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Executive summary

We just got back from two, separate week long (SUN-FRI) trips to the Cape and we left with

3x 21/2 gallon spring water containers under galley
9 gallon fresh water tank under bow.

We returned from each week with about 2/3 of the 9 gallons gone, and one of the 21/2 gallon containers consumed

Crew of one adult and twin 10 year old girls


We sponge bathed every night - you can do this with an amazingly little amount of water. I used to use more when I shaved until I discovered the Admiral likes to 'greet' me on my return if I dont shave....since then I havent been able to find my razor.

I would think the bladder would be an awful lot of work.

BUT if you could imagine a bladder of about 1/2 to 2/3 the ballast volume which would ensure that incoming water/ballast would not be constricted.

This way, you'd still have 75 gallons or so.

As far as half empty situations, the only time a half-empty condition would arise would be on the trailer(after dumping ballast for trailering). SO, you'd need a real efficient way of emptying the bladder when needed.

If we are going to use tight tolerances...

Here is the RCH

At 85 deg F. Pure water... no salt water, no pepper, no minerals...

8.310492392872696 lbs/gal.

Giving...
138.37928556270278708253121381646 gallons.

15 Halyard lashes for excessive significant figures

SURV1969 wrote:I would think the bladder would be an awful lot of work.
As far as half empty situations, the only time a half-empty condition would arise would be on the trailer(after dumping ballast for trailering). SO, you'd need a real efficient way of emptying the bladder when needed.

But, its a labor of luuuuvvvv.

Good point... I hadn't considered that I might get it back on the trailer with 75 gallons of water still there. Don't want to overload the trailer or travel around carrying it! Thanks. Got to add a discharge valve.

Kelly Hanson East wrote:here

http://macgregorsailors.com/phpBB/viewt ... c&&start=0

Helpful thread...
1) Some people putting on 30+ gallons or 250 pounds... I'd have to leave a friend at home.
2) Someone posted the cross sections showing the ballast... I had overlooked that the permanent ballast is under a big portion of the raised floor.
3) MARK PASSMORE had a similar thought
4) Damn! Nauta likes their plastic baggies.

Inquisitor
Don't know whether it is feasible but you could cut two access holes one at each end of the front portion of the ballast and seal them with the flush deck covers.
These would allow you to tie the corners or part of the bladder down by fibre glassing in some ties, I still think the bladder needs pegging down even if just to prevent it flipping up and covering the vent hole when filling ballast.
Not sure how much space is in there but you may be able to piggy back two 150L plastimo bladders.
Another thing to consider may be the sharp edges on the fibreglassing we had to sand these off when installing a bladder below the aft bunk.
If the deck covers are suitable for sealing the tank (neoprene seal and no head pressure) this would also allow you to unscrew and release water when retrieving or maybe this would only be needed for long trailer hauls.
The biggest problem I see is balancing the ballast and bladder levels as the tank would need to be at capacity when sailing and pumping water out of the bladders would create a vacuam so maybe a non return valve would be the answer between ballast and outside water.
Hope you do the mod as it is another option available to us all if it is successful, if not then we all know it is not a good idea

I'm a little lost on the physics involved here. If you have a bladder in the ballast tank,as the water from the bladder is drawn down,you would need to have ballast water added to replace it. Since you can't leave the gate open to take in water while you are underway,how will that work?
Are you only using water while the boat is stopped?

pumping water out of the bladders would create a vacuam so MAYBE a non return valve would be the answer between ballast and outside water.

With emphasis on the maybe as you would also need a stopcock or your ballast would fill automatically with just a non return valve.
I don't see the need for this much more water but am fairly interested to see someone else try this

Are you only using water while the boat is stopped?

I would think the only significant usage would happen while stopped. Using a few gallons underway isnt going to create a big moving ballast problem.

Once you stop, just open the ballast valve at back, the use your water as planned, the sea water

On cutting open the ballast tank - that part of the boat is under the water line, so you have to do a good job with that plate with regards to sealing under pressure. The rear gate valves usually leak a bit, so you cant count on those to stop your boat from filling with water.

Let's suppose that a bladder is the solution. When you go for long periods of not using it, what bacteria builds inside the bladder? What do you do to insure the quality of your drinking water is a good as it was before you added it to the bladder? Also, what can be done to to cleanse the bladder without damaging the bladder substance itself? The only entrance to the bladder is its filling hole. The only egress is turning on a tap.

Ray

KayakDan wrote:Are you only using water while the boat is stopped?

Only significant usage would be at anchor... the shower won't be used while sailing... especially when the boat tends to be at 45 degrees more than strait up. To hard to make the shower (and lots of other things) work at all angle.

Detail 1 - Since I expect the shape of the forward tank to be rather irregular... does anyone know of a material that can be "welded/glued" together so I can make a conformal tank?
I was thinking something like the gray sheet material that is used to make custom shower liners.

Detail 2 - I think a port solution would be best for removal/cleaning/etc... however, I don't think a deck port would be strong enough or sealed enough to retain water pressure. I would think it has to be more of the variety used for escape hatches on catamarans (in case they go sunny side down). However, I was thinking something on the order of 6" diameter.
Any ideas?


Oh... BTW... no one needs to hold there breath. This is purely academic at this point... its a winter project at best. (January not July) I may not sound like it, but I'm a truly conservative composites/structural engineer.

Inquisitor
My son inlaw installs large water tanks that use a bladder and the seams are glued, this material should be available but they would need a cover to protect them from the splinters on the fibreglass surface (if there are any).
The deck covers I was thinking of are 6", they are installed standard on the Aussie boats transom to facilitate installing the stern rails and they are watertight but there is no water pressure unless you pressurize the ballast when filling, in normal use the ports will be at the top and there is no head pressure unless heeling and even then it would only be 2' max.

You could just epoxy coat the interior hull of your boat to smooth the interior - this would eliminate the splinter isssue.

Search posts for the right product - several people have done this here.

Boblee wrote:...The deck covers I was thinking of are 6", they are installed standard on the Aussie boats transom to facilitate installing the stern rails and they are watertight but there is no water pressure unless you pressurize the ballast when filling, in normal use the ports will be at the top and there is no head pressure unless heeling and even then it would only be 2' max.

Do you have a link to the port you have in mind? If you are talking about ports I think you are...

... and maybe, I'm being a little too anal about the engineering. I agree... if the port is on top, that static pressure is nil. Two things are an issue.

1) Water hammer... like when your house pipes bang around. With the plug out and the water sloshing as it comes in, I've see it spray quite a bit under that bunk access. The load from this dynamic pressure will be quite high on a 6" port.

2) As those Aussie ports are loaded by the water pressure, they press more firmly against their seat. In our case, the pressure is going to be on the inside... thus pressing them away from the seat. The fastening system will have to take those loads.