Twin Blade Ltd
Makers of the Manta Equation twin foil mono-hull sailboat

Sails like a keelboat with the convenience of a dinghy.


Photos of the Twin Blade Manta Equation development and some construction photos. All will fit into 800X600 and are around 40KB. Higher resolution copies are available, just ask. Click the image for a full size shot.

Return to the main gallery, a gallery of movie clips showing the boat in action has also been added.

Turn over tests of the Manta Equation. We pulled as hard as we could, and just got tired! At the equivalent of a force five blow with all sails up the boat heels up to 38°, this is outside any helmsman's comfort zone, but easing the main and dropping the gennaker puts things on a more even keel. You need to be a competent sailor to be out in winds of this strength. At force six the angle increases but the boat is still stable, though we would suggest that in a force six an experienced sailor should have the main should be reefed and the gennaker kept very firmly in the chute. The Manta equation stays positively stable to 89°.

This is 24°, and starting to get exciting. The boat will be taking in some water through the rudder control rod openings and waves would be breaking over the lee foil. This is about as far as you can get with all three sails up while reaching in a force four. Either bear away or stow the gennaker and ease the main and jib to come more upright. This will be faster as the sails will be powering forward rather than just producing heel.
Now we are at 31°, a full force four with three sails up, broad reach with the sails oversheeted. Sailing at this angle is uncomfortable, we know, we have tried it. Water enters through the rudder control rod openings and some splashing from the immersed foil. Drop the gennaker, and ease the main sail to bring the angle of heel down to something more controllable and gain more forward way. Reefing should be considered, especially for the less experienced sailor.
This is 38°, the calculated maximum possible with a force five blowing and maximum sideways resistance from all three sails. In practice the boat would not be sailed in this configuration. The main and jib would be powering forward offering less sideways force and the gennaker should not be flying. Reefing would be recommended, indeed essential for any inexperienced sailor.
42°, and you really do not want to be here. This was as far as we could pull the boat with the set-up available. All sails up, oversheeted on a broad reach and hit by a force six gust might do it. Drop the genny, round up and ease the main to regain your composure. Then reef up and head for the shore, time for a stiff drink!

Sequence showing the method of mounting the foils.

You can view this as an animated GIF (downloads in about 2mins at 56K) or as a stop-motion AVI (similar download time but more colours).

Stemhead fitting. This picks up a glassed in stainless steel bighead. Most fittings are similar, seat mountings, rudder pintle mounts, mast gate mounts, all of the rudder control system and front padeye. Other fittings that you may want to move or replace screw into embedded marine ply. This is the first hull fresh out of the new mould, quite an occasion. This view shows off the keelson. The boat carries 25kg of lead at the lowest point of this keel.