No speed with a twin mercruiser i/o v6's

[mastercylinder63]

Greetings,
I purchased a used 1997 Larson 29' Cabrio boat with new 2008 engines. The drives are Alpha 1/ Gen II
The engines run excellent, but the boat doesn't go faster then 10 mph. It seems past 2500 the props seem to cavitate or spin out. I even tried one engine at a time and the same result happens. When the boat was on blocks, I replaced the zinks and took off the ss props. I reinstalled the ss props on the same outdrive where I initially removed them from. The props plastic inserts seemed to go on nice and snug, the nuts are on snug with the star washer tabs downward. I also added Lenco trim tabs and installed them according to the directions.
So I have both outdrives trimed fully down, props seem to cavitate at above 2500 rpm. I can only go 10 mph. What can it be??? Could the prior owner reversed the props??

 

[Bt Doctur]

Re: No speed with a twin mercruiser i/o v6's

and the drives are?????????????

 

[mastercylinder63]

Re: No speed with a twin mercruiser i/o v6's

The drives are Alpha 1/ Gen II

 

[Bt Doctur]

Re: No speed with a twin mercruiser i/o v6's

Both standard rotation, or is one counter .Did it perform correctly when you water tested it pre purchase.
Manual 14 can be found in the Adults Only section.

 

[mastercylinder63]

Re: No speed with a twin mercruiser i/o v6's

Yes one engine is counter rotation

 

[wire2]

Re: No speed with a twin mercruiser i/o v6's

......Could the prior owner reversed the props??

Then you would go backwards when shifted into forward. The props are pitched opposite each other.

Are the cavitation plates of the outdrives at ~ the same depth as the hull just in front of them? Are the props ventilated?

I'm thinking your props might be spinning on the hubs. In gear, can you force the props to turn against the engine with your hands? (wear gloves, blades are sharp)

 

[boat127]

Re: No speed with a twin mercruiser i/o v6's

are you trimming your drives properlym when under way?