Greg & Tracey Campbell wrote:
I took my boat to the lake yesterday for the first time this year and it
cranked right up, when I gave it full throttle, I got high RPM's but no
speed, we were only doing about 5 mph. It worked fine last year before I
put it up.

It is a 2002 Mercury 90 HP.

Any help would be appreciated.

As the others said, it could be a spun prop. This means the rubber
layer between the inner hub and the prop has let loose. It's designed
to let loose if you hit an object with the prop to protect the inner
workings of the engine - like a shock absorber. Sometimes they just
wear out,I guess, although I've never personally experienced that, it
seems to happen. It can be fixed by a prop shop. If you don't have a
spare prop, this might be a time to buy one - to use while the old prop
is in the shop and to have as a spare for the future. If your current
prop is stainless, buy an aluminum one for the spare.