1stfntn

The current setup:
2000 38' Fountain twin step (the small steps); Twin 500HP Carbs with about 490 - 500HP each at the prop (20 - 30 over stock); Bravo I drives (not XR's) with non-labbed 26P 4 blade Hydros turning IN; 5350 RPM (i.e. stock rev limiter) @ 75 - 80 mph depending on passengers, load and conditions; most recent run 5350 RPM @75 with 6 people and two full tanks of gas (260 gallons total) on 95 degree day with high humidity.

Boat seems to like a lot of trim to get the max mph; usually there's a good 5+ mph in just trimming the drives from flat to "5" on the trim indicators at WOT.

Question is what prop work to do or what prop to switch to for better top end performance while still maintaining reasonable cruise and hole shot (I know both will be compromised to some extent if I go up in pitch).

Options I see are:
Upgrading the ignition, raising the rev limiter and turning the 26's faster (maybe 5,600 RPM), possibly having them labbed and reworked to hit the 5,600; Trying 4 blade 27's or 28's in Bravo's or Hydro's and possibly having them labbed as necessary; Trying 5 blade 25's or 26's (probably Hydro's) and possibly having them labbed. Any other thoughts???? Have considered sportmaster lowers and/or shorties as well. Would appreciate ANY input.

Thanks in advance,
Brad

throttleup

I have run your slip and at 80MPH you have 9% and with a heavier load at 75 MPH you have 15%. Both of these numbers present a % of slip in an exceptable range. The Hydromotive propellers typically perform well on the Fountains as do the Herings. The key is to run the motor at the RPM were the peak HP is found. On the stock HP 500 Carb motor you need to run at 5200 RPM at WOT. So in the Rev limiter you may indeed need to consider soe propeller work.

At WOT do you have any throttle left or available, when hitting the rev limiter?

When you trim to "5" on your indicator is this were you are finding the max speed?

It is possible that you may want to re-work your propellers or consider some other propeller options.

Julie

1stfntn

Julie,

Thanks SO MUCH for the quick reply. I have a little throttle left at 5350 with light and medium loads, but currently not at full. Am still fine tuning my carbs and timing from a recent rebuild, so that will likely change to a little throttle left under all load conditions, but I mean a LITTLE. Did not dyno motors after rebuilds, but engine builder expects peak HP to be higher in the rev range than stock due to a cam change. That was why I was considering the rev limiter increase. "5" on trim is DEFINITELY top speed. Could probably gain more mph going to 6 or 7, but not good for the drives per Fountain and others experience. That's why I thought speedmasters and/or shorties might help as well. What is your program for new non-labbed props? Can I do exchanges if I try some 28's and need to move to something else? Thanks again for the help.

Brad

bbladesprops

I like the thoughts of 28 Lab Finished Bravo 1 propellers with your current set up. The B1's typically pick up the mid range speeds over the Hydromotives and you will definitely gain on the top after Lab Finishing. They will put you at about 5300 with our recipe which is where we like to prop those motors for top performance.

5 blade props should help your mid range speeds also. The top end will more than likely not grow especially when light loaded. With the heavier loads they should perform well.

Changing drive heights changes everything. If you are planning to do that, wait with the propellers dialing in.

We have a set of 28 box stock Bravo 1's currently on loan. You are welcome to try them next if it suits your schedule. All you have to do is pay for the shipping and get them back in a reasonable time frame.

Let us know if you have any other questions.

throttleup

Hello Brad,

Yes, we have a wall of test props for just this scenario. Keep in mind that the propellers are the LAST thing you will do after re-working the boat. Let me know when you are ready and we can start testing and get you dialed in!

Julie

1stfntn

Brett/Julie - Thanks for the quick replies and the input!! I really appreciate it. I am hoping to have final carb and ignition tuning done this weekend, so I will make a few more baseline runs after that with my 26P Hydro's and then will give you each a call to discuss options and getting some test props. Think I may want to try a set of 28 Bravo's and a set of 28 Hydro's and then go from there. May be worth testing a 5 blade as well, we'll see.

Thanks again for the help,
Brad

throttleup

Sound good!

Julie