Selection of Autopilot for vessel of 8 tons displacement

[Derek - Raymarine - Moderator]

The Control unit p70s or p70Rs and the EV1 sensor can be used with all variants of Evolution autopilot, the key is to match the drive unit to the steering system and then match the ACU to the drive unit selected.

In the case of a vessel of 8 tons, a wheel mounted autopilot is underspec'd for this application and although could be used as an auxiliary Autopilot when Blue water cruising, can only be used in Light winds and will quickly become overpowered especially when combined with heavy or disturbed seas.
Further details on Autopilot selection are available here

In the case of vessels of 8 tons, the choice of drive unit depends on the type of steering system installed.

If the primary steering system from the wheel to the rudder is mechanical, that is to say there are cables from the wheel to a quadrant secured to the rudder stock, or there are draglinks or rods connecting the wheel to the rudder stock, then a mechanical drive is the most suitable on most cases.

The key check here is to move the rudder by hand/ foot and check the steering wheel rotates freely. if it does, this indicates the steering system can be 'backdriven' and so a mechanical linear drive can be fitted, more details here . If the rudder cannot be moved and only turning the wheel will move it, then it is likely there is a gearbox in the steering system which is preventing this and an alternative solution possibly using a mechanical rotary drive and chain might be needed.

If the steering system can be backdriven, then based on your boat displacement, a Type 1 linear drive would be used, this is an electromechanical drive, (very efficient) which is mounted in the lazarette and securely mounted onto a solid platform and aluminium support base bonded into the structure of the hull of the boat and the other end attached to the rudder quadrant or a tiller bar pinned or keyed onto the rudderstock, (we do not advise drilling into the quadrant - advice from the steering gear manufacturers should be sought as to the best method of attachment - ideally we recommend the services of a professional shipwright).

If Hydraulic steering is already installed onboard, then click here for more information about choosing the correct size autopilot pump.

If a T1 mechanical drive or hydraulic pump is used, then an ACU200 will also be needed.

RAYFAQ#