2001 Horizon 76 - Sea Trial

A red neck way to make sure all the blades are in the same position when the prop is spun by hand.
The Idea is hold a pencil or rule or stick in place on the strut and then rudder and make sure each blade is the same distance away from the strut and rudder as the prop is hand rotated.
From the rudder at different heights, rake can be compared between both props.
My thought here is damaged blades can scoop more water and apply more torque to the hull causing a list. Not all damaged wheels vibrate.
It's a reach of mind (que Twilight Zone music), but possible.
Now that we feel the hull may have taken a hit, prop damage may not be that far out of mind.

Re your picture; Something has changed for that list to appear and not correct it self.
What was involved in turning around? Big round 180? Tight 180? Slow down, stop & spin?

I wish we could talk to your surveyor (not supplied by seller or broker).
At least, log your surveyor on to this thread.
Remember, he works for you, not the kids hired by the owner to 'sposed fix something.

Hate to say this so late, Could be air in the lines.
Air compresses and expands and changes volume with heat. The worst thing to have in a pressure line.
The wrong oil can cause foaming also.
Air should clear from the gyro fine by itself. Air at the cylinder and in some lines may not self clear.
I like the kids at Cable. I've been going thru them for many years. But even them (or I???) can mess up, and not bleed the system or install the wrong oil or look the wrong way.
Frak, I've seen better yards have lines reversed and delivered the boat.
So anything is possible. Maybe have to go over all this work to make sure all minds were/are clear.

I wouldn't recommend anything, actually. Neither a full replacement nor any upgrade to the existing system.
Not unless you are interested also in zero speed stabilization, which as I previously mentioned implies a full replacement of the system, in practice.

Those Naiads are obviously old tech, but they are as capable to straighten a boat as anything more modern, regardless of whether driven by a gyro or by electronic sensors.
New systems are different in many ways from an electronic viewpoint, and are interfaced to consider just about every boat status (like speed, rudders, gear).
Besides, they are also capable of self-learning/adapting to the sea conditions and to the boat reactions.
But the basic hydraulic operation isn't that different (if we leave aside the more recent and arguably more advanced 100% electrical fins), and if there is one thing that newer system do NOT bring to the table, that's a higher power/righting moment.
That strictly depends on the fins size and their rotation angle, plus the boat speed, and there's no way that a more sophisticated controller can improve what your fins can already do while driven by the HMG controller.

And what is funny (sort of) is that for any given fin size and rotation, a higher speed makes the stabilization MORE effective, not less!
That's very basic physics, and also intuitive.
This is the reason why it can't be a matter of fins not being able to cope with the higher speed - if anything, only the opposite could make sense.
I mean, I owned for almost two decades a boat stabilized with that very same equipment, and if the stabs ever struggled a bit to do their job, it was at VERY low speed, up to 4 knots or so.

That's precisely what I meant what I envisaged the possibility of a leak in the fin actuator (post #63).

PS: talking of the actuators, a question for the OP, what model is installed on the boat?
A consistency between the actuators/cylinders and the fin size is ESSENTIAL to the system.
According to Naiad Application Guidelines, the 12 sqft fins could be mated to a range of actuators, from the smaller "300" series all the way up to the "520", depending on the vessel tonnage and length.
But since the boat is within the tonnage and length limits also of the "250" actuator (which are only rated for fins up to 9 sqft), I am wondering if someone thought to save some bucks on the installation by mating the smaller actuators to the larger fins.

Just one last thought, totally independent of all the technicalities discussed so far.
In principle, a well designed planing hull should become more stable (i.e. more resisting to both roll and static listing) at higher speeds.
And this is true regardless of any correction system - be them trim tabs of fin stabilizers.

Was the boat behaviour tested also with no trim tabs, fins off, and rudders centered?
If also in these "fully neutral" conditions she remains straight up to 21 kts or whatever, and starts listing right above that speed, I'm afraid it's the whole hull design that should be questioned, first and foremost.
The fact that fin stabs could and should still be able to correct that (which remains true) would be just a patch to a bad hull.

F M
At least it's a start.
Stb or port (see #8 above).
Your surveyor reading this yet?

What is the maintenance history? Every oil change, I replace the fuel filters and they always look pretty clean. I ve always seen fuel pressure in the 50s on both 3412Es and C32s. I doubt that s an issue.

If a fuel imbalance was the problem it would manifest itself at lower speed not suddenly from 2100 to 2300 rpm

if they’re going to haul out, I would also check that the port fin shaft is at the same angle as the stbd shaft. If after the work the new actuator was a few degree off, it could cause the boat to heel

Btw, still wondering why they had to do all that work on the port fin. It does sound like a hit to me.

In any case there is still the issue of a 76 footer barely breaking 21/22kts on a pair of 3412Es....

Maybe. I used to run a 70’ Johnson skylounge with 6 1/4 ‘ draft which hit 29.5 on the same engines with 5200 hours. The extra LOA also adds lift... I don’t know. Just seems very slow.