Larger trim tabs and/or drop fins

Discussion in 'Sport Yachts/Yachts' started by Ray K, Feb 8, 2018.

  1. Ray K

    Ray K Member

    51
    Jul 1, 2009
    Toronto, Ontario
    2007 Sea Ray 44 Sedan Bridge
    QSC-500
    My 44 Sedan Bridge is a bit stern heavy and have been reading posts where others have dealt with this issue with larger trim tabs or drop fin addons. I have the GHS hydraulic lift on the boat which adds about 600lbs when it's empty and at a 25mph cruise I still have close to full tab to achieve the best speed. I'm only one or two quick touches of the tab button off full when loaded with fuel, water and gear, much more than my last boat. Was at the boat today (winter storage) and confirmed it currently has OEM Bennett 12" x 24" tabs. There only seems to be 28" along the transom from the prop pocket to where the deadrise flattens out as it approaches the chines. The other problem even if I was to change to a 12" x 30" tab I cannot relocate the cylinder due to underwater lights on that side.

    Many of the posts I have read where various modifications where made where on express cruisers between 30 to 40 feet. Not sure if having a slightly larger tab with drop fins custom made would help a heavier boat like this. Also have the partial hardtop option on this one. Not sure what that weighs. I am looking to just improve the performance a bit as having that much tab down always is adding drag and counter acting the lift to some degree.

    The current tabs are mounted about 1/4" up from the bottom (was surprised as I thought they should be flush) of the running surface so there would be space to perhaps have a larger tab fabricated and attached to the bottom of the existing one without taking anything apart. Maybe 26" x 15" with drop fins. If I had room for the 12 x 30 that would be the way to go but I really don't see how they could be installed as I think it will be necessary to relocate the cylinder.
     
    Last edited: Feb 8, 2018
  2. Siboatguy

    Siboatguy Active Member GOLD Sponsor

    210
    Mar 28, 2016
    Holmdel,NJ
    2005 Sea Ray 320 Sundancer
    Twins V-Drives
    2017 5.7 Mercruisers
    Theres a form on here that says Bennett trim tabs... In there, Theres a guy called tab man... He knows a lot and maybe he can help you... He helped me not so long ago about the same thing you looking to do....
     
  3. Tabman

    Tabman Member

    676
    Jan 11, 2007
    The Tab Cave
    boatless
    boatless
    Is there any way you can post a photo of the boat's transom and Trim Tabs?

    Tom McGow
    Bennett Marine
     
  4. Ray K

    Ray K Member

    51
    Jul 1, 2009
    Toronto, Ontario
    2007 Sea Ray 44 Sedan Bridge
    QSC-500
    I was at the boat and took some photos and measurements to see what options I might have. There is a maximum of 2" between the inboard side of the current 12" x 24" tab and the prop pocket and the same on the outboard side where the hull starts to curve into the chine area. I also noticed the anode is not installed correctly as it's on the bottom of the tab so I will be correcting that shortly.


    20180209_142550.jpg 20180209_142603.jpg 20180209_142640.jpg
     
  5. Ray K

    Ray K Member

    51
    Jul 1, 2009
    Toronto, Ontario
    2007 Sea Ray 44 Sedan Bridge
    QSC-500
    I just realized I should probably move this thread to the Bennett Trim Tab forum as more people will likely see it there. I'll post the photos there as well.
     
  6. juggernaut1

    juggernaut1 Active Member

    742
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    I had the same size tabs as you on my 38. A year ago I increased the size to 26 x 15.5 with three inch drop fins bent into the new plate which was stitch welded to the underneath of the original tab. Huge difference on the effectiveness of operating the tab. Also no need to change the location of your actuator if you use the existing tabs.

    The boat will now run flat down to 12 knots (tabs fully deployed) with much less throttle or pick up about 3 to 4 knots running the same throttle - previously it would only run flat down to 16 / 17 knots.

    I'll see if i can upload my drawings that I gave to the fabricator.

    My recommendation is to max out the available transom space you have using your existing tab i.e. 28 inches and run a similar chord to mine or longer with 3 inch drop fins.

    Have a look at post 1099 in this thread and click on the image for better detail.

    http://www.clubsearay.com/index.php?threads/official-380-thread.12200/page-55
     
    Last edited: Feb 10, 2018
  7. Ray K

    Ray K Member

    51
    Jul 1, 2009
    Toronto, Ontario
    2007 Sea Ray 44 Sedan Bridge
    QSC-500
    Juggernaut, I had seen your post earlier and I am leaning towards a similar modification as I am limited with space. Did you every keep track of various speed/rpm data before and after the mod? I think if I didn't have the underwater light in the way I could have squeezed in a 12x30 with a drop fin.

    A few concerns I've have are with the 3" drop fins. I get the added lift by trapping the water but I wonder how much stress gets put on the trim planes and mounting hinge if in a rough sea where the boat yaws at the stern. I've also seen a number of posts concerned about lengthening the chord too much and the stress it puts on the single cylinder. My options are somewhat limited and I would still try a mod like yours before I start drilling a lot of holes in the boat making more significant changes.
     
  8. juggernaut1

    juggernaut1 Active Member

    742
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    As mention in my earlier post, at best the boat picked up 3 or 4 knots but with increased rpm with the new tabs dug down or otherwise you can maintain your speed and reduce the throttle required to keep the boat at that same speed as the motors are somewhat are unloaded. Essentially the boat is more efficient as you have effectively reduced the shaft angles and the boat is now planing rather than ploughing.

    I was limited to the chine on the outer side of the tab and like you i didn't want to start moving actuators to use all available transom. From memory, Bennett uses a single cylinder actuator up to 30 or so inches wide by 12 inch chord, so they can handle a decent size tab. As I understand it, the concern with the longer chord is water banking up on top of the tab and damaging the actuator or fixtures and not compressive forces normally encountered by the tabs. This concern might occur when backing down or reversing into your slip with the tab deflected. My caveat is that I have an auto trim tab controller which fully retracts the tabs at no wake speeds so this is not an issue on my boat.

    After approximately a year I have not had any issues and most of my cruising is coastal ocean, and includes holidaying on moorings and anchoring where the boat is subject to constant ocean swells. Also bear in mind that a larger tab is likely to require less deflection in most conditions compared to the standard tab.

    I also had similar concerns as you with the 3 inch drop fins but was of the view these could easily be reduced in size or cut off with a cutting disc on a grinder if need be when the boat is next lifted.
     
  9. Ray K

    Ray K Member

    51
    Jul 1, 2009
    Toronto, Ontario
    2007 Sea Ray 44 Sedan Bridge
    QSC-500
    Having a local shop fabricate new custom sized tabs with drop fins now. Will report back when the boat is launched in April on the result. I had good stats on speeds/rpm/fuel burn so it should be easy to see the change.
     
  10. nofuss

    nofuss New Member

    10
    Jun 25, 2013
    Trinidad and Tobago, southern caribbean
    1996 Sea Ray 440 Express Bridge.

    No more growing pains ;-) regal 2760 now up for sale :-)
    twin 3126 CATs
    how well did the tab upgrade work ;-)
     

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