Thru-Hull Stats

[JamesG161]

I presume if they are all bonded ?

No need to bond the Marine Grade Bronze valves inside the boat to reduce Galvanic Corrosion.
But if makes you happy go for it. If you do and test it bonded, it will show you Zinc potential.

As long as your Shaft Zinc in grounded to the engine or Battery, the Zinc will protect the Bronze Valves.

If you lose your Zinc, then Galvanic Corrosion starts on the Bronze and your Stainless Steel shaft.

Of course there is alway metal corrosion in salt water. Thus the Alloy Marine Bronze, which has very low corrosion rate.
Jim...

 

[capta]

Frankly, sinking because of a through hull failure is even farther down my list of worries than being sunk by a whale. Personally, I'm more attentive to the idea of hose failure above the thruhull, so we inspect them often and change them if there is any doubt.
At any rate, I believe most of us have bungs aboard, should a thruhull fail. We service them every time we haul. Between haulouts, we get to every one every other month or so, opening/closing them several times to be sure they work.
If it bothers you that you have so many holes in your hull (we have 23), then you could install a sea chest which cuts the number down to one.

 

[dLj]

@capta How does a sea chest handle incoming water and outgoing discharge? I don't see how those two could be sent through the same thru-hull?

dj

 

[capta]

All outlet/exhaust water would be above the waterline. That is, of course, assuming one is using a holding tank.

 

[Davidasailor26]

No need to bond the Marine Grade Bronze valves inside the boat to reduce Galvanic Corrosion.
But if makes you happy go for it. If you do and test it bonded, it will show you Zinc potential.

As long as your Shaft Zinc in grounded to the engine or Battery, the Zinc will protect the Bronze Valves.

It was my understanding that to provide protection a sacrificial anode must be in the same electrolyte (salt water) and also have electrical connection to the metal in need of protection.

Reference Calder’s Boatowners Mechanical and Electrical Manual - “A sacrificial anode will protect only those metals that are both wired to it and immersed in the same body of electrolyte.”

 

[dLj]

All outlet/exhaust water would be above the waterline. That is, of course, assuming one is using a holding tank.

Interesting. All my sinks drain below th
e waterline. Of course all direct discharge does also (when one can do that). As I'm thinking about it, I've never had a boat where the kitchen sink drained above the waterline. I also don't recall having a boat where the bathroom sink drained above the waterline. I've seen them drain into the bilge but don't recall any that drained above the waterline. I'm wondering if I've simply had old boats?

The rest of my discharges are as you say, above the waterline.

dj

 

[Davidasailor26]

I also don't recall having a boat where the bathroom sink drained above the waterline. I've seen them drain into the bilge but don't recall any that drained above the waterline.

Lots of O’Days (28, 30, 34, etc) had bathroom sinks drain above the waterline. They were still below the heeled waterline though, and not protected with seacocks, which is not best practice anymore.

 

[Tally Ho]

Lots of O’Days (28, 30, 34, etc) had bathroom sinks drain above the waterline. They were still below the heeled waterline though, and not protected with seacocks, which is not best practice anymore.

My O’Day 322 head sink is that way…I can hear the water gurgling in the hose on a port tack and healed.

My galley sink drain has a thruhull below the waterline.

Greg

 

[dLj]

Lots of O’Days (28, 30, 34, etc) had bathroom sinks drain above the waterline. They were still below the heeled waterline though, and not protected with seacocks, which is not best practice anymore.

I've never owned an O'Day. I'm thinking about the boats I've owned, all have been from the 60's, 70's or 80's. I did have a trimaran from 2002 but that was a small day sailor and had no thru-hulls at all... So I have limited knowledge of more modern design preferences.

Is it current practice to put all sink drains above the water line? Just curious.

dj

p.s. I don't mean to highjack this thread - perhaps I should start a new thread...

 

[Tally Ho]

I think my 1996 Hunter 280 had a valve on the head sink drain…and the exhaust exited under the waterline too.

Greg

 

[capta]

Interesting. All my sinks drain below th
e waterline. Of course all direct discharge does also (when one can do that). As I'm thinking about it, I've never had a boat where the kitchen sink drained above the waterline. I also don't recall having a boat where the bathroom sink drained above the waterline. I've seen them drain into the bilge but don't recall any that drained above the waterline. I'm wondering if I've simply had old boats?

The rest of my discharges are as you say, above the waterline.

dj

Skipping Stone has several sumps for the sinks. I added a thruhull for the galley sink for use at anchor. These days I thought "grey water" was supposed to go into a holding tank as well as "black water"? Sumps would place the outlets above the water.

 

[Tally Ho]

These days I thought "grey water" was supposed to go into a holding tank as well as "black water"?

Depends on where you sail I guess (and your level of “environmentalism”)…

I don’t believe we need to capture grey water on the Great Lakes (at least not yet).

Greg

 

[dLj]

Skipping Stone has several sumps for the sinks. I added a thruhull for the galley sink for use at anchor. These days I thought "grey water" was supposed to go into a holding tank as well as "black water"? Sumps would place the outlets above the water.

@capta grey water tanks being required would be news to me. I've never heard of that requirement anywhere. As @Tally Ho says, it's not required on the Great lakes at this point and they are pretty tight with regulations. If grey water was also required to be put into a holding tank, that would make for a very major impact on my boat and pretty much any older boat...

dj

 

[jssailem]

Looking up the EPA's word on Grey water management...

First what is Grey Water?
From EPA:
Graywater Discharges from Vessels
EPA-800-R-11-001 November 2011

Source	Graywater Definition
Clean Water Act, 33 U.S.C. § 312(a)(11)	Galley, bath, and shower water
International Maritime Organization Guidelines for Implementation of Annex V of MARPOL	Drainage from dishwasher, shower, laundry, bath and washbasin drains and does not include drainage from toilets, urinals, hospitals, and animal spaces, as defined in regulation 1(3) of Annex IV, as well as drainage from cargo spaces

Coast Guard regulations implementing MARPOL and the Act to Prevent Pollution from Ships, 33 CFR 151.05

Drainage from dishwasher, shower, laundry, bath, and washbasin drains and does not include drainage from toilets, urinals, hospitals, and cargo spaces

On December 19, 2008, EPA issued the VGP to provide NPDES permit coverage for vessel discharges incidental to normal operation from commercial vessels greater than 79 feet into waters of the United States. Waters of the United States, as defined in 40 CFR 122.2, includes the 3-mile territorial sea as defined in Section 502(8) of the CWA, and inland navigable waters, including navigable waters of the Great Lakes subject to the jurisdiction of the United States (USEPA, 2008a). The 2008 VGP did not include discharges incidental to normal operation of vessels less than 79 ft and commercial fishing vessels3, which are exempt from NPDES permitting until December 2013,4 pursuant to a moratorium. Approximately 120,000 to 140,000 vessels fall under the moratorium, including commercial fishing vessels and
those commercial vessels 79 feet or less in length. Discharges from recreational and armed forces vessels are also permanently excluded.

Yeah... We are excluded.... at least for now.

 

[dLj]

Yes, one always wonders what "permanently" means in this kind of legislation...

Standard English may not apply...

dj

 

[Peggie Hall HeadMistress]

These days I thought "grey water" was supposed to go into a holding tank as well as "black water"?

Nope, Marine Sanitation regs only apply to "human body wastes and thewastes from toilets and other receptacles intended to receive or retain body wastes except that, with respect to commercial vessels on the Great Lakes, such term shall include graywater." Gray water can legally be discharged directly overboard from recreational vessels in all US waters except for a few closed inland lakes and the waters FL Keys National Marine Sanctuary.

And fwiw, although almost all sailboard sink drains are below waterline, almost all powerboat sink drains are above waterline.

--Peggie

 

[Peggie Hall HeadMistress]

Looking up the EPA's word on Grey water management...

John you've wandered waaaay into the weeds....for one thing MARPOL is an international treaty only applies to large commercial vessels. The only definitions recreational vessel owners in US waters need to worry about are in 33 CFR (Code of Federal Regulations) chapter 26-1322 - Marine sanitation devices; discharges incidental to the normal operation of vessels

"(a) definitions" Those applicable to this subject are:

"In this section, the term—
((5) “marine sanitation device” includes any equipment for installation on board a vessel which is designed to receive, retain, treat, or discharge sewage, and any process to treat such sewage;
(6) “sewage” means human body wastes and the wastes from toilets and other receptacles intended to receive or retain body wastes except that, with respect to commercial vessels on the Great Lakes, such term shall include graywater;
(11) “graywater” means galley, bath, and shower water;
12) “discharge incidental to the normal operation of a vessel”—
(A) means a discharge, including—
(i) graywater, bilge water, cooling water, weather deck runoff, ballast water, oil water separator effluent, and any other pollutant discharge from the operation of a marine propulsion system, shipboard maneuvering system, crew habitability system, or installed major equipment, such as an aircraft carrier elevator or a catapult, or from a protective, preservative, or absorptive application to the hull of the vessel; and
(ii) a discharge in connection with the testing, maintenance, and repair of a system described in clause (i) whenever the vessel is waterborne

If you opt to explore all of 33 CFR Chapter 26, be careful not to wade into weeds in it that don't apply to recreational vessels.

--Peggie

 

[Ralph Johnstone]

And fwiw, although almost all sailboard sink drains are below waterline, almost all powerboat sink drains are above waterline.

This is something that just escapes me as to why. Powerboat sink drains are above the waterline as I see in marinas over the years, but only about one inch. They're not going to show great long ugly streaks down the side of the hull. They present minimal concern.

Sailboats sink drains, I imagine are all under the water line although you cannot see them. They DO present a concern as far as corrosion, physical damage, and a few other concerns.

Why put them below the waterline (in sailboats) when they present ZERO concerns when placed slightly above the waterline ?

So many question, so little time .

 

[Davidasailor26]

This is something that just escapes me as to why. Powerboat sink drains are above the waterline as I see in marinas over the years, but only about one inch. They're not going to show great long ugly streaks down the side of the hull. They present minimal concern.

Sailboats sink drains, I imagine are all under the water line although you cannot see them. They DO present a concern as far as corrosion, physical damage, and a few other concerns.

Why put them below the waterline (in sailboats) when they present ZERO concerns when placed slightly above the waterline ?

So many question, so little time .

When placed slightly above the waterline the through hulls still present a risk at least half the time you’re sailing. Most sailboats are also much lower freeboard than powerboats, leaving less space to fit the sink above the waterline while still having a reasonable height sink and headroom.

 

[Peggie Hall HeadMistress]

Powerboat sink drains are above the waterline as I see in marinas over the years, but only about one inch.

That can vary depending on how full the tanks are. I remember a job surveying and trouble-shooting the sanitation system on a 46' trawler and found the manual toilet intake vented loop right at the waterline. It had been installed when the boat was on the hard with empty fuel and water tanks...the weight of 800 gallons of diesel and 200 gallons of fresh water had raised the waterline about 3 feet! I'm sure that also impacted the level of the sink drain thru-hulls too.

I need to ask a marine architect why pb sink drain thrulls are above waterline and sb drain thru'hulls are below. I KNOW why toilet and holding tank drain thru-hulls should always be below below waterline on both: visual and olfactory aesthetics: nobody wants to see or smell toilet waste pouring out of the side a boat!

--Peggie