Gents, firstly, thank you for your swift reply's, all very greatly appreciated. Now to address a few questions raised. No, I don't mean leaning to one side or another. I have found this is inherent to most fast boats that carry a deep v all the way aft. This customer's last boat was a 38 Express with CAT C12's and it had the same problem. You just have to play with the tabs a lot. I have several customers with Palm Beach 32's, 50's and a 55. These hulls are more like a New England lobster boat style, like the Hinckleys etc, and have an extremely deep V forward but it flattens out dramatically as you run aft. These boats have no tendency to lean at all. I am talking about a 2002 Cabo 43 FB. And those are the consumption figures we measured pretty accurately on a recent 8 hour run. Engine and gearbox specs in the OP. I fail to see how a 1/2 inch increase in diameter can cause ventilation. The gap between the hull and the blades has only decreased by 1/4 of an inch, that gap now is about 3 and 1/2 inches or more. I gave Veem the hull gap information in the ordering process and they didn't seem concerned by this at all. I believe the problem I have is ventilation not cavitation. My understanding is cavitation is generally (but not always) caused by poor blade design, creating tiny bubbles of air which can erode the props surface in extreme cases. Ventilation is caused when air is "introduced" to the propeller from an external source causing a much more aggressive loss of "bight" or "grip", and the revs rise sharply and the vessel turns towards the side that is slipping. Please correct me if I'm wrong on these definitions. My problem happens mostly on the port side, and is most prevalent when you try to accelerate beyond 2100 RPM not matter how gently you accelerate. Once or twice I have managed to get it to "stick" up to 2250 for several seconds, the speed rose to an encouraging 32.9 in that short space of time. Several times it has ventilated whilst accelerating around 1500 - 1600 RPM just as the boat is "climbing out of the hole". I put this down to being too aggressive with the throttle. It seems to make no difference where the tabs are, full up, partially down or full down. So generally I feel that Veem have nailed the sizing of the props spot on, we seem to be right in the ball park of all the sea trail data I have seen for this engine/gearbox/hull combo. The lack of top end is disappointing but not the end of the world. It is wonderful just to have a boat that is finally performing as it should at cruising speeds. But I would like to cure this ventilation if possible and was wondering if anyone has come across this problem before and if so how they went about fixing it. It is important to note that we have installed a new Furuno 1 kW Chirp sounder with a fairing block on the port side. It is slightly inboard of the prop shaft, I'd say at least a foot. It's about a foot in font of the main engine so at least 15 - 20 feet forward of the props. All of the other sounders on board are not "through hull", they are the internal "oil bath" style that attach to the inner skin of the hull so their signals must penetrate the hull laminate. I hope to hell that this is not the problem but am starting to suspect it as the port side is definitely worse that starboard. I look forward to hearing your thoughts. Thanks again. Sherwy.