Barge nose cap ideas please.

Discussion in 'Hydrodynamics and Aerodynamics' started by cmitchelld, Feb 9, 2017.

  1. cmitchelld
    Joined: Jun 2014
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    Location: porters lake nova scotia

    cmitchelld Junior Member

    Hello gentlemen.

    I have built myself a party barge, I had it out last summer and it was a blast.
    One issue was that it pushes too much water when the front of the barrels are in the water. So what I do is move most of the weight back untill the barrels are out of the water.
    I am looking to put a nose or bow on the front of the barrels to cut the waves.
    I'm going to try and post some pictures to get an idea of what I am up against.
     

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

    Moving weight isn't going to help much and moving enough weight, to left the bows clear will dramatically decrease the boat's stability and capacity. You're correct the pontoons need a nose fitted, but even then, it's possible the boat is just too heavy and draggy for its volume. When you launch the boat, where is the waterline in relation to the centerline of the barrels, with a full load of people, coolers of beer and equipment? I make this assumption based on a perceived scum line on the side of one of the barrels, which would be under a light load (no one aboard). It's nearly at the middle of the barrel, so with a full load, you're pressing these puppies further in than desirable. Couple this with a barndoor for a bow on each side, it's not a surprise it's plowing. I'd estimate the max desirable displacement at 1,300 - 1,400 pounds (591 - 636 kg), for this configuration and given hows it's built, you're likely all this, before folks and gear come aboard. Consider a third pontoon, down the centerline and of course, noses for the barrels.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    What is powering this splendid vessel ?
     
  4. cmitchelld
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    cmitchelld Junior Member

    thanks for the responses guys. i am running a 72 9,1/2 Hp evenrude.
    it is way under powered for that size rig,
    i had a 25 merc on the back of her but it was too heavey to take on and off after romps.
    its only on a 2x10 so im sure no one would have any qualms about tearing it off if i left the motor on.
    im looking for a good 15 or 20 hp to slap on the back.
     
  5. cmitchelld
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    cmitchelld Junior Member

    I appreciate the thought out response PAR.

    as for weight i have no idea what it weighs but i am able to lift one side of the barge by myself on dry-land. i was going to put the weight at about 900 Lbs, but you probably have a better eye for these kinds of things.
    yes the scum line is when it is sitting docked, when i have about 8 people on the barge the water line hits about the bottom of the outer platform,
    it is very stable, alot better then i thought it would be.
    if i had a 4 stroke motor it wouldn't be such an issue as i could just putt up the lake and party at the same time but my 2 stroke is so loud it kind of dampers the party.

    i have concidered a 3rd set of pontoons, i was thinking some a little smaller as to act as an over weight helper.

    my biggest issue here is i have no idea what to use for a bow or how to attache it. im not a big trial and error guy since it cost money to build this stuff just to have it fail.

    any thoughts will help significantly.

    thanks
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yeah, about what I figured (not my first rodeo), you're way overloaded. Ideally the 'toons should be about 1/2 submersed at full load. On most pontoon boats, you do want the aft potion of the 'toons to be slightly more immersed than the bow, but we're only talking about a degree or two of trim. Given the power you'd need to get anything more than displacement speeds (6 MPH on your boat) a 10 or 15 HP outboard is more than enough and it would be best if this was a "high thrust" version, not the standard gear version most sell. The high thrust small outboards are geared up better for pushing a heavy, slow craft.

    Even with shaped bows, you're not going to go any faster, you'll just plow along. Maybe with a 50 HP engine you can bust out, onto plane, but fuel economy will go right through the floor. A thrid set of 'toons will help immensely, offer reserve capacity and lifting the boat to a more desirable trim level.

    The nose piece can be done a few different ways, but attaching to roto molded barrels is always a tough thing, as nothing really sticks good to them, so you have to strap or fasten them somehow. I'd be inclined to use some sheet aluminum, bent around in a cone and angled up, so they can part the water flow. Alternatively you could use the jon boat approuch with a angled flat plate, that transitions to the barrel face, though this might be harder to do.

    [​IMG]

    This is the cone approuch. The top of the cone is level with the top of the barrels, so the bottom of the cone makes an reasonable upsweep.

    [​IMG]

    This is another way, where they just pinch the sheet metal along the leading edge. This might be a better way for your boat, as it'll slice wave better.

    [​IMG]

    This is the same thing, just a better view and proportionally longer.

    [​IMG]

    This is the jon boat approuch, even though they're square, you should get the idea, they just cut the bottom of the 'toon at an angle to help get the bow over the waves. The same can be down with a round 'toon, just slice it off and seal the end. It's not as good as a better shaped bow, but is pretty easy.
    [​IMG]

    This is how your boat should sit with a full load. The aft part of the barrels are emersed to about 50% of the diameter, while the front is slightly higher.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    It isn't going to be going fast with a portable outboard, build a small overhang on the front so you don't get splashed from water shooting up from the end of the drums.
     
  8. cmitchelld
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    cmitchelld Junior Member

    that's funny, i buddy of mine said we should strap a Seadoo drive to her.
    i know it won't be fast but i want to get it to the point where it will transport its self up the lake.
     
  9. PAR
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    PAR Yacht Designer/Builder

    A 10 HP outboard, preferably a high thrust will get you where you need to go, just don't expect more than 7 MPH. Strapping anything bigger will just burn lots of fuel, for a few more MPH of speed and ask the bigger engine to beat the water to a froth, until it dies. It's simple physics, in spite of what your buddy might suggest.
     
  10. cmitchelld
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    cmitchelld Junior Member


    hey PAR, thanks again for the great info,
    7 MPH isnt too bad, i would like to get 10MPH but it will get what i get,
    thanks again for the info up top that i never commented on, its been busy around here lol.
    there so much info in that last post, alot of eye openers for designs.
    i have seriously considered the 3rd set of barrels for a stability reason.
    im wondering if i would get any more speed out of it, yes there is less barrel in the water to push, but i have 50% more drag.

    i may have gotten a break on the barrel idea, though there is a guy down the road from me that has a pontoon barge like mine, but its just a platform and it's been sitting in his yard for years, the best part is that he has actual pontoons.
    so i am going to go talk to him this week and see if he will part with it for a reasonable price.

    thanks again PAR
     
  11. PAR
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    PAR Yacht Designer/Builder

    Speeds will likely remain the same, even with an extra center 'toon. New 'toons, preferably with clean sides and entry will help a little, but we're only talking about a 1/2 to a single MPH difference. You'd need a 50 HP outboard or bigger to really get the boat up and scooting along. This brings up other issues, such as sufficient enough 'toon attachments, strong enough engine mount, height off the water to prevent the inter 'toon structure from creating a crap load of drag, etc. The loading involved in an engine upgrade like this is, exponential in nature, not progressive or proportional.
     
  12. cmitchelld
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    cmitchelld Junior Member

    again, great info.
    i don't think i will be upgrading to 50HP, that's big $$$.
    but i think i am still going to put the extra toons under to give it a little more buoyancy.
    but if i get thoes aluminum toons from buddie, i wont need a 3rd will i?
    i will try and post some more picture of the barge maybe there is other pointers i can get.
     
  13. PAR
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    PAR Yacht Designer/Builder

    It depends on the length and diameter of the new 'toons, as to if you will need a third or not.
     
  14. cmitchelld
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    cmitchelld Junior Member

    if i do get the toons. i will get lots of pictures and measurements.
     

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

    Before buying the 'toons, measure them, so you can calculate how much they can hold up. Do this for just one 'toon, assuming they're the same length and diameter, as the result will be a twin 'toon setup maximum load (50% emersion).
     
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