Hi I have a 242ss formula that has loss speed. I am running a rebuilt 330hp at 3000Rpm my speed has gone from 30 to around 25mph and 4000rpm around 35-38 I am running a mirage 21 pitch prop. I feel like I have lost about 5-9mph when I pulled the boat out the drive was full of barnicles would that do it? The boat tops out at 4100rpm I was thinking of getting another prop with 19inch pitch to increase top speed.
Thanks
Tony

Clean running surfaces (including the outdrive) are essential to good performance, even more so as the speed rises. Clean everything off and try it again.

Your engine should run to about 44-4600rpm with the prop you have are you sure the engine is running fine. Max speed with your set up is about 50-52mph. Clean it up the bottom and outdrive and try again.

yes a crummy bottom and drive will scrub speed, even more then you may think