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  1. #1

    Default How to install trim tabs on aluminum boat

    I have a 2009 Starcraft Fishmaster 196 and I am going to install M80 Bennett trim tabs on it - Only one problem - I cannot get to the transom area to through bolt the trim tabs onto the transom. Starcraft refuses to give any information on the schematics of this area so I have to assume that the transom ,material here is .100 aluminum backed by spray in flotation. I spoke with Bennet and they insist that the through bolt should be used. I am trying to figure out a way the add more "substance to the aluminum in this area and I am thinking of bonding a piece of 1/8 to 1/4 aluminum to the hull with JB weld then using self tapping SS screws to attach the trim tabs - the screws would not only reinforce the JB weld but would also provide substantial support for the screws to hold the tabs on. Bennet says that this may work but will not "ok" the process,

    SO _ I am looking for input on this issue - has anyone ever attached tabs to the back of an aluminum boat and how did it work out. Any assistance and input is appreciated.

  2. #2
    Chief Petty Officer Kainon's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    No way to get your arm in through the side of the bilge eh?
    No Current Boat.. :-(

  3. #3
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    Default Re: How to install trim tabs on aluminum boat

    Trim TabMounts.jpg
    I think that the mounts in this photo were early options for mounting trim tabs....

  4. #4
    Senior Chief Petty Officer elkhunter338's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    I would not use JB weld will not hold over the long term. I think your idea of add ing a alum. plate is good but you need to get bolts in it with washer and nuts on the back side. At the top of the plate you mightbe where the transmom is and could use 1/4" x 1-1/4 stainless lag bolts, make sure you seal them good so water does not get in to the wood and rot. You still need some bolts at the bottom and if you have no access I would say you are out of luck on putting trim tabs on.
    I thought of putting trim tabs on my ss, but did not. I make 1-2 POB's sit up front in the cab and store most of my lead fishing weights and stuff up front.

  5. #5
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    Default Re: How to install trim tabs on aluminum boat

    This should not be much different than installing on a glass transom.The transom on both type boats is basicly the same . Providing the transom is good, measure ,pre drill holes, and coat the Stainless mounting screws to the transom. Sealed it should be ok. I have put the Bennett tabs on my 22 holiday just the same as my previous glass boats and no problem what so ever. The same with the pistons for the trim tabs mounted to the transom. Just be sure the screws are the right size and tight. The Marine Sealent should keep the water out of the boat. The only problem I can see is if a non compatable attachment is used that might be aggesive to the Aluminum.

  6. #6
    Chief Petty Officer Kainon's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    on my boat there's a gap of about 1.5" from the bottom of the boat to the bottom of the transom, leaving nothing on the back side. I think most of the trim tab torque on the transom will be pulling at the bottom.
    No Current Boat.. :-(

  7. #7
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    Default Re: How to install trim tabs on aluminum boat

    On Bennett trim tabs the only strain on the botton piece is to hold the bottom on the boat. The strain or torque is on the Hydraulic Piston that raises and lowers the trim plate. The piston is mounted well up on the transom and thru the wood in the transom. The bottom is actually only a hinge for the tab to travel on.

  8. #8
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    Default Re: How to install trim tabs on aluminum boat

    On Bennett trim tabs the only strain on the botton piece is to hold the bottom on the boat. The strain or torque is on the Hydraulic Piston that raises and lowers the trim plate. The piston is mounted well up on the transom and thru the wood in the transom. The bottom is actually only a hinge for the tab to travel on.

  9. #9
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    Default Re: How to install trim tabs on aluminum boat

    Oh great one for each eye to read. SORRY

  10. #10
    Chief Petty Officer Kainon's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    Well If the strain or torque was minimal then why is Bennet Recommending through bolting? and think about it, your trying to push down a boat weight 2000-4000lbs. I wont believe you until I see a full engineering analysis.
    No Current Boat.. :-(

  11. #11
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    Default Re: How to install trim tabs on aluminum boat

    Whatever--- My 22ft Holiday has A load of weight in the boat. Only posted for advice that works for me with no problems.I run a lot of hours in the Pacific and the local river. I have 2 motors on the back a 9.9 4 stroke Merc and a large 200 hp Johnson 2 batterys and most of my downriggers (3) and 8 21 # weights all stored in the rear. Post what you find I may have My holiday over loaded. I run at high speed on most trips Prop is a 14 1/4 21 pitch , it ran to 50 mph with out tabs and I was able to drop thr RPM a little with tabs. The best to you on your project.

  12. #12
    Chief Petty Officer Kainon's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    I wouldn't have thought you would need through bolting either. Puget you have tabs on your boat right ? are they through bolted ? I'm interested in some type of trim tab too..
    No Current Boat.. :-(

  13. #13

    Default Re: How to install trim tabs on aluminum boat

    Pugetsound - Can you please tell me exactly how you did it - Pictures would be great

    I assume yo just used self tapping stainless screws?

    What is the thickness of the aluminum at the mounting point - did you through bolt

    PS __ JB weld says there bond is permanent and it will not loosen with water immersion. I bought some today and intend on doing some tests bonding two pieces of aluminum together

    More to come

    PS please keep you ideas coming

  14. #14
    Petty Officer 2nd Class Gnarly's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    Guys , if its accessible and you want it to last I'd reccomend you rivet a 5052 doubler plate with solid 5052 rivets (blind rivets if inaccesible) and pro seal 870 or PR 1422 sealant between the hull and doubler (faying surfaces) , the larger the better up to a point as it will distribute the load and stiffen the transom skin as well. 2 1/2 to 3 diameter edge distance is a good rule of thumb with one inch rivet spacing. The attach your trim tab and actuator mount to the doubled area if possible with rivets or good quality hardware.
    these are some pics from a fuel catch can I installed a while back in a bell 205 helicopter but it shows the general idea





    In a time of universal deceit telling the truth is a revolutionary act.

  15. #15
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    Default Re: How to install trim tabs on aluminum boat

    I just asumed it was like any other boat. the 11inch adjustable tabbs are mounted with stainless steel screws. 5 hold the tab plate and three on each cylinder. 8 on each side. I also have two extra transducers mounted by just stainless screws. I did not realize there might be a problem in the future. the tab plate is level with the boat bottom, Never considered thru bolting. Perhaps your Idea is best. I have never had water in the bilge or have seen the bilge pump come on . Even if I should have shown more concern If it aint broke I won't fix it. LOL The boat is at our summer home in northern Idaho till spring.Otherwise I would send a few photos. There is a 21 ft Holiday Starcraft that uses our Skagit River with a jet pump and I noticed he had Bnnet trim tabs on his boat,

  16. #16

    Default Re: How to install trim tabs on aluminum boat

    Thanks - I am hen pecking Starcraft for engineering input. My tabs are M80 Bennetts - Deigned for up to 20 ft. They are 8" wide with 4 screw holes - Bennett recommends 1/4 from the bottom. Once I get my sample pieces bonded with JB weld I will send pictures and then I will attempt a peel test. As I stated JB weld said the bond is permanent and will not deteriorate under water *salt or fresh). I appreciate all your inputs - it is very interesting to see what others think.

    Tentatively I would use aluminum pieces that are about 1/4" larger than the footprint of the Bennett hinge plate - I would set it up allow it to bond and then use self tapping #8 or 10 SS screws - I feel this would give the screws a lot more material for support and mitigate any upward force (as minimal as it may be).

    I am really glad to see you have not had any problems or leaks but you are also using twice as many screws.

  17. #17
    Chief Petty Officer Kainon's Avatar
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    Default Re: How to install trim tabs on aluminum boat

    my concern would be that the JB Weld has a good surface to bond to like bare sanded metal vs painted metal. I'd consider JB Weld now for mounting my transducers and pitot so I dont have to drill holes. ??
    No Current Boat.. :-(

  18. #18

    Default Re: How to install trim tabs on aluminum boat

    I have contacted a company called RBC industries. They were referred to me by Loctite. Apparently these guys have the "right stuff" for underwater adhesion of aluminum. I am just waiting for info from them.

    I tried JB weld between two pieces of aluminum and let it set up for about 15 hours. I put the metal in the vice and tried to "Peel" them apart and was well past 90 degrees - only a very small gap at the very edge of the material where the aluminum had "stretched". I finally got the two pieces apart by driving a screw driver between them, I noticed that there was no separation of the JB weld from the aluminum at all - but it appeared that I did not let it set up long enough. Robert - from RBC said that I needed to let it set up for at least 72 hours before I tried the self destruct test. From what I saw it appears there is no way the aluminum is coming apart especially if I had let it cure longer. The bond would then be complete,

    Stand by - more to come

  19. #19

    Thumbs up Re: How to install trim tabs on aluminum boat

    Update
    I think I have found the solution -- I will be using stainless steel rivet nuts - 1/4 20 with a grip between .165 and .265. I will use these (4 per side) to attach 1/8 aluminum plates to the transom. I addition I will be using some type of adhesive sealant - one of the member mentioned Proseal 870. I will contact him to get more info. This method will provide a secure anchor point. All I have to do is bolt the trim tabs on using a good sealant between the aluminum and stainless trim tab plates.

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