Cost of radius chine vs. round bilge hull.

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

  1. Wynand N
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    Wynand N Retired Steelboatbuilder

    OK, I will give you an estimated figures for the different disciplines building the hull;

    1. Lofting would take much longer than the loft of a radius chine by about 40 - 50%
    2. Transferring loft lines to building table to form the frames - takes same time as loft as opposed to the radius chines that just requires two flat sides & bottom with constant radius section and these can be taken and assembled on the loft floor directly and tack welded together.
    3. RB needs every frame to be made individually (loft frame as well on building table) and has different radii and curves to content with whereas the RC its just three pieces - side, constant radius and bottom to be jointed - easy to plot frame on building table. Double the building time for RB over RC frames.
    4. Setting up the frames would take about same time.
    5. Plating - with RC (when building upside down) you lay the bottom plates, transfer the lower tangent marks from frames to plates, connect marks/fair and cut. Then simply lay the radius chine sections over frames - mark tangent lines, fair and trim. Then just pop on side plates, mark upper tangent marks from frames and the sheer, trim off and you done.
    RB you cannot follow this procedure and has to start (in my case) from the keel stem plate and slowly plate away towards sheer and moving aft. Most plates will not fit by simply lying it and will need forming. Many tighter compound curves will call for smaller plates to be fitted and formed and all this takes up a lot of time to get right. Plating a RB compared to RC will take about 80 - 150% longer if you know what you are doing and of course hull shape
    6. Welding - more joints on RB than RC and I would guess 30% longer is a fair figure.

    I would say the average round bilge steel hull will take about 75 - 100% longer to build than a comparative radius chine sister hull. Perhaps even longer if you are not a highly skilled steel worker...

    BUT, with a radius chine hull you can have all the radius chine segments pre-rolled to required radius at a local steel fabricating shop and just needs trimming when installing. With basic tools and equipment you can get the hull up.
    Round bilge hull OTOH is a totally different animal and calls for a plate roller on site (read expensive item) as well as an English wheel to roll in cambers and compound curves. No curve is alike on these hulls and plates need to be roughly shapes, checked against the frame, adjusted, reformed etc etc until you have a perfect fit - also easy to scrap plates if you do not fathom how an English wheel works. Also, if you do not have the machinery on site, forget it - you can not run between the metal shop and boat every few minutes to get a plate to fit :rolleyes:

    Simply put, if I had the choice to choose which of the two methods I would build for myself, even though I am a qualified boilermaker with +35 years hands on experience, without giving it a thought, I will go for a radius chine for all the reasons mentioned.
    And it is a better looking boat to boot with much cleaner underwater profile and faster.

    My pleasure and broke one of my vows by doing so. ;)After my retirement from steel boatbuilding I made a statement that I will only create havoc on the open discussion forums and am done with metal boat threads, therefor my webpage to speak on my behalf....
    Must follow Brent Swain's example and step out of the limelight again :cool: Hope my two rare posts in this thread helped and I will leave it to the other members to deal with this discussion - they are more credible than me anyway;)
  2. nemier
    Joined: Jan 2004
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    nemier Junior Member

    You are far too humble. Thank you for the excellent response and I did indeed learn something, so you made my day - :)
    I think you nailed the OP's original question too. Btw, I have followed your website with interest for years. You have given much back to the industry. Cheers.
  3. Tanton
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    Tanton Senior Member

    You can follow the construction of L'Oceane 40, a radiused chine sailboat by clicking on Tanton at the Gallery. To see progress, you might have to go back several pages.
  4. edik
    Joined: Jul 2011
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    edik Junior Member

    And, again, thank you for posting. There was never a question in my mind that for a home builder radius chine is the preferred method over round bilge. I was curious though if ordering a boat to be built in radius chine method by a professional yard would bring any serious long term savings (including eventual resale value). It seems it will. I also realized that if I live long enough to build my own boat, or have it built professionally, I will order plans with CNC cutting files and limit the building efforts to assembling of pre-cut parts. This would be money well spent.
  5. DCockey
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    DCockey Senior Member

    In a round bilge hull are the chine plates composed of short, straight segments, each with single curvature, or are do the chine plates have double curvature?
  6. Ad Hoc
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    Ad Hoc Naval Architect

    It depends upon the type of hull shape really.

    Since you can have at one end of the spectrum...2 straight lines joining together and a constant radius to join them.
    A radius that joins the side and bottom but with varying side tumble-home and bottom dead-rise, this would then be a constantly changing bilge radius. This requires a real plater with skill to make.

    Each has their merits, for all sorts of reasons.
  7. DCockey
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    DCockey Senior Member

    I was thinking of the situation where the sides and/or bottoms are not flat planes, which is the case for boats other than some barges and similar. Then the "chines" (intersection of the sides and bottoms if extended) are curved, and joining the side and bottom with a radiused bilge results in double curvature. Either the bilge plates would need to have double curvature, or the double curvature is approximated by a series of short sections of single curvature bilge plates.
    Last edited: Mar 5, 2012
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Yup, that's how we do it. Below is an old grainy image of a round bilge with such a hull form. I have highlighted the shell plates in red.

    shell plate - RB.jpg

  9. oldsailor7
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    oldsailor7 Senior Member

    Lock Crowthers "Buccaneer" trimaran designs were called for in plywood using chined hulls below the waterline. The triple chines approximated the shape of round bottoms.
    We built two Buccaneer 28s, one for myself. We sailed and raced it successfully for a season and then converted it to round bilge by bonding on slabs of PVC foam, sanding them round and coating them in f/glass/epoxy, to get a smooth round bottom. We could never discern any difference in performance or load carrying and it only made the hull bottom more prone to damage.
    It was a complete waste of time and money and I wouldn't recommend it.
    In the light of this experience I am convinced that properly designed multiple chine bottoms are just as good in performance as smooth round bottoms---and a lot easier and cheaper, to build.
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