Why through-hulls?

[Andrew Troup]

Originally Posted by Maine Sail

In a well built boat the thru-hull / seacock will be 100% isolated from the core. This builder seals the edges of the cut outs with solid glass strips then laminates in solid fiberglass sheet with VE resin to the thickness needed. This is for a Forespar Marelon OEM/93 Series seacock.. The hull is also infused...

Hmmm...

I'd personally rather see at least rounded corners to the inset panel, or better still a round insert, to avoid stress raisers.

Strikes me the builder could buy Micarta tube to make the sealing ring... it's available with either polyester or epoxy resin (or lay up their own around a mandrel)

[Pelagic]

Originally Posted by Andrew Troup

...The idea of situating such an 'armpit' under the keel (per the idea Noelex just posted) is novel and through provoking.

I can't use it myself as my planned keel swings into the hull, but I'm thinking of having a dedicated entry point for cooling water from the keelcase, which is effectively a big seachest, (mine will have a big enough lid to enable lifting the keel out) and which can never clog.

The Armpit analogy does not hold true Andrew.

It is a large Pipe section cut thru the skin of the hull with a large inspection hatch mounted on top for access.

As I said before, It offers no safety factor; the only difference is that the valved thru hulls are fitted to this pipe rather than directly thru to the hull skin.

Main reason for using is to induce large volumes of water thru a primary screen that can be used for firefighting, ballasting and cooling, simultaneously.

While the advantage of less suction appears to be a safety benefit a chronic problem with sea chests is that they can foul really badly very quickly with growth.*
Proper access means diving and removing heavy grate to get to the buildup under the basket. (Have done may times)*

I would not recommend incorporating a sea chest pipe within the keel.

You must always think of a grounding situation in mud or silt and whether you can still draw clean water to power yourself free or run a Gen.

Sea Chests and Thru hulls are ideally placed in the concave area between the ‘turn of the bilge’ and the keel line, so as to always be above the bottom, when you go aground and lean over

[Andrew Troup]

Pelagic

You misunderstand my proposal so comprehensively I'm not sure where to start.

I think you missed the bit where I explained that I was talking in terms of a swing keel: <<my planned keel swings into the hull>>

The retracted keel will be completely housed within the canoe body (which in the case under consideration, has a flat area around the keel case opening). There is consequently no concave area, and when I go aground, I will not in your words "lean over", not even a little bit.

Your opening assertion seems to depend on the definition you give in your second paragraph.

Your second paragraph is a description of one way of building a seachest, which is incompatible with the way I think a seachest should be built, so I suspect your first two paragraphs are circular reasoning along the lines of:

"A seachest cannot be built as a re-entrant part of the hull, because I am prescribing that it be built as a tack-on to a cut-out. The resulting sea-chest is nothing like an armpit".

I agree completely. That sort of sea-chest is more akin to an oral or nasal orifice than an armpit.

(steering carefully clear of any of the more procreational/recreational/lavatorial anatomical features !)

All I can say is: That is just one way of building a seachest.

I propose the seachest is better built as an integral part of the hull plating or skin, in the same way you'd build a recess for a stockless anchor.

But if it's OK to arbitrarily define the other guy's seachest to suit one's argument, I will adopt the same method <wink>: I hereby declare your type of seachest to be an oversized standpipe, with side-entry hose tails or thru-hulls, and a blanking/inspection port at the end.

[sabray]

I have a few thu hulls and its not a problem. Give independent control of intake and failure.

Course I lack rocket science 101. What's wrong with well installed tested thru hull fittings?

[Caracal]

Originally Posted by sabray

Course I lack rocket science 101. What's wrong with well installed tested thru hull fittings?

Nothing.

[Pelagic]

Originally Posted by Andrew Troup

Pelagic

You misunderstand my proposal so comprehensively I'm not sure where to start.

I think you missed the bit where I explained that I was talking in terms of a swing keel: <<my planned keel swings into the hull>>

Sorry Andrew, I am just having trouble visualizing what your idea is.

Is my crude sketch more or less what you mean?

[ArtM]

Originally Posted by sabray

I have a few thu hulls and its not a problem. Give independent control of intake and failure.

Course I lack rocket science 101. What's wrong with well installed tested thru hull fittings?

Nothing. It's the poorly installed and corroded thru hulls that are causing the trouble - particularly when installed through or via unprotected/unsealed wood, and even more so when that wood is structurally vital to the hulls.

[Andrew Troup]

Originally Posted by Pelagic

Sorry Andrew, I am just having trouble visualizing what your idea is.

Is my crude sketch more or less what you mean?

Yes, that's the general idea, except of course the top would have to extend above the waterline.

The key diff from an 'add-in' chest, though, is that the structure (frames, floors etc) would reinforce the sea chest, as if it were part of the hull

In my case, the keel case (like what you drew, but parallel sided and taller) could do double duty as a sea chest.

[Dockhead]

Originally Posted by noelex 77

Yes good point. I have standpipes on my boat leading above the waterline.

It's worth considering other openings. My boat has a watertight box around the rudder that leads above the waterline.
This still leaves the exit of main shaft which is difficult to make foolproof. In my boat it is at least separated so it would only flood a small part of the boat. We would not sink, but the engine would suffer some water damage.

These ideas are worth incorporating into a custom boat, but they are very difficult to retrofit.

I think the OP's concern is absolutely valid. Through-hulls frighten me, too.

My boat has caissons around the rudder (like Noelex's) and around the bow thruster. But she has 15 (!) through hulls for all kinds of things including deck drains (which seems crazy to me).

The perfect solution to this is Dashew's -- all through-hulls concentrated in forepeak and engine room, both of which are isolated from main passenger space by watertight bulkheads. Nice, eh? That's the smartest solution I ever heard. If you have a breach, the boat won't sink.

Standpipes and sea chests are fine, but I'm not sure that one big hole in the bottom of the boat is so much better than several small ones. The main advantage is that they are harder to clog.

To the OP: your "overboard radiator" is a common solution -- it's called a keel cooler. Works great on metal boats; rather harder on plastic ones. But that leaves you with the necessity of rigging a dry stack exhaust, which is really undesirable on a plastic boat. The great thing about cooling your engine with sea water is you dump the sea water into the exhaust to cool that down enough to use an ordinary hose to convey the exhaust gasses out the transom.

Concerning clogging: I have just installed redundant means to detect a cooling water clog. This after I had a lot of problems with my generator last year following a weed-clogged cooling water intake. I have put temperature sensors on both raw water pumps. An alarm goes off over the N2K network if the temperature exceeds 30C. The raw water pumps are themselves water cooled, and start to warm up if there is a compromise of cooling flow. Besides that, I have installed exhaust temperature alarms -- simple, cheap, freestanding ones -- on the exhaust elbows of both engine and genset.

If you catch a cooling water flow problem early enough, you can shut down and unclog before damage is done. I don't worry as much about an overheated engine or genset -- we all have alarms and/or shutdown devices for that. The nightmare scenario is a burned-through exhaust hose, which can cause a fire, flooding, or other serious problems. My engine room is sealed, soundproofed, and forced-air ventilated out the transom, so I would never smell a burning exhaust hose in time.

[Boulter]

Hi:

Interesting discussion.

On my Ontario 32 I started with 6 below water line thru-hulls: two 1-1/2 inch cockpit drains, two 1/2 inch water in (head, engine) and two 1 inch sink drains.

The 4 larger units were 37 year old gate valves and thus immediately identified as needing to go (I think one of them even turned, though no idea if the flow would cut off!). The two smaller units have been upgraded, but not well: plywood backing plate and valve, not a proper seacock with 3 mounting screws.

I decided to eliminate the cockpit drain thru-hulls because they have terrible access, wouldn't drain very quickly and would cost serious coin to replace with proper hardware. For less money I am routing the existing 1 1/2 inch cockpit drains out the transom above the WL, and adding a 4 inch drain, also out the transom above the WL. The 4 inch will drain like a bat out of hell down to 2 or 3 inches deep, and the 1 1/2 inch drains will get the rest after some minutes.

The sink drains are being done for sure with equivalent sized parts in the existing locations. I don't imagine there is any practical way to link up to a single exit point some 10 or 15 feet apart in a boat this size, especially when they are on opposite sides of the centre line with the water tanks and bilge in between. But I admit, I had not considered the idea and will invest 15 minutes of brain time pondering the possibilities.

Finally I have parts to upgrade the 1/2 inch water inlets to 3/4 inch seacocks. I don't know if a replacement engine one day of double the HP will need a larger seacock, but for the sake of some marginal $25 or $50 I am making sure I don't have to do this again. I need to either move this through hull position or perhaps install a mechanical linkage such that I can operate it from somewhere I can actually get to in a hurry. Something like a tie rod end on the seacock handle attached to a piece of tubing routed to somewhere I can reach easily. The head water inlet will double as a wash pump source some day, so I wanted to beef up the capacity there too.

I am not going to lose any sleep over 4 below WL thru hulls of maximum diameter 1 inch with proper seacocks correctly installed. The status quo, however was just a sinking at the dock waiting to happen.

Boulter

[wetsail1]

Look up a seachest design on the 1985 gulfstar m/v this is a super design and it all discharges under water