boat acceleration issues - 21 Oct, 2019

So i have a skiff with a 40hp tohatsu, normally it runs fine no issues, but the other day i went out couldn't get her past 22mph it'd hit 4k rpm and jump to 5500rpm with no gain in speed.

At first i thought it was a spun hub but i went out the next day with a friend and it ran perfectly. went out today and had the same issue for 30min id try to accelerate and at 4k rpm it'd jump up with no acceleration checked everything, and nothing seemed different,

On my way back to the ramp i put the tabs all the way down and accelerated and boom problem solved, it ran like a top the rest of the day not using tabs. 

Any ideas?