Through Hulls: Plastic vs Metal

[bcboomer]

canajun
Hopefully your through hulls are marelon, not plastic.
At any rate you should look at Trudesign valves and through hulls. They are certified and when you epoxy in their through hull it becomes part of the hull.
With the reinforcing sleeve they will take a 500 lb force. I don't see any reason to stick with bronze any more than I would go back to cedar over oak frames.
An added bonus is no more worries about corrosion.

[onestepcsy37]

Originally Posted by a64pilot

Least not on the underwater part, now if above the water line and we are talking about the discharge ports that are normally plastic, then yes the SS ones are pretty

You are correct. In fact I just remembered I did install a stainless thruhull on my boat, but as you say, its above water. Its the vent for the holding tank and at least 3ft above wl.

[SVTatia]

Originally Posted by Toaster

... I had a bronze valve fail in my hands - in dry dock as I was doing "maintenance" on it....

That was most likely brass, not bronze.

Originally Posted by Toaster

Marlon needs regular lubrication (mineral oil, etc) and regular operation, at least every few months they should be opened/closed. And they need to be installed correctly with a mounting plate, bolts, etc. It's non-trivial.

The same is needed for bronze, but sea-cock grease would be used. In any case, hopefully one would be closing the sea-cocks more often than every few months...

I used Marelon thru hulls and sea-cocks on my previous (steel) boat for many years and never had a problem.

One important note is to keep them equal: Marelon thru hulls with Marelon sea-cocks and likewise for bronze. Never mix them.

[Cheechako]

Bronze. No steel, no plastic.

[MarkJ]

Now just before you go off and use the good advice given by some other posters... Do your FULL calculations before you set your heart on shippings best products.

Bronze fittings for a 1 inch through hull will cost you more than $120. Thats for the thru-hull, valve, bend, and hose barb.

Now how many do you have to do???

Marelon is MUCH more expensive. The valve by itself is nearly $120.

So what does a "few" dollars mean when its your "safety at stake"? Determined by the value of your boat, where you sail it and how long you intend to keep it, and of course how many you are replacing.

Next week I haul and replace 14 of them, thats the lot! And its very expensive. But my boat takes me accross oceans for long periods, and longer periods away from dock yards.

So check to see if you actually need a new valve because of corrosion or if its just the handle wont turn. If you have no corrosion the replace what you need to, but if yours are corroded in the middle you may need to replace the whole unit, or all the units on your boat if electrolysis has gotten in.

[osirissail]

Originally Posted by rwidman

I would not use "plastic" below the waterline but some "Marelon" fittings and valves are approved for this use.

I have bronze below the waterline and Marelon above. Works for me.

There is a problem with nomenclature here - "Plastic" normally refers to PVC or ABS rigid plastic polymers which can fracture and break easily. Neither of these characteristics is good for below the waterline thru-hull fittings.

However. some people refer to Marelon as "plastic" which they are not! They are made from a advanced fiberglass material that is considerably stronger and will not crack or break like "plastic" thru-hulls. As such they are rated for use below the waterline. And two of the major boat manufacturers use Marelon below the waterline instead of metal.

Marelon versus metal ?? - The only differences I perceive is in the fact that Bronze Thru-hulls are subject to dezincafication and subsequent failure. This can happen fairly rapidly if stray electrolysis currents are present. Second, the Bronze can "stick" or make opening and closing very difficult if not impossible unless lubricated periodically. Same with Marelon but to a lesser degree in my experience with Marelon over 25 years of using them. Thirdly, metal thru-hulls can be hazardous to your health (or your boat's) during a lightning strike whereby Marelon is not because it is non-conductive.

[rwidman]

Originally Posted by osirissail

.............. However. some people refer to Marelon as "plastic" which they are not! ...........

They should know better.

Marelon® is a proprietary formulation of polymar composite compounds using composite reinforced polymer and additives to produce a superior marine-grade product.

What Is Marelon

[Rainh2o2]

If you can get away with it, consider doing away with below waterline thru hulls entirely. I got rid of mine and I sleep better knowing they won't fail.

Sent from my SM-T320 using Cruisers Sailing Forum mobile app

[Orion Jim]

My boat is 31 years old and still has the original bronze Spartan cone type seacocks. They are serviced annually and are fully bonded. There is zero evidence of dezincification and I have not had a direct lightning strike.....some very closeby though. I would replace them with new Spartan seacocks without hesitation.

[onestepcsy37]

Originally Posted by Jim Walsh

My boat is 31 years old and still has the original bronze Spartan cone type seacocks. They are serviced annually and are fully bonded. There is zero evidence of dezincification and I have not had a direct lightning strike.....some very closeby though. I would replace them with new Spartan seacocks without hesitation.

My boat is 36 years old and still has the original wilcox crittenden cone type bronze seacocks. They are fully serviced every couple of years and are NOT bonded. There is zero evidence of dezincification and I HAD a direct hit by lightning two years ago. Cant buy new ones anymore.

[Drakenkade]

My b&g forward scan came with what looks like stainless thru-hull??

[capt jgw]

Originally Posted by RaymondR

Stainless steel?

Not below the waterline. It's exactly the wrong material for most uses below water. Because it's so much cheaper and shiny pretty the makers have brainwashed people into thinking stainless is the ultimate material for everything. It is not.

[capt jgw]

Originally Posted by onestepcsy37

My boat is 36 years old and still has the original wilcox crittenden cone type bronze seacocks. They are fully serviced every couple of years and are NOT bonded. There is zero evidence of dezincification and I HAD a direct hit by lightning two years ago. Cant buy new ones anymore.

Mine's 50 years old and has Groco tapered plug bronze seacocks. They are still in perfect shape. The dumbass builders mated them with white plastic through hull fittings, but I corrected that. Now bronze on bronze. They don't make them anymore but the Spartan brand are almost the same and are still available. $750 each though.