Trim Tab Upgrade Ideas ?

Discussion in 'Powerboats' started by chas650r, Jul 23, 2022.

  1. chas650r
    Joined: Jul 2022
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    Location: california

    chas650r Junior Member

    First time poster here. I am hoping to get some input on a possible trim tab upgrade I would like to do on my 2012 Parker 2520XLD.

    First some history, I have spent a lot of time fishing on an older model 2520 Parker similar to mine before buying mine two years ago. Although I believe the hulls below the water lines have not changed, my boat is considerably different from the old model. For those not familiar with the 2520 XLD it is a 25 x 9-6 20 degree deep V hull. Although real world numbers are hard to find, the best guess is the new model is a minimum 1500 lbs heavier. Or about 8000 vs 6500 lbs. Add to that, IMO, the balance is bad due to the 300 HP Yamaha outboard that is 4+ feet off the stern on a bracket and a larger fuel tank in the the original position used with I/O models. (To far aft now, IMO) The rest of the increased weight is in more F/G and lots of HDPE (Bigger cabin, more free board and HDPE in place of F/G hatches ect.)
    My boat is pretty much stripped down with all easily movable weight forward now. The new models like mine are much faster and the additional weight is O.K. at those higher speeds, but has killed the low speed performance needed here on the lumpy west coast.
    I have proped way down with a stern lifting four blade prop which is a good change but IMO a band aid at best. The stock Lenco tabs I have are an odd configuration IMO. No idea why, but they are 12"w x 20" long (12" hinge on transom). As mounted they retract about 5 degrees above the hull as I think they should. After 2 years I have found the boat runs best with at least 5 degrees down tabs (beyond parallel with hull) at all times. The boat just feels extra stern heavy at any speed under 28 mph. Full motor in trim and full 12 degrees down tabs are need to stay on plane at less than 24 mph. Although full in trim helps to raise the stern it really lowers the bow and plows.

    So....Because i can't really change the balance or the gross weight I am considering installing large tabs to effectively lengthen the hull and raise the stern especially at low speeds. As of now I am looking at the Lenco 30w x 12 long or the 24w x 12 long.
    My questions and concerns are as follows:
    1) When are the tabs to big?
    2) Could the drag from the over size tabs defeat the purpose even in a position of parallel with the hull?
    3) will I induce ventilation issues? With the 30" wide tabs I will have 36" gap between the tabs and the single prop on center 4' behind the trailing edge of the tabs.
    4) Is the boat just a pig and won't be fixed?
    5) What are all the other things I have not considered?

    The job to replace is some what costly and involved as I must reposition the rams. So I will take all input seriously. I have done searches and lots of informative reading here on similar subjects and look forward to hearing from the experts. Any other ideas, thoughts or concerns welcome.

    Thanks in advance.
     
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Extending the boats bottom will help, as brackets don’t offer much in the way of increasing displacement or planing surface.
    I see trim tabs as band aids for poorly engineered designs. They won’t offer much if anything at below planing speeds.
    #4. Well, it’s broad in the bows, and really heavy…
    A slip neighbor has that same boat with twin 250 outboards, it is obviously down in the stern except when running on plane.
    IMO, A gasoline big block with a duoprop outdrive is probably the optimal setup for that boat, even better with a jack shaft to better distribute the weight.
     
  3. chas650r
    Joined: Jul 2022
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    Location: california

    chas650r Junior Member

    thanks kapnD, So am I correct in thinking the big tabs will add some planing surface that may help the portly stern?

    As far as power goes, the old model boat I fished albies on so much had a volvo penta diesel i/o , got more than twice the fuel mileage and planed nicely at 16- 25 mph . At 16 mph there are just about no seas to big to feel comfortable in that boat . Not as fast as my boat but I cant use the speed most of the time anyway. Hoping to get a bit closer to that type of ride w/ mine. Many of the older models did ok w/ a small block gasser I/O and the repowers went well on the 383. I bought mine w/ the single 300 just to try and keep the stern weight down because I have seen the twin models wallow around slower speeds . IF I was younger I would love to find a beater and do a 370 Cummins straight shaft as I do really like the hull.
     
  4. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I gotta be the dumb guy here.

    If you go from a 20 long by 12 wide tt to a 20 wide by 12 long tt; aren't you going to end up with a slightly different angle, but the same net performance? And even 30 wide by pick a number, sounds like incremental change for lotsa cost.

    Before I'd do that, I'd put the boat on a harsher diet.

    I'd ask over on bloody decks or the hull truth..you'll get more informed replies..
     
  5. chas650r
    Joined: Jul 2022
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    chas650r Junior Member

    I don't think that is a dumb question at all. As you say, even 30x12 is not that big of an area change but I have been told that going to the wider but shorter (out from the transom) is more effective w/ less drag for a given area.
    I wish I could lighten the boat more but as I stated it's basic as is w/ zero added weight toward the stern. No bait tank, nothing in the in the transom storage. As I mentioned IMO the fuel tank (200 gallon) is to far aft but I try to run as light as possible , usually 100 gallons max. I took out the 25 lb interior v berth door that is not needed and made out of hdpe. There is very little gear on the boat in general.
    I have even tried putting 2 men on the bow w/ little effect, again percentage wise, 400lbs of men vs 8000lb boat is not much.
    At this point I think it's worth mentioning again how much the boat changes when at say 25mph I go from fully retracted tabs to just a few degrees down. The boat picks up speed and mpg instantly. So my hope was adding 50% more tab area in a more? efficient package might be worth while.
    I have posted the question on the Classic Parker forum but thought I needed a more technical group.
    Thanks for the input .
     
  6. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

  7. chas650r
    Joined: Jul 2022
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    Location: california

    chas650r Junior Member

    I have looked into Zipwake, none of the others. If I recall correctly it seemed about 3-4 times as much for what was needed compared to the parts needed to upgrade my Lencos. A neighbor near my slip installed the zipwakes on a Tolly 26 and was very happy w/ them but never had tabs before to compare. Although he mostly liked them for auto roll control , I neither want nor need the complexity of a auto system . Not sure but I don't think I found a manual system , or the price still chased me off. The Tolly owner did say the Zipwakes were only effective at the higher end of his speed range , but I think that would be the case w/ tabs also.
    But , all that being said IF I had a report from another boat owner exactly like mine w/ interceptors I would be very interested in what he had to say. Unfortunately I only have reports re. larger tabs but take even those w/ a grain of salt.
    If anybody here has opinions tabs vs interceptors for my needs , I am all ears. I am still not clear which has the best low speed effectiveness . I sure think the idea warrants thought.
    Also if I missed a brand of interceptor that should be considered please LMK.
    Thanks again for all the replies.
     
  8. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I would go with the longer 30" tabs, as they will give more lift at slower speeds which means less need to force them down into the water, might be then the bow wont plow as much like you're saying the current tabs you have to angle them down so much at lower speeds.
     
  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Here is a great paper on optimizing trimtabs. I still think changing the tabs here is an incremental change. The only reason you get more lift is the total area of the 30" tab is larger.

    Obtaining the Practical Formula for the Trim-tab Dimensions to Reach the Minimum Drag for Planing Boat http://pubs.sciepub.com/ajme/8/4/3/index.html
     
  10. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    Important to note that the paper says
    • As the value of the chord or span of trim-tab increases, the amount of the angle of trim-tab decreases.
    It was also found that increasing the size of the span and trim-tab reduces the overall drag of the trim-tab.


    So bigger tabs are better. I can see why as less angle is needed on the bigger tabs. To get similar effect on smaller tabs needs more angle and that causes more drag.
    That is what I got out of the article, which actually is common sense.

    I have increased the size of my tabs, but have yet to put them on the boat. Kept the length at 48", but increased the depth (width) from 9" to 12". My old original 1970 Bennet tabs were eaten up with holes. They used 304 SS. I bought a 2x4 foot sheet (or maybe bigger) of 316 SS and bent my own set, then used 316 SS hammer type rivets to secure the "L" bracket cut out of the old tabs, which was still usable. Those rivets I actually heated with my acetylene torch and hammered the sheets tight to the bracket.

    album
    trim tabs - Google Photos

    I even bent in angled wing tips and matched the curved angle of the transom.
    I also painted them with silver paint from I cant recall. but it is that tough poly paint people sometimes use on metals.
     
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  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    All corrections accepted gratiously. I find the subject matter curious. But I fail to see how the tabs will be a sgnificant change, intuitively. No time to read the paper at length. I have a deadline and am tired.
     
  12. chas650r
    Joined: Jul 2022
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    Location: california

    chas650r Junior Member

    Guys, thanks for the replies. Just returned from a 4 day island trip on my boat. I will read the paper soon . The 200 total miles on the trip gave me more info at different speeds and sea conditions and confirmed my need to do something ! We had a 50 mile run home in varying seas that allowed me to try many different combos of tabs and trim angle at different speeds. At this point in the trip the boat was 100 gallons lighter on fuel and still wanted some tabs no matter what. There was no point in the whole trip even in dead flat seas at 30 mph where having the tabs fully retracted was best , I always picked up speed and mpg with the tabs at least at the point where they are parallel with the hull , essentially adding more planing surface. This makes me think the bigger the tab the better even if I only use a bit of angle to lengthen the planing surface. There is room to go even wider than 30"??
     
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  13. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    yes, then do that, go wider.
    It is the higher angle on tabs that is detrimental to performance. I think of it like pulling a board on its flat face thru the water, high resistance, while a board facing water on a thin edge skates over the water. You can experience the same thing in the car, open window, drive and hold your hand at various angles, you will feel the lift and also the air resistance. Water is so much denser than air, so the effect is greater.
     
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