Pontoon - bow shapes

Discussion in 'Boat Design' started by ddrdan, Aug 21, 2011.

  1. ddrdan
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    ddrdan Junior Member

    Are there any innovative designs for the bow of a pontoon to combat the "dive" effect? Will raising the bow height and gunwale line with a long radius help?
     
  2. Submarine Tom

    Submarine Tom Previous Member

    What speed and dimensions are we talking about here?

    -Tom
     
  3. ddrdan
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    ddrdan Junior Member

    32' long - 28" deep - 24" wide, semi-displacement tri-pontoon house boat. Max speed around 10 knots. Using the Huck Finn pontoon profile (size modified).
     
  4. lewisboats
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    lewisboats Obsessed Member

    How about something like this (the bow shape) That could easily be created in foam and glassed.

    [​IMG]
     
  5. Village_Idiot
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    Village_Idiot Senior Member

  6. ddrdan
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    ddrdan Junior Member

    I like that profile! But as you said it looks more towards speed and performance where I'm just trying to prevent wave wash from diving the bow.
     
  7. ddrdan
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    ddrdan Junior Member

    I had to look real hard to see what direction that ship was going? :)

    Will a bull nose help a pontoon ride up a wave?

    Here was my idea. Any input is greatly appreciated.

    [​IMG]
     
  8. Stumble
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    Stumble Senior Member

    As i understand it the only advantage of the bulbous shape of the Open 6.5 had to do with beeting a rule, not because it is inherintly better.
     
  9. lewisboats
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    lewisboats Obsessed Member

    It won over a lot of others... There had to be some kind of merit there.
     
  10. Stumble
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    Stumble Senior Member

    Lewis,

    The merit is that they were able to 'fool' the water into thinking the boat was longer than it was by introducing the planing area sooner. I don't think it is really an advetagious design except for in this rule beater type of situation.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Stumble is correct. That bow permits the LWL to increase in length at lower speeds when heeled (like a scow). It's a rule beater and way too buoyant for average uses.

    I think a bow shape or additions such as strakes are unnecessary in this application, particularly a displacement speeds craft, being pushed to a S/L of 1.75 (assumed a 32' LWL). Those box pontoons aren't the greatest things in the world, but a lot better then cylindrical. There's very little flare in the forward sections of that design if memory serves me, so other then gluing on some foam and trying to add some volume up there, you have what you have.

    I'm assuming the boat is trimmed too bow heavy or in fact is just plain too heavy for her hull shapes. Where does the LWL hit on the sides of the pontoons? In other words, how deep is the bury at the bow and at the stern? This will approximate the displacement and tell me if you need to move things or add things.

    In short, assuming the bows need more volume may be an unreasonable conclusion. It may be as simple as moving some weights around or my estimate, that she's being driven well past a reasonable S/L ratio and driving her bows into chop, not to mention plowing up a huge bow wave at this speed.
     
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  12. ddrdan
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    ddrdan Junior Member

    I guess it's not worth changing.

    The pontoon I had the problem with is a 20'. It's draft of 12" stays mostly level at rest, less than 1 degree difference bow to stern. Under power, I trim it slightly bow high. It really doesn't help the bow rise much at 10 knots though. That design doesn't plane well anyway.

    My problem was more of an inconvenience, slowing in 2'+ chop puts a crimp in travel time.:) I should really go to a full hull but it's not a 'from scratch" build I want to take on. I found a 50' project boat I'd rather try to restore. Been trying to identify the hull manf.? Any ideas?
    [​IMG]

    The 20' was my guinea pig for the 32' build. I'm evaluating all the quirks of the first build. That was my #1 pet peeve.
     

  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You can't expect those hulls to plane at 10 knots and with that amount of bury, it's very unlikely you will, without huge amounts of power (hundreds of HP). The 20' hulls at 10 knots, are in a 2.2 S/L ratio and literally just plowing along (huge bow wave and a slight bow up trim). You'd have to have enough power to get her doing at least 12 knots to be in semi plane mode and you'd need enough power (yep, even more) to get to a solid 14 knots to be considered up on plane. Even with this, at 14 knots, unless you had a substantial reserve of available power (even more HP) you'd get slapped off plane in a chop. Frankly, I think you're hulls are loaded up enough to prevent planning. How much HP are you tossing at this boat?

    If your 32' hulls had more volume, you wouldn't have so much bury to the hulls and you might have the ability to plane. Just sizing up the hulls, (20' to 32') runs smack into the physical laws of mechanical similitude, which exponentially increase surface area, weight, drag etc., so a proportional up sizing wouldn't work very effectively.
     
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