Steel monohull keel issue: cement-filled, rust - urgent problem?

[wanderlust86]

Hi all,

Advice needed: I'm in the process of buying a cheap, used boat. It's a steel boat (see album link below):

https://myalbum.com/album/EsXVJZZsHel4

I'm told the boat has rust near the keel, the issue is inside. I'm attaching four pictures that show where the rust is, but being new to owning a boat I'm having a hard time interpreting them. The keel is filled with cement - can you tell me what I'm seeing exactly, is the black layer with stripes actually cement on top of the box, or a protection layer of some sorts? What is the golden stripe on the side? Are there multiple cement blocks? The rust has formed on the side of the cement box, where the keel attaches to the hull.

The main question: is that a very urgent problem? I know keel issues are critical and steel boats need lots of maintenance especially in that area, but can you help me figure out whether those pictures indicate anything critical when it comes to safety? Should I expect the keel being exposed to extra stress due to that fissure? E.g., the cement blocks constantly hitting the sides of the keel (stressing the lines where it's rooted on the hull) due to the extra play that has formed? Can the keel break due to that rust, or do I just need maintenance to keep it ok? I'm told the owner has been putting oil as a protection layer on the rust.

I hope to hear from you all. Thanks in advance!

Elio

[wingssail]

Wanderlust, From the tone of your query it seems like you have not personally inspected the vessel. Even if you have then I guess you were unable to decipher what is going in the keel area of this boat.

I either event you need a good surveyor, who is comfortable with steel boats and concrete filled keels, to inspect the vessel and you should pose these questions to the surveyor ahead of time. If at all possible you should be there to see it with the surveyor and if it was me I'd like the current owner to tell me personally more detail about this.

I doubt if any of us on this forum can tell you much just from looking at these photos.

[psk125]

Cement is relatively light, as ballast goes. (Rocks would be more dense.) So it is not usually used in and of itself to provide ballast weight. It is often used as a matrix simply to hold loose stuff - like steel punchings - in place in the bilge. If water gets in there, lots of things can start to happen. The steel punchings can start to rust. Rusting makes the metal expand - causing the concrete to crack and admit water more easily. The water can also cause rusting of the steel structure, as you note, from the inside out. Damp concrete will hold moisture against the metal like a sponge - essentially a worst-case scenario. I would want to find out more about the actual composition of the cement (if punchings were used, for example) and how water got in there. A grounding could have punctured the keel envelope to let water in. Or there could be leaks on deck that end up in the bilge. In either and any case, rust never sleeps.

[gmakhs]

Cement have been used for ballast , it's not the perfect but is a cheap solution .

Wibo boats tend to heel a lot so maybe that's why the previous owner wanted more ballast .
If you plan to keep the boat for long time is better if you remove the cement and replace it with lead or cast iron.

The rust is always a problem.and you need to measure the thickness of the plates through I don't thing it's an issue of lossing the keel.on a steel boat .

[boden36]

As always with steel, what you can't see is a problem.
The concrete probably has lumps of steel in it. It was cheap way of ballasting.
When we built our boat we used lead ingots set in melted tar (and I have the burns to prove it!)

Rust between the concrete and the steel will be hard to treat.
I suppose you could weld a plate over the top, and fill it with oil, which would slow things down a lot, but that would be major work.

How thick are the keel sides? If they are half inch then you may be able to live with some rust, any less may not leave you enough allowance.
Just remember, that cheap is not always a good bargain.


Regard,
Richard.

[RaymondR]

Provided you can get access to properly seal the resulting keel space, plating over the top of the concrete and filling the void with diesel is probably the quickest and easiest solution. The plate only needs to be 1/8".

[wanderlust86]

Thank you everybody for the feedback!

I haven't inspected the boat myself yet, as it's 2000+ km away. The plates are 3 mm (1/8") above and below the waterline, not sure though if the same thickness applies to the keel, as well.

I know rust can be a pain. But to which extent, regarding safety? What is the worst that can happen right now and in 1 year if I leave it unattended? Not intending to do that of course, filling with oil (why would you want to fill those places with diesel Raymond? I bet it dissolves less oxygen than oil, but is it safe?) and plating/welding might be the best solution, I still ask just for the sake of understanding worst case scenarios.

I still do not understand fully what I'm seeing in the images (which are best opened in a new tab and zoomed in), though, especially the first one:
- Are those multiple concrete blocks juxtaposed to one another?
- Is there a black metal plate already? The top doesn't look like concrete to me.
- What is the golden stripe (looking kind painted) near the keel box walls (where the rust has formed)?
- And what are the thin golden lines radiating towards the keel box walls?

Thanks once again for all the answers!
Elio

[GordMay]

Greetings and welcome aboard the CF, Elio.

[wanderlust86]

Thank you GordMay! =)

Is there a place for introductions, by the way?

[RaymondR]

You can use a heavier oil but low viscosity diesel is more penetrating and easier to clean up if you get a leak.

I used a variety of products on my steel boat including pitch, waxoil, marine penetrol, boiled linseed oil and cement render. The waxoil and boiled linseed oil and cement proved to be two of the more effective products.

[Mike Banks]

Cement is often used to consolidate other ballast material such as metal punchings and scrap pieces of steel which are often mixed with cement, or lengths of railway irons chained or welded together, and set in cement or concrete to stop any excessive movement once they have been secured within the keel structure so that in the event of a roll-over, they do not come out and crush anyone in the saloon above the keel..

Unless you know exactly what was done, there is no easy way to tell what is going on down there or how extensive is any internal rust. Tapping the sides of the keel with a wooden or rubber mallet might allow you to discover where there is a space between the keel enclosure and the concrete inside. If the owner has poured oil into any voids, this pretty well rules out any chance of pouring epoxy resin into the spaces.

(If salt water has gone down between the keel casing and the core, sooner or later it will create bulges on the sides of the keel where rust and corrosion products have forced the steel away from the core--thus allowing more bilge water to penetrate.

The only way you can make absolutely certain is to replace the keel, and that is not worth doing, so you will have to sail it as is and keep an eye on things, or find another boat--this time of fibreglass.

[captlloyd]

If it were my boat I would flow a 2-3 inch layer of vinyl cement over the entire top of the existing cement. Stop the oxygen, stop the rust. Rust is a form of oxidation. Sometimes a small gap can form between the top edge of the cement and steel, it would be a good idea to put a wide bead of some sort of sealant there to Maintain a seal. At the worst a leak might eventually appear on your keel. Then you are looking at some replating or possibly a complete keel rebuild. The keel is not going to fall off.

[psk125]

Looking at the photos more carefully, it appears that the cement may be blocks that have been lowered into the bilge, rather than poured in as a liquid. Could the tops have been painted (?) and perhaps some of the paint has been scratched or chipped away in places? What holds them down in the event of a capsize? Can they be removed to allow inspection of the bilges? All of these questions, along with your original ones, need to be asked of the seller.

In answer to your question about rust and safety...
You say the steel is nominally 3mm thick. The rust (in places) may make it thin enough to give way the moment a wave hits it. Without a thorough inspection, you don't know. Without answers to your and other questions and further explanation from the seller, this "cheap" boat may end up being quite expensive to fix and not even worth the trip to see it.

[hpeer]

Damned if I know what you have. I doubt a surveyor would be able to tell you much more, none I’ve met could.

I’ve a few thoughts.

3mm is pretty thin for a steel hull. Perceived wisdom is to go no less than 10AWG which is a bit more than 3mm, more than 1/8”. So your hull and topsides might be 3mm but your hull is likely a bit more, likely 4mm. If you should be able to measure it with calipers where the keel box protrudes into the hull.

If the PO has been putting oil or diesel down there that’s a good thing. BUT having those spaces is bad, bad. Condensation will form and you will get water down there.

I can suggest a couple of adjustments. I’ve some experience with a similar problem.
1-fill it nearly to the top with diesel, then seal the compartment with aircraft fuel tank sealant. Will make it absolutely water tight.
2-weld a top in the compartment, install an air chuck, pressurize it to make sure air tight, then fill with diesel. Drill a hole and thread it to accept a 3/4 or so fitting to do so. This is probably the better method.

If the hull has any leaks the diesel will show them to you. Then you can weld them up. Either way you’ve made the keel a double hull. You may get fined for spilling oil but you won’t sink.

I’ve a 33’ steelie, I converted the keel voids into fuel tanks, welded tops on the compartments. I inadvertently filled the adjacent compartment voids with diesel in the meantime. I’ve convienced myself it was a brilliant move.

Actually I have two steel boats. One came with an oil filled rudder. The other I filled myself, protection against corrosion. Although I’ve heard others recommend automotive antifreeze as it has some “additives.” Don’t know, just throwing that out there.

The main thing is you won’t sink. Any serious rust will likely show itself as an oil weep and you will have opportunity to fix it. Hull repairs, provided you can get to the inside, are not tough or expensive. Keel repair you should not need to get to the inside.

I would be more concerned about serious rust in places you can’t see or touch. Especially around stringers or any place water can accumulate. Bow locker and lazzarett and under the cockpit. All hard to access areas that can get wet from chain or exhaust/bilge pump leaks. Also around sinks and such. Beat the metal with a ball peen hammer or pointed welders hammer. If it’s bad it will dent, if not your good. Seriously, the very best test.

I’ve had bad rust around my water and diesel fill in the big boat. Fixed by welding on a 316ss doughnut, a ring around the origional hole, with a new full in the center. I’ve made other repairs and modifications. You can do a LOT with a little MIG welder and in the last few years multi purpose (MIG/TIG/STICK) hobby welders have dropped dramatically in price. Adequate welding isn’t hard, pretty welding is.

I would look hard at the area where your stern tube penetrates the hull. That’s a likely candidate for an expensive repair. Constantly set and hard to maintain.

As to the ballast hitting the keel and doing damage, my gut says that not an issue. However, if you are concerned you could run some beads of 5200 or some such down the sides to help stabilize the blocks. OR some waterproof cement. I think oil would also act as a shock absorber.

Concrete is supposed to have a palliative effect in steel giving it some protection from rust.

Looks like a nice well maintained boat. Good luck.

[oceanshoretiga]

Welcome to the world of steel! I've had two steel yachts, the current one since 1984. Plenty of good advice within this thread, but a few things.

First, a good surveyor can give you a very good idea of the issues and how to solve them. Choose a surveyor known to be pedantic for a pre-purchase survey, not one people use to glide past the need for an insurance survey.

Second, there are tools to test steel depth/thickness, including the simple welder's hammer. My first experience with a surveyor was him going around the hull with a hammer, tapping hard enough to make the steel ring but not so hard that the paint was damaged (underwater). On the first thud, not ring, the surveyor told me to tell the owner to get an automatic bilge pump. I didn't buy that boat as I wasn't interested in starting with a repair job. It was very cheap, too.

Third, my current yacht has the ballast covered by a plate welded to the hull. On top of that I have double bottom water tanks. Fuel is also in a double bottom tank but right down the rear of the keel that also includes a drain plug so I can clean the tank.

Fourth, if you are buying a boat, plan to spend money travelling to inspect it. Or get a surveyor to do a preliminary survey out of the water. This way, you can reject without travel or get over to look at the yacht.

Fifth, I, as others, feel unable to interpret the photos in detail but the photos do suggest to me that there are serious problems. They may not be hard to fix but they can't be left.

Sixth, get a good surveyor and spend money.

Seventh, get a good surveyor and spend more money.

Eighth, if it is not a pretty hull design, don't bother with a boat with problems.

Take care and I hope that 2019 gets you a good boat you can afford to have.

Cheers, Jim