props

[chester91]

hello i have a 1983 wellcraft 248 offshore with a 305 boat is about 5000 lbs i can not get over 4000 rpms at 20 mph it has a 15.25 x 15p i tryed a 13.34 x17p same results u would think rpm should change engine was checked good compression good spark good timeing only thing i can think is wrong gears in outdrive HELP

 

[SparkieBoat]

Re: props

to get your RPMs up you should go DOWN in pitch not up,,..you may want to try a 13 P prop. what HP is that motor 200??

 

[craze1cars]

Re: props

Identify the gears in your outdrive for us....

Turn motor over by hand one full revolution, while someone counts the number of turns the prop makes. This will be your ratio. With that info we can run calculation and tell you if you are in the ballpark of what would be expected.

Also verifying your tach's accuracy with another tach would be smart.

I agree entirely you might need to try to find a 13 pitch to get your RPMS up (which would be unfortunate...and a regear may be in order to prevent using a 13....13's on sterndrives are not often very good for efficiency). Either that or your prop is fine, and you are simply down in horsepower...and you just haven't identified why/where the engine problem is yet.

 

[chester91]

Re: props

its a 305 with 230 hp i pulled the boat out and found barnacle all over bottom im going to clean n bottom paint then try again i will let u no what happens

 

[SparkieBoat]

Re: props

barnacles can really slow a boat down big time... 230 HP should push that boat 35+..you may have engine problems as well.

 

[chester91]

Re: props

barnacles can really slow a boat down big time... 230 HP should push that boat 35+..you may have engine problems as well.

well i scraped barnacles off and bottom painted put 15x15p back on boat goes 32 33 mph at 4000 rpms happy now but still cant get over4000 rpm maybe under power with 305 or tack off or maybe prop now still trying

 

[SparkieBoat]

Re: props

I still think you are missing some HP...230 horses should spin that 15P prop into the mid 4K rpms. or it is possible you have a faulty RPM gauge. both should be researched thoroughly.