I/O boat lists toward starboard above a certain RPM...?
 

I was on a friend's boat earlier this year and noticed it starts listing once the engine speed reaches 3000ish RPM or higher.

What would be some of the causes for this?

The boat is older Glastron 19' bowrider propelled by a Merc V6 and Alpha 1

No trim tabs
Whale tail on the outdrive
Prop pitch unknown at the time of this post

It could be a lot of things.

Water could have infiltrated the fiberglass on one side making that heavier.

The outdrive or the whale tail could be very slightly angled, just enough to affect the boat.

The boat could be loaded heavier on one side. (Stored items, lifejackets, toys Etc.)

I had a 2013 2700 Regal that was the most unstable boat I have ever operated. No matter what you did, adjusting the tabs and stern drive angle it would not stay where you had it. It would slowly roll from side to side for no apparent reason.

Sometimes the design of the hull has a lot to do with it.

All Prop...?
 

Is this the 130HP engine? I'll ask a friend with an older Glastron 19.

Great "little" boat, BTW. (Though its five feet longer than the runabout that got us into slalom skiing with only only 20HP). Gets through culverts, tiny passages, and under Wolfeboro's Smith River Bridge to Wolfeboro's secret, available, and empty Town docks. ;)

It sounds like a prop-inefficiency "at speed".

Damaged blade? Corrosion covering the aluminum? New prop, but inefficient pitch?

.

I failed to mention, the boat sits level at the dock. It seems to me to be related to power delivery or efficiency, as you both have mentioned.

Regarding the whale tail, how far out of alignment would something like that need to be to affect the ride as described?

If it has a left hand prop (kinda unusual in that application) prop torque would explain a starboard list.

My guess is that the whale tail is flexing and dipping under water on the starboard side above a certain speed.

Whaletail is Suspect...
 

My friend with the older Glastron-19 got back to me. All he could offer was that the battery may be on the wrong side. He has no whaletail. He adds that there is a tab on the stern that is factory set to compensate any irregularities, keeping it straight.

If the prop's rotation is changed from the stock rotation, the list should be constantly "wrong". I'd remove the whitetail, inspect it for flaws, and try the ride without it.