After a season of using a Porta Potti (and amazed at how much easier it was than anticipated), I plan to go forward with a proper marine head and holding tank for Rhiannon. What I've designed fits in the space behind the head area, under the shelf. With its plumbing, it will use that entire area. It will feature pumpout straight down thru the deck, a sump at the lowest spot where the line to the macerator pump will attach (mounted under the port settee berth with dedicated thru-hull and seacock), and an internal pipe that runs thru the tank bottom and goes nearly to the top (inside) for input. Of course there will be a vent (possibly two).
The tank will be made of vinylester FRP, gel coat inside, and will have a bolt-on FRP top sealed with polysulfide (Lifecaulk). I estimate its volume to be about 10 gallons (my physicist neigbor says 9.6 and another friend estimates no more than eight). When I have nothing better to do I'll measure it but it totally fills the space available and the capacity is whatever it is. I will engineer some sort of secure mounting but have yet to design that.
I plan to make this tank on a male mold, a highly finished plywood mockup. Here's the question -- I can mold two, maybe three units off this throwaway plug but if there is sufficient interest from fellow CD-27 owners, I'll go ahead and make a FRP mold that can produce more of these. It's not a matter of expense as the materials are on hand. If there seems to be sufficient interest from fellow 27 owners in having one of these custom holding tanks, I'll go to the (not insignificant) trouble to make a proper mold.
If you have interest please so indicate. Any comments, suggestions, questions, etc. will be considered. Until the design is finished and prototyped I have no idea what the cost will be so don't bother asking. Furthermore, it may only fit the series of CD-27's of which Rhiannon is a member. BTW, the purpose of this exercise is to realize the benefits of a holding tank without the plumbing nightmare that Cape Dory designed for the one in the bilge and to minimally impact precious storage space. My design features straightforward pumpout, easy connections, overboard dishcharge via a macerator pump, and the shortest possible hose runs throughout.
I'll throw this out and see what happens.
Andy Denmark
CD-27 #270 "Rhiannon"
trekker@coastalnet.com
custom CD-27 holding tank
Moderator: Jim Walsh
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Duncan Maio
Re: custom CD-27 holding tank
Andy:
Remedy (CD27 #37) has a slide-out sink behind and above the head, so I don't think the setup you describe will work for us. We have a recirculating-type holding tank that is no longer plumbed to recirculate, and which lives under the V-berth on the port side, just forward of the head. That space also contains a diaphragm pump that can be used to pump the holding tank overboard. The head is plumbed to pump to the holding tank or overboard, and there is also a deck pump-out for the holding tank.
We have considered a number of options, the most extreme of which is to add water tanks under the setees and convert the existing water tank under the V-berth to a holding tank. In an ideal world, the port water tank would be used for flush water, and the starboard tank for potable water.
The more likely solution is a new tank for the existing space, and relocating the waste pump to a spot behind the head. If you consider this space (larger than 9 gallons, even with room to get at the raw water intake) I might be interested. If anyone has a source for tanks that fit under the setees of a CD-27, I am definitely interested.
Duncan Maio
s/v Remedy
CD27 #37
Bristol, RI
mail@mysticmarine.net
Remedy (CD27 #37) has a slide-out sink behind and above the head, so I don't think the setup you describe will work for us. We have a recirculating-type holding tank that is no longer plumbed to recirculate, and which lives under the V-berth on the port side, just forward of the head. That space also contains a diaphragm pump that can be used to pump the holding tank overboard. The head is plumbed to pump to the holding tank or overboard, and there is also a deck pump-out for the holding tank.
We have considered a number of options, the most extreme of which is to add water tanks under the setees and convert the existing water tank under the V-berth to a holding tank. In an ideal world, the port water tank would be used for flush water, and the starboard tank for potable water.
The more likely solution is a new tank for the existing space, and relocating the waste pump to a spot behind the head. If you consider this space (larger than 9 gallons, even with room to get at the raw water intake) I might be interested. If anyone has a source for tanks that fit under the setees of a CD-27, I am definitely interested.
Duncan Maio
s/v Remedy
CD27 #37
Bristol, RI
mail@mysticmarine.net
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John R.
Re: custom CD-27 holding tank
Andy,
An interesting project you are about to embark on. I've dealt with this issue first hand in the past year constructing a new holding tank for our '83 CD30. I was disappointed in the cost vs quality issue with the commercially available HDPE tanks and made the decision to build my own using the original HDPE Kracor tank as a model in combination with original engineering drawings from Kracor.
I thought you might like to know the basic method I used in construction. I wanted strong robust tank walls and seams. That criteria dictated that I use plywood, glass, West epoxy and stainless fasteners to acheive the goal and create excellent longevity potential.
Gougeon has been making tanks of all types (diesel, holding, potable, etc)for many years with great success. Why everybody thinks they need HDPE tanks is a mystery to me. They crack, discolor, distort, split, and leak. You name it and HDPE probably has the weakness. On the other hand FRP tanks have been used for years also but with mixed results. Delamination seems to be a problem over time and that may be due to the classical polyester resin matrix. The vinylesters as you mention may resolve the issues that existed with regular poly. One thing is for certain and that is epoxy has an excellent track record in tank construction. That is why I chose the West as the resin base in my tank.
Since completing the tank I came to the realization it will more than likely outlast the rest of the boat. Overkill? I don't think so. I like to think of it as a very important insurance policy. I can't think of anything worse aside from sinking or fire that can occur on a boat than head or tank problems.......meaning leaks! Nasty, smelly, unhealthy....simply atrocious and should be avoided at all costs.
I kept those thoughts foremost in mind when building the tank. That made me over build the tank consciously with the reasoning.... NO MORE HOLDING TANK WOES!
I think you are making the right decision to custom build a tank. I would take the epoxy road myself. I would reinforce the glass walls with a encapsulated substrate, not just form FRP over a mold. I would not bolt the tank top in place using polysulfide or any other caulking as the seal. I would glue and glass the tank top in place and do a glassed over seam fillet on the inside as well. Same on all tank body seams.
All tank fittings (ports) should be epoxied in place. All fittings should be bronze with PVC internal evac line. You should definitely incorporate dual vent ports as high in the tank as possible. Your vent lines should run to the hull exterior with no tight bends. You should have a moderate access port installed in the tank top if you installed the tank top permanently to guarantee leak proofness.
You should incorporate internal motion damping baffles within the tank to minimize content sloshing for a couple reasons. Less chance of solution and debris getting into vent ports, less strain on tank walls and on evac tube assembly. Creates a internal support for evac tube assembly. You can't incorporate baffles into a molded tank unless you use a bolted on lid like you mention. That bolted lid can make you prone to future leaks.
Anyway those are some views I thought I'd share with you. I'd be happy to send you a few pics showing my tank under construction and in finished trim for your reference if it would be of help to you in your plans. I would be happy to discuss additional construction methods with you also.
Good luck.
An interesting project you are about to embark on. I've dealt with this issue first hand in the past year constructing a new holding tank for our '83 CD30. I was disappointed in the cost vs quality issue with the commercially available HDPE tanks and made the decision to build my own using the original HDPE Kracor tank as a model in combination with original engineering drawings from Kracor.
I thought you might like to know the basic method I used in construction. I wanted strong robust tank walls and seams. That criteria dictated that I use plywood, glass, West epoxy and stainless fasteners to acheive the goal and create excellent longevity potential.
Gougeon has been making tanks of all types (diesel, holding, potable, etc)for many years with great success. Why everybody thinks they need HDPE tanks is a mystery to me. They crack, discolor, distort, split, and leak. You name it and HDPE probably has the weakness. On the other hand FRP tanks have been used for years also but with mixed results. Delamination seems to be a problem over time and that may be due to the classical polyester resin matrix. The vinylesters as you mention may resolve the issues that existed with regular poly. One thing is for certain and that is epoxy has an excellent track record in tank construction. That is why I chose the West as the resin base in my tank.
Since completing the tank I came to the realization it will more than likely outlast the rest of the boat. Overkill? I don't think so. I like to think of it as a very important insurance policy. I can't think of anything worse aside from sinking or fire that can occur on a boat than head or tank problems.......meaning leaks! Nasty, smelly, unhealthy....simply atrocious and should be avoided at all costs.
I kept those thoughts foremost in mind when building the tank. That made me over build the tank consciously with the reasoning.... NO MORE HOLDING TANK WOES!
I think you are making the right decision to custom build a tank. I would take the epoxy road myself. I would reinforce the glass walls with a encapsulated substrate, not just form FRP over a mold. I would not bolt the tank top in place using polysulfide or any other caulking as the seal. I would glue and glass the tank top in place and do a glassed over seam fillet on the inside as well. Same on all tank body seams.
All tank fittings (ports) should be epoxied in place. All fittings should be bronze with PVC internal evac line. You should definitely incorporate dual vent ports as high in the tank as possible. Your vent lines should run to the hull exterior with no tight bends. You should have a moderate access port installed in the tank top if you installed the tank top permanently to guarantee leak proofness.
You should incorporate internal motion damping baffles within the tank to minimize content sloshing for a couple reasons. Less chance of solution and debris getting into vent ports, less strain on tank walls and on evac tube assembly. Creates a internal support for evac tube assembly. You can't incorporate baffles into a molded tank unless you use a bolted on lid like you mention. That bolted lid can make you prone to future leaks.
Anyway those are some views I thought I'd share with you. I'd be happy to send you a few pics showing my tank under construction and in finished trim for your reference if it would be of help to you in your plans. I would be happy to discuss additional construction methods with you also.
Good luck.
Andy Denmark wrote: After a season of using a Porta Potti (and amazed at how much easier it was than anticipated), I plan to go forward with a proper marine head and holding tank for Rhiannon. What I've designed fits in the space behind the head area, under the shelf. With its plumbing, it will use that entire area. It will feature pumpout straight down thru the deck, a sump at the lowest spot where the line to the macerator pump will attach (mounted under the port settee berth with dedicated thru-hull and seacock), and an internal pipe that runs thru the tank bottom and goes nearly to the top (inside) for input. Of course there will be a vent (possibly two).
The tank will be made of vinylester FRP, gel coat inside, and will have a bolt-on FRP top sealed with polysulfide (Lifecaulk). I estimate its volume to be about 10 gallons (my physicist neigbor says 9.6 and another friend estimates no more than eight). When I have nothing better to do I'll measure it but it totally fills the space available and the capacity is whatever it is. I will engineer some sort of secure mounting but have yet to design that.
I plan to make this tank on a male mold, a highly finished plywood mockup. Here's the question -- I can mold two, maybe three units off this throwaway plug but if there is sufficient interest from fellow CD-27 owners, I'll go ahead and make a FRP mold that can produce more of these. It's not a matter of expense as the materials are on hand. If there seems to be sufficient interest from fellow 27 owners in having one of these custom holding tanks, I'll go to the (not insignificant) trouble to make a proper mold.
If you have interest please so indicate. Any comments, suggestions, questions, etc. will be considered. Until the design is finished and prototyped I have no idea what the cost will be so don't bother asking. Furthermore, it may only fit the series of CD-27's of which Rhiannon is a member. BTW, the purpose of this exercise is to realize the benefits of a holding tank without the plumbing nightmare that Cape Dory designed for the one in the bilge and to minimally impact precious storage space. My design features straightforward pumpout, easy connections, overboard dishcharge via a macerator pump, and the shortest possible hose runs throughout.
I'll throw this out and see what happens.
Andy Denmark
CD-27 #270 "Rhiannon"
-
Paul
Re: custom CD-27 holding tank
I have the holding tank under the port settee (factory setup) the tank fittings are not in great shape but functioning. I may be interested in the new tank you propose but am not sure of its intended location, line placement etc. Could you describe with more detail?
I can get measurements of the settee tank if anyone is interested.
Paul
CD27 ESCAPADE #224
I can get measurements of the settee tank if anyone is interested.
Paul
CD27 ESCAPADE #224
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Andy Denmark
Re: custom CD-27 holding tank
Paul:
From all appearances, the response to my plan has been underwhelming except for you. Let's correspond via personal email or maybe even snail-mail for plans, etc. to keep from tying up the BBS. This is a winter project -- read January or February -- so there's time to work things out. Right now I'm doing some deliveries that are keeping me occupied and school is busy, too (last class Dec 3rd).
There are several versions of the head area design on 27's but I think the bulkhead spacing is close to the same. The tank I propose will mount against the hull behind the W/C and it's more or less wedge shaped and flat against the hull side, more vertical than horizontal. Hard to explain, easy to draw -- typical engineer's dilemna, thus the snail mail suggestion.
On Rhiannon, the tank would mount behind the cabinet (losing the hatch storage area) and under the shelf. Direct (short) connection on top to a deck pumpout fitting with two vent connections on top. There will be no way to inspect the tank once installed, thus the bolted on lid. Coming out of the tank bottom would be the connections for toilet output and tank drain (to macerator pump). All of this would be out of sight behind teak veneer paneling to match the rest of the interior. Y-valve would be optional and external -- I'm not going to use one.
Hope this conveys the idea a bit better.
Thanks to all who made suggestions and/or comments. Your inputs will be carefully considered.
Andy Denmark
CD-27 #270 "Rhiannon"
Lower Broad Creek, Oriental, NC
35* 05.1' N -- 076* 38.7' W (free dockage for any CD snowbirds)
trekker@coastalnet.com
From all appearances, the response to my plan has been underwhelming except for you. Let's correspond via personal email or maybe even snail-mail for plans, etc. to keep from tying up the BBS. This is a winter project -- read January or February -- so there's time to work things out. Right now I'm doing some deliveries that are keeping me occupied and school is busy, too (last class Dec 3rd).
There are several versions of the head area design on 27's but I think the bulkhead spacing is close to the same. The tank I propose will mount against the hull behind the W/C and it's more or less wedge shaped and flat against the hull side, more vertical than horizontal. Hard to explain, easy to draw -- typical engineer's dilemna, thus the snail mail suggestion.
On Rhiannon, the tank would mount behind the cabinet (losing the hatch storage area) and under the shelf. Direct (short) connection on top to a deck pumpout fitting with two vent connections on top. There will be no way to inspect the tank once installed, thus the bolted on lid. Coming out of the tank bottom would be the connections for toilet output and tank drain (to macerator pump). All of this would be out of sight behind teak veneer paneling to match the rest of the interior. Y-valve would be optional and external -- I'm not going to use one.
Hope this conveys the idea a bit better.
Thanks to all who made suggestions and/or comments. Your inputs will be carefully considered.
Andy Denmark
CD-27 #270 "Rhiannon"
Lower Broad Creek, Oriental, NC
35* 05.1' N -- 076* 38.7' W (free dockage for any CD snowbirds)
trekker@coastalnet.com