Top Speed!!! 1996 Chapparal 1830SST

[stingray165ss]

Hey guys quick question here, I have a 1996 Chapparal 1830SST with the 4.3L Mercruiser & Alpha 1 Out drive. Currently the boat has a 19P alluminum prop on it, with 3 adults in the boat i can currently get a top speed of 42MPH. The maximum rpm range on the motor i believe is 4400-4800 i feel that i could probably turn higher than that if i were to give it full throttle. The question i have is should i be able to go faster than 42mph with this boat? i was hoping that it would be closer to 50MPH. Also should i go up to a 20P prop? I know that each pitch you go up to drop around 200 RPM. I am not sure how many RPM i can go over the 4800 because i am scared of blowing the motor if i try it.

 

[Slip Away]

Re: Top Speed!!! 1996 Chapparal 1830SST

You NEED to be able to hit WOT. Put the hammer down and report back what was your top speed and RPM. Then we may be able to help.

 

[Bondo]

Re: Top Speed!!! 1996 Chapparal 1830SST

Hey guys quick question here, I have a 1996 Chapparal 1830SST with the 4.3L Mercruiser & Alpha 1 Out drive. Currently the boat has a 19P alluminum prop on it, with 3 adults in the boat i can currently get a top speed of 42MPH. The maximum rpm range on the motor i believe is 4400-4800 i feel that i could probably turn higher than that if i were to give it full throttle. The question i have is should i be able to go faster than 42mph with this boat? i was hoping that it would be closer to 50MPH. Also should i go up to a 20P prop? I know that each pitch you go up to drop around 200 RPM. I am not sure how many RPM i can go over the 4800 because i am scared of blowing the motor if i try it.

Ayuh,.... At What Rpms,..??

 

[stingray165ss]

Re: Top Speed!!! 1996 Chapparal 1830SST

So it will be ok if I go over the 4800? I believe it would probable get up around 5200. And currently the 42mph (on GPS) is at 4800 rpm. Should this boat be able to do 50mph?

 

[steelespike]

Re: Top Speed!!! 1996 Chapparal 1830SST

With the right prop it should be in 50 mph area.You need to prop for the upper end of the rpm range at wot.
Its fine to run it to the required rpm to get the full wot specs. Then we can figure out how well your setup works and what prop you need. Do you know the hp rating of your 4.3?

 

[stingray165ss]

Re: Top Speed!!! 1996 Chapparal 1830SST

ok guys i am back i went camping at the lake for a week. I picked up a used 21P Aluminum prop for $25.00 from a local shop. The boat was hitting 42 MPH at 5100 RPM. does this sound right? I had the dealer i bought it from install a brand new tach. so i know that the tach is not the issue. The local shop here told me that the 4.3 would not turn a 23p prop. so i am not sure which direction to go here.

 

[spoilsofwar]

Re: Top Speed!!! 1996 Chapparal 1830SST

The local shop is clueless; my 4.3GL equipped boat came from the factory with a 23P prop on it.

If you are turning 5100rpm @ WOT with a 21P prop, I would suggest putting a 23P on it. That should drop you to ~4800rpm or so @ WOT, which is where you should be for that motor. You should also pick up some top end speed.

The next question is why did you not pick up any top speed when going from the 19P to 21P, at WOT, if you were achieving (exceeding, really) rated WOT RPM? That I don't know..