The last build - 24 foot mahogany runabout - design help

Discussion in 'Powerboats' started by sigurdni, Feb 23, 2013.

  1. sigurdni
    Joined: Dec 2010
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    sigurdni Junior Member

    Having built 4 boats from Outhreds designs during the last ten years, I have decided to complete one more boat in this life, except this one is a good step a way from what I've done so far. I have set myself a long term goal of completing a one-off Riva-inspired runabout, as good as I can get it. One last boat, no matter how long it takes. This post addresses design issues for the project, along with some more or less necessary elaborations.

    The goal of the project is to end up with a boat which is so aesthetically pleasing as possible within its genre, inspired from the mahogany boats of the sixties, but with adaptations to recent building methods and hull design. I believe the process of creating and living 'the idea of the perfect visual expression' is more important than my own actual use of the boat (but, yes, it will be put on the waters). I'm a keen sailer and believe you can in a matter of an hour or so figure out what a powerboat can do, while it takes a very long time to figure out a sailboats' behaviour in all sorts of conditions. Despite of this, the awe-inspiring feeling of seeing a beautifully crafted mahogany runabout has convinced me that this is something I would like to accomplish over the years to come. I know there are ready plans to be bought, the closest to match is the Tahoe 24' from Glen-L but I believe the boat could be designed much more elegantly, and so it seems, the perfect boat in my eyes isn't avaliable as a ready design.

    The preferences so far are quite close to this:
    This is sketched from a 33 feet boat. I vision a variation of this, scaled down to +/- 24 feet (which would come quite close to a Riva Ariston). Further, Im in favour of a stern drive and deep V-hull (possibly stepped), giving more room for a single cockpit interior with a "sofa" at the back and two seats before the windscreen. Handcrafted chrome motor vents, exhaust pipes, and windscreen frame (with laminated glass). The boat should exceed 40 knots driven by a single V6/V8 powerplant, as efficiently as possible. Performance rates and weight from Hydrolift S24 is favourable (, but is perhaps an issue of necessary compromise for this project where aesthetics go before speed. The boat should be stripped from extra gear and 'distractions', which hopefully can save some weight too. Planned as a one-off, I reckon cold moulding is the most natural way to go in terms of construction, much in the lines of Glen-L and Van Dam's boats. Finally coated with several layers of epoxy and poly-urethane. These images of a 26' Dolvik is also a good source of inspiration:

    I hope to be a part of the process of designing and making as much as possible, but as with any other working person, my time (and skills of course) is limited and will be in the forseeable future, so the project depends on buying a few services (how many we'll see). A goal is also to sketch up a realistic plan for progress accompanied by a realistic budget once the design is realised. And so I would like to hear your thoughts about how I plan to embark on what I see as the two most crucial steps for this project.

    Step 1 - finding the ideal shape of the boat above the water
    I figure I need to spend time learning Rhinoceros (or similar) 3D drawing programme, and play around until I'm satisfied with the looks of the boat from all possible angles. Alternatively I'd have to feed my own preferences to somebody who can do this for me until the favoure design is reached (A professional in technical/boat/car design offered to do this job for around 3.500 dollars which is way over my budget for this). For extra visual check I'd even like to build a scaled down 1:10 model of this, before going over to step 2. Why I think I can do this myself is because I don't consider my ideas to be that drastic so as to ruin the potential of a well performing hull under the water.

    Step 2 - combining beautiful lines with function and construction
    Here's where I sure I'll need to buy help or find a very friendly and clever naval architect student. The trick is to combine the ideal design from step 1 with a functional hull, calculating strength/weight ratios, hydro dynamics, positioning stern drive, etc. and, end up with enough details for me to basically build the boat on my own. I reckon a full scale drawing of frames and keel are the most crucial elements. Perhaps a file for 2D routing the frames could be a desireable time-saving component at this stage...

    Now, could'nt step 1 and 2 be done by the same naval architect?
    Yes of course, but the main reason I see this as 'step 1' and 2 is that I consider step 2 to be the definetively most cost - and expertice - demanding phase. Of course, drawing a head-turning design no one's ever dreamt of before should be a task more than a handfull for a professional, but given the fairly defined and limited space of creativity, I believe step 1 can be achieved with some trial and error. Or, maybe I'm wrong. What do you think? I should emphasize at this stage that the goal here is to create what I PERSONALLY BELIEVE, is the most beautiful craft ever made. And, despite my limited experience as a boat builder, I believe it is worth to follow the urge to create, and see, if that vision in your head, can be realised or not...

    Now, bear in mind there are no commercial interests here. What can or should step 1 or step 2 cost in terms of man hours or dollars? Would it be all better to find one person to do this job in one?

    Any thoughts and comments to help this project go forward are more than welcome. Im also interested in getting in touch with amateurs, students or professional visual/technical designers or naval architects who might have something to offer in these areas above.
    Last edited: Feb 23, 2013
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you want a beautiful boat, stay away from computer programs. They produce run of the mill, indifferent looking boats. Nothing beats a pencil, splines and a good eye for pleasing lines. To start with, what kind of target speed and passengers are you looking for?
  3. sigurdni
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    sigurdni Junior Member

    As it reads somewhere in all that text, it should exceed 40 knots and have seating for 5 people. But, this is just a approximation. The main reason for a certain level of speed is that if a boat have the looks to run 50 knots but runs at 30 creates a huge gap between form and function. Hydrodynamics being a pretty hard science if you are to optimize for maximum efficiency, and hence quite expensive i reckon, my desire is for a boat that performs well enough. It doesn't have to represent the pinnacle of hydrodynamics, but should do quite better than a bathtub with a sterndrive on it. As mentioned Im quite impressed with how Hydrolift's boats performs with moderate engines, but quite unsure how difficult - or even desireable - it is to reach that kind of level with two stepped hull technology in this project.
  4. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    Gonzo, that is absolute nonsense..

    It's all about the skill and talent of the designer. If you know what you are doing with CAD you can design and develop any surface and make it look as good as you are talented.

    It's all too easy to use flat developed surface or to restrain what you are doing and make something that just doesn't look very good, but as with pencil and paper, if you are talented and know what you are doing you can create anything you want.

    The beauty of a CAD design is that you can see it long before you try to build it, and what you build will look exactly like it is designed.

    Just because others aren't as good in designing in that medium, don't condem the process.
  5. sigurdni
    Joined: Dec 2010
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    sigurdni Junior Member

    Without practice from any design technique myself, I welcome every method that could push things forward. Given the preferences and references of styles that I'd like to maintain, there is really not that much creative space to operate within here, so I guess pencil or digital work will both work fine, depending on the craftsman behind it. That being said, over the years of studying runabout designs, I've just noticed how very small variations in lines, heights and angles, completely changes the look of a boat.
  6. adriano
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    adriano Junior Member

    Hi Sigurdni,
    Have you found meanwhile any suitable lines for yr next "Runabout"?
    It would be interesting to see prototypes? or drawings?
  7. sigurdni
    Joined: Dec 2010
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    sigurdni Junior Member

    Hi Adriano!

    Sorry for this extremely slow reply. I'm afraid the project haven't moved forward one bit since last time. I think need more input on how to go forward with the process. Meanwhile, my plan is as before:
    1. Find someone who can finalize the vision/hull above water in 2D or 3D drawing.
    2. Find the architect/engineer who can interpret the vision and do the maths/calculations (weight, power, speed, construction details etc) and provide a sound set of construction plans.
    3. Break down and plan the building process.

    I would hoped for more comments on this thread. Maybe the post is too wide in scope? Should I break it down to less ambitious posts?
  8. adriano
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    adriano Junior Member

    Hi Sigurdni,
    Never mind, it's never too late!
    My suggestion, if I was you, would be to find an existing runabout building plans, close to the size you've in mind. This could be your base design on which you may do eventually both esthetic and structural changes according to yr own taste.
    This could be the first step, once you've played around with it and have a clear visual idea of what you have in mind (at least this you need to have) you may ask an engineer/designer to help you to the next step.

  9. Eric Sponberg
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    Eric Sponberg Senior Member

    Hi Sigurdni,

    I'll be happy to give you (and other readers) some insight from the professional perspective.

    First, for a complete professionally created design by a naval architect, you can expect to pay about US$1,000 per foot of boat length for boats under 30'. Above 30' (9 meters) design prices go up at a higher rate. For that design fee, you will get the following:

    A design tailored to your stylistic eye--what looks good to you--and one that performs as it should and as you expect.

    The ability to ask questions and get feedback from the designer about why the design is done the way it is, why it is built the way it is, and why it should perform the way you expect.

    Approval authority over all the drawings as they are completed. If you don't like what is being drawn, you can change it. Hopefully, these instances are minimal because the naval architect should be tuned into what you want from the beginning so that changes are at a minimum.

    Full construction plans and full-size patterns, construction specifications, and hardware choices that are tailored to what you can buy within your budget.

    For good boat performance, bottom shape is everything. If you get the bottom shape wrong, a lot of bad things can happen: not enough speed, unstable straight running and turning, porpoising, etc. And for the size of boat and speed you are talking about, simplicity helps tremendously. Chine strakes are good, but you don't need steps (easy to get totally wrong) and you don't need intermediate lifting strakes. Weight and the location of the center of gravity also figure very importantly into the boat's safe and reliable performance. Weight and CG have to be under control from the beginning. An experienced naval architect knows how to do all these things.

    For quality construction, the construction plans will be well detailed with the assurance that the parts are spec'd to the correct materials, that they fit together well, and that they can be easily built. The structure will be sound and able to withstand the anticipated loads.

    A "clever naval architecture student" is not going to have the total understanding and experience of powerboat behavior and construction. He (or she) may be clever in one or two skills, but will not have the depth of knowledge for the total picture that the experienced naval architect will have. Most new designers have terrible drafting skills and do not know how to create a good readable plan. An experienced naval architect, however, knows how to make a plan readable, and knows all of the plans that have to be created to make the design buildable.

    If you think that you can build a boat on a budget, you should look really closely at your budget and see how much you can really afford. The Gougeon Brothers book on boat construction has very good guidelines for estimating the time and materials it will take to build a boat of any type and length. Factor in all the prices for all the equipment--the most expensive bits are going to be the wood, epoxy, the engine and drive train, not to mention all the tools and any custom fabricated hardware. But you are an experienced boat builder, so you should find this relatively easy to do, and some of those costs you have probably already paid, such as the tools and the space to build. Factor in the quality of construction and the price you think the boat will be worth when you are finished.

    Then compare those numbers with the price of the naval architect to create the design and the plans, and you should be able to make a judgement call on the value that the naval architect brings to the table.

    I do not mean to be critical of your effort, far from it. Having designed a few boats like this, I get asked these questions all the time. Most people--and I am writing this for the benefit of the other readers, really--have far greater expectations of their own skills, and serious underestimates for costs, which do not jive well with the level of their wallets. "I want to build a boat, but I don't have any money." is a constant refrain that I hear almost every week. What I am trying to say is, a good experienced naval architect will give you a lot of value in the boat, and it will make your job far easier in the build with the expectations that it will perform as intended.

    Toward that end, I encourage you to continue to find ways to achieve your dream, realistically, and try not to fall into the trap of short circuiting the design and engineering process. The design creates the plan, and you build to the plan. One should not build to the wish, and then hope for the best afterwards. That is the surest way to failure.

    I hope that helps. Good luck.

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