slow boat to china:(

[linda mae]

hello all my name is ryan. i bought a boat this summer and love it!! its a 12.5 foot vangaurd ski bee. it has a 1980 johnson 70 for power. curently i am running a 17 pitch cupped prop that is 12.75 inches in diameter. i had a 15 pitch prop that is 13.25 inches in diameteron it before. the 15 pitch gets a top speed of 30 miles per hour and the 17 gets 32. i was told that a boat of this size (fiberglass)with a 70 on it should do at least 40. what gives? any comments or advice would be great!!!!!

 

[Dunaruna]

Re: slow boat to china

Hi Ryan, does your boat have a tachometer? What revs are you getting when the throttle is wide open (WOT)?

Your motor is 28 years old, probably time for a compression test to determine it's health.

 

[MikDee]

Re: slow boat to china

40mph, Yes, or maybe better, a 70hp motor on a 12.5ft boat
First make sure your throttle is opening all the way, butterflies fully open, and no binding in the carb linkage, or control cables
Second make sure the timing advance plate (under the flywheel) is moving, and moving to the full advance stop.

Just noticed, your getting more speed with the 17" prop, maybe you don't have enough pitch on the prop, and are overrevving! (not good) You really need a tachometer rpm reading, it usually shouldn't go over 6000rpm, or bad things can happen.

 

[Five O'Clock]

Re: slow boat to china

love the Jimmy Buffett reference in the title

 

[MikDee]

Re: slow boat to china

love the Jimmy Buffett reference in the title

You mean the old Mills brothers song?
I think that's who sang it originally,,, many, many, yrs ago.

 

[Five O'Clock]

Re: slow boat to china

i guess i'm too young for them

 

[oops!]

Re: slow boat to china

ditto on the motor......

look in the prop section.......pitch vs rpm.....then search here....on trim....and there was just a post called moved my motor up 2 holes and wow.

so it could be many factors