STEP TWO: DISPLACEMENT (1)
Once you have a hull that looks good and is not too long, we are going to do the first of some design steps.
The maximum design displacement (total weight) of our yacht is around 500 grams (although the hull will take twice this).
If you have (hopefully) lighter radio gear than the standard 200 odd grams, you may use either a lighter displacement or use a heavier fin bulb.
A lighter displacement may be more maneuverable and a faster accelerator, or more suited to lighter winds. A transference of the radio gear weight to the bulb gives a higher bulb to total weight ratio meaning a more stable hull or one that can take more sail area or higher winds, higher speeds and maintains speed better on changing tacks.
A heavier bulb can mean a shorter keel length giving less drag and pitching, but then we must retain keel area in relation to sail area and ours is already quite narrow.
This is where your design skills come into play. 
With this yacht you can change the keel and bulb weights and positions to try many combinations.
Because this yacht is so lightly constructed at less than 100 grams, with readily available, light weight and cheap radio gear of as little as 30 grams (5gm receiver, 5 gm rudder servo, 12 gm sail servo, 5gm LiPo battery, wiring etc) it is easily possible to make a stable yacht weighing less than 350gms with a 200gm bulb!
However with a less than optimal hull shape this is not a world beater!
COMPLETE HULL WEIGHT WITH HEAVY RUDDER AND NO FIN
Carefully mark a centre line all around the hull top and bottom with a spirit pen. This is very important for the accuracy of our build so do it using a flexible ruler and with reference to the symmetry of the hull (the top is curved differently from the bottom).
Now fill your bottle hull with the amount of water you choose for your displacement (1cc = 1 gm) and go float it (upright!) in the tub.
We want the hull slightly nose high at rest as the hull will drop forward at speed.
Because the bow is so bullet shaped it will go well downwind!
Mark the postion of the waterline all around the hull with your marker pen.
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