Volga Hydrofoils Messageboard

I came across this Volga on eBay and entered a whole new world of discovery:

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 67139&rd=1

The Volga is intriguing because it is by all appearances a submerged hydrofoil that foils without computer assist. For instance, Harry Larson's Flying Bayliner floats on submerged hydrofoils, but requires autopilot to foil.

Here's hoping that one day, I'll be able to share photos of my own Volga 70.

Hi delquattro,

You wrote: "The Volga is intriguing because it is by all appearances a submerged hydrofoil that foils without computer assist".

Yes, that is an interesting observation. The Volga and many of the larger former soviet hydrofoil craft relied on achieving heave, pitch and roll stability by taking advantage of an immersion depth effect of hydrofoils running close below the water surface. Hydrofoils loose lift as they approach the surface of the water. This effect gradually starts at a submergence depth equal to about 1.5 chord lengths, and becomes progressively larger as submergence depth decreases further. When the foil is effectively at the surface, it only generates half the lift that it does when deeply submerged at the same speed. In calm water the craft therefore rides at an equilibrium condition where lift just balances weight. As this is not a strong stabilisation effect, such craft are only intended to be used in relatively sheltered conditions, or alternatively, as in the Volga, an additional foil is placed to remain above the waterline at the bow unless the craft encounters larger waves in which case it provides additional stabilisation effect. This is much the same as the approach adopted by the earliest "ladder foil" hydrofoils of Enrico Forlanini and Alexander Graham Bell. More information on the "immersion depth" form of stabilisation is provided in a short technical paper: "The Determination of the Stability of Vessels on Shallow-Submerged Foils" by B.A. Tsarev which appeared in Vol.4, No.1, October 1964 issue of "Hovering Craft and Hydrofoil" journal. That was a translation of an original Russian paper.