Steel-made hull with fiberglass-made radius chine ?

Discussion in 'Metal Boat Building' started by xarax, Jul 5, 2007.

  1. xarax

    xarax Previous Member

    Thank you jehardiman,
    It seems there was a misunderstanding here...Please forgive me if I was a little vague in my description. The plastic surfaces I suggest are the two outside surfaces of two hollow curved plastic bodies made of fibreglass and filled with some foam. They are just like two self-supported, floating amas of a trimaran, but curved inwards, as to fit to the steel hard chines of the hull leaving as a small gap as practically possible. Something like two long, curved inwards, and quite thin "plastic bananas"!
    There is not any real reason to use many bolts, just a dozen of them would be more than adequate I reckon, and no rivets whatsoever.
  2. waikikin
    Joined: Jan 2006
    Posts: 2,383
    Likes: 151, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member


    Xarax, so what your talking about is like composite fairings, like on a motorbike or like on top of submarines to hide the chines into the topside & bottom plating? Jeff:)
  3. xarax

    xarax Previous Member

    I feel that I have to respond to this, because I think I see a dangerous thread beginning here, disguised under a supposedly sacred utilitarian high value, as all totalitarian attitudes do at the start......
    Yes, dear friend, I do like to argue just for the sake of it, not for money, social power or any utilitarian reason whatsoever, and I believe arguing just for the sake of it is a high point of western civilization, but you think otherwise, obviously. Well, I respect your view and I do not force you to argue with anybody and especially with me, but please let me also express any dream, idea, desire, etc, express it freely and publicly if this does not offence anybody, and don t have to apologize to any local or other marshal court for this, or pay anybody any price for this. Or do I own you or somebody else some fee for your expert advice and I didn’t t know? Do we have arrived to a point where we all have to wear on our bodies and spirits some kind of burkas and I haven t notice the sign?
    My idea might well be not feasible, and is probably not feasible, just like all ideas, especially at the stage of their infancy. But this is not a reason to restraint from expressing it to anybody who bothers to hear, and enjoy the sequent free and friendly discussion, with interesting comments that might come up, just for the sake of it. Your world my friend, where no ideas cast any shadows on peoples mental walls seems to me a very dark cave indeed.
    Do I have to apologize or pay anything for trespassing your private area where only “people who know” are invited? I have to say that you don’t seem to know the etymology of the lain word “amateur” . Well, there are people who use their knowledge of things to earn money, and there are people who just love to learn things, provided they don’t pay the high price I feel I own to you and your private institution of steel boat connoisseurs. It seems that trying to imagine something that was not done before wasted your so precious mental powers.
    Come on, Tim, be polite, show a little patience with other peoples ignorance, and respect their right to publish even crazy, imaginative or illusionary ideas. Do not feel as any part of the vast area of ideas, most of them not feasible at all, has to belong to you or any other individual. No hard feelings… After all, it is the love of freedom that brought us here..
  4. xarax

    xarax Previous Member

    Thank you Waikikin,

    Yes, so to speak. But these composite fairings have to be quite wide, structurally sound and insubmersible, and leave as a small gap as possible, just like the Kiwi s last Americas cup "hulas"...:) Each of them cover the space between a pairs of chines, so now we , or the water flow, don’t see any hard chines whatsoever, only a smooth radiused surface interrupted by the longitudinal small gaps. These gaps can be made less than half a centimetre, I suppose, and it might well be desirable to cover them with additional flexible plastic tapes, just to prevent boundary layer transition and reduce drag. Also, last but not least, these tapes mask the colour difference you always do have between different materials...
  5. jehardiman
    Joined: Aug 2004
    Posts: 3,045
    Likes: 560, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    1) A gap or step, any gap or step, will greatly increrase the drag, well over that of the worst built chined hull. Unless you are operating at extreme high speed (25+ knts), the difference between the SS1 and SS2 drag will be far greater than the difference between a well designed chined hull and a double curvature hull. Indeed, there is more to be made in reduction of wetted surface and the design of appendage interference drag, which is less in single curvature BTW, than there is in chine drag of a well designed hull.
    2) Attachment must resist the hydrodynamic forces on the skin, not only the hydrostatic ones. These forces are on the order of ~2,000-5,000 psf depending on speed. Additionaly it is important to consider that point loading of these forces may exceede 200-500 psi, so the attachments must be robust. BTW, the drag of an exposed socket of a flush socket headed cap screw in not inconsequential, an exposed bolt head is far more.

    Again, you seem to think there is a huge amount of work required to fair a welded seam. Maybe it is because you only "see" and remember the poor ones. You may just "assume" that the good looking ones are glass. When following good step welding procedures and heat limits (not welding skill, just good practice), there is no reason to warp a plate while welding.

    I will state again that there is NO appreciable hydrodymanic advantage of a round bottom hull over a radiused chine or hard chined hull that the chine included angles exceed 135 degrees. Additionally, the amount of work required to fair a radius chine or hard chine welded hull is LESS than that required to fair a one-off composite hull or even the fairings that you propose.
    Last edited: Jul 8, 2007
  6. Wynand N
    Joined: Oct 2004
    Posts: 1,260
    Likes: 148, Points: 73, Legacy Rep: 1806
    Location: South Africa

    Wynand N Retired Steelboatbuilder

    xarax, as for the above quoted statements by yourself;

    1. Again, I strongly suggest you visit my website and take a look what a real radius chine steel hull looks like. And as a point of interest, it really does not take much longer to built than a multi-chined hull...So why want to go bananas:D

    2. I never said it is impossible, just impractical.
    That said, the first thing you have to consider is the different coefficient of expansion of the two materials. Steel will stretch more than plastic and do I need to spell out the consequences?
    Then to find a means of attaching it the steel hull and remember, every hole drilled in that hull is a potential leak and a guaranteed rust trap. Further more, have you ever been on an angry sea with a sail boat. Chances are against you that the plastic radius bananas will be torn off cleanly by forces and impact of waves in a real blow.
    Resale value, I think that you will be pressed to find another person like yourself to sink his money in such a boat - no pun intended.

    And lastly xarax, you seem such a nice lad and I admired someone who believes in his ideas and himself, but I'm gonna leave you with this little wisdom: "keep it simple" in other words, any fool can be complicated, but it takes a genius to be simple...;)
    1 person likes this.
  7. xarax

    xarax Previous Member

    Yes, this is why the Kiwis "hulas" didn t work when they were forced by the inspectors to wide the gap between the hulla and the hull. I was only hoping that longitudinal gaps disturb the water flow less than transverse ones , but I am not sure about that. After all, the water flow never travel along the hull s skin following our lines!

    The bolts head don’t have to be exposed to the outside. I was thinking of them as buried somehow in the plastic body and fastened from the inside of the boat. But I later realized that their ends would have to come out in the most inaccessible places down the bilge...I still think that, at the end, one could find a decent way of fastening these plastic bodies so that the outcome could be satisfactory, hydro dynamically and aesthetically.

    No, but I do think that there is a lot more amount of work required to fair a lot more seams that a radius chine needs. The length of the seams on the radius chine is comparable to the length of the rest of the hull, isn’t it that so? And I just have the vague feeling, which might well be ill founded of course, that this additional work is exactly the main reason behind the fact that we see so few radius chine hulls built by amateurs around the marinas. Am I mistaken here?

    I would love to believe this, which could save us a lot of time and trouble, but it didn’t happen to me to see any relevant scientific article. There are so few studies about chine hull hydrodynamics for heeled hulls, probably because the recreational small craft industry have never invested enough in this beautiful type of boats for its own financial reasons (which have nothing to do with the quality of the steel boats themselves, naturally...) Steel construction sounds like a nineteenth century thing to young people, plastic is the name of the day...And at the end, dear jehardiman, we have to confess that there are some elements of truth in the statement that fishes don’t have hard chines...

    To tell the truth and the whole truth, jehardiman , as I already mentioned somewhere in the thread, it did never cross my mind, even for a moment, to cast these plastic bodies myself! I do hate the smell of the fibreglass boats even when they are a few years old! I hope one will not smell these plastic parts when they are outside the hull and partly immersed in water... I was simply planning to order and buy them from some place, as they are really cheap, you know...

    I repeat my simple question about the difficulty of radius chine construction that I posed yesterday and that I think is still left unanswered : If it was so easy, given that a round bilge-like steel hull is so much desired, why we see so few radius chine steel boats (made by amateurs, of course), around the marinas?

    Thank you again very much for your very knowledgeable interesting comments.
  8. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    I'm have never welded or built anything in steel, but I guess Wynand is right.
    It's probably easier to build a round bottom or bilge or chine in steel than to, for example, first make an extra chine and then use some epoxy based putty or fairing compund or foam or whatever to make a round blend on the outside.

    Is this close to what you imagine?

    Attached Files:

    1 person likes this.
  9. M&M Ovenden
    Joined: Jan 2006
    Posts: 360
    Likes: 77, Points: 38, Legacy Rep: 527
    Location: Ottawa

    M&M Ovenden Senior Member

    A few reasons can explain you see less radius chines than hard chine metal boats.

    1.Many amateur steel boat builders are cheap and they see building there own boat as a way to get a boat for not to much money. They therefore want it as simple as can be.
    2.Lack of confidence. Like you, many people do think that round chines is out of reach for there skills. The truth is that if you can build a boat the added work for round chines is not out of reach.
    3.Most ancient steel designs were chined, I believe you will see more shaped metal hulls with time. Construction techniques have evolved (CAD,CNC,better welding equipment at reasonable cost...) to go...

  10. xarax

    xarax Previous Member

    Beautiful radius chine hulls...Come on, Wynannd, they are your hulls, not mine, I could never ever build so fair radiused hulls, and I don’t think any amateur, (who usually builds one and only one steel boat in his life and then he spend the rest trying to sell it, :) ), could ever built hulls like these. Or you want to feel like you are still an amateur steel boat builder? Even your boats must have rusted by now from the old days you were still an amateur... :) I have to point out that professionals usually underestimate the difficulties amateurs confront in their first steps creating something . They tend to forget how difficult it was even for them , even if most of them had a special talent or inclination on their field and that was one reason they chose their field in the first place and the succeeded staying in it...I tell you Wynand, and all you guys that have built one or more steel boats, radius chine hull construction is beautiful but far more difficult than simple hard chine construction, period. Trust me on this please...:)

    There are some types of joints that permit a limited amount of movement along one direction, in our case the desired longitudinal one. I am sure you could solve this problem...

    I have never pretended that I am not a fool - you know, clever people don t spend their precious time building sailboats, they buy them, or, if they are more clever, they sell them...:) so how on earth or sea could I have pretended to be a genius ? :) Nevertheless, I fully agree with you at the KISS principle, given as an order by nature to men, but it was exactly this principle that get me think about the possibility of GRP radius chines in the first place. Because steel radius chine is not a simple way of having a round shape made by flat plates, and it is not simple to build a steel radius chine hull if you are still an amateur as you were in the old days. I thought that we are unlucky that steel or plywood bend easily only in simple curvature surfaces, but we are lucky that the areas of the hull where you really need double curvature is only a small percentage of the whole. So why not use a limited amount of an easily-made-round cheap material as GRP in parts that can you buy and fit in these areas?

    Thank you very much for your expert advices. I do study your site, please believe me, but, unfortunately perhaps, I am too young or too old not to search for alternatives ...:)
    "Doubt is born of knowledge and knowledge is born of doubt"
  11. xarax

    xarax Previous Member

    A trully simple method of boat construction according to the KISS prinsiple

    Why build a boat anyway?
    The answer is simple: Don't!
    Of all the amateur-builders I met, I can not remember anybody who had a clear convincing case for actually building the damn thing in the first place.
    The 2 most often cited reasons why somebody would defend his crazy idea of absolutely wanting to build his own boat are
    1. Money, and all the cash he will save and the giant profits when he will sell the thing
    2. Quality and seaworthiness, because all the others and the professional builders and/or designers just don't know what the perfect boat should look like.
    So here is what I think of these arguments. People that have only planned to build and all designers that want you to buy their plan will disagree.
    People that have actually built, sailed and sold their boat are more likely to agree with me, I believe.:)

    Gerd Muller, the Yago project
  12. xarax

    xarax Previous Member

    To Raggi Thor,

    Almost. The plastic parts need to be hollow plastic bodies made of some GRP material, filled with closed cells foam, because you want them to be structurally sound (to resist the impact of other people s boats, for example...:), and insubmersible at least. To build an extra hard chine is really an easy task to accomplish, something like just another hill to climb, even if you are a first time amateur builder/climber like me. Steel radius chine is what I , for one, call a mountain, may be a small one that you can climb after one or two attempts, but a mountain nevertheless. After you have built a radius chine hull you can call yourself a master builder/mountaineer...:) :) :)
  13. xarax

    xarax Previous Member

    I hope you are right, Ovenden,
    ...But I have a fear that, with time, we will not see any metal hulls whatsoever...Marinas, just like refrigerators, are full of almost identical plastic bottles. I feel lucky when I do find some non-plastic things around me, like the refrigerator s door...:)
  14. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    OK, what do the others think?
    Make an extra chine.
    Sandblast and epoxy?
    Make a nice "blend" ( a round fairing) of lightweight compund.
    Add glass and epoxy.

  15. larper
    Joined: Mar 2006
    Posts: 15
    Likes: 3, Points: 0, Legacy Rep: 22
    Location: Sweden

    larper Junior Member


    As a truly amateur backyard homebrew builder that’s three years into a 60 feet steel radius chine sailor i'd suggest that as a test you go get a piece of plain steel tube of some centimeters diameter (3-5 or so) grab an angle grinder and cut one meter of the tube in two lengthwise. Then snap a photo of your truly _not_ developable half tubes and post it here.

    I tell you. its close to impossible to not end up with a "banana" cutting a tube lengthwise no matter how hard you try.

    That said. i really don’t think with all due respect that you have a clue what your talking about saying that no amateur can produce a fair radius chine. Its not the radius part that’s hard to do, its the straight edge seams that’s hard! they tend to warp and need to get to know the hammer and dolly to get straight and true.

    If you really wanna build a boat choose the material that works for you. But if your afraid of work don’t build at all! If anyone feels that its easier to get the shape in plastic then build with plastics only. i don’t like plastics so i chose steel alot of backyard builders don’t like either plastics is steel so the chose aluminum or wood or even concrete, as i said, use what ever material that you feel you’d be able to handle without taking shortcuts

    Im not the guy to praise or condem your idea i just think that many of your statements comes from lack of experiance working with steel and therefore arent true.

    -- Per Larsson
    1 person likes this.
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.