Fitting an autopilot linear drive to a Swan 40

I plan to fit a built in autopilot to my swan 40 using a hydraulic linear drive, does anybody else have a similar unit? If yes I would be pleased to hear how it is arranged.

I have looked at the quadrant and suspect that it would be best to fit the drive under where the helmsman would stand possibly cutting a new inspection hatch in the cockpit floor to gain access. Will cutting a hole behind the wheel weaken the structure too much? I was thinking of getting a frame made up to distribute the load. Any comments / experience would be welcome.

Many thanks

Jason

CAN-CAN IV (40/29)

Hello Jason:
Many years ago I installed a hydraulic ram that turns the rudder. I have 40/12 and found that there was about one inch of square exposed adjacent to the quadrant installed on the rudder stock. I made a lever from one inch aluminum plate and installed it adjacent to the quadrant. The hydraulic ram pushes and pulls on that lever and that turns the rudder. It works very well and the power consumption is about one ampere hour as measured by an ampere hour measuring meter. One reason for the low power consumption is that I installed a manual valve to short circuit the ports of the hydraulic ram when the autopilot is disengaged. When I engage the pilot, I must turn the valve off. There is a bowden cable attached to the valve and lead into the cockpit. The function of this valve is normally performed by a solenoid controlled by the autopilot, but that uses about one ampere continuously. I didn't want that. Low power consumption is important to me. The autopilot is a Brooks & Gatehouse. It comes with a control head installed in the instrument cluster in the cockpit, a control module installed below, a fluxgate compass installed in the bilge and a rudder position sensor installed near the lever on the rudder stock. The hydraulic actuator I fabricated using a gear pump and a DC permanent magnet motor from Grainger rated at 5 Amps at 12 volt driving the pump via a toothed belt from Boston Gear. The important thing is to have a hard over time of less than 10 seconds. I found that commercially available power units don't move fast enough. It takes a large volume pump preferably made from bronze and not pot-metal. You only need that fast response when running downwind in a large following sea to avoid broaching. I have tested the pilot under conditions like that: The stern wave comes up to deck level and it's real scary. I just carried a #3 jib and put a reef into it.
I'm sure the pilot used much more than one Ampere hour under the conditions because it worked continuously. Manual steering would have been very exhausting and I couldn't have steered for very long.

Hi Peter, Many thanks for your information i will have a look the next time i visit the boat to see how Can-Can compares. Have you mounted the ram fore-aft or side to side?, also how do you access it? Access on Can-can is very tight behind the bunks / under the cockpit, i was thinking of cutting a watrertight inspection hatch into the floor, but i don't want to weaken the structure.

Many thanks

Jason