Rebedding a through-hull

[kmart]

So last season I noticed my through hull speed transducer was weeping a bit. Not a lot, but I could always see a trail of wet from through hull into bildge. No actual drops of water..just a trail of wet. The leak was coming in from under the lock nut
Note this is a older Autohelm ST60 through hull speed transducer.. black plastic. is threaded with a neoprene like gasket and a lock nut on the inside of hull.
Am very confident that its the sealant giving up. The throughout itself looks in great shape.
I was able to easily take the lock ring and washer off. Cleaned up some white sealant the prior owner used. It pealed right off.

Question 1. How do I remove it from the hull without damaging it. With the lock ring removed. she still wont budge. The sealant on the outside of hull is still holding strong. I don't want to ruin the threads or break it trying to force it out.

Question #2 Once its out... I'll clean it up and the inside/outside surface of the hull and rebed. I plan to use lifecalk on the outside of hull and then buytle tape on inside under locking ring. Is this the best way or is there a better sealant ... or use lifecalk inside and out. suggestions?

 

[justsomeguy]

Dunno why the interior was gooped. Try a piece of piano wire around the outer flange to cut through the sealant.
Be prepared to replace it anyway.

 

[chuckwayne]

use a piece of monofilament tied between two sticks like a saw to cut the caulk around the outer flange. You can also get some debonder to loosen the caulk bond and make it easier to remove - just did mine and it came right out, 5200 notwithstanding

 

[kmart]

Ok. Piano wire or monofilimant.
Will give that a try. From the outside. Its covered with years of antifoulimg. Need tk chip that alway before i can even get to edge.

Chuck, what sealent did you rebed with.
K

 

[BigEasy]

Undoubtedly, the seal on the outside of the hull has become compromised. It's best if you can remove it in entirety and rebed it from the outside with LifeCaulk, 3M 4200, etc. However, if it appears that you are going to break the transducer housing trying to remove it, you can do as the previous owner and seal it from the inside again. If you can purchase or fabricate a replacement rubber gasket, that may help also. It will likely last a few years without a problem before leaking again. If you are hauled out, Also inspect the thu hull housing for a possible crack/fracture in which case replacement would be necessary. If rebedding while on the hard, make that you follow the manufacturers directions for adequate cure time as it relates to ambient temperatures. A few years back, I had a yard replace a bronze thru hull for me because I didn't have time to do it myself; it was bedded with 4200. We happened to have unseasonably cold weather that fall and the yard splashed the boat day after the repair. The sealant wasn't completely cured and leaked profusely. They had to haul it out again, rebed it, & allow a few days for the sealant to cure before re splashing again, at their expense.

 

[dlochner]

A thin flexible scraper on an oscillating tool will also work to cut the caulk.

Check with the through hull manufacturer (probably Airmar) about proper sealants. Generally, polysulfide caulks (Lifecaulk) are not recommended for plastic through hulls. 5200 is also a bad idea.

 

[chuckwayne]

Ok. Piano wire or monofilimant.
Will give that a try. From the outside. Its covered with years of antifoulimg. Need tk chip that alway before i can even get to edge.

Chuck, what sealent did you rebed with.
K

The dealer originally used 5200 - hate that stuff. I used 4200. As Dave said, lifecaulk's not a good choice for plastic. My replacement is a B&G combo sender, also a plastic Airmar unit. The important things are surface prep and allowing plenty of time for the caulk to cure - they can take a week or more, depending on temp and humidity.

 

[marke14]

Is 5200 good for anything?

 

[jssailem]

I know not what others have heard but understand that 5200 is used below the water line.

 

[njlarry]

Hull to deck joints period. ....imho.

 

[lillia28]

A bit of a thread drift, although I do tend to avoid 5200, I've used Debond a few times and found it makes 5200 clean up easy peasy. Maybe it's time to rethink 5200? I have no connection with any manufacturers, I'm just an old guy with an old boat trying to learn new tricks. My routine is to spray on the De Bond and ignore for a week or so. First time, I was scared that the 5200 was barely sticking and thinking it was a good thing I decided to replace it. Third time: Oh, This stuff actually works!
5200 does provide some peace of mind, and now with easy removal, maybe it's time? Expensive as all get out, roughly $20.00 for a tiny spray bottle (think Binaca size). I'm curious of others thoughts.
Lou

 

[dlochner]

Hull to deck joints period. ....imho.

What Larry said, and to which I add, to frustrate the hell out of the next owner.

 

[dlochner]

A bit of a thread drift, although I do tend to avoid 5200, I've used Debond a few times and found it makes 5200 clean up easy peasy. Maybe it's time to rethink 5200? I have no connection with any manufacturers, I'm just an old guy with an old boat trying to learn new tricks. My routine is to spray on the De Bond and ignore for a week or so. First time, I was scared that the 5200 was barely sticking and thinking it was a good thing I decided to replace it. Third time: Oh, This stuff actually works!
5200 does provide some peace of mind, and now with easy removal, maybe it's time? Expensive as all get out, roughly $20.00 for a tiny spray bottle (think Binaca size). I'm curious of others thoughts.
Lou

The last time I read about removing 5200 with Debond, the process was to apply a little and then use wedges to gradually opening up the space, then spray some more, repeat until the fitting is free. Debond does not dissolve the 5200, it makes interferes with the bond between 5200 and the surface.

A thin flexible scraper blade on an oscillating tool also works.

 

[seadaddler]

5200 is what is used below water line and a few years ago I changed to a new Tri transducer and yes was not easy to change but any way used 5200 and had to change the housing here 3 years later to try a new housing with baffle and used metal scrapper and sharp thin chisel slowly and than put new housing with plenty of 5200 so it oozed out in side and outside and should not leak again if 5200 used.
Nick

 

[BigEasy]

When contemplating the use of 5200, think of permanent adhesion of parts that you never, ever, never want to come apart!
As NJLarry mentioned, hull to deck joints or other structural parts that you never anticipate removing. Yes, I know that there are chemical solutions that allow it to be removed; however, its a complete fallacy that 5200 is the only adhesive that can be used underwater; its an overkill for most jobs. there are numerous other sealants that are more than adequate for underwater application, such as 3M 4200, Lifecaulk, etc. These sealants are suitable for underwater use and will allow you to remove the sealed object ( think thru hulls) without damaging the thru hull, fiberglass that is bedded onto, or both. Personally, I wouldn't use an oscillating blade to remove the plastic housing because the plastic flange and underlying gelcoat will become cut & gouged. If you are determined to remove the transducer, use debond and monofilament or a thin guitar string to work around it.

 

[dlochner]

Personally, I wouldn't use an oscillating blade to remove the plastic housing because the plastic flange and underlying gelcoat will become cut & gouged. If you are determined to remove the transducer, use debond and monofilament or a thin guitar string to work around it.

My assumption is that the transducer is being removed because the system is no longer functional and there is little need to preserve its integrity. If the intention is to use the transducer for something other than landfill, then great care is needed to remove it. Of course using something other than 5200 makes the removal job much easier with lower probability of damaging the through hull.

 

[BigEasy]

Kmart stated that the transducer appears to be in great shape.
He wants to remove the thru hull fitting without damaging it. Better try the debond with patience!

 

[kmart]

Ok, First thanks for all the reply's. This site is so great for members providing a wealth of info.

Yes, the knotmeter transducer works fine. no issues. Only reason I'm doing this project is there is slight wetness from the through-hull. I probably could put it off... but me being ocd about my boat I put it under preventive maintenance. Assuming the leak is the bedding giving up and there is no damage to the through hull... I will reuse.

Now for an update.
I was able to get the through hull out fairly easily. took about 10 minutes. I tried the piano wire.. but couldn't really get it under lip of the flange on the through-hull. What worked was I used a small pick (sorta like a miniature icepick) and was able to dig a bit under the flange. Then with a flat blade screwdriver I was able to make my way around the flange and slowly pry it up. Once started, it actually broke free quite easily. .
So couple things I noticed.
1) throughhull was located on a concave area where keel turns to bottom of hull. ie not exactly flat surface
2) the whole in the hull is tapered. ie wider on the outside of hull and narrowing as it goes in
3) there was a gasket then 5200 on the throughull. (see pic). I did not expect to see a gasket there. but I guessing it was to fill in that tapered area. it would take quite a lot of sealant to try and fill otherwise.
4) the throughull itself in very good shape. no sigh of cracking or ware. just dirty.

So my plan it to get a new gaskets. and 4200. and re-bed the way it originally was. Gasket, then 4200... insert into hole. Another gasket on inside of hull and then the locking ring. As this worked well for ...years (at least 15) it should work again. Does this sound like a reasonable approach? Yes, I'll let the 4200 dry/cure at least a week (or two) before launch.

My only question is is it common to use both a gasket and sealant together??? I've always seen one or the other but not both. It looks like the sealant sealed between the gasket rough, tapered surface of the hull hole. And Not between the through-hull and the gasket.

 

[Maine Sail]

That hole will need to be fixed as that is not a correct shape hole for a mushroom/flange headed thru-hull fitting. I suspect that hole was for a flush mounted seacock and someone hacked jobbed it for a speed log. A very poor choice and potentially boat sinking unsafe practice.

I would also avoid re-using that thru-hull fitting. With the model# of the transducer, usually shrink wrapped to the cable, a new thru-hull can be purchased easily. They range form a low of about $30.00 to upwars of $70.00 +/- depending upon the transducer model. OK maybe not so easily for a DIY, because the distributor is generally wholesale/trade only, but any competent marine vendor should know exactly where to get one and can order one for you. If you have trouble with this PM me. The shape of the flange on the thru-hull is what makes the seal. It is concave and traps sealant thus creating the seal. Your screw driver has marred that surface now making the thru-hull pretty unsuitable for re-use..

Your hole should look like this when done correctly. All the bottom paint needs to be clear of the bonding area of the thru-hull fitting. If you are not competent with glass work, eg: taper repairs, please bring in someone who is.

This concave shape is what traps the sealant and creates the seal. It needs to be clean, mar free and the hole needs to be 90 degrees to the hull, be properly sized for the thru-hull, and no-bevel deeper than about 1/16"...

 

[Ron20324]

You really should not have a gasket (what's it made of?), but you have to deal with what was handed to you. Most gasket material will shrink or drot of old age, and maybe that is the cause of your trickle. On the inside you should have a washer to fit the thruhull, and preferable a larger backing plate.