A look at Kelly Slater's quad placement guy, Bruce McKee

       MCKEE’s look in detail at the NITTY GRITTY of quad fin technicalities.

How quads work & How quads differ from thrusters 

• Quads give more drive, speed, security, climb the foam better, let you drop in and drive without nursing the bottom turn. They can drive everywhere with a greater boost than a thruster so sometimes you must adjust your technique to cater for this new boost of energy. By knowing how to fine tune them they can be adjusted to perform in practically any way you desire.
• Quads are faster due to having all fins driving through turns, or even just running across  a wave face. All fins are propelling the board forward much like sails or propeller blades. This is because a board in these situations, is in a constant lateral drift and the water passing under the board, divides between the fins to pass out both sides of the tail while redirecting off the fins, rearward, to form thrust.
• The back fin of a thruster generally sits in the dividing line of this displaced water so provides no added speed but gives direction and control with a dragging effect.
• Depending on your fin positioning or ‘cluster’, your quad can be as pivotal as you want. The goal is, though, to select a fin positioning formula that provides a balance of looseness, drive and security, a happy medium you might say. Like cars, you can have a long wheel-base or a short wheel-base, or something in the middle. It’s the same with fin positioning on surfboards. The McKee Multisystem formula is a good choice for that ‘happy medium’. 
• Comparing quad fins to car wheels is a simplified way of imagining the corresponding affects of changing fins. Big stiff fins= Big grippy tyres. Flexy fins= Soft  low air tyres. Thus big stiff wheels on the front plus Soft or small low air tyres on the back gives a car with a lot of oversteer.  Bigger rear tyres than front = like a formula one race car. 
• Pivot can also be adjusted depending on your fin selection. Rear double-foiled fins, compared to flat-faced fins of the same size, will pivot more.  Larger proportioned front fins than rear fins will also pivot more. Fins that have less rake are more pivotal.
• The fins should be balanced around what is called the ‘sweet spot’. The sweet spot is generally the position of the back foot when performing a cutback or top turn. Boards will ‘over-steer’,’ under-steer’, or feel neutral depending on all these factors of rake, size and foil and how they relate to the location of the ‘sweet spot’.
• The sweet spot is determined by the tail area, plan-shape and length of the board.
• If one side of the board has different fins to the other side, it will be like two different boards when turning right or left. Asymmetric mixes are another way to ultra fine tuning a board for point break conditions.
• Control
• Control comes from the correct choice of fins for the surf conditions.
• Depending on the type of board and size of the wave, a different turning arc and amount of hold are needed.
•  Quads with the correct fin choice have much more hold than ‘Thrusters’. The worry of the Thruster’s central tail fin leaving the water is eliminated with a quad. No more ’nursing’ the turn.
• Drag
• Too much toe-in of the fins can create a quick accelerating, loose but ultimately draggy board as the fins start to wedge-up at high speeds. Increased Vee will reduce the effect as it ‘feeds’ the fins.
• Low speeds
• More ‘toe in’ as with three-fins and twin -fins loosens up boards for small waves and low speeds. This is generally determined as the shaper’s choice.

Choosing a quad

• Different shapes for different waves:
• My shapes for quads are exactly the same as I would shape for three fins, though obviously for those wide tailed fish or with any wide tailed board, if you want them to hang-in in bigger waves, then a quad setup is the best choice. 
• VEE tails do ‘feed’ a quad’s two back fins by dividing the water between the fins thus reducing the possibility of a wedging effect, though with the correct ‘toe-in’ angle this should not be a problem when a concave tail is required.

Quad fin selection

• The mentality that quads are for small waves and three fins are for power waves is still promoted by some die-hards. I would suggest that they actually try a quad in power waves and thus this incorrect fallacy would be instantly extinguished      

• The addition of an extra fin on the tail will obviously add to the total fin surface area thus providing more hold. 

• The addition of the fourth fin leads many to reduce the size of the back fins in relation to what would have been used if the board were a thruster. A heavy back-footed surfer will relish in the extra hold of an extra back fin of equal size to that out of their thruster set. This requires a new full-powered approach to surfing and the only limit will be your own leg strength and talent.

• ‘Front-foot’ surfers or those needing a less demanding effort to turn will benefit from reduced size back fins of double foil and or all fins of reduced size.

Fin placement & rear fin choice?

• In the past l have placed fins in hundreds of different positions all over the tail. For the ‘M4Quattro’ purist, the ‘Mckee M5 Multisystem’ is just a security blanket or like training wheels because for them the ‘Thruster’s’ central fin is obsolete. The quad cluster can be moved forward to loosen up a board and for shapers of custom boards, many compensations can be made for weaker riders or for special needs such as looser guns but with the advantage of not losing drive. Although taken off the current formula there is the shapers option to move the cluster at any amount not exceeding the stupidity level. I personally had great results on pintails by moving the positions forward up to 2cm or ¾” forward. The videos of Tom Carroll in Hawaii are examples of the result of these positions --- The variations are limitless!

With the rear fin positions, the closer they get to the rails the more hold, yet the greater the time delay in re-centering the board in preparation for the next turn. You also produce a greater ‘twin-fin’ effect, with the board feeling like it is staying on one tack, needing you  to throw it across between turns. Also you increase the risk of ‘rail-grabbing’.  There is a correct distance  between the back fins correlated to the tail width at 12” up. Fins close to the rail mean that they have to be reduced in size or toed-in more than fins placed closer to the stringer. There is a happy medium that provides a ‘thruster-like’ re-centering with the correct amount of drive. This also allows for the use of larger rear fins, still providing looseness but without having any rail grab to worry about.

• Choice of rear fin should be determined by your weight, power, wave size and type of board, say shortboard or gun.
• Guns and boards for waves with push, generally need more control than drive and a more forgiving lateral movement when riding forward on the board, so double foiled back fins are my choice here.  
• Fish and guns over 6’8” generally gave a greater difference in size between the front and rear fins. Shortboards under 6’8” for power waves can have fins of a closer size depending on the looseness required.

• The further forward they are on the board 

The looser and more pivotal a board will become. Overdoing it, and you enter into a situation of over-steer. You are moving the fin positions forward of the ‘sweet-spot’ so the board can become unbalanced.

On guns and long-boards, this is can be an added benefit. If you forget about the ‘Multisystem’ concept (the option of a central ‘Thruster’ tail fin), the cluster can be moved forward to leave those guns and longboards as loose as you like without the worry, as in three fins, of the tail fins leaving the water. I recommend a maximum of an extra 2cm further forward on the McKee formula so as to not get too crazy. On shortboards big movements forward are not so advisable as there is not as much nose length and weight  to counterbalance the oversteer…Though if you like 360s..

If you use the McKee Quattro & Multisystem formula the size ratio between the front and back fins can become a lot closer, even to the point where a strong surfer in power waves may choose to have bigger back fins than front for full directional drive.

Distance from the tail and the location of the cluster in relation to the sweet spot will be a determining factor on choice of front and rear fin size correct for your weight and ability.

Tuning your quad fin setup to work best for you.  

Is the tail sliding too easily?  Go with a larger rear fin set

Is the tail too tight?  Go with a slightly smaller rear fin set

Is the board lacking drive?  Go with slightly larger front fins.  

Is the board too hard to turn? Go with slightly smaller front fins and rear fins.  

Does the board feel out of control? Try a rear fin with a symmetrical or 80/20 foil

Wanting drive off the bottom and loose of the top? Place a flatter foil or bigger rear fin for the bottom turn side and a smaller double foiled rear fin on the off the top side.. note that this will also be the cutback side so study your choices.

      Well have fun and I look forward to some feedback! 

                                                                                       McKee.

All my experience up until just recently had been with edge quads, not McKee. I'm liking McKee better at the moment. A lot more drive and still I can tune it loose.
Dwight