[1badavenger]

Well I posted a while ago abdout my cavitaion problems and have narrowed it down to the prop. It is a LH 13x13 Ni-pral 3 blade. The boat is a 20' Campbell Tunnel Daycruiser. Motor is making roughly 525HP. Velvet drive transmission, and a chmpion v-drive. It is my understanding that gears in this drive cannot be changed so the gears in it are stock, specs are unknown. Any help on which prop to go with or any other insight would be much appreciated.

 

[Weaverman]

No problem changing gears in that box.

I just saw this exact (prop) question recently here, and don't think it was you asking. Maybe a quick search or just scrolling backwards thru the v-drive section will shed some light. For sure, the prop you've got isn't the one to have!

 

[R.B.]

12-15 3 blade

 

[FLTFLYN]

12-15 3 blade

http://www.rbprops.com/3blade.html
There's your answer from the man. No need to look any further. Click the link and pick up the phone C'MON...

 

[palhal]

If you are cavitating you don't reduce the dia. or blade area. You are not providing enough info on RPMs.

 

[1badavenger]

If you are cavitating you don't reduce the dia. or blade area. You are not providing enough info on RPMs.

Not sure I know what info your looking for, but it feels like I loose the prop all together at about 2900rpm's

 

[J Shelfo]

12-15 3 blade from R. B. These props kick ass, and if they dont work for you, there is something wrong with your boat.

 

[palhal]

If it doesn't cavitate badley when comming out of the hole then your diameter is ok. If cavitation comes on later when the boat is on a plane then something in front of the prop is causing it to cavitate.

At one time there were bronze struts made that had water pickup scoops on each side of the neck of the strut and it would mess the water up at various speeds and the RPMs would go up and the speed would not.\

Tunnel boats are real bad about cavitation especially in any kind of a turn.

 

[InsaneInjun]

prop ?

gear ratio is stamped on the case and when it has been changed it is restamped.

 

[AlohaJeff]

12-15 3 blade from R. B. These props kick ass, and if they dont work for you, there is something wrong with your boat.

I talked to RB about a month ago and he recommended the same 12 / 15 prop for my 24' Spectra. My concern is the 24XS is heavy and I don't want to spend the $$$ and time testing out a 12/15 if it's not the "right" prop for this size/weight hull. I too have a Champion box that's approximately 20% over getting power via a TH400 and a 600hp BBC. I just sold the 12/14 3-blade prop that was on the boat because it wasn't working well with the upgraded power. If an RB 12/15 is the answer to my prayers so be it, but if something else out there will work better I'd like to know about it before I plunk down $750 for what appears to be a 1-size-fits-all cruiser prop. I know not all cruisers are the same so my pea brain is having a hard time accepting the same prop will work best on all of them. If I can get 55mph out of the boat at 5000' of elevation I'm a happy boater.

The other issue... the current setup is a 1" shaft. Some people have said that I'm right at the limit for a 1" shaft... the last thing I want to do is upgrade the prop and then go home crying because of a shaft failure.

Aloha

 

[overpriced hallett]

why is the shaft 2 small if its because the power its fine

 

[AlohaJeff]

why is the shaft 2 small if its because the power its fine

I'm not sure the 1" shaft is something to worry about or not. Some say it's fine, others say it's close to it's safe limit. The quality of the shaft is unknown to me and for all I know it's the original 35 year old shaft that might be on the verge of failure or just getting into its prime. The boat is not a racer, never will be. She is heavy dry and with the family and a days worth of "gear" it requires a fair amount of throttle to get going and even more throttle to pull a 200lb guy out of the water on a ski. I like to think the current lack of acceleration and performance is largely due to the wrong prop. I know I need a new prop because with the old 12/14 prop I was getting terrible prop slip numbers. I just want to be sure that when I spend a good chunk of money on a new prop it's going to be right for this particular application the first time.

Aloha

 

[overpriced hallett]

it's probably fine but if its 35 years old and was thinking about getting a new prop i would probably replace it but i would listen to rb hes the prop guy and if your thinking of changing to a 1 1/8 your opening a can of worms. srut shaft coupler ect.. another guy to talk to is glenwood marine in el segundo ca
hes a old timer and he will tell you either way

 

[R.B.]

opening a can of worms is the perfect way to say it. if your worried about the shaft? then put a new one. but stay 1 inch for sure, thousands of others have 1 inch.

 

[AlohaJeff]

An old thread back from the dead...

So here's an update. I ran the boat at Parker last year in early November. I had 1 buddy in the boat with me for the test and we ran 3/8 full on each tank. All of the other crap from the day was still in the boat... tubes, bbq, etc.

11/13/2010 - 850 Holley w/River Jetting
Location: Parker Strip
Spectra 24XS
12x15 3 Blade RB Prop
15% Overdriven
5000rpm = 50mph
Slip = 40%
Theoretical Speed @ 25% Slip = 63mph

With the same above setup and 4 adults and 4 kids we ran 47mph down river about an hour before this test.

So today I borrowed a buddies Kindsvater 14/15 prop that was designed to get big skiers out of the water. The boat was basically exactly as it was when I did the Parker test last November. Same buddy in the boat, same carb, same (old) fuel load, etc. I normally run a smaller vacuum secondary carb on Arrowhead and the 850 mechanical at the River. Today, for testing purposes only, I ran the River carb on Arrowhead with poor results.
　
5/3/2011 - 850 Holley w/River Jetting
Location: Lake Arrowhead (5106' elev)
Spectra 24XS
14x15 3 Blade Harold Kindsvater Prop
15% Overdriven
4000rpm = 44mph
Slip = 34%
Theoretical Speed @ 25% Slip = 50mph

My prop slip numbers seem terrible! I have talked to a few other Spectra 24 owners, including Campbell Carl and his Spectra splash, and it seems like they are running in the 20-25% slip range. Which leads me to believe I've got a lot of work to do on the bottom of this damn boat.

Aloha