Why through-hulls?

[Caracal]

Excellent! Thanks, Noelex

[sestina]

My boat has high quality Blakes bronze seacocks. They are 26 years old. Maintainence takes about 10 mins a year. Why have anything else?



The design is probably Victorian. Though these days they have an integral grease nipple.

Incidentally, loads of work boats, fishing boats and the like have keel cooled engines. The coolant is either piped outside the hull or on metal boats through tanks integral to the hull. Add a dry stack for the exhaust.

[kmason]

I'm pretty sure the Lagoon and Leopard cats are solid glass below the waterline, not cored. As a matter of fact, I don't know of very many boats that are balsa cored below the waterline. I'm sure there are a few but percentage wise, not a lot.

A radiator below the waterline borders on the ridiculous and would require 4 through hulls as opposed to 2. Remember the heated water usually gets expelled with the exhaust after the heat exchanger where a radiator has a "TO" and "FROM" the engine. Or, an above deck radiator would provide 2 furnaces in a location of your choice. Ok, I guess for cold weather cruising but not very suitable for the tropics.

I suggest you buy a boat; either spec it out during the build without through-hulls or get a production boat and glass over all the through-hulls. Then see how convenient or necessary these things are. I think you will soon find that it is better to maintain these devices in good working order than to live without them.

Here are some suggestions though for eliminating through-hulls...

Engine cooling - use an outboard or go sail only (this also eliminates that pesky prop shaft/saildrive through-hull)

Head - composting or above waterline, over-the-side cheek-hanging device.

Everything else - bucket and rope.

[Pelagic]

Originally Posted by ArtM

I'm not a nautical engineer, though I am a rocket scientist (I.e. I have a physics degree from a major US university)

Despite that pedigree, though, I have long wanted to pose the question - why through-hulls?

For all the problems they appear to pose, I often wonder how critical they are to a sailboat's operation, and what options have been considered?
- Engine cooling: I've heard enough jellyfish stories that I've developed a deep appreciation for my automobiles closed coolant system
- Toilet system: Boat owners I know close off their sea-water valves in favor of using fresh water. Dead sea critters appear to be a major source of nasty head odors. If I really REALLY want to use sea water in my toilet, I can keep a nice Clorox bottle full in my head next to my "repository"
- What else? If sea water is really critical to any other systems (at this moment only AC comes to mind, which I have no plans to operate while cruising), can't I just PUMP it in without compromising my cheaply built french balsa-cored plastic hull?

Nautical engineers, I humbly await your flames.

The primary advantage of using cooling thru hulls is that it is a single pass-thru system with maximum heat exchange factors and deep enough to maintain positive pressure in the dynamics of a lively sea way.

Positive Pressure translates to more energy efficiency of pumps and by placing thru hull at maximum depth, you will capture cleaner sea water.

Keel cooling tubes are common on certain commercial boats that operate in muddy waters, but not exactly a closed system. Works well in cold waters, not as well in warm sea temps and has increased drag with vulnerability in grounding.

My own Dutch steel yacht was built with “Skin Cooling” so is an efficient closed system.

It has a large area of steel double bottom to exchange heat from closed engine cooling water. This is more efficient and flush, but PO changed to SW cooling when he re-powered to larger main engine. So I am guessing Tropical temps was his worry.

Anchor wash-Fire Fighting needs copious amounts of reliable water… so personally have not found any advantages to reinventing this particular wheel.

Important design factors are to consolidate and place thru-hulls in locations that are easy to inspect/service and turn off when away from yacht.

Google Image Result for http://www.tpub.com/engine3/en3_files/image188.jpg

[David_Old_Jersey]

Why thru hulls?

Because they are simple to understand and simple to use. Plus they last a longggg time with minimal maintanence. Well, they do if you don't fit any made of tin plate or plastine - or a composite of both!

IMO if someone does not know enough to take care of a few through hulls (or can't be bothered) then anything else is gonna be more complex and therefore will really stump them - or go predictably wrong from the fit and forget approach.

[Kettlewell]

It is highly desirable to reduce the number of through hulls to a minimum and keep the ones you do have highly accessible so they can be checked easily. Usually, the failure point is the hose attached, not the through hull or sea cock itself, though they have been known to let go. I had a 32-foot cat that didn't need any through hulls below the waterline except for a single intake line for the head and a discharge line for the holding tank when I was offshore. Today I would use a composting head and get rid of those two. It was outboard powered, so no through hull there. The galley and head sinks did drain overboard, but above the waterline so no sea cocks were needed. There are lots of desirable cruising areas in the world where there would be no way to pump out gray and black water tanks, so you do need some sort of overboard system unless you have an enormous boat with enormous tanks. Very few cruising boats have grey water tanks.

[Capt Rottnest]

Originally Posted by Caracal

I question the safety of choosing an outboard which runs on petrol in order to avoid through-hulls. Not that I think that's the reason you have a boat with an outboard.

Its good you didnt think that.

Diesel is one legit reason to need a seacock and a wife who cant stand to use a compost head is another. My better half has no pobs with that..

[sestina]

Why is it the norm to have two hoseclips? Every time I've tried to get a hose off a seacock, I've ended up cutting the hose as the damn thing is welded on.

[David M]

Originally Posted by sestina

Incidentally, loads of work boats, fishing boats and the like have keel cooled engines. The coolant is either piped outside the hull or on metal boats through tanks integral to the hull. Add a dry stack for the exhaust.

Keel cooler.....

[rtbates]

Originally Posted by sestina

Why is it the norm to have two hoseclips? Every time I've tried to get a hose off a seacock, I've ended up cutting the hose as the damn thing is welded on.

Redundancy. IF one clamp breaks the other hopefully is still intact. And having the hose 'welded on' is a good thing. Sure don't want it slipping off or leaking.

[David M]

Not all hose barb/hose connections weld themselves on. Some actually need the clamp to stay on.

[Bash]

I'm surprised no one has waxed poetic about the merits of a sea chest at this point. Sea chests are common on ships, and eliminate the need for thu-hulls. I had a buddy with a Gulf Star 50 who eliminated all his thru-hulls, consolidating all the salt-water intakes with a central sea chest. Seemed like a lot of work/expense just to eliminate perfectly functional thu-hulls.

Sea chest - Wikipedia, the free encyclopedia

[noelex 77]

Hose clamp failure is reasonably common.
The internal screw is often not 316, and corrodes.

Two hose clamps below the waterline are good insurance. Unfortunately, often the barbs have insufficient depth to properly accomodate two hose clamps. Trying to squeeze on two can sometimes be counterproductive.
In an ideal world these fittings would be avoided, at least make sure the hose clamps are of the highest quality and inspected.

Above the waterline the consequences of hose clamp failure are much less severe, but also give some consideration to other important systems, such as the engine fuel supply.

[Panope]

Originally, Panope had a raw water seacock made of cast aluminum. A complete dis-assembly of this through hull revealed pitting approximately 1/2 of the wall thickness after 18 years of use.

As a result, I decided to weld tubes and standpipes for all under water hull penetrations.

Pic #1 Raw water intake. Visible is a 1/4" aluminum disk welded to hull.

Pic #2 Raw water standpipe. Was welded to the above disk in my workshop. Then, the whole assembly was welded in place. Not visible is a second tube inside the outer tube (both schedule 80 pipe). The small void between the two tubes was filled with epoxy. The Tube was sandblasted internally and epoxy was poured to coat the inside completely. Marlon valve is above water line. When strainer lid is removed, a strait rod easily clears blockages.

Steve

[Cheechako]

How will you pump it in without a thru hull...? I dont know about others , but "all the problems with thru hulls" doesnt sound accurate to me. I just make sure they are good when I get the boat and forget them.... as long as theyre not plastic. Keel cooling is great until you have to claean all the critters out from between the tubes... and does cause some drag also. The best keel cooled system is an indent in the hull in which the keel cooler sits so it's not exposed. I've seen fishing boats with "keel coolers" that are nothing more than a long pipe. running fore and aft.