A little autopilot help

[Deborah Ann]

Is there a way to drop the line pressure in a Raymarine type 3 pump?


I have a K-19 Hynautic steering ram on the vessel. It calls for a type 1 pump to accomplish steering. But as I have operated the boat I noticed that I prefer to have the faster response of the higher output of a type 3 pump. However the type 3 has an operating pressure of 1100PSI vs the type 1 of 760PSI. Anyone have experience adapting this to a lower pressure?

 

[Iggy]

Have you called Raymarine? I don't know much on this topic but what comes to mind is. That extra PSI may help in that response time.

If your running along and now want to turn, due to the water pressure its going to take more force to move it faster. Yes?

 

[O C Diver]

Is there a way to drop the line pressure in a Raymarine type 3 pump?


I have a K-19 Hynautic steering ram on the vessel. It calls for a type 1 pump to accomplish steering. But as I have operated the boat I noticed that I prefer to have the faster response of the higher output of a type 3 pump. However the type 3 has an operating pressure of 1100PSI vs the type 1 of 760PSI. Anyone have experience adapting this to a lower pressure?

The Hynautic pump system has a bleed block / over pressure valve that is either separate or part of the reservoir. It prevents excess pressure by bleeding the excess back to the reservoir.

Autopilot pumps don't run at their rated pressure. That is the maximum pressure they can generate. The pressure level is determined by the force required to move the rudder. It's likely that your system operates well below 760 PSI. When the rudder hits an obstruction or the ram in the cylinder bottoms out, that's when the pump pressure instantly shoots up. The bleed block / over pressure valves are designed to protect the system from that. It's also important that the rudder angle limits are properly set in the autopilot computer to prevent the pump from bottoming out the steer cylinder.

Ted

 

[Capt. Jon]

I found something on line that made me think the K-19 Hynautic steering ram was rated for about 500psi. Just because you pump is rated for a higher pressure does not mean it will be operating at that higher pressure. Not really knowing enough about your system setup it would most likely has some type bypass relief valve. If not you could install one in your system and set the bypass pressure at the amount needed to bypass the steering ram if it’s not all ready there.

 

[Iggy]

Just for my understanding, please. So the pressure will go up during resistance? As in, if it takes 500psi to move the rudder thats all the pump will put out even if its rated higher?

 

[O C Diver]

Just for my understanding, please. So the pressure will go up during resistance? As in, if it takes 500psi to move the rudder thats all the pump will put out even if its rated higher?

Yes.

If you think about a 2" steer cylinder and don't consider the rod, the surface area is about 3.14 sqin. With 500 PSI of hydraulic pressure, the cylinder would have 1,570 pounds of force. Hopefully it takes a lot less than that to move your rudder.

Ted

 

[C lectric]

Just for my understanding, please. So the pressure will go up during resistance? As in, if it takes 500psi to move the rudder thats all the pump will put out even if its rated higher?

CORRECT.

A hydraulic pump of any type, no matter the rating will produce only the pressure needed at any time to move the load. In this case the rudder.

Further if the pump is working hard , when the pressure is seen to go up, it is not just the pressure that determines the rudder movement speed as long as the pressure is enough to move it, but VOLUME which is speed.

If the new pump moves the same volume of oil as the other pump the rudder will move at the same speed UNLESS the previous pump was in fact running at its pressure limit at time.

What the pressure will do is if the rudder is hard to move such as in a rough sea then the pressure will determine whether or not it moves at all.

You may need to plumb in a pressure guage to actually watch what kind of pressure is being generated by the existing pump under rough conditions.

Darned near forgot to add; Pumps are rated for BOTH pressure and volume. The ability to actually do work is the pressure, the speed with which that work is done is volume.
Neither will work without the other at least not as expected/needed.



Call Raymarine and discuss what you want and why. They may have a fix but just a higher pressure pump may not be what you need. I will guess that in fact it is not what you need by itself.

 

[psneeld]

If Raymarine doesn't help...try a good hydraulic shop if one isn't too far away.


They might have good suggestions to not worry or sell what you need to reduce the pressure for the system.

 

[EngNate]

So, the action of pressure in the system explained, you can't change the pressure capability of the pump, and bigger pumps will usually be capable of higher pressures. Some pumps have a flow adjustment you can use to set the desired speed (see Octopus pumps).

First, if the A/P rudder limits are properly set - and if there is a jog steering lever, limit switches installed and setup, excessive pressure from the pump won't be a situation that arises. A properly selected fuse or circuit breaker can back that up by limiting the motor load, and at last resort relief valves inside your helm pumps will go to work.

By faster response, you mean moving the rudder manually when maneuvering, or pilot performance? If pilot performance, settings checked - rudder gain and rate of turn limit? Check the hardover to hardover time with a stopwatch. If it's more than 15 sec you won't have good performance, 12 or less should be no problem. 10 or less is nice if you like to use jog when maneuvering. I don't know about the new models, 'classic' Raymarine the 'Response', with only 2 settings, is sea state filter on/off. Press +1&-1 buttons for 10 sec for the rudder gain setting. Unless its the jog, don't decide you need a bigger pump till you've played with this, if pilot performance is the issue.

 

[SoWhat]

The K19 ram is 9 cu in and a factory installation would match it with the Type 1 pump (5-14 cu in) As you have discovered, substituting a bigger pump will give you more volume and faster response. The larger pump has a stall pressure of 1450psi, but you will only see that if something gets jammed. If you are still using the 750psi hoses they will pop long before anything else breaks.

As mentioned, make sure autopilot setting response level is set correctly.

 

[Deborah Ann]

Thanks for all the help

Moving forward I will be considering all of your inputs. The only area where the faster response time is necessary is during a following turbulent sea such as an inlet crossing. There I am using rapid rudder movements to stay on course. I am also a little "OCD" about heading issues when in such a channel. I am a single engine trawler operating at blazing speeds in the 6 knot range. I just get pushed around with the natural contour waves and then it is complicated by larger boats and their wakes.

 

[EngNate]

Hmm.. what kind of boat, just curious - it isn't the Thompson 34 I see in pics (?), which doesn't strike me as to expect good handling in seas. That one definitely isn't designed with 6 knots in mind.

 

[Ric]

I am having comparable problems with our new boat, which has a Raymarine Type 1 pump. The autopilot works fine in flat water where small rudder corrections are effective. But in a seaway, with the bow being knocked around, we end up hunting with 30-degree swings to either side of the course line. So once things get a bit lumpy, I have to turn off the Autopilot. Has anybody else had this problem, and was it solved?

 

[Capt. Jon]

If you have one of the newer Raymarine Evolution auto pilots let us know. In my experience you need yo make sure that yo7 have the latest firmware update and if you don’t have a rudder sensor you might want to install one. Our last boat we ran without the rudder sensor on an Evolution system . Works great in smooth water but had issues with it hunting in rough waters. Even though Raymarine says that it will work without the rudder sensor (and it will) it certainly does work better with the rudder sensor. Be sure to also go through all of the calibrations also.

 

[Ric]

We have a new Evo, with a rudder sensor. I will check the firmware vs the latest version, thanks for the tip. I have run through the calibration at the dock twice, and got two different results; one a lock to lock of 16.7 sec and now a lock to lock of 12.5 sec. I will take the boat out and do a full calibration as soon as the current battery work is done. Thanks again,
Ric

 

[Capt. Jon]

Ric, I think you have given yourself a clue! If you are having low voltage issues due to battery problems you may have found your answer. Not sure if you are tying your AP into a (NMEA or Raymarine bus) but voltages are important. Get much below 12.4 volts you may start having issues.

 

[Ric]

No battery issues, new boat with 880ah AGMs, but perhaps a connection isn't secured properly. Entire nav system is Raymarine via Raymarine bus but other systems reporting over NMEA. Thanks for the suggestion, will check connections for any signs of wobbliness.

 

[SteveK]

Rapid rudder movement may not affect steerage rapidly. In other threads stating similar concerns there are those who increased the size of the rudder(s), or added shapes like plane wings. A sailboat rudder can turn the boat on a dime. Power boats it is gradual.
Recently, after reading about toe in on twins I measured a 1/2 inch on mine. So I changed it to one inch. It did make a difference to tracking in nearly calm water.
I need to instal a rudder position indicator to see what the autopilot is doing. My guess it is still steering one way and when a wave catches the other way takes a long time to get over, rinse/repeat. I can only compare to my steering turning the wheel before it needs to be to get it in position to that of auto which waits for direction from a compass course.