Proper pitch prop. 96 caravelle

[Grizzy1967]

Performance issue trying to fix.
Too high of rpm @wot

Current prop manufacture.
Mercury marine "vegelante"
Stainless

Current prop dia. and pitch.
14.5" 19p

Wot rpm
6 grand only hold it there for just a second (scares me) lol. I also don't really know if the tach is correct. I know this is too much wot should be 4400-4800 rpm

Wot speed
42mph gps

Engine
4.3 mercruiser lx gen+ 96 model I've heard different hp. I'll call it 190 @ crank. It is carbureted.

Drive
Alpha 1
Don't know the ratio.

Boat is a 96 caravelle 1750br 17' iboats specs says 2000 lbs dry.

Looking for over all preformance prop.
Thanks in advance.
Ben

 

[Slip Away]

Re: Proper pitch prop. 96 caravelle

You need a 14.25 x 21 3 blade aluminum to be in the correct rpm range. 20 pitch 4-blade will also work if you tow tubes.

 

[Grizzy1967]

Re: Proper pitch prop. 96 caravelle

Ok thanks, I'm no expert by no means. But I don't know if the 2 more extra inches of pitch would be enough to lower my rpms by 1200 or not :-/

 

[jestor68]

Re: Proper pitch prop. 96 caravelle

The most common gear ratio with a 4.3L is a 1.81.

With a 1.81 ratio, a 19 pitch at 42 mph works out to about 4225 rpm.

Put another way; a 19 pitch with a 1.81 ratio running at 4600 rpm with 10% slip equals 42 mph.

Looks like a tachometer problem.

 

[Grizzy1967]

Re: Proper pitch prop. 96 caravelle

Thanks for the reply. I'll look into the tach. Anyone have any experience with tiny tach?

 

[jestor68]

Re: Proper pitch prop. 96 caravelle

Another example using a 1.62 gear ratio(the other possible ratio for your size boat); 4250 rpm with a 19 pitch at 10% slip shows 42 mph.

It may be useful to clean the connectors on the back of the tachometer, as they can get gummed up over time. When the pins on my tachometer get dirty, it causes the tach to read high. Pulling off the plastic three pin connector(in my case) and cleaning the pins fixes the problem.

The Mercury prop selector for your boat calls for: 21 pitch with 1.81 ratio, and a 19 pitch with a 1.62 ratio.

It's 190 HP at the prop.

 

[Grizzy1967]

Re: Proper pitch prop. 96 caravelle

Thanks jester, I'll look into it when I get a chance. I just bought the boat in January and have only had it on the water 3 times. The first time I took it out wot was around 5300 on the tach. The last two times I have taken it out is when it pegs the tach out at 6 g's. so you're probably right. Sounds like a quirky tach. Idle rpm on the tach is about right I think.

 

[Bondo]

Re: Proper pitch prop. 96 caravelle

Thanks jester, I'll look into it when I get a chance. I just bought the boat in January and have only had it on the water 3 times. The first time I took it out wot was around 5300 on the tach. The last two times I have taken it out is when it pegs the tach out at 6 g's. so you're probably right. Sounds like a quirky tach. Idle rpm on the tach is about right I think.

Ayuh,... Welcome Aboard,.... Sounds like ya might have the right prop, with a Bad tach....