DIY Foilboards

Surf Foilboard

Reference , Trimming , Shimming & Foil Position

References:

When you are riding your foil board on the water - the board is in charge. Mounting the foil at the correct angle and place will allow the board to behave efficiently when its on the water surface.

As a reference datum, parallel a line off the back of the surfboard deck. (flat area where your back foot places towards your front foot) This will ensure a neutral ride angle.

When foiling - the foil is in charge. The foil always tries to fly level beneath the water. The designer of the foil will ensure that it is balanced and flies correctly according to his particular design criteria.

Trimming:

There may be a way to change the trim angle of your stabilizer in relation to the main wing. This is sometimes done by adding or removing spacers. What this does is trim your particular foil for the speeds you would prefer to ride at your particular weight. This can be related to trimming a model aircraft to maintain level flight.

Shimming:

If you are finding it more difficult to paddle your board (you feel as if the board is towing weeds), or the board feels stuck to the water, (needs a good kick with the rear foot to start foiling), then check the pedestal shim angle that will cancel the boards tail rocker that may be present.

The foil should be placed at the same angle as that with which your board will move over the surface of the water when you are riding (kite) or paddling (surfing) on it normally.

A quick method of shimming is to use washers in between the pedestal and mounting plate at the rear bolt attachments. Shim to your ride preference. As many as 4 or more washers may be required.

Once your favourite shim angle has been determined, a simple angled coupling block can be made and attached between the board and the pedestal.

It must be emphasized that a single degree change can make a very big difference in your board's efficiency.

Foil Position:

Moving the foil rearwards will increase stability. This is particularly useful when surfing, and helps with the pop when attempting steeper waves. However it will also increase back foot pressure to maintain "on foil". This is most noticeable if you are kiting using the same mast position, and find your rear leg getting tired when riding toe side.

Placing the foil too far forwards will decrease stability and the foil may become "skittish". You may also find the foil is uncontrollable and tries to fly out the water at every pop attempt when surfing.

It is important to ride (kite) or surf the board first. Check where your front foot is positioned when you kite, or where your front foot is positioned when you pop (surf), and then work backwards to mount your foil.

You might find that for one particular board you have two optimum foil positions. One that works efficiently when kiting (equal leg pressures on heel and toe side), and one that allows your front foot to be placed at your particular popping position when you paddle surf the very same board.

Moment Arm

The DISTANCE between your FURTHEST FRONT FOOT EDGE and your FOIL’S MAST CENTER.

Longer boards and, in particular, boards that have a high tail volume and weight behind the mast will require a greater moment arm.

It would be advisable to use "stick on" mounting rails to determine the perfect position of your mast before cutting up your board. As explained above, paddle surfing the board and kiting the same board efficiently may require two completely different mast positions.

From our experience the following moment arms have worked well:

Body Board 107cm:

Arm = 55cm

Paipo / Skimboard 120cm - 135cm:

Arm = 60cm

Short ,Flat Bottom Surfboard 5.4' / 163cm / 30 Liter volume:

Arm = 65cm

High Volume Shortboard 5.8’ / 173cm / 50 Liter volume:

Arm = 68cm

Longboard Surfboard 8' / 245cm / 58 Liter volume:

Arm = 75cm

Maintenance & Care

Kiting Setup

Surfing Setup

The pedestal and hence mast is positioned in relation to where the foil board is most easily ridden on the surface of the water. With this particular high volume board, the front foot needs to be quite far forward to ride it efficiently on the water surface. Hence the mast is positioned a bit further forward.

Surfing Setup

The pedestal and hence mast is positioned in relation to where one would normally place their front foot after attempting a standard surfing pop on this particular board. The high nose volume on this board made it tricky to initially get the front foot far enough forward. Hence the mast is positioned a bit further back.

Kiting Setup

Surfing Setup

Equally balanced front and rear leg pressures. Unbalanced forces are most noticeable on toeside where one would experience a tired back leg. Front foot is higher up the board deck where it will ride most efficiently off foil on the water surface. Back leg is on or just forward of the mast.

Surfing Setup

Your back leg has far higher pressure with unbalanced forces when it is kited. When the foil board is surfed these forces are hidden due to the lack of side & upward pull from the kite force vector, and the changing swell energy you are riding on. Your front foot is positioned where you would normally pop to. Your back leg is on or just forward of the mast.

Board Sizes

Board Differences

To start , choose the volume surfboard you would use to normally catch the same type of wave you now intend to foil. This normally means referencing the beginner volume tables.

Board Differences

Foilboard longboard. Converted mini mal into a foilboard

An 8` converted longboard (58L) and 4.8' short foil board (30L). Note that the longboard has been shimmed with an angled coupling plate due its tail rocker. The foilboard is designed flat towards the tail. The longboard makes a perfect surf foil learning platform from which one can progress to smaller , shorter boards that offer more feel and maneuverability. Once the technique is learned it is still possible to catch smaller , mushy foiling waves with these short boards.

Coupling Plate Shim

Skimboard vs Surfboard

Coupling Plate Shim

When you build your own foil board, by converting a surfboard with inserts or rails, keep in mind The height difference between the rear and forward holes of the (140mm) pitch coupling plate shim, 5 to 10mm seems to work well in cancelling most tail rocker.

Foil Mounting Plate

Skimboard vs Surfboard

Coupling Plate Shim

invaderfoil hydrofoil kite foiling surf foil surfing

A great method to easily attach the foil to your favourite surfboard or SUP ! Self adhesive, 3M taped rails , allow the fine tuning of your foil position. This will vary with body weight , stance preference, ability and swell size.

Skimboard vs Surfboard

Skim: ( Approx 120 - 148 x 45 - 50 )

Pros:

Really fun , light , small , easy to carve and maneuver on flats or swell. Easy to water start with a single center front strap. Cheap , easily DIY stiffened and modified. Easy to carry and push through shorebreaks or breaking waves.

Cons:

Little floatation , very unforgiving when off-foil , may require stiffening to limit flex.

Surf: ( Approx 4.6 - 5.6 )

Pros:

Much easier to initially learn on due to the extra floatation and forgiveness when off-foil. Easier in light wind conditions. Dual purpose foil/surf boards. Various strap positions.

Cons:

Too much floatation is often a problem entering and exiting in bigger surf. Expensive , and often less robust. Heavier if made tough. Bigger plan areas are not as fun to carve and turn. Can lose the " walking on water " feeling.

Skim Foilboard

Build or Adapt Your Own Skimboard Foilboard

These are the basic planform dimensions of our Paipo foil board.
The pedestal to footstrap positions are important and optimised for our foil. They may be adapted and used on many different skimboards.
The smaller the volume of board that is placed behind the mast , the greater the ride stability.
The length and width indicated are what we have found to be the most fun. Our thickness is 20mm and nose rocker begins at two thirds the board length. A simple sanding of the nose ( approx. last third of your board ) to a 5mm thick tip will work well. The entire deck can remain perfectly flat and actually helps one ride at the correct angle between water and foil
Larger or even slightly smaller dimensions will definitely work. Our normal rider weight range is between 60kg - 90kg on these given dimensions.
The benefit if you build your own board is that you can remove the tail rocker. The pedestal should be mounted completely flat and parallel to the datum line of the board.
It is critical that the skimboard is made as stiff as possible with very little or no flex.
Kite specific skimboards are generally stiff enough, but may need some glass or carbon reinforcing around the pedestal mounting area. See how to build or adapt your own skimboard for step by step instruction.
Ply or Paulownia wood type constructions will need glass cloth / carbon cloth and epoxy reinforcement on the underside of the board at least. Particularly around the pedestal mount area.
A very thin deckpad and a flat top deck will enhance the control and feel between yourself and the foil.

Pedestal Dimensions

Build or Adapt Your Own Skimboard Foilboard

These are the important dimensions of the pedestal in our foil sets.

It also gives indication of the mast thread pitch (M8) , which is used for the fuselage. (45mm)

The total mast chord width is 118mm and max thickness is 14mm.

Build your own foil board