Trim tab Hole detail requested

[JGrider]

I am starting install Bennett M120 trim tab. I am a little scared of putting holes in the transom so I need a little encouragement! I have looked at all the posts and I think I want to put epoxy plugs to attach trim tabs. Several posts seam to be just putting 5200 around the screws per Bennett instructions. I have looked at all the repair pictures and I am still a little uncertain. My question is what size plug hole do I need for just the small screw to attach the plates? Is there any balsam where these holes go or is this area solid?

 

[Sunbeam]

I share your concerns, and I'm not comfortable with caulk alone sealing off balsa core - especially beneath the waterline.

I am just installing a set of the M-120's myself. My boat has core where the trim planes (and the actuators) attach, and my guess is they all do. What I did for the planes was overdrill 1-1/4" deep holes with a 1/2" or 9/16" drill bit. That allowed me to get in with a Dremel and pick to "back cut" the holes and get the balsa out of a larger area behind the surface fiberglass -- and yet the hole still stays hidden behind the trim plane mounts. After filling the holes completely with thickened epoxy, I re-drilled and tapped for cap screws, but I could also have used "pointy screws." When I mount the trim planes I will also bed them, but it won't be (just) the bedding that is keeping water away from the balsa. I feel happier that way.

I posted some photos and details on a recent thread called something like "Ack! This is why I like to do things myself." I'd be happy to explain further if you decide you want to do a similar installation and have any questions (and I should get some photos up in my Sunbeam thread, but have not taken the time yet). A number of other people have used the overdrill/fill method too so they have good advice.

It is a bit tough to drill into the pristine transom, below the waterline! I had to get up my nerve too

Edited to add: Here is a link to that thread:

http://www.c-brats.com/viewtopic.php?t= ... c&start=15

Sunbeam

 

[JGrider]

I did not find your post when I did my searches. Your pictures are worth a thousand words.

 

[thataway]

There may be a void where the actual tab hinge screws go. There may also be core...depends. I don't drill as large holes a Sunbeam does. You can get a 1/4" Dremel bit, which will give a reasonable undercut, so just over a 1/4" hole is enough for me for the Plate hinge screws, to drill, and undercut, fill with epoxy and then pilot hole, and put in sealant, screwing the plate in place.

 

[Sunbeam]

Glad they helped! I think I may have some other photos or description in my "Sunbeam ~ 22 Cruiser" thread. Not on the trim tabs specifically, but on other epoxy filling tasks.

Couple of other details (some of which I got the ideas for from other good folks here :thup).

-I put blue tape on the transom where everything was going to sit, then marked on that with a pencil to lay things out.

-Used a level jacked up against the hull to lay out the trim planes with the negative angle they specify.

- For the actuators, I used an office hole punch to punch out a hole at the center of the locations and then was able to site through the holes to do a final line up of the actuators on some black dots I'd made previously.

- I did not drill the size hole they specified for the hydraulic line, because I am going through the transom with brass pipe nipples, and they do not require such a large hole.

- I set everything up just as if I were drilling the final holes the first time, but then of course drilled larger holes and then had to re-line things up to drill the "final" holes in the epoxy plugs. But it all came out pretty well centered on my plugs the second time, which was a nice double-check.

Blind holes can be a pain to fill with epoxy. I talked about that a bit in that other thread, I think.

Sunbeam

 

[JGrider]

Thinks guys,
Sunbeam I also bought a mini jacker and I was wondering if your M120s have the longer rams. Did you have any interference problems.

 

[Sunbeam]

I don't drill as large holes a Sunbeam does. You can get a 1/4" Dremel bit, which will give a reasonable undercut, so just over a 1/4" hole is enough for me.

You know, I almost went back and edited to mention that those were "largish" holes. I don't usually make them that big, and they certainly don't have to be. But in this case I really wanted to be sure there was plenty of epoxy around the edges, and I wasn't sure my holes would all end up perfectly centered on the plugs the second time around (i.e. when re-drilling). And it just made it easier to work in those deepish holes. Also, since they end up hidden under the trim planes and actuator arms, there was not a huge downside, to me.

On the actuator holes I used a smaller bit, but then I actually sort of connected all the holes on the inside, which made it so none of them were "blind" holes and they were thus easier to fill. But then I might just as easily have done any of these things slightly differently, detail-wise. It sometimes depends on my mood of the day, and occasionally I would tweak a detail if I were doing it again.

Sunbeam

 

[JGrider]

Explain what you said about brass pipe nipples. I've never seen that before.

 

[Sunbeam]

Explain what you said about brass pipe nipples. I've never seen that before.

Okay, well I think I saw detailed photos in.... Tyboo's album? I also think this is how many of the "non sport" tabs are done. Anyway, instead of directly connecting the hydraulic line/fitting to the actuator arm (which puts the connection inside the transom and also then the tubing needs to make a bend coming out of it to get going athwartships), you put a ~3" long, 1/8" brass pipe nipple into the actuator arm (this runs through the transom), then a 90º brass fitting on the inside (this puts the tubing running along parallel to the transom), and then attach the hydraulic tubing to the 90º fitting.

Seems like it would work fine the other way, but I preferred the idea of my sealant "goop" on the pipe nipple and not the hydraulic line fitting, and I like how the elbows make a nice, solid 90º turn on the inside. I actually got the nipples and elbows from Bennet, but they are just common parts like you could get anywhere.

Sunbeam.

 

[JGrider]

Ok. I will look into that. Sounds like the way to go.