ComNav Marine & NX2 Autopilots

[Stevens 47]

Greetings Sailors,

I am considering installing a ComNav Marine NX2 autopilot. The systems I am considering is driven by a hydraulic to a linear drive arm. My boat steering system is cable.

My boat displaces 40,000 lbs when in the water and tanks are full and all the junk is on board.

Does any body out there have any negatives or positives with Comnav, they have gone by the Nexus name.
Because I am doing a complete overhaul of the boat I am not limited to any system at this point.

I liked the look of the Raymarine stuff but it is twice the price.

Looking forward to your feed back

Jack

[Rick]

The first thing that potential customers always see with any autopilot sales & marketing info is the display. The next thing you are "hit" with is all of the bells and whistles. Truth is that with the ubiquitous microprocessor any number of bells and whistles can be added via software to the point of confusion.

What are you going to use the autopilot for? If you are merely keeping a course in protected waters any "toy" autopilot such as the one you are considering will probably work. If you are going offshore you need POWER available in both the electric drive control unit as well as the actuator. You will only find medium and high power available in the electro-hydraulic units. Linear drive units are lower in power, in general. The one that you are considering is less than 50Watts rating. That is way less than one tenth of a horsepower. For offshore control a vessel of your size would need a quarter of a horsepower, minimum, in my opinion, especially when considering that with a heavy following sea at reasonable speed the power developed must not only rapidly turn the rudder in order to avoid an excessive yaw (and a potential knock-down) it must overcome the friction of having to "backdrive" the cable steering system.

So, if you are going offshore, at least buy an autopilot system having a power unit capable of driving a higher power pumpset even if you don't initially install one. I don't believe that the one that you are considering is capable of doing that.

[DeepFrz]

Rick, output is more like 250 watts.

[hglad]

Installed the Nexus instruments including hydraulic linier arm auto pilot in my Nordic 40 because of cost and ease of installation in 2000. The entire system was flawless for over 10,000 miles of blue water cruising from Portland to Alaska to Mexico to Hawaii and back over the next two years in all sea conditions.

[DeepFrz]

Rick, do you have some motive for bad mouthing ComNav?

[Rick]

I have a problem with the sales and marketing info from most autopilot manufacturers in that it is difficult, if not impossible, to find out just how much power their units are capable of driving. They all give you information showing the human interface as though THAT constitutes the autopilot yet it is the power drive and actuator along with the attitude of the vessel information that marks the primary functionality of an autopilot.

DeepFrz helps point out my "complaint" in that I was not easily able to glean the fact of a 250 Watt drive capability of the ComNav units. That means a 1/3 hp drive capability which, if a continuous rating...not peak...is a reasonable number. Just because a power unit can drive a lot of horsepower does not mean that the pumpset will consume that amount of power unless it is needed. It is just like when you drive the boat fast as a big wave comes from behind. You have to use all of your muscle power to turn the wheel fast enough to keep from broaching...that is the power that must come from the autopilot. If the pilot cannot turn the wheel fast enough you are in trouble.

I apologize for any negative slant put on my input regarding ComNav as I have no negative experience with that company.

[Stevens 47]

Yes it is really hard to get info on the actual drive unit. The guys I was sailing with yesterday recommended Robertson Drive units which I believe is now under the Simrad Company. Have spent hours trying to find drive units and all that comes up is the control heads. Finally found info at http://simrad.psicompany.com/prodasp/ap27.htm

Thanks Rick for the detailed response I take it that the unit in question from ComNav would be powerful enough to handle my vessel in a all sea states? Another factor I need to consider it the stroke of the drive and that it matches my rudder setup, the ability to not have the drive unit restrict the turning of the wheel from stop to stop, I am told that I can blow the drive unit up by turning the wheel if the stroke is less than the stops on the mechanical rudder. I suppose the length of the Autopilot quadrant would give me the adjustment needed but the shorter it is the more torque power is required, is this correct?

I want to install a unit that is sound strong and reliable and not cut corners. That said I do not have the money to purchase the B&G instruments and all the top shelf equipment. I will spend on the best drive unit as long it is compatible with other systems.

Thanks for all of your comments.

Jack

[DeepFrz]

Rick, it is true that most of the autopilot companies don't advertise their pumpsets and hydraulic cylinders and concentrate mainly on the "sexy" electronics. That has been a frustration for me as well.

But I looked at the specs. on the ComNav website (actually I looked at the specs for the ComPilot) and under drive output it says 20 Amps. The 1500 has an output of 25 Amps. and the NX2 has an output of 15 Amps. max (which is actually only about 190 watts.).

Jack, I would seriously consider the 1500 or ComPilot over the NX2 Pilot just because of the more robust drive unit output.

[hglad]

Given the size of your boat I would heartily agree with DeepFrz. As I recall the Nexus was just a rebrand of the Comnav. There is no question more power is better. It's just a question of how much the budget will stand. Today a big part of the equation is the abillity to interface with other brands.

[Rick]

The next thing to verify is the power capability of the actuator (linear drive unit if that is what you must use). It is not obvious to me that the linear drive unit is a "20A" unit. Locating either a hydraulic ram or a linear drive unit is worth your time to work out the geometry.

Use a large piece of cardboard to draw out full scale the center of your rudderpost, "tiller arm length" to which the actuator attaches (ram or linear drive) and the angle, port and starboard limits, over which the rudder may operate. Draw, using straight edges and a compass, the excursion length of the ram or linear drive so that you can accurately locate the exact pivot point location of the actuator. Notice that the optimum pivot point location will be on a line perpindicular to the center line of the rudder post passing through the points where the tiller arm length at both rudder extremes exist and NOT on a perpindicular drawn at the tiller arm length positioned at rudder center. This makes the location of the ram or linear drive look like it is at an angle when the rudder is on center (straight ahead) but it will be in line at both port and starboard extremes. Do not assume that an installer will get this right.

Try to mount the actuator as low as possible so as to not force an unnecessarily large torque couple far away from the upper rudder shaft bearing. The security of the strength and stiffness of the mounting pad for the actuator cannot be to great.

Investigate the quality of the compass or gyro input for the autopilot. Future autopilots will be using 3 to 5 axis accelerometers as directional inputs (which is what a gyro really does) now that solid-state accelerometers exist to do just that. Do not assume that any flux-gate compass will deliver stable directional information to the autopilot at high angles of heel or high rates of yaw and pitch acceleration. When such an error occurs (like when a huge wave comes from behind) the autopilot actually might steer in the wrong direction and wham!

[alanperry]

I have Nexus instruments on my boat and have had many dealings with Com Nav.

Their autopilots are primarily for commercial big ship applications and this is a big plus for the commercial boater as I beleive their ratings are much more realistic than the "Toy" systems of Raymarine et. al.

All of my dealings with Com Nav have been incredibly positive, especially when they fixed my Fluxgate compass for free, free shipping under warranty and it was bought by the previous owner years ago...

[alanperry]

I meant "Recreational" boater not Commercial in the above post sorry...