I installed a new thru hull couple months ago. I used 3M 4200 sealant. After the install I also did the bottom paint. Boat is still on the hard. The other day I was screwing the valve on top of the thru hull. As I was doing that, I twist the thru hull a little bit. I can tell by the bottom paint that was covering the thru hull. It's cracked a little bit. My question is ..... will me twisting a thru hull a little bit break the water tight seal and can it be fixed or do I need to take everything apart and re-seal again. Any opinion is much appreciated. Thank you.
Thru hull question
- Thread starter sasafil
- Start date
You did not identify whether your boat is on a trailer on has to be hauled and is on stands. IMHO if you are already out of the water and will be for awhile with no immediate crisis to have to splash, it would be prudent to take off the thru hull clean it up again and re-seal. There is know way of knowing for sure if it "may leak" but unless you are a trailerable boat the cost to haul and do it later iif it does leak is way too much. Just chalk it up to a "lesson learned."
Our yard recommends using 3M-5200 below the waterline and 4200 above. That is what I do. Whether your seal has been compromised, hard to say, but appears suspect. It might be wise, while still on the hard, to redo the fitting with 3M-5200. Some people do not like the product because of its bond strength. Peace of mind for me. I do not want a below-the-waterline seal to fail. Once cured, 3M-5200 will not do what just happened to you.
Boat is on stands, not on trailer. Plan was to splash this coming Saturday but now I am not sure what to do. Should I postpone and reseal.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,914
Not sure where you are, but if the temps are above 55 you should be good to reseal the thru hull. Once you turn a set fitting you do break the seal. Yes you may get water coming in. Only way to know is to splash and then check.
Why take the chance? I would redo the bedding of your thru hull. I would get a helper on the outside using a thru hull wrench to hold the bedded fitting while you secure the thru hull to the deck and the secure the valve to the top of the thru hull.
Good luck. Let us know how it turns out.
Why take the chance? I would redo the bedding of your thru hull. I would get a helper on the outside using a thru hull wrench to hold the bedded fitting while you secure the thru hull to the deck and the secure the valve to the top of the thru hull.
Good luck. Let us know how it turns out.
You're lucky! You found out the seal was bad before nature did for you. Absolutely, re seal and re bed the through hull before launch. Besides the proper sealant, you'll want a proper wooden or fiberglass backing plate. It should be similar to these illustrations. Consult the thru hull manufacturer's instructions. Or google search, "Seacock through hull installation. There are a number of different methods.... here's two.... but the idea is still the same. The thru hull flange nut, or seacock base, does not touch the hull.
If I understand you correctly, the valve body twisted and that broke the seal of the mushroom. That should not be possible because valve should have a flange and that flange should be screwed to the hull using one of the 2 methods @Joe showed.
If the seal is broken, then it needs to be repaired and a proper flanged valve installed with a backing plate.
If the seal is broken, then it needs to be repaired and a proper flanged valve installed with a backing plate.
Finding out whether or not it leaks after paying someone to put her in the water would be an expensive way to go. You'd have to pay again after you repaired it. Do you feel lucky?
Sasafil, take the time and do it right. Either get a real seacock or use a flanged adapter for your valve. You can do the job in just a couple hours if you have the parts and tools in advance. Use MaineSails instruction website for step by step instructions. Here's the link Replacing Thru-Hulls and Seacocks - Marine How To
Absolutily rebed it now while it is easy to do and then rest easy. Thru bolts should have kept it from turning. If not thru bolted have someone outside hold the flange with a thru hull wrench.
Imo never ever use 5200 on any part that may need maintence in the future including hull keel joints. Deck to hull ok. It is unecessary and not productive unless you plan to lift up your hull by pulling it up by the thru hull. I have used boat life caulk on underwater fittings without a leak. My preferred thru hull is silkens 298. Even 4200 is overkill with no benefit. Be sure to bevel any fiberglass edge that will be receiving caulk to give it more surface area.
Second the suggestion on Maine Sail article also some good stuff on you tube, Capt Canning and others.
Imo never ever use 5200 on any part that may need maintence in the future including hull keel joints. Deck to hull ok. It is unecessary and not productive unless you plan to lift up your hull by pulling it up by the thru hull. I have used boat life caulk on underwater fittings without a leak. My preferred thru hull is silkens 298. Even 4200 is overkill with no benefit. Be sure to bevel any fiberglass edge that will be receiving caulk to give it more surface area.
Second the suggestion on Maine Sail article also some good stuff on you tube, Capt Canning and others.
Last edited:
Terry Cox made a good point about using only 5200 below the waterline. 4200 is a very similar compound but with but about 60% of 5200 (if memory serves). This deliberate 'weakness' is meant to make parts bonded with 4200 easier to remove, should that become necessary (such as with deck hardware, which I think is Terry's point).
The NUMBER-ONE reason for 5200 adhesion failure is poor preparation of one or both mating surfaces during installation. In reality, the stuff itself does not fail. You did not mention how well you sanded and prepped with solvent. The presence of even a little dust or dirt in a bilge can render the application of 5200, even if otherwise well-done, pointless. Also, there are TWO absolute Achilles heels with 5200/4200/4000UV compounds: gasoline (you cannot repair a fuel tank with it) and denatured alcohol (a good acetone substitute for really anything but prepping for 5200. The 5200 will simply NOT stick to even the least bit of residue of either one.
(I'm not mentioning silicone residue here because I don't care to get worked-up about it now. If what you're replacing was ever installed with any silicone at all, you're SOL on that.)
MY advice would be to dismantle the whole thing, mechanically scrape and clear away all the residue to start again.
I like that Joe included a diagram but I don't like the second diagram at all. What attaches the backing plates to the hull? That diagram shows buried bolt heads to attach the seacock. If one of them spins free , the seacock gets loose and you'll get a leak you can't fix. Don't do it that way. If your seacock has bolt holes, you can either ignore them (for example OEM-style Forespar Marelon seacocks, the only ones I use, have, and need, no bolt holes) or drill them all the way through the backing plate and the hull, at which point you are constrained to use only bronze mounting bolts which will be a point of regular inspection for the life of that seacock.
I respectfully disagree with NJLarry because I know 5200 to be absolutely the strongest thing for underwater fastening in the market. All respectable boatbuilders install lead keels with 5200. My boat is 47 years old and any original 5200 is still holding. The tensile strength is only one of the reasons (LifeSeal is like half the strength; and I stopped using Sikaflex after I found I could not work it even during installation - it turned into silicone-like boogers). The real reason is the chemical compatibility with fiberglass and most resin-based plastics and the sheer durability of the compound once it's been properly installed. For example, Marelon seacocks are corrosion-free and extraordinarily durable. Install one and you're looking at 40 years or more in regular saltwater use. You can't say that about bronze ones. If you were to install, properly, a Marelon seacock with 5200, it's essentially a life-of-the-boat installation.
Raider Yacht and Cherubini Boat have used Marelon seacocks with 5200 exclusively since I've been directly involved with them. I've never seen a single hassle with them.
The NUMBER-ONE reason for 5200 adhesion failure is poor preparation of one or both mating surfaces during installation. In reality, the stuff itself does not fail. You did not mention how well you sanded and prepped with solvent. The presence of even a little dust or dirt in a bilge can render the application of 5200, even if otherwise well-done, pointless. Also, there are TWO absolute Achilles heels with 5200/4200/4000UV compounds: gasoline (you cannot repair a fuel tank with it) and denatured alcohol (a good acetone substitute for really anything but prepping for 5200. The 5200 will simply NOT stick to even the least bit of residue of either one.
(I'm not mentioning silicone residue here because I don't care to get worked-up about it now. If what you're replacing was ever installed with any silicone at all, you're SOL on that.)
MY advice would be to dismantle the whole thing, mechanically scrape and clear away all the residue to start again.
Use a good piece of fiberglass, like a flat-ish scrap (cutouts from cockpit speakers are great) or a new piece (such as from mcmaster.com). It doesn't need to be much more than 3/16" thick; but it needs to be large in area. All of the working of a seacock is in wracking it back and forth, from turning the handle. Good bonding with the 5200 and large area for the backing plate will spare the 5200 seam from the stress.
Plywood can be used for a backing plate but only if it's marine-grade and thoroughly saturated in WEST epoxy. As this might be judgment call, I'd advise going with a piece of fiberglass, or Coosa. Metal, StarBoard, and other plastics, or waferboard (yes; I've seen all of these done) must be strictly forbidden. Don't over-think it - do what's known to do well.
Sand and shape both the inside of the hull and the backing plate to get a pretty good fit. Gaps are okay if, in general, it fits flush to the hull. Typically I grind the fiberglass right down to bare green 'glass (no gelcoat, no paint). Wash the whole area, inside and out, with acetone - several times. Vacuuming might be good to start. Typically I blow the dust away or wipe it away with a paper towel, and then I use the acetone, flipping or exchanging the rag often, to remove all the rest. Sand and acetone-wipe the seacock base and the head of the through-hull as well - this is one area for failure many people overlook. If it's metal, degrease it well (like with methylene chloride) and THEN wipe down with acetone.
Run the 5200 bead around the outside perimeter of the backing plate, in a bead like 1/4" or more in diameter. Make a bead around the inside hole as well. Put at least as much on the bottom of the seacock. Have the outside guy add a fatter bead to the inside of the through-hull flange (not necessary to do more than a tiny bit on the threads; it will find its way onto them and that'll be enough), and then both of you should assemble the whole arrangement - through-hull, backing plate, seacock body, together. One or the other of you turns his part till the desired attitude of the seacock is achieved inside (ensure the handle will swing fully each way; parallel to the centerline is best). Then the outside guy with a large flat file or a special tool like the ones I make turns the through-hull home while the inside guy holds the seacock in position.
As the ooze comes up, wipe it around the edges of the backing plate, the seacock body, and the through-hull, like for fairing it. When you cannot rock the seacock (when there is no noise or additional ooze if you do), STOP turning. With a finger wipe the rest of the 5200 around the seam, like to fair it finally, and you are done.
Leave it sit for at least a week. Don't paint over the 5200 yet, don't attach or work the handle, DO NOT attempt to attach the hose, DO NOT MESS WITH IT. I've broken them loose (due to impatience) at like a week plus. It can happen, especially when forcing on the hose (especially Type-148 septic hose! - another reason to use Marelon is that their hose tailpieces are made for real-world hose installations, not the dated standards of wire-loom India-rubber hose as used in the 1940s).
I like that Joe included a diagram but I don't like the second diagram at all. What attaches the backing plates to the hull? That diagram shows buried bolt heads to attach the seacock. If one of them spins free , the seacock gets loose and you'll get a leak you can't fix. Don't do it that way. If your seacock has bolt holes, you can either ignore them (for example OEM-style Forespar Marelon seacocks, the only ones I use, have, and need, no bolt holes) or drill them all the way through the backing plate and the hull, at which point you are constrained to use only bronze mounting bolts which will be a point of regular inspection for the life of that seacock.
I respectfully disagree with NJLarry because I know 5200 to be absolutely the strongest thing for underwater fastening in the market. All respectable boatbuilders install lead keels with 5200. My boat is 47 years old and any original 5200 is still holding. The tensile strength is only one of the reasons (LifeSeal is like half the strength; and I stopped using Sikaflex after I found I could not work it even during installation - it turned into silicone-like boogers). The real reason is the chemical compatibility with fiberglass and most resin-based plastics and the sheer durability of the compound once it's been properly installed. For example, Marelon seacocks are corrosion-free and extraordinarily durable. Install one and you're looking at 40 years or more in regular saltwater use. You can't say that about bronze ones. If you were to install, properly, a Marelon seacock with 5200, it's essentially a life-of-the-boat installation.
Raider Yacht and Cherubini Boat have used Marelon seacocks with 5200 exclusively since I've been directly involved with them. I've never seen a single hassle with them.
Reseal Reaseal with 5200 I used 5200 to seal a few thru hulls never leak and even using
5200 on thru hulls was able to change out.
I repeat never any leaks with 5200.
Nick
5200 on thru hulls was able to change out.
I repeat never any leaks with 5200.
Nick
So whats your point? The same thru hulls would not have leaked with any sealant if installed correctly. Why are other sealants even made if 5200 must be used everwhere? Thru hulls should be mechanically strong, the sealant just seals out water. Want to use 5200 everywhere, go for it but the OP was asking about a thru hull that was not secured, any sealant would need to be rebedded. Like most hardware, thru hulls do not last forever and must be replaced. Google 5200 removal to see how hard it gets with time. I repeat, never any leaks with other sealents either.
But 5200 gives you security, go for it. Its a good product but difficult to remove after it hardens like a rock.
Last edited:
At Cherubini Boat we typically dealt with 25-30-yr maintenance cycles. Of 35 boats since 1975 I know of 4 or 5 not still being regularly used or undergoing full restoration to be used another lifetime. The rest are still out there owing to the standards we maintained.
Sorry, Larry, I’ve never seen 5200 ‘harden like a rock’. The stuff has been out there as long as I’ve been in the business and I’ve always seen it pliable - and, with heat and a good scraper, workable to be removed. Done it a lot actually (typically exchanging 30-plus-yr-old bronze seacocks with Marelon ones). You put a torch to it and it gets runny like it’s new out of the tube. Scrapes right off so well you’re tempted to just reuse it!
Sorry, Larry, I’ve never seen 5200 ‘harden like a rock’. The stuff has been out there as long as I’ve been in the business and I’ve always seen it pliable - and, with heat and a good scraper, workable to be removed. Done it a lot actually (typically exchanging 30-plus-yr-old bronze seacocks with Marelon ones). You put a torch to it and it gets runny like it’s new out of the tube. Scrapes right off so well you’re tempted to just reuse it!
Last edited:
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,914
I agree with @njlarry . Too many other good sealants to choose from that are not considered permanent. Thru hulls must be held in place by a mechanical means and sealant used to prevent water ingress. 5200 is overkill on my boat.
I am glad to hear that Marelon thru hulls are considered to have a long life. Thats why I chose them for my boat.
I am glad to hear that Marelon thru hulls are considered to have a long life. Thats why I chose them for my boat.
Thank you all for a great advice. I went ahead and did those thru holes again for a peace of mind.