Concrete as ballast in bilge?
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What protection is used to keep rebar from rusting in Concrete construction? Millions of buildings depend on it.
DCDC
Senior Member
We have a 40' steel sailboat with concrete in the bilge which will be scrapped this month. The boat was professionally built in 1973 with a round hull and 13 tons displacement. When we bought it in 1990 it had one or two very small spots under the waterline which would not dry after weeks on the hard. We drilled them and epoxied the holes. although not visible from the inside they spread over time. becoming larger, more numerous and obviously followed the ballast line. Water had seeped into the interface and rusted through the hull. The first spots were around the chain locker and stern tube but spread out from those spots. Repairs were estimated but very expensive, not due to the steel work but because the concrete would have to be removed before repair. Several interested welders looked at it but in the end we could not even give it away. Although it may be easy to install, concrete has several disadvantages:
> concrete is porous and can wick water. Additives are available to decrease porosity and it can be coated but the steel-concrete interface will always be a concern
> the coefficient of thermal expansion is somewhat different than steel so it will move independently with temperature change.
> you can try to keep the bilges dry but that is difficult over time. Potential leaks from hoses, packing, hatches, chain locker and condensation will eventually allow water ingress.
> concrete has a relatively low density - 2.4 vs steel at 8.0 and lead at 11.3
> it is more or less permanent and prevents any future inspection or maintenance of steel behind the ballast.
If you decide to use concrete it would be worth lookin into the optimum cement mix and provide a high quality bilge coating system before proceeding.
> concrete is porous and can wick water. Additives are available to decrease porosity and it can be coated but the steel-concrete interface will always be a concern
> the coefficient of thermal expansion is somewhat different than steel so it will move independently with temperature change.
> you can try to keep the bilges dry but that is difficult over time. Potential leaks from hoses, packing, hatches, chain locker and condensation will eventually allow water ingress.
> concrete has a relatively low density - 2.4 vs steel at 8.0 and lead at 11.3
> it is more or less permanent and prevents any future inspection or maintenance of steel behind the ballast.
If you decide to use concrete it would be worth lookin into the optimum cement mix and provide a high quality bilge coating system before proceeding.
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Nomad Willy
Guru
Your problem w concrete ballast has mostly to do w access to the hull inside the boat.
If you put lead pieces light enough to extract by hand in the bilge you could more or less easily pull them out for inspections or maint.
I did that to my lazerette bilge about 14 years ago. Fortunately I haven’t needed to extract the lead but refinishing or other work can be performed if needed. On your boat you could tell that your bilge had rust within buy the brown bilge water. And perhaps tar would be an appropriate coating. Tar coating was almost universal on the decks of wood fish boats in Alaska and perhaps steel boats as well.
And the above would be economical depending on how and where you obtained the lead.
If you put lead pieces light enough to extract by hand in the bilge you could more or less easily pull them out for inspections or maint.
I did that to my lazerette bilge about 14 years ago. Fortunately I haven’t needed to extract the lead but refinishing or other work can be performed if needed. On your boat you could tell that your bilge had rust within buy the brown bilge water. And perhaps tar would be an appropriate coating. Tar coating was almost universal on the decks of wood fish boats in Alaska and perhaps steel boats as well.
And the above would be economical depending on how and where you obtained the lead.
mikecambrai
Veteran Member
Ballast
Firstly you need to know just how much ballast is necessary to maintain stability and where it should be put. My first boats in the 60's all had loose ballast which had to be removed and painted every few years as water got into the bilges.
In Europe inland waterways it is true that they do not now allow concrete ballast since the 90's and this was because of the difficulty of raising a sunken barge with ballast that could not be removed. I have had 3 39m barges and have added ballast in the form of of both concrete and railway stone ballast. Before adding either it is normal practice to use what is called Dutch Fat which is just grease. Get a 20kg can of grease and heat it up until it is molten. Then take a broom and spread the grease where you are going to put the concrete.
it is common practice on ships to put concrete in the bilge (special fast drying stuff) if you have thin plating or have had a collision. In fact it is mandatory for all barges in Europe to carry such cement for this eventuality. It really does work. And I have seen old steel hulls which have had concrete in the bilges and when they were scrapped there was very little steel left and it was the concrete that was holding the ship together.
So as long as you prepare the steel with grease then I don't regard the practice as problematical.
Concrete is much less dense that steel so to reduce the vulume adding steel in small pieces is a good idea, just grrease the steel first!
Firstly you need to know just how much ballast is necessary to maintain stability and where it should be put. My first boats in the 60's all had loose ballast which had to be removed and painted every few years as water got into the bilges.
In Europe inland waterways it is true that they do not now allow concrete ballast since the 90's and this was because of the difficulty of raising a sunken barge with ballast that could not be removed. I have had 3 39m barges and have added ballast in the form of of both concrete and railway stone ballast. Before adding either it is normal practice to use what is called Dutch Fat which is just grease. Get a 20kg can of grease and heat it up until it is molten. Then take a broom and spread the grease where you are going to put the concrete.
it is common practice on ships to put concrete in the bilge (special fast drying stuff) if you have thin plating or have had a collision. In fact it is mandatory for all barges in Europe to carry such cement for this eventuality. It really does work. And I have seen old steel hulls which have had concrete in the bilges and when they were scrapped there was very little steel left and it was the concrete that was holding the ship together.
So as long as you prepare the steel with grease then I don't regard the practice as problematical.
Concrete is much less dense that steel so to reduce the vulume adding steel in small pieces is a good idea, just grrease the steel first!
foreverunderway
Senior Member
This is very common in steel boats but it is not free form art! You will need a naval architect to figure out exactly how much concrete ballast you are going to need and it's placement.
Normally, in the past, the hull would be coated in a thick layer of tar to insure that water did not get between the steel and the concrete, but today there are epoxies that may do a better job.
This is not something I would attempt lightly, especially considering the ramifications of needing to remove the cement if it doesn't work as planned.
Normally, in the past, the hull would be coated in a thick layer of tar to insure that water did not get between the steel and the concrete, but today there are epoxies that may do a better job.
This is not something I would attempt lightly, especially considering the ramifications of needing to remove the cement if it doesn't work as planned.
fgarriso
Guru
The reason LEAD is used is it is heaver than concrete. Lead ingots are small and can be stuffed into odd places. Also lead is not corrosive to steel.
I take it you are doing on you own and do not have the Stability, Center of Gravity, and Center of Buoyancy drawings and notes. If so you need to be carful as you do not KNOW how much and where the ballast needs to be added or subtracted. This is a balancing act that can go wrong if you do not know what you are doing!
I take it you are doing on you own and do not have the Stability, Center of Gravity, and Center of Buoyancy drawings and notes. If so you need to be carful as you do not KNOW how much and where the ballast needs to be added or subtracted. This is a balancing act that can go wrong if you do not know what you are doing!
Comodave
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Talk about ballast gone wrong, look at the Golden Ray...
OP
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LeoKa
Guru
Thanks guys. I have learned enough to say that I will not go the concrete ballast way. My bilge is hard to access at some parts of the boat. I do not want to have a situation, where I need to break the whole interior to get to the problem area, if that happens.
Perhaps, I will just re-organize some of the heavy/movable items inside the boat and/or install heavy items, which can help to lower the central weight point of the boat. (large hot water tank, extra battery bank, storing things in the engine room, etc.) I can also remove things from the top and bring them down lower.
As I have mentioned earlier, the issue is not critical for now. I mostly sail in inland waters. However, after few years, I will go out to the open sea. If things are out of wack, I will have to make a decision about the ballast. It seems that concrete will not be the solution, either way.
kapnd
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Sounds like this “custom build” was accomplished without proper pre engineering. BR should have been consulted.
You may be entitled to some recourse with the builder, as they are obligated to meet certain standards that were obviously ignored in this build.
OP
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LeoKa
Guru
This is a balancing act that can go wrong if you do not know what you are doing!
Yes, you are totally correct. When it comes to it, I will look for the NA who was involved at the correction process.
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LeoKa
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jimisbell
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My BR 44 Ketch had punchings and concrete poured into the keel. When we cut the keel off to redesign it I was surprised I still had a keel. It was rusted badly from the inside. All the punchings had rusted and swelled up to break up the solid concrete into not much more than gravel. We welded a 4" thick 6' wide slab (3400 lbs) of solid steel to the bottom of the stub keel (like a winged keel). Dont use concrete, steel is cheaper.
fsarcone
Member
I owned a ComPac sailboat. They used concrete as a ballast. The surveyer found wet spots on the hull. The fix was about 3 gal of resin pulled from the bottom up using a vacuum pump. Took about 3 weeks around the clock to pull enough resin to fill the voids created when they originally poured the concrete.
No matter how careful you are, concrete will have voids & water will find those voids.
Have you considered lead? Check a marine salvage yard. They may have some lead from a wrecked boat that may be compatible with your hull.
No matter how careful you are, concrete will have voids & water will find those voids.
Have you considered lead? Check a marine salvage yard. They may have some lead from a wrecked boat that may be compatible with your hull.
Brooksie
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My Willard 36 had 6500 lbs. of concrete and steel punchings for internal ballast. Concrete is light compared to steel thus the punchings. I never had any trouble with rust as I poured epoxy over it and down between it and the hull when I first got the boat. On a steel boat I would want to coat the steel first b/4 I put anything on top of it. Coal tar, epoxy. Por15 ?? I don't know what tho.
FF
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Once sealed air can not get to the iron so there will be little rusting
ben2go
Guru
Two of the boats I am reconsidering to build use CMU ballast blocks for ballast. They can be moved around. The hulls have boxes built into them to house the CMUs.
6"x10"x16" laid on edge in the ballast box. Here's a pic of them holding down a solar array. Most any place that deals in concrete can get them or tell you where to get them. They are different and heavier than standard concrete block.
6"x10"x16" laid on edge in the ballast box. Here's a pic of them holding down a solar array. Most any place that deals in concrete can get them or tell you where to get them. They are different and heavier than standard concrete block.
jimisbell
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There is NO reasonable way that concrete can be adequately "sealed" to prevent rust in embedded steel. Just look at any concrete bridge over 20 years old and you will find cracks that are oozing rust and soon to be spalling off chips and further exposing the rebar. I want my boats to last longer than 20 years.
As soon as ANY water hits the steel the rust starts. Rust expands steel by 7 times its size. The expanding steel cracks the concrete and then MORE water gets in.
ben2go
Guru
I've seen it used without rusting in sailboats. I've never seen it used in an M/V. The concrete is mixed with very fine to no aggregate. The rebar and steel punchings are kept at least 2 inches away from the sides. There are some additives used as well before pouring. Usually, the pour is made directly into a prefabricated steel keel. In wood and fiberglass boats, it's poured into molds and then fitted to the hull. With fiberglass or wood hulls, the concrete ballast is epoxy coated and fiberglassed. Of course, the keel is usually built and stored to cure while the boat is being built so it's as dry as possible before prep for glassing and installing onto the boat. George Buehler has a chapter in one of his books about building concrete and steel keels.
FF
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On many boats that use steel in concrete there is GRP covering the ballast so the area in the keel can be used to collect bilge water to be pumped.
GRP is air tight.
GRP is air tight.
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My thought exactly. And you can get by with a LOT less weight for the same affect the further down it is on the keep. For my money, I would go with lead formed to "tuck" into the i-beam on the bottom of the keel. Easily secured, and if attached in 80lb or so blocks, easily removed/moved to fine tuner trim without hauling the boat.
Nomad Willy
Guru
Do you know any secret (cheap) places for lead?
I got my lead from various sources .. probably 6-7.
I’m glad I did as most sources produced lead in various shapes and sizes. Like a 6” rod 3” in dia. and some rod 1/4” dia that looked more like an electrical cord and some plate 1/2” thick .. ect. Finally I found quite a bit of bird shot and that trickled down to fill a lot or most of the voids. Per pound what I paid varied quite a bit and most of the large pieces came from a large machine shop where I previously worked (and received a generous discount) and the bird shot almost entirely from one source.
Took some running around and a few bucks at a time but turned out much better than I perceived it would when I started the “gathering”.
Since I partially filled the space occupied by the concrete (I’m guessing 80to 85%) I’m sure I have more weight in ballast in the lazerette than I had w the concrete. Especially w my water tanks full. But I almost never fill those two water tanks. Also IMO being heavy aft has almost no downside compared to being heavy fwd. I would strongly avoid being heavy fwd. I probably should dig some out though but 50 gallons of water is fine.
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OP
OP
LeoKa
Guru
It is interesting what you say about being aft heavy. Could you explain this?
My boat has an air tank attached to the aft below, because it was aft heavy. The existing lead bricks I have found are all in the forward bilge area. The waterline seems even from outside, as of now.
I just want to understand, why the forward heavy can be an issue? Mine is a slow speed boat, about 6 knots. Pushing a heavy bow could slow me down? Or, any other reason?
My boat has an air tank attached to the aft below, because it was aft heavy. The existing lead bricks I have found are all in the forward bilge area. The waterline seems even from outside, as of now.
I just want to understand, why the forward heavy can be an issue? Mine is a slow speed boat, about 6 knots. Pushing a heavy bow could slow me down? Or, any other reason?
landsend
Member
Concrete !!,,
As a ready mix concrete producer I confirm all the negatives regarding using it as ballast, it really is just a big sponge. It is cheap which is why it is the worlds most used construction material. If you add a vapor retarding admixture Logik900, a corrosion inhibitor such as DCI and wrap in heavy mill plastic you will have a cheap ballast. Good Luck
As a ready mix concrete producer I confirm all the negatives regarding using it as ballast, it really is just a big sponge. It is cheap which is why it is the worlds most used construction material. If you add a vapor retarding admixture Logik900, a corrosion inhibitor such as DCI and wrap in heavy mill plastic you will have a cheap ballast. Good Luck
FF
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Remember power boats fall of waves and can be knocked down.
Secure the ballast so it doesn't bounce loose around the boat after an event..
Secure the ballast so it doesn't bounce loose around the boat after an event..
Steve
Guru
Ask at a Caterpillar, or other track type tractor dealer, they replace the pins when they rebuild the tracks.
Nomad Willy
Guru
LeoKa,
Boats are designed to float “on their lines” and thus to be in trim. That is, the weight of a boat should be of a specific amount and distributed (percentage wise) fore and aft (as designed) so the boat floats level if you will and under these conditions will perform as designed.
I’m no marine architect but I’ve found boats w too much weight fwd will have the forefoot deeper in the water making the bow reluctant to move to the side. Directional stability (usually considered a good thing) then limits the ability of the bow to swing from side to side facilitating turning. Boats with a lot of submersed area at the ends are very reluctant to turn. But waves and current have a profound affect (direction ability wise) on boats deep in the water at their ends. Plumb stemmed boats from the 20’s and 30’s and canoes w a straight keel don’t want to turn, so they turn very slowly. Norwegian prams or river fishing boats w a lot of rocker are too eager to turn and are hard to control whereas boats w deep ends have maneuverability issues resulting from too much directional stability. Also hard to control.
The biggest problem for a trawler re directional stability IMO is from boats w too much weight fwd so in following seas the bow plows deeply into the next sea and becomes sorta stuck there. The stern, relatively high on the wave under the sea aft becomes too mobile .. that is it has too little resistance to lateral movement. So the wave has too much control and can easily move the stern around. This is how broaching happens.
And perhaps directional stability while steering in calm waters is much more often a problem (but not as dramatic) from one end of the boat being much more or much less willing to move laterally result in steering response being too slow. But a bow too deep in the water produces an instability tendency. A boat that wanders willingly will usually result. Steering in calm weather becomes work and when it gets rough it’s dangerous.
Most all boats are slim and pointy fwd and wide and flat aft. As long as the boat is trimmed correctly (as she was designed) will correct steering response and control be available.
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