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Old 12-10-2009, 12:30 AM   #1
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My boat is glass but, as ever, I'm always skulking around boat yards looking at rotty hulls for sale in the hopes of one day stumbling on a, much bigger than my current 36footer, diamond in the rough... lately I've been seeing lots of old steel boats... some of them seem to be structurally ok, to my untrainted eye, but are definitely in need of LOTS of TLC. Which being steel boats would probably mean either lots of time with an angle grinder and cup brush, but as I understand it using a brush or sandpaper for rust actually damages the metals paint/epoxy/primer holding capability because it is effectively polishing the metal... where as sandblasting leaves behind a surface which is cleaner, as the sand can get in the pores, and makes the steel into something like invisible velcro which supposedly bonds better with paint/epoxy/primers....

some of the deals I'm seeing on big metal boats lately are almost insane, practically being given away... presumably because fixing them up would either be VERY labor intensive (if one used a grinder/sander) or prohibitively expensive (paying someone to sandblast and paint them)... but I've been doing some looking and a sandblasting set up isn't all that pricy....

Does anyone here have experience with sandblasting?? What would be your reaction if I said I was going to DIY sandblast a 50ft metal boat with a 90lb pressure tank using a 20cfm/100psi compressor? Is that too small?? Any idea (once a person gets the hang of it) how many square feet 50lbs of abrasive will strip?? From what I'm reading white aluminum oxide is the abrasive of choice but is SUPER expensive ($70/50lb)... Has anyone ever used just good old playbox sand (non silica sand) with good results??

thanks for humoring my curiosity
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Old 12-10-2009, 05:41 AM   #2
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Steel Boats and sand blasting - one of the most important requirements is that it should be done in a controlled enclosed environment, i) to stop the grit and scale from blowing everywhere and

2) to recover grit.

Here is a very good site describing the method CLICK Here is another HERE
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Old 12-10-2009, 07:23 AM   #3
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These might interest you:

http://www.boatdesign.net/forums/metal-boa...hull-29888.html

http://www.boatdesign.net/forums/open-disc...hull-12738.html
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Old 12-10-2009, 08:27 AM   #4
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Thanks Magwas ,, good Links - good advice!
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Old 12-10-2009, 12:30 PM   #5
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Originally Posted by MMNETSEA View Post
Steel Boats and sand blasting - one of the most important requirements is that it should be done in a controlled enclosed environment, i) to stop the grit and scale from blowing everywhere and

2) to recover grit.

Here is a very good site describing the method CLICK Here is another HERE
That's why I'm interested in the whether or not playbox sand is a viable abrasive if well sifted and kept dry... it might make a dusty mess but is harmless and is cheap enough to not have to capture and reuse. Unlike white aluminum oxide which requires a blasting chamber for recovery... which is what makes sandblasting so darn expensive... I don't even want to guess what it would cost to have a big hull professionally tented, sandblasted inside and out and primed... another thought may be to just use a grinder on the outside, and then sandblast on the inside where you can't get a brush into all the nooks and crannies and can usea shop vac to recover the abrasive from the bilges....

again, this is all just a mental exercise. I own a glass boat, which I see me keeping for a while, but I like to play with the what if/how to's of all boat types.
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Old 12-10-2009, 04:24 PM   #6
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Are you also an accomplished welder? If not, if you are considering undertaking a steel-hull project, you might wish to take a class at a local community college and/or find another way to get good training. After training, you can easily obtain an AWS cert, btw. The only folks I know who have successfully taken an old, inexpensive, steel hull and brought it into a high level of structural integrity have been people with significant welding expertise. Many people with limited welding experience will pick up a steel hull on the cheap, blast, grind, etc to get down to decent material, do a couple inappropriate "cosmetic" repairs rather than good repairs and then end up with continued hull problems and corrosion issues. Very tricky, IMHO, to re-do a steel hull properly and on the cheap.

My familiarity with steel pressure vessels and weld repair (from a previous job as a mechanical structural engineer) made me shy away from the purchase of a couple steel hulled boats. Part of that was because that while I can do excellent weld design, I am not a proficient welder and neither is hubby. Since part of my job was designing welded repairs/approving the repairs designed by other engineers and/or inspecting the repair after it was performed--I have a very high standard regarding acceptable welded repairs. I figured that neither hubby nor I would be able to achieve the quality level that I find acceptable and we wanted to have a boat that we could work on and repair with high quality workmanship ourselves. This is also the reason that we passed on a lovely 47 foot aluminum hulled boat that was being sold in North Carolina for moorage fees due to a marina ($7,500).

Good luck in getting everything together that you might need to successfully do such a project!
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Old 12-10-2009, 08:03 PM   #7
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Part of that was because that while I can do excellent weld design, I am not a proficient welder and neither is hubby.
Whilst being the first to admit to my limitations, this approach is, to my way of thinking, somewhat doubtful.

One says no to a project because one knows the theory but not the practice and thereby is aware of one's limitations. On the other hand, following this concept, one says yes to another type of project where both the theory and practice are unknown.

To my way of thinking, it is better to work with something which is partially known than something which is totally unknown. At least by following that path one would be able to accurately asses the faults in the end product and ask for professional assistance when needed.

Of course, in theory at least, the best thing to do is to have your boat built by a professional. Unfortunately, even professionals have produced inferior products from time to time. But you know what they say about theory and practice?

"In theory, theory and practice are the same but in practice they are not."

Aye // Stephen
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Old 12-11-2009, 03:05 AM   #8
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Whilst being the first to admit to my limitations, this approach is, to my way of thinking, somewhat doubtful.

One says no to a project because one knows the theory but not the practice and thereby is aware of one's limitations. On the other hand, following this concept, one says yes to another type of project where both the theory and practice are unknown.

To my way of thinking, it is better to work with something which is partially known than something which is totally unknown. At least by following that path one would be able to accurately asses the faults in the end product and ask for professional assistance when needed.

Of course, in theory at least, the best thing to do is to have your boat built by a professional. Unfortunately, even professionals have produced inferior products from time to time. But you know what they say about theory and practice?

"In theory, theory and practice are the same but in practice they are not."

Aye // Stephen
Hi, Stephen.

About those professionals doing the work...The best laid plans sometimes go awry. When we purchased our boat and planned the rebuild, we hired a well-known and well-respected shipwright to oversee the project and to perform the lion's share of the hull work. We had an agreement with him that David and I could perform some of the work and that he would also supervise our work to make sure that it was of sufficient quality, etc. We THOUGHT that having this fine professional and his team of skilled labor work on our boat would allow us to observe and learn much and that we would in-the-end have a very well re-built boat. We did always plan on doing the interior work ourselves but the hull and rig we'd planned on those "professionals" really doing the work. Let us just say it didn't work out that way, we ended up with a costly move of the boat to another boatyard where we could perform all the work on our own on the hull. Not the way it was planned...nope...not at all.

Regarding what one knows partly vs not at all...my problem is that I've done many welded repair designs and seen many fine welders still perform substandard welds. Therefore, knowing that it takes years to become a proficient to good welder and I don't feel like having lots of defects on MY boat's welded repairs, we passed on the opportunity to work with steel or aluminum in a boat hull. Further, while there are some very old steel boats out there, there are many more steel hulls that just don't last because of corrosion problems. I didn't want to deal with that particular issue.

However, I must admit that the "tipping point" for us towards a wooden hull vs metal was that we wanted to own a pre-WWII boat with the added criteria that it was built as a cruising yacht from the start... and the likelyhood of it being anything other than wood was slim for that reason.



On the other hand, Atavist won't likely have all my weird criteria for things like pre-WWII as well as reliability and maintainability and can happily go forth with a good steel hull!
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Old 12-11-2009, 05:37 AM   #9
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Just read from an experienced steel boat builder:

Sanding is just plain hell, but it must be done.
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Old 12-11-2009, 08:27 AM   #10
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Okay,

I have never worked on a steel hull. I have worked with steel and done welding and prep' work on steel and other metals to prepare for everything from simple soldering to MiG and Tig welding. Have done a bit of work with plasma (have family that has better experience there and let them do the plasma as set up is a pain and needs to be very well done for best results). IF you choose to grind back the layers than you have to etch the metal with a mild acid so that the surface will bond well to the primer (or any sealant used). Once you have the sealant on the metal things get a lot easier. Remember this is from dealing with land based steel and mild steel structures (interesting the things engineers build with in the Army).

In the Water I would assume the need to insure complete coverage and sealant of the metal would be even more important. This is why to my knowledge steel hulls used to be zinc dipped or sprayed down with zinc to act as a barrier and an easily primed surface as well (zinc is wonderfully ionic active and as such bonds well to other materials IF they are compatible). Welders come in many different flavors, the best being those that do the work inside Nuclear reactors during construction. The person who taught me the very basics, pointed out that getting a solid weld was more than just putting down enough rod. It takes a bit of time and knowing your temp's by sight (which is no mean feat when you understand how much a mask cuts down on what you see. If you feel up to it than my best suggestion is go for it. If you have or can get access to some scrap steel of the same thickness get in some practice and do a few practice passes each day you are going to be welding before you start to get the feel back in the hands and such.

Now IF you have a good bit of experience than some of the advice above does not apply to you and No insult was meant. best of luck and remember when welding it is better to stop and go walk a bit than to just fudge a bit as that will come back and bite you.

Michael
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Old 12-11-2009, 12:36 PM   #11
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I can give a little insight on sandblasting as I am SSPC certified in Fundamentals of Protective Coatings, and occaisionally oversee bridge painting projects.

The reason sandblasting provides a better surface preparation than sanding is because the grit leaves an anchor profile for the paint to grip the surface, tiny pits 2-5 mils deep. This allows the paint to hold on to the steel better.

Playsand may not work as well as a traditional blasting product as playsand has rounded particles, like wind blown sand on a beach, this is so that it doesn't cut the kids eyes when they get some in there.

Containment will most likely be necessary at the least to avoid having every other owner in the marina mad at you because their boats are covered with dust, and also depending on the composition of the original coating. If the original coating contains lead you will not only have to contain the waste but will probably have to dispose of it at a licensed facility. You can buy lead detecting wipes at most home building stores, to test for lead. Containment is not all that hard as you would first lay down a tarp for ground protection then tarp the entire boat so the dust is contained. On bridge projects we employ negative air machines, giant vacuum type apperatus that sucks in more air than the compressor is putting out creating a vacuum type condition where the waste won't exit the containment, these machine are equiped with huge filters that remove all contaminants from the air and in the case of steel shot recycle the shot for re-use in the blasting process. If you are using a small volume compressor like the one you are talking about it might not be necessary.

One of the most important things to take care of in the removal process is to get rid of any residual chlorides on the surface. Sandblasting won't do this completely on it's own as it has a tendency to drive the chloides into the afore mentioned pores. What we do for bridges is to pre-wash them prior to sandblasting with a pressure washer solution containing a chloride remover, Chlor-rid is one product we use for this. Another method which used to be employed is to allow the steel to flash rust after blasting. Basically when you are done blasting just let it sit for a day or two depending on the humidity. As the residual chlorides cause oxidation some of them are carried to the surface by the light rust alowing them to be removed with a brush off blast. This is nowhere as effective as the pre-wash method, but it is a good way to check if you have removed all the chlorides after blasting. In other words don't start painting right after blasting, you could be trapping chlorides against the surface which will adversly impact the life cycle of the coating. In this case rust is your friend as it is telling whether more prep is needed.

You will want to wear some type of coverall garment to avoid taking the waste with you on your clothing and a respirator, not a particle mask, especially if the paint contains lead, arsenic, benzyne or other hazardous compounds. Even the silica from the blasting medium can cause serious health problems down the road.

It is doable providing you take the time and effort to do it properly.

But proir to purchaseing an older steel boat you would want to check for section loss of the steel, especially if it is an older boat that has seen use if saltwater. This can be done in a non-destructive manner with a "D-Meter" a device that has a sensor you place on one side on the bare steel of the hull, about 1' diameter, it measures the thickness of the steel. Any surveyor that has experience with steel boats should have one, if not find another surveyor as this would be comparable to a moisture meter that would be used on a fibreglass boat.

Hope this helps a little.

Sam
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Old 05-23-2010, 04:28 PM   #12
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Well, I say do NOT attempt to sand blast yourself. It is not all that expensive to get it professionally done. My boat was blasted with slag from a steel making furnace. The resulting surface is very coarse. It was done in a shed whilst I happened to have no mast on the boat. The job took almost a whole day. What's more the first coat of primer MUST be applied IMMEDIATELY after blasting (within 4 hours, and that means the paint job has to be finished very quickly too) so you should pay a professional to do that first coat too. If you need to do any serious welding .. forget it. Don't bother. Patching a few plates is ok, but if the stringers are gone it isn't worth repairing. Note that since a steel boat invariably rusts from the inside, you will have to gut the whole boat to sand blast the interior. Exterior sand blasting is NOT done to remove rust. It is done to remove paint when it is no longer possible to keep covering up the old paint job. Rust will be removed as well, but that's not the main purpose, and there usually isn't very much on the outside.
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