4mm steel hull

Discussion in 'Metal Boat Building' started by Guest, Jul 30, 2003.

  1. Wynand N
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    Wynand N Retired Steelboatbuilder

    Thanks for your thoughts Mike ;)

    I really am considering plating the hull below waterline with 4.5 - 6.0mm plating. The weight saving is tempting though. Plating should commence about Jan 05.
    I'll keep you posted.

    best regards

    Wynand Nortje
     
  2. D'ARTOIS
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    D'ARTOIS Senior Member

    steel hull assembly

    Yes, it can be done, however I agree with the chap who said: Who do you want to fool?"
    Normally, one uses for a 55' 5 mm for the sides and 6 to 7 for the keelbox and bilges. If you space your stringers, longitudinals a bit closer and add a few more frames, it is ok. The high impact resistance is still good enough if you use Lloyds grade (not st 37). Actually there is a simple trick to check the quality of your supply of steel: bent a piece of sheet material till both ends meet. Bring the metal back in its original flat position. If there are no hair cracks you might assume it's ok.
     
  3. Ron Cook
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    Ron Cook Junior Member

    longitudinals slotted 1/2 way into frames

    Wynand,

    I've just read an earlier post by you where you said that you only slotted the longitudinals 1/2 way into the frames.

    I have read that to do so that the scantling proportions are slightly different then when the frames touch the plate. As yet I have not found a source explaining what those differences may be.

    Could you shed some light on this? Also I saw one of your earlier posts with the pictures of the 65 and the 57. It was a big suprise as to how fair the overturned 57 is. That picture is a real positive shot in the arm.

    Ron Cook
     
  4. CDBarry
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    CDBarry Senior Member

    If the transverse web frames don't have adequate shear connections to the plate, then the palte aspect ratio changes, which may change required thickness. Also, the transverses will have to be bigger to get the required section modulus, since the shell plating won't be effective as an outer flange.
     
  5. Wynand N
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    Wynand N Retired Steelboatbuilder

    Ron,

    Thanks for the interest.
    I mentioned that the frames do touch the hull at high load areas, eg. the keel floors, engine beds and sheer. Remember that the longitudinal stringer slots solidly into the frame and welded tight, meaning that the frame is not weakend.

    I attached four photo's for you. One showing the stringers going into the frame slots. Two, shows detail of stringer and frames on inside - note the hull plating sitting clear of the frames. If you look carefully, you can see in the right hand top corner the hull touching the frame.
    Three, Dix 57 going over, with the building strongback still in position. Notice the frame floors in the keel vicinity against the hull - below waterline. Raduis chine and plating nice and fair at this stage.
    Four, Three Dix's in a row, 65, 57 (to be turned over) and 38. No dreaded fairing near the 65, only blasted and epoxy prime coated.
    Take note that all three these hulls were built from 4mm mild steel plate.

    I disagree with CDBarry. Proof in photo 4. The Dix 38, if you have not noticed, is totally frameless!!. Only tempary deck stays holding the sheer in shape. And this kills off another myth, with the necessary skill you can produce a frameless round chine/bilge hull.

    Ron, feel free to contact my by e-mail if you want to chat about this type of building.
     

    Attached Files:

  6. yago
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    yago __

    Great hull Wynand!
    One of these days I will have a look at radius chine design.... Who knows, there might be a way to do origami - radius..? ;)
     
  7. JimCooper
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    JimCooper Junior Member

    IMHO (in my humble opinion)

    surely you should be looking for better grounding strength than to use such thin plate underwater ?

    I have seen a few 4mm boats looking very dented and sorry after 30 years sure its not structural since your frames are so close together but very very cosmetic. You will dent the first time you come alongside hard.

    If you have ever sailed around coral areas I recknon yu'd quickly change your view, thin plate has a habit of denting and catching rather than sliding past with a bit of deep scratching.

    Youre also going to have to keep those interior frames stringers and plate in tip top condition 3mm corrosion in 6mm still gives you a good margin and I've chipped enough rust inside boats to know how it corrodes when left.for a decade or two.

    Go heavy below use your 4mm and a mighty rubbing strake on the topsides and superstructure.

    Chine hulls in thicker sheet seem the most sensible yacht steel designs I've seen robers 53 chine hulls consistently beat the radiused one in the club races and his replating will be soo much simpler when it comes.

    Functionality and safety then ease of construction then beauty. Too many round boats get finished and they wore the owner builder out by the time they are at hull stage chine 53 takes 3 months round 53 takes a year unless you're an experienced metalverker

    Just a seamans view
     
  8. Wynand N
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    Wynand N Retired Steelboatbuilder

    Jim, If a hull & deck are properly shotblasted (dislike pre-blasted/primed plates) and epoxy coated, especially on the inside after building, there should be no problems as long as preventitive maintenance is done, as is true with other materials as well. I uasually sprayed (airless) the inside with a coaltar epoxy with a minimum thickness of 180 microns after blasted to spec SA2.5.
    Older boats, especially home builts were prone to rust, because very few were ever shotblasted in backyards. I've seen some guys using chemicals to remove rust prior to painting,others just wire brushing!! and some just touch up paint on welds etc on pre-primed plates. These are all guaranteed recipes for rust.
    Remember, paint is only as good as its preparation. With modern knowhow and epoxy paints it is not neccessary to "build-in" the rust factor. In fact, a well built & epoxied coated steel boat will outlast any fibreglass one.


    If you look at the photos elsewhere above on this page, there is one with three boats in it, a 38, 57 & 65ft - all raduis chined. The green primer painted
    65 only took 12 working weeks to the stage you see on the photo.
    Also note that a 65 is about double a 53ft hull ;)

    Ps. I only built one Robert hull in my career and it was one to many. Dated designs and not very builder friendly and structurally rust traps, contradictory what Bruce preaches to the home builder
     
  9. yago
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    yago __

    Jim, I have reviewed boats I built over 20 years ago, 4 of my own building and several others built by friends in the same period. They had been all been shotblasted and covered with epoxy paint. Not a spot of rust inside, nothing at all.
    On the outside they had a few spots on deck repainted, where the paint had worn off over the years but that was always on welded on eyebolts, cleats etc, fittings that should have been stainless anyway. Hull and Deck were spotless.
    Properly blasted and painted, rust is no longer an issue, and certainly not something that you would want to increase plating for these days.
     
  10. globaldude
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    globaldude court jester

    "The longitudinal stringers are half way slotted into the transverse frames, then welded to the frames. The stringers are then space welded along the length of the hull to the hull plating. In effect you have a hull with longitudinal framing. This completely eliminate the "hungry horse look" effect."

    Hey Wynand, my 50 ft hull I've purchaced is built same way, but reading another post on this site, the writer said that " space welded" stringers were the main reason for rust developing as there was no way of completely sealing the "crack" between the hull & stringer .[ even with good limber holes ] .
    So I was thinking to fully weld them, mig , and 1" intervals, not continuing untill the previous weld completely cold, so a bit here, then forwd, aft etc !
    What do you think ??.
    I'd thought after blasting to white steel [ given I can't get the "crack/overlap"]
    that the epoxy paint would be good enough to seal it !!, the writer of the post said that years on, the epoxy can crack due to movement and allow water in --- .
    Am I being paranoid ??
     
  11. Wynand N
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    Wynand N Retired Steelboatbuilder

    Hi globaldude,

    I would not recommend welding longitudinal continoiusly to the hull plating. You may just end up with a hull that will look like it is build by corrugated plating;)

    In my heyday as a builder we use to weld stringers; 50mm weld - 200mm spacing on one side and the same weld on the other side of stringer, spaced in between the weld opposite. If your stringers are docked solidly against the plating and the welding sequence carried out as above, you will have no movement between plating and stringer to crack your expensive epoxy.
    By the way, after shotblasting to an approx spec SA2.5 (white metal) we sprayed the inside with coal tar epoxy to a thickness of about 140 - 170 micron. Needless to say an airless spray unit was used to elliminate air trapped under paint, especially in corners. Our unit sprayed at about 220 bar pressure on nozzle.

    Perhaps you are a liitle paranoid....
     
  12. globaldude
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    globaldude court jester

    Cheers Wynand, I'll take your advice . The hull is very fair & I'd hate to undo that.
    I'd intended to spray [ compressed air ] useing gear I owned already , but it seems I'll be hasseling my friend for use of his airless unit now !!.
    I'm concerned about putting 2 pack epoxy through his airless sprayer, is there an easy and complete way of cleaning all residue out of the pump/gun ?, as I don't want to stuff it for him - or me !!.
    I haven't worked with 2 pack epoxy's before and realise they cure chemically within a time frame, so is it the same as washing out -- say enamel paint ?, that is, rinse out completely with apropriate thiners then blow it through the gun untill it runs clear !?
     
  13. MikeJohns
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    MikeJohns Senior Member

    globaldude

    The yards here often use Methyl Alcohol (Methylated spirits) as a cheap and effective way of cleaning up the unset mixed epoxy, the thinners are often too expensive for cleaning when you are blowing out spray paint equipment. Other alcohols would probably work too.
     
  14. Wynand N
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    Wynand N Retired Steelboatbuilder

    globaldude

    All I can add to Mike's advice is that if you go the airless way, wash the system out with "washing thinners". Much cheaper as epoxy thinners and does a sterling job, and you can re-use it again; just pour the used thinners in a container, let it stand overnight and the following day all the old paint and residue will lie in the bottom. Just pour (scoop)the clean thinners out and clean your system again with it. And again, again......
     

  15. lazeyjack

    lazeyjack Guest

    Have you thought about using Corten? this hi tensile plate is wonderful and extremely strong, good wheels will form it, but its springy, as you would expect, the Dutch used to use it a lot, in fact it is used ashore without paint, , it,ll get surface rust then stops
    Best though if you are a welder as you will need low hydrogen rods
    4mm, or 5/32 inch was very popular
    As I have said so many times, its a yacht not a ship, keep your welds small,
    you thinking chines or round bilge?
     
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