throttleup

Keep in mind that these props are stock not lab finished. We have typically seen 2-4 MPH increases with labbing.

Julie

Turbojack

If on my last run with the P5x I would have gotten a computer log of the run I would then know at least what RPM I was running & call throttle up as to where to go from there. Since I thought I was running a log I did not pay any attention to the RPM. I have now pulled the motor to freshen it up since it has been 3 years since I have been thru it. Once I get motor back together I will go back out & see what the P5x will do on top end. I know I can not run around with the 30 bravo since my min. planing speed is 30mph when I am running the high x

ROTAX454

This question is to Julie at Throttle-Up: What is the correct way to measure the X dimension. The one method that your company will recognize as good information on choosing the right prop (or at least a good starting point baseline).

Information that may be helpful on the above question? Awesome 31' Thundercat w/twin 525HP 600 Lb.torque motors with standard 1998 Bravo 1 drives. No cones. Since the motors are new and not in the boat till spring, the only reference I can give you is on the previous set-up. Twin 7.4L mags with 330hp, bravo 1 four blade 28P props. 70mph on GPS @4600rpm. Would not plane under 30mph. The ONLY time the props would blow out was under a very very tight turn under heavy throttle.

Getting to the point-------looking for the correct prop for a good starting point.

throttleup

Rotax454,
Since there are so many 1", 2" and even 3" shorty lowers out there and many are running with spacers the best way is to measure from the center of the prop shaft to the bottm running surface of the hull.

Where the props you an before lab finished? What will be the WOT rpm of your new motors? Do you have dyno runs on the new motors?

There are many considerations when chosing a prop, it's best if we have the opportunity to talk to you and we can get all the information we need to make a recomendation. We also have test props that may be a good starting place.

Robbie Racer

What should the trim be set at when measuring this way? On my 25' Carrera cat, I measure the centerline of the prop shaft dead even with the outside sponsons (lowest part of the hull) when the trim is out where I run it at top speed (about +7 degrees from the sponson angle). If I lower the trim all the way down, the prop shaft centerline will be something like 2" below the outside sponsons.

throttleup

For reference purpose we need to know where the prop shaft is when the drive is positioned so the prop shaft is parallel with the running surface of the bottom.

shawn

ROTAX 454 I will bet you could use the set of P5-32s I have for sale. They ran 5100 RPM on my HP500s. Let me know.

Shawn

ROTAX454

Thanks Julie for the quick response. Do I measure from the "lowest" point of the hull (sponson) running surface? Of course to the centerline of the prop shaft. The props were NOT lab finished. The new motors will have a 5200 rpm WOT criteria. The heads/cams are being built for that specific 5200 usage. I am not planning on dyno testing the motors. Although I would certainly like to, just don't have a good source. I will try to Tyler Cocket and see if he (providing he has a dyno) willing to dyno my motors.

I am considering installing the 2" IMCO shorty lowers. Looking for your professional opinion on whether to stick with the stock bravo lowers (98 & up model) or going to the IMCO lower, and if so what height? Let me know on the X dimension question, then I will measure it correctly and get you the dimension. May help in answering so of my latter questions. Thanks again. Richard

ROTAX454

Shawn, I will keep those in mind. The motors will be producing approx 550 HP and 600+ Lbs of torque. Don't know (only testing will show) if your props will hold the motors to the desired 5200 rpm level at WOT. What size cat do you have? How did the boat react to these props? Richard

shawn

Richard, I have a 36 Spectre with HP500s. I moved to a smaller prop because the boat was right around 65-70 MPH at 3200 - 3400 RPM and I was right where the boat porpoises. By going to a P5 31" I was out of the porpoise range during cruise speed where I spend most of my time and they would still run the same speed at a higher RPM. As far as your lower, I would go with a short one and use spacers as needed to get where you want. This will give you the most amount of adjustment. There are a lot of guys on this board that will let you test used parts and either return if they don't work, or you buy them if they do work, or you scratched them.

Good Luck

Shawn