3 vs 4 blade

[chop]

Thought I'd get some opinions. Did all the calculators read all the numbers, still not getting the info I want . The calculators don't take into account weight. So here it is 86 sleekcraft,soft V bottom, 26ft, 400hp sm block, 1.5 ratio apha, 3000rpm 30mph, 4000 rpm 40mph. Runs same with 3 blade mirage 21 as 4 blade mirage 19 hmmmm. Are we getting more lift with the 4 blade?

Boat is way heavy or engine builder told lies. Here's what we want...50mph at 4000. Yea yea I' tried the prop changes 22, 23 still stuck at 40-42.

Should I get the engine up in the 4800 -5000 range with prop changes first?

Anyway interested in all your opinions.
Thanks

 

[wca_tim]

Re: 3 vs 4 blade

not sure what you're trying to do or what you expect, but that's a lot of boat to be trying to push that fast with a relatively mild small block - especially if it's a stock displacement 350 (torque is what it takes to push that boat through the water). Not sure where your engine build is supposed to make peak power... if it's a 350, or evena 383 chances are it's not pulling that kind of horsepower until the 5000+ rpm range at a minimum...

The answer to your question below is that yes, you need to prop to put your rpm at wot where your max horsepower is. Based on the numbers you posted above, you're probably talking more about a 19 pitch prop to get you there. both my gut and the data you've posted say that you just don't have enough engine to push that boat to 70+ mph where you would be if you pulled 5000 with a 23 pitch prop and some guesses at slip numbers). Probably not even close... I'm betting you're talking more like 50's at 5000 rpm's with a 19 pitch prop Mirage is a good choice. You're not going to know until you prop down to where you can hit your engines peak horsepower at wot...

Also, if you hammer that alpha drive behind that heavy of a boat... you'll reduce it to bits of metal before long at all.

on lift, you're getting more slip with the 3-blade, that's for certain...

Knkow this is not what you wanted to hear, and i could be wrong...