Cost of radius chine vs. round bilge hull.

Discussion in 'Metal Boat Building' started by edik, Mar 1, 2012.

  1. edik
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    edik Junior Member

    I understand why a DIY builder would prefer radius chine construction over the traditional round bilge design. Advantages are obvious: basically, you have two flat surfaces and one constant radius chine. In the environment where you may not have all the equipment necessary and may lack the skills, building a radius chine boat makes perfect sense. But I'm noticing that even professional boatyards, more and more, are starting to build radius chine boats. Why? How much would a builder save by ordering a boat to be built utilizing this method over the round bilge? I think it would not be all that much. Any opinions on the subject?
     
  2. gonzo
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    gonzo Senior Member

    Are you talking about sailboats?
     
  3. edik
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    edik Junior Member

    Yes, of course, sailboats. Again, how much does one save on the cost of construction by ordering radius chine boat instead of the traditional round bilge? I suspect not very much. Or am I wrong?
     
  4. Tad
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    Tad Boat Designer

    The argument makes no sense as they would be two different hull forms. If one is radiused chine and the other fully-developed but the same shape, the difference will be nothing. But if one is fully developed and the other radius chine, the difference will depend on how complex the fully developed hull is and it's construction method. If you are building a round-bottom transverse framed hull where every frame is hand rolled and every plate hand-formed with an English wheel, the difference in man hours will be huge. It also requires considerable skill to do well.
     
  5. edik
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    edik Junior Member

    Thanks for responding. My original question was prompted by the fact that many designers offer their products in various methods of execution: the same model can be offered as a hard chine, or round bilge, or radius chine boat. If I'm buying plans to build myself, then that's one thing and radius chine is clearly easier to build than, as you put it, fully developed form. But if I will have a professional yard build the boat for me, will there be any significant $$ savings if I order radius chine plans over round bilge?
     
  6. Tad
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    Tad Boat Designer

    Not sure about "many" designers. The material and technique really control the shape. To my way of thinking the shape of the topsides (as well as the bottom) will be completely different with "round" shape (curved in two directions) vs multiconic development of sheet material which can only be bent in one direction. I'll guess the designs offered are intended for construction in different materials. Aluminum, steel, or plywood for hard or radius chine, and fiberglass, cold-molded wood, or ferro cement for round bottom........

    Ultimately a well drawn (shapely) and properly built round bottom hull will always be more valuable than a slab-sided sheet material hull.

    That's completely up to the yard doing the work, ask them........
     
  7. edik
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    edik Junior Member

    Well, Bruce Roberts, Van de Stadt - to name a few...and these are very respectable designers with many years of experience.
     
  8. Tad
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    Tad Boat Designer

    Well......I don't think VDS offer any radius chine designs, they do offer their own "quick build" multi-chine hull or round bottom (intended for professional yards).

    And Bruce Roberts stuff is aimed at amateur builders so I don't think you'll find many (or any) of his designs for round bottom metal construction (unless it's some custom variant). He does offer plenty of designs in both multi-chine and radius chine plans.
     
  9. edik
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    edik Junior Member

    Look, I'm not trying to argue a point, I simply asked a question...
     
  10. nemier
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    nemier fascinated with distance voyaging, power or sail.

    Keep plugging away at it edik, I have wondered/pondered the same question.
     
  11. edik
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    edik Junior Member

    Well, you see, I often heard the argument in favor of round bilge hull over hard chine in that the savings are there, but they are insignificant relative to the total cost of the boat, and that hard chine boats will have a lower resale value which would, eventually, negate all the initial "savings." So, naturally, I started to wonder, would not there be a similar issue of radius chine vs. round bilge? BTW, Berkemeyer makes a very interesting argument on the subject. http://www.berckemeyer-yacht.de/
     
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  12. Eric Sponberg
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    Eric Sponberg Senior Member

    I have had to deal with customers for all three types of craft--hard chine, radius bilge and round bottom. Here in the US, I have found that small shipyards simply have lost the skills required to produce a round bottom hullform. Whereas it was there 50-100 years ago, now it's gone. Why?

    In my opinion, because of the oil industry in the Gulf of Mexico. Oil producers put up oil rigs in the Gulf, and they needed LOTS of boats to service them. The obvious choice was to utilize the shipyards along the Gulf shore, but the building capacity was not enough. A lot of vessels had to be built very quickly to support the oil industry, and the shipyards could not spend the time and effort to train people in building round bottom hullforms. Chined hulls would be sufficient and they could be built quickly, easily, and cheaply with the minimum of training and specialized equipment. The number of small shipyards grew, and they began looking for other markets for their craft. Chined hullforms were what they had to offer, and in most instances they work perfectly well. As a result, the skilled workers who really knew how to build round-bottomed hulls retired and died off. The necessary skills were not passed on; the essential bending and rolling equipment languished, was discarded, and new appropriate machinery was never purchased. The idea of round-bottom hullforms disappeared. Go to any small shipyard today and ask for a round-bottom hullform, and they will argue you should go for the chined hullform because it works well enough, and it is quick and cheap. Press them further, and they will finally, but reluctantly, admit that they simply don't know how to do round bottomed boats, and they don't have the equipment for it.

    Fast forward to the early 21st century: There are still some people, particularly in the smaller yacht market, who resist the look and style of chined hullforms, and so the round bilge hullform came into being. Above and below the bilge, the plates are still pretty flat and can easily conform to simple frames. The bilge plates require only one degree of curvature in the transverse direction. You still have to make these plates relatively small and there is some skilled joint-matching that has to be done to obtain decent longitudinal curvature. Small shipyards in general can deal with round bilge plating with the skills and equipment on hand. So the round bilge hullform is a compromise, as are all things in boatbuilding.

    We still see sufficient plated bending and forming skills and equipment in the large shipyards and in megayachts, which are built in large shipyards. So the skills are not totally dead. But the choices for the small boat owner and builder are limited, and this is not purely because of economics--the economics caused an evolution that drove the necessary skills to oblivion.

    That's my take, from the naval architecture perspective, culled from dealing with both clients and shipyards in this regard.

    Eric
     
  13. edik
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    edik Junior Member

    radius chine

    BTW, when choosing the radius for a radius chine sailboat how do designers choose the radius? It stands to reason that the larger the radius, the closer the hull begins to resemble a round bilge design. No? And also, would it not be possible to build a boat entirely from a round chine plates? There would be three layers - the topsides, the chine and the bottom. Just an idea.
     
  14. Wynand N
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    Wynand N Retired Steelboatbuilder

    Having built both traditional round bilge and radius chine steel boats in my tenure as steel boatbuilder, my vote goes for the radius chine boats. Except for the fact it is faster to build, it is also the better looking boat boat.
    I personally do not think a RC would sell less for than a similar designed RB boat if the workmanship are the same. The RC would probably have the better performance as well with its "clean" hull shape.
    To answer your question; it is not only the plating of the hull that is problematic with the round bilge due to the fact that it has many compound curves and need some shaping on the English wheel, but also the frames are a ***** to build. These matters takes up a lot of extra time and time is expensive and a further drawback I found building a RB is the extra welding it need because of many smaller plates used in the hull construction.

    My old friend Dudley Dix was one of the pioneers of radius chine steel (and later plywood) and his designs are some of the best in my honest opinion and most builder friendly having built radius chine boats of other designers as well.

    The Dix 65, 57, 43 and the 38 (I commissioned) are testament of these boats and you can see these sleek hulls I built in my webpage under construction.

    A very well known designer from Cape Town now residing in New Zealand, once looked at a steel hull of a Dix built boat and commented that it is one of the nicest round bilge steel boats he ever seen and was flabbergasted when told it is in fact a radius chine hull:D

    Finally, a radius chine I found not so nice is the Bruce Robert designed ones having built one of his boats with this method....

    EDIT:

    In short yes. But the trick is to have a balance between too small and to large ;) but the "smoother" the hard chine line is the better the resulting radius chine will be. But the trick is in the bow of how the upper tangent line meets the lower tangent to form a smooth transition into the bow. This is an area Roberts have not refined IMO. The radius chine is discussed briefly in my webpage under the heading Design/radius chine explained.
     

  15. edik
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    edik Junior Member

    Thank you so much for posting. I'm also very much impressed with designs of Dudley Dix. For my own taste though, I prefer the work of the Australian designer Graham Radford. I've always thought that anybody even with the basic skill can design a functioning sailboat. But it takes a talent to design a boat that is also pretty. I think Mr. Radford's boats are exceptionally beautiful.

    And since you have the experience, what, in your opinion, is the time saving in building, say, a 50 foot radius chine boat over round bilge boat? Of course, the question means the time necessary to complete all the welding since everything else would be the same.
     
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