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Running Angle

Discussion in 'Post Yacht' started by Greg Page, May 14, 2024.

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  1. Greg Page

    Greg Page Active Member

    Joined:
    Mar 4, 2017
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    Location:
    Annapolis MD
    Can any other 43 or 46 owners provide what their cruise running angle is? I put a digital level on the map table static and at 24 kts cruise. I get a 6 degree bow up difference at speed, tabs full up. Seems low but don't have any data to compare.

    Thanks - Greg
  2. Pascal

    Pascal Senior Member

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    Miami, FL
    Not specific to Posts but 6 degrees seem a bit high. Have you tried running with some tabs down and see what happens to the speed? Ususally you can pick up a little speed with some tabs before loosing
  3. Greg Page

    Greg Page Active Member

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    Location:
    Annapolis MD
    Thanks. Just trying too see if our trim is close to typical since the CATs weigh about 1000# each less than original detroits and wondering if would shift cg forward enough to tell a difference. Eyeball comparison of where the spray comes outside the hull sides and I can see it and comparing to a Post 42 brochure photo it seems similar, but not a very precise measurement. I haven't found someone to get a nice side view running at speed yet.

    I really haven't looked at speed with a little tab as it seems to handle best under normal conditions with the tabs up, and I don't need to use the tabs to get on plane.
  4. Capt Ralph

    Capt Ralph Senior Member

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    Lighter engines; CG went aft when operating.
    I wish you did this angle measurement before you re-powered.
    Add some tab (in deep water) and report if hull speed picks up. I believe it will increase.
    Keep us up on what your findings are.
  5. Greg Page

    Greg Page Active Member

    Joined:
    Mar 4, 2017
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    398
    Location:
    Annapolis MD
    The prior owner did the repower so I have no expierence prior to the change for comparison. My fast boat experience, where only the back half of the hull was in contact with the water, is not helpful.

    I design aircraft so spend half of my life on the exact placement of every system and component for best handling and performance. In this case I have no data on the balance prior to or after the repower to even determine if a significant cg/trim change would be possible. If the engines were/are at or aft of the cg, the cg would shift forward with reduced engine weight and decrease the running angle. Since the engines are also 18" shorter, the actual engine cg moves aft along with the reduced weight, which may or may not conteract the actual weight loss. As an engineer having no useable data is not satisfying.

    I played with the boat on the way home from the weekend trip in a moderate 1 to 1.5' wave to see if removal of the original owner added 'spray rails' was good, bad or indifferent. I think it was better as I could run a very shallow crossing angle on the waves (running across them 10-15 degs off beeam) and did see less roll and almost no steer-off on crossing. I also played with the AP and running heading mode, it is faster to respond than I am, further reduced the roll but I don't know if that will persist in larger seas.

    I would like to know where the bottom actually enters the water along the length and if the current location is close to the original design intent or not. Our boat is faster than most other of the period, and it is obvious in rougher seas that it 'likes' 22 kts more than 24-25. It gets noticibly light on the pins at 29-30 kts. It also 'seems' to like keeping 100 gallons more fuel in the aft tank (the forward tank, between the engines, is 200 gal capacity, the aft tank under the cockpit floor holds 350). Just trying to explore the boats capability and get more comfortable. My Scorpion Racing hull would go through anything, so I need to adjust my expectations.

    Thanks for the info.