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Boat trim - am I missing something?

Discussion in 'Post Yacht' started by Greg Page, Sep 8, 2021.

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  1. Capt J, Sep 21, 2021
    #41
    Capt J

    Capt J Senior Member

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    Well, your holding tank is near the bow.......so there's that weight up there.
  2. Greg Page, Sep 26, 2021
    #42
    Greg Page

    Greg Page Active Member

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    Ran day trip to St Michaels yesterday. Way out was glass smooth. I decided to play with the tabs a bit crossing large boat wakes at different angles. I was surprized that running tabs to be sure they were full up was only about 1/2 knot speed difference then trimming bow down for best speed at constant RPM. It seems it really doesn't need much if any tab. The slight change to full tab up did improve roll going over the available wakes enough to be noticable. Coming home had a small chop and just left the tabs full up.

    I also tried letting the autopilot run cross angle to the bigger wakes. I do a much better job than it does. Tended to steer too much and get into an oscillation (PIO if your familiar with the term) going across close sets. It does ok in fairly steady chop, but can't anticipate the sets of large close waves.
  3. olderboater, Sep 26, 2021
    #43
    olderboater

    olderboater Senior Member

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    If the autopilot is steering too much, then it is because you need to adjust the sensitivity. You control it's responsiveness based on how you set it.
  4. Greg Page, Sep 26, 2021
    #44
    Greg Page

    Greg Page Active Member

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    You can't directly set gains. The AP "learns" from the setup wizard and sets them internally.
  5. Capt J, Sep 26, 2021
    #45
    Capt J

    Capt J Senior Member

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    Which autopilot do you have? I've been able to set the sensitivity on all of them. The reason you're boat benefits little from trim tabs for speed is because that boat is too bow heavy. Like the other poster said, he runs an extra 100 gallons in the stern tank to get the COG aft. Having too much weight forward is also the main why they turn back and forth and ride like they do in a following sea. They got the 50' Post right after they changed the tankage in the early years of the model and it doesn't do that.
  6. mapism, Sep 27, 2021
    #46
    mapism

    mapism Senior Member

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    By "close sets" of waves, do you mean a few waves completely different from those depending on the sea state, (as typically happens with navigation waves from other boats), which you must cross briefly before returning to the "normal" sea state?
    If so, you will never find any a/p capable to anticipate them.
    Of course you can do a better job in that situation, because you can see those waves approaching, while the a/p can only react as soon as the boat is affected by them.

    But other than that, if the a/p makes the boat behave as if she were under PIO conditions, I must reiterate my post #17.
    In fact, I fully agree with CJ: I also never came across any a/p where it was not possible to tune the gain manually - though I did come across several where doing that is somethat tricky.
    Did you RTFM?
  7. bayoubud, Sep 27, 2021
    #47
    bayoubud

    bayoubud Senior Member

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    We were looking at Post years back, they finally moved the fuel tanks aft In the mid 90's which help the ride a lot. Any Post prior to that had a tracking problem. Talked to a few Post owners that said they are squirrely in following seas.
  8. chesapeake46, Sep 27, 2021
    #48
    chesapeake46

    chesapeake46 Senior Member

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    For my 46 with the older style hull and lower Hp, it's not a following sea as much as a quartering sea.

    In either case , I raise trim tabs to bring my bow up and if I can speed up just enough to get ahead of the wave sets, the ride is much better.

    A stern quartering sea is still more work than a straight following sea though and I too have changed course for a more comfortable ride.

    I do not have a tender on the bow, which I think really hurts their performance.

    I can see a speed increase by bringing my bow down going into head seas of between 0.5 and maybe 1.5 knots depending on conditions.
  9. Greg Page, Sep 27, 2021
    #49
    Greg Page

    Greg Page Active Member

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    AP is Garmin 20. Garmin tech came and redid the (prior owner) setup. He showed me how to access the dealer only setup we used, there is no mention of how to get to it in any of the manuals I have been able to find online. He also said can't access gains directly, just through the automated setup functions.

    He called Garmin to ask about a problem we couldn't find anything for and they had no information he didn't. That problem went away the next time I powered on the electronics.
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