Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 16-10-2020, 01:03   #1
Registered User

Join Date: Oct 2017
Location: Sunshine Coast, QLD
Boat: Roberts 370 Expedition
Posts: 42
Through hull fittings on Aluminium sailboat

Hi All

I hope that everyone is well in this potty world we currently live in. It's occurred to me for many years how fortunate we are to have found a pastime/career/lifestyle such as sailing. The amount one can learn is limitless, unlike many other sports (or careers/pastimes). I for one am amazed at how little I know about so many aspects of a sailboat, particularly those that venture far afield. Anyway, enough of the naval gazing.

Having now bought the aluminium cutter of my dreams, I am putting together a maintenance plan for when she's next slipped. I've read a lot about through-hulls and stop cocks and would much appreciate your hands on comments.

There's a real mish-mash of types of through-hulls and stop-cocks. Some show a reasonable level of corrosion (not too good). Ideally, whilst making sure their integrity is 100%, I'd like similar fittings when I next slip her.

I've attached (or at least I hope I have) some photos of the questionable fittings associated with the head waste and holding tank. Do you have any suggestions on what I should do with them?

Attachment 1. shows a heavily taped marelon fitting (black water discharge). Maybe a cracked or poorly matched fitting.
Attachment 2. S/S stop cock for macerator discharge.
Attachment 3. Corroding valve on discharge elbow.
Attachment 4. Multi-metal corrosion on raw water inlet.

There are also 2 skin fittings with plywood backing plates. I don't have photos but my surveyor advises that the plates be replaced (as the ply may cause paultice corrosion) . I don't yet know with what, given it's an aluminium hull. Suggestions here also very welcome.

Thanks very much! Wideocean7/Andy

Click image for larger version

Name:	1. Marelon Stop Cock.JPG
Views:	111
Size:	124.3 KB
ID:	225272

Click image for larger version

Name:	2. Stainless Stop Cock.jpg
Views:	107
Size:	120.4 KB
ID:	225273

Click image for larger version

Name:	3. Corroding <a title=Elbow.jpg Views: 100 Size: 104.0 KB ID: 225274" style="margin: 2px" />

Click image for larger version

Name:	4. <a title=Raw water inlet.JPG Views: 106 Size: 119.6 KB ID: 225276" style="margin: 2px" />
Wideocean7 is offline   Reply With Quote
Old 16-10-2020, 01:21   #2
Registered User

Join Date: Dec 2019
Posts: 159
Re: Through hull fittings on Aluminium sailboat

Use nylon fittings https://shop.tnorrismarine.co.uk/pro...SABEgIAnfD_BwE
Michael Cobbe is offline   Reply With Quote
Old 16-10-2020, 01:50   #3
Registered User
 
Sherpa17's Avatar

Join Date: Jun 2019
Posts: 93
Re: Through hull fittings on Aluminium sailboat

Perhaps G10 backing plates put down with West System Gflex would help isolate the fittings from the hull should you be limited to metallic thru hulls. Gflex is formulated for aluminum and G10 flat stock is non -conductive and easy to cut and shape.
Sherpa17 is offline   Reply With Quote
Old 16-10-2020, 01:50   #4
Registered User
 
double u's Avatar

Join Date: Feb 2016
Location: forest city
Boat: no boat any more
Posts: 1,769
Re: Through hull fittings on Aluminium sailboat

if you are aware of intricacies of corrosion as "poultice cor." you are already way ahead.
On the french Alum. Sloop we owned for 10 years & rtw-ed twice all through-hulls were Polypropylene ball-valves (French) screwed directly onto tubes that were welded to the hull. One area with zero corrosion or maintenance probs.
__________________
...not all who wander are lost!
double u is offline   Reply With Quote
Old 16-10-2020, 02:07   #5
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 39,234
Images: 241
Re: Through hull fittings on Aluminium sailboat

Poultice corrosion can occur when stagnent (oxygen-free) water is trapped against aluminum, such as under (porous) wood backers.
In this case, the wet wood backing plate is the poultice, and aluminum hydroxide (showing white powder-like deposits/blooms) would be the result.
Bare aluminum must be kept clean and dry, and free of any wicking (absorbent) materials.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 16-10-2020, 02:14   #6
Registered User

Join Date: Oct 2017
Location: Sunshine Coast, QLD
Boat: Roberts 370 Expedition
Posts: 42
Re: Through hull fittings on Aluminium sailboat

Thanks All. I had been lead to believe that an internal “plate” is necessary to spread the load. Is this right? If so, the fittings suggested by Michael wouldn’t do the trick (or would they?). Also. would any backing plate need to be through-bolted as I hate the idea of yet more holes in the hull. Finally, why would G10 plated suggested by Sherpa17 be any better in circumventing poultice corrosion that ply?

Thanks again. Andy.
Wideocean7 is offline   Reply With Quote
Old 16-10-2020, 03:34   #7
Marine Service Provider

Join Date: Dec 2010
Location: Little Compton, RI
Boat: Cape George 31
Posts: 1,460
Re: Through hull fittings on Aluminium sailboat

^^G10 is non-porous, so it wouldn't hold water against the hull. You would of course pot it with Pro-set so there was no gap.
But the best solution has already been mentioned: welded-on tubes with threads at the end on which you put a seacock. As long as you have a good welder, I don't know of a better way to do through hulls in aluminum. I have the same system in my boat, only with fiberglass tubes glassed to the fiberglass hull. The tubes go above the waterline before the ball valve happens, so a failure there can't sink the boat.
__________________
Ben
zartmancruising.com
Benz is offline   Reply With Quote
Old 16-10-2020, 05:01   #8
Registered User
 
Sherpa17's Avatar

Join Date: Jun 2019
Posts: 93
Re: Through hull fittings on Aluminium sailboat

randex.fr supplies CNB which makes aluminum boats.
Quote:
Originally Posted by double u View Post
if you are aware of intricacies of corrosion as "poultice cor." you are already way ahead.
On the french Alum. Sloop we owned for 10 years & rtw-ed twice all through-hulls were Polypropylene ball-valves (French) screwed directly onto tubes that were welded to the hull. One area with zero corrosion or maintenance probs.
Sherpa17 is offline   Reply With Quote
Old 16-10-2020, 05:43   #9
Registered User
 
double u's Avatar

Join Date: Feb 2016
Location: forest city
Boat: no boat any more
Posts: 1,769
Re: Through hull fittings on Aluminium sailboat

yep, these ballvalves. boat was Pouvreau built
__________________
...not all who wander are lost!
double u is offline   Reply With Quote
Old 16-10-2020, 05:45   #10
Registered User
 
double u's Avatar

Join Date: Feb 2016
Location: forest city
Boat: no boat any more
Posts: 1,769
Re: Through hull fittings on Aluminium sailboat

chapeau, Sherpa17, btw!
__________________
...not all who wander are lost!
double u is offline   Reply With Quote
Old 16-10-2020, 08:01   #11
Registered User
 
funjohnson's Avatar

Join Date: Mar 2010
Location: Out cruising again (Currently UK)
Boat: Building a Max Cruise 42 cat - previous 37' aluminum mono
Posts: 2,661
Re: Through hull fittings on Aluminium sailboat

Most of our thru hulls were welded on pipe nipples as shown, but I did have two that required Marlon thru hulls - engine intake and transducer. For those we used FRP green board (cheaper than G10) and West System G-flex to adhere the backing plate to the freshly abraded aluminum hull. This works extremely well.

All seacocks and hose barbs were Marlon until at least above the waterline.

If you are going through the trouble of welding on new pipe nipples as thru hulls, see if you can extend those to above the waterline to make stand pipes. You are then free to worry about other things sinking the boat besides a failed rubber hose Keep in mind that stand pipes usually require additional vertical support besides just the circumference weld and should still have a valve on top.

Matt
__________________
Youtube MJ sailing - Vlog
Rebuilt Aluminum Boat Over 2 Years... Now Back Cruising!
funjohnson is offline   Reply With Quote
Old 16-10-2020, 09:08   #12
Registered User

Join Date: Oct 2019
Posts: 271
Re: Through hull fittings on Aluminium sailboat

Remember the table of metals, which is very important on an aluminium boat. I would go with the nylon or anything else that is not metal unless it is monel coated.
Same when you screw a metal fitting to the superstructure. Insúltate it and use plastic to insulate the screws.
Stewie12 is online now   Reply With Quote
Old 16-10-2020, 09:15   #13
Registered User

Join Date: Nov 2018
Location: Ventura,CA
Boat: 1979 Acapulco 40
Posts: 62
Re: Through hull fittings on Aluminium sailboat

Matt Johnson always has good technical ideas and engineering help. I’m curious to know where his sources his FRP green board and what the actual product name is, cheers
Glassdog is offline   Reply With Quote
Old 16-10-2020, 09:31   #14
Registered User

Join Date: Jan 2016
Posts: 56
Re: Through hull fittings on Aluminium sailboat

Trudesign thru hulls.
bobgarrett is offline   Reply With Quote
Old 16-10-2020, 09:52   #15
Registered User
 
northwestsailor's Avatar

Join Date: Nov 2009
Location: Tromsø, Norway
Boat: Meta Arctic Voyager 47
Posts: 362
Images: 13
Send a message via AIM to northwestsailor Send a message via Skype™ to northwestsailor
Re: Through hull fittings on Aluminium sailboat

Our two Joubert designed Meta built aluminum hulls have all stand pipes for all water entering or exiting the boat. This is good in almost all cases except where you are expecting to freeze in for the winter then care must be taken using one of several methods.
__________________
Victor Raymond
M/V Arktika
1984 Meta Arctic Voyager 47
northwestsailor is offline   Reply With Quote
Reply

Tags
boat, hull, sail, sailboat

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Through hull fittings - How much "play/distance" is ok? Cpt. Black SOL Plumbing Systems and Fixtures 17 29-04-2018 18:23
Does anyone recognize this aluminium through hull design mstopo Construction, Maintenance & Refit 11 25-09-2016 04:49
Redundant Through Hull Fittings... reiner Plumbing Systems and Fixtures 3 29-02-2012 07:41
Through Hull Fittings - Straight Answers Needed TimPeacockUK General Sailing Forum 18 18-11-2011 12:47
Through Hull Fittings Ian McD Construction, Maintenance & Refit 10 07-11-2011 00:35

Advertise Here


All times are GMT -7. The time now is 19:10.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.