bow flare

Discussion in 'Boat Design' started by kapnD, Dec 24, 2011.

  1. kapnD
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    kapnD Senior Member

    I am a big fan of long/narrow powerboats, and have enjoyed all the discussion of same here on this forum, but am wondering why most of the designs of such have straight sides in the bow area.
    In my (ocean) experience, this causes lots of water to be thrown into the air, and then, of course, it pours back over the boat and its occupants.
    The famous photos of the Dashews effort show incredible amounts of water being slopped across the decks, and as a result, the waterproof window budget is astounding! Any activity underway outside the snug cabin will result in a soaking.
    Wouldn't some graceful bow flare as is used on the Carolina sportfishing boats as well as most of the far eastern fishing fleets be appropriate here? Even the infamously ugly "tongue depressor" bows of the west coast Radon and Davis boats are very effective at keeping the boat dry when under way.
    The increasing buoyancy of a flared bow as it is immersed is also a plus, and though it could be argued that it will increase pitching, I would personally prefer the boat to stay on top of the water rather than diving through every wave!
    Any thoughts appreciated, as I am currently penciling in bow flare on boats like Passagemaker Lite, and think it looks pretty darn good.
  2. gonzo
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    gonzo Senior Member

    Flare is more difficult to build, particularly for amateurs. Also, few designers are able to draw a hull with a lot of flare that looks good from all perspectives. Most look fine in profile or plan view and horrible from other angles.
  3. Tad
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    Tad Boat Designer

    If you are using sheet material it can only be twisted so much to form flair, and if you do twist it the stem becomes raked. A raked stem means shorter waterline for given overall length, or longer overall length for a given waterline. Overall length has become a big deal due to the cost of marina moorage.

    Two other reasons are styling and interior volume. Slab sides forward are modern and "edgy" because Wally (among others) used them and established a recognizable feature. Interior volume will sell the boat, popularly the master double is stuffed way forward into the bow, bulge the topsides out and make that bed huge.........

    Forward windows on any boat need to be waterproof, thickness is adjusted with pane size, height above waterline, distance from the stem, and forward speed.....

    You can see some flair in the forward sections of this strip-planked PL46+ under construction........any more than this distorts the sections close to the stem if the stem is vertical. You get a weird bulge down low, just above the spray shelf......And the spray shelf does work at moderate speed.....

  4. michael pierzga
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    michael pierzga Senior Member

    Your observation is correct. The modern, highly styled , plumb stem, slab sided yachts are wet.

    Attached Files:

  5. Boston

    Boston Previous Member

    nice looking work Tad
  6. FMS
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    FMS Senior Member

    I always prefer some flare at the bow.
    I like to keep my glasses dry at the helm over the "modern look".
    Some flare helps the lines, at least to my eye, too.

    Yes, very nice looking Tad.
  7. yipster
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    yipster designer

    Long narrow boats aim at a low pc / froudenr hence a long waterline with fwd stem
    by going polyhull instead of sheet material a concave even carolina style topside is possible on f.e. a straight up stem, will ride and look different tho
    want to share and upload what you pencilled KapnD?
  8. Easy Rider
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    Easy Rider Senior Member

    THe Dashew boats I suspect are intended to be a bit of a wave piercing hull as a boat that light would experience some terrible G forces if any amount of flare was employed. Plus the designer was a sail boat person and obviously had sail boat in his head when designed his passage makers as it's obviously a modified sail boat and I do'nt think getting wet was of any concern at all.

    Easy Rider
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  9. timothy22
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    timothy22 Junior Member

    Bob Perry is on record as saying that the slab sided bow is faster (more easily driven) because it takes less energy to slide through a wave than to lift over it. Also a noted sailboat designer. Like many other features of succesful race boats, the narrow slab sided bow has been adopted into cruising boats where a dry (er) bow may be preferred by a particular owner.
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  10. viking north
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    viking north VINLAND

    Why not make it an afterbuild add on. Experiment with a flared shaped a foam piece that attaches at and below the deck edge running from the bow back. Play with it until it blends in and looks pleasing to the overall hull lines. More or less a rubbing strake idea. It doesn't take much flared area to deflect large amounts of water. Once you have developed the shape simply glass it over and thru bolt it in place or develop a mold --semi mass produce and sell as an aftermarket item for that particular craft. Do the Harley Dance sell the entire bike as aftermarket add ons :p

    P.S. the photo below while not designed as a spray deflector will do so to a great extent. A similar set up but cross sectionally shaped properly, will go a long way in deflecting the heavy spray.(enlarge to better view)

    A yacht is not defined by the vessel but by the care and love of her owner--

    Attached Files:

    Last edited: Dec 28, 2011
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  11. michael pierzga
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    michael pierzga Senior Member

    The axe bow workboats use addition spray deflectors running parallel. to waterline

    Attached Files:

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  12. HJS
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    HJS Member

    It is NOT difficult to create a boat with flare and with developable surfaces.
    You just have to put the curvature in another direction than what may seem obvious.


    Attached Files:

  13. Perm Stress
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    Perm Stress Senior Member

    It is not allways so easy to make mathematically developable surface to develop in the real world :(.
  14. viking north
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    viking north VINLAND

    I seem to recall some of those old Popular Mechanics/Science plans did have flared bow sections. If designed and presented as a home build it would certainly be more difficult to build for the general building public. They would be more in line with factory production where the cut tolerances and hand skills were available. It's possibly a case where, if the designs are made available for home build the designers would have to put up with too many complaints of the underskilled and over a period of time thru word of mouth the design would be unfairley labeled as too difficult or a poor design. Damed if you do and damed if you don't situation.--

  15. DCockey
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    DCockey Senior Member

    Two questions which I know the answers to:
    - Do developable surfaces have straight frames?
    - Do straight frames always result in developable surfaces?
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