Skimming Wing Amas
Designed by: Mark S. Palmquist
Skimming wing amas are outriggers that utilize hydroplaning lift and low buoyancy rather than relying on buoyancy lift alone. I call them "skimmers"
The SW Amas can be attached to most small to medium monohulls and they are specifically designed to integrate directly to the Spark Sailing Canoe to turn it into a trimaran.
In low wind conditions the amas are above the water line not creating any drag but helping to steady the boat in rough waters or gusty conditions.
When your boat reaches about 5 knots, it will start to heel, and the outriggers start to generate hydroplaning lift that grows with the square of the boat speed. So, the lift will double every time the speed of your boat increases by 41%. For instance, at 6 knots, the skimmers generate about 43Kg of lift, however, at 9 knots, the skimmers generate 97 Kg of lift. The lift generated by the skimmers grows at the same rate as the heeling action of the sail, however, due to the high density of water compared to air, the skimmers generate more than enough lift to counter the sail's heeling. This allows a boat with skimmers to accelerate beyond the point where most boats would hit their hull speed limits and burry their leeward
floats.
Testing has confirmed that the top speed of a boat with skimmers can increase by as much as 20% above the same boat without skimmers and about 10% beyond a comparable boat with long and skinny outriggers.
Other advantages: the skimmers do not interfere with your paddles as they only require 1 crossbar, also, you can carry more sail area than a monohull. The lateral stability with the skimmers is similar to a 6’ wide hull, almost the same as a typical beach cat. So in theory, you could put a Hobie 14 sail rig, or similar, on a Spark sailing canoe with skimming wing amas.
Dimensions and Specs:
Each skimmer:
Width: 32-36" [81-91cm]
length: 30" [76 cm]
Height: 9-10" [23-25] cm
Cross bar length: 8'-12' [243-365cm] long
Total width from outside edge to outside edge is 11'-15'
Each skimmer and half cross bar weigh approximately 30-32 lb, so the total weight of 2 skimmers and 1 crossbar is 60-70lb [27-32Kg]
Note: at about 7 knots, the skimmer has equal lift to a 100% volume outrigger, at about 9 knots, the skimmer has about the same lift as a 200% volume outrigger. At about 13 knots the skimmer can support the entire weight of a 1 person boat. This causes the center hull to lift partially out of the water and therefore its resistance is lowered. When the skimmer is hydroplaning, its wetted area and drag is less than a long and skinny outrigger, therefore, the boat can continue to accelerate.
The skimming wing ama is similar to the skimming disc ama. Here are the differences: The skimming wing has slightly more surface area and more volume, but it has squared off edges and is slightly heavier than the skimming disc. Both can handle 2-3 foot waves but the skimming wing amas are better at climbing over the larger waves and when they go under water, they are slightly more hydrodynamically clean. So, they are recommended on larger boats that traverse bigger wave conditions.
Also, you many think that in big waves that the skimmers would slam into oncoming waves, but in reality, the front of your hull does most of the slamming and the impact on the skimmers is less severe because the skimmers are positioned behind your bow, not in line with your bow like a typical trimaran’s outrigger.
Also see the Skimming Disk Amas
Here is a comparason between Disk and Wing amas:
