Why not use ballast tanks filled with water?

Combined with a pump, you would have the ability to adjust the ballast as needed.

http://en.wikipedia.org/wiki/Ballast_tank

In two words:"available space". (is the reason why not tanks).

We do not want to sacrifice any of the main salon. Our main salon floor is the bottom of the former fish-hold - and we can pour concrete between that floor and the inside surface of the hull.

Clearance available is subject to ribs and frames, eliminating any useful space for tanks under THERE. but concrete can fill it up.

Lead is our first choice - but we are not getting any younger OR richer and need to move this thing forward.

I am anticipating that I can use penetrating epoxy in the areas that will be in direct contact with the concrete as a preservative.

So when the concrete gets wet where is the water coming from? Can you dry out the water easier/faster when it is not bound in the concrete? Can you dry out the space anyhow anyway? I agree that lead would only get wet from the outside. But once there is water it still will get wet near the (Spruce) Hull.

What am I missing in this?

Other than that you might wanna talk to some floor maker. I think bathrooms and other wet areas do get a layer of water tight cement. Sorry dont know enough but somebody here might be able to help.

It is part of the nature of concrete to hold and to transmit moisture.

It is because of this known characteristic that concrete foundation walls receive either "damp-proofing" (AKA. black paint) or "water-proofing" (often in the form of a rubber-asphalt, or perhaps a vinyl membrane). Concrete floors are poured on a moisture barrier - often in the form of 6 mil or heavier polyethylene - for the same reason. These solutions are impractical in the bilges of my boat, however.

As to the "where is the water coming from" question - well, boats and water go together. It would be reasonable to assume that water will be present, either as liquid or vapour, from any of several normal sources on board.

See this is where I fail to see why the moisture in the concrete is a problem when it is going to be wet anyway.

To have a problem with the moisture in concrete you need to have means of getting rid of water it in the first place.

Is the problem that concrete keeps parts wet over a period of time that would not when using lead?

Try to look at it like it is a piece of precast, or a water tank, or sewage mill.

Water will be present.

That does not necessarily mean there is some other defect that must be remedied.

I found this article that addresses the question asked and am following up a few leads as a result:

http://www.waterproofmag.com/back_issues/201004/integral.php

thanks for the assist.

Any additive is not going to eliminate all the hygroscopicity of concrete. They will reduce the porosity but not eliminate it. Additional treatment after it is poured will be needed.

Go the old time route and use bricks. Much denser then concrete. They can be treated before hand. The weight can be distributed as needed.

The objective may be grey, rather than black or white. I will accept a significant reduction as success.

There are products that deal with this and I need the name of one please. If you know of any pre or post pour treatments by name or manufacturer then I would like to have a line on it.

Bricks are suitable as cargo ballast only in my experience. Concrete has a long history as permanent ballast, as do cobbles and beach rock.

I will be staying with concrete - even were they all equals (they aren't)- as space is irregular and very tight. Concrete gives me complete cavity fill.

BTW, I will be using penetrating epoxy on the inside of planking, ribs and frames that are to be in contact with the concrete as I fully expect some moisture to continue to be present.

Found: 3 types of integral waterproofing for concrete in this article.

http://www.waterproofmag.com/back_issues/201004/integral.php

NOW to track down a supplier or two!

Thanks everyone, for your input.

I can't answer your question, but it sounds like you have some leads. And if you waterproof the inside of the hull as you described, I'm not sure concrete is much different from lead. You might want to use as little water in the mix as possible in order to minimize shrinkage and the formation of fine cracks that would hold water.

However, I would recommend you find out how wood sailboat keels are detailed. Is the lead (never heard of concrete being used in a sailboat, but maybe) placed directly against the wood, is a sealer used, is some air circulation gap left, etc.? The reason I say this - years ago I knew 2 friends that built a wood power boat. They fiberglassed the outside. Then, for good measure, they glassed the inside of the hull. Within 2 years they had to scrap the boat, because of rot. Apparently, moisture was trapped between the 2 layers and could not escape. I'd hate for you to set up a similar situation.

Do you think that my plan to use penetrating epoxy stands any chance of success? I have no practical way to force it into the wood of the planking, ribs and frames other than serious over-thinning with acetone. The hull has been pressure-saturated with vinyl-ester from the outside. the GogeonBros website (west system epoxies) makes many references to restoration of relic vessels by saturation of the wood with epoxy to impart new strength and to stop rot by preventing moisture ingress.

That encapsulated moisture in the wood of the hull, like in the powerboat that you described, is my nightmare scenario! I too have been party to encapsulating wood in an attempt to make structural use of RED oak (bad idea) and watching it rot almost before my eyes.

I want to maintain ventilation, even to the point of fan-forcing a flow of air between the ballast and the hull. Perhaps some equivalent of those top-hat section foam ventilation ducts that they use to assure attic ventilation from eaves in superinsulated attics - will be my solution. Issues unresolved include crush-proofing and assuring good permeability.

My initial question - well answered by that article (http://www.waterproofmag.com/back_issues/201004/integral.php) gives me a tool to help mitigate what would otherwise be a large sponge laying against the hull. I am seeking to turn that sponge into a non-absorptive mass -as any metal would be. I would not have an issue - but for the high price of lead and a shortage of sailboat wrecks in our neighbourhood lately.

At the present time there is excellent airflow and only minimal ingress of water from:stuffing box, shower pump, raw water pump (maintenance seepage), freshwater tank overflow, etc.

Recent practice for ballasting sailboats uses todays technology in combo with todays hull designs. I have a modern sailboat too and would never think to do concrete ballast on it. My obsession has been to retrodesign a traditional Northumberland fishing boat to its sailing vessel roots.

I am using a traditonal wide hull and traditional ballasting method as shown in Howard Chappelle. Essentially two masses in counterbalance and as far off the centreline (symetrically) as the hull allows.

Among changes made to date are lengthening the hull by 11 feet to remove the transom sterm and the drag that it creates. As a result, at idle speed of 4.2 knots, she leaves NO wake!!!

I considered ballast tankage and pumps, and have done it once before with fuel tanks (but also with a 4 ton lead slug on the bottom of the keel), but at the specific gravity of any liquid I can pump I will require huge tanks...essentially filling up my living room. We want to keep our living room as it is.

This boat is at year 5 of RE-construction and we have lived aboard for 2 years - excluding the deep winter months. Our sail rig is laying on our deck awaiting this ballast as well as a nice feathering 4 blade 32" prop.

Sorry, I can't help you. I had not even heard of penetrating epoxy. You are already addressing the concern I had. Thought you might have access to wood boat experience. All my sailing was in the new-fangled stuff.

Thanx for your help. Sometimes it is more important to talk thru the considerations than it is to get set-piece advice.

Thanks greatly.

The industrial shops sell several different so-called super-plasticiser products.

Not all of them serve the function of 'waterproofing' as increasing plasticity of wet concrete so that water (and thus shrinkage)can be reduced in the mix is their prime objective.

I will have another look at the acrylic ones.

Try zypex Chemical corporation

It is now on the list

Thanks

Hycrete.com, hycrete additive reduces water absorbency by at lease 50% and works even underwater to prevent moisture absorption, i know of nothing that will completely stop the process, some claim they do, most have failed in RL testing, however if your going to waterproof the wood hull anyways, a thought could be to use flowable fill, it gets almost as hard as concrete, but contains no rock, the rock is what wicks and retains the majority of the moisture, flowable fill is just sand water and lime, the water evaporates leaving a solid dense mass with no voids.

Sorry I meant to say flowable fill is water, sand and CEMENT, not lime lol, although that gave me another thought, lime powder, that has been left in the rain gets so hard it has to be broken up by a bulldozer prior to being worked with, but any water it absorbs might evaporate to slowly for your application, you might also consider plaster, the same type used to make concrete/shotcrete swimming pools water tight.

Hmmm...I will take a dig for my old concrete and cement textbook. Some of those "traditional" mixes might have some benefit. I can see a benefit in the placing of the product in these small and awkward spaces.

Thanks much,

hycrete is on the list

Thanks for this

You will need a barrier to prevent the concrete from contacting the wood otherwise the enzymes and bacteria in the concrete will make short work of the wood. A good epoxy coating may work with a membrane of plastic or silicone for added protection. I do not have the specs but a cementitious grout similar to what we used in machine bases may be safer to use on the wood, just a suggestion with no background. Also the wood hull probably has some flex taking place and this would cause cracking in the concrete so the epoxy barrier and membrane would be good to possibly minimize the cracking.

I was not aware that concrete contained enzymes and bacteria. I held the notion that concrete supplied the moisture creating a fertile environment for destructive bacteria residing in wood in close contact. However, I have been wrong before--LOL.

Good point about the flexing matter. These hulls have some flex. Some shrinkage of the concrete may be a very good thing so that each "slug" of concrete lies like a billet in its space, contained - but not attached to the structures around it.

This turns the whole question on its' head. Perhaps I need something that causes the concrete to shrink a lot, thus creating the ventilation space as it dries.

just when I thought I was getting somewhere on this too!

There was a previous post regarding setting wood posts in concrete and a lot if information was provided in this area. I am not aware of any utility company that will allow utility posts of wood set in concrete. Life before failure is very short.

Saint John Energy. Pressure treated power poles embedded in concrete - but not at the bottom of the hole. In downtown areas on shale bedrock.

Have you thought about the need to have a Keel of some sort?

Separate from the Ballast entirely.

For example:

1. wind pushes on the sail (forget about pushing it over for a moment)

2. In order to track and not be pushed around by the wind (weathervaning), you need not only the rudder, but something to be used as a stabilizer. (KEEL)

Think of pushing a cart with 4 casters vs. a cart with only 2..

The 2 non castering wheels act as a keel. Pushing on the side of them causes little movement (Keel) , but pushing on the castering wheels will turn it (Rudder)

The 4 Wheel castering cart, it doesn't matter where you push, fore or aft, the thing will turn.

On a boat with no keel of any kind, the wind may push you all over the place, even with a rudder.

Clear as Mud?

This hull comes with a keel of generous proportions when compared to any motorsailer and some sailboats. It is 36 inches deep and 35 feet long.

I have used Skene, Chapelle and Herreschoffe for my calcs of lateral resistance and all that other stuff.

The time has passed for fundamentals of the design,, we have moved on to the finer points of execution on this project.

CuSo4 would be gentle on my fasteners too I suspect.

The original fasteners on the edge-nailed hull are 4" spiral box nails with eroded galvanizing. refastened (one direction only, not the edges) with 316 screws prior to air-bagging the vinylester skin in place.

I have a call in to LeFarges' bridge deck specialist - thus far unanswered.

I may go make a nuisance of myself at the pre-stressed Strescon plant next.

The Copper sulfate sounds like a constructive addition to this stew!

Thanks! all good ideas.

Derek Sollows - (aging) retired contractor

The big problem everyone seems to have missed here is the alkaline property of portland cement. You must form a seal between the wood and concrete or the wood will start to degrade very quickly. I have used hot mop roof tar on a number of wood boats and found this will work just fine. I had a John Hanna designed Chesapeake Bay boat and the ballast was on the bottom of the keel and that may be a solution you can look at.

Having used "roofing tar"for half a century, I can assure you that its adhesive and penetrant properties are exceeded by almost anything else. That goes for all of the asphalt types and to a lesser degree the (now unavailable here) coal-tar pitch.

There are plans for trimming and balancing the sailing characteristics using ballast on the keel shoe. It will follow after this phase.

Most anything you put down there will cause problems since it is almost impossible to keep water from getting between the ballast and the hull. It would not matter whether the concrete absorbed moisture or not....it is the problem of mould and rot between the concrete and the wood.

I thought normal practice was to tar the surface of the wood, and add the ballast on top of that. Can this not be done? What do the old guys sitting around the quay say?

Yes - I think that your words sum up the issue at hand here.

Pine tar was used once upon a time.

My penetrating epoxy application was to have replaced this. Nice small molecule, soaked into the wood from all angles using lots of acetone. Repeat coating cut with much less acetone. Maybe a third coating neat. Do you think it will not be adequate?

I figured the epoxy would be superior.

Smell alone is a reason for me to reject pine tar. And then there are skin rashes and so on too!

Most of old guys have opinions - and opinions vary here on my dock, just as in this forum. Most of these guys have limited experience with penetrating epoxy - but a number of them have boats that pump bilges way too often. Deeds speak louder than words sometimes.

You mentioned cutting epoxy with acetone, are you using epoxy or polyester, both will work but epoxy has very little smell compared to polyester. Polyester can be cut and cleaned up with acetone but to cut it for penetration you should use styrene. I did this on an old row boat with excellent results and perfect adhesion. There is the fiberglass smell with polyester and it is quite brittle when cured whereas epoxy retains some elasticity and tends not to crack.

Epoxy for this. Need deep penetration. I used vinyl-ester on the outside with pressure bladders to force penetration(very effective).

I follow where you are coming from on the Pine tar(used to work for a roofer when I was younger; I helped tear off a pitch roof- once!).

Don't know if it helps, but there are a number of waterproofing solutions for concrete that help retard moisture transmission and reduce the natural hygroscopy. I believe most of them are potassium silicate based- they wick into the concrete, and fill the natural void spaces. Apparently they can also help seal the natural growth of microcracks and reduce chloride corrosion as well. In this situation you would probably have to be able mix it in with the concrete though. I do know that your epoxy idea has worked very well for outdoor funiture, and getting it to penetrate seems more important than building the layer on top.

Yuk...and that BTW, would have been Coal-Tar. The dust forms HCl (yup hydrochloric acid) when combined with body sweat!

I too had that pleasure in my early years.

Pine tar is not much nicer - and comes under the descriptives: RARE, and EXPENSIVE to boot!

Penetrating epoxy....hmmm. Can't see why this would NOT work. The link says it can be used for just this purpose.

However, I believe it is a myth that expoxy needs to be thinned in order to provide a good bond. This study seems to support this idea. I think that weakening the epoxy by thinnning it gives you...um...weak expoxy. It will bond just fine to a rough surface. If you want it to be runny enough to soak in, a heat lamp on the area will kill mould spores, and warm the resin, making it flow better, and as the wood cools, it will suck in the resin.

You should not put expoxy onto wood that you even have a vague suspicion "might" be starting to rot. And certainly not on both sides! There are materials which work really well to pre-treat. Anti freeze has been mentioned, as well as copper sulphate. I have used anti-freeze. Readily available in Canada. But I don't know if the epoxy will grip a piece of wood which was soaked in anti-freeze. This fellow seems to think it bonds okay. Sounds like experiments are in order, but everybody agrees that you should let the glycol soaked surface dry as much as possible for as long as possible. The afore mentioned heat lamps might help with this.

Then, when the surface is clean and water proof, you can pour any quantity of concrete you like onto it. And don't worry about it being hydroscopic. It won't matter at that point unless there is more to the story.

Is this helpful?

There is quite a body of experience with penetrating epoxies, and generally they are 'reduced' with either alcohol or acetone - both of which, you may note, mix with water.

THe glycol replacement technique requires literally years to displace (first) the old mucky water with glycol, which has a plasticizing effect on rotten wood cells, and then (second) the replacement of the active glycol with epoxy.

The Vasa, the Rose and the USS Constitution are all in this league of attention. My little bateau is not. There is virtually no rot to strengthen.

My objectives in the use of epoxy in this venue is to keep concrete and wood separated, while preventing moisture absorption by the wood in the areas where contact can occur. A "surface" treatment would likely wear away due to abrasion from even minYute motion in a relatively short time - so - deep penetration is my solution to that liklihood.

The study that you linked to is informative. The observations important. I too have been a skeptic of the use of epoxy or any other exotic material as a simple body-fill on rotten substrate. And I was surprised to read of such limited penetration.

Gougeon (West System) used to have a very detailed program for conservation techniques specific to boats on their website. I went looking for it just now and failed to turn up the link. The practices used were a lot more comprehensive than just "brush-it-on", and heat can really help the 'draw' too.

A previous poster noted success using penetrating polyester - and I too have had success with that stuff - but am attracted by the smaller molecule of epoxy.

Heat is a help. We need something better than a portable heater to warm the wood. Microwaves are used on lumber - but I suspect that I would cook the outer glass layer off of the hull in a structure with varying masses and thickness - interspersed with fasteners- too many things to learn at once.

that third link has a LOT of info. Thanks again for that.

My hull is 22 years old. True AA Marine fir plywood with West epoxy/glass outside and Gluvit epoxy inside. I suggest a flowcoat (dunk or drench) the cured concrete pieces. Each piece to be sized for its place so that it locks into the frame and bears its load on nubs. The inner hull would be Guvit coated also. It seems hard to do but is quite simple once you get the hang of the confines. I used cardboard cutouts quite often to define areas and volumes since my hull has few places that form at perpendiculars. The Mog uses batteries but the idea was the same for fitment. I would be happy to discuss by phone or email at greater length if you would like.

I was planning to pour the concrete 'in-situ'.

It sounds like your installation has air-flow around the ballast - which is the condition I want to have.

Need to communicate at length on this if you can.

email:

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Load with granite blocks of a manageable size. Then pour concrete to stabilize. You could even use epoxy to fill the gaps, if the budget allows.

Good luck, Ky.

whew! now that would be a lot of epoxy!

concrete is just an easier to handle version of granite blocks to me - I can have it pumped aboard - instead of craning 12000 lbs or whatever through my hatch in 100lb lumps

BUT you have started me thinking that perhaps I could use the aggregate ONLY and draw ventilating air through it to provide the needed ventilation.

HMmm

thanks - will pursue it.

How about a collapsible water tank,used as a liner?Available at Government Surplus sites?

This will make a very heavy duty waterproof lining, and will add ballast in and of itself.

Available in various sizes.

Just make certain that your interior is dry before installing.

Fill it with the desired amount of concrete.It should conform to available space,then trim and seal to suit after curing.

www.govliquidation.com/auction/search?cmd=results&fromsearch=true&words=water tank

I think you might be on to something. He really NEEDS some way to cast the concrete and leave "nubs" to hold the concrete away from the wood for ventilation. Ridged plastic might well be the answer.

If I was doing it, I would lay half inch thick strips of styrofoam onto the wood, hold them there with double sided tape. Then, tape down a vapor barrier on top of the styrofoam, cast the ballast on top of that, then try to figure out how to get the styrofoam out from under. Cast lifting rings in place perhaps? Cast in more manageable sections? You would not have to lift the ballast very far, just enough to pull the styrofoam out from under. A crowbar might be enough.

I don't like the idea of dissolving the styrofoam with solvents, but yeah, that would work as well for really tight spaces.

(But come to think of it, you could do the same thing with rope instead of styrofoam. And rope would be capable of being yanked out from under.)

(see if I can draw what I mean....)

concrete goes up here

_____________________________________ vapor barrier

_______////////////////__///////////////___ styrofoam strips

wooden hull down here.

What an interesting variation! I do not know why they refer to the design process as a design spiral (with the diminishing radius), The possibilities seem to grow!

The clearances on this boat vary from 2 inches to 10 inches and with various frames and ribs at all locations and the occasional refasten screw installed by uninspired help that sticks into the available space - but the use of bags (cheap inflatable dunnage bags would be eminently suitable too, I suspect) is a great idea.

I have built 2 ocean going yachts of ferrocement which is concrete with a lot of steel reinforcing. Both have done many thousands of miles cruising in the Southwest Pacific. One is 35 years old and the other is 25, Neither had any special additives to the concrete. Both have ballast of steel punchings embedded in concrete.

However, my real reason for this reply is to warn you, in the light of some of the ideas that have been forthcoming, to make sure that whatever way you decide to make your ballast, to secure it properly. If you were to roll the vessel ( let's hope you don't) the last thing you need is for 6 or whatever tons of ballast to detach itself and crash through your coachroof on its way to the bottom.

Duly noted. Secure the ballast! And thanks for that reminder!

The only reason for the additive is the protection of the adjoining wood.

Securement came up from one or two other respondents and I guess it is starting to sink in.

As I sent in a personal email...... Ballast removal is key to repairing a hull penetration........ Trying to pound a correct size bung (always have a set) into a hole that can not be located, may place a bit of stress on the captain and crew.

In my rapid response to your email, I failed to point out that captain and crew of these boats will pump, beach or sink under such a circumstance. It could happen.

The fish-hold floor is essentially a sealed fiberglass hull within a hull, and is required to be by food-handling regs. Think of it as a way of keeping bilge slime from reaching the food product. It is the space between these two "hulls" that I wish to utilize for ballasting to balance a sail rig.

There are NO thru-hull penetrations in the area of the hold. That would be very poor planning indeed! Therefore - no bungs.

These boats are often over-engined so that they can "shoot" across sandbars on their way home. Holes in hulls from this kind of activity are practically unheard of - these boats are not lightly constructed.

My inclination is that poured in place concrete will not weaken the impact resistance and could improve it. Suspended billets would become gigantic "hammers" if any one of them became loose in a serious grounding or punching, and as such could produce extra damage by themselves.

Sounds as though you have a thorough idea of the situation and a method for the addition of ballast. I had suggested form fit, mechanical keyed and nubbed cast blocks. I am sure the poured cement will add rigidity, fill the gap and take less time. Please be aware that wood boats (even with fiberglass covering) are made to expand, contract and wrack with the wave action. Placement of a solid fill may transfer/concentrate minor acceptable flexing to other areas not originally designed to flex in the new manner. However, virtually all great boat ideas are tested at sea and I am confident you will employ the best practices at hand.

Here are a couple different ideas:

1. If sufficient lead is too pricey, consider taking advantage of its density and compatibility with wood, using only a small amount to fabricate lead liners....into which you can pour the concrete. This avoids the 'hammer effect' of pin supported ballasts.

2. If not lead perhaps very thin sheets of a different corrosion resistant malleable alloy like brass could be hammered into place to create metal lined volumes into which the concrete could be poured. Preserving space for ventilation of the hull would be fairly straight forward with this approach.

3. Another approach would be to run a small bilge line at the lowest point, and small ventilation lines, cover the interior surfaces with at least two layers of thin metal mesh. Pump some water into the space, then add concrete contained in something like exercise balls...something stretchable thick and durable. Pump the water out when the concrete has cured and the mesh should have created a ventilation space, but provides more contact area for the ballast than pins.

4. Maybe scrap metal held in place with a small (more affordable hopefully) amount of lead or a rigid marine expanding foam. Steel is three times more dense than concrete, and may be more readily available as scrap. Painting it, binding it and various methods of securing it in the hull in hull may offer some advantages...I guess it all depends on what is around....Who knows...a junkyard might have a variety near fit shapes in solid iron that noone is buying anymore....

5. Some combination of secured scrap metal and pump-able water ballasts?

6. OK if anyone was bothered by some of the previous suggestions, spare yourself the heartache an just skip right over this suggestion.... Reduce the necessary amount of ballast by constructing one or two extendable outriggers (either, one that can be moved to either side, or one for each side.)

I assume you will typically be a long time on each tack, an since side slippage won't be reduced too much with ballast that is added (but not in a keel), and in light of the speed penalty for additional displacement of the added ballast, there could be worthwhile performance and stability gains for deployable outriggers combined with a reduced ballast addition.

Design and fabrication would not be a trivial task so it is certainly more of just a brainstorming type suggestion....

I would probably use the plastic liner that is used by the flooring industry and by foundation waterproofers. It would allow 60% of the hull wood to have a free flow of air across it from the extractor venting system.

However, I will be using stainless 'dams' to prevent ballast movement into the keel, where lives a 22 foot long drive shaft.

If I fail to find a concrete additive that stops concrete from "breathing" moisture, I may be moving to granular ballast.

You may have noted my reference to "steel punchings" in an earlier posting in this thread. Steel punchings(the waste product of punch-presses), nuts and bolts and the like are common aggregate in ballast concrete.

Converting this boat to a trimaran or a proa at this or any stage would not be in the cards (much less a multihull with 'de' and 're' attachable parts). I know a couple of guys in this locality who have "obsessed" with the variable-geometry multihull notion. May they live long and full lives, their project boats will never swim!

Had a quick thought, crushed granite, im wondering if in your application, it might be possible for you to use crushed granite, either poured into the gaps on its own, or in a loose netting of some sort, how big of areas do you have to work with, i saw you said some where between 2 and 10 inches, im assuming thats an average, if u used a crushed aggregate you would have room for airflow thru the spaces in between, you also could then pump water from a low point in the hull, water will flow thru the granite, one other thought, and bear with me, its somewhat absurd lol, there is a type of concrete that floats, i have never worked with it personally but i have been to a few places that had used it, a science museum in texas has a fountain full of small muffin shaped concrete object's that float, i also got the chance to see it being used at the world of concrete expo in las vegas, my thought was line your ballast spaces with plastic, if it is possible, and use that, if you get significant water penetration the concrete will simply lift off the hull until the pumps have done there job, i have seen a few suggest using plasticisers in your concrete dont bother plasticisor is used so that not as much water is needed to achive the desired slump, it will not make the concrete water proof, it will cause fewer shrinkage cracks that gives a more solid and less permeable surface, but it will NOT be waterproof

The crushed granite idea occurred to me too - as I looked back on one of the postings suggesting granite 'blocks'.

I cannot remember all of my crush grades but if there is a grade such as 2" clear, or perhaps a slightly larger size, then I would suffer a density loss of only 15% over the use of concrete and could 'draw' ventilating air through it to maintain a lowish level of humidity in the ballast pockets.

As another poster pointed out, I will not want large masses of ballast shifting during violent seas. It may be possible and practical to reinforce the structural connection of the (outer) hull with the (inner)hold to assure safety in that regard too.

As for floating concrete, I don't see an application for the stuff here. I need mass.

I have worked in years past with one called "ciporex" that had foamed air cells and at other times with "lightweight" concrete that had a percentage of vermiculite entrained. From my perspective these materials failed to deliver the goods. They both suffered compatibility problems with adjoining materials. Water absorption issues led the parade of problems. It is those experiences that led me to ask if anyone out there has the "magic bullet" yet.

Your take on the plasticizers is much like my own.

Consider bubble wrap on top of the plastic water tank liner.This will allow ventilation under the concrete.A ventilation pump should be provided, because fuel vapor is heavier than air and will accumulate in the lowest point.The bubble wrap that is inflated at point of use is the preferred type, because once the concrete has set,the air can be released,creating an air gap between hull and concrete.Inflating the bubble wrap to the bursting point of the bubbles after concrete has set will provide air circulation channels under the concrete.The ones that do not burst will be flattened by the external air pressure.Once air flow is established, a slight positive pressure is all that is required to maintain ventilation.

Alternatively, a vacuum could be pulled on the bubble wrap to create the ventilation channels after concrete has set.This may be preferred because the collapsed bubbles will form a plastic liner under the concrete.

The geometric pattern will enhance the strength of the concrete also.

Remember to pour a thin layer first, and allow to set, this will help maintain the air-bubble pattern.Then pour final layer.Even though the weight of concrete is less than 1 psi, it will compress the bubbles somewhat at first.

Concrete absorbs moisture while curing, so if you use a very low-slump(dry) mix it will absorb any free water in contact with it while curing.After curing, use sodium acetate to coat the concrete, and it will eventually purge any residual moisture and prevent absorption of water in the future(see my previous post on Sodium Acetate).

As previously mentioned, the concrete should be firmly and securely anchored to prevent even the slightest motion.In rough seas, it can act like a battering ram if there is any free motion.

Hope this helps.

I like the ideas.

.

The one thing that concerns me about using bubble wrap is the surface that will be created by the mold.... essentially like a serrated surface; a very coarse file.

.

If support failed to maintain sufficient clearance, that surface would be hard at work chewing a hole through the hull.

Abrasion will be a concern. Even the smallest movement makes the concrete into a sanding block - rubbing against softwood. Not much of a future there ...and a good point to bring up !

Bubble wrap may have a place in a future project. Interesting notion!

On this project I think this approach would bring me back to the "hammer and anvil" situation, your codicils about securement notwithstanding. The practicalities of working between two separate and close hulls remove some of the possibilities which one might enjoy if the vessel were under (new) construction.

The button faced membrane(name eludes me at this time) which I mentioned in a previous post would achieve much the same objective and without building in multiple impermeable layers - the very definition of "vapour trap".

Coast Guard and DOT do not require ventilation re. diesel fuel. That aside, the tanks are in a separately compartmented part of the hull. All of the ventilation to which I have been referring would be focused on maintaining a level of moisture that is not conducive to the growth of micro-organisms. I believe the threshold is at 17% as measured in the SPF softwood -but if someone knows a better number with corresponding authority - I'd love to have some feedback.

Sorry...... 2 to 10" (inch) space below the fish hold....

The former fish-hold, 20 feet long and 16 feet wide, once carried 20 tons of herring at a time. I contemplated buying sheet lead and doing exactly as you suggest. If I did it while she was out, I figure that Susan might not even notice the slight bump in the floor where the ballast lay beneath the foam tiles.

The steel ballast required would not need anywhere near 4" to give me what I need. A friend suggested using railway tracks as baseboard - and if he produces the rails I will probably ask him for more to secure to the keel and call it a day on ballasting! :)! LOL. That having been said, the chances of getting any rails legally is practically NIL - so this is a null option.

Using other steel - it is still a good option!

The fish-hold is (of course) designed to be at the centre of buoyancy. Therefore, that which you propose is very practical. It is ALWAYS desirable to keep the ballast low. and the difference in height if I focus the ballast as far from the centreline as possible is only a few inches.

My plans are not carved in stone (never are - LOL) - and your reminder of the steel internal option (which is by far the least intrusive on a vessel upon which we live for at least 8 months a year) - takes me back once more to the 'ever expanding' design spiral!

I will revisit this in detail since steel is affordable.

Thanks (again)

Derek

I had another thought for you, pending affordability, instead of crushed granite, that will also absorb water and need a large volume of drying air, consider this, pour your concrete outside of the boat,with the waterproofing additive of your choice, after it cures have it crushed, and then load it into your boat, now you have your waterproof ballast and u have a built in airspace from the voids between the crushed concrete, this might be more affordable then it sounds, my company has taken large volumes of concrete that we have removed from job sites, most concrete plants have the ability to crush and recycle concrete, we have done this many times, usually they will take it from you for little or no charge, another thought, perhaps you can convince the plant owner/manager to allow you to do the whole thing on site, they batch the concrete with the waterproof additive of your choice, lay out a large amount of plastic, pour the concrete once it dries, they can crush it on site, you just have to arrange for transport and loading it into the boat, you would just have to figure up the volume of crushed concrete you would need, I'm sure you can probably do the math =)

I suspect that "water-proofed" concrete pieces would hold just as much water in the interstitial space, as would granite - granite being as waterproof as any material can be.

I agree the water in between the pieces would be equivalent, my only reason for the suggestion was that, having worked with crushed granite in the constriction industry for many years, the granite will still absorb water, it is not as porous as say, limestone, but since you were hoping to try for full waterproofing thought id throw in the suggestion to look into waterproofed crushed concrete in place of the granite, anyhow, good luck =)

In Fish Hold, Bag Wet Sand under False Floor. Use food and commercial grade, heavy duty, hot seal bags and rent a sealer. Fill with water and sand. Treated 2x4s (screws and SikaFlex) on the hold floor on edge with water/sand bags in between. Cover the floor with MDO (medium density overlay plywood which uses exterior glue). Fit panels, number and screw plates down. Add a few drops of bio-detergent to keep sand/water in a clean state. 3" depth by 16x20' should yield 5100 pounds with just water only.

That sounds like "high maintenance" over time and perhaps even in the short term. This boat lives in an icey climate and during the coldest months we leave her and move ashore. My ballast would be ice blocks then - not a problem until the spring thaw, when the ruptured baggies spill their contents.

It has a lot in common with the ballasting method of the MacGregor 26 - a very successful design which only takes water ballast aboard when it is needed -and jettisons that ballast when not needed.

Since the floor of the ex-fishhold is now the floor of my living room, I would be affecting doorways, kitchen counter and other kitchen elements as well as the stair to the pilothouse. My ceiling height would drop from 7 feet to a "too cosy" height. This would make it "expensive" ballast to accommodate at this stage of construction.

I dunno...how hard would it be to hang a railway track under the keel? Flanges right there to bolt it to the wood.... And what a skid plate!!!

Probably a 'pipe' (or dare I say- a 'track') dream.

The quest for a substance that eliminates hygroscopicity would apparently be contrary to the hydrous naqture of concrete as explained to me by a local consultant.

So it is baqck to using steel inside the hold I guess. Rods conforming to the slight rocker of the hold floor and the curve of the hull, all fastened and epoxied in place. ceiling height loss of 1" or 1 1/2" . maybe not too bad an effect on countertop and stovetop height.

This thread has been a lot of fun.

thanks for all of your input.

If you don't epoxy them together, they will allow air flow in amongst the rebar.