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?

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

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.

Advantage of 1/2 seacock is that the boat sinks more slowly when the silly little bugger breaks off

Check trudesign.
I believe they offer 1/2

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.

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.

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.

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

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