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Old 06-24-2019, 10:05 PM   #1
Jeb
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Default Boat Plug - Threaded?

Folks,


Just got a Weldcraft and I noticed that the plug hole appears to be threaded. I've seen this on some fiber glass boats that use a threaded brass plug (Garboard), but not on an Aluminum boat. But only the standard rubber type plug came with the boat. Can I use this rubber plug or should I invest in something else?



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Old 06-25-2019, 07:28 AM   #2
namu mac
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Default Re: Boat Plug - Threaded?

Use a 1” aluminum pipe plug. Make sure it is aluminum. Where is the original plug?


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Old 06-25-2019, 07:30 AM   #3
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Default Re: Boat Plug - Threaded?

I'd get a threaded aluminum plug to match the size, looks like maybe 1/2npt or 3/4? Measure exactly and Google pipe thread size. You can get the aluminum plugs at mcmaster car or auto parts store that carries performance parts as they're used in racing applications. Install with tef-gel or similar and don't over tighten. A stainless steel plug would be my next choice but avoid brass/bronze at all costs. Some do use a rubber plug in there but why when you have a better threaded hole installed?
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Old 06-25-2019, 07:47 AM   #4
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by namu mac View Post
Use a 1” aluminum pipe plug. Make sure it is aluminum. Where is the original plug?


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Good question. It was a used boat and only came with the typical rubber T plug, not the Garland style.


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Old 06-25-2019, 08:39 AM   #5
namu mac
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Default Re: Boat Plug - Threaded?

My NR had that type plug and as I remember it was 3/4”. You can try a steel pipe plug for size but use aluminum.


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Old 06-25-2019, 08:59 AM   #6
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Default Re: Boat Plug - Threaded?

The rubber screw down plugs work just fine. My boat is the same way.


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Old 06-25-2019, 08:59 AM   #7
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Default Re: Boat Plug - Threaded?

If you are going to moor your boat, do NOT use a standard rubber boat plug. Many, many horror stories about them
corroding and sinking boats while moored. Best avoided, especially when your boat was 'done right'
with a threaded plug.

Because aluminum to aluminum tends to gall, I would instead use a plastic pipe plug.
I believe you have 1/2" NPT (tapered) plug there (which has a nominal OD of 0.84").

Here's an HDPE (plastic) version available at Fastenal:
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Old 06-25-2019, 09:30 AM   #8
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Default Re: Boat Plug - Threaded?

I would first look for either the plastic plug cited above or a PVC plug which can be found at any hardware store.

Second choice is to get an aluminum plug and use anti seize compound on the threads. Permatex makes one for Aluminum. I also use this on all my motor bolts and screws.

Be sure to cary a spare (expanding rubber type) for that rare occasion when someone forgets to put the plug in and you don't find out until your launch the boat. You can install it from the inside on most boats with outboard engines, including those with the extended motor mounts.

Last edited by LGB; 06-25-2019 at 09:32 AM.
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Old 06-25-2019, 12:55 PM   #9
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Default Re: Boat Plug - Threaded?

You folks might be surprised how well tef-gel on a good aluminum pipe plug works, doesn't need more gooping but maybe every dozen uses unlike pipe dope or Teflon tape that needs redone every time, and is just plain stronger than the plastic. I've just seen too many people strip the plastic plugs by overtightenning which if not caught can lead to plug failures. Careful tightening of HDPE plugs works well though.
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Old 06-25-2019, 01:23 PM   #10
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Default Re: Boat Plug - Threaded?

Quote:
Because aluminum to aluminum tends to gall, I would instead use a plastic pipe plug.



And the plastic plug won't wear the threads out, which is bound to happen eventually. IMHO, use a plug that's UV resistant and won't get brittle. I wouldn't trust a hardware store PVC plug.
The good thing about an aluminum plug is that you can weld on a t-handle or something similar to make it easier to handle.
The rubber plug will work fine as long as you're not mooring it, but the threads in the pipe will probably chew up the rubber after a while.
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Old 06-25-2019, 03:28 PM   #11
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Default Re: Boat Plug - Threaded?

NR redid my plug due to some boats sinking at the dock. They recommended using # 14 Permatex Teflon pipe seal.


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Old 06-26-2019, 12:45 PM   #12
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by 1pump View Post



And the plastic plug won't wear the threads out, which is bound to happen eventually. IMHO, use a plug that's UV resistant and won't get brittle. I wouldn't trust a hardware store PVC plug.
The good thing about an aluminum plug is that you can weld on a t-handle or something similar to make it easier to handle.
The rubber plug will work fine as long as you're not mooring it, but the threads in the pipe will probably chew up the rubber after a while.


Yep to this.
My ThunderJet has the threaded aluminum as well and I have never used anything but the better quality rubber plugs (the ones that screw in to tighten, not the lever lock ones).
Get a couple new ones every year and toss the old one (always have a backup in the boat bag, just in case).
(I do not moor so this works for my boat)
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Old 06-26-2019, 02:24 PM   #13
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Default Re: Boat Plug - Threaded?

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Originally Posted by Thundertaker View Post
Yep to this.
My ThunderJet has the threaded aluminum as well and I have never used anything but the better quality rubber plugs (the ones that screw in to tighten, not the lever lock ones).
Get a couple new ones every year and toss the old one (always have a backup in the boat bag, just in case).
(I do not moor so this works for my boat)



I second the motion.
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Old 06-29-2019, 12:57 AM   #14
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by positize View Post
If you are going to moor your boat, do NOT use a standard rubber boat plug. Many, many horror stories about them
corroding and sinking boats while moored. Best avoided, especially when your boat was 'done right'
with a threaded plug.

Because aluminum to aluminum tends to gall, I would instead use a plastic pipe plug.
I believe you have 1/2" NPT (tapered) plug there (which has a nominal OD of 0.84").

Here's an HDPE (plastic) version available at Fastenal:
Plastic plugs are a great option, but should be considered a wear item that you replace from time-to-time. Also, not all plastic formulations are the same. Make sure you choose the proper material type for your application.

Stainless steel is also a good choice, but needs to have some anti-seize compound applied to the threads.
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Old 07-09-2019, 12:07 PM   #15
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Default Re: Boat Plug - Threaded?

I'm a new boat owner with a threaded plug and I'm wondering what the problem is with a threaded plug?
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Old 07-09-2019, 12:19 PM   #16
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by badkarma View Post
I'm a new boat owner with a threaded plug and I'm wondering what the problem is with a threaded plug?


People that don’t like them generally don’t like the time and wrench it takes vs a compression plug.

People that do like them have seen boats sink because a compression plug has failed.


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Old 07-09-2019, 05:58 PM   #17
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Default Re: Boat Plug - Threaded?

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Originally Posted by The Pew View Post
People that don’t like them generally don’t like the time and wrench it takes vs a compression plug.

People that do like them have seen boats sink because a compression plug has failed.


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Thanks Pew! I'm happy to keep a wrench in the transom with my plug!
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Old 07-09-2019, 08:07 PM   #18
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Default Re: Boat Plug - Threaded?

Few things have kept me up at night since I moored my boat than the stupid drain plug. Mine is not threaded and I almost contemplated welding it up as my bilge pump gets more water out than removing the plug. I ultimately settled on taking one of those red tru-plug mini leak plugger things, cut it down and stuffed it in the hole. I kept a zip tie attached to it so I could pull it out if needed. Then I used a stainless rubber plug on the outside and coated it with tefgel. I will replace that part every season. I’m happy with the redundancy and I tested it to make sure no water gets in even without a plug.

Not an option for everyone but figured I’d share. I mean how often do you come across a boat plug thread...
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Old 07-10-2019, 03:21 PM   #19
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by The Pew View Post
People that don’t like them generally don’t like the time and wrench it takes vs a compression plug.

People that do like them have seen boats sink because a compression plug has failed.


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Excellent observation. I'd add that smaller boats, drift boats and such can get by with a rubber compression plug - carry a spare. Especially if you can get to the drain hole easily. Larger boats where access to the bilge is limited are probably better off with a threaded plug - carry a spare. Whatever you use, be aware of dissimilar metals and galvanic corrosion risk.
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Old 07-11-2019, 12:24 PM   #20
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by Don G Baldi View Post
Whatever you use, be aware of dissimilar metals and galvanic corrosion risk.
This. Never, ever use a brass plug on an aluminum boat.
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Old 07-11-2019, 07:44 PM   #21
badkarma
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Default Re: Boat Plug - Threaded?

Quote:
Originally Posted by MattPark View Post
This. Never, ever use a brass plug on an aluminum boat.
Why not?
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Old 07-11-2019, 08:15 PM   #22
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Default Re: Boat Plug - Threaded?

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Originally Posted by badkarma View Post
Why not?


Corrosion. In Saltwater the rate of corrosion would be even worse. To the point of creating holes in the boat.

Stainless is closer to aluminum so it doesn’t corrode as bad but you still want a little anti seize as mentioned.


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Old 07-11-2019, 08:30 PM   #23
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Default Re: Boat Plug - Threaded?

I drove down almost to Medford to look at a sled a few years back. It was older and I was looking for something to bang around in. The owner had replaced the plywood backing on the transom with pressure treated wood. You could already see pin holes where the copper had eaten away the aluminum. I'd have had to replace the full transom so I walked away. Aluminum don't even like aluminum if it's a different alloy.
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Old 07-11-2019, 08:37 PM   #24
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Default Re: Boat Plug - Threaded?

Brass compression plugs corrode to the point that there is little to no metal left in a short amount of time, especially in salt. You are left with just the rubber, and whatever is left of the corroded brass plugging the hole in the center of the plug. Years ago I attempted to pull the plug on my buddy's NR OS after being moored for just over a month, the plug fell out in my hand, there was no metal left. They have sunk numerous aluminum boats in the last 20 years.

The thought of a brass threaded plug in an aluminum boat should never cross anyone's mind. Brass doesn't belong in contact with sea water on any boat, and if it's in contact with aluminum, that makes it much worse.

Here's a link to some lucky, and not so lucky brass compression plug experiences.

A side note, some of the boats mentioned in the thread (and many others from 10 or so years ago) came with zinc anodes from the factory. Those are not correct for aluminum, and they are essentially useless. If you have an aluminum boat with zinc anodes, you should replace them with aluminum anodes ASAP. The good news is many aluminum boats are equipped with outboards, which have aluminum anodes that will protect the boat to some degree.
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Old 07-11-2019, 09:49 PM   #25
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Default Re: Boat Plug - Threaded?

I have a 3/4" threaded on mine, put in a stainless ball valve. Yes, there can be some galvanic reaction between SS and AL, I intend to keep an eye on it but dang it's convenient! If they make a threaded plasic pipe nipple I could always switch over it that, along with a plastic valve.



Before that, I had the plug on a lanyard and was going to have a wrench laser-cut out of SS and put it on a lanyard.



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Old 07-12-2019, 10:37 PM   #26
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Default Re: Boat Plug - Threaded?

Guess I'll start looking for a SS plug. Thanks for the info.
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