Bravo one to sportmaster = -4mph?
 

Team Yahoo, 36 Skater, 500 EFI's, props shaft 2" above the bottom before and after. Tested with 3 sets of props and lost 3- 5 mph and 200-400 rpm. Skegs were cut down 2". Reason for change: cracked 4 lowers just above the carrier! Has anyone had or heard of these results and has anyone found any solutions? This is like loosing 60-80 HP. This is very depressing. Thanks for any replies. John B

Sounds like the boat needs to go back to THE LAKE and get dialed in again. Whenever you make a drastic change like that your going to expect some changes positive and negative. You just have to work through them.

Good Luck:D

What ratio?

that boat had #6s on it, did you make the change or did you get the boat that way. It was the fastest 500hp 36 with #6s I've seen. Those boys from TX had it dialed in.

Also, sounds like the drives are too low based on the larger props and built-in set back of the drives if mounted at the same propshaft c/l as the Bravo's..

See below

Guys, Light it was running 113, now it runs 109 light. The drives (shaft height is the same as before + 2" from bottom), and props are the same. These skegs are much thicker (may be 3/8's") and longer front to back than the B1's. The water pickups are smeared all over the lower nose cones and the case is a little bigger diameter. The water coming off the bottom only hits the carrier case on the bottom below the shaft centerline, hence the water pressure runs between 8 and 13 lbs.

Velocity, This is the original Yahoo 1 which set the APBA Kilo record in 1999 at 112.864. I bought it from Curtis when he was buying a Supercat. He was accustomed to winning and wasn't so he bought another 36 Skater to run in F3 and called it Yahoo Too. That one had 6 drives. Yahoo 1 was tested in Powerboat Feb 2000.

Marc, 1.36

Anybody else?




Go back to the previous page.

I am stupid! I should read more carefully, I assumed you meant you went to speedmasters, you mean you went to sportmasters!

What pitch props? Any chance you can raise the drives? What was the ratio before change?

It sounds like you just have too much more drag. Bigger cases and thicker skegs will do that. Maybe shave the skegs down to razor sharp leading edges and see if you can a get a tad bit more.

Also, aren't the gears cut differently (more square) in the Sportmasters? If so, you are losing a few more ponies in the drive itself; especially since it is spinning thicker (read heavier) shafts, right?

Sounds like a walk around the dry pits before a race and taking a few notes and pictures would help. You know those guys make them as fast as they can.

If you went from Bravo's to #6's at the same x dimension, you need to raise the x dimension. #6's are designed to run higher.

OK, Bravo 1 to Bravo 1 sportmaster lowers. Uppers are the same as before 1.36 XZ's. The lowers were bought empty and my XZ large prop shafts and gears were installed with new bearings by a Mercury facility.

Props tried B1 34's labbed without diffuser, B1 35's labbed with diffuser, and 33 Q5's labbed without diffuser ring.

The rev limiter was moved to 5700 two years ago.

Too much drag...most likely. I can't believe I am the first one to learn this.:eureka:

Sportmaster Lowers
 

John,
It is surprising that the Sportmasters are slower at 110+ mph than the std. Bravo lower at the same "X". From what I have learned in back to back comparisons, the Sportmaster lower unit is 1 to 1-1/2 mph slower than the IMCO unit at the same x dimension ( Two cat's and one "V" ). These comparisons were at 105 - 115 mph. Most opinions related to the speed difference were skeg length or thickness. I wonder if the water pick up design on the Sportmaster vs. the IMCO or the std. Bravo unit is causing a decrease. As there is a chance that the speed loss is related to this, maybe you can temporarily plug a few Sportmaster water pick-up slots for a test.
Could you have a temporary loss of HP that is effecting the test results?
If you need your 1/2" spacers back, I not using them... Remember, it's all about the hunt.
Good hunting,
Sprague

Quit foolin' around with that old cat, buy a Magnum and start enjoying boating again. See you on the lake.

Sprague, Anything is possible. I have waited until I tried half a dozen different days (temperature & humidity), loads, and tried all my props before this post. I am hoping to find someone with similar experiences before I start hacking away at Mercury's engineering marvel.

Bob, I hung upside down in your bilge for 5 years trying to run 80. Now I can sleep between my engines and get depressed if I only run 100.

Love the quote!!!

Everytime I think about doing something else to my boat I am told by friend "That change should only be good for a 4 or 5 mph lose"

I just found out Mercury sportmasters have (TWO) different styles of water pickups on these drives; a long system that the std. flush kit doesn't work on and a newer shorter style that the flush kit covers. I have the long style. Does anyone know what is up with this deal?

Appreciate your info on "things that don't work". I'm in the middle of a lab prop adventure that resulted in a negative 3mph. Labbers response was, "what happen to your engines?"

How do you just "raise an X dimension"? Isn't it set from the factory based on the length of the drive lower casing and where the drive is mounted to the transom? What am I missing? I know with outboards you use a jack plate to accomplish this but that can't be done with inboard/outboards rigs...can it? I thought the only way to adjust the X dimension once you get the boat from the factory is by installing a shorter lower casing.

Curt, This boat has Stellings boxes (drive extenders), which allow the drives to be raised or lowered 2 inches, without redoing the transom. Now I can go up or down 1 inch without to much trouble.

Has anyone sharpened the skeg on these sportmasters yet?

How about the water pick-up changes Mercury made?