Marelon Thru-Hulls

[Warren Milberg]

My H28.5 has four white Marelon thru-hulls. All are a foot or more above the waterline (anchor well drain, fresh water tank vent, holding tank vent, and bilge pump outlet). After a recent sail in breezy and wavy conditions, I found that one of the thru-hulls at the bow had been punched in and I had a bit of water get in as a result. I have since checked the other 3 and found one where the mushroom disintegrated when tapped with a screw driver handle. My guess is these Marelon thru-hulls have deteriorated with age and exposure to UV rays. I suggest that everyone who has similar thru hulls on an aging boat inspect and replace any that have given up the ghost. Nothing lasts forever....

 

[wetass]

Are you sure they were Marelon and not plain old plastic - Should say RC Marine or Marelon on them. I have seen plain plastic ones like those from Perko disintegrate, but never a real Marelon one - Could happen though I guess.

 

[mitiempo]

I too would bet they were either nylon or more probably plastic and not Marelon which is about as durable as the hull it attaches to. If they were all above the waterline most builders wouldn't use Marelon.

 

[Scott T-Bird]

I'm surprised by that because I, too, have marelon thru holes and have found absolutely no degradation. The age of the boat is 27 years now. I look at them pretty carefully whenever I scrub the bottom (when in water) and when dry stored in the winter. The smaller ones which have a flange on the outside are the bilge and 2 cockpit drains (just under the stern at waterline), the galley sink drain below waterline, the head sink drain at waterline, and the anchor drain above waterline.

My tank vents were chrome plated and were pitting so I replaced them with SS vents. 2 are on the stern next to the chainplates (for fuel tank and water tank) and the holding tank vent is in the anchor well.

 

[Maine Sail]

My H28.5 has four white Marelon thru-hulls. All are a foot or more above the waterline (anchor well drain, fresh water tank vent, holding tank vent, and bilge pump outlet). After a recent sail in breezy and wavy conditions, I found that one of the thru-hulls at the bow had been punched in and I had a bit of water get in as a result. I have since checked the other 3 and found one where the mushroom disintegrated when tapped with a screw driver handle. My guess is these Marelon thru-hulls have deteriorated with age and exposure to UV rays. I suggest that everyone who has similar thru hulls on an aging boat inspect and replace any that have given up the ghost. Nothing lasts forever....

Those are most likely not Marelon but more likely nylon or PVC thru-hull fittings. Marelon will not do that as it is a highly UV stabilized product. Lots of builders used Marelon below water then nylon or PVC above water to save money.

 

[Peggie Hall HeadMistress]

They sound like nylon to me

Too many people are too quick to assume that any plastic thru-hull has be marelon...when in fact, at least 90% of those that were OEM installed are nylon, which has -0- UV inhibitors in it.They're above waterline, so there's no safety issue, and nylon is a LOT cheaper and won't fail till the boat is well past factory warranty.

So Warren...the affordable solution to your problem: replace 'em with REAL marelon.

 

[Warren Milberg]

Great responses. I am really not sure if the old disintegrated thru-hulls were Marelon or not (they went direclty into the dumpster), but the replacements were clearly marked Marelon. In any event, still a good idea to check these kinds of thru-hulls if you have an aging boat like mine.

 

[Gunni]

I've experienced the same deterioration. Originally painted (to provide UV protection?) they turned chalky and crumbled where the paint fell away. Mine were Perko thru-hulls. All were well above the waterline, but need to go during lay-up this winter.

 

[Warren Milberg]

Gunni: When the plastic/nylon or whatever material thru-hull failed on my boat recently, it was on a day when the wind and waves were really up on the bay. As a result, my boat was heeled to 25-35 deg most of the day -- and on the side where this particular thru-hull was located. It was a good 18" above the waterline, but due to to heel angle, it allowed a fair amount of water into the boat that soaked both my forepeak and main cabin berth cushions before the water ever got to the bilge to get pumped out. If you can change your disintegrating thru-hulls before haul out, I suggest doing it sooner rather than later. When I replaced mine, I did not have a second person handy to hold the new thru-hull in place while I tightened the nut on the inside. What I did was place the new thru-hull mushroom down on a strip of duck tape, applied a bit of cault to the inside rim, then slid it in place and pressed the duck tape to topsides to hold it there. On the inside, I put a bit more caulk on the perimeter of the new thru hull and then tightened the nut. I then removed the duck tape on the hull, and smoothed out the excess caulk.