Easy to build

Discussion in 'Boat Design' started by tomac, Jul 22, 2012.

  1. tomac
    Joined: Jul 2009
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    tomac Junior Member

    Hi all experts out there.
    Is there any considerations for this design, must be easy to build and will be used for inshore waters. Hopefully able to do 9 kts.
     

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  2. messabout
    Joined: Jan 2006
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    messabout Senior Member

    You have drawn a boat on top of a boat. The long slender part has some theoretical advantages and it will provide some, probably not all, of the required displacement. Long skinny hulls like the lower part of this one, have the advantage of generating a smaller wave train than fat hulls do. So far so good.

    The whole deal is off because you have given the boat much more wetted surface than is necessary. You have also put about six hard corners in the underwater sections that will be eddy makers and cost some performance. The way it is drawn, it will be slow to turn.

    If you are hoping for nine knots then you are not smitten by the speed fever. You are operating in displacement range if your boat is really long and in the semi planing range if it is a small boat of 5 or 6 meters or so.

    You will do a lot better to build a simple design that is proven. There are loads of proven plans available at little cost. You will defineitely save time, money and disappointment if you will simply buy a set of proven plans.
     
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  3. noli
    Joined: Jul 2012
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    noli Junior Member

    .

    Hi messa

    Where can I get plans for :

    * 35 foot catamaran
    * displacement hull
    * can carry 3.5 tons
    * outboard power



    Thanks!
    .
     
  4. tomac
    Joined: Jul 2009
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    tomac Junior Member

    Ok Messa, I understand your point.
    My goal is a dispacement boat in 3mm steel, 10.4 x 2.2 meters. 9 kts. 2.7 T.
    It have to be very easy to build. I have to build it in 2 m pieces and weld it
    together on place. Any suggestions for a more proven easy desig?
     
  5. ASM
    Joined: Sep 2005
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    ASM Senior Member

    Hi Tomac
    I do like your design, it is what I have had in mind for years as well. No ultiple curves, just 1 dimensional curves and flat surfaces for inland water use only. What you have created is a power keel arrangement, so you can nicely have the weight very low for stability. I am not a naval architect so we have to go on people liek messabout, but I could manage with lesser speed, so 7 tops and make it in prefab sandwich or plain ply and make it more lighter.
     
  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    That is an odd interpretation of a box keel design, which can offer some advantages, but it has so many fundamental issues, that discussing them all would be nearly encyclopedic.

    I don't know the basic dimensions (LWL, centers locations and percentages, etc.), but you'll have a sorted bit of difficulties with her and good luck trying to maneuver in a tight anchorage, even with a bow thruster.

    Is there some reason behind these design decisions? What's the basic SOR, besides an easy build, of which this wouldn't especially be (instead of a single chine hull you've elected to make a triple). Have you any weights and propulsion figures? Which alloy?
     
  7. tomac
    Joined: Jul 2009
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    tomac Junior Member

    Hi ASM
    My reason for chosing 3 mm steel is that i have to build it in small sections, quit easy to transport and weld it together on place. The weight for the steel hull is aproximatly 1,3 T. I need to do all work outside, partly during winter time.
     
  8. tomac
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    tomac Junior Member

    Hi
    I first want to say that i am simple amateur i shipdesig. Here is my thougts:

    1. The lower hull is to be taken mosty of displacement, 2.2 -2.7 t. Dimension is 10.4 long, 0.8 width, and 0.4 deep. The slim hull is to reduce wavedrag.

    2. The upper hull dimension is 10.4 long, increasing width from bow to 2.2 m transom. The waterline is 0.4 m. The upp hull just dip 2-4 cm under waterline.
    Upperhull is thougt to create stability in this way.

    3. Hopefully the release of water from the upperhull is advantageous due to wery shallow hull deep and flat bottom (just my thoughts).

    4. The wide stern will maby reduce digging down when speed close to maximum bulding up the bow wave.
     

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  9. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    Take a look at the Atkin boats , that have a similar box keel, but use reverse deadrise to allow the boat to be faster with the same power,or use less power.

    Might be hard to use an outboard , most were inboard.

    ON your design the huge area aft might negate the advantage of having much of the displacement supported by the box keel.

    FF
     
  10. groper
    Joined: Jun 2011
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    groper Senior Member

    Im sorry, but i have some negative comments about your design - please dont take them personally.

    You have a wedge shape plan form with a very wide transom, which will create alot of wave drag.

    That bottom shape with keel also has a very high wetted area per displaced volume, which will create alot of viscous drag.

    So you have high drag in BOTH areas - it will never be an efficient design like it is... and certainly not optimized for 9 kts...
     
  11. tomac
    Joined: Jul 2009
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    tomac Junior Member

    Ok Thanks for all comments.

    Is there any alternative for 10.4 m long and 2.2 m wide, 9 kts, easy to build hull in steel, you can propose?

    Maby there is som nice Delftship files or similar here in Boatdesign.net.

    I had tryed the search option with no results.
     
  12. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    tomac,

    If the object is to keep costs down and be simple to build, you need to be able to specify the operating conditions. Weight and the nature of any cargo are the most important. That and your speed requirement goes a long way to establishing the length, wetted surface, beam, and stability needs of the vessel. Your best bet is to copy a design that is used locally for same purpose.

    Please give us a nice, wordy description of what you are trying to build, and a better handle on the build constraints you mentioned. You will probably end up with some boring looking craft looking like a sharpie or a panga, but they are quite efficient.

    nine knots is an awkward speed for a boat this size. Steel is also rather heavy for a boat this small. It comes into its own around 13m. The two together suggest you will need a schoolbus diesel to move her at 9 knots. Or a big outboard.
     
  13. tomac
    Joined: Jul 2009
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    tomac Junior Member

    This boat is for plesure only. The loads is aproximate at most 4 adult and 2 children (10-12 yers). Normally crusing 2 adult persons + 1 (12yers).

    I planned it wery simple inside. Inflated madrasses for beds, simple camping kitchen etc.

    Basic it is a emty hull with an engine to begin with. Only one compartment for the toilet. Freshwater 200 kg, fuel 150 kg, The size is 10.4 m, beam 2.2, draft 0.3-0.6 m. Preferebly up to 9 kts if it´s possible.
    I like steel as a material because it is easy for me to weld. Estimated maximum weight around 3 tons, not more than 40 hp engine.

    I have to make the hull outdor in smaller sections partly during coold winter in middle of Sweden, about 2 meters in length, 3mm steel.

    The hull shape and the principal i am looking for is kind of an old steem boat hull, crusing lakes in Sweden back in old days . Normally there are made of revited sheetmetal. Se posted picture. They are not so easy to find in the market. And sometimes when the do the are quit expensive.

    I hope this short brif will give a more clear picture.
     

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  14. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Let me show you something "easy to build", which I found somewhere on these forums, but, as a boat, is a disaster.
    A part of the joke, which I apologize if anyone is offended, Tomac, I think that your hull with so flat stern and bottom, sharp bilge, can experiece very strong shock waves, making her navigation very uncomfortable and inefficient. On the other hand, the flat bottom, attached to a relatively large beam, will arise in an initial transverse stability very large so that the movements of heeling will be very sudden, very annoying.
    You see in the picture the amount of foam (water displaced) that is capable of producing such a simple "boat": a sign of a hull completely ineffective
     

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  15. noli
    Joined: Jul 2012
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    noli Junior Member

    .

    I am learning soo much here. I've joined boatdesign only 5 days ago and am learning soo much!

    Please keep the pics coming as they def better explain the concepts.

    I'm sure no one will be upset...these are growing pains :)


    .
     
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