2001 Horizon 76 - Sea Trial

While there are many shops that say they work on Naiad equipment, The Naiad factory shop was just to the west of you.
Sadly, getting them out to your boat takes a while.

trim tabs at hull speed pretty much don’t do anything.

Then what are the stabs doing then? They keep the boat vertical. Both need water flowing.
On a stabilized boat, the only reason I see tabs are for bow trim (up/down - not P&S) and maybe to help the stabs with a constant beam wind.

The older systems (IMO) were the best.
No computer or logarithmic functions programing (operator tuning). Just a trusted hydraulic gyro and some electricity to turn it on (two solenoids on the top).
Performance mostly depended on boat use / fin size selection, once set, never have to touch it again.
Only a few things to go wrong, most diagnosed with a pressure gauge.
Sometimes the hardest part of fixing something; Understanding what the failure is. It may not be all the tech's issues.
Heck, You may already have a loose fin.

That later super Naiad model (Multi-Sea System II) Burned my temper on performance and repair cost.

Not even that, actually, 'cause that old "Center-Off-On" stuff had no interfaces at all.
The system is totally unaware of the boat speed, gear position, rudders angle (if any).
So, fins only depend on the embedded gyro inputs, and it's irrelevant whether the boat is rolling or constantly leaning.
If necessary to keep the boat horizontal, fins can stay slightly rotated forever.
In other words, yep, tabs should strictly be used for trimming, in any boat with those stabs.

Nope, actually that system should indeed straighten not only a rolling, but also a heeling boat, regardless of the reason - be it beam wind, steering, weight distribution, whatever.

The system is not driven by acceleration sensors and several other inputs, as modern stabilization systems are.
There is "only" a very accurate gyroscope, which senses in real time even the slightest deviation from the horizontal position of the vessel.
I mean, transversally horizontal, of course.
The system doesn't care about longitudinal deviations, i.e. pitching, because fins can't contrast that.

Anyway, based on these gyro inputs, fins constantly try to straighten the boat, regardless of whether she's rolling or heeling.
That's the reason why, if fins are working as they should, there's no need to use tabs to correct heeling.
Tabs should only be used for (minimal) adjustments to the longitudinal angle of attack, depending on speed and sea conditions.

Righting the boat is the overall rough goal of operation. The servo valve on the fin unit itself changes the rate, the gyro sense the error.
The bass ackwards result, the boat stays vertical but some side motion may be detected by some sensitive people as the hull is pushed back under (sideways) the roll. That is why I call BS on the trim tab story.
BTW; I usually ensure these sensitive people are not on board again.

The later models try to predict the next wave action and either over compensate in adjustment or don't swing that far expecting the next roll on the other beam.
logarithmic programing, self learning and manual input may help these systems. Rate of roll (periods) is the larger calculation with the fancier systems.
The old Servo throttle did this pretty well pending fin selection.

The bottom line, the ship stays vertical (or very close).

It's a fluid gyro. Ideal; it will keep level where it was when engaged. Constant running under a forced angle may cause some loss of level after a while (hours).
Back to the OP issue, the boat should have never rolled on throttle up. Tabs or not.

Then you've obviously never seen a boat with Naiad fins driven by their so-called Hydro-Mechanical Gyroscope (aka HMG) controller.
As I said, that bit of kit doesn't even know if the boat is rolling or listing.
It just rotates the fins as much and for as long as required to straighten the boat.
Btw, at 20 kts the fins angle that it takes to correct a list is very minimal - as opposed to trim tabs, which in case of a relevant listing, on top of introducing more drag, could even be unable to fully straighten the boat.
The righting moment that fins can transfer to the hull is huge, compared to tabs.

That's pretty much theoretical, though.
In practice, in a boat listing due to unbalanced load or strong beam wind, the fins never stay just at a constant angle for hours.
That's what should happen if the boat would be cruising in perfectly flat conditions, but actually the fins will contrast BOTH the roll and the list.
So, they will constantly flap in both direction - just more on one side than on the other, on average.