The cult of the Proper Flanged Thru-hull

[OneBoatman]

To Tetepare. I've mostly only see boats sink in the movies but a leak by definition is always below the waterline and given enough time the weight of the vessel increases due to fact that water is heavier than air. The leak continues and the waterline keeps getting higher and higher until the boat sinks unless there a watertight bulkhead limiting the increase in weight and there remains sufficient reserve buoyancy.

[svislandgirl]

We recently replaced all 10 of our original 30yo thru hulls which were ball valves with no backer block. It was truly a pain, but we did discover almost all the bedding had failed and they readily spun in the holes. Two were starting to fail just below the valve - could have been a nightmare - and one was frozen open on our main galley drain. Proper preparation prevents piss poor performance. Glad wwe got that done before we thru off the lines. .

[Simi 60]

Originally Posted by Sailorman97

I have 15 thru-hulls. Every single one of them is a thru-hull with a ball valve.

Wow, we are 60 ft with main engine, Genset, watermaker and 2 bathrooms.

We have 2 through hulls
Only 2.

[Simi 60]

On metal boats through hulls are usually pipe welded into the hull

On fiberglass and composite boats I have done essentially the same, fiberglass tube coved and glassed in making it part of the structure.

[svislandgirl]

I would think you would have 2 just for the water intake to cool your engine and similarly for your genset Do you not have thru hulls for any of your drains, gray water, or black tank?

[contrail]

Originally Posted by goboatingnow

CW602N brass from good quality manufacturers is entirely suitable for seawater and will remain suitable for decades . This is behind the DNZ marking ( CR)

There’s no field evidence that flanges are needed

The entire BVI charter industry, which includes hundreds of boats, would disagree. That material is only specified to last for five years, per EU certification, and often lasts much yes. It is a complete time bomb and articles have been written about how irresponsible it was for the EU to allow such junk, at only a minimum cost savings compared to proper bronze. If yours are more than a few years old, they almost certainly need to be changed, and, as others have mentioned, you will probably be able to break a few with your hand. Oh, and by the way, I broke a 1.5 ID thruhull made of this stuff, simply closing a well lubricated ball valve.

[boatpoker]

Originally Posted by svislandgirl

I would think you would have 2 just for the water intake to cool your engine and similarly for your genset Do you not have thru hulls for any of your drains, gray water, or black tank?

Two seachests would cover it. One in, one out. Any others well above (ABYC 4") the max heeled waterline do not require secocks.

[mvweebles]

Originally Posted by svislandgirl

I would think you would have 2 just for the water intake to cool your engine and similarly for your genset Do you not have thru hulls for any of your drains, gray water, or black tank?

I too have only two below-waterline thru-hulls with properly backed flanged seacocks. . Both oversized, easily accessible, and each seving an easily serviced oversized seastrainer with an oversized manifold (effectively a seachest) to serve multiple users. Both are in the engine room which has water tight bulkheads on either end. One of my pet peeves is having thru-hulls scattered throughout a boat, often with puny strainers (if any at all). I chose to centralize.

I have many above-waterline thru-hulls, each with proper loops, but only two below waterline.

[rslifkin]

I've got tons of above waterline thru hulls and 8 below waterline. Not particularly scattered though, as 7 of them are in the engine room and all are easily reachable (and most are fairly close together). Only exception is the intake for the forward head and anchor washdown (located under the forward head).

I certainly don't trust inadequately specified or installed hardware for thru hulls. I don't want stuff that'll probably last or hold up. I want stuff that will definitely last.

[Jammer]

Originally Posted by svislandgirl

Do you not have thru hulls for any of your drains, gray water, or black tank?

There is a school of thought in yacht design where sink/shower drains lead to a central sump box with a pump to send the waste overboard above the waterline. Usually this is done with a large-diaphragm pump with clog-resistant valves. These systems are not perfect and require maintenance, but reduce the risk of sinking the boat.

[pcmm]

As far as I'm concerned, there should be as few thruhulls below the waterline as possible. And the ones that are there should be absolutely bombproof!!!! The ABYC specs for seacocks is far superior (and more realistic) than the EU "Standard". Boats and the stuff inside get thrown around. The last thing you want are things banging against a weak assembly! I'm fully in the ABYC version of reality for seacocks!

Don't even get me started on how dangerous I think EU Propane assemblies are!

[rslifkin]

Originally Posted by Jammer

There is a school of thought in yacht design where sink/shower drains lead to a central sump box with a pump to send the waste overboard above the waterline. Usually this is done with a large-diaphragm pump with clog-resistant valves. These systems are not perfect and require maintenance, but reduce the risk of sinking the boat.

Depends on the boat too. On many powerboats the sinks are high enough to gravity drain above the waterline, for example. I'd bet that's the case on Simi's boat.

[mvweebles]

Originally Posted by Jammer

There is a school of thought in yacht design where sink/shower drains lead to a central sump box with a pump to send the waste overboard above the waterline. Usually this is done with a large-diaphragm pump with clog-resistant valves. These systems are not perfect and require maintenance, but reduce the risk of sinking the boat.

If discharge is below waterline, that certainly is an option. But let's be clear: these types of sumps tend to get pretty gross and smelly. If gravity is an option, a much better approach. Aa a reminder, any pump discharge needs a vented loop. I'd hazard a guess that a pump charging a siphon is more common reason for sinking than a failed seacock.

[s/v Jedi]

Originally Posted by Simi 60

On metal boats through hulls are usually pipe welded into the hull

On fiberglass and composite boats I have done essentially the same, fiberglass tube coved and glassed in making it part of the structure.

Those are called “standpipes” and should raise up to above waterline. They don’t require valves.

We have two watertight bulkheads and all seacocks in the bow and aft sections, which won’t sink the boat. All discharge is done through standpipes.

[Simi 60]

Originally Posted by s/v Jedi

Those are called “standpipes” and should raise up to above waterline. They don’t require valves.

We have two watertight bulkheads and all seacocks in the bow and aft sections, which won’t sink the boat. All discharge is done through standpipes.

Nope, had them come out of the hull no further than a skin fitting tail, threaded fiberglass tube, ball valve onto that.