Design challenge

Discussion in 'Boat Design' started by fpjeepy05, Jul 11, 2019.

  1. fpjeepy05
    Joined: Jan 2010
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    fpjeepy05 Senior Member

    I'm curious what you guys would design given the following prompt.

    Requirements
    • 16 knot cruise @ 35hp (70% of 50hp)
    • Shade
    • 270° enclosure
    • Bow to stern access with no steps
    • 2ft gunnel height with self-bailing sole
    • 80% max beam @ transom
    • Remote controls
    Maximizing
    1. Cost savings (for production model)
    2. Seakeeping ability (at 7 knots)
    3. Load carrying ability
    4. Style
     
  2. jehardiman
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    jehardiman Senior Member

  3. fpjeepy05
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    fpjeepy05 Senior Member

    Whalers have a huge following.
    In this instance, they don't have bow to stern access with no steps, 2ft gunnel height, or a self-bailing sole. Additionally, they are expensive, bad seakeeping, and bad load carrying ability.

    By contrast, a freighter canoe is inexpensive, better seakeeping and better load carrying.
    [​IMG]
     
  4. Doug Halsey
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    Doug Halsey Senior Member

    What's it like at 16 knots?
     
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  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Does this boat have a length and breadth specification ?
     
  6. fpjeepy05
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    fpjeepy05 Senior Member

    Ask these guys...
    [​IMG]
     
  7. HJS
    Joined: Nov 2008
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    HJS Member

    I'm curious what you guys would design given the following prompt.

    16 knots with 35 horsepower is a very interesting project.
    By utilizing the aftship interceptor technology, one can get very far.
    An initial calculation shows that the boat can be 7.8 x 1.7 meters in the waterline.
    In order for the above requirements to be completed, the boat must not weigh more than 2.1 tons including everything.

    http://sassdesign.net/An optimized motor boat 20121212.pdf

    JS

    8,4 x 2,2.jpg
     
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  8. fpjeepy05
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    fpjeepy05 Senior Member

    No, I was figuring maximizing length and minimizing breadth would be the best solution. I would say anything over 40ft would be impractical, since it wouldn't fit in a shipping container. And anything narrower than 42" might be too unstable, if you are forcing me to put limits on it.
     
  9. fpjeepy05
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    fpjeepy05 Senior Member

    2.1 tons in a little on the light side but doable. 7.8 x 1.7m seems like a reasonable size. I was originally thinking around 8 x 1.5m

    I question how much use the interceptor would be at these low volume Froude numbers... If I'm not mistaken interceptors begin beating out trim tabs at high planning speeds (6+ SLR) whereas this boat would be semi-displacement at 16 knots (2.3 SLR).

    I think a tough part of the design in having a walk through capabilities on a full enclosure at 1.5m beam.
     
  10. HJS
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    HJS Member

    The aftship placed interceptor is a prerequisite for this concept to work, 16 knots 2,1 ton, 35 hp. It contributes about 60% of the lifting force. The drag is reduced by about 40%.
    The aftship placed interceptor is not a substitute for trimtabs. It is a completely different technology.

    http://sassdesign.net/Interceptors in theory and practice.pdf

    JS
     
    Last edited: Jul 13, 2019
  11. fpjeepy05
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    fpjeepy05 Senior Member

    There are other designs that can do 16 knots at 2.1 tons and 35hp. The aftship placed interceptor is not a prerequisite.

    If your idea reduces drag by 40% why has no one in the industry used it?
     
  12. jehardiman
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    jehardiman Senior Member

    Actually the whaler is better on both counts than the canoe was well as having a self bailing capabilities due to the construction. <shrug> to each his own. Anyway, why ask for a brief if you have already decided what you like. FWIW, a garvey or sea sled could easily be built to meet all requirements far better that any canoe style hull
     
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  13. fpjeepy05
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    fpjeepy05 Senior Member

    You might want to do some more research. They are called “freight” canoes for a reason. Google “26 Nor-West Chisasibi”
    Also, self-bailing means that water that lands on the deck exits through a scupper by gravity alone. Whalers are unsinkable because of foam floatation; this is not the same thing. A swamped boat in a rough sea is not somewhere you want to be, even if the boat doesn’t sink.
    I didn’t decide what I like. This is boatdesign.net not boatbuyersguide.net. What I’m thinking of I don’t believe exists currently. Or I haven’t seen it. I thought freight canoes, pangas, Sesse canoes, or electric launch boats might work and I was looking for other ideas. Maybe a combination of these designs. A lot of canoes have too narrow of a stern to fish off of which is why I added that 80% requirement. Also the freighter canoes might be difficult in a following sea with the curved stems they have. Style wise I like Carolina boats, but they don’t work well with inexpensive builds.

    I apologize if I came off harsh I just was in disagreement that a 15x8ft low-gunnel, cathedral hull was a good solution. In America that’s a favorite boat, because it’s fast on calm water, it can fit four people and fits in a garage, or the slip fee is for a 15’ boat. Go on google earth and zoom in on the beaches of Central and South American. They all have long narrow canoes or pangas on them. Mostly because they are inexpensive to power and run.
     
  14. gonzo
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    gonzo Senior Member

    Whalers are both unsinkable and self-bailing. The freighter canoe you show is not self-bailing. I can't tell if it is unsinkable.
     

  15. philSweet
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    philSweet Senior Member

    It would help matters if you specified the type of use, amount of use, powerplant, prop arrangement, and sea conditions. We are talking about a smallish craft, and aero drag is going to play a big factor here. Also, self rescuing is not the same as self bailing is not the same as one that drain some splashes out and washdown water out. It sounds like you want self rescuing from a swamping. That is going to restrict the hull design and weight distribution quite a bit.

    And I am clueless how a 270 degree enclosure and bow-to-stern access go together.

    How much shade? shade creates a lot of drag in small boats, raises the cg appreciably, and interferes with self rescuing considerably. First idea is shade is removable by one person in 30 seconds and can be left to float free if swamped. Area and vertical clearance needs to be specified.

    Pangas are decent for what they are good at, but this isn't it.

    It sounds like there won't be more than about 10 propulsive hp available for hydro drag if the 35 is from an outboard. That can be improved upon by a small inboard diesel. But obviously much cheaper to just buy a bigger OB.

    I ran a Yamaha 25 powered recreational crabbing skiff in the Florida Keys. It did 16 knots with about a 600# cargo and crew load. It wasn't designed to do that job, but otherwise met, or could have met your requirements. For a versatile craft and not one that is just tweaked for one narrow operation range, I have the max weight all up at about 1.3 ton. I reckon from seat of the pants that that translates to about 950 pounds of hull to get one that self rescues it's cargo and an OB motor installation. That works out to something like 19' by 6'. Which isn't terribly different to HJS's if you were to blunt the bow and make it a garvey.


    I'm with jhardiman in thinking a garvey is a good point of departure here. Hull mostly built of okume plywood for the buoyancy benefits. Liner probably GRP. However, I'd round over the chines and gunnel in the forebody and arc the bow transom. Forward motor position as in HJS. Instead of interceptor, a slight step at the aft floatation boxes to accept generous floor drains. File bottom with very slight warp in aft 50% - probably 8 degrees at midbody and 7 at motor transom. Aft 18 inches of floor is cut away to form a sump and is covered by a grate. Sump drains aft under floatation boxes.

    Shade must be a rigid hardtop, canvas just has far too much drag. Mount to a conventional three hoop Bimini frame. Being able to pivot the hardtop is important. Mount the Bimini and straps to an aluminum rail at the sidedeck, and have that rail so that it can be removed by pulling one farmer pin.

    Your power/performance specs are actually quite similar to the what was the the heart of the recreational market back in the mid to late 50s. Only the self rescuing part is different. You could always pick up a '57 Dumphy Marauder and add some flotation and shade, and travel in style:)

    [​IMG]
     
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