I have visited the forum off and on but have never posted anything. . The work the members are doing is admirable and some of it is spectacular. I will describe a homely project that does not compare with some of the things I see here.
I am an old guy in the U.S. I have an improbable young friend in Lithuania. We met on another boat forum several years ago and we have become fast friends. He thinks of me as his mentor because we design boats together and I have been at it much longer and have some education in Hydrodynamics. Justinas is overtaking me rapidly in terms of technical application. His interest is sailing small dinghies....full sized ones in regattas.
Justinas is a bit impecunious and cannot afford an RS Aero or other factory made hot rod. The option is to build his own. But of what design ?.....do we copy the RS boat, the Melges 14 or whatever. No, lets design our own boat so that it will fit into a small budget and satisfy the parameters that we have laid out for it. Justinas is an IT whiz who does his design work with the Solidworks engineering program. I do my design work the ancient geezers way with a drawing board, splines, and duck weights.
His boat is to be 4 meters long, must weigh no more than 40 kilos. It must plane like a demon........or hopefully so. It is to be an open transom, self bailing dink with about nine to ten square meters of sail. The whole rig, skipper, and all, is to weigh no more than 138 KG. (304 pounds......or something like 22 stone ???? if you are a Brit)
Sorry about that wall of text for a lead in to the construction of the actual model. I have almost finished a quarter scale model of the boat I have labeled "wet Dream". At quarter scale it is one meter long. The scale weight must be no more than 5 pounds. Impossible because in a fit of enthusiasm I used 4mm Ocumee ply for the skin. Well there was the economy factor. I already had several sheets of that ply. It will work out to be about 5.8 pounds when finished with the electric motor and all the parts, batteries, ESC, and such, that go with the mechanical drive.
WHoaaa! I said it was to be a sailboat and now it is a motor boat. Well the sailing model would need a fin and bulb that would weigh in at about 1.5 pounds and then the overall weight (displacement would be in scale terms, more than 400 pounds ....181 kg.) No way it is going to plane under sail with that weight being dragged around. Very well we will have to use a motor of modest output to see if it can plane with modest power. Provisions with the model have been made to convert motor boat to sailboat with minor changes to the operating machinery. When converted to sail we will determine whether it can be competitive in lighter airs or at less than planing mode. What kind of wake will this thing make, what of the turbulent boundary layer, the Reynolds numbers, how will it behave when heeled, are the righting moments any where near those that were calculated in the design stage???????
In the real world, models can not furnish exact information that would apply reliably to a full sized boat. But the model can give us a general idea of the capability of the full sized one.
Here are parts of the project. I have been in no rush to complete the project because of the corona virus and the restrictions that it has caused. Sooner or later I will get the model in the water with both motor and sail propulsion tests.