I’m designing my own model sailing boat for an indoor competition in 3 months. This is for my study, but seeing my designing experience is only with full size ships I thought posting in this forum would be a good idea! The race is basically a time trial, very easy to sail. It consists of one part with downwind in a strait line, and one past downwind and a part upwind. I wonder what kind of hull is best to use as initial basis to start on. I was looking into the J-class, it being a boat thats designed for laminar flow sailing (no-planing) or maybe into a clipper kind of shape, all though i don’t know the consequences of scaling these boats down, apart from problems with hull stability of course.
The rules for the design are limited to:
height: max 1m, from water (box, rule. the boat must fit into a box of these dimentions, the mast and stays may swing out, a moving keel must remain within these constraints)
length: max 1m
width: max 30cm
Depth: max 60cm
Weight. 4.9 kg
materials for the hull are lazer-cut balsa and cast-iron for the keel.
there are 4 servo’s allowed
What wind speed are you expecting to sail in. This will make a big difference on whether you are looking for laminar flow.
How much downwind versus upwind is there? It is relatively easy to optimize a boat for upwind or downwind. Getting one to do both is challenging.
For example, if you are expecting a lot of wind and mostly downwind sailing, a wider, full aft section would be optimum. But that would not go upwind as well, and in light air it would have way too much surface drag. Your idea of a J-boat type hull would work in very light air, but the overhangs limit the waterline length and as you approach theoretical hull speed you will hit a very steep wave drag wall.
Also, look at US One Meter and Marblehead designs (not IOMs) to see where the most highly refined monohull designs (THAT FIT YOUR RULE) are.
But a catamaran is probably the fastest due to their superior stability to weight ratio, unless your 4.9 kg is a minimum as well as a maximum and you are sailing in lighter air.
Still thinking that a catamaran would be the way to go. You just can not beat it for stability to weight ration. When a cat heels, the center of buoyancy goes all the way out to almost the beam immediately. A monohull puts it at closer to half the beam.
If you are insistent on a monohull, I would look at scaling a marblehead design, such as the Gothic by Frank Russell. It is freely available (http://www.frankrusselldesign.com/Plans.htm). Pick the displacement that you want and then scale it one dimension at a time. For example, cutting the length from 50" to 39.5 would be 39.5"/50" * 4.5kg would bring your displacement down to 3.6kg. Then do the same to the width and the depth. The scaling for the width and depth do not need to be the same 39.5/50, they can be anything that you want. You could keep them at 1 if you want a displacement of 3.6 kg.
With a 12 inch beam catamaran in 8 knots, I would think that you would still need some ballast on the keel. Unless your upwind is a single tack, then as Mij suggests, all your weight in the windward hull. But that also opens the door on all of the asymmetry possibilities.
3 months left is not much for building and a first practice.
I would try a streched RG65, perhaps with 2 swing-rigs, displacement about 2kg.
More acceleration near the windmachines and less drag in the lowwind-zone with a RG65 than with an IOM with a short rig.
Why not a multihull?
0.3m beam is not much. On the running a rc-multihull is not so much faster than a mono. At the beating every tack has to be succesfull. At an indoor event you don’t have stable windconditions and not so much space to play out the multihull advantages (if there are some with a 30 cm beam-multi).
Sorry, not that much tec-revolution, if you want to be the fastest at this event.
Have you ever think of a boat that in the transom will have the shape of W?
I would also add a keel like this…
This way you will have the upwind you would like since there is going to be a narrow waterline and low wetted area of a catamaran with the benefit of the stability of a monohull.
All the categories of rc sailing and 1/1 sailing do not allow that because I think they know that it will rip them apart…