What makes Gemini fast? Primarily, 4 features.
1. The top speed of a sailboat is limited by friction with the water, so designers try to minimise the wetted surface area of the hull. In modern boats, they do that by making the hull broad but shallow. With Gemini, the design is for a narrow but relatively deep hull.
2. The narrow hull means Gemini leans over rather easily, compared to the stiffer behaviour of modern broad-hulled boats. To counteract that effect, Gemini has a heavy keel – 5 ½ tonnes of lead! This means that although she starts to lean over rather easily, she rapidly resists leaning over too far. Ultimately, this means she can carry more sail in stronger winds without leaning over excessively. This makes her fast in heavy weather – she can keep pushing hard through a gale.
3. A very tall rig, which means she can carry large sails. Gemini’s mast is as tall as modern boats of the same size. Gemini still has her original wooden mast. Contrary to what one might assume, wooden masts are pretty much as strong as aluminium masts. But they are much heavier. That extra weight up high is undesirable, so wooden masts are actually hollow. The mast is built in sections. They take a log, cut it lengthways down the middle, reverse the two halves and glue them back together, back to back, after hollowing out the middle. This construction method means that if the original log had any tendency to warp as it dries out, it is now trying to warp in opposite directions at the same time. So the construction holds the mast straight. Clever guys these shipwrights!
4. Finally, Gemini has a very distinctive canoe-shaped stern. This feature gives the hull an exceptionally streamlined shape, and is easily worth ¼ of a knot or so – a big speed boost. It’s also very seaworthy – it gives a very strong hull construction, and it cuts through the waves when they come from behind. But it is a very uncompromising design choice. Essentially it means you lose a whole cabin from the layout below. Gemini is a 41 foot boat on deck, but down below, she has about the same space as a modern 32 foot boat.
Read on to find out how the design brief was fulfilled: