Auto pilot stroke size ?

[skwanderer]

Scoping out what parts and costs I need to install an auto pilot. Trying to determine which Hynautic cylinder I have already. I'm exhausted trying everywhere else to answer my question, so thought I'd ask here. I think it's either a K-8 or K-9. The number vaguely stamped on one end is aged enough I can't tell if it's an 8 or 9.

Is the length dimension of the cylinder itself the measurement of the stroke? Or is it the length the rod actually travels hard to side fully extended the stroke?

The actual length of my Hynautic cylinder is 14ish inches. Actual rod length is 28ish inches (rod diameter .75 inches. Clevis pin mounting to rudder collar).
Rotating my helm wheel to full extension of the rod (hard to port) measures 9ish inches exposed out the end of the cylinder. That's likely just how it's set up on my boat, but is that the critical measurement to determine stroke? See the uploaded chart; The stroke of the K-9 is 14.5 inches (actual length of my cylinder); the stroke of the K-8 is 9.5 inches (actual length of the rod fully extended out the cylinder on my boat when hard to port). I'm getting confused.
The difference in cubic capacity displacement is huge (K-8 is 39.2 cu. In. vs K-9 is 55 cu. In.), Which is extremely relevant for sizing the correct AP parts, ie the ACU and the hydraulic pump).

I'm going with a Raymarine EV-1 sensor to tie into my Axiom MFDs, and am trying to determine if the ACU-400 is correct, or should I use the ACU-300, both very different from each other. Raymarine has a comparison chart https://www.raymarine.com/en-us/lear...ydraulic-drive

Any help appreciated. And if anyone can recommend a marine hydraulic mechanic in San Diego area, Id appreciate it.

[PippaB]

Stroke is the distance the rod travels. The used stroke would be the distance the rod travels from hard to port to hard to starboard. This is usually a bit less than the cylinder stroke spec so you are not hard against the cylinder stops with hard over helm. From Hynautic;

These stroke lengths are specific to each cylinder model and are used to describe the linear distance the piston travels within the cylinder.

To confirm actual stroke disconnect the clevis and use the helm to fully retract the rod, then turn the opposite direction to fully extend. This removes all the other things rudder related that might limit the stroke.

[skipperpete]

PippaB explained it already. Those two rams are identical except for the stroke….. just measure the stroke as he suggested.

[barnakiel]

Assuming they are matched as per manufacturer sheets, the pump with higher flow will move the same arm faster. If reaction time is important in your application, given both are OK by specs, use the bigger pump for faster lock to lock travel.


The stroke (distance it travels) will matter given your arm mounting place vs. the rudder shaft - we want more stroke when the cylinder is mounted further from the shaft, give the same required rudder angle.


Normally, we will avoid very short shaft to mount/pivot distances - just like we will not grab a tiller too close to the rudder's shaft when steering by hand. Further mount = less force to handle, aote.



b.

[Sailor 99]

Originally Posted by skwanderer

Scoping out what parts and costs I need to install an auto pilot. Trying to determine which Hynautic cylinder I have already. I'm exhausted trying everywhere else to answer my question, so thought I'd ask here. I think it's either a K-8 or K-9. The number vaguely stamped on one end is aged enough I can't tell if it's an 8 or 9.

Is the length dimension of the cylinder itself the measurement of the stroke? Or is it the length the rod actually travels hard to side fully extended the stroke?

The actual length of my Hynautic cylinder is 14ish inches. Actual rod length is 28ish inches (rod diameter .75 inches. Clevis pin mounting to rudder collar).
Rotating my helm wheel to full extension of the rod (hard to port) measures 9ish inches exposed out the end of the cylinder. That's likely just how it's set up on my boat, but is that the critical measurement to determine stroke? See the uploaded chart; The stroke of the K-9 is 14.5 inches (actual length of my cylinder); the stroke of the K-8 is 9.5 inches (actual length of the rod fully extended out the cylinder on my boat when hard to port). I'm getting confused.
The difference in cubic capacity displacement is huge (K-8 is 39.2 cu. In. vs K-9 is 55 cu. In.), Which is extremely relevant for sizing the correct AP parts, ie the ACU and the hydraulic pump).

I'm going with a Raymarine EV-1 sensor to tie into my Axiom MFDs, and am trying to determine if the ACU-400 is correct, or should I use the ACU-300, both very different from each other. Raymarine has a comparison chart https://www.raymarine.com/en-us/lear...ydraulic-drive

Any help appreciated. And if anyone can recommend a marine hydraulic mechanic in San Diego area, Id appreciate it.

I use the one out of BC. It is hydraulic it is an octopus. Reasonably priced and reliable.

You will have to put a tiller arm on the rudder post or hook it to the quadrant. The length you need is entirely dependent on how long your tiller arm is or what distance you have from the rudder to the mounting post.

I have a 7 inch one I could let go for a very reasonable price considering what they want for new which is about 2900 cdn.

https://www.amazon.ca/Octopus-OCTAF1.../dp/B007ILDT02

PM me if you would like to talk.

You need one longer than the total distance the ram would need to move or you will break it. If you need 8 inch then mine will not do at all. The option of course is to either extend the shaft on the 7 inch one by changing the ram at a hydraulic shop, reducing how much the rudder turns or moving it closer to the shaft.

[deblen]

Some tech info https://www.sbmar.com/articles/marin...ering-systems/


Ram displacement (cc/cu.in.) & pump displacement should be sized to give a hard over to hard over time of approx. 12 seconds for most pilots.


Cheers/Len

[seandepagnier]

You want +- 20 degree to generally hold a course, but +- 30 degrees for decent tacking under autopilot.



12 seconds is going to give marginal performance. Prefer 6-8 seconds or faster, but it depends on the boat and usage. For larger/heaver and slower boats you need less speed.



I went to a 2 second hard-over drive and was pleased with the performance especially traveling downwind at 12-15 knots surfing swells.