triple t

triple t

John Casey tells us more about the Osprey foiling trimaran that we spotlighted on yesterday’s Front Page. Keep an eye on John’s site for the latest insider high performance multihull news.

The Osprey is a one-off foiling trimaran built by Falcon Marine for a customer that submitted the plans for construction. Sam Bradfield’s crew needed a test platform as part of the Harborwing project. Their original work was the Rave trifoiler. The production version of the Rave built by Windrider had some performance issues, because they ended up making it out of rotomolded plastic with metal foils, which made the Rave affordable but heavy. They made a large mainsail in the sailplan to compensate, but the platform ended up being off balance and, really, no fun in lighter wind. In an attempt to get better light wind performance, the designers went another direction.

They came to Falcon Marine with foil drawings and sketches and Falcon Marine went to work. They had a basic length and width and where they wanted the beams and gave profile drawings for the foils and Falcon Marine had them machined. The rest was working with the client’s liaison, Tom Hammond. Tom would describe what he was looking for and they got together to make it work.

What they ended up with is a 20′ wide x 18′ long trimaran with three ‘T’ foils, similar to a moth. The carbon foils on the fiberglass outer hulls, or amas, are controlled by what’s called a wand. Depending on the ride height, the wand controls the pitch of the trim tab on the back of the horizontal foil, which provides the amount of lift the foil creates. Falcon Marine built all of the wand gearing and linkage as well.

The T foil rudder is basically just for stabilization. The fiberglass rudder was the first foil built in the project. Since it’s all one piece (the horizontal foil isn’t glued on after the build) and Falcon Marine uses an infusion process, it was imperative to use fiberglass instead of carbon so the builder could see the infusion process taking place through the fiberglass matt. Before they dropped $1000.00 worth of carbon in the mold, they had to make sure the flow was right. Once they knew they had full infusion with resin, they then built the carbon foils with the same process, so both amas have carbon foils.

The Osprey is a sloop rig with a sprit for the jib and about 240 ft/sq of Randy Smyth-designed sail area. It weighs in at 475 lbs. The mast is one of the first carbon Marstrom-built Tornado catamaran masts from when they tested the carbon rig for the Olympics. The crossbeams are also carbon, so all of the high load structural parts are carbon, and the lower load areas are fiberglass. This keeps costs down while testing.

Looking at the video, the crew weight should be further forward once foiling to reduce overall drag. The incidence of the foil is too high with the crew weight back. That’s one thing they drilled into me when I sailed the Moth for the first and only time, “Get your weight forward!” They kept yelling at me. The hulls could probably lift quicker as well if the transoms are squared off to let the water release instead of sucking the transoms in like an old square rigger of the 1600s. It’s actually a simple, stable design in flat water. They can run the jib further in on the track and generally increase mainsheet tension as well. Yep, i’d have that thing boned in!
Here is a pic of it on the trailer:

I know, it looks like a mess, but it give you an idea of the profile view of the foils that are underwater in the video. On the left is the fiberglass rudder and on the right is a carbon foil. The hulls are on the right and on the left are the ‘D’ shaped crossbars.
– JC