My powerboat plan

Discussion in 'Boat Design' started by adrocha, Oct 30, 2014.

  1. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    I´m new on this forum.
    For a long time I have been following some discutions on this forum. Now I want to share some of my ideas about my ideal cruising boat.

    I came up with the lines that I show in the images.

    Main dimentions:
    LOA: 12m
    LWL: 11m
    Beam: 4,1m
    Displacement: 15T.

    The idea is to have a cruising boat for 2. It will have a small engine (about 40cv).
    Main usage will be coastal cruiser.

    What do you think about this plan?

    A. Rocha
     

    Attached Files:

  2. gonzo
    Joined: Aug 2002
    Posts: 14,557
    Likes: 684, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    It looks more like a sailboat. The rocker is excessive for a powerboat. Is there a reason for the vertical sides? They will make it wet, water splashing over it. How did you come up with the lines? Have you calculated where the weights go, engine size, etc? All that is what will determine the final design.
     
  3. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    It's a beginning but does not appear to be based on much factual input. Just lines on paper at this stage. At displacement speed the rocker may be OK but it needs much more work before asking for comments.
     
  4. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    You are right Tom. This are just some lines not a plan. I will add some more pieces and hopefully (with your help) someday I might have a real plan.

    Gonzo is also right, this can be a sailboat. I can imagine it rigged as a motorsailer. I attach one picture of this vision.

    This boat is not supposed to plan. It is suppose to sail at displacement speed (I have time).

    I chose this V-bottom and almost vertical sides to maximize the interior space maintaining a low displacement. I believe that at displacement speed water splashing will not be a problem.

    I created this lines based on the assumption that this boat would be built with plywood/epoxy. The hull curve is very smooth and I suppose the plywood will blend without forcing.

    Usually I draw my models lofting on paper with some nails marking the main stations. If I can fit a balsa batten in all the nails without break it I think I will have no problem with the construction. At least this work for models. One day I will try on a small real boat.

    I followed this procedure to create this lines that I show here.

    Now I have more pieces for this "plan". Using simpson rule, I found a displacement of 7,7T (about 17,000 lbs) at the design draft of 0.56m.
    In one of the pictures that I send you can find the load distribution.

    Next I will calculate the power that I will need to move this boat.
     

    Attached Files:

  5. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    Using Gerr displacement speed formula, if my calculator is working as it should, I need about 20 HP to move this boat is 7 knots!!!!
     
  6. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    Correction:

    I just found I didn't calculate the displacement correctly. The correct displacement is about 34,000 lbs.

    With this new value for displacement the power needed to move this boat at 7 knots is 40 HP.
     
  7. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 300, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    With such a large sail area and a so flat bottom (no drift area), you're likely to need a large keel and perhaps some solid ballast. Would be nice if you calculate all this before you calculate the power of a ship whose displacement is still unknown.
     
  8. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    This is a power boat. I'm not sure if it will have a sail like that described. Another option is to have a small sail just for stability and emergency purposes.

    I prefer the second option. I will try not to have an external ballast but that´s something that will be defined as I find more information about the weight of the boat.
     
  9. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 300, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    The title of your thread is "my powerboat plan." In response to Gonzo you say "this can be a sailboat." Now you say it might be a "motor-sailor."
    Really, first things, the very first thing, you have to do is define the type of boat. It is completely stupid to talk about the shapes, weight, power, etc. etc. if you do not know what type of boat you are talking about.
    I would help but the definition of the type of boat, and SOR, only you can do.
    As tom28571 says," .. it needs much more work before asking for comments"
     
  10. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Adrocha, what most are trying to say is there's a reasonable way to approach the design process and this begins with the goals of the design. This includes all the things you'd like to see the boat do, fuel efficiency, target speeds, propulsion preferences, hull form preferences, accommodations, stores and tankage, etc. With the goals in mind, most of the design self develops, in an effort to address these goals. Without a spicific set of goals, set out in a SOR, you're just shooting in the dark and so many variables can come to play, that discussion is fruitless. For example, you're hull form is primitive and not well suited as a powerboat, nor a motorsailor and as a sailor, it's quite burdened as well. This is the result of the lack of definitions, which need to be established in the SOR, before you draw a single line. Lastly, you seem to be making assumptions about how to arrange plywood panels, to make the boat easy to plank, that aren't quantifiable. Simply put, you can create an easy to plank, developed set of shapes that will offer the ride, hull volume and underway characteristics you desire, without resorting to a slab sided, box like, nearly continuous deadrise structure, you've shown. This suggests a limited understanding of the practicalities of developed shapes and hull forms in general, not to mention the hydrodynamics and engineering involved. You'd be best advised to find a set of plans in the basic size range you want and make the appropriate styling changes to suit your needs, knowing the physics and engineering portions of the project have already been handled properly.
     
  11. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    Everything would be easy if I just look at my pocket and buy a boat that fits on my budget. But that's not what I am looking for.

    I could buy a complete plan and build it, but I want to start from the beginning.

    I am not a Naval Architect and I don´t pretend to be. I just want to design and eventually build a boat with my own ideas.

    I could attend a course on this field but I don´t have much time. If that's what I need maybe I will.

    I think we could have a good thread showing the process of design a boat.

    Are there any volunteers to help and guide me from the beginning?

    So let´s start from the beginning. The objectives:

    Boat type: Motor boat.
    Length: 12m.
    Max Beam: 4m.
    Type of hull: displacement.
    Cruising speed: 6/7 knots.
    Range: 1000 miles.
    Accommodations: permanent: 2, and 2 occasional guests.

    Next???
     
  12. TANSL
    Joined: Sep 2011
    Posts: 6,238
    Likes: 300, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    1000 miles at an average speed of 5 knots (you can not always go at maximum speed), involves about 200 hours of engine operation. How consumes a 40 HP motor (Giving your calculations as good, which seems unlikely) ?. About 4 liters / hour ?. That is, you need 800 liters of fuel. Does it seem right ?.
    You ar not a n.a. nor you want to learn many things (you want to design without learning) but you do should start thinking.
    This could be the first lesson : first think, then act.
     
  13. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Well, a step by step process, through the design stages, wouldn't be practical here, just way too much information and decision making, to make it a viable possibility. If you're not willing to learn the things you need to know, to self design, you will have to pay for it or consider a correspondence course, such as West Lawn. Both routes will cost about the same, yet one permits you to have plans in hand nearly immediately, while the other has you absorb months of study, before you can consider developing your plans.

    Personally, I don't think you realize the level of understanding you'll need to acquire, for any reasonable level of success to be expected. This isn't a personal dig at you, most folks don't realize what's required, but the various engineering disciplines involved can be daunting to most. Simply put, you could probably make a 15' skiff work fairly well, with some effort, but a 38' likely ocean capable yacht, well this is well outside rational. Again, no insult intended, but would you design a 10 story office building? How about a passenger airliner? You might be able to muster a storage shed, maybe an ultralight aircraft, but . . .

    You just don't (yet) have the understanding necessary. For example, your target speed is 6 - 7 knots, while a 35' LWL craft's displacement speed will in the 8 knots range, which simply means you're denying yourself a 15% speed improvement, for no good reason. Additionally, with some thought and a clever design, you could easily exceed 10 knots with reasonable economy, though some concessions in other areas will come due.

    What will be uniquely "yours" about this design, that isn't available on an established design? What part of the propulsion, hull form, accommodations, storage, etc. will require a full up, self designed 38' yacht, that can't be had in a stock design package, especially considering a stock design could be modified (maybe by you) to suit whatever style or needs you desire?
     
  14. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    Thanks PAR. I have to go for a course. I will. The question here is that I want to know how to design a boat. Just to know. I know the courses in West Lawn. That's the way to go.

    About you TANSL <removed>. This is the second time that you are trying to be offensive. <removed>
    You think a boat with 800L fuel is a strange thing! Have you ever seen a boat? There are bigger boats that those that you see on the beach.
     
    Last edited by a moderator: Oct 30, 2014

  15. adrocha
    Joined: Oct 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Lisbon

    adrocha Junior Member

    To the moderator:
    That member insulted me first. I skipped the first but I couldn't let the second pass. I was not to hard on him.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.