Solarcat Design questions

[Georg]

Hello

I’m an amateur boatbuilder who does his first boat-design. My aim is to build a lightweight catamaran powered by solar energy (electric motor and Li-polymer batteries). As a first step I designed hulls with the free programm Michlet/Godzilla which produced optimize shapes at a given displacement and design speed. I used 4 meters as maximum LOA, because I want to be able to put the cat on a car roof. I then exported the hull to Freeship, also a free programm. Both tools are quite easy to use for amateurs. What a great thing to find such tools for non-commercial applications for free in the internet. Many thanks to Leo and Martijn for their great work.

I the enclosed files you can find the details to the status of my planning.

- solarcat7_linesplan - including the concept of the platform etc.
- solarcat7 design hydrostatics
- solarcat7 hydrostatics – for different displacements
- solarcat7 weight components


Before I progress with the planning I would like to put the following questions the forum members:

- What height of freeboard you would propose. In the proposed design it’s around 18 cm (see green area in the linesplan. As maximum displacement I defined 300 kg. I intend to ride the boat on medium-wave climate (lakes and near-shore marine).
- Could you give me any advice of the necessary physical parameters for the 2 connections of the two hulls (e.g. strength of aluminium pipes).
- Could you advice me on the best positioning of the platform in the longitudinal direction (including the load scenario mentioned in the linesplan). The length of the platform should be 2 meters.
- What is the most efficient method to build the hulls? KSS and Duflex seems to be the favourite ones? Does anyone have any experience with these methods for similar kind of hull shapes/dimension?

Thanks a lot for your help I advance. Regards. Georg

[Gilbert]

I am not sure I am going to answer your question about freeboard.
I wish to comment on the shape of the stern. Since this boat will be traveling at low speeds you have sellected an excellent immersed section for minimum wetted surface. I think, however, that you should not have the transom dragging in the water causing turbulence. I believe it should be out of the water when at rest and with you aboard. The transition would not have to be done over a very long distance to be satisfactory. It would move the center of gravity forward a bit.
I think I would add a few more inches of freeboard but I don't really know that it is necessary and I am not basing my opinion on anything scientific. If you are reluctant to add the extra weight this would require, you might consider putting some half cone shaped fairings on the first couple of feet in the bows to help water get off the deck quickly if the bows get waves coming over them. This last suggestion could be added after trials if it looked like a good idea.