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  • Homemade Surf Tabs

    • Year: Choose Below Brand: Moomba Device Type : Tab Style Surf Device Material: Aluminum Control: Powered via Switches (no controller) Cost: $500-$999 Platform Type: Fiberglass

    I went round and round in my mind about whether to make a set of surf gates or tabs for my boat. Gates seemed easier, but when I made a ghetto gate to test the "proof of concept", the wave wasn't very good, and my boat didn't like it much. So tabs it is.


    I looked at the tabs that come on basically all the manufacturers that used them, and ended up essentially copying what's on the MB boats.

    I made about 100 drawings, and at least 3 cardboard mockups until I was happy with it, then gave those measurements to my buddy, who put them into CAD.

    I wouldn't recommend using the measurements in this drawing to make a set.  This was one of my first drawings, and the measurements are pretty far off.








    I also made some cardboard mockup actuators, at retracted and extended length to see how everything would fit.  They were a little flimsy, so later I made some out of paint stir sticks.



    We got the metal waterjet cut, bent at a local fabricator, and then welded them up. I could have saved about $150 by cutting everything myself and welding on the side pieces instead of bending them, but the finished product is much nicer this way. 





    I also had to make the lower actuator brackets, which is of 2" square aluminum tube with one side shaved off.  The tabs are 3/16" 5052 aluminum plate, roughly 17.5" wide x 21" long.



    Everything powdercoated satin black. 

    Lenco uses #14 screws for their trim tab hinges, so that's what I was going to do too. They say to drill the pilot holes with a 3/16" bit. Drilling into the hull was more than a little nerve-wracking. First screw cracked the hell out of the gelcoat and froze in place about 1/2" in, and the head broke off. F*%k!!! I decided to leave that screw alone, and used #12 screws for the rest. 

    I also had to use the Lenco remote gland seal kit to route the actuator wires into the boat, because where the actuators mount is below the floor in the lockers. Broke one screw on each of those too. 1" thick fiberglass does not like being screwed into. 






    For controls, I'm initially using regular Lenco trim tab switches. I made a mounting plate to mount the switches in the huge hole left by the Sony remote next to the throttle. 



    I made a relay panel, for when I get a controller.  The switches and Lenco wiring would work fine without it, but the controller can't handle that kind of amperage.




    The relay panel is behind the rear panel in my starboard locker. 



    The first day of testing had mixed results. The wave forms almost instantly, and the shape is much better and more fun than the Nauticurl wave, but at the moment doesn't have as much push. I need to move weight around to see where it needs to be.  

    (Most of this was written as I went, obviously I have made progress and know results of a lot of this. One thing here, was not playing enough with tab deployment.  It was almost full deployment, 18 degrees down, for this initial testing)

    I need to remove some weight from the bow, because the tab pushes the nose down, as well as lists the boat. That may add some push.




    My biggest mistake was using aluminum hinges. That’s what MB uses, but I guess theirs are much thicker than what I used. My hinges started to bend, particularly at that one broken screw. 

    I pulled the tabs back off, and was able to get that broken screw out. My buddy suggested we tap the holes for ¼”-20 machine screws, which is what we ended up doing. The threads are the same depth as the sheet metal screws, but there are many more of them, so the holding power will be much greater. I don’t know why Lenco and others don’t suggest doing it this way.

    I ordered some new, thicker, stainless steel hinges. They are significantly stronger and better.




    Got the boat back in the water for more testing after the hinge replacement. I moved all the lead I had in the bow to the floor in front of the rear seat on the surf side. I also initially only filled the bow ballast halfway. Nose was way too high, needed more speed and wakeplate full down. 

    I filled the bow ballast the rest of the way, and really seemed to make a powerful wave. The proof is in the surfing, but I was the only one in the boat, so surf test would have to wait.

    (An updated note here again.  I still hadn't fully played with tab deployment angles, so these still were not the optimum wave or weight placement.)



    So at this point, I started to A) worry about the length of these tabs and the forces being put on the hinge and transom, and B) wonder if a shorter, simpler tab would work as well.  After all, the stock Moomba Flow 2.0 tabs are quite a bit smaller and work great.

    Started making smaller test tabs. There is be a 1.5", 30° bend where the line is on the right, both for rigidity and to help direct the water.



    No Waterjet this time, since they don't need to be quite so precise. Used a circular saw, and got them within 1/16".  Not too bad. 



    Once again, I made the lower actuator mounts out of 2" square 1/8" wall aluminum tube.  This time I left a reinforcing piece on the top, to keep the sides from flexing in and tightening too much on the actuator.  Smoothed everything out and rounded all the sharp edges, then started to test fit.




    I wasn't sure what angles I wanted the tabs to deploy.  You can see the marks for various angles written on the plastic.  I went to my local Moomba dealer and had the sales guy deploy a set for me so I could see.  Moomba's max down angle is 30 degrees, but most seem to run them at 60%, so 20 degrees.


    So it gave me something to work with for setting my tab angles. I had originally made lower brackets that had a single hole for the actuator. But I decided  I wanted to have some adjustability. I made a couple different versions, but ended up with a design I like. They have 4 actuator holes (of which only 3 are really usable) which will provide 18, 24, and 30 degrees of deployment. I also made it so I can move the mount itself a half inch to change the angles more.

    Tabs were bent to 30 degrees, holes drilled.

    I also made diversion fins for the bottom of the tabs, 2 on each. I'll see how these work, and may play with the angles a bit with those as well. They are currently set at 60° from the transom.






    For the first test surf, the wave felt better and larger than the black tabs.  However, I wasn't sure if that was because of how the boat was weighted, tab angles, etc.




    What we ended up doing was a head-to-head test with both sets of tabs. 

    I went out with some buddies (we all surf regular) to test both sets of tabs I made to see if one is better. 

    We filled all the bags (1100s rear, 400 center, 750 IBS, and a 400 on the floor in the pass through) and 150 lead in each locker, 50 under right rear seat, 150 on surf side rear floor, 170 under bow filler cushion. So just about 4k total.  3 guys at 210ish and 1 girl maybe 140.

    The first set were the smaller of the 2. At 11.0 and wakeplate up, the wave was great, big with lots of push.  For reference, my buddy in the pics is 6'2", 220+.




    Then we went back to the dock where I swapped out the starboard tab for the larger, black one. The pic shows the size difference between the two.


    • We went back out and surfed the black tab, same weight and placement, just less gas. If I didn't tell you the tabs were different, you probably wouldn't know the difference. But the wave seemed a little bit larger, a little bit longer, and a little more push. It also seemed "harder" or firmer. It was kind of weird and took some getting used to.

      The most surprising thing was how little downward angle the tabs had for the best wave. I measured the silver set just before swapping out, and it was only 5° down. I wasn't able to measure the black set, but the angle was similar. 

      Overall, I'm torn on which set I'm keeping. I like that the black set wave is a tiny bit better, but I also like how much smaller the silver set is. Decisions, decisions... 







      So here's what I have in everything so far.  

      Black tabs:

      Aluminum 3/16" plate - $120

      2" square tube, 1/8" wall - $8

      Waterjet cuts - $100

      Bends - $37.50

      Powdercoating - $80

      Total: $345.50


      Silver tabs:

      Aluminum 3/16" plate - $30

      2" square tube - leftover from above

      3 ft of 1" angle aluminum 1/8" wall - $10

      Cutting/bending - $0

      Polishing or powdercoating to come

      Total: $40 + finish


      Everything else:

      Hinges .09" stainless, 1/4" pin - $50

      Lenco 101xds actuators - $360/pr

      Lenco trim tab switches - $70

      Lenco cable extensions - $60/pr

      Lenco remote gland seal kit - $28

      Misc stainless hardware - $50

      Misc electrical - $50

      3M 4200 sealant - $14

      Extras total: $682

    User Feedback

    Recommended Comments

    11 hours ago, Jeffo said:

    Great job!! Good write up also.


    i will be building a set in the near future.

    Do you know anything about metal work, Jeffo?   JK!    


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    On 11/21/2018 at 10:58 AM, Leebo said:

    Lining up a Black Friday purchase to do this over the winter. What was the length of the hinges (or where did you get them)?  Thx!

    I cut them down to 12", but you could use any length that works for your boat and tab width. 

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    37 minutes ago, grantgibson99 said:

    Which tab did you decide to stick with? and where did you buy your 3/16 aluminum plate, and square tubing? thanks

    I kept the black GSA-style tabs. I got the plate and tubing at a local metals supplier. 

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    Fantastic work man. Love everything about this project. Super clean electrical too. Thanks for the write up. 

    Just out of curiosity, the trees and hill look like PNW or maybe even NorCal. Where are you located?? Your lake looks great!!

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    1 hour ago, freeheel4life said:


    Fantastic work man. Love everything about this project. Super clean electrical too. Thanks for the write up. 

    Just out of curiosity, the trees and hill look like PNW or maybe even NorCal. Where are you located?? Your lake looks great!!

    Thanks! It's Hayden Lake, Idaho. 

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    This is an incredible job!! Do you have the measurments for the black tabs? I would love to have some of these made for my 24v Tige.

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    Since I made this write up, I've had several people ask if I can make them a set of the black tabs, or provide them with the CAD file or measurements for them. GSA has a patent on that design, so unfortunately I can't. I can provide help with the silver tabs, but not the black ones. 

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    I think it's great that you took a stab at a unique design and demonstrated that it works. I have mocked up a couple different tab shapes and always wanted to trial them out but never have. In that process I spent quite a bit of time studying the different tab styles and I'd be curious if the difference in performance is simply related to the total and projected surface area presented to the water at the ideal deploy angle. e.g. the silver tabs at 5 degrees present less projected area and total surface area to the fluid passing over it versus the black tabs and also have less surface area directing water outward thus generating slightly less yaw. 

    Deploying them further would increase the projected area similar to some other mfg's but it would also increase total lift on that side decreasing overall wave effect. Your addition of the inside down turned flange as well as the outward angled fins adds to the amount of projected area as well as redirects water outward instead of only downward generating more yaw at less overall lift. I'd be curious if slightly more fin height or angle and/or more inside flange height or angle could bring the performance closer, but in a smaller (and more manufacturable) package. I've also wondered if it would be possible to have a base tab surface that deploys to a set location for the ideal amount of lift and a second set of surfaces that could be controlled/adjusted separately to vary the amount of yaw generated.


    I've noticed that newer MC's use tabs that no longer attempt to direct water exclusively outward/downward, but instead include down-turned flanges on all sides. However, the tabs are mounted at an angle greater than the deadrise of the hull such that when deployed they naturally generate slightly more yaw and slightly less lift while still generating substantial overall drag to yaw the boat. 


    On a totally different note, I noticed you used AL instead of SS and you also mounted the hinges above the tab surface rather than below. Any reasoning for this approach? 


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