Water tank install? Inside water ballast tank

[Ixneigh]

I know this subject has come up x times before.

But I think I got it so maybe the engineering guys on the board could give me some input.

Here's the plan.
I never realized until a few months ago that the bottom surface of the rear bunk area on the M is actually the top of the water ballast tank. I thought it was the inside surface of the hull and that the hull in that area was just very thin. (this area gives quite a bit if you push down on it)
From looking inside the ballast fill with a flashlight it looks as though there is about six inches between the actual hull and the top of the tank. The stringer like structures seem filled with foam.

So what if I cut a square out of the top of the tank large enough for a 30 gallon vetus or similar rubber bladder type tank. I can hear everyone cringe. Now I would then glass in all four sides from hull to top surface to make a box with top open. So now that area is isolated from the tank system. Drill drain holes in the sides of the box so now it's no longer isolated.
Cover inside of the area with carpet for chafe protection and lay the bladder tank inside. Cover the bladder with a panel sealed and fastened however you like, and plumb tank to fill line and sink pump and maybe cockpit shower. I might be inclined to glass the cover back on with a few light layers of glass along the edges.

When you fill the tank, open the boats ballast gate valve and allow the tank to expel salt water. As you use fresh water, periodically open the boats gate valve to allow water in. One might also have a one way valve on the boat if you also have the vent to anchor locker mod, making for automatic operation.
This would only make sense for owners who use the boat more then a week or who like me, don't like Jerry jugs and already have things in the side lockers and forward veeberth area.

Some objections might include
What it the top panel leaks? It shouldn't if it's sealed and fastened properly. Or if it does only a few drops. That area is always damp on my boat anyway even when she's out of the water :p

What if it somehow weakens the boat? Those glassed in parts should restore the strength and then some.

What if you forget to open the boats ballast valve? If you forget on filling the tank I assume water would spurt out the anchor locker vent. If you don't have the vent I think it just wouldn't fill with your average dockside water pressure.
It you forget to open the valve and you used a lot of water, the boat might be more tender then usual but with only 30 gallons of water missing I doubt she'd be terribly compromised. I seem to loose water out of my boat just sailing so once in a while I open the valve to let it top off.

The hardest part of this might be insuring water tight seals where the plumbing exists the cover of the water bladder box.

[Steve K]

I've thought of doing something like this at one time.
I have also been toying with the idea of building a sealed compartment, down in the ballast tank for batteries. I have a D boat and there is enough depth, right in the center of the tank, to do this (I'm pretty sure). The weight of the batteries would come close to the weight of lost ballast water. The batteries would be low and centered in the hull and the overall weight of the boat would be around 150 to 190 pounds less (I have three batteries, one a normal flooded deep cycle and two, VERY heavy gel cells)

As I mention above, I'm not positive about the depth of the ballast tank in it's deepest part. I'll have to be sure of this before doing any cutting, but I think the rounded hull makes the ballast tank deep enough, right at it's deepest point, to do this. Just too busy right now to start any new projects.

Where your water tank is concerned:
You may even find that just removing the weight in the rear might improve sailing performance. I'd try sailing her a couple times, after the compartment is installed, but before you drill the flood holes.... and with the fresh water bladder empty. (you're talking about 260 pounds of weight with 30 gallons of water). Who knows, other M owners may wonder why your boat is faster than theirs..... and why you're always thirsty
I know, it sounds like a lot of weight to remove, but remember, the boat sails well without an outboard attached, right?
Food for thought

Best Breezes,
Steve K.
Mac 26D "Three Sheets"

[Russ]

I'm not so sure the ballast tank is the way you think.
From this pic, it looks like the "tank" is the 2 ridges on either side and between that is the hull.


I guess you could drill a small hole in the top (with the boat on the trailer) and if you don't punch through the bottom, it would confirm you idea.

If what you claim is true about the ballast tank, you might have an excellent mod. A small water inlet would allow sea water to fill as you pumped fresh water out.
Interesting idea. Let us know how you make out with this.

[Steve K]

Russ could be right.
I had the tank on the X boat in mind. Looks like the M may be different.

Still going to investigate the D boat tank. It's different than either M or X.
SK

[DaveB]

Don't even think of it!
Ballast tank should be left as is with no penitration of the holding tank.
You will need a Strucual Engineers Lic. certifying and document all changes you made for any liability and Insurance issues.
Any penitration can result in fitting problems that may fail in future and cause a unballasted boat.
Best to put water bladders next to stringers with a 1/2 inch rubber mat to protect from Chafe, the bladders are close enough to center of gravity and for inspection.
Mine works great.
Dave

I know this subject has come up x times before.

But I think I got it so maybe the engineering guys on the board could give me some input.

Here's the plan.
I never realized until a few months ago that the bottom surface of the rear bunk area on the M is actually the top of the water ballast tank. I thought it was the inside surface of the hull and that the hull in that area was just very thin. (this area gives quite a bit if you push down on it)
From looking inside the ballast fill with a flashlight it looks as though there is about six inches between the actual hull and the top of the tank. The stringer like structures seem filled with foam.

So what if I cut a square out of the top of the tank large enough for a 30 gallon vetus or similar rubber bladder type tank. I can hear everyone cringe. Now I would then glass in all four sides from hull to top surface to make a box with top open. So now that area is isolated from the tank system. Drill drain holes in the sides of the box so now it's no longer isolated.
Cover inside of the area with carpet for chafe protection and lay the bladder tank inside. Cover the bladder with a panel sealed and fastened however you like, and plumb tank to fill line and sink pump and maybe cockpit shower. I might be inclined to glass the cover back on with a few light layers of glass along the edges.

When you fill the tank, open the boats ballast gate valve and allow the tank to expel salt water. As you use fresh water, periodically open the boats gate valve to allow water in. One might also have a one way valve on the boat if you also have the vent to anchor locker mod, making for automatic operation.
This would only make sense for owners who use the boat more then a week or who like me, don't like Jerry jugs and already have things in the side lockers and forward veeberth area.

Some objections might include
What it the top panel leaks? It shouldn't if it's sealed and fastened properly. Or if it does only a few drops. That area is always damp on my boat anyway even when she's out of the water :p

What if it somehow weakens the boat? Those glassed in parts should restore the strength and then some.

What if you forget to open the boats ballast valve? If you forget on filling the tank I assume water would spurt out the anchor locker vent. If you don't have the vent I think it just wouldn't fill with your average dockside water pressure.
It you forget to open the valve and you used a lot of water, the boat might be more tender then usual but with only 30 gallons of water missing I doubt she'd be terribly compromised. I seem to loose water out of my boat just sailing so once in a while I open the valve to let it top off.

The hardest part of this might be insuring water tight seals where the plumbing exists the cover of the water bladder box.

[Ixneigh]

I've already done some other stuff that violates Lloyds of London, i am sure. I usually have no problems making things strong. or stronger even. But opinion noted.

I assure you there is a double bottom in the back of the M model with water in between them. Looks like about 4-6 inches of water.

The idea is to save weight be having ballast water be usable and not having to carry extra water. And a lot of water.
In the Bahamas thirty or forty gallons of water would be great. if I can save weight by having double duty ballast water I can chuck a few hundred pounds more lead in the bilge too. Or a couPle Agm batteries.

I do realize something like this can hurt the resale value of the boat. Not that I really care. I think this is my last boat. But it is fiberglass, and fiberglass can be repaired if need be. I am quite certain i could restore the ballast tank to pre-Ixneigh if I ever wanted to. I would use vinyl ester resin for this job to get maximum bond. Glass a few stringer across the bottom maybe, not that the boat needs them. The bottom is plenty thick. Thicker then it needs to be in fact on the M. They used an extra layer as ballast. Guess resin and glass is cheaper per pound then lead.

[Russ]

I assure you there is a double bottom in the back of the M model with water in between them. Looks like about 4-6 inches of water.

Very interesting. Well, as I said, drilling a hole would tell you exactly how much room (if any) there is under there. Patching it would be easy if it doesn't work.

I've often thought about the mod you are proposing. I can't afford any more weight back there. That's why my tanks (jugs) are in the v-berth. If what you are proposing works, it would be a brilliant mod.


--Russ

[seahouse]

It’s a fairly easy matter to confirm the ballast tank extents by sticking a long broom handle, or similar, into the open gate valve at the transom. Ok – no proctologist jokes here…

You could also use a bendable stiff wire, or similar, in an “L” shape to accurately (to within ½” or ¼”) confirm the height of the space at any point you can reach. (Say, withing 10' of the gate valve, if your wire is long enough).

- Brian.

[mastreb]

I also think you should leave the salt water tank in place, and simply add longitudinal bladder water tanks. If the D is similar to the M, your best bet for improved ballasting would be between the two tank ridges; that said, anywhere along the bottom hull is fine so long as the tanks are (a) run the length of the boat or are centered for to aft and (b) are drained evenly.

If you wanted to be overly serious about performance, you'd install the bladders at the port and starboard extents with a water pump between the two having a switch to pump from port to starboard, and then fill the windward tank on every tack. A simple inclinometer switch made from an old thermostat could be used to auto-pump the water on each tack, with a cut-off switch that triggers on a drop in resistance/increase in voltage which would indicate that the pumping is done. You'd have to use a pump with a reversible backflow preventer. Fun project!

[Divecoz]

I wouldn't mess with the Integral Ballast system.. But That's Me I have a 30 Gallon water bladder that sits under the rear berth..works fine.. I have something I tossed in under the bladder for chafe issues and don't remember what I used.. Its pretty darn smooth in mine, by and by JSYK..

[Russ]

I wouldn't mess with the Integral Ballast system.. But That's Me I have a 30 Gallon water bladder that sits under the rear berth..works fine.. I have something I tossed in under the bladder for chafe issues and don't remember what I used.. Its pretty darn smooth in mine, by and by JSYK..

Many have used bladder tanks under the aft berth. Perfect location because most of that space is useless for anything else.
However, 30 gallons of water is about 250 pounds. That's a lot of weight in the aft of an M that already sits low in the aft. I have 24 gallons of fuel and a heavy 70hp Suzuki. Adding more weight back there is not a good idea. So I added more up front and it helps a lot.

What he's thinking of doing is not adding any more weight to the boat. Simple replacing sea water with fresh water. I've often thought all that ballast would be great if it were drinkable. Such a waste to put sea water in there that is not potable.

My question is if there is room in the tank between the 2 stringers. If so, I'm sure that area can be made as strong if not stronger with a some good glass work. If what he's describing is true, I doubt the ballast tank adds any structural strength either. The "ribs" do look like they add strength, but that's not where he's planning on cutting into.

The M has 1150 lbs of water ballast. That's approx 140 gallons. If you've ever seen how much 140 gallons looks like (aquarium etc.), it's not very big. That's why I doubt there is 4 inches between hull and tank. I hope I'm wrong because I'd love to see this mod done. Ixneigh is certain there is 4" there. I believe there is across the transom, but not sure how wide this is. I'll be watching the progress of this one.

[Ixneigh]

There's a lot of water between the "hulls" I havent measured but it's a good guess I could easily get a thirty gallon capacity even if I had to use a larger tank but not fill it all the way.

When I first got my boat the whole bilge was wet due to dealer forgetting vent plug. I spent my first evening bailing out my boat. In the back under the births I was dismayed to see how thin the "bottom" was. I could kneel on it and deflect it!!! Plus I could hear water through it! Like there was a delaminated space or something. Beh. I chocked it off to typical mac lightness and if the boats bottom fell out, well it's insured.
I forgot about it till I had the boat on the trailor. I thumped on the hull thinking about a few layers of fiberglass there as a project but hey! It feels really solid. Really solid. Inside I pick up the back berth cusions and tap around. There is a big void there!! It sounds hollow. Because it is. Iooked into the ballast drain. I had thought that the stringers were filled with water and that was it. Seems not true. From what I could see they are at least partially filled with foam. On the inside they appear not to be even glassed to the hull. It was then I realized I might be able to have my water and drink it too.
I do not want any More weight in back. It does affect sailing for the worse.
Im not asking so much IF it's a good idea only if it would work as I envisioned. I will have to decide for myself if I want to undertake this project this winter along with others.
Maybe someone who's boat is out can verifie exactly how much space is in there. The glass work would be straight forward. It's unpainted. Just a scuff and good cleaning and lay in plenty of glass.

[Russ]

Iooked into the ballast drain. I had thought that the stringers were filled with water and that was it. Seems not true. From what I could see they are at least partially filled with foam. On the inside they appear not to be even glassed to the hull.

Very interesting. Brings up lots of questions for me.

Maybe those ridges are not ballast, but are for strength. Foam in there huh? I keep ballast in all summer and add chlorine tabs to keep it from growing nasties. I wonder if mine is water logged now. My hot tub cover gets water logged from saturation from steam and chlorine. Turns it into water logged mushy rubber blob that is very heavy.

So if you do this, you'll need to "vent" the ballast so it can fill with sea water as you draw fresh water from the bladder. That should be easy. Simply install a small thru-hull someplace center (like near the batteries under the steps) with a valve that enters the ballast tank. Running without ballast, you would shut this so water doesn't creep in. Of course the air vent in the v-berth would need to be closed so you don't suck air in there. As long as the air vent was sealed shut, ballast water would stay in the tank and draw new sea water in as you empty the bladder.

Like you said, if that glass is as thin as you say, sealing it and making it stronger should be a simple task. I wonder if some kind of access port could be created for inspection and maintenance. All hose clamps and such on the bladder would need some special attention because they would be submerged in sea water.

Now, how would you keep the inside of the bladder clean? A few drops of chlorox would do the trick I guess. Just make sure you put clean water in there all the time. Same issues as other bladders except harder to remove if you had to.

The idea of having a lot of fresh water is exciting. Cruising long periods of time and storing potable water is a challenge on a 26' boat. Having 30 gallons of fresh water without adding a single extra pound of weight is very cool.

[March]

If the main issue here is, having extra drinking/clean water, a desalinator would provide that with minimum hassle. I had the opportunity to test them on our trip to the Bahamas. The smallest model is useless. It may work in a dinghy adrift and may keep you alive, but the larger model Katadyn 35 worked pretty well. In five minutes of leisurely pumping, you have a quart of excellent water that tastes even better than the market purified stuff. We always took turns pumping for half an hour every day and sweet water never went missing--for dishes, cooking, washing, etc.

When you consider that the additional watertank has to be kept in pristine conditions, and the water inside is likely to taste, well, like the kind of water you would get at the dock, at best... I dunno. With the desalinator, we always had ice-cold, fresh water in the cooler. And when we were out of it, we could make it on the fly.

But maybe the issue is not really extra drinking water, but something else. Sweet water has a different molecular mass from sea water. That might also affect the boat's sailing capabilities.

[Ixneigh]

Even with a desal unit I would keep ten gallons on hand. And washing with desal water means 20 minutes pumping? ( assuming one gallon to bathe at the end if the day) and when you are not using it it needs to be laid up correctly.
Not to mention the 2000 dollar cost.
I'm betting this mod would cost 2-300 in materials. A weekend of work.
Id be more inclined to get the power version and run it when I ran the motor.