Hi both the engine oil and the drive oil were changed this spring a week before I put the boat into the water so the oils should be fine at this point which is just under a month of being in the water. Both oils are Mercury synthetic oils so they should be good for at least my whole boating season which I will change them again this fall.

Hi Yes the RPM is showing the same that it was running at 72 mph. Which is what makes me wonder about the current prop hub Flo Torq II the Delvin / nylon main hub. I just ordered the solid hub version for over 400 HP today. Hopefully this will fix the problem but as I said it doesn't appear to be slipping at lower speeds and it doesn't seem slipping at WOT but I guess that it could be flexing or slipping some as I used the boat more and more over the past few weeks.

I have no idea what the fouling capabilities of your , or any , lake is but the only way to properly clean the bottom of a boat that's left in the water is to don a mask and physically get under it. It wouldn't take much fouling to see a 4 mph loss . And remember , the prop has to be spotless as well .

Pull the boat out of the water and clean the bottom and inspect prop. Prop hubs are either bad or they aren't. They won't just slip a little bit.

growth / scum line on the bottom and outdrive and prop will slow one down from 4 to 10 miles depending on how much growth. Also make sure your not holding water that is entering the hull.

When I clean the bottom of my boat at the Sandbar it gets very clean I don't have a lot of buildup on the bottom just some water scum and it all gets scrubbed off with the brush and pole that I use. I do half of the boat at a time starting at the transom and working forward on one side and then doing the other side the same way. I also clean the outdrive and prop as well. It's not perfect but in the past it has provided me pretty much the same WOT throttle speeds as when I first put the boat into the water. AS I said in my original post if it's a humid or really hot day I don't even bother wasting the fuel doing high speed runs as I know that those conditions will Rob the engine of major HP.

So without any Alarms going off in the boat are there any codes that would only allow the boat to reach say 90% power instead of 100% without sounding an alarm or beeps? I thought that I have read that with the prop hub that I'm currently running on the prop if it overheats or hits something it would heat up and twist some and then cool down and still spin the prop normally after that but I'm wondering if it's heating up the Delrin / Nylon hub and slipping some at WOT?

I would check the condition of the prop itself. If you are in a lake where you have a sandbar, chances are you have other shallow spots where prop damage could occur as well.

BTW, these boats were never intended to be left IN the water for a full season, and especially not a West Coast boat like a Shockwave. The majority of the West Coast boats have a LOT of wood in their construction. I am NOT familiar with the layup schedule and materials that Shockwave uses, but be aware that you could potentially be absorbing water into your transom and stringers at mounting and through-hull points. (Tabs, ladders, rings, indicators, transom assembly, underwater lights, bilge plugs, etc. etc.).

Simple physics and elimination. If the motor is spinning the same rpms and the driveline is solid the prop is spinning the same rpm. So your speed loss is not engine related.
So now that we have eliminated the motor as a variable, that means somewhere you have lost efficiency. that leaves 3 possibilities.
1. your prop is tweaked
2. you have more drag
3 you are moving more weight.

4) The more accurate than GPS , speedo is incorrect. :)

Dude, I tried to tell you to leave the skanks to the fountain guys....

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