Aluminum trim tabs from 1/4 inch plate?

Discussion in 'Powerboats' started by sdowney717, May 25, 2015.

  1. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Know someone who does a lot of aluminum welding, has a bending brake.

    My current Bennet tabs, from 1970, have got some corrosion holes in them. I found out the boat really does need trim tabs, if you want to go faster, I left them off when I went back in as they have those issues.

    I am either going to buy some 316L SS plate and bend new ones or maybe go with aluminum. I think Bennett uses 304 SS, so 316 is a better choice. Is it worth bothering with thinking of using maybe 1/4 inch aluminum?

    He can also bend the SS plate. But might be cheaper to use aluminum. There is the corrosion issue, so I just wonder about aluminum staying in salt water all the time.
     
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 5,810
    Likes: 284, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    It depends upon the grade of aluminium too. Do you know which alloy it is?
     
  3. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    I might be able to find out.
    Unlikely to be a marine grade.
    He works for a sign company, they build large and small signs to be outdoors in the weather. He does the welding and construction. He has free or very cheap to get aluminum 1/4 inch sheet panels.
    He is a family member, and has taken an interest in boating with us, so I was talking to him about these trim tabs.

    The other thing that I might could do is silver braze and repair the existing tabs. But I dont know if that is worth my time, the price of the gas or the Harris 15 sticks. If I had to get Harris 56, forget it.
    Then would welding on Silver brazing affect the metals underwater corrosion making it worse?

    I found this site selling SS 316 sheet, seems like a decent price to pay.
    https://www.onlinemetals.com/merchant.cfm?pid=9865&step=4&showunits=inches&id=325&top_cat=0

    0.12 is thicker than the current tabs which are maybe .08

    I would need the big sheet,so 36 by 48.
    I was going thicker gauge since I was thinking of going from 42" by 9" to 42" by 12" inch tabs or maybe even 48" long by 12" width tabs.
    Think the hydraulic cylinders can stretch a little further out?
     
  4. keysdisease
    Joined: Mar 2006
    Posts: 795
    Likes: 40, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    Bennett does sell replacement tabs only for a very reasonable price. Put a zinc on them and paint them per the paint manufacturers directions and they should last longer than you could care. Your current tabs have some issues after 45 years? Does anything on a boat last that long? Especially something that moves underwater?

    www.bennetttrimtabs.com

    ;)
     
  5. BMcF
    Joined: Mar 2007
    Posts: 964
    Likes: 44, Points: 28, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    42" tab beam and 9" tab chord (length for/aft) right? The more lift-efficient direction to go would be an increase in only the tab beam, unless you are routinely operating them more than 8-10 degrees down, in which case increasing the length might help too.
     
  6. tabman
    Joined: Aug 2008
    Posts: 25
    Likes: 3, Points: 3, Legacy Rep: 28
    Location: Mount Pleasant, SC

    tabman Junior Member

    Bennett Trim Tabs

    As keysdisease points out we do sell replacement Trim Tab Assemblies and Dealers often can get them for you at a discount.

    As he also mentioned, when properly protected by a zinc anode or incorporated into a bonding system the Tabs often outlast the boat.

    They are manufactured from 304 stainless.

    The largest "stock" tabs we make with a single actuator is 54" x 9" or 42" x 12".

    Adding span (side to side) is generally more efficient than adding chord (fore to aft).

    Tom McGow
    Bennett Marine
     
  7. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    You bet they are old and have lasted well for all those years in the ocean.
    Bennett makes good stuff. I am the fifth owner of the boat so prior owners who knows how well they maintained the zincs.

    I likely will do what I think will save me the most money, time for me is not a concern.

    I have looked into coating the old tabs with POR 15 SILVER which has added metal fillers. The tabs are not like they are falling apart in your hands, but I know I have to do something for them. I called the company that makes POR 15, and they say it sticks great to SS and it will rebuild some lost strength., and they claim they will not corrode. Since I like fixing stuff I already have, (if I can) and like experimenting which I do a lot, IF I do this I will post back how it goes. But for now boat is going to be in the water for several more years till the antifoul wears out and the tabs can go back on.

    Tabman, do you have a color chart wire diagram to wire up the old original design with the 4 solenoids? I disconnected the 4 colored wires and don't know which goes where, although I can figure it out eventually.
     
  8. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    What I recall about tabs versus no tabs was even just straight flat tabs, the boat ran much better than no tabs. I was wondering if real big tabs work like making the boat longer, the water line length is greater and so the speed of the boat is better.

    Looking at Tab shapes, seems the 12 inch cord, the hydraulic cylinder is still in the same distance from the transom, and they have a bracket in the middle of the tab and the tab has bent edges on three sides. It would be easier to fab longer tabs and keep the chord at that 9 inches, so if I make tabs, they would be 48 by 9. that would give me an extra 12 inches total both tabs.

    The SS sheet steel comes as 36 by 48 and not wanting to waste any, I will see what I can do, if I go that way, maybe make them 10 instead of 9, I dont know how far the cylinder can stretch out and still work ok. Likely mock up patterns to experiment. w'ill see eventually. Maybe I will silver braze on a middle support bracket. I can silver braze, but I dont have the equipment to weld SS, maybe find out if my friend can do that.
     
  9. tabman
    Joined: Aug 2008
    Posts: 25
    Likes: 3, Points: 3, Legacy Rep: 28
    Location: Mount Pleasant, SC

    tabman Junior Member

    Here you go.

    [​IMG]

    [​IMG]

    [​IMG]
     
    1 person likes this.
  10. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Thanks!, very helpful.
     
  11. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Ok, here are pics of the old tabs.
    IMO the mounting plates can be reused along with one tab.
    The other tab is swiss cheese in the middle back bent up part, so that might collapse under pressure with no repair.

    I did find a free piece of SS years ago, same gauge, with a bend in it that was almost the right size. I sliced off the upward part which I am planning to bend to form the hook on the tab front. Question is attaching that piece then. I am wondering about riveting which I could do, or having it welded which someone else will have to do.

    I plan to coat all the parts with POR 15 Silver which has metal fillers. I called POR 15 company and was told they will be waterproof and the POR 15 silver will strengthen the metal. I still plan to use a zinc.

    So I need some thoughts on the joining of these 2 pieces to form a tab.
    pic of mounting plates
    [​IMG]

    Old tabs in back, worst one far back you can see the holes.

    replacement new tab in front

    [​IMG]

    I had 'glued' the bad tab to the replacement tab years ago so it has some wear on the metal surface.
    I cleaned up all these parts with muriatic acid.
     
  12. tabman
    Joined: Aug 2008
    Posts: 25
    Likes: 3, Points: 3, Legacy Rep: 28
    Location: Mount Pleasant, SC

    tabman Junior Member

    You are on your own here, I would simply replace them with new ones and get another 45 years out of them :)

    The angle of the bend on leading edge of the Tab is very critical to fit into the bottom mount to get the proper travel and still stay in the mounting plate.

    We like riveting since it doesn't alter the stainless like welding and invite corrosion. The Tabs we do weld are passivated afterwords to return the anti corrosive proterties to the stainless.

    Tom
    Bennett Marine
     
  13. keysdisease
    Joined: Mar 2006
    Posts: 795
    Likes: 40, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    Those are 9" chord Bennett tabs, there are no rivets anywhere on them. What do you plan to weld or rivet?

    And I was curious about this product POR15 Silver so I looked it up. It seems to be a rust prevention product, and any claim to "strengthen" metal is probably irrelevant because the stainless steel in the correct gauge doesn't need strength.

    As good as it might be, once the surface is broken (abrasion at the hinge plate, hole for zinc, holes for actuator, a path has been created.

    Good luck. :cool:
     
  14. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Yes they are 9 inch chord tabs, but only the top 2 are original Bennett tabs.
    The bottomest tab in the picture is a piece of SS sheet steel from the attic of a house which used to be owned by someone in the ship building industry.

    It happened to have a 90* bend and was almost the right size, too long and too tall but a little too short on what will be the chord dimension. So I sliced off the end and cut down the height and leftover is the long piece sitting in the front to the tab. That piece will need to have a bend and then be riveted to the the new tab. I am pretty settled on using 3/16 inch SS rivets spaced every inch. I can do that myself and then sealing with POR 15 silver (with metal fillers) to protect from corrosion. The prior haulout time, I 'glued' the two 'tabs' together so it has already sat in the water and is not pristine. POR 15 will stick well to the SS as it is surface corroded and not smooth like new..

    If silver brazing sticks were not so pricey, I could braze it or even save the old tabs as silver braze flows so very nicely into SS cracks and little holes. I use 15% Harris silver sticks with white Stay-Silv flux a lot. Typically you use 56% silver sticks and on large sheets maybe the black Stay-Silv flux as it handles heat better protecting the SS from forming carbonates.

    I do believe I used the Harris 15% to braze SS pipe to bronze and it has held wonderfully for 15 years on an exhaust fitting..

    I talked to the POR 15 company also about adding strength and he claimed it would if using the POR 15 with metal fillers. And I emailed a separate company based in Australia, and the response was POR 15 silver would repair and give back the strength to corroded tabs even with holes. I dont have any experience using POR 15 but I do think it will work out fine for my purposes.

    I dont plan to repair the worst tab, and the other tab is good enough to just reuse as is. And I will have a new tab for the cost of rivets and my time.

    My other option is I would buy new piece of 316 SS and fab them, but I can apparently get by with this other idea.

    The little piece that will get the hook, I think I will lay on top of the bigger piece. That will help support from the force of the water flow against the parts. The parts will want to be forced together, otherwise water pressure will want to force them apart.
    I really dont know if that matters much.

    I will put the rivet head on the inside so when smashing it flat, I will be hitting the bottom side of the tab and wont accidently damage my hook. I will back up the head on top of a piece of thick steel plate. To keep the pieces tight while riveting I plan to place some temporary bolts to hold the pieces together. After riveting I may need to lightly grind the whacked down rivets a little. The POR 15 will also glue it all together.

    Having someone arc weld them together is an option, but I think that might be pricey. But I will find out. Using POR 15 the corrosion issue I think should not be a concern.
    I still plan to zinc them. I am thinking to just coat the tabs. Then remove a bolt head sizes area of POR 15 on the tab bottom. Then attach just one half of a zinc which will sit on top of the tab.
    The bolt head will electrically connect tab to zinc. If the tabs are sealed from sea water they wont be electrically conductive or say wont have as much exposed SS, so the zincs should last a longer time.

    The inner round hinge of the mounting plate, I can use a dowel and spread the POR 15 on the inner surface. I will just have to see how that works out when the time comes.
    I specifically asked them is POR 15 would wear off the hinge where the two parts are bearing on each other, and was told it would not, the surface formed is that hard.

    I was impressed with Jay slamming the pipes together and the coating was still fine.
    https://www.youtube.com/watch?v=OMxCWNUHNoU
     

  15. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Thinking some more, I could just slice off the hook from the bad tab and rivet that to the new tab. I just looked at it and realized the hook area is in good shape for reuse, that would be the easiest thing to do. I permanently destroy the old corroded tab, but why not. I am unlikely to try and restore it. That way I could create a greater overlap of the 2 parts.
     
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.