Smooth Operators

While most boat owners love the gentle, rhythmic motion of the ocean, too much of a good thing is not only uncomfortable, but can be downright dangerous. That’s where fin stabilizers come into their own, helping restore some balance to your boating adventures. Here’s the lowdown on inspections and maintenance to keep your stabilizers at the ready.

What they are

Located below the waterline on opposite sides and perpendicular to a boat’s hull, fin stabilizers provide resistance (an opposite force) to dampen or counteract excessive rolling of the vessel in either direction. There are two types – stationary and mechanical, or active, fins. The big difference between the two is that stationary fins are fixed, while mechanical fins (the focus of this article) articulate and constantly change position to respond to a boat’s movement.

Both types work to a modest degree to counteract rolling while at anchor. However, they’re primarily designed to operate using the flow of water across them as the vessel is making way. The stabilizing ability of the fins increases exponentially with speed as the vessel moves through the water.

Properly installed fin stabilizers do not extend past the vessel’s beam or depth (to protect them from damage). However, they’re still susceptible to strike damage, as well as snagging lines or debris.

Gyroscopic stabilizers (such as those offered by SeaKeeper, Tohmei, or Quick S.p.A.), by comparison, consist of a computer-controlled gyroscope. When the boat rolls, the sphere tilts, producing a powerful gyroscopic torque that counteracts boat roll.

Gyroscopic stabilizers work well while at anchor and underway. They also have no external hull appendages, eliminating the worries of snagging or strike damage associated with fin stabilizers. Gyros do come with their own set of cons, however. A gyro relies on precession (a rapid change in the angle of the gyro’s axis) to counteract movement. Under certain sea conditions (such as a steady crosswind) a gyro’s effectiveness can be limited by its precession distance (i.e., stroke or throw).

Other potential negatives include weight, space requirements for installation, and (with few exceptions) the need for AC power, meaning a generator or inverter supplied by a robust (or dedicated) battery bank is required for operation.

Maintenance basics

Fin stabilizers work in a demanding, highly corrosive environment and experience constant movement while in use, both of which can take a toll on the system. Although robustly constructed and designed to require little if any day-to-day upkeep, like any other system they must be properly maintained to ensure reliable operation.

The best place to start on the path to fin stabilizer maintenance nirvana is by reviewing your owner’s manual and warranty literature. There, you’ll find what you need to do and when, from routine maintenance to more complex tasks due at more infrequent intervals (some of which will require that the boat be hauled to complete).

In addition to the stabilizer fins themselves, active fin systems may include several other components including seals, sensing mechanisms, actuators, hydraulic pump(s), hydraulic fluid tank or reservoir, a raw water circulation system (used to cool the hydraulic fluid), and more.

Routine maintenance requirements for these are similar to other complex onboard systems you may be familiar with, such as your engine or generator. They include basic items such as checking fluids, noting pressure readings, swapping out filters, and greasing or lubricating moving parts.

Routine inspections

Familiarizing yourself with the stabilizer system beforehand (while everything is working properly) will maximize the effectiveness of routine checks. Knowing how everything looks and sounds during normal operation will make spotting problems much easier.

• Start with a visual check of the system while looking for fluid leaks, drips, or unusual stains such as running rust (an indication of corrosion or leaking). The hydraulic system will consist of a hydraulic pump, filter(s), oil reservoir, hoses and fittings connecting everything together.
• The hydraulic pump will either be driven from an electric motor or (in many cases) via a propulsion engine power takeoff (PTO).
• Check around all equipment (pumps, reservoir, filters) for leaks, while inspecting all hoses for leaks, deterioration, swelling, and chafe points. Hydraulic hoses should be properly supported, installed twist-free and with ample bend radius for longest service life.
• Check the fin actuator assembly equipment (manifolds, hoses, servo valves, cylinder rods) for leaks or other issues. The fin actuator may be located beneath a cover, and if that’s the case with your system, periodic removal of the cover to allow inspection is recommended.
• Verify that the reservoir fluid level is correct, something that should be done during each engine room check while underway. If your system uses a PTO from the engine, check the oil prior to starting the engine. Doing so ensures the hydraulic fluid is cool and will provide a more accurate reading. If checking the fluid level during operation, keep in mind that warmer fluid will expand and change the reservoir fluid level.
• Check the color, consistency, and temperature of the hydraulic fluid. Good hydraulic fluid is transparent with an amber or honey-colored appearance and a thin consistency. Darker, thicker hydraulic fluid, on the other hand, is a typical sign of age, contamination, or both, and indicates the need to change your hydraulic fluid. Hydraulic systems are very sensitive to dirty fluid. If you have to add fluid, use clean fluid from a clean container poured through a clean funnel. Adding fluid should be an infrequent requirement, so if you find yourself adding fluid regularly, check the system for leaks. \
• Temperature checks are another way to gauge the health of your hydraulic fluid. Older, thicker fluid is unable to disperse heat properly and, in some cases, may reach temperatures high enough to change the paint color of the hydraulic reservoir or cause it to bubble and peel off.
• The cooling system for your stabilizer will include a water pump, intake strainer, and heat exchanger, along with the required hoses connecting the system. Inspect each of these for leaks, deteriorated hoses, corroded fittings, and other such issues. Some installations may utilize the engine raw water-cooling loop, however, a dedicated stabilizer cooling system is a better option. Along those lines, the raw water cooling system for your stabilizer system should never be used to supply cooling to other equipment or systems.
• Finally, be on the lookout for unusual vibrations or strange noises during operation. This is where familiarization with your system will help tremendously when trying to determine if a noise or vibration is new and something that needs further investigation.

General maintenance

Required maintenance schedules vary from one manufacturer to another and can be based on hours of use or periods of inactivity (such as extended storage). Regardless of the maintenance requirement or its frequency, you’ll want to stick to the schedule to maximize reliability and service life.

While you’ll always want to follow the manufacturer-provided maintenance requirements for your specific fin stabilizers, here is a generic list of items that can be used as a starting point to develop a maintenance schedule for most any stabilizer system:

1. Check hydraulic fluid level (prior to each use).
2. Heat exchanger zinc anodes (check monthly and replace when deterioration is noted). The heat exchanger will have one or more anodes to prevent internal corrosion due to sea water circulation.
3. Check water pumps and seawater strainers (monthly). Raw water pumps and strainers must be cleaned and serviced regularly to maintain proper flow rates.
4. Cylinder rode end and trunnion bearing lubrication (every six months). Refer to the owner’s manual and note all lubrication points and grease fittings as well as the type of grease recommended.
5. Hydraulic accumulator/noise suppressor charging (every six months). Many systems have nitrogen-charged accumulators at each actuator and noise suppressors on or near the pump(s). The pressure for these devices should be checked every six months and recharged as necessary.
6. Check bonding connections (annually). Verify that each fin actuator assembly is attached to the ship’s electrical bonding system and that the bonding system is intact and corrosion-free.
7. Check cooling water supply (annually). Confirm the raw water cooling system is functioning properly and receiving adequate cooling water. Part of this verification will be checking that the hydraulic fluid temperature remains within the recommended temperature range during all phases of operation. This temperature will vary between units, but is typically between 120 F and 140 F.
8. Change hydraulic system oil filters (annually). If your system has both pressure and suction filters, they may have different replacement schedules. Verify with the owner’s manual.
9. Fin shaft seal replacement (every three years). The vessel will need to be hauled for this. Be aware that some manufacturers may call for the seals to be replaced more frequently if the fins see limited use (i.e., less than twice per month).
10. Change the hydraulic fluid (every three years).
11. Replace all hydraulic hoses (every five years).