Building an FRP Holding Tank & System - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance
 Not a Member? 
  #1  
Old 03-10-2009
Member
 
Join Date: Dec 2008
Posts: 57
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
matt2 is on a distinguished road
Building an FRP Holding Tank & System

I have read most of the articles here on this issue, but still need a bit of advice.

Toilet
It looks like a Lavac vacuum toilet uses a lot less water than a macerator evacuated toilet. But do they use enough water or to do they clog?

Configuration
I like the set up where all waste going through the holding tank and then to a Y valve with one line to the deck and the other to a macerator pump and overboard.

Size
For living aboard for two people.
berths * days between emptying * 2= size in litres
2 * 15 * 2 = 60 litres -> /3.8 = 16Gallons

This seems pretty large, what do other people think.
I am not sure I have room for a tank this big.

Material
I have seen the HDPE (bread board) tank stuff, but the limitations of the shapes and fit would make it very difficult to get a large enough tank without effectively losing an entire hanging locker (at least in a functional sense). So I was thinking of making the tank out of fiberglass and glassing it into the inside of the hull, below the toilet. There is already a semi structural closed area of close to the right size. It would be a much bigger job than a HDPE bread-board prefabbed.
My question is what internal lining in an FRP tanks should be used to ensure no leakage?
Any construction techniques or tips to avoid leakage?

Shape
The FRP tank would also be long and flat. i.e. 3 feet long, 2 feet across and would follow the hull from 1 inch to about 10 inches high. So size would be 3*2*10/2=30cubic feet or 91cm*5cm*25cm/2=568cm (57 litres)
(Divide by 2 because bottom of tank follows hull form.)

Position
Better under the toilet or above?
Better close to the toilet?
The output uptake should be at the lowest point in the tank and run directly outside.

Venting
How long can the vent run be, e.g. to the top of the windgen pole?

Tank Level
What indiactors are useful here?

Siphon Valves
These have never worked properly for me since they clog up with salt.
If the toilet is above the waterline, they should not be required. Do you agree?

In Practice
If you do all this do people still get problems with smells?

Last edited by matt2; 03-10-2009 at 10:18 PM.
Reply With Quote Quick reply to this message Share with Facebook
  #2  
Old 03-10-2009
celenoglu's Avatar
Senior Member
 
Join Date: Dec 2008
Posts: 568
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 6
celenoglu is on a distinguished road
Fiberglass is not a good material for the tank. You will have a lot of osmosis damage and most probably the tank will leak very soon. HDPE is a better material.

Your size is big. 5 liters/day/person is the minimum.

Makesure you use high quality hoses otherwise they will cause odor. You can cover them with aluminum tape (used for air ducts in buildings) to overcome odor.
Reply With Quote Quick reply to this message Share with Facebook
  #3  
Old 03-10-2009
dgr dgr is offline
Member
 
Join Date: Apr 2008
Location: Rocklin (Sacramento)
Posts: 79
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
dgr is on a distinguished road
celenoglu,
My boat is a fiberglass tank and has been keeping water on the right side for 40 years.

Matt, there are a couple of articles on the internet on builidng a wood/FRP tank and an all FRP tank. Seems pretty simple. What I took away from them was to use a few layers of mat and resin rich on the wet side.



Here are a couple of links. There's more out there.

http://www.epoxyworks.com/18/pdf/tanks.pdf
MARKSTANK
__________________
----------------
Just a Columbia 28
Reply With Quote Quick reply to this message Share with Facebook
  #4  
Old 03-10-2009
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
Fiberglass is fine for a holding tank, provided it is properly constructed... after all fiberglass boats have lasted many years...

Long flat tanks have a problem in that they'll be harder to empty completely. If you leave much waste sitting in the bottom for extended periods of time, it can eventually build up and reduce tank capacity. A taller, more vertically oriented tank is usually a better idea IMHO.

If the tank inlet is high on the tank, as it should be, having the tank higher is probably a good idea, since it may allow you to gravity drain the holding tank.

The vent line should be at lest 5/8", preferably 1", and as short and direct as possible to maximize oxygen getting into the tank. Anaerobic bacteria is the stuff that makes the tank stink... Aerobic bacteria are good...

Tank level—can be managed in several ways, but I'd recommend putting an inspection hatch in the top of the tank with a clear deckplate, like the Beckson I have installed, since that makes it easy to visually inspect how full the tank is as well as gives you an option if you need to clean out the tank.

I like the Lavac, as it is almost bulletproof and generally uses less water than traditional designs.

Siphon valves— if the head is above the waterline on all angles of heel, you may be able to eliminate it...

One major source of head odors is not using fresh water to flush the head when the system is going to be left alone for an extended period of time. Salt water micro-organisms left in the bowl and hoses will die and leave an awful stench.
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Quick reply to this message Share with Facebook
  #5  
Old 03-10-2009
Member
 
Join Date: Dec 2008
Posts: 57
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
matt2 is on a distinguished road
Size

Quote:
Originally Posted by celenoglu View Post
Your size is big. 5 liters/day/person is the minimum.
So for 2 people, 15 days between pump outs would make it
5*2*15=150 litres? -> divide by 3.8 to get 40 Gallons

So since 1000 cubic cm is 1 litre, to get 150K cubic cm the rough dimensions would be 100cm*15cm*10cm, which is workable.

What size tanks do other boats have?
Are there downsides to excessive tanks size?

Are folks happy or unhappy with your tank size?
Reply With Quote Quick reply to this message Share with Facebook
  #6  
Old 03-11-2009
Member
 
Join Date: Dec 2008
Posts: 57
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
matt2 is on a distinguished road
A Difficult Problem

Quote:
Originally Posted by sailingdog View Post
Fiberglass is fine for a holding tank, provided it is properly constructed... after all fiberglass boats have lasted many years...
That is reassuring.
Are there any special advantages to HDPE?
Is it possible to fabricate your own HDPE tanks?

Quote:
Originally Posted by sailingdog View Post
Long flat tanks have a problem in that they'll be harder to empty completely. If you leave much waste sitting in the bottom for extended periods of time, it can eventually build up and reduce tank capacity. A taller, more vertically oriented tank is usually a better idea IMHO.
That is what I feared. So a flat tank in the floor under the bowl would probably not work well. To get the right verticality I might have to rip out the sink and redo the vanity so a holding tank can go inside the cabinet. I am not at all keen to lose the hanging locker to a holding tank.

Quote:
Originally Posted by sailingdog View Post
If the tank inlet is high on the tank, as it should be, having the tank higher is probably a good idea, since it may allow you to gravity drain the holding tank.
I think I will have a macerator pump (a requirement in may areas where discharge is allowed) to pump out the tank. As I understand this pump is positioned after the Y valve on the overboard seacock outlet. i.e. pumpout stations have their own pump.

Quote:
Originally Posted by sailingdog View Post
The vent line should be at lest 5/8", preferably 1", and as short and direct as possible to maximize oxygen getting into the tank. Anaerobic bacteria is the stuff that makes the tank stink... Aerobic bacteria are good...
The vent is clearly very important. If the vent is too small or too long the tank will be anaerobic (bad), but if the vent is not positioned far enough away from the cockpit it could stink (also bad).
Would it work to have a small diam and short run inlet vent and a longer larger diam vent running up the wind gen pole?

I guess I am concerned that for a very short vent there is a risk of waste coming out of the vent when it is full and the boat is in rough sees and heeled. I suppose it is important that the vent exit is high enough above the tank that this cannot happen. (Which makes my planned config difficult, since the locker where the tank could go would be very close )

Where do folks position the vent outlets?
Anyone regretted their vent or tank installations or thinking of changing them?
What about using an air inlet vent in combination with an air outlet and a small fan to force air through?
Can folks ever smell the tank when outside on a calm day?

I guess what I am saying is that if there is any smell from the tank, I would consider the installation a failure and certainly my wife would justifiably freak out! So no matter what the cost I cannot have a smelly tank. So if holding tanks do lead to unpleasant odors, perhaps a Lectrasan or some other processing tank might be needed. So I really need to know, do ALL holding tank installations stink or just badly vented tanks?

Quote:
Originally Posted by sailingdog View Post
I like the Lavac, as it is almost bulletproof and generally uses less water than traditional designs.
Does it use enough water to keep things moving so to speak?

Last edited by matt2; 03-11-2009 at 01:05 AM.
Reply With Quote Quick reply to this message Share with Facebook
  #7  
Old 03-11-2009
Member
 
Join Date: Dec 2008
Posts: 57
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
matt2 is on a distinguished road
Thanks for the FRP Tank Links

Quote:
Originally Posted by dgr View Post
Thanks for the links, very helpful!

Reading the MARKSTANK article (quoted below) I did wonder about how the tank is joined together again. Looks like it says create a rough scarfed joint and glue together using epoxy and chopped mat. But chopped mat would wick and cause osmosis and leakage. So I guess I would need to cut an access port in the top of the tank and sand down the internal join and coat it with epoxy, to make sure it is waterproof. Then I guess strengthen the join on the outside as well.

Quote:
Originally Posted by MARKSTANK Article
"Sand or grind (a 7-inch right-angle grinder does a great job here, but a belt sander works) a 3-inch scarf on the inside of the top and the outside of the bottom. Great
accuracy is not needed; just draw a reference line at 3 inches to start and taper to a
feather edge. Wet out the scarf with straight catalyzed resin. Make a glue by adding
chopped fibers (easily made by cutting your scraps into 1/4-inch pieces) to the resin,
apply this to the joint, and assemble the two halves of the tank, smoothing the
squeezed-out glue with a putty knife. Be sure to tap the top into place until it is parallel
with the bottom. Wrap another layer of biply around the sides of the tank. If you want a
non-tacky finish, you can either use finishing resin for this step or wrap the tank in
plastic wrap while it dries. The top and bottom can likewise be coated with finishing
resin or with plain resin and covered with plastic, but this is entirely optional."
Next step is probably to create a lid for the access port and screw it down using 5200 as the sealant. Probably best if the screws don't penetrate the inside of the tank, so the tank needs to be quite thick at the top where the access port will be.

Does this look ok?

Last edited by matt2; 03-11-2009 at 06:21 AM.
Reply With Quote Quick reply to this message Share with Facebook
  #8  
Old 03-11-2009
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
Quote:
Originally Posted by matt2 View Post
That is reassuring.
Are there any special advantages to HDPE?
Is it possible to fabricate your own HDPE tanks?
Not really, since most HDPE tanks are either rotomolded or blow molded in a single piece. The problem is that not much sticks well to HDPE, and IMHO it would be rather difficult to seal a homemade HDPE tank well.

Quote:
That is what I feared. So a flat tank in the floor under the bowl would probably not work well. To get the right verticality I might have to rip out the sink and redo the vanity so a holding tank can go inside the cabinet. I am not at all keen to lose the hanging locker to a holding tank.
Even a cubical tank is workable... wide, flat tanks just are too difficult to drain completely, unless the bottom is fairly heavily sloped.

Quote:
I think I will have a macerator pump (a requirement in may areas where discharge is allowed) to pump out the tank. As I understand this pump is positioned after the Y valve on the overboard seacock outlet. i.e. pumpout stations have their own pump.
I prefer using a non-electric diaphragm waste pump rather than a macerator. If you have a problem with the electrical macerator pump at sea, you're stuck with a full holding tank.

Quote:
The vent is clearly very important. If the vent is too small or too long the tank will be anaerobic (bad), but if the vent is not positioned far enough away from the cockpit it could stink (also bad).
Would it work to have a small diam and short run inlet vent and a longer larger diam vent running up the wind gen pole?

I guess I am concerned that for a very short vent there is a risk of waste coming out of the vent when it is full and the boat is in rough sees and heeled. I suppose it is important that the vent exit is high enough above the tank that this cannot happen. (Which makes my planned config difficult, since the locker where the tank could go would be very close )

Where do folks position the vent outlets?
If the tank is mounted low, this is usually not an issue, if it is mounted higher, this can be an issue on a monohull.

Quote:
Anyone regretted their vent or tank installations or thinking of changing them?
What about using an air inlet vent in combination with an air outlet and a small fan to force air through?
Can folks ever smell the tank when outside on a calm day?
If the tank is well ventilated, it shouldn't be too much of an issue... the cause of the holding tank really reeking is usually anaerobic bacteria in the tank, and having a well ventilated tank solves that. A solar powered fan and using two vents would be a great solution, but a bit overkill IMHO.

Quote:
I guess what I am saying is that if there is any smell from the tank, I would consider the installation a failure and certainly my wife would justifiably freak out! So no matter what the cost I cannot have a smelly tank. So if holding tanks do lead to unpleasant odors, perhaps a Lectrasan or some other processing tank might be needed. So I really need to know, do ALL holding tank installations stink or just badly vented tanks?

Does it use enough water to keep things moving so to speak?[/
If you're serious about this, I'd highly recommend you sign up at the SBO forums and ask Peggie Hall directly. She's an expert on their forums. Why ask us hacks when you can ask Peggie??? It would help if you said what kind of boat you have and where the head is located in it. It sounds like you have a boat with an aft head.
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Quick reply to this message Share with Facebook
  #9  
Old 03-11-2009
Member
 
Join Date: Dec 2008
Posts: 57
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
matt2 is on a distinguished road
A Possible Solution

Quote:
Originally Posted by sailingdog View Post
Even a cubical tank is workable... wide, flat tanks just are too difficult to drain completely, unless the bottom is fairly heavily sloped.
Thanks, your comment has given me an idea that I think will work. I am thinking I will cut a hole in the non-structural bulkhead between the hanging locker and the vanity and shape a tank with wider almost cubic base but with less height. I can get the volume and keep the top of the tank well below the vents. This will use up some space at the back of the vanity unit which is not that accessible anyway. It also means a smaller intrusion into the locker, so the locker will remain functional.

Quote:
Originally Posted by sailingdog View Post
I prefer using a non-electric diaphragm waste pump rather than a macerator. If you have a problem with the electrical macerator pump at sea, you're stuck with a full holding tank.
Yes I know other experienced folks have also used this setup. Though in some areas it is a requirement to only discharge macerated waste. Whatever pump I use will have to be self priming.

Quote:
Originally Posted by sailingdog View Post
If you're serious about this, I'd highly recommend you sign up at the SBO forums and ask Peggie Hall directly. She's an expert on their forums. Why ask us hacks when you can ask Peggie???
Absolutely serious! What choice is there. Have to have a holding tank of some kind these days. Thanks, I will check out the suggested forum, but I must say I am very happy with the advice I have received here.
Reply With Quote Quick reply to this message Share with Facebook
  #10  
Old 03-11-2009
Bender of Nails
 
Join Date: Jan 2009
Location: West Coast BC
Posts: 66
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
Deadeye is on a distinguished road
Just an addition here - it sounds like you've got the answers you're looking for.

Sealand makes a carbon filter that you plumb into the vent to kill odors. From the ones I've seen (smelled...), they are probably 75% effective vs no filter. No idea what they cost though - for us it's just another service item.

In powerboats up to about 45', the 10 gallon Sealand holding tank is pretty ubiquitous here - I don't think I've ever been asked to install a bigger one.

FWIW I plan to build my own as well from epoxy and ply and the inner coating of epoxy will probably be laced with graphite to make it harder and more 'slippery'. I'd caution against using epoxy with mat because mat requires styrene based resin to dissolve into a 'mush'. It will physically work to build up bulk, but it's pretty wasteful of epoxy IMHO.

I used to work for a shop that built sportfishers to about 30'. They used a solid 'glass tank made over a triangular plug mold that fit in the forepeak against the stem. I always wondered why they gelcoated the outside but not the inside of the tank...ewwww.....
__________________
"Verbosity leads to unclear inarticulate things"
~Dan Quayle
Reply With Quote Quick reply to this message Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Siphoning holding tank Sixbrothers Gear & Maintenance 18 10-25-2008 12:08 AM
holding tank removal gwhar Gear & Maintenance 4 10-03-2008 09:39 AM
Holding tank or Type 1 MSD for Cal 39 costaricanwannabe Cal 4 03-13-2007 07:10 AM
Holding tank jeanneau 51 Myblueheaven Living Aboard 3 05-25-2006 05:06 PM
Sealand Holding Tank System sjacovino Gear & Maintenance 4 02-08-2001 03:48 PM


All times are GMT -4. The time now is 07:36 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.