I should be leaning towards a 17" pitch, I'm thinking no because we run on a river and you could travel 30 minutes to find a secluded spot to play and there are maybe 2 marinas to get fuel... usually at the other end, so I also need range. I had a messed up high five 19" pitch ( it was rebuilt from someone that know zero about props) that came on the boat... hole shot about 1-2 sec. better slow speed on plane for kneeboard and learning wake board and the 21" five took about 3-4 secs and better speed for cruising, neither have vents open.

nhsd

Wow, a 300 HP Alpha with a 2.0 ratio and you are only running a 21 pitch prop (and considering a 17 pitch)! I am running a 220 HP 5.0 carbed engine with a 1.62 Alpha 1 and running either a 20 pitch Alpha 4 aluminum prop or a 21 pitch Turbo. I tried a 19 pitch Rev 4, but it was too much prop. I would think with that big **** engine and that very high ratio (that is a higher ratio than my old boat with a 4 banger engine had) that you would need to run a huge prop!