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Discussion Starter #1
I have a 1972 Tartan 30 and am replacing ball valves with sea cocks or flanged adapters. My problem is three of the thru hulls are tapered flush fit 1/2 inch thru hulls. I cant find sea cocks or flanged adapters in anything smaller than 3/4. Any suggestions?
 

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Bore the hole bigger? You can put any size hose barb on the 3/4” flanged adapter.
 

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A 1/2" seacock won't pass very much water if you get even a little bit of growth in the line. I've always felt 3/4" was the minimum anytime I was adding a seacock.
 

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Discussion Starter #6
Thanks...I would prefer the 3/4 but these are flush mounted and the hull was fabricated to fit the taper. If a 3/4 thru hull has the same flange diameter it might work. Otherwize they will have to be re glassed and drilled...something I am trying to avoid.
 

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A 1/2" seacock won't pass very much water if you get even a little bit of growth in the line. I've always felt 3/4" was the minimum anytime I was adding a seacock.
I’ve never—in the 23 years I’ve owned my current 35’ boat—had a problem with growth in my 1/2” raw water intake. I have, however, had a problem with weeds getting hung up at the elbows in the line—and that is only within the past 3 years when an invasive weed species showed up near my shallow water dock.

The new weed has a stiff, open structure, like a Tuffy scrubbing pad. This kind of weed will allow water to flow through, until something like eel grass get sucked in and forms a plug when it piles up against the open structure weed. This is a problem when the blockage is ahead of the raw water strainer.

My solution was to realign the raw water strainer for ready access and to eliminate the elbow at the thru-hull.

My bottom line: You can keep your 1/2” line, but you might want to look at eliminating any elbows that are not absolutely necessary.
 

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Thanks...I would prefer the 3/4 but these are flush mounted and the hull was fabricated to fit the taper. If a 3/4 thru hull has the same flange diameter it might work. Otherwize they will have to be re glassed and drilled...something I am trying to avoid.
Understood. However, you're also dependent on the next manufacturer of the 1/2" thru-hull having the same outer dimensions as your last, not just the penetration dimension.

I'd glass in the recesses and give up on the flush mount, for exactly the problem you're experiencing. The absolute last thing I would do is buy any off the wall thru hull, just because it fit. If you're spending money on new thru hulls, top quality is the only way to go.
 

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Discussion Starter #9
I agree...fix it right the first time because youll just have to do it again. And maybe not under easy circumstances.
 

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You might be looking at a thru hull and seacock going 30ish years. Throw your own guess out there...
If youre replacing any, youll pro ably never do it again.
I wouldnt go too anal on..some things
 

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You might be looking at a thru hull and seacock going 30ish years....
A quality bronze thru-hull will last that long, which is why you do it right and never think about it again. There are low end versions that literally recommend inspection/replacement every 5 years.
 

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Discussion Starter #12
Ok so I can put in 3/4 flush Buck Algonqin thru hulls, same tapered flange, just bigger hole. So that is what I am going to do, but... Now a question: I also came across 1/2 NPS thread tap. Wondering if tapping the NPT female side of a ball valve that is currently NPT would work? Would it allow more threads to contact? I am probably going to try it on an old gate valve that I can throw away when done. Just to see if it solves the old "cant mix nps with npt" problem. Anyone done this? Tap is about $24 bucks so this isnt a money saving route unless you could do 3 or 4.
 

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I would not recut the threads. Just get the proper flanged adapter for the inside.
 
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