Bow Shape

Discussion in 'Sailboats' started by SuperPiper, Aug 23, 2013.

  1. tugboat

    tugboat Previous Member

    Mike you are quite correct- maybe I should have specified harbor tugs or ship assists...many of the offshore supply tugs and salvage tugs have raked stems... but I personally don't consider them classical tugs- they are butt ugly! had opportunities to work on them and refused...
     
  2. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member


    Most ship assist harbour tugs these days have a raked stem with flare up to a pronounced knuckle which provides the bow fender mount. It's clearer if you look at a profile drawing. This has some advantages.
     

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  3. tugboat

    tugboat Previous Member

    it does allow for more "set" into the push... as long as the fendering is adequate. some of the newer tugs even have almost a rounded bow, similar to the counterstern. If the tugs duties were largely ship assist- I would design in a plumb bow though- but that's me...and I personally like the plumb bow on a tug and the classic tug look.

    sigh...sadly most new tugs wont ever have those beautiful classic lines to them, such as the steam tugs did...my 30 ft'er's lines are much like a steam tugs not short and squat but lean and thin...( I broke my own rules too!)
    this is so beautiful...(see pic) they were and are still quite functional work boats ...but obsolete as a design...
     

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  4. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    I wonder if steel gives the designers more latitude in designing hulls vs wood.
    No doubt those oldies are beauties compared to some of the new tractors.
    Speaking of latitude, are you going to toughen the bow for limited ice service?
     
  5. tugboat

    tugboat Previous Member

    not sure if your question is directed at me, but for my tug yes, the extra material is going to be used at the bow. and keel area.

    Steel is much harder to work than wood- -with wood you can create beautiful round hulls using plank on frame carvel etc. not so in steel--used to be good designers and builders could build round bilge tugs in steel-as seen by the ARMY st tugs by John Alden.

    But today its all about how fast the vessel can be built -cost effectively and put into service. so usually the boat is limited to a hard chine developable type which is- arguably- not as efficient.

    im in love with that Wallace Foss...one of the top 5 most beautiful tugs ever built- period!
     
  6. Milehog
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    Milehog Clever Quip

  7. tugboat

    tugboat Previous Member

    does it still have the steam plant?? nice!


    what's interesting is I've worked on 90 ft tugs that were built around early 1900's and they are still working strong. Usually to do barge work. and the shape of some tugs up till around the 1960's or so haven't changed much - back in the late 80's early 90's tug hulls and configurations started to change due to modernized propulsions systems such as the voith -Schneider vane propulsions and the z-drives.
     
  8. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    No, the vessel now has a direct-reversing Washington Estep diesel engine.
    If you missed it click the Clickey in my previous post, or here.
    Click this Linkey as well. It gives a good account of the machinery, construction and history.
     
  9. tomas
    Joined: Nov 2012
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    tomas Senior Member

    What is the proper name and design intent of this bow shape please?
    Is it a "piercer" with added reserve buoyancy for when the waves become larger?

    According to the Flickr description, it is a Samoan fishing canoe.
    To my untrained eye it is hydrodynamically sophisticated and beautiful.

    from Francis Pimmel's Flickr

    [​IMG]
     
    Last edited: Sep 1, 2013
  10. MikeJohns
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    MikeJohns Senior Member

    It's practical to extend the forefoot as the one piece keel runs right under the stem and is sown to it, it needs a decent length of attachment to keep the stempiece well attached. And to keep the weight out of the stempiece it was shaped back as they realised that the lighter the canoe the faster is was to paddle. They were specifically a fast light weight craft for catching bonito and were paddled out to seabird feeding frenzy attacks on the driven up bait fish .

    It would have been a bit impractical for catching when sliding the canoe over obstructions and it has no great hydrodynamic advantage so close to the surface. But it's a nice carving and they were artistically minded and as influenced by style as most humans tend to be.
     
  11. schakel
    Joined: Jul 2008
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    schakel environmental project Msc

    Reversed bows,
    An akward shape that is intriguing, in catamarans it is applied to prevent them from diving.
    Certaintly looks artistic.
    Windea-La-Cour_8322df0607d33d159e98854ad5fe62f5.jpg Bravenes van Oord X bow.PNG Acta-Auriga-sea-trial_180314_162644_3580431e48aedf97dcedf972d1481942.jpg
    This is the wiki about it the with history and explanation.
    And even more boats like A yacht and Zumwalt.
    Creating a larger working deck is an engineering consideration in the boats above.
    Inverted bow - Wikipedia https://en.wikipedia.org/wiki/Inverted_bow
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    And how do you figure reverse bows prevent diving ? Certainly not on the same waterline, you would think.
     
  13. schakel
    Joined: Jul 2008
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    schakel environmental project Msc

    I said in catamarans, where diving is more an issue, by moving the planning surface as much to the front with the reverse bow the catamarans creates more lift in the front. F18:
    F18 catamaran.jpg
    F18International Formula 18 Class Association - Official website for the International Formula 18 Class Association. https://www.f18-international.org/
    With the working vessels above I believe creating big buoyancy in the bow is the main factor to have the bow reversed.

    From the wiki: Inverted bows maximize the length of waterline and hence the hull speed, and have often better hydrodynamic drag than ordinary bows. On the other hand, they have very little reserve buoyancy and tend to dive under waves instead of piercing or going over them.

    It's a paradox. That's why I find it intriguing.
     
  14. tlouth7
    Joined: Jun 2013
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    tlouth7 Senior Member

    I think the appeal of reverse bows on performance catamarans is that when they do nosedive slightly you do not get a sudden increase in drag. It is the sudden increase in drag low down on conventional flared hulls that causes cats to pitchpole.
     

  15. The Q
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    The Q Senior Member

    I went round and round the design loop when I made my little Keelboat. I would have loved to build a long ended traditional looking keel boat, but you can see why I didn't,

    The final decisions were...
    Plumb bow for, 4 reasons.. Mooring fees are on measured length of the Hull, Broads tax (based on length X Breadth block area), water line length = speed, and manouverability. Not the exact manouverability of the hull in open waters, but I sail in very limited overcrowded waters, long overhangs mean you have to tack earlier from the river bank and other boats, while worrying where a long stern might swing..

    The bow is flared sideways, to keep the spray off and reduce nose diving.
    I've also designed it with a retrousse stern, to reduce weight, especially of the junk I tend to accumulate and while heeling less chance of hitting something with the stern....

    Design I discovered, when you have limits, forces the design shape, even if you don't particularly wish to.. Something many on here have much more experience of than me..
     
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