The Hull Truth - Boating and Fishing Forum - View Single Post - Please Explain a Garboard Drain
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Old 06-02-2018, 05:20 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.

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.