By Brian Finch — Foil The World

 

---

 

Introduction

Small adjustments create big changes in hydrofoiling. Shimming, changing the angle of your tail wing or mast, lets you tune your foil for speed, stability, turns, pumping, and glide.

This guide will teach you why shims work, how they work, and when to use each so you can tune your foil precisely for your preferred feels and conditions.

Whether you’re chasing increased glide, carving harder, riding faster bumps, or stabilizing your setup for learning, understanding shimming is one of the most important skills in foiling.

 

---

 

The Physics of Tail Shimming 

To understand shimming, you need one key idea: 

The tail wing produces downforce, not lift.

Your tail wing (stabilizer) generates downforce, pushing the tail downward to balance the front wing’s lift and keep the foil stable in pitch.

Because the tail produces downward lift, shimming behaves the opposite of what most riders assume. Additionally, installing a tail shim is generally done with the board on the ground and the foil kit upside down, creating further confusion. When reading this guide, imagine that your foil is attached to your board and you are riding in a straight line for best visual comprehension. 

 

---

Positive vs. Negative Shim: What’s Actually Happening

Trailing Edge Down (Positive Shim)

Adds angle → more tail downforce

• More tail push down

• Nose pitches up

• More front-foot pressure

• Tighter turning radius

• Helps early lift and control

• Adds drag → less top-end speed

Use for:
Front footed feel, tighter carves, smaller waves (more perceived lift).

Typical positive shimming range +.25° - + 1° 

Too much positive shim: 

 

---

 

Trailing Edge Up (Negative Shim)

Reduces angle → less tail downforce

• Tail pushes down less

• Foil rides flatter (less drag)

• Back footed feel

• More speed, glide, and efficiency

• More pitch sensitivity

• Higher stall speed 

• Mitigates board tail rocker that forces nose up

Use for:
Back footed feel, fast-moving downwind bumps, higher top speed, high-efficiency pumping, breach control in bigger surf, mitigate excessive tail rocker in board.

Typical downwind range:
-0.25° to -0.5° trailing edge up

Typical Big Wave range -0.5° to -1.5°

 

---

 

Why Riders Say “More Lift” or “Less Lift”

These phrases usually describe baseline pitch and liftoff, not actual front-wing lift:

• “More lift” = more nose-up pitch from more tail downforce

• “Less lift” = flatter, faster riding from less downforce

Once this clicks, shimming becomes predictable instead of trial and error.

 

---

 

Baseplate (Mast) Shimming

Baseplate shims tilt the entire foil system by changing mast angle:

Nose-Up Baseplate Shim

• Gets you on foil sooner

• More front-wing *lift at low speed

• More front-foot pressure

• Slower top-end from increased drag via angle of attack

 

---

 

Nose-Down Baseplate Shim

• Lowers front-wing angle of attack

• Reduces front-foot pressure

• Increases speed and glide

• Mitigates tail rocker of your board

• Great for linking glides and DW runs

 

---

 

How Tail Shims and Baseplate Shims Interact

Think of the tail shim as fine-tuning
and the baseplate shim as coarse-tuning.

Tail Shim = controls downforce, pitch sensitivity, drag

Baseplate Shim = controls when the foil lifts and how much front-foot pressure you feel overall

Example:

Downwind Setup

• Tail: –0.25° to –0.5° trailing edge up

• Baseplate: slightly nose-down

Result:

• Less tail drag

• More speed

• Foil runs flatter

• Less front-foot load in fast bumps

Small Surf / Learning Setup

• Tail: +0.25° to +0.5° trailing edge down

• Baseplate: neutral or slightly nose-up

Result:

• Early lift

• High stability

• Predictable pitch

 

---

 

Practical Recommendations by Discipline

Downwinding (SUP, Parawing, Wing)

Use:

• Tail: –0.25° to –0.5° (trailing edge up)

• Baseplate: slight nose-down

Benefits:

• Increased board speed and faster bump entry

• More efficiency

• Lower drag

• Easier trimming at speed

• Longer glides and less pumping

 

---

 

Surf / Wake 

Use:

• Tail: Neutral to +0.25° or +0.5° or more if needed

• Baseplate: Neutral or Nose up 

Benefits:

• More stability

• Better low-speed lift

• Predictable carving

• No unexpected pitch changes

 

---

 

Pumping / Flatwater

Use:

• Tail: Neutral or slight negative (-0.25°)

• Baseplate: Slight nose-down

Benefits:

• Better sustained glide

• Flatter riding

• More efficient pumps

• Reduced foot pressure

 

---

 

Big Waves / Tow

Use:

• -0.25° to -1.5°

Quick Reference Cheat Sheet

 

---

 

Basics Summary

Trailing edge down = more stability and low-speed lift feel.
Trailing edge up = more glide, more speed, less front-foot pressure.
Baseplate shims change when your foil lifts - tail shims change how it rides once you’re flying.

Too Much Shim?

Too much positive shim → slow and draggy, nose excessively high, stance too far forward on board, difficulty controlling breach, launched into air on takeoff, front leg burning out.  

Too much negative shim → Twitchy, nose excessively low, back leg burning out, hard to lift off water or maintain balanced flight, stance too far back and/or excessive swing weight from board. 

 

---

 

Key Variables That Affect Shimming

Shimming isn’t one-size-fits-all. Your ideal setup depends on a mix of rider factors, foil design, and the environment. These are the variables that matter most:

1. Wave Power

• More powerful waves = need less tail downforce (more negative shim).

• Weaker waves = need more tail downforce (more positive shim).

 

---

 

2. Wave Speed

• Faster-moving bumps or groundswell = negative shim (trailing edge up).

• Slow, mushy waves = positive shim for early lift.

 

---

 

3. Rider Weight

• Heavier riders often need slightly more downforce (small positive shim).

• Lighter riders can run more neutral or negative shim.

 

---

 

4. Front Wing Size & Design

Large, low-aspect wings

• Strong lift → often need slightly more negative shim.

Small or high-aspect wings

• Lower low-speed lift → often need more positive shim for early lift.

 

---

 

5. Tail Wing Size & Design

• Bigger tails = more inherent downforce → can run more negative shim.

• Smaller tails = less downforce → may need more positive shim for stability.

• Flat tails vs dihedral/anhedral change pitch sensitivity.

 

---

 

6. Fuse Length

• Longer fuselage = more pitch stability → allows lighter (more negative) shimming.

• Shorter fuselage = more pitch sensitivity → may need more positive shim.

 

---

 

7. Mast Angle (Baseplate Shim)

Baseplate angle changes the overall lift profile, not just the tail behavior.

• Nose-up mast = earlier lift, more front-foot pressure

• Nose-down mast = speed, stability, efficiency

Tail shim + mast shim must work together.

 

---

 

8. Rider Stance

• Forward stance = may need more negative shim

• Rearward stance = may need more positive shim

• Width of stance also changes pitch leverage

 

---

 

9. Ride Speed

As speed increases, front wing lift increases.

• Riders who cruise fast = negative shim

• Riders riding slow = positive shim

This is one of the biggest hidden variables.

 

---

 

10. Board Angle / Track Position

Some boards inherently ride nose-up or nose-down depending on:

• Bottom rocker

• Track placement

• Mast position relative to center of buoyancy

This can require shimming to correct trim.

 

---

 

11. Rider Skill Level

Higher skill = can run negative shim for speed, sensitivity, and glide
Lower skill = needs positive shim for pitch stability and forgiveness

Congratulations! You are now a shimming expert!