Round chine vs. Hard chine... Basic differences?

Discussion in 'Boat Design' started by thill, Mar 4, 2014.

  1. tom28571
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    tom28571 Senior Member

    I don't see a normal round bottom here. There is a hard angle in the side/bottom joint that runs form the stem to the transom. It is in both the drawings and the transom view and very plain in the last photo. So it appears to be a modified round chine with a flat bottom aft and a small chine flat that serves to break the water flow at the chine. I've seen this on round chines that were after market modified to make the boat dryer and quicker to plane. When it works as you say, it seems the designers got it right.

    Hard chines are often the result of the least costly use of available building material that does not require expensive tooling. This does not make the round bottom/chine boat better than the hard chine ones. It is the result of compromise to deliver the desired goals and either may be better for some use than the other.

    Plenty of modern boats are not designed by knowledgeable people but those who only make them look like they think they want without much real boating knowledge. Boats that work well at low, median and high speed are fairly rare no matter what the basic hull design is. You apparently have one.
     
  2. thill
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    thill Junior Member

    Tom,
    Actually, there is NO hard corner at all in the bottom, neither is the side/bottom joint in the corner. The joint between the bottom and sides of the boat is under the bottom of the boat, and the rounded part is actually formed into the side panels. The spray rail is applied, and does NOT correspond with any of the joints in the skin.

    This picture of a Commodore, which is a slightly flatter, lighter-duty version of my Viking, gives a clearer view of things:

    [​IMG]

    In this picture, you get a clear view of the bottom contour:
    [​IMG]

    And in this picture, if you watch where the seam is, you will notice that it does not coincide with the spray rail, only intersects and crosses it up near the bow:

    [​IMG]


    I know this is a different boat than mine, but the basic assembly pattern is the same. The only real difference is that mine has more deadrise in the back, and a deeper hull and more V in the front. But the basic pattern is the same.

    -TH
     
  3. thill
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    thill Junior Member

    PAR,
    I'm leaning toward your second suggestion of a full width bench. So far, in moderate chop, I have not taken any water over the transom, but it's a matter of time, so I like the idea of a splash well, to keep my butt from getting wet!

    Another addition I'm considering is adding a small bimini top, sized to lay flat and out of the way when not in use.

    Here is a picture of the boat, fully loaded with extra batteries and so on, as I tested it last week. In this picture, the cell-phone "fisheye" lens distorts the length of the covered bow section, and makes the bow appear longer and racier than it does in real life. Makes the boat look mean, though!

    [​IMG]


    Here is a shot of the wake, with the boat doing about 25 MPH. This wake pattern is very different from my Grady. Interestingly, there is almost no wake height on the outside, with most of the actual wake falling very far back in the center. The Grady, for on the other hand, throws a sizeable wake on the outsides, and less in the middle. My older Renken runabout used to have both wakes almost even, if that makes any sense.

    [​IMG]


    I guess this wake is mostly generated by the motor, since the boat is so light, hence the center portion being the largest?

    -TH
     
  4. tom28571
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    tom28571 Senior Member

    I see,

    Sometimes a picture is not worth a thousand words.:D
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    The bottom is formed from one continous sheet by the looks of it. Would not stand up to hard use in steep chop, but the alloy must have been OK otherwise it would have gone to God long ago.
     
  6. PAR
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    PAR Yacht Designer/Builder

    The Commodore is a completely different hull shape (though related) than yours. What you have is an arch warped bottom or the modified Jersey Skiff, seen towards the end of the warped bottom days, while the Commodore is the traditional earlier Jersey Skiff form, with dead nuts (technical term) flat deadrise at the transom. It doesn't seem like much, but this and many other, some quite subtle differences, can make a world of difference in most regards.
     
  7. SamSam
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    SamSam Senior Member

    Maybe as a safety thing they allowed bigger motors on round chined boats because hard chined boats were much more susceptible to the outside chine catching and 'tripping' when in a turn, which tends to be kind of a violent movement, throwing people around or even out of the boat.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Tripping is much more common on warped bottoms, especially those with very modest or zero deadrise at the transom and particularly those hulls with negative flare in the aft sections, like that seen on barrel backs. Both round and hard chine boats can trip, but it certainly is much more common on hard chine. Tripping is more a function of skipper foolishness then anything else. If you crank over the helm at speed, the boat will warn you. If you elect to ignore the warnings, then a trip is probable. It's hard to blame the hull form for this. Strakes and round bilge boats don't allow bigger engines. This is simply a function of hull volume, regardless of shape and accessories (strakes, chine rails, etc.). I have a relatively narrow, negative aft flare design that can trip at the drop of a hat if pushed too hard. It's since been redesigned to have an anti trip chine and more deadrise aft. This things can be addressed, but you do have to have some experience (some learned the hard way, like my Drummer). I also have a inverted V design, patterned after the Hickman Sea Sled. After the prototype and some serious testing, I went the same route as Jackson and raised the sheer and installed an anti trip chine. The result is a very stable platform, without a trip tendency. Most designs are an evolutionary process.
     
  9. thill
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    thill Junior Member

    I've seen the commodore, and as you say, PAR, there are a number of subtle differences.

    I also saw one without the spray rail. It was... interesting, but not a boat I would want. It had the look of a very wet boat, although I have no way to know this for sure, besides knowing how important that rail is in deflecting spray in my boat.


    And you bring up something I find fascinating... It is amazing to me how combinations of very subtle, almost unnoticeable differences can have such an incredible difference in how a boat handles!

    Case and point, is a Parker 21SE and an Offshore 22. Side by side, they look very, very similar. Same deadrise at the transom, same Carolina flare, but the offshore has a different chine system and is 6" narrower and 6" longer.

    But on the water, the Parker will beat your fillings out, and the Offshore runs straight and flat and SOFT, and does the same speed with a 115 HP that the Parker does with a 150, getting much better fuel economy to boot. Why??? All due to those subtle differences? Yup. They matter that much.

    Anyway, I find marine architecture to be a deep, deep subject.

    -TH
     
  10. aaronhl
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    aaronhl Senior Member

    Can someone post a picture of a V hull with a hard chine but with a non-trip or beveled chine near the transom? And also explain how a small bevel should be designed to prevent tripping and other benefits?
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    aaronhl, "tripping" is only really an issue for planing hulls that turn "flat", that is they don't bank much when turning, which means vee-shape bottoms are pretty well exempt, as they bank to varying degrees, and the side of the boat on the outside of the turn is above water somewhat. A flat-bottomed hard chine boat will turn quite flat, and the hull sides could dig into the water, which will tend to tilt the boat, much like a car turning sharply and swaying to the outside of the turn. A bevel offers a surface that is less 'catchy'.
     
  12. PAR
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    PAR Yacht Designer/Builder

    V bottom boats can trip too, though are much less likely as deadrise goes up. The boats we've been discussing here are warped bottoms, of quite modest (if at all) deadrise at the transom. These boats are quite prone to tripping if hard chine.

    Explaining the design considerations about chines, regardless of their intended employment, can take a whole book of text and understanding.
     
  13. aaronhl
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    aaronhl Senior Member

    Gotcha that makes sense to me- I was reading in another one of my threads "dutchmen" is this something completely different? Pictures help
     
  14. PAR
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    PAR Yacht Designer/Builder

    Can you elaborate or what you're referring to? A "Dutchman" is typically a patch job, a crutch type of repair, a scabbed on type of thing, generally not looked on positively, though often they work nearly as well as a "proper" repair.
     

  15. aaronhl
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    aaronhl Senior Member

    This is what I'm referring to:

     
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