Plumb now planning hull??

Discussion in 'Boat Design' started by daaavo, Sep 1, 2019.

  1. daaavo
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    daaavo New Member

    hi guys, long time member, first time poster! just wanting to run a concept idea past you.

    Im a boat builder by trade, mostly fibreglass planning hulls.

    I am currently dreaming up an attempt to design the perfect boat (for me).

    I am wondering if there is any reason why a planning hull shouldn’t have a plumb bow. I can’t think of a better way to achieve a smooth ride on a trailerable hull than to go with a plumb bow. I am no naval architect but relying on common sense, I dare say that a plumb bow is going to better slice through chop and small waves and hence keeping the hulls front from ‘ramping’ sharply upwards over chop in a superior manner to your average trailerable planning hull which has a bow sprit much further forwards in relation to the point at which the bow meets the keel.

    I look forwards to hearing your thoughts. Cheers
     
  2. gonzo
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    gonzo Senior Member

    They are usually wet which is uncomfortable. Another issue is broaching when surfing downwind. I suppose some hulls with pronounced rocker on the forefoot may prevent that.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    In reality, it isn't so much the bow area that does the "slicing" in the kind of water that leads to a jarring ride, it is the underbody further back, otherwise the deep-vee style hull would never have come into vogue.
     
  4. daaavo
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    daaavo New Member

    Interesting points raised, thanks for your input!
     
  5. DCockey
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    DCockey Senior Member

  6. Barry
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    Barry Senior Member

    Ranger tug produces a 29 that has a plumb bow that goes almost all the way to the keel. (unlike the Axopar above)
    After we got rid of our 49, we thought we would try a trailerable boat, all our other ocean boats to date were planing hulls with flared bows. The tug was the wetest ride that we have ever had. In a couple of feet of chop and a touch of wind, the windshield wipers were always on. While one would expect a tug to be a displacement hull, in fact the aft 1/2 - 2/3 is a pretty constant deadrise and is meant to be a planing hull. Runs nice at 14 - 16 knots. As Gonzo said, wet ride,
     
  7. KeithO
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    KeithO Senior Member



    Not the same class of vessel at all, but here you can see an ocean going work boat with a high speed hull and a specially designed vertical bow. Note the spray coming off the bow right as the clip starts at 1:50 and if you re-run the whole thing from the start you will see that there are what would be called "fences" (in aviation terms) on the bow to limit/block the vertical progression of the sheet of water that is clinging to the bow.

    Smaller planing boats are so light that they have hardly any draft, which is why a similar tactic would not be effective on a much smaller and lighter boat.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    That's owing to the stagnation point location created by the method of construction. They use a tube for the bow/stem.
    It is the same on all their vessels. If they create a hard sharp fine edge, like a knife, it removes this stagnation point and there is no sheet of water up the side of the hull.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    One suspects the plumb bow fashion is a way of getting boat length down to fit into a marina berth, in some cases, and still have much the same running characteristics.
     
  10. Barry
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    Barry Senior Member


    Bow comparisons

     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Rather different to planing craft, are the displacement plumb bows, at speed they don't come into play that much when up on plane.
     
  12. fredrosse
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    fredrosse USACE Steam

    Looking at several reviews of the Ranger29 tug, I see nothing but praise, praise, praise, and no mention of the wet ride. Which boat review venue gives both the positive and negative features of a boat?
     
  13. daaavo
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    daaavo New Member

    Thanks very much for sharing your thoughts guys, much appreciated. A special thanks to Gonzo for bringing up the issue of the vessel being more vulnerable to broaching when plummeting down a wave into the wave in front in following seas, especially with a smaller craft that will be less capable of straddling 2.5+ waves at the same time. Plenty of food for thought here
     
  14. DCockey
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    DCockey Senior Member

    My guess is the current fashion of plumb bows originated with racing sail boats where a plumb bow was used to maximize waterline while staying within an overall length constraint, or to maximize waterline length for a given rating. Then plumb bows became associated with "fast" sail boats so they were used on boats to make them look "fast".
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Not necessarily going to be broach-prone, the whole boat comes into play there, not just a stem profile, it is true to say, though, that you are not going to get much dynamic lift out of plumb topsides, so you are not getting much help there, but in the total calculation, need not be crucial. I think the wetness factor could be a deterrent though, and the aesthetics of it does not appeal to me, at all.
     
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