Michlet and model boats

[Tox]

Hi,

I am currently designing a small model sailing catamaran with a length of 0.5 m. Although I do not have a weight estimate yet, I am hoping to obtain a model mass of roughly 300 grams (displacement 300 milliliter). I created the hull form up to the deck (arriving at a model displacement of about 600 grams, i.e. 600 milliliter or 6e-4 m3) and now want to run Michlet. However, I get the message that the displacement is incorrect. When I scale my model by a factor of 2 (displacement 4.8 kg), then the program runs fine. Does anybody know about any restriction on the displacement in Michlet?

Thanks for the help,
Tox

[Leo Lazauskas]

Hi,

I am currently designing a small model sailing catamaran with a length of 0.5 m. Although I do not have a weight estimate yet, I am hoping to obtain a model mass of roughly 300 grams (displacement 300 milliliter). I created the hull form up to the deck (arriving at a model displacement of about 600 grams, i.e. 600 milliliter or 6e-4 m3) and now want to run Michlet. However, I get the message that the displacement is incorrect. When I scale my model by a factor of 2 (displacement 4.8 kg), then the program runs fine. Does anybody know about any restriction on the displacement in Michlet?

Thanks for the help,
Tox

Looking deep inside the source code I see...

#define MIN_DISPLACEMENT 0.001
#define MAX_DISPLACEMENT 999999.9

I wouldn't rely too much on any skin-friction predictions at very small scale. The flow is likely to be as much laminar as turbulent over the hull.

Good luck,
Leo.

[Tox]

Dear Leo,

Thanks for the clarification. I am aware that the resistance of my boat will be very much driven by viscous effects and that estimations of the friction will be very difficult. I am using circular cross-sections to have as little wetted surface as possible. I am trying to obtain an indication of the wave resistance and rough estimate of the friction resistance to see whether I should put some effort in optimising to reduce the wave drag. Hopefully, Michlet will help me here. Fortunately, the hull spacing will be large so interference drag should be negligible.

Thanks for your time, I will just run my calculations at scale 2:1 :)

Tox

[Leo Lazauskas]

Dear Leo,

Thanks for the clarification. I am aware that the resistance of my boat will be very much driven by viscous effects and that estimations of the friction will be very difficult. I am using circular cross-sections to have as little wetted surface as possible. I am trying to obtain an indication of the wave resistance and rough estimate of the friction resistance to see whether I should put some effort in optimising to reduce the wave drag. Hopefully, Michlet will help me here. Fortunately, the hull spacing will be large so interference drag should be negligible.

Thanks for your time, I will just run my calculations at scale 2:1 :)

Tox

No worries, Tox. I do have code that includes viscous effects on the wave resistance and I'm working on including surface tension and surface elasticity, but it is not quite ready for release yet (i.e. it only produces columns of numbers which is just not good enough for "hypermodern" naval architects :rolleyes: )

Leo.