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Old 15-07-2017, 20:05   #1
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Plastic through hull replacement?

While polishing and waxing my topsides, I noticed a hairline crack just inside the bore of one of my plastic through-hulls on the transom for the bilge pump discharge. It's about 6 inches above the waterline while the boat is at rest, so it's not an emergency, but I'll be replacing it (and its twin) soon. I plan to replace them while in the water.

There is no sea-cock inside the fittings, just a hose barb. They're about 1 1/4", as I recall. I'm wondering if I should replace them with bronze, or would Marelon be OK? I'm guessing the crack was due to UV exposure - if so, I'm assuming the bronze would be more UV resistant than any sort of synthetic material.

Assuming this evolution goes well, I'll probably replace the cockpit drain through hulls soon after. They're on the underside of the hull, just at the water line. Due to their location, they're probably not UV damaged, but 30 years old just the same. I'm pretty sure I can roll the boat over enough with some with docklines to provide adequate access without hauling.

Any recommendations appreciated.
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Old 15-07-2017, 20:34   #2
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Re: Plastic through hull replacement?

If it was white, it is probably nylon, and these don't hold up well in the sun. Marlon will do fine.
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Old 15-07-2017, 20:50   #3
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Re: Plastic through hull replacement?

Marelon is the way to go, IMHO.

All of the Marelon sea cocks and transducer thru-hulls on my Olson 40 were still in good shape. But we are replacing them all, with new Marelon.

The newer ones are stronger -- the ABYC standard was upgraded.
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Old 15-07-2017, 22:06   #4
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Re: Plastic through hull replacement?

There some NZ designed thru hulls and valves (TRUDESIGN) that have ABYC approvals and have been exhaustively tested through fire /UV /even left in Antarctica for season then re tested, they have all sorts of innovations and well worth checking out here:Seacocks And Through Hull Fittings | TRUDESIGN

Cheers Steve
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Old 16-07-2017, 06:41   #5
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Re: Plastic through hull replacement?

I prefer bronze thru-hulls but if you're going to use plastic, I agree with Captsteve, go with Trudesign. They are distributed in the USA by Raritan.
http://raritaneng.com/category-pages...sign-products/
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Old 16-07-2017, 06:46   #6
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Re: Plastic through hull replacement?

I'm not familiar with the True Design but it looks like it is made the same/similar to the Marelon. Marelon would be more than adequate. Bronze would be overkill for an above the water thru-hull. I trust Marelon for below the waterline too. It is good that they may have some competition in the US now with the new one.
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Old 16-07-2017, 07:06   #7
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Re: Plastic through hull replacement?

The TrueDesign products have great documentation, which is nice to see. Impressive.
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Old 16-07-2017, 10:09   #8
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Re: Plastic through hull replacement?

I replaced my raw water intake thru-hull with marelon and I took it out after a couple of years.

Here's the issue: you need to keep the marelon valves greased at least every six months, see the literature. If you don't the valve is elastic and can set in a locked or unlocked position, a problem for someone who is 300 miles away from their boat and sails once or twice a month. Greasing a marelon valve can be challenging without a haul-out. So I replaced it with bronze.

Just my experience.
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Old 16-07-2017, 10:19   #9
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Re: Plastic through hull replacement?

Marelon is fine above the waterline. I have installed all Trudesign below the waterline. Raritan is the US supplier. I have seen some bits and parts on other websites (Defender, Fishermen supply). If you see it on the Trudesign website but don't see it on the Raritan website, contact them directly - they will make sure you can get it.

Very good reputation - ABYC certified -
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Old 16-07-2017, 11:58   #10
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Re: Plastic through hull replacement?

+1 for Trudesign.
They are not the same material as Marelon and don't have to be lubricated to stay functional.
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Old 16-07-2017, 14:09   #11
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Re: Plastic through hull replacement?

One thing about cockpit drains. You can pretty much be assured that they're too small, & too few in number, when the boat rolls out of the factory. Well, unless you have an open transom. So you might consider upsizing things. Especially when you consider how much cross sectional drainage area in them is lost to the internal hose barbs & such. Sometimes like 50%. And if in doubt, try stoppering up your current drains, filling up the cockpit, & then seeing how long it takes to drain Just a think.

Also, reflected UV can eat hoses as well, including from the inside out. And were it me, I'd plan on replacing 30yr old hose clamps, to perhaps be happily surprised to find them in good health. Which, the solid ones are far better than the slotted sort.

Do the current through hulls have valves, or seacocks? Kinda' seems like they should given their described location.
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Old 16-07-2017, 22:26   #12
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Re: Plastic through hull replacement?

No, no sea cocks. I watched closely when I was on a day sail today, and both were under water both under sail and motor. I bet the crockpot drains are too. So yeah, probably should have sea cocks. Hoses and clamps are fairly new though.
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Old 16-07-2017, 22:28   #13
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Re: Plastic through hull replacement?

Do the Trudesign seacocks require the same type of backer plate that bronze ones do? Their literature seems to imply that they do not, since they use a "load bearing collar" instead.
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Old 16-07-2017, 23:53   #14
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Re: Plastic through hull replacement?

They do come with a standard nut, the load bearing collar is an innovation mainly when using a sea cock valve as well, it's there to help with strength should the valve be kicked or other un for see able impact event ,

I have used these thru hulls and valves and have never had to lubricate them, also a word of caution re the posts using "bronze" there's many so called manufacturers/re sellers using that term loosely, the correct marine bronze fittings are getting harder to find even companies like Defender Marine sell under quality Bronze fittings such as Apollo fittings which are mostly not suitable for under water marine use , only one or two as advertised are true certified Bronze(you need to really read the fine print) as to the difference which ones carry a certificate,

Cheers Steve
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Old 17-07-2017, 01:02   #15
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Re: Plastic through hull replacement?

I think that the idea behind a (proper) seacock is that even if the through hull mushroom fails, the bolts holding the seacock onto the backer plate & hull will keep it in place. And thus the skin fitting won't leak. This as opposed to what happens when/if a through hull mushroom fitting with an attached valve fails. As that's an automatic invite for Neptune to take up residence inside of the boat.

The collars are intriguing though. Lots of new ideas showing up every time I blink. Load Bearing Collars | TRUDESIGN

PS: Add "buy or make soft wood plugs" to your chores list. So that you have a few spares, in addition to the ones which you'll be tying to the valve stems/bodies.
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