Which one to use?

[Icefire55]

I bought a boat last year, 19.2', fiber, Thundercraft Flamingo with a OMC 350/OMC 800 drive.

It came with a 14 1/2 x 19 installed, dinged and a brand new 14 1/4 x 21, both Alu and 3 blade.

Long story short, got the boat on plane once with the 14 1/2 x 19, the carb was messed up (running only on 2 barrel, would die if throttle was put too far).

Currently having the carb fixed, and put the 21 pitch blade on it as the other is pretty dinged up.

The boat it heavy, I would say 3500lbs+, so any tips?

 

[junior1113]

Re: Which one to use?

all has to do with wide open throttle rpms being within manufactures recomendations for optimum performance and engine life . 19 was prob. on for a reason. believe you'd like to see 4400 need wot rpms and speed

 

[Icefire55]

Re: Which one to use?

Well the guy was tubing with his family, and I'll probably buy one.

I guess the x21 was for topspeed and the x19 was for power?

 

[junior1113]

Re: Which one to use?

rather be under pitched and limit rpms than be overpitched and screw up motor

 

[Icefire55]

Re: Which one to use?

Yep! I'll keep it under 4800 WOT

 

[180shabah]

Re: Which one to use?

4800 is too high for that vintage.

 

[Icefire55]

Re: Which one to use?

4400?

 

[180shabah]

Re: Which one to use?

I don't have any OMC manuals, but mercs of that era were 3800-4200WOT.

 

[Icefire55]

Re: Which one to use?

Looking at many post, 350 OMC (260hp) were 4200-4600 rpm @ WOT)

I'll shoot for 4200-4400 max, and will rarely use that, maybe to launch skier, dunno

 

[junior1113]

Re: Which one to use?

id take it to 4400 max with ethanol

 

[Icefire55]

Re: Which one to use?

Finally fixed the carb (not sure now)....

with the 14 1/4 x 21 at WOT I was getting 3600 rpm
Only thing I could see is that my Carb/throttle bracket might be wrong and not allowing the 4 barrels to open fully..

We were 4, 100L of gas, no other stock in the boat.

One problem I had at first, would WOT it, RPM would go to 4000 but the boat wasn't getting on plane, looked like it was slipping like hell. Shut down the boat, tilted up, down, started again and now it was getting on plane quite easy, cruising at 3000 rpm, WOT was 3600.

If the carb is good, I guess I'll need to get a 14 1/2 x 17 to get to 4200 ? 3600 - 200 (1/4" bigger diameter) + 800 (4" less pitch) = 4200 ?

Also, when under high load, (7 persons, full gas tank, tubing) how do I change the pitch?

 

[junior1113]

Re: Which one to use?

this 3600 that your getting is with trim out as far as possible without venting? is tach is accurate? what is speed at 3600 rpm? what is gear ratio in out drive? if everything is correct you could expect 4200-4400 with a 17. under load this prop will still do just fine.

 

[Icefire55]

Re: Which one to use?

Under load, is it better to have a lower pitch or higher pitch?
I need to play with the trim, I'll bring the 2 propeller tomorow to see and I downloader a Phone Apps, to get speed via GPS.

 

[steelespike]

Re: Which one to use?

I feel that with the motor running right you should be in the 40 mph range.
probably on a 17 or 19" prop.A 19 should put you around 4,000.