Repaired-recreated my Bennett bottom mount trim tabs

[sdowney717]

I have been planning for a long time to do this. The original 50 yr old tabs were badly rotten.
I bought a piece of 316 SS of 2x4 feet to to make larger tabs of 42 by 12. Originals were 42 x 9" type 304 ss.
The hardest part was cutting the SS sheet metal. Separated the big piece with a shear and bent the hook edge on a brake. The wing edge drop fins had to be bent at an angle as the transom is curved. Cut the old tab upright edge off to form the new backbone of the tab using my jigsaw and specialty SS blades. Regular metal cutting blades failed. That SS sheet metal is very hard to cut. I then coated the tab with Por15 silver. I simply sanded the sheet metal, but maybe next time will use their metal etcher, phosphoric acid. It is supposed to make them waterproof, so should help deal with corrosion. Por15 is just like paint except it becomes a very hard plastic surface. I looked at Rust Bullet and MasterSeries coatings, but the POR15 was cheaper and for this purpose is fine.

I used SS 3/16 rivets to join the back to the plane. I heated the rivets red hot while in position and slammed them down with a 4 lb sledge. A piece of old iron for the otherside of the rivet gave it the support to do that.

Then I re-coated another coat of Por15.

 

[Larry M]

Nice job on the new tabs with the 316. Question though, why even use the por15?

 

[sdowney717]

Even 316 will crevice corrode, just not as badly as 304.

I think the Por15 will improve the corrosion resistance. It is impervious to water, so the metal will stay dry, means it wont corrode.

Por15 silver has aluminum suspended in the paint, so its good at coating and sealing holes. The base plate had some damage, so I used painters tape to back up the holes before painting. Por15 is very hard coating, like a hard plastic. But it is not UV resistant. To get hard and UV resistant, you have to buy RustBullet or MasterSeries Silver, Masterseries is a little more expensive then Por15. I figured its going underwater and to be covered with bottom paint so wont have UV exposure.


I left an electrical path to the base plate as I did not coat the inner hook, and I used a flat spade bit to remove the coating where anodes and cylinder bolts attach. I think the anodes will last a lot longer, if they have less exposed metal to protect. 316 is a little better than 304 regarding corrosion, the 2x4 SS sheet was about $140.
This time I got aluminum anodes instead of zinc.

If you could buy Duplex SS 2205 plate affordably then you would not have any corrosion. That new metal is very good for the sea water. High end boats are starting to use it as castings instead of bronze.

https://www.upmet.com/products/duplex-stainless-steel/2205

https://arcticsteel.com.au/stainless-steel-2205-for-underwater-applications/

 

[Keysdisease]

You got 50 years out of the original tabs? Not bad for underwater metal

 

[sdowney717]

You got 50 years out of the original tabs? Not bad for underwater metal

Yes I did but they were going out, the hooked hinge edges of the original tabs were breaking free of the tab in places along the edge and there were holes in the tabs. Manufacturers use 304 SS for this as it is cheap SS sheet metal and easily protected with anodes if owners keep up with the maintenance.

I am all for using better materials to gain longer usefulness. If you can cut down on the exposed metals underwater, that will improve their useful life.
Newport News Shipbuilding which builds for the Navy coats underwater metals in a resin, a polyester FG on for example prop shafts , a former shipyard worker told me the smell and acetone would make him feel sick.

Here is my old tab controller from 1970 which I rebuilt, it all works good. I also have 3 old gray good working joysticks I cleaned and repaired. they can be completely taken apart. The pump was in very good shape, did not need to be taken apart. But all the relays needed repairing due to eternal rust. Most of the wires were fine.

 

[Keysdisease]

That pump is vintage and predates any Bennett Pump made in the last 40 years, and there are many still in service.

I get this:

"I am all for using better materials to gain longer usefulness. "

But I temper it with 50 year old 304 ss original tabs.

Nice work

 

[C lectric]

I agree, very nicely done.
I'll take a lesson. Mine are not as old but approaching 40 yrs.

 

[Keysdisease]

Bennett does sell replacement tabs only for any model they have ever manufactured. You can contact Bennett at 954 427-1400 and get more information.

The 9" and 12" chord tabs attach to the actuator (ram) in the same place on both chord tabs, so if you want to upgrade to a 12" chord tab from a 9" and not change anything except the tab the hinge plates and actuator mountings will match up identical.

The above is for standard transom and bottom mount tabs. Bennett made and still makes many custom size tabs in a variety of configurations for various boat manufacturers, all are available as tab only.

Mine are not as old but approaching 40 yrs.

 

[sdowney717]

Bennett does sell replacement tabs only for any model they have ever manufactured. You can contact Bennett at 954 427-1400 and get more information.

The 9" and 12" chord tabs attach to the actuator (ram) in the same place on both chord tabs, so if you want to upgrade to a 12" chord tab from a 9" and not change anything except the tab the hinge plates and actuator mountings will match up identical.

The above is for standard transom and bottom mount tabs. Bennett made and still makes many custom size tabs in a variety of configurations for various boat manufacturers, all are available as tab only.

Sure for a goodly price they will.
But they can not or wont make them like I made mine.

They dont sell the bottom mounting plate separate from the bottom mount tab, and the bottom mount tabs are different, the bent hinge is not as wide. This according to Tabman who worked for Bennett before he passed recently. He told me you can not mount a bottom mount TAB on a transom mount hinge, it may fall off. But it seems to me, there is plenty of room in the roll hinge of the bottom mount plate to take a wider hinge. A tab is only supposed to deflect down 20 degrees, more than that he said it creates more drag, and looses the benefit of the lift.

I also plan to use a 316 SS chain to chain the tab to the transom, in case the cylinder plastic pin shears, I dont want to loose all my work. I am going to drill a hole in the upright back of the tab and attach a 3/16 piece of chain and bolt other end into the transom.

In some cases, like backing down with tabs extended, people have sheared the cylinder pin and lost the tabs., its rare but why take that chance? I could also replace the Delrin plastic cylinder pin with a SS pin.

 

[Keysdisease]

Oh...K. Not everyone has the skills or desire to make their own trim tabs, so I thought it was a good idea to let TF'ers know the tabs are available separately. Tom (Tabman) is of course right on all counts, but I would consider the chain stop and plastic pin replacement redundant. If you install the chain as a hard stop the pin isn't going anywhere.

When Industry Veterans meet at shows there are always a group of us ready to hoist a salute to our Friend Tom McGow, a great guy and a friend to many

Sure for a goodly price they will.
But they can not or wont make them like I made mine.