Any trim tab detectives?

[drburke]

This is an image looking directly down the transom of a 1970 53' MY at what appears to be the port trim tab.

Some sort of recent event seems to have dislodged the (non-working) trim tabs placing one askew.

I can only think the entire piano hinge must have let go at the pivot point and it is hanging on by the cylinder.

Diver coming tomorrow, but anybody ever seen this? Any other ideas or causes come to mind?

DAN

[Pascal]

Could be the screws pulling it of the hull. I had this happen on 70 footer.

[SEVEN]

It could only be one of two things the piano hinge or the screws coming out of the transom. I’m gonna give you a call Dan.

[rustybucket]

Several screws along the outside edges of each tab were pulling out on mine at last haul. I determined the stress/pull was being caused by too much flex in the tab. I removed the tab and welded a 3/4" or 1" SS angle iron along the aft edge of the tab. This greatly stiffened the tabs. This actually improved the lift of the tabs considerably, they are much more responsive and I don't have to use near as much tab as before this mod.

You likely have several screws pulled out, or, if you are lucky, the piano hinge has just let go and the screws and hinge are still well attached.

If you are unlucky, like me, it's likely you have several holes without screws in the bottom of the boat. This is never a good thing. A good diver may be able to remove the tabs, clean the holes, and insert new screws with sealant on them (3m 550 or 4200) to get you by til next haulout.

When you choose to re-install the tab I would suggest thru-bolting any screws possible. Think I was able to thru-bolt all but 4 or 5 screws which landed on stringers.

[jmooney]

Part of the hinge can corrode, I am replacing both trim tabs now because of this .

[drburke]

Update: pretty much all of the comments were true.

The first photo is Feb 22 (just a few months ago) during a bottom job. The trim tab mechanisms were inoperative so the yard opened at least one to clean and paint (the failed one, actually).

But apparently no issues discovered.

In fact, one can see in the detached tab that nearly all of the screws into the hull had wasted away, the pivot rod corroded, and the hinge was in half in more than one place.

The screw *may* have reached the end of it's service life...

Mostly posting as a caution so that others can be aware...

DAN

[Captain Ralph]

There should have been one or two thru hull machine screws. These on the inside of the hull would offer a bonding path to/from the tab assemblies. These tapping screws in your picture would be less noble than the sheet metal, so the screws would wear away faster.
If the screws failed from crevasse corrosion, then that is a different line of thought but still possible.

[cww]

My 53 has the same tabs. As long as there's a thread about it, this boat is ass-heavy when planing. If I through-bolted and/or epoxied some stainless plates onto the bottom of the tabs to where they stick out the back maybe another 4-6" to give me more tab surface area, would the rams that are on there be able to handle it?

Or should I just do what I did on my Chris-Craft Commander, where I ripped them out and replaced them with large Lencos? On the Chris-Craft I didn't have a choice, they use these little 12v worm gear actuators that were woefully underpowered, most 47 CCC owners have to slow down to put the tabs down because the motors can't overcome the force of the water. I knew that would never work on that boat. This boat already has large hydraulic actuators though, I'm thinking it should work?

[SKYCHENEY]

My 53 has the same tabs. As long as there's a thread about it, this boat is ass-heavy when planing. If I through-bolted and/or epoxied some stainless plates onto the bottom of the tabs to where they stick out the back maybe another 4-6" to give me more tab surface area, would the rams that are on there be able to handle it?

Or should I just do what I did on my Chris-Craft Commander, where I ripped them out and replaced them with large Lencos? On the Chris-Craft I didn't have a choice, they use these little 12v worm gear actuators that were woefully underpowered, most 47 CCC owners have to slow down to put the tabs down because the motors can't overcome the force of the water. I knew that would never work on that boat. This boat already has large hydraulic actuators though, I'm thinking it should work?

I extended my OEM tabs. The results were not noticeable. I had thought about removing those built in tabs, glassing that recessed area back in and going with new tabs attached to transom. But maybe I won't need them with the repower. We'll see.

[Captain Ralph]

We added another 4" to our double ram tabs. Also added another 3" to the back and bottom of our rudders.
44 years ago fuel was cheap and these monsters ran at speed all the time. Slow speed was for wimps.
Well, My wimpy wallet cant run fast any more or the boat.
It may have effected some (some) high speed performance but helps the mid and low speed operations.

Our boats do not run fast enough for those fancy interceptors to work, IMO.