Deltarat

I have a 98 27 foot Fountain with a single step. I currently run a 502 EFI with a Whipple (3 to 4 pounds of boost) and HP 500 cam and valve train. I had a Bravo 1 and I ran a 28 pitch non labbed bravo prop. With that set up I would run right around 82 to 84 MPH at 5100 RPM. I might add that the motor wanted to spin faster but I would always back out of the throttle and stayed right at 5100 RPM because the rev limiter would scare the crap out of me every time. I blew the drive and replaced it with an IMCO SC with a 2 in shorty. My question is I reversed the rotation of the prop and have lost close to 8 MPH. I ran a labbed 28 pitch and lost about 8 MPH at 5100 RPM and had a considerable amount of slip in the lower midrange rpms. Should I try a larger prop or should I lower the lower an inch or so. Any help would be great as I want to get this thing dialed before spring. Does any one know what the optimum X Dimension is on this hull? How much does the rotation of the drive affect the performance of this hull?

Thanks in advance

throttleup

I am not quite clear on something. Are you running the opposite rotation of the original from Fountain? Did you run the stock 28P after changing prop rotation? Your slip wnt up because of the 2" shorty. Post your numbers so I can take a look at them.

What is your gear ratio?
What is your WOT RPM?
What is your WOT MPH via GPS?

You most likely will need a spacer. Can you also describe what happened when you changed the prop rotation, please.

Julie

Deltarat

Yes I am running the oppsite rotation of a normal Fountain, when I put on the new drive I changed the rotation. I ran a labbed 28 on the only trip I have taken since the drive change. I think this weekend I am going to try to run the stock 28P again and see if the prop was bad or if I have other issues.

One thing that I did notice was the boat seemed to track way up under the nose and not back by the step as before.

WOT throttle for me is 5200 rpm and then the rev limiter starts cutting the engine out. That is why I always run it up to 5100 rpm and hold it there. It was the same with either of the 28P props, labbed and also non labbed.

I run a 1:50 ratio

Before all of the changes, which I was stupid and made all at once, WOT throttle was 5200 at 83 on GPS with the non labbed 28P. Now with the labbed 28 WOT is 5200 rpm at 73 on GPS.

I am not sure if any of this was caused by the rotation change or not, so this weeked I am going to reverse rotation and run the orignial 28P prop and see what happens. I just want to get this resolved I can start looking for a prop to purchase.

throttleup

Most likely this is the 2" chorty causing this to happen. It sounds like you don't have enough prop in the water.

I calculated your slip with the stock 28P Bravo I and you had 8% slip which I am questioning. Typically a Vee bottom will run 8% with a 5B prop, less commom with a 4B prop, as they just arn't that efficient. But with the Lab Finished 28P on the shorty you have 18% slip which tells me the shorty is not working well on your boat. I would go back to a stock lower or install a 1-1.5 inch spacer. Hope this helps.

Julie

Deltarat

Thank you Julie for the help I will see if I can borrow a spacer some where and see if that makes a difference. I notice tat you work for a prop shop? Might I be able to give you a call and get some info on haveing a prop made for my boat?

bbladesprops

Single Fountains in the 27 and 29 foot range have run left hand props for years to combat listing. The rotation helps the boats attitude to run true.

With stock X diminution's we have set up countless Fountains like yours with Lab Finished Bravo 1 props. The combination of raising the drive and putting a Labbed prop on has put your slip through the roof. Who Labbed the prop? Prior to the drive change you were running under 6% with the stock prop. (that is probably too good to be true but that is what the numbers say)

Running the box stock prop will be a good experiment. You will still have higher rpms than before and most likely the slip will be higher than the box stock prop with the old depth. It will tell us what to do next.

Your boat should have no problem running a Labbed prop. We just need to get the X dimension and rotation correct. If the slip isn't too bad with the B.S. prop, we can test with a Maximus 5 blade or a P5X 5blade. If the slip is still rediculous we will need to space the drive down.

throttleup

Deltarat,

You are quite welcome! I own a High Performance Propeller Lab in St. Petersburg, FL. Please feel free to call me anytime at 727-531-2255
I look forward to hearing from you.

Julie

Deltarat

I have know idea about slip ratios as this whole thing is new to me, I have always had a jet boat before I bought the Fountain. I really appreciate all of the help. I am going to go drain the drive and change the fluid right now so that I can get on the water this weekend with the old prop and check it out. I did notice the listing that you are talking about and if going back to the left hand rotation cure that I will be happy, I didnt like that list at all. Thanks again for all of the advice and I hope to have some more info in a day or two.

Deltarat

So I did get the boat out for a couple of hours this weekend and here is what I found. I reversed the rotaition back and that took care of all of my ill handleing problems. It ran a strong 77.5 mph on gps with the non labbed 28 bravo at 5200 RPM in flat sticky water. It pulled strong all the way up, and it came out of the hole nice. So the questions is where do I go from here? Should I try a labbed 28 again while running the proper rotation or should I try a labbed 30?

throttleup

WELL WHEN YOU LOOK AT THE STOCK 502 ITS PEAK hp IS AT 5000 rpm, but when adding a whipple you will see the peak move at least 200 RPM, sometimes more. So you really need to change your rev limiter chip to allow a higher RPM. That being said...you are currently running yor motor at 5200 RPM in flat sticky water so you really cannot afford the RPM increase from Lab Finishing. Or should I say there would be no benfit from doing so. So I would recommend a 30P lab finshed and change your chip.

Julie