Suggestions Please : Re-propping an Azure 188 4.3GXI SX

[rdl212]

I have an Azure 188 with a 4.3GXi Volvo Penta 225hp- SX drive with 1.79 gears(I understand that most come with 1.63?). Boat weighs in at 2900lbs. I currently run a 14 X 23 aluminum prop, and a 14.3 X 21 aluminum prop. With the 14 X 23 I can hit the recommended WOT of 4800rpm with only myself and no gear and hit about 57mph. With the 14.3 X 21 I can hit 5100-5200 rpm with people on board(ie. underpropped) and a top speed of 51mph. I use the 21 pitch currently for towing the tube, or if a few people are coming along to get on plane faster. Recently I have installed Smart Tab SX and they seem to help a bit as well although I am still playing with the settings. For quite some time now I have been thinking of getting a stainless 4 blade prop. My end goal is to 1. have a stainless prop and not just aluminum, 2. gain some faster hole shot/on plane times/lower plane speeds - especially for tubing and a few people on board, 3. maintain the majority of top end speed(although I do understand that this may suffer slightly). I have been thinking of a Michigan Wheel Apollo perhaps, but am looking for some suggestions - precision prop, powertech, merc, solas, etc. Any help or experiences are appreciated.

 

[craze1cars]

Re: Suggestions Please : Re-propping an Azure 188 4.3GXI SX

The only 4 blade stainless prop I personally have experience with an I/O is my Solas HR 4 Titan. I am extremely pleased with the performance of this prop, and they are very competitively priced IMO. I can provide no informed input on any other brand.

Keep in mind a couple rules-of-thumb when you are pitch shopping: 1. Drop an inch of pitch when switching from aluminum to stainless. 2. Drop an inch of pitch when going from 3 blades to 4 blades.

With these in mind, I believe if you purchase a high performance, 4 blade, stainless prop, you will need get a 21 pitch for your boat, even though a 21 pitch is currently over-revving in your 3 blade aluminum setup. If you buy a 23 pitch in a 4 blade stainless, your boat will struggle to get into rpm range and your holeshot will suffer.

All that said, there is one thing about your numbers that is throwing a wrench in things. Your current data: 1.79 ratio, 23 pitch, 4800 rpm, 57 mph.....that calculates to 2% slip. That's FANTASTIC...hardly even realistic, ESPECIALLY for a 3 blade aluminum prop. Makes me wonder if one of your data points is wrong. Is your speed GPS verified? RPM confirmed accurate?

Your 21 pitch numbers calcluate to 11% slip. That is more realistic and typical.

Anyway...if you TRULY have 2% slip on your current prop, you may not gain much switching to a stainless 4 blade...because the whole point of making the switch is essentially to reduce slip. It's awful hard to reduce slip with your current 2% being already unrealistically low....and if 4,800 is your target rpm, and you're already at that rpm with your current prop, and you already have 2% slip, then on paper you will have little to nothing to gain by making ANY prop change...at top speed anyway.

But 4 blades will give better holeshot and maybe smoother operation. So I'd still say a 21 pitch would be best to start with, based on your figures.