25 hp mercury

[rooster1]

i have a 15 ft v hull with a 25 hp mercury i took it out for the first time sat and it seemed like the engine would rev up but the boat wouldnt go any faster after about half throttle any ideas?

 

[Barnacle_Bill]

Re: 25 hp mercury

It sounds like you have a spun hub which according to my prop man is quite common on those 25 Mercs for some reason. Using a magic marker put opposite marks on the inner and outer parts of the hub and try it again. If the marks are no longer lined up the prop will have to be re-hubbed.

 

[rooster1]

Re: 25 hp mercury

i was thinking maybe it was too short of a shaft would that sound common what does rehubbing involve?

 

[Barnacle_Bill]

Re: 25 hp mercury

Take it to a prop shop and they will press out the old and press in a new one. What makes you think the L/U is too short? Where is the anti cavitation plate in relation to the bottom of the boat? It should be somewhere around even with to 1" above the bottom.

 

[rooster1]

Re: 25 hp mercury

its about even with the bottom theres a round plate on that piece but about half of it is broke out will that affect anything

 

[Barnacle_Bill]

Re: 25 hp mercury

its about even with the bottom theres a round plate on that piece but about half of it is broke out will that affect anything

Your motor height is OK. Not sure what round piece you are talking about unless it is on the bottom towards the rear. That would be your trim tab and would have a small fin pointing down. Replacement is pretty cheap.

 

[TheOzzieMechanic]

Re: 25 hp mercury

I agree. Sounds like a spun hub not a major repair. Takes about 1/2 hour if that. Try marking the prop as describe above and if the markings move in relation to each other after you have got the engine to cavitate again then send in just the prop for rebushing. It also pays to have a spare prop in the boat just in case. Id rather stick on a spare than row home! Lets compare it to the car. When to you leave without a spare tyre? at least with the car you can walk to for help