Transom Drilling

[Hooks]

Hello All, I've read many threads about penetrating the transom of the boat.

I am installing trim tabs on my boat, and a panther kicker mount to clear the tabs (currently directly on the transom).

So I have two types of holes; thru-holes for the kicker mount, and screws to attach the tabs.

Whats the best way to screw the tabs to the transom, while protecting the transom core?

Anyone want to challenge the overdrill and fill technique for thru-holes? It seems like 5200 should do the trick, and I doubt most of our primary motors are overdrilled and filled....just saying.

Thanks for the help!

 

[Sunbeam]

I always overdrill and fill. No need to challenge since each person can do their own boat as they see fit, but for my own self, I don't consider 5200 the right product for that job (sealing off the core). But then I've suffered through a number of re-cores on previous boats (later on in a given boat's life, so I had no choice about preventing it).

I also overdrilled and filled the engine holes (all the holes in the transom, actually). But again, that's my choice. I will say that the hole where the transom drain went through was already starting to get moisture in it, and when I bought my boat it had been stored indoors, had no bottom paint, and had 52 hours on it. I also store it indoors.

For the trim tabs (screws into "blind" holes), what I did was overdrill and fill, then drill and tap for bronze machine screws.

I do also use bedding compound, but just to bed the items, not to seal off the core.

One thing I love about boats is they are a place where each owner can do what they like, so I'd say do it how it pleases you. For me that means overdrill and fill on cored areas -- and then use a bedding compound (something less adhesive than 5200, so I can relatively easily re-bed when necessary, or remove/reinstall something that breaks or wants an upgrade).

 

[Hooks]

Ok...I like the advice.

A few clarifications.

What do you like as a bedding material?

Have you ever come across self tapping bronze screws? Would stainless be sufficient?

Do you have a specific recommendation for the filling material; thickened epoxy I'm assuming?

I have a lot of holes to fill

Thanks again,

 

[Sunbeam]

Hi Hooks,

Here are my thoughts:

What do you like as a bedding material?

I like and have used a variety, sometimes depending on the job. I don't tend to use 5200 as it has more adhesive than I generally need (I'm typically fastening something mechanically and the bedding compound is "just" bedding). I have used 5200 in the past on "permanent" things such as below-the-waterline through-hulls, but don't really have anything on the C-Dory I would personally choose it for.

I'd say that what I use most these days is good-quality butyl. Much of the butyl I've bought in recent years is nothing like the "good old' stuff, but I have found a source for the good stuff, which is here. It acts just like the stuff that was put on the boatyard stockroom shelf 20 years ago (which is still going strong). Nothing else I have found in recent years (except for that below) is nearly as good. This is sold by a fellow boater (who also does boatwork for a business).

http://www.pbase.com/mainecruising/butyl_tape

But I don't use it for everything. For example I used white 3M4000 when I re-bedded the little drain between cabin and cockpit. I wanted something white, and with a bit more adhesive than butyl. In the past (pre-4000) I might have used 4200 for this (polyurethane like 5200 but less adhesive), or a similar Sika product, but they can yellow in UV, which 4000 apparently does not do. So for this I used 4000 (polyether).

On the fuel fills, I used polysulfide, because butyl can be attacked by fuels.

But butyl is my go-to, meaning I use it unless there is a reason not to.

One thing that I just hate to see on the boat anywhere is silicone. :amgry Banished! Others may like it, but I don't (poor bedding, endless contamination, etc.) I have not found butyl to damage any plastics that I have used it on so far (sometimes the reason silicone is recommended).

Have you ever come across self tapping bronze screws? Would stainless be sufficient?

I have a number of "pointy" bronze screws, although maybe not technically self tapping. I tend to pre-drill. That said, I prefer to drill and tap if I can. I do use stainless on the boat in many places (mostly because that matches the original "look" plus it is hard to find bronze), but I try very hard not to bury stainless in an oxygen starved environment (like in the transom). It is prone to crevice corrosion in that type of environment, which is not good. For example, I bought a used dinghy wherein the transom fittings were stainless screws. I went to re-bed the fittings and every one of the screws broke off inside - due to wasting ("wasp waste") where there wasn't oxygen. If you do use stainless, 316 grade is a bit less prone to corrosion than 304. But anyway, that's why I used bronze on my trim tab planes and actuators - both sets of fasteners are "buried" in the transom, and often below the waterline.

(For the engine and kicker bracket I used Armor Coated "graded" fasteners, for their strength -- not stainless or bronze. I get them from McMaster Carr, which is where I also get 316 fasteners. The Armor Coating is something like galvanizing in effect, IIUC)

Do you have a specific recommendation for the filling material; thickened epoxy I'm assuming?

If it were me I'd use a good marine epoxy (WEST, System Three, MAS, etc.). I like to first "paint" or soak the bare core with neat (non-thickened) epoxy, then do the bulk filling with the thickened. For the thickened I'd either use colloidal silica, or a high density filler (like WEST 404) or a combination of the two. Or the "pre-made" WEST 610 in the tube (neat and tidy but a bit expensive - nice stuff though!). Even with the 610 I like to pre-soak/paint the area with neat regular epoxy though.[/quote]

I have a lot of holes to fill

Buy stock in disposable gloves and blue tape, then let 'er rip! You'll get a routine down. There are quite a few tips in other threads for various helpful tools and etc. for reaming out core, getting epoxy in, etc. I'd rather spend an hour laying down protection than an hour cleaning up, so I use plenty of tape, plastic, etc.

It's always interesting to see what you find when you dig in. If it's dry, you can feel like "Great, caught it before it became a problem!" If it's wet, then, "Well, at least I'm getting this cleared up before it gets worse."

 

[Marco Flamingo]

I just bought a lifetime supply of butyl tape from Amazon for $12.

http://www.amazon.com/gp/product/B00FHH ... ge_o05_s00

I'd have to buy a 60 foot boat to use it up. Hey, that's an idea.

One of the advantages of boring out your motor mount holes and filling with an epoxy putty is that you have increased the compressive load carrying ability of those transom holes. Balsa has good compression numbers for it's weight, but nothing fantastic compared to other materials. Balsa core construction can get spider cracks in the fiberglass layer from stress on the fitting or from over tightening when the fitting was installed (usually the latter). A nice plug of epoxy putty then drilled for the mounting bolts gives extra protection.

Were I going to install something on a balsa core without making an epoxy-lined hole (which I wouldn't), I'd use butyl tape, not any of the tube caulks. I'd fasten down almost tight, touch a soldering iron to the screw for a few seconds, then finish tightening. Hot butyl probably sticks to Teflon, though I haven't tried it.

Mark

 

[Sunbeam]

Interesting on the butyl tape. I had a few old rolls that I'd been using for years, then when I started running low, tried about five different kinds. None of them stretched/were elastic anything close to like the "good old" stuff I had (which was at least a decade old) -- until I bought the Bed-It. It behaves just like the old stuff. I can stretch a couple of inches a loooooong way (feet!) before it "breaks." (Whereas all of the other "new" rolls I could stretch a piece maybe 6" before it would break. Not very butyl-like to my mind.)

So, interesting that you found some on Amazon that behaves like the good stuff. Always good to have more sources.

Also, good point on how the epoxy annuli make excellent compression "posts," whereas fiberglass skin-balsa (or foam)-fiberglass skin tends to "dent" when you tighten a fastener, thus creating a well and a future issue.

 

[thataway]

Although I agree on much above, I don't agree on the Butyl tape. It is used extensively in the RV world mainly because it is easy to use. Butyl tape has a well known history of leaking with time. It has to be in compression to work properly. It is OK for deck fittings, but I would not use it for an application for trim tab screws. or under the waterline fittings. Most butyl tapes I have removed had dirt under the metal surfaces...if there is dirt, moisture got in there.

I do agree with Sunbeam that there is a real difference in Butyl tape material. Many are not good--and it is good that Sunbeam has a trusted source. I would not buy butyl tape on Amazon. In my book you need to be able to check on the tightness of the fittings.

I also believe that you should over drill, and make an epoxy plug, then pilot drill into it. Yes, you can tap the plug, but you have to use a blind or bottom tap, and that is not always easy in a short screw hole. Bottom taps are available in 10-24 which is an appropriate size. Note that the tabs come with 1 1/4" screws.

Bronze screws vs SS screws: Your trim tabs are gong to be SS. I find it is best to use SS screws, if possible the same alloy as the Trim Tabs. Bennett Trim tabs come with 1 1/4 #10 SS screws. Truth be know the vast majority of SS screws sold in the USA today are made in China and are really unknown alloys. The same may be said of many "Bronze" Screws. If you really want the best, monel metal or Silicon Bronze 655 is very close to the 304 SS on the tables. It will be hard to find these alloys in a 10 x 24 x 1 1/4" machine screw, but I am sure you can find it for a price, somewhere.

http://www.corrosion-doctors.org/Defini ... series.htm

SS Corrosion should not happen in properly sealed installations.

I have no issue with 4200 or 5200. These are not just "sealants" They are structural adhesives: I use them regularly under the water. I have removed fittings bedded with 5200, and 4200. Look up the spec sheets on the 3 M web site for shear strengths.

Stolen from Dan Casey Boat US web site:

http://www.boatus.com/magazine/2013/April/how-to-pick-the-right-sealant.asp

Finally, the thickened epoxy: I happen to use West Systems, 501 epoxy, with the appropriate hardener. I mix it 50/50 primarily with cabosil.(Fumed Silica) 404 high density filler. Painting the core with a thinned epoxy is a wise idea.

Those who say that the outboard mounting holes are not properly protected are correct. Any deck fitting under compression (such as the windlass) also needs that "ring" of solid material. Balsa is very crushable, if the right amount of pressure is applied. I have seen instances of the depressions in the deck caused by over tightening to back up plates, and deck rot in the deck core.

 

[Sunbeam]

Just to clarify, I'm not recommending the type of "putty tape" or even so-called "butyl putty tape" that is used on RV's nowadays. All of it that I've tested has been junk. On the other hand, the good stuff remains flexible and very, very elastic and sticky decades later. I don't use it because I'm looking for cheap or easy - that's not my style.

It is a bedding compound though, not a structural adhesive. Most things I bed are mechanically fastened, but if not I would choose something else.

That said, everyone should use what they are comfortable with (as long as it's not silicone :wink ).

I just wanted to clarify, in case it sounded like I was using RV-grade putty tape, or choosing it because it was easy/cheap.

 

[Hooks]

Thanks for the detailed response folks! Gonna get started this weekend with all of the hole patching....if I don't fish instead :wink:

Under separate heading I'll ask for mounting recommendation on Bennett bolt tabs.

 

[Kushtaka]

I"m about to move my kicker from an articulated garelick mounted well to starboard to a fixed mount mini jacker.

I had thought about bolting the mini jacker through the transom above the waterline only, putting the whole thing on bedding compound, and then using larger diameter, but shorter screws "blind" into the transom below the waterline. I would overdrill, fill and redrill these blind screws. This would not lead to compression, and I can't think of when I've used reverse on my kicker, which is when these screws would pull against the transom. Otherwise, in forward they would push. Granted, through bolts would be better for torsional stiffness.

Decisions decisions. Am I asking for trouble or on to something?

 

[Sunbeam]

I thought about that too, for the same reasons as you. But then I thought about backing down in a hurry, and how the motor then wants to lift. No idea if that means through-bolts are needed or not for the lower attachment, but I decided that it was something I would rather not think about later, so I through bolted both upper and lower mounts (overdrilling/filling/re-drilling them all). I used Grade 8 3/8" "Armor coated" fasteners from McMaster Carr. It helped that I had the fuel tanks out at the time.

 

[ssobol]

So how thick is the transom where you bolted through? I am looking to install a swim step and I'd like to get the hardware in advance.

Thanks.

 

[Sunbeam]

Let me look in my notes and post back. There were two different thicknesses because the lower bolts went through "just" the transom, whereas the upper ones go through the transom plus the splashwell molding (which is gelcoated fiberglass plus some filler between it and the "real" transom).

 

[Kushtaka]

It helped that I had the fuel tanks out at the time.

Yup. I plan on taking out my fuel tanks as well so that I can re-fasten them to the deck properly (of course meaning over drill, widen, fill, redrill, seal, fasten into bedding compound)

However I have seen a lot of sense in mounting the tanks to star board.

Why must the tanks be fastened to the floor anyway? Couldn't they as easily be strapped aft and down, and set on starboard bedded in 4200? Just a thought.

Sorry, I'm starting to hijack with a gas tank job, but it's the same job and Sunbeam started it!

 

[Sunbeam]

Sorry, I'm starting to hijack with a gas tank job, but it's the same job and Sunbeam started it!

I started it?! :wink

Okay, on the transom thickness. I can't find my measurements of the exact thickness, but I want to say the transom is 1-1/4" to 1-1/2" (it's consistent but I just can't remember which), and then there is around 3/4" additional for the splashwell molding and filler.

What I *can* say for sure, is that I ordered 2-1/2" and 3-1/4" fasteners for the Mini Jacker and looking at my photos they were just the right length. These didn't only go through the transom though.

The upper (splashwell) ones were the 3-1/4", and they went through the Mini Jacker, then the transom, then the splashwell molding, then 1/4" (or 3/16"?) FRP "washers" I made, and then a regular washer, lock-washer, and nut. I'd guess the Mini Jacker is around 1/4", say the fiberglass washers 1/4" and the regular washer plus lock washer 1/8" or so, and the nut maybe around 5/16" or so? That'd leave around 2-1/4" of transom-plus-splashwell which sounds about right.

The lower fasteners went through the Mini Jacker, the transom, then regular washer, lockwasher, nut. So subtracting what I'd guess for the "extras," that would leave around 1-1/2" of transom. There is a bit of that fastener standing proud of the washer, but not a lot. So that's inconclusive on 1-1/4" or 1-1/2" of transom.

If I run across my actual measurements, I'll re-post.

On the fuel tanks, hmmm. Well I can't see why *to* put them on Starboard, and give up that 1/2" or whatever of height. Plus moisture underneath could possibly get trapped and kind of gross. I went about it slightly differently. First I took the old ones out and cleaned the area up. Then I did a jillion other projects that "had" to be done while the fuel tanks were out (Filling in old holes, mounting Mini Jacker, hydraulic trim tabs, bilge pump hose routing, transom drain, new fuel filler hoses, new vent hoses, etc. etc. Suddenly it seemed like the whole boat was "behind" the fuel tanks!

Then I got some strips of rubber that were of a medium durometer. The tanks are supposed to be fully supported but the boat is not completely flat there, so I figured this would help take up the slack. I also wanted space for drainage (that's the space between the rubber "slats"). Then I cut some pieces of fiberglass angle - one for ahead of each tank and one for inboard. I bonded those to the hull, leaving the recommended amount of space for tank expansion. I had previously removed the footman loops that were fastened to the cockpit sole (into the core of course). The strap setup for the original tanks was kind of weird: The straps went from a footman loop aft of the tanks at the sole, up and over to a footman loop at the TOP of the starboard tank face covers. Not sure who figured out that leverage (wonder why those face covers were levering the cleats out of the sole - that plus no expansion room).

Going back, I mounted the aft footman loops on the transom just about at the top of the tanks, using Weld Mount adhesive. Then the forward loops were bonded to the angles at the forward base of the tank. Seems like a better "lead."

I used a few pieces of the same rubber to temporarily take up the extra space between the tanks and the angles (which diminished as the tanks expanded).

I figured it was possible the angles would pull off or somehow that bond would fail, but so far so good. If it ever does I'll likely just overdrill/fill/tap some holes and fasten them down. The tanks would actually have a hard time completely coming out due to the fill hoses (even if something failed), but of course you don't want that stress on the fill hoses or tank necks.

Anyway, that was just one way, and I could think of a few other good ways too. I probably wouldn't go for Starboard, but then I use the space above the tanks and woudn't want to give up the space, plus then you have to hold the Starboard in place, and the tanks to it. But I'm sure there is a good way to do that, too. For my boat, it was not hard to improve on the original.

One last note (Kushtaka is making me do it :lol: ) is that I went with new 23 gallon fuel tanks to replace my original 25-gallon ones. These are a bit lower (they were made lower to accomodate the cockpit liner when they went to that system in around ...2007?), and there is a bit less room between them. On the other hand they don't "stick out" past the splashwell lip (which is I guess when they started making the solid fiberglass tank cover panels that run up under the splashwell lip). I got some of those panels intending to install them, but ran short of time before a trip and made some quick and easy fabric covers out of navy fake Sunbrella. Well, those have been so convenient that I'm not sure I'm ever going to fit the "real" ones! I can easily shove them aside right below the filler neck to see how the turbulence is doing when I fill, easily get to/see things in the space above the fuel tanks, and they're lightweight. Well who knows, the solid panels do look tidy, so I may put them in at some point.

 

[thataway]

However I have seen a lot of sense in mounting the tanks to star board.

Why must the tanks be fastened to the floor anyway? Couldn't they as easily be strapped aft and down, and set on starboard bedded in 4200? Just a thought.

I sold my 1993 C Dory22, a number of years ago--but my recollection was that the tanks were strapped down, with cleats screwed into the bottom of the hull. I don't remember a flange built into the tank to screw it down. None of the adhesives adhere well to the Starboard.

I also don't see any reason to put the tanks on either solid or strips of Starboard, unless have one of the aluminum tanks.. If the tank/tanks are aluminum, you do not want to use any rubber (except silicone), because of reaction.

The 2006 we have currently has the cleats glassed into the bottom of the boat, so no screws into the hull.

 

[Kushtaka]

I do have the aluminum tanks with the bridge between each side. They fasten to the cockpit sole on flanges all the way by the sides, facing inboard, three screws in each flange. I don't need to worry about expansion.

I'm planning the previously mentioned kicker move, largely to correct the list at rest and at slow speeds because of the poor balance. I have long had my various deck screw holes nagging at my mind, and there is even a screw hole that is empty, but for water (!!!!). I keep a pile of salt on top of it as a stop-gap to prevent freezing and stop the rotting.

A fair amount of work that needs doing will be best done in one bite with the removal of fuel tanks. I'm working on running them down right now and only have a few gallons left in one of them. Soon I'll begin the work.

The more I think about the fuel tanks, the more I'm thinking that I'll just re-install them in epoxy plugs and call it good. They sit nicely off the bottom, the boat needs to be pretty full of water for it to reach them where they are positioned and dirt/debris and water flush nicely below the tanks with some room left above to work if needed. I can certainly see why it would be a good idea, but I'm on the fence. Someone convince me otherwise.

Any thoughts (Dr. Bob?) on whether blind holes below the waterline would be sufficient on a kicker bracket?

 

[Blueback]

Finally, the thickened epoxy: I happen to use West Systems, 501 epoxy, with the appropriate hardener. I mix it 50/50 primarily with cabosil.(Fumed Silica) 404 high density filler. Painting the core with a thinned epoxy is a wise idea.

.[/quote]
I believe there may be an issue of cost/quantities on small jobs that may only require 2 small holes we may be dealing with. While everybody would agree that on the good-better-best scale, over-drilling and the method you describe is the "best". However, costs for one small job are not discussed. Would you give a a break down of the smallest quantity one can purchase "West Systems, 501 epoxy, with the appropriate hardener. I mix it 50/50 primarily with cabosil.(Fumed Silica) 404 high density filler."
Many of us have one small job and given the limited shelf life of the epoxy it will probably not be used again.
Thanks for your expert opinion here.
Geoff

 

[Kushtaka]

I"m not sure what it costs right now, but for me, I've got a bunch of west systems and use it a lot for boats and non boat wood working.

I've found the material to last years. A long shelf life as long as you don't treat it badly.

It's certainly more work and cost than the factory is willing to put into the boat, however one might speculate that at that level they could devise a quick and easy way to mass-produce that result and cut the cost substantially.

If I were to purchase a new C-Dory I would get the boat empty, and have all of these penetrations prepared in the "best" method, and then install my cabinetry, motors, bilge pumps, etc. No moisture would ever meet my core.

That my boat sat for 20 years as-is, makes me approach the issue with a little less urgency. Not because I think everything is okay, but because I know I'm going to be pulling nasty rotten core out regardless.

I'm not sure what you're asking about the cost to do this, but if your nagging voices get after you for optimizing $$ to results, you'll probably like 5200 a lot. If your nagging voices get after you when you could have spent a little more $$ to get a better result, well that's me, and it requires me to overdrill and plug every time. My nagging voices are so insistent on this requirement that they don't even let me consider a cost comparison.

BUT, if I had to guess, and if my time working on my boat is as valuable as my time in the office (that's a whole different debate) I'd say that each of these plugs cost me about $35 all in after materials and time.

 

[thataway]

I don't have current prices on epoxy products--and there are many sources. I keep at least a gallon of epoxy in the shop--and it is used regularly.

If you just want to do one or two hole, Marine Tex works fine. It is probably best to just coat the inside of the reamed out hole with a standard clear epoxy first, (Although you can use the 5 min, I prefer standard set time). Use a small paint brush, or even a "Q" tip.