Stainless Drain Thru Hull

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Stainless Drain Thru Hull

Postby LGJTTU » Sat Feb 10, 2018 11:42 am

I have seen a few instances on this forum where someone used stainless tubes in place of brass tubes for thru hull drains. However, not much detail was given on how difficult this was.

It seems like the use of stainless may negate the chore of replacement/repair in the future. Stainless cold works quickly, so flaring is likely more difficult. But once in place, it seems it may be a permanent fix.

I like the idea proposed in the FAQ section to shop McMaster-Carr for the tubing. One can obtain 1 inch OD, .035 wall, 316 tubing, which is close to the aforementioned 1 inch OD, .032 wall brass tubing. It seems like this may fit up with with the standard Moeller flaring tool. If someone could affirm this, I would appreciate the confirmation.

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Re: Stainless Drain Thru Hull

Postby dtmackey » Sun Feb 11, 2018 9:48 pm

I think you will find it very difficult to flair 316 stainless. Brass is far more malleable than stainless, especially 316SS.


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Phil T
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Re: Stainless Drain Thru Hull

Postby Phil T » Mon Feb 12, 2018 10:32 am

Oldslowandugly is the only member who I recall has installed stainless tubes and he used epoxy and Marine Tex.

The challenge with installing drain tubes is the need to heat the end prior to flaring AND the angle cut is not necessarily 90 degrees.

Given that I don't think stainless will flair well and the brass tube will last 20 years, why go to the added expense for a less that ideal fit on a through hull fitting?
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

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Re: Stainless Drain Thru Hull

Postby Oldslowandugly » Sat Feb 17, 2018 9:15 pm

Phil is correct: I did it. The reason was simple.

I researched how to replace the brass drain tubes and tool needed to flare the ends. I realized that my hull was in pretty bad condition on both the inner and outer surfaces where the flare and O-ring sealed. Up inside the foam was pretty chopped up, too. So faced with building up the areas with repair fiberglass anyway, I elected to just glass in the tubes with a combination of resin and Marine-Tex.

Also while passing through the yard of Outboard Service Corp in Freeport, I saw my guy Mike doing that exact job with brass. I asked if stainless tube was acceptable instead of brass and he agreed it would probably last longer, but could not be flared. I explained that I would glass in the stainless tubes flush with the transom surfaces and he pointed out that if I did that with brass I could never repair the tubes again. I replied that I only wanted to do this job once and stainless would probably outlast me. He concurred.

I took one-inch-round 304 stainless steel tubing like they use for hand rails and cut slightly too long sections to fit all of the hull drains. As I said, there was lots a damage around the drain holes, so once the tubes were in place I used Marine-Tex to build up the areas where they poked through both inside and out. Once the epoxy cured, I drilled some small holes through the hull right above the tubes. I mixed up some polystyrene fiberglass resin and injected it through the holes into the cavities surrounding the tubes where the foam was missing. This completely locked in and sealed the drain tubes. Then I cut the ends of the tubes flush with the hull surfaces with a cut-off wheel.

A one-inch stainless rubber drain plug fits the one inch tubes perfectly and never leaks. It has been five years now with no signs of cracks or leaks around the tubes. I'm sure down the line when gone, someone will probably curse my efforts. But I don't expect to be bothered by drain tubes ever again.

Fig. 1. Transom of the boat on which the drains were replaced.

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Stainless Thru Hull Drains

Postby RichS » Tue Jun 11, 2019 12:50 am

I'm in the process of replacing three splash well drains on my 1988 Outrage 18. I was ready to order the brass tubing from McMaster-Carr when I spotted some stainless tube handles I had salvaged from an old wall oven. They were exactly the right size (1.25" OD x .035 wall). The only negative was that they were marked 304 alloy and I would prefer 316.

I am aware of the work hardening problems with stainless but the price was right--what did I have to lose?

I'm always looking for something to make on my old South Bend lathe, so I decided to make my own flaring tool (Fig. 2.) As you can see in Fig.3 and Fig. 4, the resulting flares were much better than I expected. I don't know if the commercially available flaring tools would work as well on stainless.

Fig. 2. Flaring tool made on lathe.
IMG_0889.JPG (32.09 KiB) Viewed 7607 times

Fig. 3. Flared stainless steel tube
IMG_0892.JPG (23.08 KiB) Viewed 7607 times

Fig. 4. Flared stainless steel tube, reverse view
IMG_0891.JPG (29.54 KiB) Viewed 7607 times

I was encouraged, and I ordered some 1" OD x .035 wall 316 stainless tubing (McMaster part #89785K867) for the two smaller thru hull drains along with the needed O-rings (McMaster Part #9557K486 and #9557K482).

The tubing has a soft temper, and I'm hoping it will form as well as the old oven handles. Even though the old brass tube on the center splash well drain came out in two pieces, the wood showed no rot and was only slightly damp. I positioned a fan to blow thru the hole for a day and then sealed the wood with some low viscosity epoxy.

I haven't installed that tube yet and thus haven't formed the opposing flare. As soon as I do, I will post more images.

Malcolm Goodfellow
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Re: Stainless Drain Thru Hull

Postby Malcolm Goodfellow » Tue Jun 11, 2019 2:15 pm

RichS--no help here, but we're on similar paths.

Yesterday (June 10, 2019) all five of the (brass) drain tubes were replaced on my 1988 OUTRAGE 18, with Tom W. Clark doing the heavy lifting. All five were original from 1988 and showed no signs of leaking, but the tubes did show deterioration only visible after removal. [Inside was] nice crispy snow white foam. The center splash well tube was the trickiest. The boat sat in my hangar with tubes OUT for almost nne months. To see the boat with the new tubes was very satisfying, especially since they were installed by the very particular craftsman T.W.C.

To size, shape, anneal, flare, and install (with [3M4200 Fast Cure] to get the best seal at the tube-to-O-ring-to hull) took 1.5-days. They are beautiful.

Best of luck

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Re: Stainless Drain Thru Hull

Postby RichS » Sat Jul 20, 2019 2:36 pm

Sorry it's taken this long to post the installation of my stainless drain thru hull. The opposing flair formed very well. I was afraid that I would over form the existing flair in forming the opposing one. To help prevent this, I used some high pressure grease on the opposing flair and some #100 carborundum grit on the existing one to lock it in place on the forming die. This might not have been necessary as the pressure from the o-ring may have prevented it from overforming. I also used some Loctite PL Marine Fast Cure Adhesive Sealant on the o-rings. I think this is similar to 3M 4200.

I haven't replaced the remaining thru hull tubes yet (having too much fun fishing), so I can't say how well the McMaster 316 stainless alloy tubing will work.

Attached are two images showing the inside and outside of the installation.
Inside view
IMG_0908.JPG (70.13 KiB) Viewed 6930 times
Outside view
IMG_0907.JPG (81.64 KiB) Viewed 6930 times

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Re: Stainless Drain Thru Hull

Postby ALI-OOP » Wed Aug 14, 2019 6:40 am

Very interesting, I'm always looking to build a better mouse trap. Those stainless steel tubes are sweet. Love the craftsmanship. admirable work

Tony G