Is this speed about right?

S

scooter4n

Seaman Apprentice
Joined
Jul 15, 2007
Messages
45
Hi, I have 18' 1990 Chaparral 1800SL with 3.0 Mercruiser
Motor and carb and outdrive has full rebuild over last year, compression is perfect in all 4, starts and runs perfect. New plugs, cap, and all that tuneup stuff, timing and all...

I had 17 prop and it only gives me 26-28mi/h(GPS) at 4500-4600rpm at WOT
then I put 19 prop and now Im getting 31-32mi/h(GPS) at 4200rpm WOT

is this all I can get or should I try 21 prop???

Thanks all
 
Bondo

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,513
Re: Is this speed about right?

Ayuh,... That sounds that's All she's got... A 21" will dog the motor...

Use the 19" for Cruisin',+ the 17" for skiing or tubing...
 
junior1113

junior1113

Senior Chief Petty Officer
Joined
Jan 29, 2009
Messages
763
Re: Is this speed about right?

sound like a lot of slip. what type of props are they? allum,or ss? there is probably a chance of getting more power and speed with a good ss 4 blade prop. they tend to have a lot less slip.
 
Chaz7R

Chaz7R

Seaman Apprentice
Joined
Jun 7, 2009
Messages
47
Re: Is this speed about right?

I have a 18ft 1993 thompson with the 3.0. I had a 17p 3blade and it runs 39mph at 4800 wot. I put a 20p 4 blade on and it runs 40mph at 4300 rpm wot I can get it to about 43 mph with trimming up then the rpms go to 4700. I was just commenting because our boats have the same engine and same length
 
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