I boat a old 16ft 1972 Terry Bass Boat last Jan. It has worked great for me, for being my first running boat. It gets me up to 21 (by myself) and it drops down a lot when I get one other person in it. And if their is more then 2 of us it goes the same as if it is just two, but that added on person from being by myself drops dramatically. Being a 55HP some people told me it should be able to push me around at about 30mph. The compression levels on the 2 cylinders are about 140 both. Could the lower unit be causing this? How fast should I be going with a 55HP? 20 mph is fine for me, but I just wish it wouldn't drop as much when someone else was in the boat. I have been thinking about upgrading to maybe a 85HP during this winter, but if it something with the lower unit then maybe if would be easier and cheaper just to replace that. Automotive engines I know things about, but outboards are new to me, so any advice of help would be great. What do y'all think?