Sta­bil­ity Con­cerns

Passage Maker - - Contents - BY STEVE ZIM­MER­MAN

The World of Stabilizers Steve Zim­mer­man

Sta­bi­liza­tion op­tions for cruis­ing power­boats have evolved from steady­ing sails and bilge keels to ac­tive fins and gyro stabilizers. These new tech­nolo­gies of­fer far more than in­cre­men­tal im­prove­ment over the older meth­ods. While ac­tive fins and in­ter­nal gy­ros dom­i­nate the market, a num­ber of other choices can also be ef­fec­tive for sta­bi­liz­ing your power­boat. We’ll be­gin by exploring the pros and cons of each type of sys­tem and then we’ll ex­am­ine the main­te­nance needs of fins and gy­ros.

But first let’s set ex­pec­ta­tions up front. Stabilizers ex­cel at re­duc­ing roll and this makes for a much more pleas­ant cruis­ing ex­pe­ri­ence overall. Keep in mind, how­ever, that your boat will still rise and fall with each wave—it just won’t rock as much. And when beat­ing into head seas the ben­e­fit of stabilizers is min­i­mal, if at all—it can still be a mis­er­able ex­pe­ri­ence.


A par­a­vane sys­tem uses two wing-shaped weights (of­ten called “fish” or “birds”) that are dragged through the wa­ter on ca­bles. Long booms, usu­ally alu­minum, hold the fish out some dis­tance from the hull and re­lated rig­ging holds the booms in po­si­tion. These sys­tems are fairly sim­ple and can be quite ef­fec­tive if de­signed cor­rectly for the boat. We once set up a Wil­lard 30 with paravanes and took the boat com­fort­ably to Ber­muda and back. On the other hand, the sys­tem does take more ef­fort to de­ploy than other means of sta­bi­liza­tion, and we once re­paired a 50-foot trawler af­ter one of the fish flew through the saloon win­dow due to mis­han­dling by the crew.

Paravanes must be de­signed by some­one fa­mil­iar with their re­quire­ments. The length and di­am­e­ter of the alu­minum poles, the size of the fish, and the lo­ca­tion of the rig­ging at­tach­ments must all be prop­erly engi­neered.

Pros: A par­a­vane sys­tem is sim­ple, low tech, re­li­able, and rea­son­ably ef­fec­tive.

Cons: Paravanes take some ef­fort to de­ploy and re­quire a wide clear­ance (not suit­able in har­bors or close quar­ters). Drag cre­ated by the fish im­pacts speed and fuel econ­omy.


An in­trigu­ing op­tion, a flume ar­range­ment controls the flow of wa­ter through a cham­ber to off­set the mo­tion of the ves­sel. Like paravanes, they of­fer a sim­ple, low-tech op­tion for sta­bi­liza­tion. These sys­tems have been used ef­fec­tively on ships but they are rare on cruis­ing boats. Over the years I’ve met a hand­ful of peo­ple who have a flume and all of them seemed pleased. You can learn more and find some videos at

Pros: Sim­ple, low tech, and re­li­able, a flume sys­tem cre­ates no drag as noth­ing pro­trudes from the hull.

Cons: The flume tank adds weight and re­quires space. The flow rates must be ad­justed for the par­tic­u­lar con­di­tions. And as these sys­tems re­spond much more slowly than gy­ros or ac­tive fins, flumes are most suited to open-wa­ter sit­u­a­tions where waves come in a reg­u­lar rhythm.


Un­til re­cently, ac­tive fins dom­i­nated the cruis­ing boat market and a num­ber of com­pa­nies com­pete in this arena, in­clud­ing ABT-TRAC, Na­iad, Side-Power, WESMAR, and Gyro- Gale. A gy­ro­scope senses the mo­tion of the ves­sel and hy­draulic ac­tu­a­tors ro­tate the fins un­der the hull. The move­ments are quick and com­pen­sate for mo­tion with re­mark­able effectiveness un­der­way. Fins can be pow­ered by hy­draulic pres­sure, com­pressed air, or elec­tric power. Un­til re­cently, ac­tive fins only pro­vided sta­bi­liza­tion while un­der­way. Most man­u­fac­tur­ers now of­fer some ver­sion of sta­bi­liza­tion at rest. In each case, the power de­mands re­quire run­ning a gen­er­a­tor to en­er­gize the fins.

Pros: Ac­tive fins are highly ef­fec­tive and pro­vide quick re­sponse. They re­quire sig­nif­i­cantly less space to in­stall than gy­ros and af­ter­mar­ket in­stal­la­tion is pos­si­ble on most cruis­ing boats.

Cons: Ac­tive fin sys­tems are com­plex and re­quire ex­pen­sive com­po­nents to be ex­posed to the elements. In ad­di­tion to the sens­ing mech­a­nisms, the hy­draulic com­po­nents in­clude an en­gine-driven hy­draulic pump, a hy­draulic fluid tank, sea­wa­ter

cir­cu­la­tion to cool the hy­draulic fluid, ac­tu­a­tors, seals, and more. In ad­di­tion, the fins pro­trude from the hull, adding the risk of in­cur­ring ma­jor dam­age un­der­way.


Gy­ros are the prime al­ter­na­tive to ac­tive fins. The ba­sic con­cept is il­lus­trated by those pull-the-string spin­ning gy­ros many of us had as kids: The ro­ta­tional force pro­duces sta­bil­ity. The gyro stabilizers ex­cel at keeping a boat steady, both un­der­way and at rest.

Pros: Gyro stabilizers are highly ef­fec­tive at an­chor as well as un­der­way. No fins pro­trude from the hull, min­i­miz­ing the risk of dam­age.

Cons: These sys­tems are power hun­gry. And while they can be in­stalled as a retro­fit, find­ing the space for in­stal­la­tion and engi­neer­ing the gyro sup­port struc­ture can be a chal­lenge.


Let’s get this out of the way: There is no best sys­tem. The best sys­tem for you de­pends on your bud­get, the space you have avail­able to in­stall a sta­bi­liza­tion sys­tem, and your need for sta­bil­ity at rest. If, for ex­am­ple, you place a pri­or­ity on min­i­miz­ing roll at an­chor or in an ex­posed slip, the gyro will be your best bet. For faster plan­ing hulls, gy­ros ex­cel, but for slower full dis­place­ment trawlers ac­tive fins will be more ef­fec­tive. If you are cross­ing oceans and not con­cerned about coastal cruis­ing and if you have a tight bud­get or place a pri­or­ity on sim­plic­ity, paravanes or a flume would be the way to go.

An­other con­sid­er­a­tion is speed. As boat speed in­creases, forces against the bot­tom cre­ate dy­namic sta­bil­ity that re­duces roll. On a semi-dis­place­ment or plan­ing hull, in­creas­ing speed usu­ally im­proves com­fort. Full dis­place­ment trawlers do not ben­e­fit from this fac­tor and have a greater need for sta­bi­liza­tion. In ad­di­tion, trawlers tend to be heav­ier and the added mass cre­ates the need for greater sta­bi­liza­tion forces. On lighter and faster boats trim tab sys­tems—like those made by Humphree or Zip­wake— now pro­vide sta­bi­liza­tion as well.

And one of the most im­por­tant fac­tors that is of­ten over­looked is how much time, ef­fort, and money it will take you to main­tain the sys­tem over the years. While some of the sys­tems on the lowtech-end re­quire min­i­mal main­te­nance, ac­tive fins and gy­ros are com­plex sys­tems with their own cool­ing sys­tems that need to be main­tained.


Low-tech so­lu­tions are low main­te­nance. Other than in­spec­tion of ca­bles and at­tach­ment points, paravanes re­quire very lit­tle up­keep, and the same ap­plies to flumes.

Ac­tive fins fall at the other end of the main­te­nance spec­trum, re­quir­ing at­ten­tion to the cool­ing sys­tem, hy­draulic sys­tem, and fin seals. Main­te­nance in­ter­vals and de­tails de­pend on the man­u­fac­turer but should be fol­lowed, es­pe­cially when it comes to re­plac­ing the seals. In the boat­yards, we of­ten see avoid­able

dam­age and un­nec­es­sary ex­pense in­curred when boat own­ers ne­glect the seals on their ac­tive fins. At­tached to a shaft that passes through the hull, each fin re­quires an in­ner seal to re­tain lu­bri­ca­tion and an outer seal to keep out sea­wa­ter. Ne­glect­ing the

outer seal will al­low sea­wa­ter into the as­sem­bly. The sea­wa­ter will then di­lute the lu­bri­cant, even­tu­ally dam­ag­ing the in­ner seal and pos­si­bly the shaft it­self. Re­plac­ing the outer seals might cost you $1,500 per side, but if you ig­nore them too long the cost for

re­plac­ing in­ner and outer seals plus the shafts them­selves will run up­wards of $4,000 per side.

The cool­ing sys­tem for the ac­tive fins mir­rors the main en­gine sea­wa­ter loop: in­take strainer, wa­ter pump, heat ex­changer. The same pro­ce­dures used for main­tain­ing en­gine cool­ing sys­tems ap­ply here (see “Troubleshooter” April 2017 and July 2018).

The hy­draulic sys­tem in­cludes an oil reser­voir, an en­gine-driven hy­draulic pump, and a fil­ter. Other than mon­i­tor­ing the fluid level, which should be done as part of your rou­tine en­gine room check, these com­po­nents should gen­er­ally be ser­viced on an an­nual ba­sis. Coolant pump fail­ures are one of the more com­mon is­sues and this crit­i­cal com­po­nent must not be over­looked.

If you have ac­tive fins, one more sit­u­a­tion must be con­sid­ered. The hy­draulic sys­tem re­lies on a pump at­tached to the main en­gine or trans­mis­sion. If this pump starts to over­heat due to poor lu­bri­ca­tion or failed cool­ing by the hy­draulic fluid, the pump can seize. If the over­heat­ing sit­u­a­tion can­not be re­solved, the pump will need to be re­moved. In this case it is help­ful to have on hand the orig­i­nal plate that cov­ered the open­ing so you can run the en­gine or trans­mis­sion with­out the pump at­tached. This plate comes with the en­gine or trans­mis­sion and is re­moved (and un­for­tu­nately of­ten dis­carded) when the pump is in­stalled. If you don’t have the cover plate it would be wise to ob­tain or fab­ri­cate one to have on hand.

Gyro- Gale, a 40-year-old com­pany based in Stu­art, Florida, of­fers a vari­a­tion on the ac­tive fin sys­tem. By us­ing com­pressed air in­stead of hy­draulics, their sys­tem avoids some of the com­plex­ity by elim­i­nat­ing the fluid reser­voir, the power take­off (PTO) pump, and the lines full of hy­draulic oil. In­stead, this sys­tem cools and com­presses the air and moves it at a high speed. Gyro- Gale has a patented fin de­sign with an ar­tic­u­lated trail­ing edge that en­ables these sys­tems to use smaller fins more ef­fec­tively. They also tend to use more fins—for ex­am­ple, a sys­tem in­stalled on a 48-foot trawler might use four fins. Ac­cord­ing to Gyro- Gale, the ex­tra fins im­prove roll con­trol and help re­duce pitch. While this sys­tem still re­lies on seals, the elim­i­na­tion of the hy­draulic sys­tem and re­lated cool­ing com­po­nents re­duces main­te­nance needs. How­ever, these com­pressed-air sys­tems do have other main­te­nance re­quire­ments, such as bian­nual air fil­ter re­place­ments.

Like the hy­draulic ac­tive fin sys­tems, gyro-stabilizers also de­pend on a cool­ing sys­tem with a heat ex­changer, and this com­po­nent has sim­i­lar main­te­nance needs. Although the gyro does not re­quire seal re­place­ment, it does have ser­vice re­quire­ments at 2,000 hours for the brake mech­a­nism and hy­draulic com­po­nents.

Which­ever sys­tem you choose, pay close at­ten­tion to the recommended main­te­nance in­ter­vals and you will get many years of re­li­able ser­vice.


Left: Three-di­men­sional ren­der­ing of the gyro mech­a­nism in­side a Sea­keeper sta­bi­lizer.

Above: Fin and me­chan­i­cal de­tail of a NA­IAD ac­tive sta­bi­lizer fin. Below: An Ital­ian com­pany, Quick is rel­a­tively new to the market of gyro sta­bi­liza­tion, of­fer­ing sizes for boats dis­plac­ing up to 250 tons.

Above-Left: Close-up view of the outer hull-to-fin shaft seal and in­ner bear­ings. Each man­u­fac­turer has a spec­i­fied re­place­ment in­ter­val. AboveRight: Many ac­tive fins rely on hy­draulics. As the hy­draulic oil passes through the sys­tem, it heats up and must be cooled. On the right is a heat ex­changer that works just like the one on an en­gine: sea­wa­ter cir­cu­lates, re­mov­ing heat. Like the one on your en­gine, this one has an­odes that must be main­tained. At the top, a me­ter with a spin­ning vane vis­ually con­firms the flow of sea­wa­ter.

Above: This fin sta­bi­lizer shaft has been dam­aged from fail­ure to re­place the outer seal. When the seal fails, sea­wa­ter en­ters the bear­ing as­sem­bly, di­lut­ing the lu­bri­cant and caus­ing cor­ro­sion on the shaft. Right: This ac­tu­a­tor moves the fin. Hy­draulic fluid en­ters at the bot­tom of the im­age. The hat-shaped cap in the cen­ter cov­ers the up­per end of the shaft. At the top is the lock­ing pin. This pin locks the fins when the en­gine is put in re­v­erse or when “LOCK” has been se­lected on the con­trol panel.

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.