Stabilizers | Bow Thrusters  |  Service


What model and fin is right for my boat?

Overall length alone is a poor indicator of required fin size. The vessel’s speed in particular and its displacement are the driving factors used to calculate the best fin and model for a given project. Other factors include the waterline beam and transverse metacentric height (GM; a measure of initial stability). NAIAD has perfected a method of precisely determining a vessel's stabilizer requirements based on decades of experience and many thousands of successful installations. We are always happy to provide recommendations for the best roll control solution.

Where are the fins normally installed?

For modest hull speeds, the fins are positioned within the middle one-third of the waterline length. If the vessel exceeds 20 knots, this region is limited to the middle one-fifth. The fin and corresponding fin actuator assembly are installed perpendicular to the hull bottom (to assure full range of motion) and as far from the keel as practical (to achieve the best possible leverage). The fin is also located to assure that its tip stays within the envelope of the beam and keel.

Will I lose speed?

All underwater appendages add some drag. However, our cavitation tunnel tested, hydro-dynamically efficient fins offer minimal drag and result in surprisingly small effects on the vessel's speed. All NAIAD systems help minimize drag by limiting fin travel to exactly match the roll tendency. In addition, when so much of the vessel’s natural roll is removed, yaw (wandering from intended course) is improved. Therefore, fewer rudder corrections minimize rudder-induced drag, somewhat offsetting fin drag. Straighter course headings improve point-to-point arrivals and speed made good. Many of our customers state that their fuel economy actually improves after adding the NAIAD stabilizer system. (And the comfort improvement is outstanding!)

How much roll reduction can I expect?

In beam seas where the period of the waves tends to match the natural period of the vessel, NAIAD stabilizers typically achieve 90% roll reduction. The latest in stabilizer technology, the MULTISEA II and DATUM three-term controls provide even more roll reduction, particularly in following or stern quartering seas.

What is the operating procedure when getting the boat underway?

The NAIAD stabilizer system virtually runs itself. When leaving the dock or during any astern maneuver, the system should be in the CENTER mode for safety. Once underway, simply turn the system to ACTIVE before bringing the vessel up to speed. Due to the fully proportional nature of our controls, the fins will respond automatically to varying sea conditions and adjust their speed and angle of attack accordingly. The control systems also feature sensitivity adjustments at the operator panel to permit “fine tuning”, especially helpful in following or stern quartering seas.

Does adding NAIAD stabilizers increase the value of the boat?

The NAIAD system virtually pays for itself in increased comfort over the life of the vessel and reduced wear and tear on other vessel machinery and systems. In addition, due to the NAIAD brand name (and inherent high durability and low maintenance), the stabilizer value is typically recouped upon resale. A NAIAD stabilized boat tells prospective buyers the vessel is outfitted with the best equipment.

Can the NAIAD System be supplied with two or more pair of fins?

Absolutely. We typically recommend one pair of properly sized fins for maximum efficiency in a conventional stabilizer system, but NAIAD Stabilization at Anchor (AtRest) systems commonly utilize a four-fin arrangement due to the unique requirements of this exciting package. Interestingly, NAIAD can provide full roll reduction with just a single fin, which tends to reduce installation labor. Whether the requirement is for one fin, one pair, or multiple pairs, NAIAD has the capability and expertise to guarantee performance and maximize return on investment.

What if we hit a substantial object with the fin?

NAIAD fins are durable and rugged, but also designed to breakaway in the event of a very severe impact. With proper fin actuator assembly installation (as shown in our installation drawings and technical manuals), the composite fin design will yield first, leaving the internal stainless steel fin structure. In addition, our uniquely heat-treated stainless steel shaft will not appreciably bend because its yield strength and ultimate strength are virtually identical. While this shaft material costs more when compared to typical stainless steels used in the marine environment, this feature prevents the fin structure from being driven into the hull as a result of shaft bending. In the event the impact is very severe, the shaft will break cleanly at the location of its highest bending moment, nearly flush with the hull and below the dual lip seawater shaft seals.



Bow Thrusters

What size thruster is right for my vessel?

The overall length of the vessel, its shape above and below the waterline, and the available power are all considered when selecting the right thruster. If the boat is a displacement trawler type with a great deal of windage, it is best to slightly increase the power of the thruster if possible. For a sleek, planing hull with low windage, a smaller diameter thruster can be selected, which has the benefit of reduced tunnel area to minimize the possibility of tunnel effects at speed.

What is the difference between proportional and non-proportional controls?

Non-proportional controls are the standard for smaller thruster systems. When operated these controls provide full thrust, either to Port or Starboard. When thrusting toward the dock, a quick, offsetting burst away from the dock is typically sufficient to decelerate the bow. 

Fully proportional controls provide finer operator control. These controls allow variable power from zero to full throttling up to the thruster’s maximum output for complete control of the bow. These controls make docking virtually effortless since the bow can be manipulated with a touch of the operator’s finger.

What is the difference between a Right Angle thruster and an In-Line thruster?

The Right Angle thruster provides additional flexibility in selecting the power input to the thruster, either hydraulic or AC electric depending on the owners preferences and what is most economical and efficient for the vessel. 

In-Line thrusters are hydraulic only and feature an extremely compact arrangement that saves in-board space at the tunnel location and reduces mechanical components to nil. The only items on the outside of the tunnel are the hydraulic connections themselves, allowing the installer additional flexibility in thruster positioning. In-Line thrusters are easier to maintain and save weight.

What is the likelihood of losing hydraulic fluid through the thruster shaft seals?

The working pressure region of the in-line thruster assembly is isolated from the dual seawater shaft seals to eliminate concerns of hydraulic oil leakage into the environment. In addition, the seawater shaft seal cavity is protected from system oil leakage by a unique drain pressure control assembly, which vents any oil leakage to a controlled onboard path. 

The right angle thruster has lubrication oil in the thruster housing to lubricate the spiral bevel gearing. This fluid is vented to atmosphere and supplied by a lubrication header tank to assure positive pressure at the dual seawater shaft seals.

Thrusters have a reputation for being noisy, what are the major contributors to thruster noise?

  • -Underway? The installation of a concave teardrop shape aft of the tunnel or a convex tunnel eyebrow forward of the tunnel can greatly reduce water disturbances which contribute to noise while underway. In addition, properly installed grating can help minimize noise while underway. Contact NAIAD for additional installation guidance. 
  • -While in operation? Noise can be caused by a tunnel installation that lacks sufficient depth of immersion. If the tunnel is in close proximity to the water surface it can suction air into the tunnel while thrusting. Noise can also be caused by sharp tunnel openings. An ample radius at both ends of the tunnel minimizes vortices at the inlet flow field and at the outlet. Contact NAIAD for additional installation guidance.

What choices are available to power the thruster unit? 

The Right Angle thruster is available in either 50 or 60 Hz AC Electric Drive configurations or Hydraulic Drive configurations. A proportional control is available for both hydraulic and electric drive packages. For electric drive packages, an AC inverter can supply proportional control. For hydraulic drive packages, the thruster can be supplied with a closed loop hydrostatic drive, which also provides proportional control.

For both In-Line and hydraulic Right Angle thrusters, NAIAD typically drives the thruster pump from either a Generator or Main Engine PTO. The available power from either of these sources is evaluated to arrive at the best possible match for the vessel. 

What other shipboard equipment can be run from the thruster hydraulic circuit?

Virtually any shipboard hydraulic system can be (and has been) powered from NAIAD thruster hydraulic circuits. Because the thruster has a substantial amount of power available, and it is an intermittent duty device, it makes perfect sense to utilize this hydraulic resource for other shipboard equipment such as windlasses, capstans, and davits. NAIAD routinely addresses the hydraulic requirements of these devices as well as a myriad of other equipment with our Integrated Hydraulic Systems.

Can the stabilizer and thruster run from a common reservoir and pump arrangement?

As with other hydraulic equipment, the stabilizer is routinely supplied as a package with the thruster and utilizes the same hydraulic pump & reservoir. This saves a substantial amount of space in the engine room, solves the issue of finding an appropriate place on the engine to run two hydraulic pumps, and reduces routine service on two independent reservoirs. 

For owners with existing NAIAD stabilizer systems, we can provide this feature, but not with the existing stabilizer pump. The flow requirement of the thruster is far in excess of the stabilizer pump; the thruster requirement determines the pump selection. Contact us to review the possibilities.

Can the thruster be used in a stern application?

Yes. NAIAD has supplied many Bow/Stern combinations for owners who demand absolute control and the ability to spin their boat within its length. The available onboard power and other factors need to be evaluated for these packages. Contact us for additional details.




What oil should I use?

For HMG controlled stabilizers use SAE 10W40 motor oil. For MultiSea II or Datum controlled stabilizers and for thrusters, ISO 32 hydraulic fluid is preferred or ISO 46 is acceptable (particularly in warmer regions). Mobil DTE 24 or Shell Tellus 32 is recommended for integrated systems using a common reservoir, the same as thruster systems.

How often should the system be serviced?

For stabilizers—

Oil—change the oil in the reservoir every three years or 4000 hours of use.
Oil Filter Element—replace when the DIRT ALARM approaches the yellow arc when system is operating in either CENTER or ACTIVE.
Accumulators & Noise Suppressors (if applicable) - Check nitrogen pre-charge every 6 months.
Lower Seals—replace every three years or 4000 hours of use.
Cooling Water Pump—Check the water pump impeller for wear periodically and verify adequate flow.
Zinc Anodes—Check monthly on heat exchanger(s) if applicable.

For thrusters—

Zinc Anodes—Check monthly on heat exchanger(s) if applicable.
Oil—Change hydraulic and/or lubricating oil every three years.
Shaft Seals—Replace every three years. 

I need to have my stabilizer or thruster system serviced. Where is the nearest dealer?

See our Worldwide Service Providers