How long will interior paint on steel last?

Discussion in 'Metal Boat Building' started by hiracer, Jul 7, 2006.

  1. hiracer
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    hiracer Senior Member

    Assuming competent preparation and application, am I buying into an interior paint job if I were to purchase a 1985 steel sailboat? Epoxy paint. 3" of foam insulation. Single owner boat. Very well maintained. Just completed circumnavigation that took 11 years.

    I will have a survey, but I'm looking for a general baseline of how often a steel hull sailboat like this should be repainted inside, assuming no misuse and proper initial application of paint.

    Or, are these newer paints so new that the verdict is still out on the longevity question??

    TIA.
     
  2. jehardiman
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    jehardiman Senior Member

    Paint on steel or on foam? Formula 151 epoxy or something else?
     
  3. hiracer
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    hiracer Senior Member

    Not sure what kind of epoxy paint. Epoxy paint applied in the Netherlands when the boat was new in 1985 with foam sprayed on for insulation after paint was applied.

    Thanks for your interest. I am concerned whether I need to be concerned. Obviously, actual inspection of the boat is required, but if it's almost certain that I'm buying a painting project then I may not even get to the point of getting a survey and will look for another boat instead.

    The problem is that my knowledge of steel boats is very limited. I DO know that steel sailboats usually rust from the inside. Beyond that I kind of need help.
     
  4. MikeJohns
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    MikeJohns Senior Member

    They rust in the areas that trap water. Usually from poor construction methods and no drain holes in the low parts of the longitudinals.

    A good foam job usually prevents water getting trapped , the bulk of the interior rust will always be in ..............the bilge area; around and adjacent to openeings on the deck, and below portholes etc . The remainder can sit for decades and decades without any attention so long as it is dry.

    When getting a steel boat surveyed you need a surveyor who really understands steel.

    Good luck
     
  5. lazeyjack

    lazeyjack Guest

    I spent years building in steel
    painted PROPERLY with correst blastt profile, 75 microns zinc, 300 microns epoxy , will last forever, EU yards rarely used longtitudinals, neither did I .
    If there is no rust now, there never will be after 11 years
    there is steel and then there is steel, some mild steell is crap, some hi ten steels last forever on land unpainted
    Someone said you need a good surveyor, true OR better still a boatbuilder with experience
    I,ve met surveyors who no ZILCH Met a Llloys guy once who surveyed the yacht I was building under Llloys supervision, who wanted me to fill the tanks with fuel to test for leaks!! alloy yacht, Christ he was so thick, he had never heard of a mano meter
    Fly me to whereever I,ll survey your boat for free
     
  6. lazeyjack

    lazeyjack Guest

    sorry bout typos my "d" was not working, read lloyds
     
  7. jehardiman
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    jehardiman Senior Member

    I concur with lazyjack. If the foam is not coming off and there is no sign of rust bubbles or flaking in the exposed paint, leave it. Realistically though, after 20 or 30 years (sooner in enclosed spaces with large electrical equipment due to the ozone), the epoxy will get brittle and you may begin to see paint cracking, generaly at the welds and other areas of flexure. However, for the most part, well applied interior epoxy is for the life of the hull (say 40-50 years). As the paint ages, you just have to keep the whole surface touched up or else the rust will just spread under the coating and it will come off in huge sheets as the rust levers the brittle paint up off the surface. When touching up always cut back to well adheared paint and then build up...primer,basecoat,topcoat... to match the existing surface profile. Also note that painting over epoxy with more epoxy will just make the coating too thick and your cracking and peel problems will increase, the paint needs to flex with the hull.
     
  8. hiracer
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    hiracer Senior Member

    Thanks for your responses. I'm glad to hear that the paint is long term, assumption proper application and care.

    About the paint getting brittle, this is a 34-foot steel boat so the idea of hull flexing seems a bit foreign to me. And I can't see a flat surface on the hull at all, only on the cabin and maybe the bow. The rest of the hull is all curves.

    Question: Why is the life of the hull only 40-50 years? This is longer than I will live, so in some ways it's irrelevent to me--except perhaps resale value. If the hull's paint inside and out is properly maintained, shouldn't the hull last longer than 40-50 years?

    The boat under review has had but one owner, and the maintenance thus far has been first class. Professional care every step of the way.
     
  9. lazeyjack

    lazeyjack Guest

    the life of the boat COULD be forever, if there is no rust, there are allready ships around more than 100 years old now. Email me or phone me 0061754561210 I hate typing
    Stu
     
  10. MikeJohns
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    MikeJohns Senior Member

    hiracer
    The hull will always flex in response to the loads, that is the nature of materials. However flexure in a steel hull is usually considerably lower than for other construction methods.

    I think 40-50 years is a bit short for the hull life, a properly designed and maintained steel hull can go on forever. Properly designed means scantling sizes thick enough to prevent stress levels rising to the point which induces fatigue weakening. Light weight boats will have a shorter life-span but the problem areas can be re-built relatively easily if access is easily achieved inside.
    Life span depends on the maintenance rather than any intrinsic ageing characteristic.
     
  11. lazeyjack

    lazeyjack Guest

    a small steel boat properly built moves very little, because it fits with wave patterns Sitting in hot sun a 43 footer can :"grow" quite a bit, bit not enough to crack paint things like tankers, bulker, have gauges on Bulkheads etc to show how much the ship is twisting, hogging,or humping, and even then paint does not crack
    It seems to me that this conversation is small and nitty picking
    i jsut wonder how many of you are or have been builders? or are you theorising? this is what it seems like to me
    i would avoid, anything amateur built, and anything with stringers, esp if those stringers were hidden look around the floors, ideally floors should be seal welded, but look in areas that are hard to get at, if there is no rust you have a boat that was properly prepped
     
  12. jehardiman
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    jehardiman Senior Member

    40-50 years is indeed the economic life of a hull, and like MikeJohns says, it is not so much that the material is the problem, but the economic cost of stripping out the equipment, cabling, and piping to inspect, repaint, repair and repower. Cheaper to build new. Only the military would pay to maintain a hull longer than that. In the commerical world idealy, eveything would wear out at the sime time and would would just scrap the hull for the ammout of the last finance payment. Of course, repaint and refurbish is much simpler the smaller the hull gets, but the cost in man-hours, paid or not, is still there.

    Also, there really is a finite life to a metal hull. As the vessel works in the seaway, there are low cycle|high strain and high cycle|low strain loads. These cause fatigue. Now granted, we are talking like >10^8 cycles here for most vessels (design for 3:1 on yeild), but a commerical hull operating 200 days per year in 5 second waves thats only 28 years with only a little margin left over for the ramdom critical strain. This fact is reflected in the pricing and insuring of older hulls. Eventually, from a commerical standpoint, the risk of fatigue failure becomes too high.

    lazeyjack is also correct that thermal expansion is a real factor. Rule of thumb is 1/2 in (13cm) per 100 feet (31m) ove the course of a year (50F or 28C change in temperature). Again, this is not enough to crack a new, plastic, epoxy. But with age, most epoxies shrink and become brittle after a few years. Then the temperature extremes and flexture (an inch or so in a small hull, several feet in a large hull) cause the paint to fail.

    He is also correct that the prevalant commerical practice of skip welding longitudinals and decks is the death of most hulls. In my years in the yards, it is my experience that most corrosion starts in painted over skips. That is one of the reasons why military ships are so expensive, skip welding is not allowed and this effectively doubles the cost of welding on the hulls.

    Oh yeah...25 years in steel construction yards, both commerical and military. Give me an older military ship built in a public yard any day...overbuild, painted with Formula 151 and no skip welding...easy to maintain the hull, not like the new commerical yard building POS practice.
     
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  13. Milan
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    Milan Senior Member

    If this boat is professionally built by the Dutch yacht builders, (who have vast experience in metal boat building and work to very high quality standards), she will have very long life, no vories. If in doubt, measure the plate thickness.

    Do you know boat type, designer, yard?

    Milan
     
  14. hiracer
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    hiracer Senior Member

    Full keel with cutaway forefoot cutter built by Yachtbouw Klein in Sappemeer, Holland in 1985 to a Koopman design. Very well maintained. Circumnavigated without incident. Mercedes diesel. A cruising design. Thanks for your interest.

    [Edit: Google is telling me that maybe it's spelled Jachtbouw, not Yachtbouw. Sorry if I got it wrong, but I'm just relating what I get from the broker.]
     

  15. hiracer
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    hiracer Senior Member

    I'm not an engineer, but . . . .

    I thought ferrous alloys (a/ka steel) have a threshold below which a repeating load may be applied an infinite number of times without causing failure, called the fatigue limit or endurance limit. Aluminum doesn't exhibit a fatigue limit, meaning that even with a miniscule load it will eventually fail after enough load cycles. That's one of the differences between steel and aluminum.

    Are you saying that the typical loads on a steel sail vessal exceed its fatigue limit, or that steel does not have a fatigue limit?

    I understand that for a recreational steel sailboat this is all perfectly academic (even for aluminum), but I am curious.
     
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