Intermittent rudder failure Futaba servo S3802.
Not a twitch, just no response. Either direction. Then rudder would work again in 5-15 seconds.
Sat it was ok, then Sunday after a few races, it started. Got worse and finally unable to sail.
NOT a battery problem. Load Tested and swapped 4 different ones. No water in the boat.
Futaba 2.4 6EX. RMG 280DL works perfectly.

Unable to duplicate the problem out of the water, or at home after the regatta. Might be a distance factor, but since the winch or jib trim is not affected don't see how.

No mechanical binding. Cannot find a frayed wire or connection/corrosion problem.
Any suggestions on possible causes, how to find the problem at home would be appreciated.

There are a lot of things that could be the problem and they will probably only show up while sailing. So it is going to have to be trial and error. But my guess is the rudder servo is going bad and has a small dead spot on it. That is, it won't work if it is in just the right spot.
Next best thing would be to replace the rudder servo and go sailing. I have a lightly used Futaba 3802. I can send it to you. If it works, problem solved. If not, then we know it is not the rudder servo.

Put in another servo, as with the old one, it works fine from up the block. Finally got to test the boat on the water, and everything worked fine.
Old servo examined and bench tested and works perfectly.
Bilge phantom still out there waiting.

I agree with Dick;replace the servo.I've tried nursing less than perfectly performing servos to my detriment.Change out now.

I have the same radio and I found out that my random rudder failues were due to a bad rudder pot in the transmitter.

Thanks for the input. I have now had a couple of long sailing days with swapped servo and no problem. Still unable to duplicate the problem with the original servo, but keeping it to try at some point.
Since it could be the pot, I know to swap the channel if it happens again. And carry a spare transmitter/rec. to away games.