49' steel houseboat repair

Discussion in 'Metal Boat Building' started by Pose, May 14, 2007.

  1. Pose
    Joined: May 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Portland, OR, USA

    Pose New Member


    I am considering the purchase of a 49' x 21' steel pontoon housboat.

    I don't know a whole lot about about steel or boats,
    but this would allow me to fufill a lifelong dream of
    living on the water. The boat has 700 sf of living area
    with 100 Amp shore power and continuous holding tank pumpout.

    It has a 6' x 47' center pontoon and
    two 3' x 44' side pontoons, I estimate
    it displaces about 25-30 tons.

    If I were to buy this boat it would be a liveaboard spending
    most of it's time at dock in a river running 2-3 mph.
    The 1942 Navy surplus engine is not currently operable.

    The seller claims the pontoons are 5/16" steel and looking
    at the end welds, this appears to be true.

    It was homemade in 1992 and has been sitting in
    fresh water since then, does not appear that
    paint or zincs have ever been applied.

    It is my understanding that once a steel hull loses 20% of
    the original steel, the structural integrity becomes compromised.
    It appears to be approching this point.

    I had a former comercial diver inspect the pontoons.
    his "guestimate" was that the pontoons sounded solid
    and that there is about 1/32" of corrosion on the outside.
    He handed me a rust flake and it looked more than 1/32" to me,
    but it broke when I tried to measure it.

    Because of its 21' beam, I can't lift it at any of the
    local boatyards. A shipyard bid about $23,000 to drydock,
    blast and paint the pontoons with anticorrosive paint.

    I am getting two opinions on this:

    The minority opinion is that if this is essentially going
    to be used as a floating home, I can have the pontoons
    filled with foam and it will float for another 20 years.

    The majority opinion is that the pontoons can be saved,
    but I have to pay to have the shipyard paint them soon,
    and it is never going to be cheaper then the current price.

    It is my understanding that if I paint it, I preserve the
    existing stuctural integrity for about 15 years,
    when it will have to be lifted and painted again.

    What I can't get a good understanding of is
    what will happen to these pontoons over the next 15 years,
    if I fill them with foam and don't paint them?

    Can anyone here venture some opinions?


    Attached Files:

  2. lazeyjack

    lazeyjack Guest

    sounds very much like you should get an ultrasound, this gives a very accurate measure of the steel thickness , same as ships surveys have(compulsary)
    A rust flake will always appear thicker, , much thicker

    Anyway if here are no deep pits, evidence of corrosion, thats a start, IF the hulls are airtight, they may be sound, BUT I would not buy that boat unless you can get that thickness test done
    After this, and all ok, then a blast, , then 75 microns DFT zinc, then 300microns dft high build epoxy from Devoe, then it could very well last 50 years
    25 microns is one thou:)) you can apply the high build in one hit, 15 double header passes using a wet film gauge
  3. Pose
    Joined: May 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Portland, OR, USA

    Pose New Member

    Thanks for the response,

    Sounds like another vote against the foam.

    Just to be clear, there is a layer of
    corrosion over the entire underwater
    area of the pontoons, estimated
    at 1/32".(400 micron)

    There is pitting, I might guess maybe an
    additional 1/32", but I am not very experienced
    at judging.

    It doesn't appear to be leaking.

    I did not know about rust flakes appearing much thicker, thanks.

    I have inquired about ultrasound testing,
    my understanding is that they only do
    a limited number of spot checks at various points.
    Is this a valid means of assessing the rest of
    the pontoon/hull that wasn't spot checked?

    It looks like Devoe makes several high build epoxies.
    Any recomemdations on the best one?
    The advice I have been given has been for coal tar epoxy.
    Devoe makes something called Devtar 5A which does not contain
    coal tar but claims to be superior to products that do.

    The shipyard I have been discussing this with has
    been particularly unforthing about the particulars
    of the paint and how it will be applied.
    The bid just read: "Sweep blast to SP-7, one coat
    of anticorrosive paint".
    They did say they would provide
    the manufacturer's product info.

    I would have thought that for $20,000,
    they would be more accomodating,
    but I guess they realize that if I want
    the pontoons painted, my only option is
    to have them do it.

    Coming from a position of ignorance, I am reluctant
    to request a detailed bid specifying exactly how the
    paint should be applied, without having a clear
    understanding that my spec is significantly better
    than what they ordinarily do.

    These people do deal with oceangoing tugs and barges,
    so I assume they know something about what kind of
    paint works good, but you never know...

    Having said that,
    Does the paint last 50 years or just the hull,
    when it is painted every 15 years?

    Finally, assuming that there still is 20% left of the
    original 5/16" (8mm) steel, anyone care to try to explain
    what will happen if the pontoons are filled with foam,
    but not painted?

    Not to belabor this second option, but the seller seems
    to think that is the prefered strategy.
    So far, I haven't been able to get a compelling explanation
    to take back to the seller as to why this might not be a good idea.

    Anyway, thanks Lazeyjack for providing specific information.

  4. SamSam
    Joined: Feb 2005
    Posts: 3,825
    Likes: 161, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    If you have 20% corroded away that leaves 1/4 '', pits can go deep and leave you with the possibility of numerous pinholes. Steel can be corroded worse on the inside than the outside, have you looked there? To be limited on hauling out to certain places that charge a massive amount of money is a decided disadvantage. Have you looked around at other houseboats so you have an idea of what they are worth? Sam
  5. lazeyjack

    lazeyjack Guest

    you are welcome and thanks for saying thanks!!! I used to blast my own builds and I do know the key is dry film thickness, if the film is not thick, the metal will be wet, simple,
  6. lazeyjack

    lazeyjack Guest

    oh give tar a big miss, cant be overcoated with anything else
    235 is a good one, you can paint it is one as I explained, and it is as hard as rocks, to age coat it, you will need to use 201, but then you should neevr need to paint it, as far as it goes, if the owner is willing: get a sharp pick and go along and belt the thing here and there, IF the metal is dozey it,ll either dent it or go right through, this is how you survey a ship WITHOUT ultrasound
  7. Pose
    Joined: May 2007
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Portland, OR, USA

    Pose New Member

    These pontoons do not have ready access to the
    interior bulkheaded compartments.

    One of the compartments did have an access plate,
    but it required removing a deck access panel in
    the middle of the owner's living area and then removing
    some 1" bolts with limited wrench clearance.

    The owner wasn't interested in having me do that.

    The owner is of the opinion there is no problem
    with the pontoons, and that I should just address
    any concerns I have about the pontoons by having
    them filled with foam.

    One compartment that was accessable was one
    containing the non-working diesel engine.

    There did not appear to be significant corrosion
    in the interior of that compartment.

    When I had the diver inspection, he went all over
    with a hammer and chisel, he reported everything
    sounded very good.

    I don't know how to compare this to other boats.
    I have looked at some other houseboats and cruisers,
    but I haven't seen anything like this, with all-steel
    construction and set up like a house with almost
    2000 square feet of deck area, wired for 100 AMP power,
    1000 gallon holding tanks, inboard wastewater pump, etc.

    FYI, The seller agreed to slightly less than their $50,000 asking price,
    conditional to my being able to obtain a satisfactory bid
    for lifting, blasting and painting.
    I haven't decided yet if $23K is satisfactory.

    If the beam were just 18" (.5m) narrower,
    I would have several other options for
    having the work done.

    If the engine was working, there a couple of
    other shipyards I could take it within 30-50 miles,
    but this is still a small-dollar job to them and
    I have been advised they are unlikely to be any more

    So, if I get this hauled out, I want to do everything
    possible to make sure that I don't have to go through
    this again for a very long time.

    Looking at the manufacturer's info for Devoe Bar-Rust 235,
    this sounds like the verbal description of the paint I
    received a bid for.

    I have several more questions.

    A coat of 0.012" (300 micron) is about 50% more than the manufacturer's recomendation.

    Is a painter likly to consider this multiple coats?

    What is age coating?

    Is the moisture resistance of the High Build epoxy
    comparable to that of the coal tar?

    This may be a dumb question, what is wrong with
    a tar coating that cannot be overcoated?

    Is it impossible to build a tar coating up to 0.012"?

    Even if the engine were ever to be rebuilt, the boat
    would seldom ever go out, is there a need for an
    antifouling coating?

    Again, thank you all for your time and opinions,


  8. lazeyjack

    lazeyjack Guest

    first no, you dont need antifoul as long as your wife is prepared to get over the side and scrub once in awhile
    Age coating is when you have to paint again , even after 6 months you need a paint that will BITE into the 235 or whatever was there
    yes you maybe right about the thickness, I was thinking measured wet(it then dries thinner)
    Seems so much money to paint, a commcercial; rig can blast a 4x12 foot plate in 10 mins, but I dont obviously no abt your prices in your part of the world
    if I member right the zinc is 302, but 201 is a lot cheaper will do ok
    look you are in the drivers seat, offer him 35
    its a tricky deal buying a watercraft,
    What the diver said , seems like it's sound enough,
    I,m not there so I can't help much :))
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.