Articles about Aerodynamics

Advances in sail aerodynamics
Sail aerodynamics - part two
Sail Dynamic Simulation
Streamlines & swirls
WindTunnel Movies
Sails shape & aerodynamics
The Quest for the Perfect Shape
Note on the effect of side bend
Anatomy of a Mini-Transat
Mini boat - Maxi challenge >
Mini boat - Maxi challenge
470 Aerodynamics
Lifting bows with foresails
Telling tales ...
The scientific Finn
Wind tunnel images

Mini boat - Maxi challange

Building progresses slowly but surely

The lack of a main sponsor (read money) has not speeded up the building, but also as it became obvious the boat would not sail this season, things have tended to calm down.

The deadline for the hull & rig is now set for the Helsinki boat show at the beginning of February, where the more or less finished boat will be displayed. These pictures were taken in mid-December.


The Styrofoam mold that we told about in part I of our story, was not a complete success. Both the hull and the deck sticked to the mold so intensely that the molds had to be destroyed to pull out the laminated boat. That much for the plan to use the molds for a second boat.

Regular (cheaper) polyester resin was used to build the hull and the deck of the boat. The styrene in polyester resin melts Styrofoam like a hot oven melts butter. The Styrofoam was therefore covered with a thin layer of epoxy prior to lamination. In some places, however, the layer of epoxy was not sufficient and the resin penetrated though. As a result, the hull would stick to the mold and the mold could only be removed in pieces.

This was not a failure of the building method per se, but rather a result of lack of experience - next time we will know better. In any case, Reiska, the most skilled sailmaker in Finland, is well on his way to become a cunning boat builder as well.

The sail plan of the Mini-Transat boat is huge. The total height from the bottom of the keel to the top of the mast is limited to 14 meters, the boom may not pass the stern and the bowsprit is nearly 2 meters long.

That leaves plenty of room for canvas, needed to make the best of the rare days of light air these boats meet on their Atlantic crossing. Upwind, the 30 sqm mainsail is most of the time reefed, and the 10 sqm fractional jib is used. It has a reef in it, too.

The bowsprit is hinged at the bow and bends back to the side of the boat when not in use. Downwind the 65 sqm masthead asymmetrical powers the boat easily over 20 knots.

The underwater appendages are no less unusual. A 250 kg bulb at the bottom of a very narrow stainless steel fin can be angled 35 degrees to the side, to increase stability - the boat carries no water ballast.

In front of the canting ballast keel, a dagger board is needed to add to the lateral plan. Wings fitted to the canting keel is being considered as an alternative to the dagger board.

An additional dagger board in front of the twin rudders is needed for directional stability, to relieve the autopilot's burden when running off the wind.

The deck plan gives an idea of the extreme proportions of this amazing little boat, nearly as wide as it is long.

The young designer, Karl-Johan Stråhlman can be reached at

Perfect fit - with the deck on, the boat starts to reveal its nature. A very comprehensive internal structure adds slightly to the weight but gives an extra boost of confidence to the builder/sailor - nothing more unpleaseant than finding your boat disintegrating in the middle of the ocean.

Not much of interiors or headroom to boast of for the skipper-builder Reima Alander.

A couple of millimeters recess was built into the mold, to allow lamination of the deck-hull joint from the outside as well as the inside. You can also distinguish the recess for the stem fitting.  


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