Interesting observation.

[Britboater]

Just a little bit of info, not sure if it would apply to you twin engine guys.
On a recent trip in our SX190, I had the engine set at about 6250rpm, the GPS was reading about 28mph, or there about. I had six in the boat, all adults, two in the bow, two in the captains seats and two either side in the rear.
My son, who was at the back, decided to move up front to the bow to talk to his mother, he weighs about 180lbs, after he sat down I notice the speed drop to about 24, 25mph, then upon returning it regained its original 28mph.
It goes to show, speed and economy can be affected by weight distribution, but I guess the aviation guys among us know this already.

 

[Gym]

That's why the airlines are charging for bags now. More weight = more fuel burn. You can bet they are charging a lot more than the cost of fuel per bag though.

 

[Boat Crazy]

He pushed the bow of the boat down into the water a bit creating more drag.

 

[dbrunone]

Right...like you said its like an airplane...if your CG is too far forward, you have to pull the stick back more to keep flying level, and the greater elevator deflection creates more drag. I would assume something somewhat related is happening here. That's why most pilots (glider pilots at least) like to fly with the CG near the aft limits. But dont go too far aft or else you risk an non-recoverable spin!! (not a problem in I/O's but could be in jets hahaha)

 

[OrangeTJ]

Yeah, the kid basically caused you to "trim" down when he walked up front and "trim" up when he went to the back. This is one of the reasons an I/O can often run faster than our jets, all else being essentially equal - they can trim up at speed to get more hull out of the water.

 

[Britboater]

Exactly, as with the thread with @Speedling if our boats had a trim we could get a more efficient plane and higher top end. Most Waverunners have trim?

 

[Speedling]

I gained like 1 mph with 2 degree pump wedges installed. Even more important for most is that i get better fuel economy i believe as well. I only had one really good test on this and no exact numbers but i know that with repeating trips for before and afters i saved close to 5 gallons of fuel. This is due to having the hull out of the water just a bit more. There are two downsides to doing this. First, larger jet wash for any pull sports and the like. Second, we noticed a bit more bouncing off the waves or porpoising. The economy and speed tests were on a flat calm lake and the ride discomfort was comparing similar conditions on lake michigan.

As for the trimmable nozzle, yes it can be done but it will take bolting brackets to the hull that you will not like if it doesn't work. You will also need to fabricate some of it, and find a way to control it at the helm. Only about 75 percent of the stuff fits from the skis.
Adjustable trim would be much better than my wedges though!

 

[woodard1983]

https://jetboaters.net/threads/lectrotab-trim-tabs.71/

some good info in here on trim tabs

 

[Speedling]

Tabs can trim you down, not up, right? I guess if they hung off the side of the boat a bit, they could trim ya up

 

[Britboater]

The Waverunners nozzles move and are connected to the pump nozzle, you wouldn't bolt anything to the hull?

 

[Speedling]

Hmmm, I thought they were, but I was just trying to figure it out from pictures on google, so who KNOWS what I actually came up with. I haven't seen one first hand.