How to Install Spare Autopilot in Parallel

[myocean]

I have an old Raymarine ST60 installation and like to install a second autopilot computer (either an identical device, a used one or a new SP-X30) in parallel to the existing one. I envision a switch which allows to easily change to the other autopilot if the first one fails.
Pump and hydraulics should be the same while I think each autopilot needs its own display unit.
How would a schematic for this look like? How do I need to set this up?

[sailvayu]

If you are looking for a back up I would suggest it be completely separate for the other. Including power source. This way if what ever goes wrong with 1 it will not effect the other. You could use the same pump for both with just a switch but as the pumps or drives are often a problem I would want that separate as well. I have 2 APs with one under deck and the spare a wheel pilot that is the simplest approach and has worked well for me.

[noelex 77]

My boat has two completely independent autopilots.
2 displays, 2 computers, 2 flux gate compasses. 2 rams.
It was set up so that with a Flick of switch you could change from autopilot 1 to autopilot 2. This system might suit you, but it does get fairly complex when you need to switch interfacing with chartplotters etc.

I believe components are protected from lightning damage by being completely disconnected, especially in metal boat.
So following a refit I have changed this to autopilot 1 which is normally used and fully interfaced, and autopilot 2 which lies completely unconnected. It can be connected and working in about 5mins. Fully functional, but not as well integrated.

In many ways this goes against my love of complex, perfectly functioning, integrated systems, but on a boat I have learnt the KISS principal.
If my primary autopilot goes down I can live without MARPA and tide data untill I get into port and fix the the problem. It's more important that that I can change a couple of wires and my new, completely independent autopilot will function.

Very simple, very easy, but I think its the best solution.

In a fiberglass boat with items like an autopilot computer I would store it in a metal box and waterproof it. Make sure you can change it over, but all the wires are a simple screw terminal fit.
30 mins to change over in anchorage. In a bouncing passage say 2-4X as long, but a crew to hand steer, or for a solo sailor to heave too.

[myocean]

Originally Posted by noelex 77

My boat has two completely independent autopilots.
2 displays, 2 computers, 2 flux gate compasses. 2 rams.
It was set up so that with a Flick of switch you could change from autopilot 1 to autopilot 2. This system might suit you,

Sounds good. However I would go without dual rams I think. If one rudder fails we have the second on our cat, that should fairly work.
So you have put all wires on connectors which you disconnect quickly or how have you done this?

[noelex 77]

Originally Posted by myocean

Sounds good. However I would go without dual rams I think. If one rudder fails we have the second on our cat, that should fairly work.
So you have put all wires on connectors which you disconnect quickly or how have you done this?

That sounds reasonable. I have only one rudder.

For my system I simply unscrew the power wires and screw them into the new autopilot computer. This could be easily accomplished with a change over switch. The switch could also change the instrument data, but if their is voltage spike from a ligtning bolt it will jump the switch.
Completely disconecting the wires ( rather than a switch ) adds a degree of protection, although in a non metal boat the level protection is less.

Nevertheless it is simple and ultrareliable with the minimum number of shared components. It is not as functional. My second autopilot does not provide the integrated data the first one does, but if the SHTF I want an autopilot that is as reliable and independent as it can be. If I need the second autopilot I am trading frills, for independence, and reliability.

Many owners would not accept this. I can imagine the boatbuilder saying:
If the first autopilot fails flick this switch and the second one will work
Verses:
If the first autopilot fails remove the panel and change these wires over. BTW MARPA will no longer work.
The second option is more reliable, which is why I prefer it, but its not for everyone.

[NahanniV]

I am looking at this as well.
I have two sets of identical components: autopilot(computers, compasses, displays, pumps) and rams.

I'm thinking of installing one autopilot and keeping the second stored (wrapped in tinfoil and vaccume packed ?).

For the hydraulics, I'm thinking of installing both pumps with an electrical selector switch.

It's on my TODO list to find out if there is a practical hydraulic disconnect fitting that I could use.

[noelex 77]

I think a lot depends on how handy you are on swapping components from spare parts.
One caution I would add is don't underestimate the extra difficulty of doing this offshore.
What is an easy half hour job at anchor can turn into a many hour marathon when you have to hang on with hand, while you are working.
Some people get incredibly seasick doing this sort of work. They would rather die than screw in a couple of wires.
I am not exaggerating.

[Dockhead]

This is an interesting conversation.

I do have a spare hydraulic pump (although it needs to be overhauled).

I now have a spare computer, control head & fluxgate, although I was thinking of selling them. Do the computers break down? I've never heard of it. If I had a reason to do so, I could keep all of these as spares.

I do not have a spare ram -- do these ever break?? I thought these were extremely reliable. I suppose I could acquire one.

I think I am ok changing bad components under way -- I do not get seasick, and in the worst case you could heave to to give you a more or less stable platform. Seems like a lot of complexity to have two separate systems installed, as opposed to having spares on board. Not the end of the world if someone has to hand steer for a few hours, nicht wahr?

[msponer]

Originally Posted by Dockhead

I do not have a spare ram -- do these ever break?? I thought these were extremely reliable. I suppose I could acquire one.

I think they're super reliable. Mine developed a slow leak around the shaft after ~20k miles (though it wasn't steering for most of that). Replacing the rubber seals fixed it.

[svBeBe]

Originally Posted by Dockhead

This is an interesting conversation.

I do have a spare hydraulic pump (although it needs to be overhauled).

I now have a spare computer, control head & fluxgate, although I was thinking of selling them. Do the computers break down? I've never heard of it. If I had a reason to do so, I could keep all of these as spares.

I do not have a spare ram -- do these ever break?? I thought these were extremely reliable. I suppose I could acquire one.

We are 3/4ths complete on our circumnavigation. In our experience, we know of 6 auto pilot failures including one on our boat, BeBe. In 5 out of all 6, it was the electric drive that failed; and the drive pump failed on 1 hydraulic. We have 2 drives, a Raymarine Rotary and a Raymarine linear drive. We select the drive with an A/B switch that switches 4 output wires from the computer (2 for drive motor and 2 for the clutch).

I am of the opinion that you do not need spares or redundancy unless you are crossing oceans, and I have not met anyone crossing oceans that cannot handle changing a course computer underway.

Bill

[Dockhead]

Originally Posted by svBeBe

We are 3/4ths complete on our circumnavigation. In our experience, we know of 6 auto pilot failures including one on our boat, BeBe. In 5 out of all 6, it was the electric drive that failed; and the drive pump failed on 1 hydraulic. We have 2 drives, a Raymarine Rotary and a Raymarine linear drive. We select the drive with an A/B switch that switches 4 output wires from the computer (2 for drive motor and 2 for the clutch).

I am of the opinion that you do not need spares or redundancy unless you are crossing oceans, and I have not met anyone crossing oceans that cannot handle changing a course computer underway.

Bill

Thanks. And do I really need to keep a spare course computer? Does it happen that these die underway?

I have a spare hydraulic pump (will have, after my old one gets overhauled, and the active one is only 1 1/2 years old), which seems to me the most failure-prone element.

[44'cruisingcat]

I have two autopilots and two hydraulic pumps. I can run either pump with either pilot. I simply have two heavy duty DPDT switches in the wires from the pilots to the pumps. One at the pump end, one at the pilot end.

[noelex 77]

Originally Posted by Dockhead

Thanks. And do I really need to keep a spare course computer? Does it happen that these die underway?

I have a spare hydraulic pump (will have, after my old one gets overhauled, and the active one is only 1 1/2 years old), which seems to me the most failure-prone element.

It is difficult to generalise, given the large number of brands and units available but my impression of autopilots is that from least reliable to most reliable the order would go.

Simple Connection/ power problems
Computer
Head / display unit
Fluxgate Compass / heading sensor.
Drive unit ( hydraulic tend to fail slowly, but more often than electric)
Rudder sensor.

The drive units are mechanical/ electric / hydraulic so you would expect a high failure rate. This is not what I generally see although perhaps these units make disturbing noises which alerts the owner to future problems so they are replaced, whereas items like the computer fail catastrophically without warning, stranding cruising sailors.

[44'cruisingcat]

Originally Posted by myocean

I have an old Raymarine ST60 installation and like to install a second autopilot computer (either an identical device, a used one or a new SP-X30) in parallel to the existing one. I envision a switch which allows to easily change to the other autopilot if the first one fails.
Pump and hydraulics should be the same while I think each autopilot needs its own display unit.
How would a schematic for this look like? How do I need to set this up?

Assuming it's a reversing motor pump, you just need to install a DPDT switch in the wires from the autopilot to the pump.

Make sure it's heavy enough to handle the peak currents. DPDT switches that can handle 50 amps are readily available.

A DPDT switch has 6 terminals - 3 pairs. The centre pair would be connected to the pump, each other pair to the drive output of a pilot.

The pilots would be wired in the normal way, each would need it's own compass, rudder reference, and control head. (Unless you are willing to swap these over when you need to switch pilots.)

[myocean]

Originally Posted by 44'cruisingcat

Assuming it's a reversing motor pump, you just need to install a DPDT switch in the wires from the autopilot to the pump.

Make sure it's heavy enough to handle the peak currents. DPDT switches that can handle 50 amps are readily available.

A DPDT switch has 6 terminals - 3 pairs. The centre pair would be connected to the pump, each other pair to the drive output of a pilot.

The pilots would be wired in the normal way, each would need it's own compass, rudder reference, and control head. (Unless you are willing to swap these over when you need to switch pilots.)

Thanks a lot, that is what I was asking for!