Kushtaka asked about blind holes below the water line. Yes, I have made the holes, coated them, and then set theaded rod into epoxy. That way, you can set the washer, lock washer and nut tight from the outside. I don't think I would be comfortable, with just putting a lag boat into hardened epoxy.
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Transom Drilling
- Thread starter Hooks
- Start date
It slightly depends on the situation of what I'm doing, but I often drill and tap thickened epoxy for a machine screw.
I make fairly large overdrill and fill holes (as opposed to just slightly bigger or just "painting" edges of holes). I like a healthy sized plug that interlocks with one or both skins.
I find the challenge with blind holes (especially on a vertical face like the transom, where part of the hole is like a "blind cave" up above) is to get them chock full of epoxy. My favored way, in this situation, if there is an appropriate place to do it, is to make a tiny air release hole up near the top of the "cave." For example, when doing the holes for the trim tab actuator mounts, I made a tiny air release hole inside the boat (behind the fuel tanks). That just ends up filled with epoxy at the end, and isn't visible behind the fuel tanks.
The hardest holes I've done were the large, blind holes for the trim tab planes, which had the same "upper caves," but for which I didn't want to make an air hole in the transom. Instead I stuck a piece of clear tubing (was small clear shrink tubing) in the upper part of the hole, then gunned in epoxy and let it overflow into a cup (for re-use), then pulled the tubing out. That helped a lot and the holes filled well. Smaller or vertical holes (like in sole), you can just stick a syringe down to the bottom and let the air come out up top. Overfilling those then slicing off the "muffin top" after it gets to the green stage also helps (you can poke at the air bubbles that come up and the extra epoxy will sink into the hole).
I think everyone finds their own little tips and tricks and favorite ways over time.
As much as I am (was) a die-hard "mix my own" person, I have now found many times I like to use the WEST Six10 pre-thickened epoxy in a tube. Very easy to just "make" a little bit, no waste, no muss. It's not quite as strong/hard as true thickened epoxy, but this is fine (or possibly an advantage) for some situations. The one thing I do differently than they say for the Six10, is that I still mix a bit of neat epoxy for bonding and "soak in" when filling cored holes. But for other uses it's just the Six10, super neat and tidy. No, I wouldn't build a boat with it ($$$$), but for small jobs it is great. I still keep the full arsenal of regular epoxy and thickeners, but I find the Six10 is a great complement to it. Oftentimes I don't use one of the tips, but just gun a little bit out and mix it by hand (then you don't waste the stuff that otherwise stays in the tip).
I make fairly large overdrill and fill holes (as opposed to just slightly bigger or just "painting" edges of holes). I like a healthy sized plug that interlocks with one or both skins.
I find the challenge with blind holes (especially on a vertical face like the transom, where part of the hole is like a "blind cave" up above) is to get them chock full of epoxy. My favored way, in this situation, if there is an appropriate place to do it, is to make a tiny air release hole up near the top of the "cave." For example, when doing the holes for the trim tab actuator mounts, I made a tiny air release hole inside the boat (behind the fuel tanks). That just ends up filled with epoxy at the end, and isn't visible behind the fuel tanks.
The hardest holes I've done were the large, blind holes for the trim tab planes, which had the same "upper caves," but for which I didn't want to make an air hole in the transom. Instead I stuck a piece of clear tubing (was small clear shrink tubing) in the upper part of the hole, then gunned in epoxy and let it overflow into a cup (for re-use), then pulled the tubing out. That helped a lot and the holes filled well. Smaller or vertical holes (like in sole), you can just stick a syringe down to the bottom and let the air come out up top. Overfilling those then slicing off the "muffin top" after it gets to the green stage also helps (you can poke at the air bubbles that come up and the extra epoxy will sink into the hole).
I think everyone finds their own little tips and tricks and favorite ways over time.
As much as I am (was) a die-hard "mix my own" person, I have now found many times I like to use the WEST Six10 pre-thickened epoxy in a tube. Very easy to just "make" a little bit, no waste, no muss. It's not quite as strong/hard as true thickened epoxy, but this is fine (or possibly an advantage) for some situations. The one thing I do differently than they say for the Six10, is that I still mix a bit of neat epoxy for bonding and "soak in" when filling cored holes. But for other uses it's just the Six10, super neat and tidy. No, I wouldn't build a boat with it ($$$$), but for small jobs it is great. I still keep the full arsenal of regular epoxy and thickeners, but I find the Six10 is a great complement to it. Oftentimes I don't use one of the tips, but just gun a little bit out and mix it by hand (then you don't waste the stuff that otherwise stays in the tip).
For multiple reasons I have issues with drilling and tapping epoxy plugs where there may be a considerable shear load. The embedding of threaded rod to make a "bonded stud" makes a lot more sense, and will be structurally stronger, and not subject to those issues with tapping epoxy of various compositions.
AstoriaDave
New member
Bob, what are your concerns? I have drilled and tapped well cured Sysrem Three resins, both filled and unfilled, in threads from 10-24 up to about whatever coarse thread a half inch bolt would use. You have to go slow, and a dull tap will ruin your whole day. Ordinary tapping fluid seemed to work fine.
The filled resin was usually amended with milled glass fibers and Cabosil, aka fumed silica, in a 1:4 ratio.
The filled resin was usually amended with milled glass fibers and Cabosil, aka fumed silica, in a 1:4 ratio.
Marco Flamingo
Active member
When I first knew that I was going to have to fill some holes, I bought a little kit of West System that comes in tear open packages. Once I removed a few items from my boat and saw the likely extent of the problem, I bit the bullet and bought a gallon West with the pump system ($140). Glad I did. Even for filling a small hole, one squirt of A, one of B, and throw out what I don't use. Material costs weren't that much compared to the time spent on my project.
I also bought some 2-part clear penetrating epoxy, maybe a quart total. http://www.smithandcompany.org/CPES/ Every penetration into balsa got some of this before a putty fill. On deck fittings, I put duct tape over the underside hole and basically poured the penetrating epoxy in until it wouldn't take anymore. You have to stop after a minute because the solvents in it can make the tape release. This epoxy dries without an amine blush, so subsequent epoxy putty, like West and wood flour, will adhere. And then should the epoxy plug fail for some reason, the entire area surrounding the plug is protected by the penetrating epoxy.
The West "putty" was mixed to the consistency of honey and also poured into the hole with the underside taped. Most of my holes were small enough that I didn't need to worry about heat build up as the epoxy cured.
My tests with epoxy putty lead me to use microballoons and wood flour (3:1) as the best screw holding mixture. I tapped all the screw holes into the epoxy plugs, but in the tests without any tapping the microballoons in the mixture seemed to crush similar to wood rather than having the epoxy plug split.
For holes through a vertical surface, I used a little paint brush to get penetrating epoxy on the balsa. If you wipe it up quickly, it comes right off. Then I used a thicker than normal putty to stick to the upper surface.
I bought a package of 500 "continuous feed" table napkins at a restaurant supply house and have used almost half of them. Wipe up a dribble and throw the napkin in the garbage can. Don't try to use it again or you will end up walking on it, sitting on it, etc. This isn't the time to recycle. Do something "green" on another project as penance.
I also bought a couple hundred Popcycle sticks, a hundred disposable latex gloves, 20 disposable eye droppers, a package of red "kegger" plastic glasses, and I kyped some little hot sauce cups from Taco Time. Some of the best deals were at an artsy craftsy store. Not chasing down a mixing stick or finding a cup that can be used again saves a lot of screwing around.
Mark
I also bought some 2-part clear penetrating epoxy, maybe a quart total. http://www.smithandcompany.org/CPES/ Every penetration into balsa got some of this before a putty fill. On deck fittings, I put duct tape over the underside hole and basically poured the penetrating epoxy in until it wouldn't take anymore. You have to stop after a minute because the solvents in it can make the tape release. This epoxy dries without an amine blush, so subsequent epoxy putty, like West and wood flour, will adhere. And then should the epoxy plug fail for some reason, the entire area surrounding the plug is protected by the penetrating epoxy.
The West "putty" was mixed to the consistency of honey and also poured into the hole with the underside taped. Most of my holes were small enough that I didn't need to worry about heat build up as the epoxy cured.
My tests with epoxy putty lead me to use microballoons and wood flour (3:1) as the best screw holding mixture. I tapped all the screw holes into the epoxy plugs, but in the tests without any tapping the microballoons in the mixture seemed to crush similar to wood rather than having the epoxy plug split.
For holes through a vertical surface, I used a little paint brush to get penetrating epoxy on the balsa. If you wipe it up quickly, it comes right off. Then I used a thicker than normal putty to stick to the upper surface.
I bought a package of 500 "continuous feed" table napkins at a restaurant supply house and have used almost half of them. Wipe up a dribble and throw the napkin in the garbage can. Don't try to use it again or you will end up walking on it, sitting on it, etc. This isn't the time to recycle. Do something "green" on another project as penance.
I also bought a couple hundred Popcycle sticks, a hundred disposable latex gloves, 20 disposable eye droppers, a package of red "kegger" plastic glasses, and I kyped some little hot sauce cups from Taco Time. Some of the best deals were at an artsy craftsy store. Not chasing down a mixing stick or finding a cup that can be used again saves a lot of screwing around.
Mark
I hear you on the bulk supplies. When I bought 1,000 tongue depressors (about fifteen years ago) I thought it would be a lifetime supply. Guess how many I have left? About twenty. I'm sure I've gone through thousands of gloves. And I agree with you on the paper towels. Trying to reuse a piece, even once, always leads to heartache (at least for me). I cut them into small pieces to make them go further, but don't re-use.
I don't use penetrating epoxy, but I will mix up a batch of neat epoxy and fill a hole with it (using a syringe). Let it soak a bit, then suck the remainder back out, thicken it and re-use it.
I had to laugh (a friendly, to-myself laugh) the other day when a new RV-er with a bunch of projects on the table said something like "But when I went to the store to buy acetone, they only had the one-quart square cans - how would I ever use that much?! Hahaha.
I don't use penetrating epoxy, but I will mix up a batch of neat epoxy and fill a hole with it (using a syringe). Let it soak a bit, then suck the remainder back out, thicken it and re-use it.
I had to laugh (a friendly, to-myself laugh) the other day when a new RV-er with a bunch of projects on the table said something like "But when I went to the store to buy acetone, they only had the one-quart square cans - how would I ever use that much?! Hahaha.
Just so I understand you properly, you embed a threaded rod "blind" into the transom as a stud, so you only penetrate the outer skin, or does the threaded rod stud go through the transom.
I have two holes mounting my main motor below the water, and I'd like for that to be all.
I have two holes mounting my main motor below the water, and I'd like for that to be all.
Kushtaka":1gzw67c1 said:Just so I understand you properly, you embed a threaded rod "blind" into the transom as a stud, so you only penetrate the outer skin, or does the threaded rod stud go through the transom.
I have two holes mounting my main motor below the water, and I'd like for that to be all.
I think you are probably addressing "Thataway," who may have embedded a threaded rod. But since I'm not sure, I'll say that what I did was hollow out a decent sized area (leaving the outer skin intact) and then fill that area with thickened epoxy. Then I tapped for a 1/4-20 bronze hex headed machine screw. I found it works best if you use a one-size smaller drill before tapping than you would with metal (did experiments on samples).
On my boat, I could hollow out around 1/4" to 3/8" past where my fastener was going to end (forward in the transom/bottom) and then I would just "touch" the fiberglass "wall" that must be the forward edge of the transom (in other words, the transom core doesn't directly "connect" to the hull core). This worked out fine as I could easily stop there and just scrap all the balsa off that forward point. That gave the new epoxy a bit of glass to stick to at the forward end of the hole (not that it needs that; it just turned out to be handy). IIRC, I used 1-1/4" long fasteners into my tapped holes (I could look it up).
I did the trim planes this way because you can't practically through fasten them. If you did drill "through" you would end up in the hull core between the top and bottom skins (you'd have to get through the fiberglass "wall" first as well).
I did the actuator fasteners the same way (but there is a through transom hole there for the hydraulic pipe in the center of them). I made little connector paths between all four of these holes (three actuator fasteners and one center hole) so it was easy to fill the whole shebang with no "blind" issues).
I'm not sure how you could fasten the trim planes without any holes. I did consider using Weld Mount studs, but I would have had to grind off the gelcoat, and even then I wasn't sure the bond strength would be enough (I did tests with a cutout piece of laminate, Weld-Mounts, and a sledge hammer - highly scientific). Ultimately I decided that with ample filled areas (not just a thin layer that could crack or just a "paint on" of resin) and tapped fasteners, I would feel more confident than with Weld Mounts. Haven't had any second thoughts on that since doing it.
I did also remove every other fastener and through thing from the transom (shown in the Sunbeam~22 Cruiser thread). A few of them looked like problems waiting to happen (especially the lower transom drain). So I think anything you do with care and forethought will be an improvement, and there are probably several good ways.
I secure crazy loads to cliff faces by using rockite to secure a threaded rod into a drilled cavity. This sounds like what is being suggested here, EXCEPT, I simply embed the rod into the wet rockite and let it cure there. You (Sunbeam) plug completely and then use a tap to thread the epoxy itself, then your thread the threaded rod into the tapped cavity, presumably using some sealant in the hole as well, like 5200?
It seems the difference as I understand Dr Bob's method is he embeds the threaded rod into the wet epoxy, exactly as I do on rock faces. I'd probably favor the Dr. Bob method because It's like something I already know how to do and believe strongly in as a fastening method, and I can see there being a stronger bond than tapping.
Sunbeam, this whole thing has had me looking at your album and I see that we have tackled a lot of the same jobs, and I am planning a layout similar to yours in the end. I wish I had looked more closely at your album before I did my locker drain. I got very lucky I didn't end up drilling my drain right through a strake. It ended up just below and I used a threaded fuel vent that I cut the nipple off of. It works great, and I tapped the inside so I could plug it if I wanted to (skeeters). But I digress. I just wish I had done half as good a job documenting and sharing. I always mean to but life, and more often work, gets in the way.
It seems the difference as I understand Dr Bob's method is he embeds the threaded rod into the wet epoxy, exactly as I do on rock faces. I'd probably favor the Dr. Bob method because It's like something I already know how to do and believe strongly in as a fastening method, and I can see there being a stronger bond than tapping.
Sunbeam, this whole thing has had me looking at your album and I see that we have tackled a lot of the same jobs, and I am planning a layout similar to yours in the end. I wish I had looked more closely at your album before I did my locker drain. I got very lucky I didn't end up drilling my drain right through a strake. It ended up just below and I used a threaded fuel vent that I cut the nipple off of. It works great, and I tapped the inside so I could plug it if I wanted to (skeeters). But I digress. I just wish I had done half as good a job documenting and sharing. I always mean to but life, and more often work, gets in the way.
I want to re-mount the trim tabs on my boat (previous installer didn't do a good job) and called West Systems about the best material to use to fill the holes before replacing the screws. Their tech was very helpful. He said they've done a test in which the winner, for holes into which you will drive a screw, was their G-Flex thickened epoxy. I ordered some. When it arrived, it was packaged as "Plastic Boat Repair Kit." That's presumably because the material remains more flexible than standard epoxy after curing. The package information on the back tells us it is good to re-bond attachment points. I plan to use it when the weather is warmer.
I've only used G_FLex to repair plastics (rotomold windrider trimaran) and it didn't do all that well. It wasn't very flexible and the repairs needed to be redone. It could have been user error as I hadn't used GFlex before, but have used a lot of other west system. I'm planning to use the normal thickened west system. I'll probably paint some gelcoat over the top of it.
I have been off the net for a few days traveling. The concerns with threading epoxy filling into the transom are several fold. First, the composition of the filler. Adding glass fibers strengthens the mix considerably. West Systems, suggests adding fibers and or aluminum powder. Plain thickens epoxy does not have all that good load bearing shear enough that I would be concerned with a transom mount engine bracket--which was the question. There will be vibration, and this will slowly weaken the epoxy/filler mixture. If you embed the rod, or better yet put in a rod with a small nut on the end (can even be rounded off, to just give a better grip. deep in the mixture it will be better). Best is the embedded threaded rod, because the epoxy has set into the threads, and it will not vibrate loose, or start backing off the threads. The problem with tapped machine screw is that you may not be able to get all of the threads, contacted, then secure with a lock washer. you have to know the precise depth, and then run the risk of stripping or damage to the threads if you tighten up really snug, as you should do with the transom bracket for a kicker.
If the material you are going to mount is not heavy, or subject to vibration, you can get away with tap and thread--but why not do it the right way to start with? The issue of crevice corrosion was brought up--it is not an issue with the thread embedded into epoxy--it can be when tapped, and then moisture gets in along the threads...
If the material you are going to mount is not heavy, or subject to vibration, you can get away with tap and thread--but why not do it the right way to start with? The issue of crevice corrosion was brought up--it is not an issue with the thread embedded into epoxy--it can be when tapped, and then moisture gets in along the threads...
thataway":35onzhpg said:Adding glass fibers strengthens the mix considerably. West Systems, suggests adding fibers and or aluminum powder.
This all sounds about right to me. I've never used aluminum powder. Is the fiber added a West System product, or can I just break up some chop mat? I don't have great access to all of these materials here, but I really want to do this without a bolt through my transom and am headed to Cali for a couple weeks, so maybe I'll have to send myself a care package!
Thanks Dr. Bob. This is super helpful.
AstoriaDave
New member
The aluminum is new to me. Is that some anticorrosion additive?
On the added glass, sure, chopped mat would work, the shorter the fibers the better for this application. I think WEST and System Three sell milled glass fibers, designed specifically for strengthening cured epoxy. I have used it quite a bit, maybe about a teaspoonful with 2 oz of mixed resin, stir well, and then add the Cabosil, aka fumed silica, usually about 4 times the volume of the milled glass. You can play with the latter to get the consistency you want without interfering with the effect of the milled glass.
On the added glass, sure, chopped mat would work, the shorter the fibers the better for this application. I think WEST and System Three sell milled glass fibers, designed specifically for strengthening cured epoxy. I have used it quite a bit, maybe about a teaspoonful with 2 oz of mixed resin, stir well, and then add the Cabosil, aka fumed silica, usually about 4 times the volume of the milled glass. You can play with the latter to get the consistency you want without interfering with the effect of the milled glass.
Marco Flamingo
Active member
Don't bother with cutting up mat. I have some 1/4" chopped strand that I bought for my balsa core fix. I probably have more than a quart and hope to never need any again. How much do you want? It's cheap and easy to send a little in an envelope.
Mark
Mark
Hooks":2sj9roun said:Hello All, I've read many threads about penetrating the transom of the boat....
Whats the best way to screw the tabs to the transom, while protecting the transom core?
Sunbeam":2sj9roun said:For the trim tabs (screws into "blind" holes), what I did was overdrill and fill, then drill and tap for bronze machine screws.
Just to clarify: When I mentioned tapping filled epoxy, I was talking about trim tab planes that get mounted into "blind" holes (due to their location they can't be through bolted). I did tapped holes for the trim planes, the trim tab actuator tops, and the transducer block. Everything else on my transom got through bolted (overdrilled/filled holes). Everything else in my case being the main engine, the Mini Jacker (kicker bracket), the swim platform top holes (lower ones were lag screws into green epoxy), the swim platform grab handle, the splashwell drain, and the garboard plug on the lower transom drain.
I'm very comfortable with the strength of the tapped-epoxy (filled epoxy) holes for the things I used them on. But NO WAY would I use that technique for the main engine or Mini Jacker bracket. Maybe it would work fine; but I'd be nervous about it and that takes the fun out of boating, for me, so no.
Yes West Systems has the "403", milled fibers additive. The aluminum powder "420" is intended to add abrasion resistance, as well as UV resistance. The use of Aluminum powder is discussed in the below link on attaching fasteners.
West Systems has page on attaching fasteners:
http://www.westsystem.com/ss/bonding-hardware/
My main use of the aluminum powder was when I recoated the very bottom of the "V" of a RIB I owned, each year. We regularly went ashore in Alaska onto rocks and gravel beaches. I put on a strip of cloth and then several coats of aluminum powder and epoxy to protect the underlying fiberglass hull. It worked well.
West Systems has page on attaching fasteners:
http://www.westsystem.com/ss/bonding-hardware/
My main use of the aluminum powder was when I recoated the very bottom of the "V" of a RIB I owned, each year. We regularly went ashore in Alaska onto rocks and gravel beaches. I put on a strip of cloth and then several coats of aluminum powder and epoxy to protect the underlying fiberglass hull. It worked well.