Revo Foil - Disrupting the Surfski World...
The prototype Revo Foil - based on an F-One SUP foil.
“Think outside the box?” laughs Revo Kayaks CEO Greg de Beyer… “What box? For us there is no box!”
The brief interview I’d read on surfskinews.com (not to mention the plethora of comments on Facebook, not all of them positive) left me with lots of questions…
Revo Foil - What is it?
The Revo Foil is a standard Revo R3 surfski equipped with a hydrofoil on a single mast attached to the boat by means of a Tuttle Box. (The Tuttle Box is essentially a reinforced slot inserted into the bottom of the hull.)
It's intended to be a wave-riding (i.e. a downwind) boat. It's not intended for flat-water paddling.
The Hydrofoil itself looks a little like an aircraft: a large foil in front and fuselage with a smaller stabiliser wing at the back.
In theory if you get the boat speed high enough, the foils lift the hull out of the water, radically reducing drag and increasing speed (and surprisingly to me at any rate, manoeuvrability). There’s no reason why one shouldn’t be able to turn and cut back as though you were on a surfboard, according to Greg.
Prototype: SUP foil
Revo is on prototype #6 – and up to now have been using an F-One SUP foil. But, says Greg, the SUP foil has the wrong dynamics and simply cannot work with a surfski. Part of the reason is that the technique of initiating “flight” on a SUP can’t be replicated on a surfski.
The F-One SUP foil is extremely difficult to use with a Surfski. Can't be done, said Greg
To fly a SUP, Greg says, you have to get the back of the board down to increase the angle of attack of the main foil; once the board is flying, you walk forward to get it back to neutral. But you can’t do the same thing on a surfski.
The angle of attack is critical, says Greg. Consider that a foil set at an angle that produces 100kg of lift at 11kph will generate 300-400kg when it gets to 20kph. If you can’t control it, you’ll go airborne! This effect can be seen in a video from 2004 by foilKayak who were experimenting with foils on a K1... Watch the "jumps" at about 1:16.
Achieving lift-off
A breakthrough has been to work out how to get the surfski out of the water… And the secret is in the initial angle of attack of the main foil and stabiliser.
And once in flight?
Getting the boat out of the water is one thing, but you then have to control the foil – and this is achieved by moving the centre of gravity over the mast.
Provisional Patent
And this is what Revo have taken a provisional patent on. Their solution is to create a movable seat so that the paddler can shift their weight forwards and backwards.
The design allows for two types of movement – static and dynamic. The static part is the initial positioning of the seat assembly, which works in a similar manner to conventional footplate positioning. So when you first get your Revo Foil, you’ll need to go through a once-off initial positioning of the seat. The dynamic part is that the seat can also be slid forwards and backwards so that you can adjust the centre of gravity as you’re flying… The movement is controlled by means of springs so that it’s self-centring, with the seat tending to move back to the centre/neutral position.
To control the height of the boat out of the water, you’ll shift your weight backwards to climb further out of the water, forwards to descend. Optimum “altitude” is about 400mm according to Greg.
“But what about paddling?” I cried… “Your paddle blades will be waving around above the water!”
Patiently, Greg explained that the whole point is that once you’re flying, you don’t need to paddle. If you’re good enough, you’ll take-off at the beginning of a downwind run and then ride the waves like a foiling SUP paddler until the finish…
Greg expects the boat to weigh in at about 17kg with the foil installed.
Who will be able to paddle this thing?
Greg says that anyone will be able to fly the boat. Once it’s foiling, the stability actually increases dramatically; instead of balancing a round hulled boat, you’re riding a wide wing.
When will it be in production?
“We’re almost there!” says Greg. The current prototype has “flown” but it’s too difficult for the average paddler to use.
A new foil design, optimised for surfski, was being carved out by a CNC machine as I was speaking to Greg, and he said that they hoped to try it in the next few.
The new Revo Foil, in the CNC machine...
And the new foil plug... getting closer
Greg says they considered keeping the project secret. “But rather put it out there and let people come along for the ride,” he says.
Given the interest on social media, there’s plenty of people who share the dream… Stay tuned...