Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-04-2013, 01:14   #1
Registered User

Join Date: Oct 2011
Boat: WTB Lagoon or Leopard 38'-40'
Posts: 1,273
Why through-hulls?

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.
__________________

__________________
ArtM is offline   Reply With Quote
Old 25-04-2013, 01:37   #2
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,863
Images: 4
Re: Why through-hulls?

Engine cooling is a big deal. Automobiles have a radiator and fan, and the outside air for their closed-loop cooling. At home I have a big emergency generator with a fan-cooled radiator and dry-stack exhaust. I sure wouldn't want that noise, space, and heat inside my boat. Instead I use seawater in the heat exchanger. That's one thru-hull.

When at sea I use seawater to flush the head. The waste goes overboard. The head sink drains overboard. We have two heads, one near the bow, to port, and one near the stern, to starboard. That's six more thru-hulls.

Galley sink drain as a thru-hull. Salt water spigot in the galley, and watermaker salt water feed share a thru-hull. Saltwater deck-washdown needs a thruhull.

Some of these could be combined with a manifold, but I think the required hoses would be more of a threat than the well-installed thru-hulls. I do carry wood bungs tied adjacent to each thru-hull. plus other emergency leak-stop supplies.

Most of my thru-hulls could disappear if my boating was limited to day-sails, always returning to the dock for fresh water and pumpout. But that's not how I sail. Yes, I could eliminate a few of the intake thru-hulls if I chose to collect the seawater with a bucket. That's difficult in rough conditions, but obviously in the days of "wooden ships and iron men", that's how it was done.
__________________

__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 25-04-2013, 01:46   #3
Registered User

Join Date: Oct 2011
Boat: WTB Lagoon or Leopard 38'-40'
Posts: 1,273
Re: Why through-hulls?

Quote:
Originally Posted by Paul Elliott View Post
Engine cooling is a big deal. Automobiles have a radiator and fan, and the outside air for their closed-loop cooling. At home I have a big emergency generator with a fan-cooled radiator and dry-stack exhaust. I sure wouldn't want that noise, space, and heat inside my boat. Instead I use seawater in the heat exchanger. That's one thru-hull.
How about a below-water radiator? Closed system, but cooled by seawater? or above deck radiator, cooled by ambient airflow?

Quote:
Originally Posted by Paul Elliott View Post
When at sea I use seawater to flush the head. The waste goes overboard. The head sink drains overboard. We have two heads, one near the bow, to port, and one near the stern, to starboard. That's six more thru-hulls.
All sailboats I know of have grey and blackwater holding tanks with pump-out capability. My main experience is with RV's. On RV's, the advice it to keep those tanks closed, even when connected to sewer, and only open them to drain. Is there any reason this wouldn't work on a sailboat?

Quote:
Originally Posted by Paul Elliott View Post
Galley sink drain as a thru-hull. Salt water spigot in the galley, and watermaker salt water feed share a thru-hull. Saltwater deck-washdown needs a thruhull.
Are these above water-line? I was really talking about below-water throughhulls. Above water through-hulls to drain wastewater are perhaps mildly troublesome, but it seems to me the real potential for trouble is below-waterline.

Quote:
Originally Posted by Paul Elliott View Post
Some of these could be combined with a manifold, but I think the required hoses would be more of a threat than the well-installed thru-hulls. I do carry wood bungs tied adjacent to each thru-hull. plus other emergency leak-stop supplies.
I'm not thinking of potential for sinking nearly as much as the risk of hull-rot for cored hulls. It just seems unnecessarily risky for the benefits to put holes in my hulls that are below sea-level. Why risk the hull integrity for what seems (to me) to be some very minor gains in convenience?

Quote:
Originally Posted by Paul Elliott View Post
Most of my thru-hulls could disappear if my boating was limited to day-sails, always returning to the dock for fresh water and pumpout. But that's not how I sail.
Agreed, so why is it not an option? I feel like I should be able to spec a sailboat with NO below-water holes. Even if I want to use seawater to cool my engines, it seems that I could just as easily pump it in through above-hull hoses as through below-waterline through-hulls.
__________________
ArtM is offline   Reply With Quote
Old 25-04-2013, 02:12   #4
Moderator
 
carstenb's Avatar

Cruisers Forum Supporter

Join Date: May 2012
Location: Copenhagen
Boat: Jeanneau Sun Fast 40.3
Posts: 4,936
Images: 1
Re: Why through-hulls?

Quote:
Originally Posted by ArtM View Post
How about a below-water radiator? Closed system, but cooled by seawater? or above deck radiator, cooled by ambient airflow?

The big issue with a below water radiator is how do you mount this without affecting sailing performance. Even hung off the transom on a lifting bracket, it would be in the water, creating drag while sailing (on the motor) Potentially it gets knocked off if you hit something.


I'm not thinking of potential for sinking nearly as much as the risk of hull-rot for cored hulls. It just seems unnecessarily risky for the benefits to put holes in my hulls that are below sea-level. Why risk the hull integrity for what seems (to me) to be some very minor gains in convenience?

[COLOR="rgb(65, 105, 225)"]Done properly, using bronze valves, it really isn't that big of an issue
[/COLOR]
Agreed, so why is it not an option? I feel like I should be able to spec a sailboat with NO below-water holes. Even if I want to use seawater to cool my engines, it seems that I could just as easily pump it in through above-hull hoses as through below-waterline through-hulls.
[COLOR="rgb(65, 105, 225)"]Above hull hoses hanging over the side? Again, inhibits performance. What happens when you dock? Gets caught between the boat and the dock (a rock and a hard place?). Not to mention suction head issues. Additionally, the part going from the deck to the water (and below) would have to be a pipe not a hose, otherwise when you movement occurs, the hose will bend and move backwards until the mouth is above the water and suck air.

Art - while certainly possible - It just isn't worth the effort for the potential gains. I think you would have a hell of a lot of potential disadvantages beyond what I've sketched out.

But we should always be thinking "outside the box" Never know what turns up[/COLOR]

__________________
I spent most of my money on Booze, Broads and Boats. The rest I wasted - Elmore Leonard
carstenb is offline   Reply With Quote
Old 25-04-2013, 02:14   #5
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,863
Images: 4
Re: Why through-hulls?

Quote:
Originally Posted by ArtM View Post
How about a below-water radiator? Closed system, but cooled by seawater? or above deck radiator, cooled by ambient airflow?
Are you thinking that the below-water radiator will be fed by hoses going up and over the side? That's a lot of trouble just to avoid a thru-hull, which, when installed with the proper technique, can give problem-free service for decades. And that radiator had better be a low-profile plate built into the hull or at least conforming to it, or it's going to create a huge amount of drag.

Quote:
All sailboats I know of have grey and blackwater holding tanks with pump-out capability. My main experience is with RV's. On RV's, the advice it to keep those tanks closed, even when connected to sewer, and only open them to drain. Is there any reason this wouldn't work on a sailboat?
I am at sea for weeks at a time. We have no grey-water tanks. I suppose I could have an over-the-side hose to pump out the black-water tank, but again, my thru-hulls are properly installed


Quote:
I'm not thinking of potential for sinking nearly as much as the risk of hull-rot for cored hulls. It just seems unnecessarily risky for the benefits to put holes in my hulls that are below sea-level. Why risk the hull integrity for what seems (to me) to be some very minor gains in convenience?
I suppose I see the situation from the opposite point of view. I consider a properly-installed thru-hull to be a quite reasonable solution to what would otherwise be a fairly inconvenient situation. I worry more about rotten hoses causing a major leak, than I do about core damage. I do regularly inspect my thru-hulls, hoses, and clamps. My boat has a partially-cored hull (balsa), with the core going down to just below the waterline. Some of the thru-hulls penetrate the cored section, but the builder has cleared the balsa in the thru-hull area and filled it in with fiberglass/resin. If the core gets wet, it probably won't be because of the thru-hulls.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 25-04-2013, 02:52   #6
Registered User

Join Date: Apr 2013
Posts: 201
Re: Why through-hulls?

Quote:
Originally Posted by ArtM View Post
I'm not thinking of potential for sinking nearly as much as the risk of hull-rot for cored hulls. It just seems unnecessarily risky for the benefits to put holes in my hulls that are below sea-level. Why risk the hull integrity for what seems (to me) to be some very minor gains in convenience?
Drill a hole, dig out some of the core material, clean and dry, fill the void where the core was with thickened epoxy= no water into the core.

As for cooling, some systems make use of a closed system, with the heat exchanger in or near the keel. If on the hull side, you need to have a single skin where it is placed. This is doable, even in a cored hull, if removing the inner "shell", do the epoxy thing, and putting it against the outer skin.


Quote:
Agreed, so why is it not an option? I feel like I should be able to spec a sailboat with NO below-water holes. Even if I want to use seawater to cool my engines, it seems that I could just as easily pump it in through above-hull hoses as through below-waterline through-hulls.
You can spec anything you want. You just need to know what those specs entails. You will also have a hole where the propeller shaft or saildrive pokes through. So if no holes whatsoever, you cannot have an inboard engine for propulsion.

In reality, it's not through-hulls per se which is a problem in this modern age where we don't have leaking and sponge like wooden hulls. It's the installation that matters.
__________________
Caracal is offline   Reply With Quote
Old 25-04-2013, 02:57   #7
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: Why through-hulls?

Any hose that can suck in sea water and goes below the water line inside the hull, still has the potential to sink your boat through a syphon action. No pump needed.

In a cored boat the core material should be removed and replaced with solid fibreglass around any hull penetration. This applies above and below the waterline.

The goal of reducing the through hulls is sound aim, but to try to eliminate them all together is a compromise that not many would be prepared to live with.

A sea chest can be used to consolidate many through hulls into one.
__________________
noelex 77 is offline   Reply With Quote
Old 25-04-2013, 03:02   #8
Registered User

Join Date: Apr 2013
Posts: 201
Re: Why through-hulls?

Quote:
Originally Posted by noelex 77 View Post
Any hose that can suck in sea water and goes below the water line inside the hull, still has the potential to sink your boat through a syphon action. No pump needed.

In a cored boat the core material should be removed and replaced with solid fibreglass. This applies above and below the waterline.

The goal of reducing the through hulls is sound aim, but to try to eliminate them all together is a compromise that not many would not be prepared to live with.

A sea chest can be used to consolidate many through hulls into one.
Also, I feel I should mention standpipes for single through hulls (Not that I have that on my boat).
__________________
Caracal is offline   Reply With Quote
Old 25-04-2013, 03:11   #9
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: Why through-hulls?

Quote:
Originally Posted by Caracal View Post
Also, I feel I should mention standpipes for single through hulls (Not that I have that on my boat).
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.
__________________
noelex 77 is offline   Reply With Quote
Old 25-04-2013, 03:22   #10
Registered User

Join Date: Apr 2013
Posts: 201
Re: Why through-hulls?

I wonder if the deck of your (Art) boat is cored too. I'm pretty sure it is, since the hull is. If so, do you worry about water entering into the core there? It's much more likely that rotting will happen in the deck and in the assembly between deck and hull than a properly fitted through-hull.
__________________
Caracal is offline   Reply With Quote
Old 25-04-2013, 03:23   #11
Registered User

Join Date: Apr 2013
Posts: 201
Re: Why through-hulls?

Quote:
Originally Posted by noelex 77 View Post
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'd love to see your standpipe solutions. But perhaps that's for another thread.
__________________
Caracal is offline   Reply With Quote
Old 25-04-2013, 03:33   #12
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,863
Images: 4
Re: Why through-hulls?

By the way, my previous defense of thru-hulls in no way means that I think looking for options and improvements is a bad idea. ArtM (and others), please keep trying to find better ways!
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 25-04-2013, 03:37   #13
Registered User
 
Capt Rottnest's Avatar

Join Date: Nov 2012
Location: FN QLD
Boat: Junk rig Schooner
Posts: 209
Re: Why through-hulls?

No below WL through-hulls on my boat.
The fact it has an outboard for auxiliary and a composting head helps.
Even the sink drain through-hull is 50-60cm above WL.

If ever need seawater there's canvas bucket on a rope for that.
__________________
Capt Rottnest is offline   Reply With Quote
Old 25-04-2013, 03:42   #14
Registered User

Join Date: Apr 2013
Posts: 201
Re: Why through-hulls?

Quote:
Originally Posted by Capt Rottnest View Post
No below WL through-hulls on my boat.
The fact it has an outboard for auxiliary and a composting head helps.
Even the sink drain through-hull is 50-60cm above WL.

If ever need seawater there's canvas bucket on a rope for that.
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.
__________________
Caracal is offline   Reply With Quote
Old 25-04-2013, 03:55   #15
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: Why through-hulls?

Quote:
Originally Posted by Caracal View Post
I'd love to see your standpipe solutions. But perhaps that's for another thread.
It is an aluminium boat so the standpipes are just aluminium tubes welded to hull till they are above the waterline. This allows the use of non bronze seacocks (if the seacock fails, or leaks it is above the waterline). Bronze and aluminium do not play together nicely.
Marelon is reasonably safe below the waterline, but fitting it above the waterline removes any risk from its slightly more fragile nature.

The biggest advantage is any hose failure will not sink the boat even with the seacock open.
Attached Thumbnails
Click image for larger version

Name:	image.jpg
Views:	134
Size:	164.6 KB
ID:	59869  
__________________

__________________
noelex 77 is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 21:52.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.