What did we don't understand that they did?

I suggest he learn something about his subject, along with that.

English as a second language is difficult and should be given a little tolerance.

 

The title of my subject was to make sure that I don't start an old debate over steel vs grp vs wood vs etc.

I basically wanted to know what do they do differently to have such nice and well maintained steel boat.

From what I learned, it might be that they are using higher grade of steel to begin with and also they probably use zink flamed spay before sealing it with epoxy.

PS: I am sorry if english is my third language. I will make an effort to not reply from my cell phone with the auto correction "on" in french. Auto correction is an awsome tool but at the same time it is very annoying when changing from one language to an other. I apologize for the inconvenience that it might of have created to some of the member on this blog.

 

I don't pretend to be any expert on this steel subject, having been mostly involved with multihull boats. I was trying to learn more myself, when I began to think of building that Pilgrim 40 vessel with a steel hull.

From some of my research on the subject I think I recall hearing that the use of zinc was no longer a preferred method, and rather the builders were utilizing a preconditioned steel to start their projects with (less rust in the raw steel product delivered to the builder, then less rust during the building process). And finally a good barrier coating of (?) applied just after completion of the build, and prior to delivery to the client. (and no special steels if I recall?).

I think I would do a lot more research with the Dutch steel boat builder's methods.

PS: I believe I was also looking at utilizing a bit heavier steel plating in a 'frameless construction method', combined with some modern adhesives technologies that would help limit the number of nooks a crannies on the interior of hull, making maintenance of these bilge areas easier. Exterior surfaces are much more easily detected and maintained.
I also wanted to do a little more research on the polyurea protects as protective materials, but still had a number of questions about their ultimate adhesion to steel.

 

As it would be almost impossible not to be clambering around a boat and having the steel covered with some construction debris during the build, you will almost have to sandblast before painting. Removal of the mill scale is perhaps the most important part prior to painting. If you paint over the scale, eventually it will flake off and then rust will start.
The big problem will be where you skip weld say stringers onto the hull as the area just beneath the stringer will not be coated with any paint.

If I were building a steel boat, I would purchase wheel abraded and shop primed sheet. The wheel abrading removes mill scale and the shop primer is an extremely thin covering that resists rusting but you can still weld through the primer.

I believe that for thicker plating, sand blasted and shop primed is available. Then before the final paint prep of the hull, the shop primer is then sand blasted off the hull very easily.

Just one option

 

Not familiar with welding thru shop primer - but my engineering degree instructor said that is the worst possible thing you can do to a weld.

But that was 40 years ago. Hopefully things have advanced and this is good practice.

 

The composition of shop primers is especially careful so that the weld is not contaminated by them. I think it is much more than 40 years ago, and so far, that the most correct thing to do is to shot blasting steel plates with metal grit to SA2.5 grade and immediately paint them with a shop primer that will protect them for at least 4 months. I have not visited a shipyard of metal hulls for some time, but I do not think that something different is being applied at the moment.
Of course, all welds should be painted with oxidation-protective paint.

 

I believe that is what I had read as to what the better builders were doing.

I was not sure that 'sand blasting' was utilized? Sure might contaminate the nook and crannies when a next coating would be applied?

 

My conclusion for a good way to built a steel boat is as follow*but if someone has better step modify the one below so that we can have a good solution for steelboat building sequence.

1. Using a design that all the part can be CNC cut for the best fit and speed of assembly.

2. Best to use preprimed steel plate and after the CNC cut is done priming the edge right away would be best.

3. Assembling all the part together. This needs to be done quite fast because the pre prime steel usually have a maximum time before re coating.

4. By having all the part pre primed and all the edge primed after the CNC cutting. I think shot blasting can be skipped can't imagine being inside a boat and shot blasting!!!

5. Applying zink rich coating inside of the boat.

6. Sealing the inside of the boat with epoxy.

7. Applying zink rich coating outside of the boat.

8. Sealing the outside with epoxy.

9. Painting the outside with polyurethane based paint.

10. Painting the bilge with polyurethane based paint.

11. For insulation inside of the boat some apply sprayed polyurethane. I have also red somewhere that a better way is to spray some kind of rubbery paint and then using polystyrene board to insulate. Not sure what is best!

12. Lastly finishing the interior and rigging the boat. (That is probably 75% of the job).


PS*: Shot blasting is not sandblasting but similar process, the media used is not the same. Also probably best to have a professional builder do all the welding of the boat so assembly can be done quickly. The rest I think a DIY with good motivation can manage if he does not let the boat sit for too long in his yard!!!

 

Valery, you mentioned that you like to do some modifications, like on the rudder system. I think that is No 1, as that may or may not changes the design and drawings. Special if you do CNC cutting . Bert

 

My opinion is that there is no need to describe a New procedure to obtain an optimal construction/finishing of steel hulls. Everything is already discovered and many years ago it is applied in serious shipyards. Now I'll comment some of the points of your post.
1.- it is impossible, or at least very expensive, to cut all the parts with numerical control.
2.- The shop primer should be mandatory and can protect for more than 4 months. It is not necessary to paint the edges of the pieces after their CNC cutting.
3.- There is a margin of months to be able to assemble pieces without rusting. The little rust they may have, may be good for better adhesion of the final paint. Of course, each weld should be painted immediately after it has been made.
4.- it does not make any fault the shot blasting after the welding of the parts. It is enough with a correct painting procedure. Only in very, very exceptional cases would the shot blasting be necessary, although I can not think of an example. The sand blasting for parts and even large sets, is more frequent.
6 and 8 - will not add anything to a good painting scheme. Remove it from the list.
9 and 10 - it is sufficient to apply the appropriate paint scheme. Not only the type of paint but the necessary thickness and taking great care of the atmospheric conditions during the application.
11.- Expanded polyurethane is only used to isolate in situ refrigerated stores and places of difficult access. The rest of the insulation, especially if it should be anti-fire, is made with rock wool. This insulation does not protect against corrosion. For that is the painting.
All of the above will not be worth anything if the maintenance of the ship is not done correctly. Ah! and of course, use only naval grade steel.

 

In my pre graduate years I was doing some industrial painting in an oil refinery. The company was international and they had precise specs as to the paint application process.

With the refinery supplied paint came a film thickness indicator. So the process was to sand blast to some whiteness grade that I do not remember then prime with a thickness that would enable the film to cover the valley of surface irregularities and then the peaks and have a certain thickness over the peak. Numbers escape me. The concept was to cover the irregularities of the surface roughness.

The thickness of a proper primer, ie the stuff out of a paint can might be several mils thick after drying. The shop primer that often comes with the abraded/sandblasted sheet/structural is extremely thin. Likened perhaps to the thickness of paint that you would apply with a 12 oz spray can of paint. Ie thin. Thin enough to weld through.

Later in our manufacturing business, we did quite a bit of steel tubing welding and were unable to sandblast due to cost. The product un primed would come in covered in oil to prevent rust and was a bear to degrease/deoil. Our steel supplier recommended the shop prime tubing, degreased but a very thin coat of primer that when were finished welding, we would apply another coat of a thicker primer over top, and then finish coat. Over that the final coat or coats.

Seemed to work pretty well. Perhaps the term "shop primer" is incorrect, but that was the term the supplier used when we ordered it. Very thin

 

Hi Valery,

If you want to learn first hand about sandblasting the interior of a steel boat my wife and I are offering a very complete hands on course in the next month or so...fees are very reasonable... lol. We are about 1.5 hours from Montreal.

http://boatmutts.ca/sandblasting/

Cheers,
Mark

 

There are plenty of "primed" steels plates perfectly weldable in the naval industry since ages.
In general the plates are sold by the factory primed (after a a roll straightening and a shot blasting) to the small shipyards.
The big shipyards have their own facilities for roll straightening, shot blasting, and priming. Almost all plates are primed, nobody now wants to sandblast or shot blast and priming a 600 feet hull.
Sandblasting an entire hull is reserved to small boats in non equipped shops, the process is long and very messy. Even with a good aspiration system you'll find sand dust everywhere including your underwear and sockets. Imagine the tooling...Silica is not good to breath.
Shot blasting is pretty messy also the entire shop ends covered with a fine layer of scale and rust that contaminates everything...
So primed plates, and blasting only the welds with a special gun has been used since more than 40 years in the advanced shipyards.
The zinc primary vaporises under the heat of the gas carbonic MIG or the submerged arc in the automatic weldings. Both are very hot and fast to have a minimal HAZ and distortion. Very neat processes.
A good Kemppi MIG (my favorite brand) with cheap gas carbonic and pulse makes welding 2.5 mm primed plates without distortion a breeze. With a ordinary MIG is hard, with a stick is pure art.
About the non rusting nordic yachts (specially Dutch who are high masters) it's very simple; lot of work of preparation, premium paints, and lot of care ny the owners. The marine steels they have help a lot. But the most important is the high quality of craftsmanship.
The French have switched to aluminium 45 years ago. Tabarly Pen Duick race sailboats incited to the alumimium use and created another tradition. Also Pechiney sold marine alloys at good prices during decades, the famous AUG3 and AUG4. With the Pechiney prices alu became soon competitive with steel.
People saw also that alumimium is easy to cut, to form and does not need blasting. Many hours are saved and it's not dirty like the steel The advent of MIGS for alu around 80 made alu welding an easy task.

 

@M&M ovenden: Awsome project just 1.5 hours away from me!!! I am actually thinking of sailing from Montreal, Lac des deux Montagne, to Ottawa this summer. Can I come check your project?

@ Ilan Voyager: This is also the impression I have big yard would avoid to sandblast. The special gun you are talking about to prep the welds I think I seen it on youtube. It is some sort of electrical laser blasting gun. Cant find it anymore. But that is probably the way to go.

@TANSL: It seams very opposite to what I have found online not to use epoxy to seal the steel. It looks like it is the way to go, anyway for pleasure craft. Commercial might be different.

 

This is whay I am talking about!

https://www.youtube.com/shared?ci=1Muh6-NNNH0