Below Decks Autopilot selection - Input Requested

[SailFastTri]

I echo the thoughts of @kenbo above - your primary wheel steering is via cable and chain. However, a rotary AP drive relies on the same mechanism. A failure of any component (cable/chain/sheaves and bushings, etc.) means reliance on the emergency tiller (a terrible situation with shorthanded crew under even benign conditions). I’ve been in that situation where steering failed at 1AM about 40 NM off Cape Fear in 15-20k winds and 6 foot seas, and we had to hand steer the emergency tiller into the CF River. Luckily we had 6 crew and could do 20 minute shifts, and it wasn’t a storm, but it was tough going for whoever was steering.
This is why IMHO you should only consider a linear drive AP which interfaces direct to the steering quadrant, or direct to rudder post via an auxiliary tiller arm. It would enable you to operate short handed and sail/motor to your next safe port where you can anchor and seek repairs.
Edit - my current boat came with rotary drive AP and I’m in the process of converting to a linear drive for reasons above.

[stormalong]

Originally Posted by japarker11

M84

"We learn by doing" , A very painful and expensive way to go with Raymarine Autopilots. We are in year 8 with our highly modified blue water cruiser.

Linear vs rotary drive - Rotary drives live a charmed life due to the fact they have an approx 12 to 1 gear ratio between the internal belt drive AND the diameter of the radius of the rudder post mounted sector. Bad news is most failures of chain/wire rope wheel steer systems occur on this load path.

Linear drives do have much higher working loads. In our installation, the Type 2s acts upon a separate arm attached to the rudder stock in the vicinity of the upper bearing. It's length approximates the radius of the sector. This configuration allows the autopilot to function as an emergency tiller in the event of the loss of the wheel steering mechanisms.

The 2019 refit replaced the ancient fluxgate compass and CCU with the Garmin Airmar 9 axis heading transducer and a G-wind electric chicken.

So 2022, sees us heading southwest to Hawaii utilizing the wind hold feature in 5 meter following seas, steady 25 kn AWS.........36 hours and the 2s lost the PLASTIC planetary gears. Game over. Arriving back at the mainland we found Raymarine has an upgrade kit with brass/metallic gear assemblies.

For parts support, Low power consumption, and noise, we are staying with the 2S. Consider seriously using the mounting location separated from chain/wire rope wheel assembly. The Airmar heading transducer comes from Garmin's Avionics unit so processor speeds handle 200 knots, 8 knots needs to be on power saving mode. BTW, Odyssey weighs in at 30,000 with a fin keel and skeg hung rudder.Attachment 270121

You must have a very old type 2 drive. I have the same boat and a type 2L drive. They have not made the plastic drive gear for a very long time.

I have three drives. The one that was on the boat when I bought it in 1990 and two that I bought used. I have a lot of miles on my boat - 135,000. I used to replace the plastic gears regularly and got quite good at it. Since getting the metal gears I have not needed to replace them.

I carry two drives. The third, the original, is in my garage. I set these up with a generator connector so I could switch drives quickly at sea. I can swap the drives in about 10 minutes with someone hand steering while I am in the lazarette. However, as I said earlier I have not had a drive failure in a very long time. I wore out the brushes in the original one a long time ago, had to sand down oversize brushes to match. If your drive has a Klaxton brand motor you can't get replacement brushes from Raymarine. They will want to sell you a replacement motor for several hundred dollars. At least that was the case many years ago when I tried. Klaxton, I was told has been out of business for a long time.

PS. Are you a member the Nordic 40/44 owners google groups. Send me a pm if you want to join. We share a lot of information about these old boats.

[noelex 77]

Originally Posted by SailFastTri

This is why IMHO you should only consider a linear drive AP which interfaces direct to the steering quadrant, or direct to rudder post via an auxiliary tiller arm. It would enable you to operate short handed and sail/motor to your next safe port where you can anchor and seek repairs.
Edit - my current boat came with rotary drive AP and I’m in the process of converting to a linear drive for reasons above.

I think your concerns are valid. However, a linear drive is not the only option that can directly drive the steering quadrant. See post #8.

[SailFastTri]

Originally Posted by CaptJPMcGuire

Well a lot has been said about AutoPilots. They are very good running down the ICW and the river -roads. Offshore you will leave a S wake and the pilot will be very busy correcting helm for every slight wind speed/direction or puff.
Couple your pilot to a wind vane system. trim your sails for a balanced helm and let the wind vane carry you to the sunset.
Some systems will control your big rudder others will have their own to adjust the course. I have even seen the wind vane used to directly input control into the electrical autopilot. My thinking is if you can skip the energy consumption of a auto pilot with a wind vane your way ahead in the energy game to run electronics and keep the food cold.

The S wake you describe is indicative of a poor performing installation. Whether it's caused by the settings or course computer/gyro/compass heading sensor, it's not typical of APs in general.
All of my boats that have had APs were generally able to auto-steer better than any human crew member could.
(The only exception I can recall was in large following seas and force 8 winds when I was running with an unbalanced sail plan. The boat wanted to round up and was unable to track well downwind. I admit that circumstance was the fault of the skipper, and it was also very challenging to hand steer.)

[SailFastTri]

Originally Posted by noelex 77

I think your concerns are valid. However, a linear drive is not the only option that can directly drive the steering quadrant. See post #8.

That's interesting. Jeffa also makes rotary (sprocket) drives and when I initially read post #8 it wasn't clear to me how that unit you show works.

[noelex 77]

Originally Posted by CaptJPMcGuire

Well a lot has been said about AutoPilots. They are very good running down the ICW and the river -roads. Offshore you will leave a S wake and the pilot will be very busy correcting helm for every slight wind speed/direction or puff.
Couple your pilot to a wind vane system. trim your sails for a balanced helm and let the wind vane carry you to the sunset.
Some systems will control your big rudder others will have their own to adjust the course. I have even seen the wind vane used to directly input control into the electrical autopilot. My thinking is if you can skip the energy consumption of a auto pilot with a wind vane your way ahead in the energy game to run electronics and keep the food cold.

Wind vane pilots have some advantages, but accurate steering performance is not their strong suit.

[noelex 77]

Originally Posted by SailFastTri

That's interesting. Jeffa also makes rotary (sprocket) drives and when I initially read post #8 it wasn't clear to me how that unit you show works.

For an autopilot drive such as the Jefa DD3 the arm is connected to a pushrod that in turn is connected to an arm directly bolted to the rudder post. This produces an identical effect to a linear drive without some of the more complex and loss inducing gearing involved in converting the rotary movement of the drive motor to a linear output.

The drawback of the arm on the autopilot drive is that more room is needed, as the arm will traverse an arc.

[Plumbean]

Originally Posted by SailFastTri

The S wake you describe is indicative of a poor performing installation. Whether it's caused by the settings or course computer/gyro/compass heading sensor, it's not typical of APs in general.
All of my boats that have had APs were generally able to auto-steer better than any human crew member could.
(The only exception I can recall was in large following seas and force 8 winds when I was running with an unbalanced sail plan. The boat wanted to round up and was unable to track well downwind. I admit that circumstance was the fault of the skipper, and it was also very challenging to hand steer.)

I have both a Monitor wind vane and, as mentioned earlier, a Simrad DD15 drive unit. The Simrad is controlled by a B&G NAC-3 and gets input from a suite of B&G instruments, including a Precision 9 rate gyro/compass. I replaced every bearing in the Monitor recently, but even so I find that it is more likely to steer in a lazy S than the NAC-3. I like having both, and the Monitor obviously uses a lot less power. But so far I think the NAC-3 is more accurate.