Sea trialed new boat and fuel burn was way off.

What is whisper wall? Never heard that name. Are you talking about the glued foam backed Veltex and then panels velcroed on it ? I hate that stuff

Well you don’t have to run the 55 at 32 kts... slow down to 20/22 and it will be more comfortable and even more economical.

75% cruise on the 84 Lazzara I run is 25/26kts but if not running at hull speed I ideally run at 20/21kts Smoother and easier on the cats

Don't get too hung up on the numbers. If the boat was at the Palm Beach show it's a Florida boat. Stuff loves to grow on boat bottoms in Florida water and it's been growing for 14 months. Also if the owner got his numbers going with wind and current (along with a clean bottom) and you got yours going into it that too will make a big difference.

Yes, but don't know where Tim got his speed numbers as the Yachtworld ad only says 18 knots. So there is a conflict in information and the 21 knots doesn't appear reasonable.

When people bandy about a lot of numbers, especially when some are guestimates and others may be puffing, the numbers lose their value. Especially when you then add in the variables. K.I.S.S. If you can afford the boat and want the boat, it reaches it's RPMs and load, doesn't blow out a whole bunch of smoke and passes survey, then buy it. You'll run the boat different than the last owner. You may get better or worse gph or mpg. So what. Use fuel burn figures as rough estimates, not gospel. As the saying goes "Mileage may vary". There's a reason car companies put in that disclaimer. As for the speed difference were they taken in the gulf stream? Going with the current or against it could account for that in many places. Real speed numbers are gotten by going a set route into the current and then with the current and averaged. Seen anybody doing that lately?