Boat trim - am I missing something?

Does the boat perform the same with autopilot engaged?

On our 1980 42 with the flat bottom I found there were times I just had to run a different course to get a comfortable ride. Even if it meant heading several miles north or south of the inlet. The extra time was paid off in comfort.

And as far as AP goes, some will say never
But, a good fast acting autopilot will definitely help taking some of the work at keeping a heading. AP’s with gyro sensors will start correcting before you feel the boat going off.
And with some override is as simple as grabbing the wheel and turning.

My 46 pitches and yaws in any kind of following or quartering sea at various speeds. I think it's a Post thing. For boats of this size they really don't have a lot of wetted surface area, and a pretty flat stern.

I only cruise between 15-17 kts depending on wind and current with my gassers.. but yes in following seas my tracks look like I’m 10 sheets to the wind.

I drive her the same way my dad taught me as a little kid. Find your heading. Find the farthest thing away you can to align yourself to, and just aim for whatever it is. I don’t stress too much after that about being off a little one way or another I just drive the conditions for comfort and just make sure I’m generally headed towards the “spot”.

You have three tools at your disposal and should continue with all three until you find what works best for you.

1. Speed. This is a matter of timing with the waves and it may be faster or slower. The tendency is to slow, but often just applying a bit more speed can be the answer as well.
2. Trim. Only complicated a bit by the fact you're experimenting with speed at the same time.
3. Autopilot. Practice and tune and learn all the functionality of your autopilot. Learn how it responds with different sensitivity settings. A good autopilot, properly set for conditions, can track better than you can manually. Rather than resisting the tool, practice and learn with it. The average boater just sets it one way and uses it that way, failing to take full advantage of all it's settings and versatility.

Every boat will have different characteristics so not surprising you're finding a condition that's a bit challenging on a new boat. I remember fairly early as my wife and I were getting trained, our training captains were working us in the Gulf of Mexico. Conditions worsened. Rather than heading in, they used it as an opportunity to teach us. We had to practice with the waves hitting us from all directions. Learning the speeds and trim and angles was definitely a new challenge, but we learned more that day about that boat and about ourselves. Now for each boat since, the principles have remained the same but the speeds and trim and settings haven't. We set out in a new boat in Europe in May and have had to learn it all again with triple jets and Humphree interceptors and stabilizers and less weight than we're use to in a boat that size. While we've never operated it, our Captains who trained us have a 66' Viking and one of our thoughts when we first went out with them on it was the differences in it and other boats we'd operated. Trolling was definitely a new experience. Just embrace the differences and continue to learn, but don't be shy about experimenting.

So the boat is hunting while traveling in a quartering following sea? If so after time you'll get to know exactly how the boat will react to each wave and can preemptively adjust heading. That will counteract the boats hunting. After time you will do it without thinking. I look back periodically to judge how straight my track is when on new boat or different than typical sea state.

I did fail to mention in my post that there is nothing wrong with Tacking a little bit. Doesn't have to be wide, but pursuing the best angles for comfort is perfectly ok. Nothing is written in stone requiring straight lines or always the shortest distance. If your boat will perform better by doing so, then take advantage.

Can you expand on what you said in your initial post and what you mean by "acceptable heading control" ? Are you trying to hold a straight line without rudder adjustments? I'm asking as doing this in a quartering sea is unlikely to happen.

Ah-OK. Yeah that would be a little unsettling. I thought perhaps your expectations might be unrealistic. Your description doesn't sound that way at all. I would be looking for improvement too if I were in your shoes.

Sounds like you are getting the hang of it (your Post) already. You made a good choice in your run.

My 42' Ocean Yachts aft cabin is very similar in handling to what you describe. My boat also has a flat transom and bottom then goes into a vee bottom forward rather quickly much like the Post.
Following seas want to push the bow down while the water lifts the aft and pushes you around. Gets freaky at times. Especially coming in an inlet with swift following current and breaking waves.
There will be a time when you will probably have to work one throttle more or less than the other to help with severe situations. Really not fun.

I think it's a Post thing along with my boat and others.
I totally agree with you on the AP being off when things get choppy. I prefer to ''feel'' the boat as I run it and I'm able to react to what I feel the boat is ABOUT to do and make the correction before she goes into a big yaw, .... y'all. But, yes it can be a workout.

Enjoy your boat and keep on practicing, it never ends. Which is a good thing I think.

THIS, and your autopilot will hold a much better heading than you ever will. Also you should be able to steer to over-ride the autopilot.

Do you mean it's normal for SFs to "pitch and yaw in any kind of following or quartering sea at various speed"?
In a two feet sea, which is what the OP is referring to?

Now, my experience with this type of boats is very limited, but I'm sure to have read some of you guys claiming, more than once, that they are great sea boats, can be used for long distance cruising, and so on and so forth - to the point of claiming that full displacement trawlers aren't much better...
Hype, or what?!?

In a boat where the AP can't handle any kind of sea better than the helmsman, my first thought would be to fix the AP (and/or understand how to use it properly), rather than not use it.

It is common for those particular SF's. Not for today's SF's.

I agree with that. A properly set up and used AP can maintain course better than a person. Then add that the person can adjust as needed so serve as secondary.

I got the rate gyro added to my Raymarine and it made all the difference in the world. I use to yaw quite a bit now it tracks straight. Well worth the investment.