Thru-hull discussion - Upgrades and issues

[jonelli]

I'm sure this has been beaten to death, and I've already had the lectures from others "never use plastic anything or you'll die!".
My 87 MkII has all maralon through hull fittings and what appears to be Forespar 850 series ball valves.
I'm guessing the thru-hulls are original looking at them. I suppose the ball valves could be original too. What I've noticed is that most of my thru's and valves look like this:

From the research I've done, it looks like like most of that is typical except for the missing backing plate? And I've noticed that this one in the picture is upsidedown, but not sure that matters much in this situation.

This is Forespar's instructions:

Since all of mine are very likely the original ones, I should probably change them, even if they appear to be working. Opinions?
Next, for same the price of the same maralon thru hull and same ball valve, it's almost a no-brainer to use the newer 93 series since the cost is so close anyway.

Lastly, what about the backing plates? Why don't I see any backing plates? Was this normal on Catalinas? are they just glassed in and it's okay to use without? The instructions for the 93 series say they require a large flat surface and always recommend backing plates. Do we need extra backing plates? Has anyone installed these 93's on their 30 and have pics?

Open to opinions/advice/discussions or even links to previously discussed info.
Thanks!

 

[jonelli]

Nobody responded to this discussion so far. So, I'll ask ask a specific question.. Is the bulgy fiberglass around the thru-hull enough to double as a backing plate? Or would you still want an additional backing plate? Is the backing plate simply to take some forces away from breaking at the hull?

 

[Don S/V ILLusion]

While you will likely never have a problem without backing plates, it’s always preferable to install them.
Is a $5 backing plate worth potentially saving your boat or your life?

 

[Hayden Watson]

I upgraded all four on my Mk2 C30 to those thru-hulls a year ago and am very happy with them. One thing to note is that you cannot use the flush thru-hull fitting on a Mk2 because of the flush countersink that is built into the hull with is different than the profile on the Marlon fitting.

 

[Hayden Watson]

Here is a link to a very long thread that has a full discussion of the problems and fixes that I went through to get the Marelon thru-hulls installed. 3 out of 4 of mine leaked when I launched and that was because I followed the instructions from Marelon and used Teflon tape to seal the threads. given the buttress threads, Teflon does not seal adequately. I used a brush on paste type thread compound to reseal and have not had any further problems. In post #8 I provided a drawing about how the cast-in recess can be resolved with a mushroom head.
Note that all of mine leaked with Teflon Tape but I ended up backing the valve almost all of the way off the threads and smeared on pipe dope and retightened and have had no further leaks.

After all of the trauma would I use the Marelon flanged seacock again. Yep, but not ever with Teflon tape regardless of what the instructions say.

 

[Kings Gambit]

I’ve read in an American Boat and Yacht Council statement that thru-hulls and seacocks/ball valves, etc., should withstand a few to several pounds of lateral (side) static force w/o snapping. If something struck or pushed against your assembly as high as the valve arm with 500# force would it hold? Here’s my Groco upgrade.
.

 

[Hayden Watson]

I’ve read in an American Boat and Yacht Council statement that thru-hulls and seacocks/ball valves, etc., should withstand a few to several pounds of lateral (side) static force w/o snapping. If something struck or pushed against your assembly as high as the valve arm with 500# force would it hold? Here’s my Groco upgrade.
.

This is correct. The Marelon flanged seacock in 1/2"ø and 3/4"ø exceed the required 500# for 30-seconds static testing. And they cannot be damaged by electrolysis or galvanic corrosion.

 

[Hayden Watson]

I’ve read in an American Boat and Yacht Council statement that thru-hulls and seacocks/ball valves, etc., should withstand a few to several pounds of lateral (side) static force w/o snapping. If something struck or pushed against your assembly as high as the valve arm with 500# force would it hold? Here’s my Groco upgrade.
.

In this testing video, the smallest Marelon flanged seacock broke at 750# which interestingly is the same value that he tested a Groco flanged seacock. I have not seen any testing on a ball valve mounted on a bronze thru-hull but given that a flanged seacock broke at 750# I would suspect that the thru-hull would not be as strong and might not meet the requirement. There is a reason why ABYC has recommendations for only flanged seacocks below the waterline.

 

[JamesG161]

Look here for the HOW To...
Seacock & Thru-Hull Primer/Pre Information by Compass Marine How To

Jim...

 

[Ralph Johnstone]

Teflon does not seal adequately. I used a brush on paste type thread compound to reseal and have not had any further problems.

Interesting you should mention this.

What most people outside the engineering world don't realize is that teflon tape "is no screaming hell for sealing pipe threads." It only has one claim to fame "It's not messy like paste sealants."

I would never use teflon tape by itself on pipe threads on my boat. Teflon tape used with a light surface wipe of paste sealant exceeds the sealing ability of either when used alone. If the joint's in a hidden location, I use Permatex #2 over teflon tape which looks like hell as the black Permatex smears badly. This is an industry standard. This is the best sealant against leakage particularly against salt water on bronze valves which show green verdigris even after several years of no staining. If it's on display, I use white teflon paste as a smear over tape to keep everything nice and white.

 

[JamesG161]

Teflon tape

Was developed to reduce the friction heat build up when tightening, Stainless to Stainless threads.

Evert time I have said "Teflon Tape" is not a leak preventative, I get clobbered by others.

Ralph's comment is Spot on!!!
Thanks again to my hero, @Ralph Johnstone

Jim...

 

[Ralph Johnstone]

Thanks again to my hero, @Ralph Johnstone

Please, just send money .

 

[Hayden Watson]

Yep, I agree and never even considered using Teflon tape until after the call with the Marelon tech department where they impaticaly told me that Teflon tape was what they wanted me to use.
That was the whole reason for the thread, to warn others from doing what Marelon told them to do for install.

 

[jonelli]

Okay, I’ve read through Mainsails seacock primer. There’s a lot of talk about flanged seacocks and thread mismatches. That is all good info but I’d like to swing this conversation over to a First-Time-thru-hull-analysis for a capable boater who has never dealt with them before. More general info if possible. I won’t use Teflon.

I have an 87 mkII with very likely original Maralon thru hullls. The Maralon 850 series ball valves may or may not be original. All the ball valves work currently. So, specifically asking about my Cat30 with Maralon hardware:

1 - do I need to change the thru hulls at any point???? And WHEN exactly is that point? There doesn’t seem to be much guidance for Maralon. Are they good forever?

2 - there are no visible backing plates on the existing thru hulls. Just the built up glass bump that is part of the boat. Is that bad? Do I need to take action next haul?

3 - if I do decide to refit thru hulls and valves, I feel like Maralon is a great choice. The newer 93 series from forespar look great. Hayden has provided some great input about those. Is there any other consideration?

4 - lastly, what about the other “holes”? Two sensors and the direct pump head hole? Those are all different. The main 4 I have are: engine, macerator, galley sink, head sink. Those are all the same. Should I ignore the others?

 

[Hayden Watson]

Okay, I’ve read through Mainsails seacock primer. There’s a lot of talk about flanged seacocks and thread mismatches. That is all good info but I’d like to swing this conversation over to a First-Time-thru-hull-analysis for a capable boater who has never dealt with them before. More general info if possible. I won’t use Teflon.

I have an 87 mkII with very likely original Maralon thru hullls. The Maralon 850 series ball valves may or may not be original. All the ball valves work currently. So, specifically asking about my Cat30 with Maralon hardware:

1 - do I need to change the thru hulls at any point???? And WHEN exactly is that point? There doesn’t seem to be much guidance for Maralon. Are they good forever?

2 - there are no visible backing plates on the existing thru hulls. Just the built up glass bump that is part of the boat. Is that bad? Do I need to take action next haul?

3 - if I do decide to refit thru hulls and valves, I feel like Maralon is a great choice. The newer 93 series from forespar look great. Hayden has provided some great input about those. Is there any other consideration?

4 - lastly, what about the other “holes”? Two sensors and the direct pump head hole? Those are all different. The main 4 I have are: engine, macerator, galley sink, head sink. Those are all the same. Should I ignore the others?

I will try to answer but this is just my opinion. and your mileage may vary. FWIW, on my 88 the 850 ball valve was OEM.

1. The Marelon tech says they are good forever. (Of course, that was the same guy who told me to use Teflon tape.) I know that other types of plastic get brittle over time. Couple that with the fact that the OEM install used bear thru-hulls without backing or flanged seacocks I just at my last haulout i decided that it was time for me to change them. I only need to haul every 8-9 years, so it was now or another decade.
2. There are no backing plates on the C30 Mk2 and the mound that you see is not any thicker than the rest of the hull. It is the result of the large countersink that is cast into the hull. I cut out backing plates from some marine ply I had on hand, coated them with epoxy resin and attached them over the hump with thickened epoxy resin.

3. The factory recess is a challenge because the flush mount recess doesn't have the large flange that was on the OEM. I could have built up the hole on the outside but that would have required a lot of grinding for a proper bevel and then filling with many layers of glass. Instead, I mounted the mushroom head in the bottom of the recess. The top of it was just about flush with the surface of the hull. that leaves a donut recess around the mushroom. I filled that recess with pre-thickened G-flex epoxy which I had on hand for filling the small Catalina smile, so I filled it with that. It could also be filled with an underwater fairing compound.
I replaced all four with the series 93.

 

[Member 142719]

Here is a link to a very long thread that has a full discussion of the problems and fixes that I went through to get the Marelon thru-hulls installed. 3 out of 4 of mine leaked when I launched and that was because I followed the instructions from Marelon and used Teflon tape to seal the threads. given the buttress threads, Teflon does not seal adequately. I used a brush on paste type thread compound to reseal and have not had any further problems. In post #8 I provided a drawing about how the cast-in recess can be resolved with a mushroom head.
Note that all of mine leaked with Teflon Tape but I ended up backing the valve almost all of the way off the threads and smeared on pipe dope and retightened and have had no further leaks.

After all of the trauma would I use the Marelon flanged seacock again. Yep, but not ever with Teflon tape regardless of what the instructions say.

Having experience in working in a power plant and doing piping work, I would like to give you a warning on using paste style sealants on plastic fittings. Many liquid or paste style sealants have a warning on the label. DO NOT USE THIS PRODUCT ON PLASTIC OR COMPOUND FITTINGS. So I would go back and read the label for the product you are using and ensure that the sealant is compatible with plastics.

 

[jonelli]

Thanks Hayden for the detailed explanation!
I'm still unsure what I “need” to do next time I pull the boat out. I’m planning on pulling it out next year because my bottom paint already looks crappy and it’s only 2 years. Going to invest in better paint and get a couple small blisters filled. That’s about it.
I might try dropping the rudder and replacing the bushing washers.
I HAVE to address one valve that is attached directly to a sea strainer. There’s a rusting metal coupler between them, so that will get sorted probably sooner than later while it’s even in the water.
Other than that, I have no desire to change through hulls for no good reason if they should be fine for another 30 years. There are many other torturous projects I can think of. Maybe change some of the ball valves if needed but they still all seem fine to me.
So if someone can tell me that I should replace them for any specific reason I’m listening. Should I just add backing plates to them? Is that even possible with OEM thru hulls? Will that backing nut even come off?
should I bother?

 

[Hayden Watson]

Thanks Hayden for the detailed explanation!
I'm still unsure what I “need” to do next time I pull the boat out. I’m planning on pulling it out next year because my bottom paint already looks crappy and it’s only 2 years. Going to invest in better paint and get a couple small blisters filled. That’s about it.
I might try dropping the rudder and replacing the bushing washers.
I HAVE to address one valve that is attached directly to a sea strainer. There’s a rusting metal coupler between them, so that will get sorted probably sooner than later while it’s even in the water.
Other than that, I have no desire to change through hulls for no good reason if they should be fine for another 30 years. There are many other torturous projects I can think of. Maybe change some of the ball valves if needed but they still all seem fine to me.
So if someone can tell me that I should replace them for any specific reason I’m listening. Should I just add backing plates to them? Is that even possible with OEM thru hulls? Will that backing nut even come off?
should I bother?

Backing plates are for the purpose of providing a reinforced base for the flange to lever again. Given that, the thru-hull with a non-flanged ball valve will not benifit from adding a backing plate. The difference between the OEM installation and any type of flanged seacock is in how the load it placed on the thru-hull fitting. In the OEM thru-hull with ball valve, a sideways load to the top of the valve will BEND the thru-hull. The same load on a flanged seacock will not bend the thru-hull, it will PULL on the thru-hull and push down on the flange and backing plate. In engineering speak, the flange creates a moment couple with equal and opposite tension and compression forces.
The ball valve bends the pipe section of the thru-hull and that is the weakness. pipes are much much stronger in tension then they are in bending so any flanged seacock will be much stronger than any ball valve.
As to the question of whether YOU need to change to get the increased strength, only you can answer that question.

 

[jonelli]

Hayden, thanks again for responding. Seems like conversation between me and you! Lol
I understand the physics behind it all.
My concerns or questions are directed to the experiences everyone’s had with their oem thru hulls.
i mean I’m assuming everybody else has these. Did everyone else change them?

 

[Ward H]

@jonelli
I had missed this thread back in Oct so thought not too late to answer your question above.
As for me I did change all of my OEM Marelon ball valves back in 2019. Here's a link to my thread from back then.
Marelon Ball Valve Seacocks

However, after a year those 93 series ball valves stiffened up a bit I got nervous as they seemed to flex a bit. My wife won't even touch them. And then I found another test by @Maine Sail on Marelon Thru Hulls where the mushroom head failed.

Even though I used the flush fit thru hull I decided to improve the thru hulls even more.

Last spring I planned to upgrade further to Series 93 OEM Flanged Seacocks with the Buttress thread thru hull. Note: The buttress thread thru hulls have a much thicker body than the #251 thru hull that failed in the above video.
I special ordered two but they came in too late for me to install. I did find one with a mushroom head on Defender and installed that for a new AC water intake.
That new valve feels so secure I'll replacing the three remaining ball valves with the Series 93 flanged seacocks and thru hulls this spring.
I'll follow @Hayden Watson 's procedure for using the mushroom head thru hulls.

Edit to add: I already have backing plates cut from 1/4" G10 for this job.