Adventure 40 April Bulletin—The Design Spiral


I had always thought, like most sailors I suspect, that a naval architect sat down with his or her computer and over a number of weeks a fully formed design emerged. But, in fact, nothing could be further from the truth, as I’m learning watching Erik work on the design of the Adventure 40.

Boat design is an iterative process with many steps that are well explained in great detail in the Principles of Yacht Design. See the diagram above. A simplified explanation goes like this:

First iteration:

  • Specify the boat broadly to meet the usage envisioned (in our case offshore voyaging) by defining numbers like sail area, size (more a matter of weight than length), beam, load carrying capacity, various important numbers like sail area displacement ratio and prismatic coefficient, as well as that all important number, target price.
  • Draw a hull to meet those specifications.
  • Evaluate the hull against the specifications.
  • Repeat till satisfied.

Second iteration:

  • Draw a general arrangement that includes sail plan, deck layout, and interior layout.
  • Scratch head a lot and think about all the different things we would like to get into the boat. Select the ones that contribute the most to the goals of the boat. Discard those that will detract without adding anything really important. This is hard stuff to get right and requires lots of offshore experience as well as laser-like focus on what really matters. It is also the point in the process where it is easiest to go off the rails and design a bad boat.
  • Re-draw general arrangement.
  • Do a rough costing to check that the boat can still be built for the target price.
  • Repeat till satisfied.

Third and subsequent iterations:

  • Engineer the boat including scantlings.
  • Specify and design the mechanical equipment, deck gear and rig. The last two require figuring out the static stability.
  • Figure out what all this is going to weigh.
  • See if the hull designed in the first iteration will float on its marks at that weight. (It almost certainly won’t.)
  • Change hull shape so it displaces exactly the same weight of water as the boat will weigh dry (an iterative process in and of itself).
  • Check that everything specified in the second iteration still fits in the new hull.
  • If it doesn’t, change hull and/or stuff that goes into it.
  • Make sure the boat has the correct static and dynamic stability to be safe in heavy weather offshore.
  • Check that the boat can still be built at the target price. Take out stuff or make boat smaller (probably means lighter) if the target price has been exceeded.
  • Repeat until done.

Last iteration

  • Run hydrostatic and velocity prediction programs on the design to make sure that the boat will be the best possible for the usage defined in the first iteration.
  • Make small tweaks resulting from computer model runs.
  • Have the design reviewed by another naval architect to make sure nothing has been missed.
  • Go back to the third iteration if things change a lot.

As I write, Erik is just finishing the second iteration, with input from me and based on the original specification with its attached comments.

Before he goes on to the next steps, we are going to do something pretty unique: publish the initial design so that you, our readers, who have given so much to the project to date, can see where we are now and contribute suggestions while it’s still comparatively easy to make changes.

To that end, while Erik is away in the Arctic over the summer, we will be publishing three posts (hull, rig/deck, and interior). In these posts I will not only unveil the design, but also discuss the design decisions Erik and I made, including sharing many of the things that we considered and rejected.

And although Erik will be in the Arctic with limited internet, he will be part of the process and able to answer questions, since he and I will be in constant communication via satellite email.

One key thing I want to make clear is that this is a preliminary design and is subject to change. For example, right now we don’t know for sure how long the boat will be. You see, length is one of the parameters that can be most easily adjusted to accommodate changes required by discoveries in the third and subsequent iterations. And, in fact (and probably surprisingly to many), changing length, within reason, has little effect on price, as long as static stability remains the same.

Principles of Yacht Design 4th edn-2Thank you to Lars Larson, Rolf Eliasson and Michal Orych, authors of Principles of Yacht Design and their publishers A&C Black Publishers, an imprint of Bloomsbury Publishing Plc, for permission to use the design spiral diagram.


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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

21 comments… add one
  • dj Apr 21, 2014, 9:34 am

    awesome post! thanks!!

  • John Harries Apr 21, 2014, 9:40 am

    Thanks, dj, all encouragement gratefully received.

  • RDE (Richard Elder) Apr 21, 2014, 11:02 am

    Hi John,
    Best description I have ever read of the proper design process!

    • John Apr 21, 2014, 1:52 pm

      Hi Richard,

      Thanks very much for the kind words, all the more valued when I consider the source!

  • Hoftman Apr 21, 2014, 12:29 pm

    Are you guys filming a docu about the design process?

    • John Apr 21, 2014, 1:54 pm

      Hi Hoftman,

      No, while it’s an interesting idea, we don’t what to get sidetracked from the primary task: designing the very best ocean voyaging boat we can and there are three things one must do to make that happen: focus, focus, focus.

      Oops, sorry about the bad pun: filming…focus…ouch.

  • FAIVET Apr 21, 2014, 12:32 pm

    Remarquable analyse technique dont nombre de constructeurs ( comme Hanse ) devraient s inspirer ? ……

  • Eric Klem Apr 21, 2014, 1:33 pm

    Hi John,

    Very well said. One of the most important things to me is that Erik is being allowed to actually go through the design process. Many designers are not given the “Repeat until done” ability as there are monetary and scheduling pressures that prevent it. Often, these pressures means that an inferior product gets to market later than a superior one could have if the process had been followed. Obviously, a balance is best as some designers won’t ever stop tweaking if management doesn’t make a decision that the design needs to be released.

    I am looking forward to seeing the posts this summer.


    • John Apr 21, 2014, 1:59 pm

      Hi Eric,

      That’s a really good point. Because this process was, and still is, being driven by the drive to come up with a great boat, rather than make money (although that would be nice) we don’t have the pressure of business people trying to hurry the process along.

      Of course the down side is because neither Erik or I are getting paid we have to do work related to the A40 project only after we have done the work that puts bread on our respective tables.

  • richard e. stanard (s/v lakota) Apr 21, 2014, 9:52 pm

    unusually exciting stuff…shades of henry ford and thomas edison, but hopefully without all their dead ends…st lucia bound as of fri 🙂

    r e s (tampa bay)

  • Ed Finn Apr 21, 2014, 10:32 pm

    John Erik
    Keep at it…
    If designing a great boat for a reasonable price was easy….
    Then there would be lots of them around already, and no need to design another.. Obviously there are not many…
    “Nothing is impossible to diligence and skill”— Johnson
    Keep at it.

  • Gene Sofen Apr 22, 2014, 12:59 am

    If reinventing the wheel becomes too costly there are a few good designs from the 60’s thru the 80’s that may be taking a look at. Since you’re going to Europe later this year It might be worth the time to check in Tylers & Halmatic (spelling) They build alot of hulls from several designers as well as finishing some completed boats to sell. I doubt that either of these are still in business but it wouldn’t be too hard to locate someone who could put you in touch with the old owners, Also, Rival built some good offshore boats. These were all from the UK & I’ll bet some of the molds are still around. Someone earlier mentioned the Caliber 40 which also might be an interesting possibility. Just thought I’d mention these as it might be a quicker & far less expensive way to go if you could find the right design. Gene Sofen

    • John Apr 22, 2014, 7:20 am

      Hi Gene,

      While that may be a possibility, we don’t have any interest in using a warmed over old design, good though some of them maybe. Much of what will make the Adventure 40 great is using modern techniques, both construction and design wise. For example we can only hit the price and quality goals we have set by using computer aided design and manufacturing to reduce the labour hours to build the boat. I guess we could apply that to an existing design, but really I think it’s better to start fresh while keeping in mind what can be learnt from older designs.

  • Tristan Mortimer Apr 22, 2014, 6:31 pm

    I only recently joined up to AAC after having been a free tag along for a number of years and am familiarising myself with the adventure 40. Sadly I doubt I will be able to afford one any time soon, however I feel from what I read that the yacht, once she hits the water will carry many attributes that are difficult to find in both the price and size bracket of most of what’s available new today and she would be high on my list if I ever find myself in the position to replace me elderly Rival.

    I had the pleasure of being moored alongside Rolf Elliason and his wife’s yacht in the Canaries and spending a number of evenings with them numbing pre Atlantic departure nerves a little, I was just wondering if the authors of the Principles of Yacht Design are having any input beyond what is doubtless an excellent book.
    Thanks for a great site.

    • John Apr 23, 2014, 8:46 am

      Hi Tristan,

      No, Rolf is not involved in the project at this time, other than as the author of the book that is helping me understand what Erik, a professional Naval Architect is doing!

      However, Erik is insisting that another trained professional review his final design, as is always the case in the commercial world, and Rolf might be in the short list for that. Rest assured that whoever it is will be an A player at the top of his or her game.

  • RDE (Richard Elder) May 13, 2014, 10:47 am

    Here is a great shot of Hugo Boss on the dock at Newport today where she is having her mast rebuilt. This view of a state of the art Open 60 answers all the questions one might have about how to do a stern hung rudder on the A40 with no compromise in hydrodynamic performance, full kick up fail safe protection, , and rudder protection when docked with the rudder down.

    And also note that this monster is tiller steered!

    The other extreme is a simple vertical transom and rudder hung on a removable hollow SS shaft . —–along with a spare in the lazerette.

  • Gwenael May 16, 2014, 7:13 pm

    Hi, what do you think of these aluminum boats from the Netherlands yard K & M, they seem very well builded for high latitudes. Their pilot house of Bestevaer series seems very practical. The owner of Bestevaer 56 Tranquilo, seems has been blocked 10 months in Canadian ice before they get released. Cordially.

    • John May 18, 2014, 8:39 am

      Hi Gwenael,

      I have no first hand information on the K & M boats although after a quick look I like the look of the designs.

      By coincidence I was having lunch with two knowledgeable Dutch sailors two days ago and the subject of K&M boats came up. One of them pointed out that all the K&M boats have vertically lifting keels, rather than pivoting keels like many of the French boats like those from Boreal or Ovni. The advantage of the latter is that if you touch bottom the keel simply pivots up with no chance of damage, not so with a vertically lifting keel that must be built massively strong to withstand the impact of a grounding.

      • Erica Conway May 2, 2020, 6:34 pm

        I am searching for an offshore cruising boat and, of course, am getting so much out of all the articles and posts here. I don’t see much about the Bestevaers, mentioned above, in any of the articles. What is your opinion of them other than the keel?

        • John May 3, 2020, 8:16 am

          Hi Erica,

          I hear good things about Bestevaers and I have seen a few over the years that look interesting, but I have not put any time into researching the boats, so I don’t have an opinion other than that.

  • Gwenael May 18, 2014, 4:50 pm

    Hi john, yes, indeed , there is the option of the retractable keel in K & M , it may be a very effective system and the yard will say it is reliable and the technique is mastered . But I think it’s too complex for a boat that needs to go away and autonomous. Have a retractable keel is useful for search speed and performance , maybe because these boats are relatively heavy, I do not know.
    I think that in traveling and in exploring it is not useful to seek the ultimate speed or get the ultimate level of upwind performance. What you lose in performance are gaining peace of mind. I think Boréal sailboats with their tilt keel are quite effective, and that hold all the solutions that are known to work with the aim of simplifying and tranquility. Nevertheless, the Bestevaer are sexy, hull seems reinforced to shocks in the front part , but the bow seems a bit too upright to break a layer of ice , not much storage bunker, and they are …. very expensive too. Cheers

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