Surfing--following sea, auto pilot

A couple of days ago when I was looking for a spot to anchor I attempted to cross an inlet on the lee side. I soon realized that the waves were way too big to take on the beam, so I turned downwind and surfed the rollers. Maybe 4-5'.

At first I tried using the auto pilot but it made me look like a drunken sailor veering from side to side. Hand steering I was able to stay perpendicular and actually got up to 9 plus knots going down the faces of the waves.

Is it not a good idea to use AP in a following sea or is this just a peculiarity of my boat?

Did you try adjusting your speed? Sometimes when the AP is struggling, you can speed up or slow down and that will help eliminate or reduce the yawing.

Larry M said:

Did you try adjusting your speed? Sometimes when the AP is struggling, you can speed up or slow down and that will help eliminate or reduce the yawing.

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Yawing-- that's the word I was looking for.


I didn't adjust the speed. I will try that next time. The wave period was about 4 seconds if that makes a difference. Really close together.

This boat has a pretty big rudder and I was surprised how well I could control it on the waves hand steering.

What's the biggest following sea you've been in? Does your AP keep up well?

Most APs have a double intensity button or setting. It speeds up response time.

BUT. Most boats don't do well in a following sea. Especially that size.

What type boat was this on? Length?

cappy208 said:

Most APs have a double intensity button or setting. It speeds up response time.

BUT. Most boats don't do well in a following sea. Especially that size.

What type boat was this on? Length?

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Basically a rounded sailboat hull but with a big swim platform. 41' overall but only about 36' LWL.

My Raymarine was set up for calm conditions and slow response.

Following rollers this spring kept driving the AP nuts and giving me an off course warning.

Changed the response time and gain and it locked on like on rails...well close and conditions worsened but still held course just fine.

Look in the manual for adjustments.

I also have A Raymarine. ST 6002.

I will check it out. Thanks.

I operate my troller on AP in large following seas w/o any problem, sometimes at night for hours (canoe stern) My lobsterboat, on the other hand, has problems in following seas and I do not always trust her on AP in those conditions. Both boats are the same length.
I am convinced the transom stern on the lobsterboat has too much boyancy, and altho the rudders are of equal size it is very hard to straighten her up once she starts to broach w/o using the throttle, which the AP can't control.
In a head sea, the troller lifts to the seas much more readily because the stern can settle easly w/o the transom's boyancy so no pounding or spray. I don't even know if my WS wipers even work...

Sounds like conditions very similar (steep & deep with short frequency) to what we get here in BC's long channels. What works for us is to slow down to the speed of the waves and ride the trough, which results in much less wallowing about.

Another trick, if you want to move across a channel when traveling downwind, is to speed up and ride the trough diagonally across the face of the waves. If there's not enough distance for that option we wait for a flat section, make a turn into the waves, and take the waves (at an angle) on the bow for a while until that sets us at a comfortable angle for another downwind shot at it.

At a certain point though the waves start playing with the boat more than the boat is playing with the waves...best to duck in and hide somewhere before that starts happening

cardude01 said:

I also have A Raymarine. ST 6002.

I will check it out. Thanks.

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Cardude,

I had the same autopilot on a previous boat. Next time you are in following seas try selecting response level 3 which turns off the AutoSeastate (seastate) and adds yaw dampening (counter rudder) compensation. The instructions are in the Owners Manual on pages 7-8. These settings will make a huge difference.

Like Psneeld said, it should steer like it is on rails.

Slowing down too much can take too much prop wash off the rudder....and worsen tracking.

Every boat is a little different and some just handle or don't handle certain conditions well.

But AS have a pretty wide range of operation and should handle 4-5s with that size boat no problem. Of course there is always exceptions such as they are so steep because of strong wind against current that they are stacked to the curl breaking point and broaching starts.

In addition to following seas pushing the stern if the waves are over taking the water flow over the rudder is reduced and possibly even reversed thus the loss of rudder effect.


Riding the trough or back of the waves means you are in water that is not moving relative to the boat thus rudder effect is normal.

I always turn off the AP and hand steer coming through a rough inlet. I want to feel the boat and determine how much control I have. Often have to work the throttle up and down to balance between bow steering and low rudder effect.

cardude01 said:

A couple of days ago when I was looking for a spot to anchor I attempted to cross an inlet on the lee side. I soon realized that the waves were way too big to take on the beam, so I turned downwind and surfed the rollers. Maybe 4-5'.

At first I tried using the auto pilot but it made me look like a drunken sailor veering from side to side. Hand steering I was able to stay perpendicular and actually got up to 9 plus knots going down the faces of the waves.

Is it not a good idea to use AP in a following sea or is this just a peculiarity of my boat?

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All the above. Each boat handles those conditions differently as does each autopilot. However, the one thing I suggest anyone do with their autopilot is read every page of the manual and experiment with every setting to see what each setting will do. A lot of people set their autopilot and never change those settings but most AP's have a lot of tuning and many different levels of response to which they can be set. Play around with the settings safely away from land and inlets.

BandB said:

However, the one thing I suggest anyone do with their autopilot is read every page of the manual and experiment with every setting to see what each setting will do..........Play around with the settings safely away from land and inlets.

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Good advice! I do this often, just to refresh my knowledge of my pilot.

Just like hand steering...sometimes a lot, sometimes a little.

Never changing the settings is either over or under working it and not good except for a small range of conditions.

psneeld said:

My Raymarine was set up for calm conditions and slow response.

Following rollers this spring kept driving the AP nuts and giving me an off course warning.

Changed the response time and gain and it locked on like on rails...well close and conditions worsened but still held course just fine.

Look in the manual for adjustments.

Click to expand...

: thumbs:

My ComNav is similar in that the description of the settings are fit brainless people, but they don't read the manual anyway.

Auto setting does NOT work.

The rougher the seas, the more I set it as for flat seas, do it responds instantly.

It works so well.

Those short period waves are the only ones I ever seen to see.

But as Paul as said, you MUST change settings based on conditions.

For beam seas, I keep out on a medium setting. For large following seas, it must be on the most sensitive setting.

I too have found that the slower I go, the worse the control.

Other then coming in or out of bad inlets, or in situations with other traffic, ComNav does most of the steering.

Our Harmon has same response adjustments. We have set it on the faster settings and on a recent night crossing in the gulf we had substantial swells build up on our starboard stern. The ap kept up with it just fine dropping us back down straight after each set. Probably 8' or so but well spaced and not capping at all. Since it was pitch dark we felt better relying on "uncle auto". That was in our 42' 1981 GB