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PVC Elbow Thru-hull Replacement

Cory B

Sustaining Member
Hi everyone,

Our insurance company has asked us to replace the pvc elbow on the pump-overboard thru-hull on our boat. I know some of you have already done this. To save time and money, I was wondering if anyone had simply "unscrewed" the pvc elbow from the thruhull, and replaced it with something else, instead of replacing the thruhull or installing a new one. It looks like there may have been a little pvc cement applied to the fittings... how strongly does it bond to the thruhull itself? We'd replace the elbow and valve with of 90 degree Marelon valve fitting.
 

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treilley

Sustaining Partner
PVC cement effectively melts the plastic in order to form a bond so getting these apart without destroying them would be difficult. The link you provide shows an elbow that is NPT on one end and hose barb on the other. In order to use this you would have to screw the marelon valve dirrectly to the through hull and then attach the elbow to the other side of the valve for your hose to connect to. Hopefully the hose is long enough although there is probably not enough room in the compartment to do this. Also, I do not believe Forespar makes a M to F NPT elbow to directly replace your PVC elbow.

I think mine has a bronze elbow on teh original marelon through hull going to a blonze ball valve.
 
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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Take a look at the Forespar model in the picture in reply #3 in this thread:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=1138&referrerid=28

I would say that it's that or an equivalent bronze one-piece valve and base. No more worries about insurance or breaking the old valve-on-an-elbow scheme that Ericson used.

What you have is typical of the install from mid-late 80's Ericsons, including the setup we replaced in the head compartment on our Olson.

Loren
 
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u079721

Contributing Partner
Well first I'm not sure there will be a problem with the cement, because I don't think the nylon filled plastic of the Marelon valve is sensitive to the solvent the way the PVC pipe is. (But is the through hull PVC too?)

But I would be very uncomfortable having an elbow upstream of the valve, as I would worry that I would be stressing the elbow every time I operated the valve - scary stuff, even if it IS a Marelon elbow. Ball valves mounted on through hulls aren't really seacocks anyway, even if they were original equipment on most of our Ericsons. But a load bearing elbow just makes things worse.

The other thing I have seen inspectors write up boats for is someone putting a bronze elbow or nipple into a Marelon valve. The coefficient of expansion of the bronze is greater than for the plastic, and you could crack the plastic fitting that way. Putting a plastic nipple inside a bronze valve also isn't great, but seems to be less of a concern.
 

rwthomas1

Sustaining Partner
Looks a lot like my E38. Heres how I did it:

Yes, not a "true" seacock but there is no way to install one in the space. I could eliminate it but actually think the ability to pump over board is a good thing when allowed. RT
 

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chaco

Member III
Whoa Baby !

Look what you got us in to now Olley !
1. What is the ThruHull construction ? Brass is most common, nylon is next.

Most likely PVC glue was not used. This is a replacement 90 on an existing Brass ThruHull. Pick at it with an Awl. See if it is pliable = pipe sealant. These ThruHulls are Straight Thread for the Hull Nut and Tapered Thread on top for the Pipe Fitting. PVC glue is rarely used on threaded fittings and will not stick to brass, marelon or nylon. But....PVC is really Britle. VERY gently see if you can unscrew the 90 from the ThruHull. Be ready with a Tapered Plug for the removal. Replace the 90 with brass or Marelon. Next time you are Hauled replace the ThruHull with a SeaCock. ThruHulls are no longer considered good Marine Construction Practice. Check it all out on www.groco.net

Happy DRY Bilge :egrin: :egrin:
 

Maine Sail

Member III
Look what you got us in to now Olley !
1. What is the ThruHull construction ? Brass is most common, nylon is next.


I think you meant bronze as brass is never suitable for a thru-hull. I also don't recall ever seeing one other than a few red brass models imported from China. Red brass is much more corrosion resistant than yellow brass and contains less than 15% zinc where yellow brass contains as much as 40% zinc. That being said Groco, Perko & Apollo, the most popular manufacturers, all make bronze thru-hulls not brass..

It's actually good to see insurance companies beginning to require industry standards are adhered to especially with thru-hulls & seacocks. Sorry you have to do this project but it is the right thing to do..
 

Tom Metzger

Sustaining Partner
Very bad idea

Putting a plastic nipple inside a bronze valve also isn't great, but seems to be less of a concern.<!-- / message --><!-- sig -->

I have to argue with this one. I was on Hunter 40 several years go in a heavy chop in the New York City harbor when a 3/4" bronze valve popped off of the plastic thru hull. Fortunately someone was below at the time and saw the water coming through the floor boards. Screwing it back on made for an easy fix, but lots of pumping to get a lot of water out of the boat.
 

u079721

Contributing Partner
I have to argue with this one. I was on Hunter 40 several years go in a heavy chop in the New York City harbor when a 3/4" bronze valve popped off of the plastic thru hull. Fortunately someone was below at the time and saw the water coming through the floor boards. Screwing it back on made for an easy fix, but lots of pumping to get a lot of water out of the boat.


Actually Tom I never thought about the case where one would mount a bronze sea cock or ball valve on a plastic through hull - I was thinking of the common (at least to me) sight of someone using a plastic nipple or elbow in the bronze sea sock. In that case there would at least not be the risk of the plastic expanding faster than the bronze, and cracking it - which can be a risk with the reverse. But your point brings up a whole 'nother issue - the compatibility of the threads of plastic vs metal. I wonder if that bronze valve even matched the threads of the through hull?
 
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Tom Metzger

Sustaining Partner
I wonder if that bronze valve even matched the threads of the through hull?

The pipe threads are pipe threads whether in bronze or plastic. No problem matching them. I have no idea if both were straight or tapered.

The problem is the two materials working against each other. The softer plastic deforms and can eventually separate.

Ironic that I was writing about sinking in the NY harbor at the same time as US Airways plane crashes in the harbor. Fortunately everyone survived both occasions.
 

Maine Sail

Member III
The pipe threads are pipe threads whether in bronze or plastic. No problem matching them. I have no idea if both were straight or tapered.

Will they thread together? Yes. Should NPS & NPT be used together? Not a good idea.. Most thru-hulls unless special ordered as combination thread, are straight threaded and most ball valves are tapered thread..


NPS to NPT (LEFT SIDE) NPT to NPT (RIGHT SIDE)
91533235.jpg
 
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CapnTommy

Junior Member
This is my first post so here goes. I am a SAMS surveyor in south Fl. The picture looks like a similar arrangement to my 82 38'. First NEVER use white plastic thru hull fittings under the waterline. Marlon is a good option. Second NEVER put a valve on a plastic thru hull even above the waterline. The stress will eventually lead to a failure. Be advised that ABYC recommends a valve on all thru hull fittings of course below but also in the topsides of a sailing vessel due to heel, therefore Bronze or Marlon are the options available. Further Marlon fittings are straight and most ball valves (not seacocks) are commonly tapered. If you use Marlon, a very good option, use all Marlon components to a point where hose is used. If you use Bronze use all bronze-period and scrutinize the thread type. PVC valves below the waterline and even PVC fittings below the WL for that matter are for K-Mart sailors. This is a very important area from a safety standpoint.
Hope this clears up things
CapnT
 
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