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Old 30-04-2012, 14:23   #1
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PVC Manifold

Caliber 47 has a "sea chest" which is actually a fibre glass box siliconed to the side of the bilge at the same level as the starter motor.This is then connected with a 2" exhaust hose to a 2"seacock. Raw Water for the engine/gen and forward head come off the box.
It is virtually impossible to change the starter motor so I was thinking of removing the box and replacing with :-
a/ a bronze manifold with suitably sized offtakes - very expensive

b/ PVC or ABS pipe manifold.

Either of these could be easily removed for access.

What are the pro`s and cons of using PVC/ABS as a manifold ?
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Old 01-05-2012, 09:25   #2
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Re: PVC Manifold

Using PVC or ABC for a seawater manifold is generally a bad idea. PVC is brittle and as it ages it becomes even more brittle. ABS is similar property wise to PVC except gasoline, acetone, etc will dissolve it over time (a very short time). So not good...

CPVC/ CORZAN pipe is somewhat stronger and less brittle, but I generally I would not use it below the waterline except maybe in a aluminum hull...

Pex (cross linked polyethylene) might be OK to use below the water line. Its stronger, flexible, Heat resistant. Not sure I like the crimp connections, etc, but the material is strong enough for below water use. Good as marine hose anyway.. PEX is tubing so 1/2" pex will fit inside 1/2" PVC. Pipe is sized by the interior dimension, tube by the exterior dimension.

Bronze (not brass) is the way to go. Brass is copper- zinc based and the zinc can and will leach into the water over time. Happens even in domestic building plumbing. Just faster in seawater. Bronze is Copper -tin based and is reliable but $$$$.
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Old 01-05-2012, 09:54   #3
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Re: PVC Manifold

Yeah... what she said! I have had some issues even with schedule 80 PVC in industrial applications so dont trust it too much... seems like it should be good away from the sun but..... how often do you anticipate changing your starter? I've had sailboats for 40 years, all were used when purchased and the only starter I've taken off was to rebuild it prior to going on a cruise..... Then again... there are some notes of Yanmars starter issues on this forum.... Just sayin', if it's do-able but a pain... is the cure worth the effort?
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Old 01-05-2012, 10:26   #4
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Re: PVC Manifold

Is it impossible, or just a PITA ?? If its a PITA live with it cus the sea chest is better then messing about doing a bunch of work and spending big bucks on GOOD Bronze manifolding system, and ending up being able to change 1 starter easier just my 2 cents, but it seems like a negative fix to me !!
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Old 01-05-2012, 10:49   #5
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Re: PVC Manifold

If the sea chest is only siliconed to the bilge, cut it loose. And then build a mounting bracket where it can be remove easier.
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Old 01-05-2012, 14:20   #6
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Re: PVC Manifold

Guess you could use copper pipe and fittings. But hows your soldering??. Would not trust the new slip on "sharkbite", etc., type fittings below the waterline either, BTW. They work fine on domestic water, but would not trust it to float your boat.... They all use a single simple o-ring seal. Like Nasa I've not fond of single 0-ring seals. when they don't work it gets messy quick... Plus they are brass with that de-zincing issue...

One other thing about plastic pipe, its not fire rated. It will burn and melt far sooner then marine rubber hose. just fyi.
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Old 03-05-2012, 05:59   #7
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Re: PVC Manifold

Thanks for the input. I like the build a proper mounting bracket for existing chest to allow easier removal when(if) required.
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