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Thread: Trim tab mounting position question

  1. #1

    Trim tab mounting position question

    Due to boarding ladder need to mount trim tabs 12 inch's from chine edge instead of recommended 3 -4 inches, how much latitudal effectiveness will i lose, 5%, 50%, 90%?

  2. #2

    Re: Trim tab mounting position question

    Quote Originally Posted by Crunchy View Post
    Due to boarding ladder need to mount trim tabs 12 inch's from chine edge instead of recommended 3 -4 inches, how much latitudal effectiveness will i lose, 5%, 50%, 90%?
    the outer edge of mine are 7" in from the chine and work very well. They are 18"x9" tabs though. Can't imagine bringing them in a bit will be too detrimental.

  3. #3

    Re: Trim tab mounting position question

    How often do you use the ladder? Might be better off modifying it or fitting a bracket like Cruisecraft do to keep the ladder from hitting the tab. Can't help with the percentage loss - some of the engineers around here might know the math

  4. #4

    Trim tab mounting position question

    9.786534213%... nah that's wrong, think it's 9.786534214% actually .... nah maybe it's....

    You explain this first Crunchy
    Quote Originally Posted by Crunchy View Post
    ... latitudal effectiveness ...
    and then I'll tell you any number you like .

    Seriously now, if you are talking about correcting lateral trim issues, i.e. a lean or heel, think of the correction required (uplift) by the trim tab as a righting moment - or 'force at a distance'.

    If you halve the distance (trim tab mounted half way out to the chine), it needs to generate twice the uplift to generate the same righting moment. Generating twice the uplift will induce more than twice the drag. (probably twice squared = 4 times the drag, but it's too late on a Friday for this )

    This is why you will/should find that all good trim tab installation instructions suggest that they be installed at or within 'x' distance from the chine/reverse chine line etc. (Too close and they can create spray issues etc.)

    I always like to install them where they are supposed to be (out near the chine) for this reason, as who wants excess drag? Hence consider Scotty's suggestion re ladder.

    If you're a numbers man Crunchy.... and you can only install your tabs at say 80% of the distance out towards the chine where they are recommended to be, they will need to create 1/0.8 = 1.25 = 25% more lift to correct a heel, and possibly (1.25 squared) = 56% more drag in doing so.

    Obviously for both tabs to trim the bow down (no heel correction), there is no difference where they are on the transom, so long as they are in the water .
    Cheers & happy drilling.
    Brendon

    PS. Remember, measure once drill twice... no that's not right... what is it again ...




    Sent from my iPhone using Ausfish mobile app

  5. #5

    Re: Trim tab mounting position question

    The ladder mounting bolts right where the actuator head will go, ladder integral part of the set up, not easy to move unfortunately....I'll work around it

  6. #6

    Re: Trim tab mounting position question

    Could you make interceptors fit under the ladder?

  7. #7

    Re: Trim tab mounting position question

    All done, I had to move the tabs about 8 1/2 inches in from the chine which should be fine as the tabs are for fine tuning not solving any major issue I have with the boat.....it was the ladder mounting bolts that were in the way not the ladder itself.

    So installation was pretty straight forward but took a lot longer than I thought it would, 2 x half days to mount the tabs, still got to wire them up. Lots of measuring, re-measuring and then measure again! 20 new holes in the transom but lashings of 291 so should be all good. Hardest part was physically screwing the screws into the transom on a 38 deg day, bloody near killed me.

  8. #8

    Re: Trim tab mounting position question

    So the wires come through in the splash well, thoughts? I can drill holes in the splash well (Not more holes!) and take them through or run some conduit and take along the splahwell and run them through the motor harness hole.

  9. #9

    Re: Trim tab mounting position question

    Closing off....

    The tabs are great, significantly improved ride heading into a choppy sea....

    12x9 tabs on the 650 seem to be plenty and mounting inside recommended 3" by 5" is no problem at all.

    only took short time to realise I didn't need the indicator switch option, its all about feel. So the basic switch has some advantages, the relays are built into the switch so only one wire loom direct to actuators whereas the indicator models have seperate relay units so more wires, more joins and more things to potentially to go wrong but some may appreciate the indicator panel and auto retract function

    quality seems good so far, will report back if any issues arise. One harness plug was wired wrong.

    Happy tabbing
    C

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