Sailing in Maine

Sailing in Buzzrds Bay

Friday, October 10, 2008

Using Boat Design Software

As a first step in coming up with a design to meet the "design brief", I've taken a look at the hydrodynamic properties of some of the designs I previously mentioned, using Gregg Carlson's wonderful "Hulls" boat design software, which may be downloaded for free at http://www.carlsondesign.com/software/add-ons/shareware/hull-designer . I use Hulls as a first step in designing boats because it is easy to enter a few offset points , create a wireframe model and move the frames around until I get a rough model that meets the design goal and fits on standard sheets of plywood. Its also easy to take a look at waterline height, prismatic coefficient, hull speed, displacement, and more. Here is my model of the Selway-Fisher "50-50 canoe":









And here is Beth:











After I create the model, I look at the heeling resistance at 5, 10, and 15 degrees of heel, the prismatic coefficient (how fine-ended it is), and how many sheets of plywood it will take to lay out the parts. I then import the Hulls model into FreeShip, another boat design software package that has more sophisticated capabilities, and I look at wetted surface area, resistance curves at speed, the metacentric height (which relates to initial stability), the stability curve out to 180 degrees, and the curve of areas. Freeship is now DelftShip, which is available in free and pro versions at http://www.delftship.net/ . There is also a FreeShip group on Yahoo Groups that has information and tutorials that allow you to get up to speed faster. The original Freeship 2.6 that I used may still be downloaded at http://sourceforge.net/projects/freeship/files/

I'm ruling out square section designs because their flat panels are not as strong as more curved types, and they therefore need to be constructed with thicker materials. Weight is very much a factor in the design decision. The initial stability is greater with the square cross section than with the more rounded cross section, but this can be made up by making the rounded cross section design a little wider. A rounded cross section design will have 20% lower wetted surface than a square cross section, so it will move more easily under paddle and under light wind conditions when sailing. Aesthetically, it is more pleasing to the eye, as well. Another factor in the design decision is the time required, since it must be done in four months. This tilts the design toward using what I have done previously, a stitch and glue hull using 4 mm Okoume plywood and fiberglass cloth set in epoxy.

3 comments:


  1. Delftship
    is a simple but very powerful boat design software. Unfortunately it lacks of features that naval architects mostly need such as construction and mep

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  2. Design software can make boat construction easier since it gives an initial view of the actual boat. I'm a boat enthusiast and I recognize the benefit of having means to see the framework of a boat. I really like the sample that you provided above. I'd probably try the software when I make my next boat.

    Boat makers should also remember that aside from the design, the materials must have the ce mark logo to assure the boat's quality. Most import boats have such logo since it is considered as an international standard.

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  3. very happy to find someone doing the same procedure as i do.
    ...Making a wireframe with HULLS and trasfering it to FREE SHIP...
    ..although i had problems initially with the different orientation of the axes XYZ and trasforming the decimal inches (HULLS) to metric (FREE SHIP)....

    HAVE A NICE DAY....i'm swimming in Corfu actually...

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