Wave-peircing & Axe bows, how about Saw bows?

Discussion in 'Boat Design' started by Squidly-Diddly, Aug 30, 2020.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    20200830_154333[1].jpg Wave bow.jpg
    Inspired by this interesting Italian ship with a Wave Piercing bow TOPPED by conventional spray defecting and nose dive arresting bow.

    Saw Bow theory is you'd get most of the benefits of Wave Piercing, throughout the range of bow going into wave, but also most of the benefits of a final spray defecting upper bow. Theory is also that spray and bow wave generated by teeth would be proportional to the (not as big at conventional flared bow) tooth above ability to mitigate. In top flared bow example, could also reduce loading spikes a typical flared bow generates when hitting a wave, and reduce popping up and thus reduce porpoising.

    My crude drawing tries to show how the indents would recess into the hull. Figure they would be smoothed and hydro-streamlined there the light pencil lines on are the field of the hulls. Size of teeth, number of teeth, angles, etc are all just my first best guess. Figure things would need to be adjusted to finer entry from the drawing's red indicator lines.

    Would this work without creating prohibitive new drag? Would it work at all? Would it work but only create lots of drag in certain rough conditions where its working would be worth it?
    Could it become the latest craze in boat design, like putting a row of six big outboards on your status symbol powerboat? "Mr Customer, just like lumber mills don't use axes but instead use SAWS, this new bow SAWS the waves in more manageable smaller pieces".

    Which one of the 4 examples makes most and least sense?
     
    Last edited: Aug 30, 2020
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  2. Will Gilmore
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    Will Gilmore Senior Member

    What are the advantages over the bulb bow? There is no WL extending effect, but otherwise, looks very similar.
    [​IMG]

    -Will (Dragonfly)
     
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  3. bajansailor
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    bajansailor Marine Surveyor

  4. Squidly-Diddly
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    Squidly-Diddly Senior Member

    apples and oranges

    Bulb bow is to decrease drag by canceling bow wave with bulb wave when cruising on calm waters at specific speed. Doesn't function if ocean waves of any consequence or if ship's speed AND water line not within narrow limits.

    Saw bow is about finding happy-medium between spray defection and wave piercing across wide range of wave heights and boat speeds, rather than optimized for laboratory conditions for a large ship.

    Note the Italian warship in 2nd pic doesn't have a bulb but "wave piercing". My guess is because WP works in wide range of waves and speeds. Bulbs are good for tankers, cargo carriers, nuclear powered aircraft carriers and other ships big enough that 95% of time waves are small compared to bow size and ship travels at same speed 95% of time.
     
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  5. bhnautika
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    bhnautika Senior Member

  6. Will Gilmore
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    Will Gilmore Senior Member

    I like how they title the article, as if real swans have detachable heads.

    -Will (Dragonfly)
     
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  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    ay yai yai, it looks like it has a bow 'viewing porch' above the wave piercing bow.

    My Saw Bow concept is all about mitigating waves AND spray where it would be encountering max size waves on regular basis.
     
  8. cracked_ribs
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    cracked_ribs Senior Member

    That is a fantastic take on that article. Complete with detachable head, just like you'd expect on a real swan!

    I mean technically every head is sort of detachable, depending on your available tools and skillset, but...I still don't usually think of myself as having a detachable head, no matter how attractive Robespierre might have found my neck. Swans do have a very convenient arrangement for the guillotine, though.
     
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  9. Squidly-Diddly
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    Squidly-Diddly Senior Member

  10. John Rivers
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    John Rivers Junior Member

    I'm definitely thinking there is something to be researched with multi stepped saw bows. A more organic and logarithmic approach to the curves applied rather than a straight line saw I believe would be more ideal. Thinking multiple bifids being thinned out and stretched toward the transom. When adding more details it's easy to get cavitation effects or something I'm worried about with small craft is loud whistling from wind over complex edges. I'm know researching what types of geometries on surfaces make whistling noises.
     
  11. John Rivers
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    John Rivers Junior Member

    Played around with some saw bow amas last night. Thinking about where to put the saws relative to the waterline. Been adding a plane wing hump inspired by x bows to the top front of amas for a greenwater deterrent and to get a little bernouli principle lift out of it. They do it on the front of racing hydrofoiled stand up paddle boards.
     

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  12. John Rivers
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    John Rivers Junior Member

    It's not a serious sketch with lots of analysis, but I'm doing a sim of a couple bows soon and will throw a saw design in there amongst them just for explorational science purposes. It may be another much better saw design shows itself after we get data from a basic rough idea.

    The bifids in kayaks have shown to hit an effiency area at about 60% of top operational speed. A kayaker was actually able to break the coast to coast race record using a small bifid build on the bottom tip of an axe bow. The amount of anaerobic energy studied was more efficient in that optimal range, so they are made for long steady speed boating.

    I'm getting into holopunis and am wondering if a saw concept up the tall from point of the bow in large wave surf touring canoes like the Polynesian and Hawaiian bows use. Can you cut a wave with a pole type saw geometry to induce the swell of the wave to collapse ? The point of those Hawaiian bows is to cut in half a wave that is curling down on the front of the boat. Can a saw geometry redirect the wave curl to shoot down as well as to each side?
     
  13. John Rivers
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    John Rivers Junior Member

    Nigel Irens...
     

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  14. Squidly-Diddly
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    Squidly-Diddly Senior Member

    My pic shows mostly more or less straight saws mostly because it was a quick and dirty over-draw of someone else's drawing. My idea would be that bow wave and bow riding up on waves and bow ploughing under would always be buffered and mitigated. No big spray blast like conventional bow and no green water coming over the bow like reverse rake wave piercer.
    I'm wondering if a saw bow would generate a lot of extra drag, not just some minor drag of it 'sawing' up and down through waves but how that might create extra turbulence that would plague the smooth flow of water all down the rest of the hull. Then again it might help reduce friction if prevents different types of bow wave action over a wide range of wave heights and speeds.
    Related might be what a clinker built boat's bow does, and there should be some data on that.
    I thought some Eskimo kayak bows were some sort of Saw Bow but turns out only related to construction and getting a seal(pardon pun) on the skin.
    I'm conviced an eskimo style upswept split bow acts like a bulbous bow, but https://www.boatdesign.net/threads/im-conviced-an-eskimo-style-upswept-split-bow-acts-like-a-bulbous-bow-but.28898/
     
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