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Trim Tabs vs. Interceptors

Discussion in 'Stabs, Tabs & Gyros' started by DOCKMASTER, May 11, 2020.

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  1. Capt J

    Capt J Senior Member

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    You can adjust the zipwakes.......both in reaction times and everything else. I find they're not necessarily good with list when you're running and you need to correct for that yourself with the thumbwheel. I usually adjust the trim of the vessel manually with them, and let them deal with the roll automatically. They are very good at stabilization on something like you're 42' at cruise. You can break them if you have them all of the way down and back down on a fish.
  2. mapism

    mapism Senior Member

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    Do you mean that you tried the same boat with tabs and interceptors, and experienced a meaningful performance improvement with the latter?
    And if yes, what type of performance are you referring to, exactly: max speed, faster transition to plane, or anything else?
    I am asking because it's somewhat rare to hear from someone who tried both systems on the very same boat.
  3. Capt J

    Capt J Senior Member

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    I have on the same model/setup/engines. The interceptors do seem to be better in transition to plane, max speed is irrelevent because the tabs were all of the way up in both cases for top speed and the traditional tabs don't extend past the transom. 45' SF expresses that cruise at 34-35 knots. Ride is definately better.
  4. AMG

    AMG YF Moderator

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    We used to have trimtabs on our smaller Aquamatic boats up to 40 feet and since several of them are with stepped hulls, I didn´t think interceptors would work because of the air bubbles created behind the steps. But we tried and it worked very well, so now we have Zipwake fitted to all of them. It is not so much for getting on plane, but to keep the boat from leaning towards the wind or when people move around. They are more effective and react faster than the traditional tabs. Our bigger models up to 80 foot have Humphree and since they are IPS boats the interceptors are mainly for trim.
  5. MBY

    MBY Senior Member

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    We've tried them all on our 33's. The first boats were fitted with Bennett XPT stainless tabs, we then moved to Lenco tabs after having consistent issues with Bennett and we then tried and eventually switched to Zipwake exclusively. Part of the reason for the switch was it eliminated a trim tab pocket that needed to be vented and took up some space in two of our aft lockers.

    Overall speed performance wise I don't see much difference between the three. You definitely feel results in the boat faster with interceptors than you would with traditional tabs. What I have found is with the interceptors fully down there is a slightly quicker transition to plane and the interceptors will bury the bow down further than a traditional tab. We did find that by mounting the zipwakes completely flush with the bottom of the hull they acted like two very small wedges and were keeping the running angle a little flatter than normal. We mount ours a soft 1/4" above the bottom of the hull and that eliminated that issue completely. I tell our customers to run the boat with auto roll off if they plan on doing very sharp turns as the auto roll will try and correct and counter the boats natural tendency to lean into a turn.
  6. mapism

    mapism Senior Member

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    Can you possibly confirm what size did you use, for both the 54 and the 80?
    The stroke as I understand is 2" regardless of the blade width.

    I'd be interested to hear also about their effectiveness through the speed range, particularly since you are talking of boats usable at either low(ish) or pretty fast cruising speeds.
  7. mapism

    mapism Senior Member

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    Not necessarily.
    I mean, it is always true that the need for stern lift is inversely proportional to speed, of course.
    And I fully accept that many boats behave as you describe.

    But some builders prefer to tune boats in such way that a touch of tabs is necessary also when running at WOT.
    The rationale is that whenever sea conditions suggest to ride with the bow higher than usual (even if at the expense of optimal efficiency/engines load), you can only do that if the "usual" conditions require a bit of tabs, and by lifting them further you can increase the AoA.
  8. AMG

    AMG YF Moderator

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    I don´t have the size figures available, but in the 54/60 they are fitted and filling the end of shallow tunnels where also the prop wash is channelled. Both the 54 and 80 hulls are designed for IPS with a slightly lifting trim so the interceptors can trim down the bow. Since both have long water lines and pretty sharp entries, they actually run smoother with the bow trimmed down also at high speeds. These boats also have Seakeepers to keep them stable in lower speeds.
  9. Capt J

    Capt J Senior Member

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    You asked about how they did at max speed compared to tabs in the same boat. In my situation, the max speed number was irrevelant because the boat ran best WOT with tabs or humphrees all of the way up and since the tabs were recessed into the hull and even with the transom, they provided no more running surface than none at all.
  10. mapism

    mapism Senior Member

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    Do you mean that the blade shape is rounded to follow the upper profile of the tunnels?
    I've seen Humphree's interceptors with a blade profile that follows the lifting rails, but never a rounded one meant to follow prop tunnels.
    I tried to google for some 54/60 stern photo on the hard, but couldn't find any.
    Do you possibly have one (or a drawing) that you don't mind publishing?
  11. mapism

    mapism Senior Member

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    Fair enough.
    I misunderstood your statement as a generalization, based on what happened with some specific boats.
  12. AMG

    AMG YF Moderator

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    The IPS are fitted on flat tunnels...

    D54 Transom1000.jpg
  13. mapism

    mapism Senior Member

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    Very interesting, thanks.