New install: Bennett Trim tabs

[ericinga]

So, I bit the bullet this year and installed Bennett Trim tabs. After a season of barging through the water, it was time for an improvement.

The boat behaves incredibly differently than last season. At 2500 RPM, it actually hits 18 MPH and planes this season. Last season, she had to be at WOT to hit that speed and never planed.

I installed the 3012EIC kit. The tabs are on the large size but respond quickly. There is very little hesitation and the tabs put the old girl on plane at 50% extension.

One lesson learned is shimming the tabs. Since the transom is not flat, the tabs required a 16" long angled shim that ranged in length from 1/8" inboard to 1.75" outboard. I used 1/8" x 3.0" aluminum strips stacked at varying lengths to fill the gap. Then the shim was coated with PC11 epoxy to provide a smooth finish. In the end, the shim worked great and looks good. Since this was my first attempt at trim tab installation, this was a little nerve racking. It worked out in the end.

Very happy with the results.

Eric

[Fastjeff]

Good for you! I too had to shim one of the tabs--the port one--since the outboard of my dink boat was way off to port. Even at full down the boat listed.

Jeff

[Toucan]

I am getting ready to install tabs on my 26' and am concerned about how to back them on the transom. How did you go about transferring the force to the hull? Did you remove the built in tabs (stationary) or attach the new ones to them? Ron

[ericinga]

Hey Toucan!

Put your info in a signature.

If you're near Atlanta and want help, call me. I'd be willing to help.

Parts and tools:
- Bennett Trim tab kit
- 1/4" x 20 bolts (40 - 1.5", 20 - 2.5" and 4 - 3.5")
- 100 1/4" flat washers
- 100 1/4" lock washers
- 12' 1/8" x 3" aluminum bar stock
- 4lbs. PC-11 epoxy.
- 2 tubes fast setting 3M 5200 Adhesive.

Dewalt Jig saw, metal saw blades
Drill
Die grinder, 60 grit wheel, 120 grit wheel

Here's the process:
1. Cut off the anode tabs. I used a Dewalt jigsaw with metal cutting blades. Took about 10 minutes per tab. Cut close to the hull. Otherwise, you will need to grind off the remaining material. Grinding off the material takes far more time. For that, I used a die grinder with with 60 grit wheels.
2. Measure the mounting area in the transom. I taped backing panel from the tabs onto the transom. From the hull side in, measure and mark every hole. Make a list of the measurements and take it with you into the bilge.
3. Measure and mark the holes on the inside of the hull. There are three bolt holes that will line up with the angle aluminum. Offset the holes to one side of the angle bracket and note the measurement.
4. Drill the holes on the outside. Slide bolts into the holes, hop into the bilge and verify bolt placement.
5. Pull the bolts, place the first tab on the transom and bolt the first 4 bolts toward the midline of the boat. I used this method to determine the shim size. Your transom will be somewhat curved toward the hull edge.
6. Measure the length of the first shim piece, start cutting the shim pieces to length and stack them to fill the gap between the tab and transom. I did this until the gap was filled. This creates a stair stepped shaped shim.
7. Stack the shim pieces and glue them. Once the glue is dried, mix the PC11 epoxy and smooth out the stair steps in the shim. I used two coats of epoxy to achieve the correct shape.
8. Mount the tabs on the hull using the inner 4 bolts. I used liberal amounts of 5200 inside and out.
9. Slide the shim into the gap. Have a helper hold the shim and drill the inner and outer most holes. Pull the shim, add 5200 to both sides of the shim and into the bolt holes. Bolt the shim and tab to the hull.
10. Drill the remaining holes, fill with 5200 and bolt to the hull.
11. Using PC11 epoxy, fill any remaining voids on the top and bottom of the shim. Allow epoxy to dry and grind smooth.
12. Paint the shim and surrounding hull.
13. I mounted a piece of hard wood on the inside of the transom for the pump and control box.
14. I measured the longest hydraulic line and made both lines the same length. I did this to eliminate the possibility of any difference in speed / pressure for both actuators.
15. Follow the remaining Bennett instructions.

Things I learned:
1. Buy oversize tabs. Our boats are slow and the wider chord (12") makes the tabs extremely responsive. I can plane at 1500 - 1700 RPM with the 30" x 12" tabs.
2. Buy hex head bolts. I bought 2Xs the amount required. I always remember that stainless steel bolts are softer than grade eight bolts after break a few of them. Screw head and cap head bolts don't allow for enough torque. I broke screw bits on the cordless drill and a hex driver trying to use the prettier looking screw heads.
3. Buy your bolts from an industrial supply house. I bought mine from Industrial Depot in Gainesville, GA. They do ship via UPS. The cost was under $30 for all of the fasteners. I think a box of 100 bolts was under $10. If you're in salt water, you will want to use 316 grade stainless steel.
4. Don't be afraid to dry install and remove the tabs multiple times. I dry installed the tabs two or three times.
5. Use lots of 5200. You can wipe off the excess adhesive. Besides, an extra tube of 5200 is cheaper than hauling out after finding a leaky bolt.
6. Call Bennett with any questions. They are extremely helpful.
7. According to Bennett, you can shim up to 3" away from the hull.

I probably missed a detail or two. Contact me with any questions.

Eric

[bcassedy]

Eric,

Outstanding detail on the process!

I wonder if our site could have a "How to" section? Jeff's previously listed "How to's" on the Tripodi site have been added as notations in previous postings. This site is a wealth of information and it'd be great to see a How To section added.

Bill

[Toucan]

Thank You very much. I copied and printed your instructions. I confess to beating myself to death at the thought of drilling any hole in my boat. But still, I have a concern, (possibly unfounded) of where the stress from the piston ground will be transferred into the hull from the transom.
Ron & Nicki Wood
"Liberty"
"67" 26' Express, Crusader 220, 305ci

[TinLizzy]

The tabs on my 28 are mounted to the anode tabs on the stern. They respond very nice. I don't see why you would cut off the anode tabs for the install, seems like a lot of unnecessary work.

[Toucan]

Hey Rodney, do the tabs still have sufficient travel being placed the some 3 1/2 " outboard ? And again, what about the transfer of pressure from the thin transom to the hull where the piston mounts to the transom.
Ron and Nicki Wood
1967 26' Express
Southwest Florida

[ericinga]

Ron-

If you're that concerned about deflection in the transom from the trim tab actuators, call Bennett and discuss the concern.

Keep in mind: Trim tabs have been installed on Marrinettes for over 40 years. If there was a problem with transom strength, it would have surfaced by now.

Mounting the trim tabs on the anode tabs will require shims at the actuator mount on the transom or extended throw actuators.

I decided to install the tabs on the transom since it provided the most direct transfer of force from the actuator to the tab. The transom mount puts the tab directly behind a corner brace. This is one of the strongest structural points in the hull.

Eric

[Toucan]

Alright then. I'm new to this power boating thing having been a sailor for the last 30 yrs. I'll position it behind the brace and trust those of you with greater experience in this area.
Ron and Nicki Wood
1967 26' Express
single 220 Crusader 305ci