A 52-foot convertible owner had invested $28,000 in a Humphree 600 2-pair interceptor system, expecting dramatic roll reduction. Instead, he got inconsistent performance: sometimes the fins seemed to work, sometimes the boat felt worse than without them.
The specific complaint: "The fins take forever to deploy. I can feel the delay. And when they finally move, they overshoot and then retract, overshoot and retract — the boat is porpoising."
The installer had checked mechanical alignment, blade travel, and control settings. Everything was "within spec." They suggested upgrading to a larger Humphree 800 system ($14,000 additional).
We logged voltage and current at three critical points for a full 8-hour offshore trip:
| System | Continuous | Peak | Observed Events |
|---|---|---|---|
| SK16 gyro | 48A @ 24V | 110A | Spin-up: 2x per trip |
| Humphree 600 (2-pair) | 6A @ 24V | 96A | Deploy: 40–60x per trip |
| House loads | 22A @ 24V | 45A | Continuous |
| Air conditioning | 15A @ 24V | 80A (inrush) | 4–6x per trip |
| Combined worst case | 91A @ 24V | 331A | Never simultaneous (good) |
| Combined realistic peak | 156A | Gyro spin-up + fin deploy + house |
The voltage log told the whole story:
| Condition | Nominal | Observed | Sag | Impact |
|---|---|---|---|---|
| At rest | 25.2V | 25.1V | 0.1V (0%) | None |
| Gyro spin-up (110A) | 25.2V | 21.8V | 3.4V (13%) | Critical — fin deploy during this = failure |
| Fin deploy (96A) alone | 25.2V | 22.4V | 2.8V (11%) | Severe — deployment time doubles |
| Combined peak (156A) | 25.2V | 19.6V | 5.6V (22%) | Catastrophic — control system resets |
The fix required three layers:
We designed a dual-bus 24V architecture:
A SaltyMarine supercapacitor module was installed on Bus A:
The existing 120A alternator couldn't keep up. We replaced with a 220A high-output unit with external regulator and temperature-compensated charging profiles.
| Metric | Before | After | Change |
|---|---|---|---|
| Fin deploy time (single blade) | 3.8–4.2s | 1.4–1.6s | -62% |
| Voltage sag during deploy | 2.8V (11%) | 0.2V (<1%) | -93% |
| Control system hunting events | 20–30 per trip | 0 | -100% |
| Roll reduction (measured) | 18% (inconsistent) | 52% (consistent) | +189% |
| Owner satisfaction (1–10) | 2 | 9 | +350% |
| Peak voltage under combined load | 19.6V | 24.8V | +27% |
| Gyro uptime (8-hr trip) | 73% | 100% | +37% |
Owner's savings: $9,600
Additional benefit: Both systems now work together instead of fighting each other. The dual-bus design is a permanent fix, not a band-aid.
ROI on assessment: $5,500 comprehensive assessment → $9,600 savings = 175% return on assessment fee alone
Adding a gyro to a vessel that already has interceptors — or vice versa — without reengineering the power system is like adding a second air conditioner to a house without upgrading the electrical panel. The breaker will trip.
When an owner says "my fins are slow," check voltage at the actuator terminals under peak load. If it's below 23.0V, the actuator is starved. The mechanical system is fine — it's being electrically choked.
The supercapacitor module cost $680. It eliminated a $22,000 hardware upgrade recommendation. The module absorbs the 2-second deployment peak so the battery never sees it. This is standard on every dual-system vessel we engineer.
When gyro and interceptors share a single battery bank, they compete for current. During gyro spin-up, the interceptor can't deploy properly. During interceptor cycling, the gyro sees voltage sag. Separating them solves both problems simultaneously.
The helm gauge showed 24.6V "all day." Our logger showed 19.6V during peaks — a 5V difference that explains every failure. Most vessels have voltage problems that are invisible until you log them.
AGM's high internal resistance creates violent voltage sag under 96A peaks. Sodium-ion's low resistance + the load-smoothing module = <1% sag. The difference between "fins that work" and "fins that hunt."