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Thread: Carlson Hull Designer import to Freeship

  1. #1
    Join Date
    Jan 2018
    Location
    Oakville, ON, Canada
    Posts
    3

    Default Carlson Hull Designer import to Freeship

    Hi All,

    I've been working on some small dinghy hulls (~12") and I've noticed that when I import a hull from Carlson's Chine Hull Designer into Freeship (or DELFTship), I seem to get some changes in the actual hull shape and dimensions. The resulting difference in where each program puts the DWL on the hull can be significant. Also, I find the .hul imported model often needs to be moved to the baseline in Freeship.

    In Carlson I'll have the DWL sitting at a particular chine, but in Freeship, at the same design draft, the chine will be a couple inches underwater. I'm using the same water density in both programs. I wonder if I'm doing something wrong.

    The discrepancy between the plotted DWL in each program seems to vary with the hull file. Some are very close and others are off by inches.

    Has anyone dealt with this behaviour?

    Any suggestions for properly setting up an imported Carlson .hul file in Freeship/DELFTship?

    Thanks in advance!

    Julian

  2. #2
    Join Date
    Jul 2015
    Location
    Frenchman's Cove, Newfoundland and Labrador, Canada
    Posts
    215

    Default Re: Carlson Hull Designer import to Freeship

    I have tried transferring a project from Hulls to Freeship once or twice when I started dabbling in boat designing, but I got frustrated by the limitations of Carson Hulls very quickly and went with Freeship Plus 3.4 pretty much 100%.

    I hadn't touched Hulls for probably 2 years, but to see what you are talking about I opened up a stock file that came with Hulls, an 18' whitehall type boat: 18white.hul. In Hulls I couldn't at first see a DWL (I didn't put one in) but when I opened it in Freeship it had one at 12", which is way too much for this type of boat. I changed it to 6", which is more appropriate, and also put one in at the same draft in Hulls. At this same draft the displacement was different in the two programs, so I believe you are right, that the models change by conversion from Hulls to Freeship. I have no idea if it is easily fixable.

    I don't really blame the creators of Freeship for not putting too much effort into developing a flawless translation from what is a pretty basic program.

    I once saw a buildblog about building a Gokstad faering where they had taken the panel developments from Hulls. It came out looking rather unfortunate and I completely blame the crude panel shape output by Hulls. I've now assembled two plywood boats from panels developed by Freeship, and many more in 1:10 scale paper model form, and I'm learning Freeship's quirks and how to deal with them.

    Do you have your dinghies only as Hulls files or do you have an image file of the linesplan? I found that if I want to create a model of another design the easiest way is to work from a .jpg file (even a pretty crude thumbnail will do but a proper study plan is nicer). I overlay it on a similar model I have already in Freeship, drag the control points till the strake/chine lines match up, and keep iterating between the three views until it is all faired out and the linesplan without the image in the back looks good. Might take me an hour for a boat with lots of strakes.

  3. #3
    Join Date
    Jan 2018
    Location
    Oakville, ON, Canada
    Posts
    3

    Default Re: Carlson Hull Designer import to Freeship

    I do have some reference drawings and some cad files that I'm modifying, and your suggestions make a lot of sense.

    Many thanks!

  4. #4
    Join Date
    Jul 2003
    Location
    South Bristol, Maine
    Posts
    209

    Default Re: Carlson Hull Designer import to Freeship

    I have used Hulls and Freeship for many years, and have found a few tricks in converting Hulls models over to F/S.

    First, be sure the bottom of the Hulls model is at 0. If your model draws 6" and the lowest point of the model is 3" above the baseline, Hulls will tell you the waterline height is 9", an obvious error. The easiest way to move the model down to the baseline, is to select Calculations - Pitch, and enter .01 for the value of pitch. This will move the model down. Repeat the Pitch command using 0 and your lowest point should be close to 0.

    Second, when F/S asks if you want to import the intermediate bulkheads, click "no". This will give you 3 control points along each chine instead of 12, much easier to manage.

    Third, F/S sets the waterline at 12" by default, so don't pay any attention to that. Any waterline you set in Hulls is not carried over. Remember that a ton in F/S is a nautical ton of 2240 lbs., not 2000.

    You should now get a close agreement between Hulls and Freeship.
    Or who shut up the sea with doors, when it brake forth, as if it had issued out of the womb?
    When I made the cloud the garment thereof, and thick darkness a swaddlingband for it,
    And brake up for it my decreed place, and set bars and doors,
    And said, Hitherto shalt thou come, but no further: and here shall thy proud waves be stayed?
    Job 38: 8-11

  5. #5
    Join Date
    Jan 2018
    Location
    Oakville, ON, Canada
    Posts
    3

    Default Re: Carlson Hull Designer import to Freeship

    Great advice - thanks Geoff!

    The tip on how to move the Hulls model down to base is gold.

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