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Hydrofoils

time dedicated:100's of hours

location: Carbon Concepts and Home

year:2005 

On this page: Hydrofoil benefits; Initial Design:  Cad, Manufacturing and testing, testing results, Specifications; Current design: Cad; Possible Future Designs: cad; next design, To Do, other interested parties

What's the benefits of using a hydrofoil?

The idea of any hydrofoil is to take some of the load of the board and carry that load in a more efficient way.

This has several primary benefits: 

-lower drag (which can lead to earlier planing, using smaller sails or going faster)

-reduces the effect of chop (which makes sailing easier, more pleasant and faster)

-greater stability (this depends on good foil design and configuration)

secondary benefits:

-quieter

-it feels very different to conventional sailing

-it looks very different to conventional sailing

-higher jumps (you continue to receive lift even when the board is out the water, this depends on the design)

Initial Design - Cad

-mk2.1 canard, strapped to front of board (mk1 canard was built without cad and wasn't strong enough, mk2.0 canard had extra angled wings, see photos below)

mk1 rear T-foil

mk2 rear Y-foil

mk2 rear Y-foil fairing close-up. The fairing massively increases the strength of the joint and reduces drag at the same time. see this boat design forum post by Tom Speer. unfortunately it increases the manufacturing cost too. 

mk1 T-foil fitted without canard. will provide extra lift and so reduce drag, but won't allow full flying

mk1 T-foil fitted with canard. Canard follows water's surface, keeping the board at constant height. Rear foil carries majority of weight more efficiently than a planing board. 

mk2 Y-foil fitted with canard. same principle as mk1 but with longer angled foils. higher aspect ratio reduces drag. slightly higher area causes earlier takeoff. angled foils won't break the water's surface as easily as a t-foil. 

Initial Design - Manufacturing and testing

Testing Results

Board at rest:

The board is more stable than usual with the hydrofoils fitted and is less sensitive to waves, even when not moving. It is difficult to get in and out of the water due to the size of the foils though. (Not much different to dealing with formula fins though)

Getting under way:

The drag of the foils and board is much more than the board alone. this makes it difficult to get going initially. especially under sail.  Once nearly up to planing speed the canard lifts out the water quite easily. The mk2.0 canard made steering very difficult while in this mode (canard out, board still in water). mk2.1 canard steered ok in this mode. The board travels on quite well  in this mode. The length of the mk2 foil means that it damps any board roll, making it slightly difficult to steer. The mk1 foil doesn't suffer from this as it is shorter and has less a shorter span.

Getting faster:

As the board gets faster the back of the board starts to lift. This only happens if there is minimal pressure on the fin. any side load on the fin causes ventilation as soon as the board thinks about taking off. this causes the board to skid sideways, roll to leeward and slow down. if the board is rolled to windward to counteract this, the board grips and turns sharply, throwing the 'pilot' off. if this weird move is treated like a conventionally spin out, ie. bearing away, reducing fin pressure and tucking the tail underneath you, the fin will stop ventilating and you can carry on. 

If ventilation does not occur the board will accelerate quickly and continue to rise. At this point the ride gets much smoother and quieter. The damping effect of the long foil span still continues, as does the problem of ventilation. this makes it difficult to produce much power and steering is a bit of a problem. Because of these problems the board has never got going particularly quickly. 

 A fence has since been fitted to the Y-foil to try to reduce ventilation.

Sailing without the canard:

Just fitting the T foil has surprising results. At low speed there is little noticeable affect, but the board gets planing earlier. At higher speed the tail of the board hardly sticks into the water, making the nose of the board feel really low. when going over chop the back of the board bounces less than usual. There is a slightly greater risk of spin out, but this could just be my technique.  

Initial Design - Specifications

2.2m separation, with  3/4 of load carried on rear foil, fitted to a Bic Techno

approximate lift drag data on Tom Speers website

lift and drag analysis:, assuming 1000N total load

Note: drag doesn't include vertical fin component (I've assumed it's in the air!) drag will be much higher pre takeoff.

Current design - Cad

mk2.2 canard

mk2.2. only change is a fence 100mm above joint to reduce ventilation

Possible Future Designs - cad

Proposed next design:

mk1/3. the next proposed design is a combination of the mk1 and the mk3, intended to be used without a canard. The lifting surfaces will be the same as the mk2, put placed more horizontally and only be half the span.  The lifting surface is placed as far forward as possible to try to get it under the riders body. 

To Do

shorter span lift/drag

smaller canard lift/drag

lower AoA lift/drag

faired strut drag

calc strut Re

find planing surface lift/drag

re-calc canrad lift/drag

calc board lift/drag

calc foil roll torque

calc board roll torque

Other people interested in this project:

'Noa' - noamarkou@yahoo.com

boogie - Burkhard Vierth- info@c3.co.nz

'old salt' - dean at www.maroopark.com.au

Wolfgang Lessacher's wolfgang.lessacher@t-online.de

kevin ozee?

ahd

'select hydrofoils?'

gerard.delerm@free.fr - http://gerard.delerm.free.fr/clair/b_page2a.htm#table

rich miller

On this page: Hydrofoil benefits; Initial Design:  Cad, Manufacturing and testing,  testing results, Specifications; Current design: Cad; Possible Future Designs: cad; next design, To Do, other interested parties

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