Need prop advise for runabout

[highpowerdad]

Hello all,
Boat is a 2005 fourwinns 190 horizon runabout, 5.0GXI VP 270 HP with SX drive.

I recently purchased a Solas 4 blade Titan 19 pitch, Solas PN 8653-141-19. With the ORIGINAL VP 3 blade SS 19P, and only me in the boat with ½ full fuel tank, was turning 5450 RPM WOT which was way over the 5000 max for the 5.0GXI. GPS speed was 52-53. With the Solas 8653-141-19, it now turns 4600 RPM with a speed of 50-51, so I am concerned when I load the boat up with more people, I will lose even more and bog the motor down. This seems like a big difference between 3 and 4 blade props, I was expecting about ~250, not 850? Is it just the difference in the blade design?
I was going to order an 8653-141-18, i.e. Solas titan 4 blade for VP in 18 pitch RH next, but that particular prop seems to be a unicorn, and I have not been able to find one actually in stock, though I am told at the end of Feb / beginning of March, they will be available. If my math is right and I am assuming the two Titans would be easy to compare, the 18 pitch would put me at about 4850-4900 which is about ideal. For a 17 pitch in that same prop which is more available, I think I would be back over 5000…maybe even 5150-5200. (estimated RPMs are based on achieving the same relative top speed of 51 MPH)

SO…my real question is, if I hold out for the 18 pitch, and get the 4900 when running light, what will happen when I put 4 or 5 people in the boat and am pulling tubes and skis and wakeboards…do I really want the 17 pitch, that may be a little underpropped when running light but more oomph when loaded. Is the 18 pitch enough of a step down or should I go with 2 steps…? I would like to stay with the pressed hubs since that is what I already have, it looks like I could get a Rubix HR4, but then I would have to use different thrust washers etc…if I have to change the props for some reason.

Thanks

 

[jimmbo]

Rule of thumb is 200 rpm per inch(using same model/lineage of Prop), so it sounds like a 17 should put you right around 5000 when lightly loaded,

 

[Bikestdy]

I would go for the 17p. especially if your using it for watersports. On my boat I run a 17p basically all the time because it works best for watersports but it does put my RPMs a bit high, to put my boat in proper RPM it takes 19p. I don't ever really run full throttle thought as I only really use it for watersports. You do have more power than I do though, and it may depend a bit on how you use it, if you plan to run full throttle much or not.

 

[QBhoy]

Hi
before anything else. Your tachometer is off. That engine won’t rev to 5400 rpm. The limiter will govern at around 5150 rpm. I have ran mine to this plenty with a couple of props. The rpm figure taken from the ecu data on readout. No way you are actually getting to 5400.

From other boats I’m aware of with similar sx drives (all be they could have different ratios) and the 5.0 gxi...I know of at least one that runs a 21” standard VP 3 blade at around an indicated 5000 rpm. Don’t know gps speed but dreamometer dash speedo is just about early 60’s at that.
not of any real use to you, but certainly worth verifying the rpm. It’s not possible to turn those rpm on your engine.
good luck.

 

[QBhoy]

Apart from all that. A solas prop of any kind will rarely out perform a standard 3 blade VP OEM prop. They just won’t. They are the bottom end of all things prop and are often known to even be way off in terms of their claimed pitch. The factory tolerance is pretty poor.
there is also the whole fact that plain and simple...some props just don’t work on some boats. As you’ll probably know.