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Screws Under the waterline -Epoxy, 5200 or 4200

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Screws Under the waterline -Epoxy, 5200 or 4200

Old 06-26-2009, 10:39 AM
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cjd
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Default Screws Under the waterline -Epoxy, 5200 or 4200

I am installing tabs/transducer on the transom this weekend, and I am torn about how to sink the screws under the waterline. (transom is fiberglass over wood)

In the past, I have drilled pilot holes, filled them with 5200, then put in stainless steel screws. I have been told 4200 is better, as it remains elastic.

Assuming I don't want to drill oversized holes, pack with epoxy, cure, then drill pilot holes, can anyone weigh in on the best method to secure tab and transom screws under the waterline?


Thanks
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Old 06-26-2009, 10:43 AM
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Chris, do you have a cored (balsa) hull? If so, you should "undercut the holes", use an allen wrench or dremel tool to cut the core away from the hole between the fiberglass layers on the inside and outside. This keeps water out of the core which is a bad thing!! Cut the holes oversized, fill it with thickened epoxy, let dry and then drill a little smaller than your screws.

If not, I'd use epoxy unless you think you ever want to take them back out. 4200 is waterproof and will make it possible for you to take them out later. 5200 is pretty permanant..

Charlie

On edit, missed the "over wood" part. You should definitely seal the hole as described in the first paragraph of my response, this will keep water from ever getting into the wood.
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Old 06-26-2009, 10:47 AM
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transom is fiberglass over ply wood. I find "routing out" plywood to be very tough

I could drill the holes oversize, tnen pack with epoxy. but I don't love that solution. I don't like screws being screwed into epoxy. I might be wrong about that, and I am open to suggestions
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Old 06-26-2009, 10:48 AM
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I would never "screw" I would through-bolt. If you clean out the hole you drill through the transom, I would go as far as saying LIFE SEAL would work, as long as the hole is minimally larger than the bolt. Life-seal, 4200, and 5200 ALL are approved, and work well above & below the waterline. No REAL difference in price for all of them. 4200 is MORE removable than 5200, and cures faster(although the fast cure 5200 claims to dry in 24 hours). I'd go with 4200 or Life Seal(NOT LIFE CALK). Straight 5200 is not too good with UV resistance, so if any spooge will be left, or seeing sun, it may discolor. Although I think they also made a product for this.
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Old 06-26-2009, 10:56 AM
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Originally Posted by Chiefsurfer View Post
I would never "screw" I would through-bolt. ..............
It could be very difficult to through bolt trim tabs. Screws should be fine.

I would drill the holes the proper size for the screws, run a screw into each hole to cut the threads, use a toothpick to get the sealant (I would use 3M 4200) actually into the holes and spread out, then install the tabs, adding extra sealant to the screws before inserting them. Yep, that's how I would do it.
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Old 06-26-2009, 11:01 AM
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Ron,

That is what I have done in the past though I never thought to rune the screw and cut the thread groove - I like that), but i wanted to be sure that I had not missed a better technique. In addition to what you describe, I use the 4200 to caulk the backside of the mounting plate that secures the tabs.

i would be very interested to see other thoughts on this, but I am leaning towards Ron's method.
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Old 06-26-2009, 11:12 AM
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I would never use just 42/5200 for anything penetrating any type of coring...overdrill/undercut/fill with epoxy paste/redrill/ then apply 42 or 5200; that is the correct procedure to prevent core damage.
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Old 06-26-2009, 11:32 AM
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matt,

so how to you guarantee a solid pack of epoxy on a transom (surface does not lie flat -gravityis you enemy, not your friend on this application). What do you thicken the epoxy with (or do you just let it sit till it gets thick).

can you squirt it into a hole with a syringe? Do you just block the hole with tape? I see the epoxy leaking out, and creating a void on the hull.

I appreciate the input
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Old 06-26-2009, 11:40 AM
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I use fast set 5200 on everything. It is tenacious but I have been able to remove some thru hulls and trim tabs that I have used it to secure and seal.
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Old 06-26-2009, 12:34 PM
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Originally Posted by cjd View Post
matt,

so how to you guarantee a solid pack of epoxy on a transom (surface does not lie flat -gravityis you enemy, not your friend on this application). What do you thicken the epoxy with (or do you just let it sit till it gets thick).

can you squirt it into a hole with a syringe? Do you just block the hole with tape? I see the epoxy leaking out, and creating a void on the hull.

I appreciate the input
Hi Chris,
I use colloidal silica to thicken the epoxy resin to a thick paste consistency and use a popsicle stick to apply it. For vertical applications I would make the epoxy paste a little thicker than I do for horizontal applications. If it's good and think it'll stick up top; begin by packing in the paste at the bottom. You don't actually need to full the entire "donut" hole if you will but just a little bit past the fiberglass skin.

A very senior and respected Captain was kind enough to put together an article for my website describing the process:

http://www.commercialcaptains.com/marine_articles
Choose the first article titled "Proper Sealing for Bolts or Screws in Cored Boats".
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Old 06-26-2009, 02:50 PM
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Originally Posted by matt_unique View Post
I would never use just 42/5200 for anything penetrating any type of coring...overdrill/undercut/fill with epoxy paste/redrill/ then apply 42 or 5200; that is the correct procedure to prevent core damage.
That seems like the "best" way, but I've enever seen it in installation instructions for tabs, transducers, etc.

Usually, it's pretty much what I described above.

We're talking gelcoat, 1/4" to 1/2" of fiberglass and then marine plywood (most likely). Sealing the holes, sealing the device being mounted, and sealing the screw heads should do the trick.

One thing I forgot to mention: Holes for sheet metal screws in gelcoat or fiberglass need to be a little bigger in diameter than you would use for wood or the screws will be hard to drive, will crack the gelcoat, or the heads may even twist off. And - use a countersink bit to relieve the gelcoat so it doesn't crack.
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Old 06-26-2009, 03:28 PM
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Originally Posted by cjd View Post
matt,

so how to you guarantee a solid pack of epoxy on a transom (surface does not lie flat -gravityis you enemy, not your friend on this application). What do you thicken the epoxy with (or do you just let it sit till it gets thick).

can you squirt it into a hole with a syringe? Do you just block the hole with tape? I see the epoxy leaking out, and creating a void on the hull.

I appreciate the input
You can mix epoxy with fillers like talc or cabosil or even wood dust to get a thick paste you can shove in the hole.
I use a "Uni drill" bit to get a cone shaped hole that I can fill with thick epoxy.
I drill the hole with the Uni bit, mix epoxy, apply a thin coat of epoxy in the holes with a small craft art brush, mix in the filler to thicken the epoxy. Push in the thickened epoxy and cover it with masking tape till it sets.
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Old 06-26-2009, 04:11 PM
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I use 5200 for my transducer screws and never had had an issue removing the screws. I coatthe screw threads with the 5200 and go from there.
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