Trim Tabs information needed

Discussion in 'Boat Design' started by ONEOFAKIND, Nov 20, 2011.

  1. ONEOFAKIND
    Joined: Nov 2011
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Jacksonville FL

    ONEOFAKIND New Member

    I am new to this forum and not sure the best place to ask this question
    I have a 18' flats boat w/tabs 9x12 on it and not getting the low speed lift needed to jump up in skinny water. I found a set of 9x18 and want to know if this will help.

    Thanks for any help you can provide.
     
  2. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 43, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    Yes,with tabs more is better. If Bennett all you need to change is the tab and hinge, everything else stays same same as long as the ram stays centered on the larger tab. Steve
     
  3. ONEOFAKIND
    Joined: Nov 2011
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Jacksonville FL

    ONEOFAKIND New Member

    Thanks
    will it matter that almost the entire lower part of the transom will be tab?
    They will not be in the way of the motor but it will take up everything else.
     
  4. MechaNik
    Joined: Jan 2011
    Posts: 139
    Likes: 5, Points: 0, Legacy Rep: 62
    Location: Greece, Italy

    MechaNik Senior Member

    As such that shouldn't matter. The problem with adding more tab is that you add unnecessary drag when you are on the plane. That is your compromise.
    If the boat still requires some trim tab at high speed i would say increasing the tab size should't affect high end performance, but improve low speed lift more efficiently.
     
  5. tabman
    Joined: Aug 2008
    Posts: 25
    Likes: 3, Points: 3, Legacy Rep: 28
    Location: Mount Pleasant, SC

    tabman Junior Member

    Actually, larger Trim Tabs do not necessarily add more drag. The larger Trim Tab will need to be deflected to less of an angle to generate the same amount of lift as a smaller one. So it will have a better lift to drag ratio.

    Also properly installed Trim Tabs angle up above the hull bottom when fully retracted. This raises them above the waterflow when on plane. When the boat is running at high speed with the Trim Tabs all the way up there should really be no additional drag.

    I would add that you will want to keep the inboard edge of the Trim Tab at least 8" from the centerline of the outboard's lower-unit to prevent disturbing the waterflow to the prop.

    Tom McGow
    Bennett Marine
     
  6. beachcraft
    Joined: Nov 2011
    Posts: 49
    Likes: 2, Points: 0, Legacy Rep: 30
    Location: Marinette

    beachcraft Junior Member

    Are you going with wide short tabs or narrow long tabs?

    I had a small aluminum skiff which required me to lean way forward to plane. This was already with the gas moved to the bow. I fitted a set of 18" long tabs which were really big for this size skiff. But they made it plane out with no trouble very quick. And they were clear of the water when running at speed mounted about 3/4" higher than the bottom.
     
  7. philSweet
    Joined: May 2008
    Posts: 2,252
    Likes: 148, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Does anyone here think that tabs will reduce the draft needed to launch? What is the technique for non jackplate boats.
     
  8. tunnels

    tunnels Previous Member

    Trim tabs
    18 x 9 against 12 x 9 The 18 is running across the boat each side and the 9 is sticking out the back ?? How do tab actually work ! All they do is difflect the flow of water down and there by lifting the back of the boat at the same time . the fast you go the more lift and flat out you should only need a very small amount of trim as you slow down you need to increase they can also be used to trim the boat while under way . The extra drag thing is not even worth thinking about unless you are doing 100mph plus !!
     
  9. ONEOFAKIND
    Joined: Nov 2011
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Jacksonville FL

    ONEOFAKIND New Member

    the tabs are 18" wide and 9" deep.
    I will have plenty of room for the motor.
    I do have a jack plate and that is why i need to push the stern up at lower speeds so that i can let it down for the initial launch.
    Does this sound right????
     
  10. tunnels

    tunnels Previous Member

    You need to try a few options Yes the prop needs more bite to get on the plane so possibly need to be lower and with the trim tabs you could be on the plane very quickly so maybe the motor need to go down just a small amount you have to do a little exsperimenting . Every situation is differant its a individual thing what works for you may not work for everyone . Seat time and push a few buttons !!do it scientificly not just randomly
     
  11. ONEOFAKIND
    Joined: Nov 2011
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Jacksonville FL

    ONEOFAKIND New Member

    that is what i was planing on doing after i made sure that the tabs would help not hurt.
    With the jack-plate all the way up i can get to about 7 MPH and after that the boat drops and starts sucking mud. I am hoping that the larger tabs will allow me to get enough speed to help lift the stern so i can hole shot to plane.
    A little more info for you to see what i am trying to get accomplished is that this boat is 18' long with the big block Suzuki 150 on it. it is on plane very fast in 3' of water but i want to get up in skinnier water so i don't have to idle out for 20 MIN to relocate.
    If you or anyone else has any ideas please let me know
    Thanks
     
  12. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 43, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    The following technique involves some aquired skill. With the boat healed by passenger weight into the turn slowly start making circles. This gets the prop off the bottom a little and starts making a little wake. Slowly increase the speed until you "feel" the time is right. The trick is to throttle up and straighten up at just the right time to use the wake and the speed you've developed to help you jump up on plane.

    This is a trick I learned in the Keys (see my screen name.) It does involves some practice so maybe try it in deeper water first and maybe transition to really soft bottom shallower water before getting yourself 30 minutes on plane into a flat.

    Good luck, :cool: Steve
     
  13. kapnD
    Joined: Jan 2003
    Posts: 547
    Likes: 50, Points: 28, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    OK, Im in for $.02.
    Post #11 explains the percieved problem: 150hp big block Suzuki!!!
    Why so much power on so little boat?
    I know there are tons of flats boats out there set up this way, but I just dont see the need for so much hp and the resulting weight and fuel.
    Most true flats boats only require 50 or less hp to run at a fair clip, and are really easy to pole around without the stern practically underwater, where inches matter in your ability to fish skinny water, as well as being able to easily plane up and get out of there.
     

  14. philSweet
    Joined: May 2008
    Posts: 2,252
    Likes: 148, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Exactly like Keys says. Sans jackplate, the motor had to be kicked up some. You could spin, trim and go with a bit of practice. I haven't seen it with a jackplate and big motor though. I think you need light weight and little transom immersion to start to plane sideways at low speed with a bit of boat heel. Turning the motor also reduces the effect of the prop sucking all the water out from under the boat.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.