24 ft "picnic cruiser" designing

Discussion in 'Boat Design' started by hirvi49, Apr 26, 2015.

  1. hirvi49
    Joined: Apr 2015
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    hirvi49 Junior Member

    Hello! I'm new on this forum and I'd like to introduce my project. I'm designing a "picnic cruiser" for slow cruising with friends and family. Boat should have seats for 6, sleeping cabin for 2, small pentry and a toilet. Of course everything should be stuffed into a hull under 24 ft.

    Idea is to have displacement hull with electric motor. I've made some calculations that max speed would be ~7 knots and cruising ~5 knots with 4 kW Torqeedo electric outboard. Batteries would be ~15 kWh AGM-batteries and range about 25 miles.

    Boat would be made from glass fiber with epoxy resin and polystyrene core.

    Idea of the layout is to have two sofas for 3 people each. (steering point is not rendered yet). At rear there are two desks for cooker and sink. Bed and chemical toilet are under the front deck. Entry to cabin will be from port side. Boarding is easy from stern and bow. (In Finland we get on board mostly thru bow)

    About the design... I've two favorite designs now and I'd like to hear your opinions. Which is better, 6 or 5d? Any comments? Thank you!

    Attached Files:

  2. gonzo
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    gonzo Senior Member

    First thing, if you are going to spend the time and money on a new build, buy structural foam and not home insulation.
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Yes, that would be a crime, almost !
  4. JSL
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    JSL Senior Member

    You have done your 'concept', now take this to a knowledgeable designer/naval architect to do the design. Doing this, he will sort out some issues like no steering position, non structural foam (thanks Gonzo), power and propeller size, high topsides ('sail area'), etc.
  5. hirvi49
    Joined: Apr 2015
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    hirvi49 Junior Member

    Thank you for comments.

    Firstly... I'm not going to hire a naval architect. I could as well buy a stock boat. That is not the point. Point is to design and build this by my self and maybe learn something. I joined this site to get feedback and tips. I've boat designing book, several engineering software and I know how to use them.

    I'm a mechanical engineer and I'm going to do strength analysis for hull before building it. I think the strength won't be a problem. Glass fiber is strong and you just need to increase thickness to get more strength.

    There are many boats built with polystyrene core. It is easy to shape, light weight, it doesn't absorb water and it is cheap. It is not as strong as divinycell, but this is a slow cruiser, not an offshore racer.

    I don't want to build a mold, so I use polystyrene as a mold that just stays in. It also gives nice solid feeling to the structure.

    I've made stability and resistance calculations with DelftShip. Everything should be fine. I'm going to use Torqeedo outboard and there is only one propeller option I think. It is large diameter prop and designed to heavy and slow vessels like sailing boats.

    I'm going to use an electric outboard because I want to do sea trials with conventional 4-stroke engine, before I buy all expensive AGM-batteries and Torqeedo motor.

    There will be a steering position at the front end of starboard sofa. Design and ergonomics of steering position are still under construction.

    Ps. It is not a hobby, if it doesn't take all your money :)
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Welcome to the forum. You can do whatever you want with your boat but you must ensure that the premises from which you boot are true. For start somewhere, your claim :
    is totally incorrect. You may have serious problems if you only care about the thickness of the laminate.
    I wish you lots of luck, because you will need.
  7. hirvi49
    Joined: Apr 2015
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    hirvi49 Junior Member

    Tensile strength of glass fiber is high. Of course glass fiber laminate will buckles when compressed. That's why there must be shapes that stiffeners the laminate. There are lot of boats without any core, made only with glass fiber laminate. It is easy task to laminate stiffeners and bars to support the hull.

    I know that tensile strength and shear strength of polystyrene are low. I'll repeat, I'm not building an offshore racing boat. It is just a slow leisure vessel for a sunny day. Strength is not an issue. Believe me, I'm an engineer. :)

    But, I'm not an industrial designer and that is why I would like to have comments about looks of the boat and about the layout. Do you like it or not? Why? What is good and what could be better? Any other ideas for layout or design?

    This forum is for boat design, right?

    Ps. I hate comments like "Oh, you'r gona lose with that.". If you don't have any argument, your comment has zero value.
  8. Builderjeff
    Joined: Apr 2015
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    Builderjeff Junior Member

    It looks great, I like the futurist lines! I prefer 6.

    Jeff Warner,
    E-Boat Inc. boatbuildercentral.com
  9. TANSL
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    TANSL Senior Member

    hirvi49, you are right, this forum is, among other things, about designing boats. As you well know, the design of boats includes many different disciplines. Therefore, in addition to tell if your boat seems pretty or ugly, which is a subjective opinion and therefore of little value, one must know if that boat is able to sail well and meet certain requirements in terms for example, safety, maneuverability, etc. That's the most important and difficult to get, and you can not say anything about just looking at a picture.
    You are an engineer, as has you told us on several occasions and, therefore, I don't need to explain that such a heterogeneous material as plastic reinforced with fiber must be calculated following certain specific procedures. As you well know, a very large thickness does not necessarily have sufficient physical and mechanical properties to withstand the loads to which it is subject.
    I know I will not tell you anything you do not know but I thought prudent to remind them.
    P.S. I think my arguments are valuable and that's why I do them.
  10. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    The low triangle just looks very off and un-fitting.

    ps I am industrial designer (and from Finland).

    pps. if you have more info on other boats built using XPS / finnfoam please share. I have searched here and all I find is quite little.
    The other guys are right though in the sense that the cost of the core will not be a big factor when your boat is done. Trust us on that one.
  11. hirvi49
    Joined: Apr 2015
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    hirvi49 Junior Member

    Thank you for comments!

    Here is one example of boat built in Finland with XPS-core: http://shalom.ponkala.net/pages/fi/shalom-vene/kuvia/keskeneraeistae.php

    Boat is designed by naval architect. Length: 15 m, weight: 9000 kg and powered by 3x 2 kW electric outboard. And it works. I've seen it! Same man has also built a smaller boat (7,85 m) with XPS-core. Those boats has only one or two layers of glass fiber on both sides. So, "eat your shorts!" :)

    PVC-foam is also possible choice for core material. I've to compare the overall cost with different combinations. With PVC-foam I can use polyester-resin which is cheaper than epoxy resin.
  12. TANSL
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    TANSL Senior Member

    I think not possible but I can be wrong, of course.
  13. hirvi49
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    hirvi49 Junior Member

    Designing has many different disciplines, but I think that looks of boat is one of the most relevant things. Of course it must float, go forward and turn. But. If you think about car industry. There are cars that works, but why someone buy Audi instead of Skoda? Because Audi looks better. Car industry puts a lot of effort for designing their products to look great and there is a reason.

    When I'm buying a boat, a car or a phone, I definitely want it to look great. If I build something, I want it to look great. Boats are too often made only for purpose, without thinking about looks. Ergonomics has also high value.

    P.S. Arguments are always valuable, if there is an argument. "Because..."
  14. philSweet
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    philSweet Senior Member

    hirvi49, good luck with your project. But please take a look at at least one book on boat scantlings. Gerr's Boat Strength is an easy to digest (for engineers) intro to boat hulls. Designing core and laminate schedules take a bit of studying as well. The main issue for home builders tends to be durability vs initial costs. If you use a weak core, you need a lot of laminate thickness to protect the core from dings. And you need to protect both sides. With polystyrene at 24', you would need a greater total thickness inside and outside than if you just used a solid fiberglass build. So you want a more solid core. Plywood is a very good choice at 24'. It will hold fasteners well, and can handle the compression from the fixtures you will be bolting through it. A foam cored 24' will be quite fussy and time consuming to build. You will need to design a reinforcement for every fixture that gets attacked to the hull. If you want to use a PVC foam core, you need to look at the 220 and higher densities depending on how thin you want the skin to be. The low density stuff is just for protected stuff like furniture.

    Try designing a cored hull laminate with epoxy/gass/foam that will match the toughness of 1/2 inch marine ply with a 20 oz epoxy/glass skin on the outside and a 10 oz skin on the inside. Think ramming a test panel with a forklift truck.

  15. Rurudyne
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    Rurudyne Senior Member

    ^ this

    Gerr is a what I'm planning on using for scantlings.

    Also look up The Design Ratios, an essay by Eric Sponberg.

    As for the styling: let me give a thumbs up to the one that looks more like a raised deck cruiser. If you want those dark areas you may want to see what IR reflective treatments will work in a marine environment ... if you figure out which one does please post it. ;)
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