boat setup

rmpenton

Seaman
Joined
Feb 20, 2003
Messages
68
i have a 84 cajun special with a 77 johnson 115 on it. i have my motor setup 2 inches above the transom and the top of my prop is even eith the bottom of my boat.it does 37.5 mph at 5000 rpms with a 13 3/8 X 17 prop.trimmed all the way down.should i get my prop cupped or get a diffrent one? when i trim up im guessing that my rpms will go up at least a grand i dont think cupping my prop will will drop the rpms enough any help will be gracious
 

FlyBoyMark

Ensign
Joined
Apr 14, 2002
Messages
934
Re: boat setup

The important part is where the cavitation plate is and not the motor clamp. It sounds as if the cavitation plate is about 1-2" above the bottom of the boat. If the prop is running entirely in the water....DO NOT run a cupped prop. Cupped props are for actually running upto the top half of the prop OUT of the water. A cupped prop on your present configuration would only slow you down. If you raise the motor UP not trim OUT on the transom then you can start to experiment with cupped props. In addition when running cupped props, they are more efficient at the upper end of the engines rpm envelope. A transom standoff bracket (jack plate) moving the motor as far aft as possible also helps. On the average, with all those modifications you can expect about 5 MPH gain in speed. A decent prop is about $400.00 and up plus the jackplate, longer cables if needed. This also stresses the motor and lower unit somewhat too. The whole modification process could cost well over a grand.
 

rmpenton

Seaman
Joined
Feb 20, 2003
Messages
68
Re: boat setup

thanks but speed isnt what im looking for.i mean its a 16'flatboat with a 115 on it. it wont be stable at high speeds.40 mph is plenty enough speed.i want to get the top fuel economy and keep my motor in between 5000-5500 rpms.i have plenty of cables for a jackplate becuase i thought of a jackplate when i bought my steering and throttle cables.my main purpose is to not lug my engine.its an oldie
 

FlyBoyMark

Ensign
Joined
Apr 14, 2002
Messages
934
Re: boat setup

You can still run a cupped prop for bottom clearance(jack it up)..jus don't prop it for speed(keep the revs down)....as far as fuel efficientcy, go to Boyesen Reeds and put set in...this helps hole shots, idle and fuel consumption with about 100 to 300 rpm increase in engine rpm at top end on most engines. I have a set in and they do everything they say they do. They are also standard equipment now a certain big EFI Mercs.<br /> web page
 
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