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Please Explain a Garboard Drain

Old 06-01-2018, 09:00 PM
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Default Please Explain a Garboard Drain

I am about to the point in my project where I will need to go ahead and install a drain in the transom - mostly so I can wash the inside of the hull out as I grind old stringer tabbing down. Rather than an aluminum or brass tube with a rubber stopper, I wanted to use a bronze drain with a screw in plug like is in my old Hydra Sports. However, when I search, all I can find is something called a "Garboard Drain". However, these things do not have any sort of pipe to get through the transom - just a 3/8" or so neck. Is this what is used, or am I missing the screw plugged drains somehow? If this is it, how does it get through two inches of transom? Confused.

If I can't have a bronze drain with a screw in plug, should I just go with the brass pipe and rubber expansion plug? I will be using it in salt water, but trailering - in and out same day.

The same thing seems to be true with the seacocks I can find. They appear to be just a flange and valve, without the "through-hull" part. Should I just use a threaded through hull and put a ball valve on it?
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Old 06-02-2018, 01:57 AM
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The brass sleeves with expanding rubber plug are often used on smaller boats with easy bilge access, so they can be installed from inside. The threaded garboard drain is used on larger boats and installed from the outside. On my rebuild, I epoxied in a PVC tube to protect the core. Another option would be to over drill, fill with epoxy, then drill and install garboard drain.
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Old 06-02-2018, 03:06 AM
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mshugg
You should never install a rubber drain plug inside the hull.
If by chance it fails (this does happen) the plug will be blown out and flood the boat. When properly used, water pressure is assisting in keeping it in
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Old 06-02-2018, 04:20 AM
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Default Garboard-transom drain plugs

A few thoughts:

Do not use PVC - epoxy-polyester resins do not bond well to it, and PVC is also quite brittle, especially when it gets cold.
If you intend to sleeve the bore through the transom get a MM Carr catalog and buy a short length of G-10 composite tubing.

I am not a fan of the thin brass tubes used for sleeving transom drain bores in small boats.
First, they are soft brass, not bronze, and are very subject to corrosion and electrolysis.
Although the brass tubes themselves are cheap, you will have to buy or borrow the swaging tool - a threaded rod with two radiused fittings - that puts the bell mouth on both sides of the tube to hold it in position.

An alternative is to use a proper long-neck bronze or stainless steel through hull fitting.
Note that if you install the through hull with the mushroom head on the outside the lugs cast into the head's bore - there so it can be stopped from rotating during installation - will prevent the use of an expansion plug to seal it up.
Put the mushroom head in the bilge and the gland nut on the outside so the fitting's smooth bore will be on the outside.
Depending on the quality of the fitting the bore may be a bit rough, and perhaps not quite the correct inside diameter for a rubber expansion plug to seal adequately. A quick tuneup with a lathe to get a correct size bore that's smooth is often necessary.

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PS:
I agree - if the transom drain is sealed with a rubber expansion plug - the plug should be on the outside, not the inside, if for no other reason than it makes it easier to do an eyeball check to make sure the transom drain is sealed before the boat gets launched.
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Old 06-02-2018, 05:19 AM
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Check out Gemlux they have a garboard drain.
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Old 06-02-2018, 05:25 AM
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Too bad that two posters here didn't have a Grandpa teach them how to operate a small Jon Boat....... I imagine they would Freak out ro see you reach down and pull that Rubber plug while underway cuz everybody knows that a boat will sink instantly with that plug out......Right???


That was a Great suggestion about over drilling the hole and filling w/ Epoxy......
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Old 06-02-2018, 05:44 AM
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Originally Posted by snagged line View Post
Too bad that two posters here didn't have a Grandpa teach them how to operate a small Jon Boat....... I imagine they would Freak out ro see you reach down and pull that Rubber plug while underway cuz everybody knows that a boat will sink instantly with that plug out.
Hmmmm.... I thought you were SUPPOSED TO pull that while underway. How are you going to get that water out otherwise? (Or at least, that was the case with my ancient v-hull.)

As to the hydrostatic pressure, while that is technically correct, since rubber expandable plugs are generally used on smaller boats, even when fully loaded and sitting still, that drain isn't that far under water, so that pressure is insufficient to "blow out" a reasonably tightened plug, and while underway, as Mr. SL stated earlier, the pressure balance is actually pushing it in.
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Old 06-03-2018, 06:00 AM
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Originally Posted by mshugg View Post
T... Another option would be to over drill, fill with epoxy, then drill and install garboard drain.
Hhmmm...this has possibilities. Though I just don't understand why they don't make a drain that goes all the way through.
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Old 06-03-2018, 07:11 AM
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I like the drain plugs with captive plug, they can be screwed on or out from either side of the boat. Makes it conviencon when you launch the boat and forget to close the drain.
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Old 06-03-2018, 02:47 PM
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I have the Garboard drains on my 34C Silverton. I boat in NJ in saltwater. and I replaced two of them about three years ago. They are Bronze with the T-Type plug. Yesterday while investigating in the bilge why I was taking on so much water, we noticed it was wet near the drain. We put our hand to wipe near the drain and one of the threaded bolts and nuts fell off. A bolt on each of them are bonded to my boats system. The bolts were stainless steel. Anyone have any idea if it was the bronze and the Stainless reacting with the saltwater? Boat is being hauled on Tuesday to have them both replaced, not sure if we should use SS bolts again or Bronze?
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Old 06-03-2018, 03:54 PM
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Originally Posted by Tony NJ View Post
I have the Garboard drains on my 34C Silverton. I boat in NJ in saltwater. and I replaced two of them about three years ago. They are Bronze with the T-Type plug. Yesterday while investigating in the bilge why I was taking on so much water, we noticed it was wet near the drain. We put our hand to wipe near the drain and one of the threaded bolts and nuts fell off. A bolt on each of them are bonded to my boats system. The bolts were stainless steel. Anyone have any idea if it was the bronze and the Stainless reacting with the saltwater? Boat is being hauled on Tuesday to have them both replaced, not sure if we should use SS bolts again or Bronze?
Tony, before I retired I worked a lot with heat exchanges and cooling water systems. We at times had problems with Stainless Steel corroding in areas that could trap water next to the stainless. The problem is that if the water is trapped it becomes acidic due to the reaction with the stainless steel when oxygen is not present.

The stainless protects itself by the very thin oxidized layer on the outside. If the oxidation layer is compromised and there is no oxygen to re oxidize it. The stagnate salt water then becomes even more acidic due to some chemical reaction that occurs. I think bronze is more resistant to crevice corrosion than stainless steel. Here is a link to an article about the problem. Good luck with it.

Dwight
https://en.wikipedia.org/wiki/Crevice_corrosion
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Old 06-05-2018, 04:54 PM
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You don't see garboard plugs with long neck s because you generally don't extend the wood/composite core all the way to the drain.

Most manufacturers and rebuilders leave the area around the drain void of a core and compensate by using many layers of glass resulting in a thickness of 1/2 to 3/4"
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Old 06-05-2018, 05:18 PM
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Originally Posted by chrisrack View Post
You don't see garboard plugs with long neck s because you generally don't extend the wood/composite core all the way to the drain.

Most manufacturers and rebuilders leave the area around the drain void of a core and compensate by using many layers of glass resulting in a thickness of 1/2 to 3/4"
Well....bummer. I didn't do that, so I guess I am stuck with the brass tube. I guess it should be alright. 18' boat that will be trailered and in and out the same day on all but very rare occasions. Thanks.
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Old 06-05-2018, 05:37 PM
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You’re over thinking this. Nothing wrong with the brass tube. Over drilling and filling with epoxy is just fine. And in spite of what has been said, epoxy bonds just fine to PVC. Just rough up the surface to get a mechanical bond, and go for it. Any of these things will work and last decades. Just pick one and go go gadget.
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Old 06-07-2018, 12:26 PM
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Get this guy from Gemlux so you can close it up from inside or outside the boat!

Angled Drain Plug
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Old 06-07-2018, 06:50 PM
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Originally Posted by Sharpest View Post
Get this guy from Gemlux so you can close it up from inside or outside the boat!

Angled Drain Plug
I saw that, but it's the same deal; wont go through two inches of transom - though it could be used with the over-drill and fill with epoxy method mentioned previously.
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Old 02-27-2019, 06:28 PM
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Did you ever come up with a remedy buddy? I'm installing a seasense garboard plug and it only has a 1.5" tube and my transom is about 2" thick. I'd like to get it done this weekend but don't want to drill until I get a solid answer from someone that has been in these shoes.

How would one go about filling an oversized hole with no air pockets etc. This sounds like the best method to keep core from water and a solid mounting surface.
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Old 02-27-2019, 07:16 PM
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Originally Posted by scallen2112 View Post
Hhmmm...this has possibilities. Though I just don't understand why they don't make a drain that goes all the way through.
When used on a new boat, the transom core has a mouse hole in the bottom so it's solid fiberglass in the garboard drain area. This creates a thinner area to mount as drilling through the core would expose it to water intrusion. Even a with a composite core, you wouldn't want water getting in there. You can see it on this coosa board transom getting installed.

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Old 02-27-2019, 07:31 PM
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Originally Posted by Island Marine Group View Post
When used on a new boat, the transom core has a mouse hole in the bottom so it's solid fiberglass in the garboard drain area. This creates a thinner area to mount as drilling through the core would expose it to water intrusion. Even a with a composite core, you wouldn't want water getting in there. You can see it on this coosa board transom getting installed.

Makes sense for builders to add this. In my situation it is a Mexican made panga and it seems to actually be thicker in the drain area. I need to figure out what I should do as launch day is coming up. My old panga had a plastic drain installed and I did not like having the rubber plug. I'm trying to have a solid plug that won't let water into the core.
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Old 02-28-2019, 03:44 PM
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Originally Posted by dmartin View Post
Tony, before I retired I worked a lot with heat exchanges and cooling water systems. We at times had problems with Stainless Steel corroding in areas that could trap water next to the stainless. The problem is that if the water is trapped it becomes acidic due to the reaction with the stainless steel when oxygen is not present.

The stainless protects itself by the very thin oxidized layer on the outside. If the oxidation layer is compromised and there is no oxygen to re oxidize it. The stagnate salt water then becomes even more acidic due to some chemical reaction that occurs. I think bronze is more resistant to crevice corrosion than stainless steel. Here is a link to an article about the problem. Good luck with it.

Dwight
https://en.wikipedia.org/wiki/Crevice_corrosion
i had the large bow eye bolt in my Albemarle 24 corrode through in this way. The bolt looked absolutely fine on both sides but it was completely corroded in the 1/2” section that went through the hull.


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Last edited by dell30rb; 03-04-2019 at 09:08 AM.
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