The two main sys­tems

Yachting Monthly - - EXPERT ON BOARD -

di­rect drive SYS­TEMS

Wind vane steer­ing linked to a sec­ondary rud­der is the most in­her­ently sim­ple of the me­chan­i­cal self-steer­ing sys­tems, but re­lies on a much more pow­er­ful trans­mis­sion of force be­tween a large-sur­face-area wind vane and the sys­tem’s own in­de­pen­dent rud­der. This has the ad­van­tage of en­sur­ing a back up steer­ing method is al­ready on board but also re­quires a heavy-duty in­stal­la­tion to bear the load and strain that will be ex­erted.

One of the most pop­u­lar mod­els is the Hy­drovane, which is now avail­able in sev­eral dif­fer­ent sizes and shapes de­pend­ing on the boat it is be­ing in­stalled on. The size and shape of the fab­ric-cov­ered windvane is di­rectly pro­por­tional to the size of yacht, and has been in­stalled suc­cess­fully on yachts in ex­cess of 50ft in length, in­clud­ing mul­ti­hulls.

When the boat veers off course, the wind hits the vane on one side or the other, de­flect­ing it away from the ver­ti­cal.

This then acts on a gear that con­verts this side­ways move­ment into ro­ta­tion to di­rectly steer a rel­a­tively large rud­der sus­pended from the boat’s tran­som via the in­stal­la­tion frame­work.

Servo-pen­du­lum

A de­riv­a­tive of the servo-trim tab prin­ci­ple in­vented by Blondie Hasler, servo-pen­du­lum self steer­ing gear uses the speed of the yacht go­ing through the wa­ter to push against the ser­vopad­dle, cre­at­ing a sub­stan­tial force, which is then trans­fered to the yacht’s own tiller or wheel by con­trol lines.

The wind it­self does not pro­vide the power for the steer­ing; rather it ad­justs the an­gle of the pad­dle, re­ly­ing on the hy­dro-me­chan­i­cal en­ergy of the boat go­ing through the wa­ter to do the work of steer­ing the boat. Pop­u­lar be­fore the ad­vent of the small craft elec­tronic au­topi­lot, it’s par­tic­u­larly well suited to yachts un­der 40 ft in length, and can be swung out of the wa­ter when not in use.

There are now sev­eral de­riv­a­tives, in­clud­ing some avail­able as a self-build kit. Amongst the Golden Globe Race en­trants, mod­els in­cluded Aries, Mon­i­tor, Wind­pi­lot and Beau­fort sys­tems.

One dis­ad­van­tage of the ser­vopen­du­lum gear is that it uses the yacht’s rud­der, mean­ing it does not dou­ble up as an emer­gency rud­der should the yacht’s steer­ing be dis­abled, although some servo-pen­du­lums can be adapted.

1 BAL­ANC­ING THE BOAT

‘Be­fore do­ing any­thing, you have to get the boat sail­ing well. It de­mands you take the time to get your boat prop­erly balanced, cor­rectly reefed and with no weather helm; so it ac­tu­ally makes you a bet­ter sailor!’, ex­plains Nick Not­ting­ham, who re­cently fit­ted a Hy­drovane to his Hall­ber­grassy 42 Spell­binder. Nick is about to use the sys­tem on an At­lantic cir­cuit.

Self-steer­ing gear works by ad­just­ing the yacht’s course in re­la­tion to the ap­par­ent wind. The first step to mak­ing this work as ef­fi­ciently as pos­si­ble is to bal­ance the boat and re­duce the amount of in­put re­quired. Sail­ing con­ven­tion­ally, the yacht should be easy on the helm and not over­pow­ered.

2 SET­TING THE SYS­TEM FOR THE CON­DI­TIONS.

Whether servo-pen­du­lum or di­rect drive, most self-steer­ing sys­tems have one or more meth­ods of ad­just­ment for the con­di­tions. In light airs the wind vane will be ex­posed as much as pos­si­ble to the wind, to ex­ert the max­i­mum force on the sys­tem, whereas in heav­ier weather, the vane’s height can be low­ered, re­duc­ing the force act­ing on the sys­tem. Some sys­tems, like the Hy­drovane, Mon­i­tor, and Beau­fort have dif­fer­ent sized vanes that can be swapped, while the Wind­pi­lot and Aries al­low the vane to be raked aft, pre­sent­ing a shorter lever.

On some set ups, the power ex­erted on the steer­ing sys­tem can also be ad­justed at the point where the wind vane meets its pivot, just like chang­ing sen­si­tiv­ity on an elec­tronic au­topi­lot. By con­trol­ling the ro­ta­tion of the rud­der or pad­dle cre­ated by the windvane, you con­trol how ag­gres­sively the sys­tem cor­rects the boat’s course. Chang­ing the gear­ing at the point where the wind in­put cre­ates the steer­ing out­put achieves an in­crease or de­crease of ra­tio.

3 En­gag­ing the sys­tem

To en­gage the sys­tem, set the yacht on course and ad­just the wind vane so that the wind is flow­ing over it with the least re­sis­tance, like a blade. If you are us­ing a sys­tem with its own rud­der, cen­tralise and lock the yacht’s main rud­der, si­mul­ta­ne­ously en­gag­ing the self-steer­ing mech­a­nism. Once en­gaged, mon­i­tor how the sys­tem ad­justs and dou­ble check your sails are trimmed cor­rectly. As the vane moves it will ad­just the steer­ing ac­cord­ingly. In heavy weather, re­duce the sys­tem’s power to en­sure the least amount of strain. Self-steer­ing sys­tems work ef­fec­tively in strong winds but most will steer com­fort­ably in light airs as well.

4 Course ad­just­ments

When the wind vane is ver­ti­cal, you are on course. When the vane is de­flected, the sys­tem is ad­just­ing course. Chang­ing the di­rec­tion you want to go in is sim­ply a mat­ter of al­ter­ing the self-steer­ing sys­tem’s vane an­gle rel­a­tive to the wind. On most sys­tems this is achieved by a steer­ing line that can be run into the safety of the cock­pit, mean­ing you do not nec­es­sar­ily need to ad­just the vane it­self di­rectly. Make small ad­just­ments un­til the yacht comes onto the de­sired course, trim­ming the sails ap­pro­pri­ately.

5 a stand­alone sys­tem?

Whilst self-steer­ing sys­tems of­fer a much more re­silient op­tion than an elec­tronic au­topi­lot for heavy weather, when there is no sail­ing wind, they cease to be use­ful. For this rea­son, most cruis­ers also have a con­ven­tional elec­tronic au­topi­lot on board to steer un­der en­gine.

In the case of sys­tems in­cor­po­rat­ing a rud­der, many also make it pos­si­ble to eas­ily en­gage a tiller pi­lot onto the sys­tem’s aux­il­iary rud­der for use un­der en­gine.

Di­rect drive sys­tems fea­ture a large fully in­de­pen­dent aux­il­iary rud­der

Aux­il­iary rud­der (left); trim tab (cen­tre) and servo-pad­dle (right) de­signs all op­er­ate slightly dif­fer­ently

The vane de­flects the pad­dle, mov­ing the tiller

Self-steer­ing re­lies on a well balanced boat. As the wind shifts, the mech­a­nism cor­rects

With the wind vane at­tached, you are ready to re­move the lock­ing pin and en­gage the steer­ing mech­a­nism

Here an elec­tronic tiller­pi­lot has been plugged di­rectly into the Hy­drovane aux­il­iary rud­der

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