Please help me!!!!!1

[wmhob]

I began the process of shopping for a new prop about 2 weeks ago and it's been a big learning experience. I've spent hours reading here trying to find specific answers to my questions and still can't get comfortable to make a decision. Here?s what I?ve got currently.
Hurricane SunDeck 21? with 4.3MPI, 220HP, 1.62 ratio with a 17 pitch MI Wheel Avenger SS. The prop is underpitched and is causing my motor at WOT to run around 52 to 5300 RPMs at 46 or 47 MPH (clocked by GPS). It should be maxing at 4800. Initially I was just going to try to get the same prop in 19 pitch but started reading here and talking to a couple of boat dealers and got lots of mixed info. Right now I can buy a Mercury Vengeance 3 blade 19 pitch for $275 reworked by a prop shop, a Quicksilver Thunderbolt 3 blade (same as Mercury Mirage) for $350 reworked or the other I was considering was the MI Wheel Apollo new for around $250. Should I be looking at a 4 blade Apollo if I go that way? I?m not extremely concerned about top end speed. We use the boat for cruising, kneeboarding, and tubing. I?d like for the boat to plane at as low of a speed as possible for slow cruising. Any suggestions or experiences with the above props would be appreciated. If I go to a 4 blade do I need to stay at 17 pitch or still go to 19? Is a 4 blade more fuel efficient than a 3? Thanks

 

[steelespike]

Re: Please help me!!!!!1

I don't think a 17 4 blade will drop your rpm enough,you need to go with the 19.a 4 blade will improve your low end performance and should plane at a lower rpm.Running at the slowest planing speed is not necessarily the most efficient speed.The most efficient speed is somewhere between planing and wot (wide open throttle)trial and error or a flow meter is the only way to find the best cruising speed.I don't usually suggest changing material but you might want to take a look at the Turning Point Hustler props.Close to stainless performance at Al. prices.You could probably get two Turning points for the price of the ss.

 

[Randybeall]

Re: Please help me!!!!!1

You have done your research fairly well. You need to increase pitch to improve cruise efficency, and the idea of going to 4 blade will be good for the towing activities. I did not check but 4 blade usually comes in even inch sizes so you may need to go with 20" pitch. If your over powering the 17" prop now it is a little hard to calculate what will give you that just right prop match. Some dealers will allow you to try before you buy, I Boat being on that list. Check it out.
To answer the final question, yes a 4 blade can be more fuel efficent than a 3, if you need the additional power transfer ability of more blade surface area. It is all a very carefully balanced problem.