Tides and Currents: How to Use Natural Forces to Improve Open Water Swimming Efficiency

Introduction

A triathlete from Taitung shared his observation: for the same 1.5 km open-water swim, he finished in 28 minutes during one time slot, but only 24 minutes in another—a 4-minute difference, with the only variables being the start time and tidal conditions.

Current is the most underestimated efficiency factor in open water. A current of 0.5 m/s can accelerate or decelerate you by the equivalent of roughly a 30% increase or decrease in your swimming speed. Over a 1,500 m swim leg, this translates to a 3–5 minute difference.

Understanding tides and currents is not just an advanced skill—it is fundamental knowledge for making training and racing safer and more efficient.

Tide Basics

Tidal Characteristics of Taiwan

Taiwan’s tides vary significantly by geographic location:

Region	Tidal Range Characteristics	Impact on Swimming
Western Taiwan (Taiwan Strait)	Large tidal range (3–5 m)	Obvious currents; timing must be calculated
Eastern Taiwan (Pacific Ocean)	Small tidal range (0.5–1 m)	Relatively mild currents
Penghu Islands	Moderate tidal range	Tidal currents are pronounced between channels
Xiaoliuqiu	Moderate tidal range	Coral reef terrain makes currents complex

Reading Tide Tables

Key information in a tide table:

• High Tide: Water level is at its highest; ebb begins afterward
• Low Tide: Water level is at its lowest; flood begins afterward
• Flood current: The transition from low tide to high tide, when water flows from offshore toward the shore
• Ebb current: The transition from high tide to low tide, when water flows from the shore toward the open sea

Key swimming strategies:

• For swims starting from the shore: choose the early flood phase, when the current helps you swim toward your target
• For out-and-back routes (such as the Sun Moon Lake Swim): choose the slack tide period when currents are relatively still (approximately 1 hour after high or low tide)

Reference tools: In Taiwan, you can use the Central Weather Administration’s tide forecasts, or apps such as Windy and Tideschart to check tidal information for various locations.

Types of Currents and How to Read Them

Longshore Current

Flows parallel to the coastline and is the dominant current type at many of Taiwan’s open-water swimming venues:

• How to identify: Observe the direction in which floating objects on the surface drift
• How to use it: If the current direction aligns with your swimming route, go with the flow; if it is against you, consider a longer but current-assisted route
• Taitung waters: In summer, the Kuroshio Current flows northward past the coast of Taitung; at an appropriate distance offshore, you can feel a northward boost

Rip Current

A strong current flowing from the shore toward the open sea (a safety hazard, as detailed earlier):

• Speed: Can reach 2–3 m/s, impossible to fight against with human power
• Swimming strategy: Never swim against a rip current toward the open sea; swim laterally to escape it

Eddy

A recirculating zone formed behind protruding rocks or buoys:

• During a race, eddies are “natural rest stops” for athletes
• After rounding a buoy, use the eddy behind it for a brief breather

Practical Applications for Planning Current-Assisted Routes

Choosing Time Slots for Open-Water Training

When training in Taitung, Hualien, or Penghu:

1. Check the day’s tide timetable (flood and ebb times)
2. Determine the tidal state corresponding to “the time slot you will be swimming”
3. If possible, plan a route where “the outbound leg is with the current, and the return leg remains acceptable”

Adapting to Currents in Races

In the race swim leg, you usually cannot choose your start time, but you can:

• Adjust your swimming line: If there is a cross-current, swim a line slightly upstream of the straight-line course, so your actual track remains straight
• Use the drafting effect: Following behind another swimmer in a current not only reduces drag from drafting, but also lets the swimmer ahead “absorb” the brunt of the current’s resistance

Practical Tips

• Check the tides the day before the race: Especially for sea events, knowing the tidal conditions during your race window helps with mental preparation
• Observe when local fishermen head out to sea: They know the currents best and typically depart during the most favorable tidal windows
• Test the current with a floating object: Before entering the water, toss an empty water bottle and observe its drift direction and speed—more intuitive than reading any guide
• Compensate for drift when navigating in a current: If the current flows from right to left, aim slightly to the right of your course so the current carries you back onto the straight line

Conclusion

Tides and currents are nature’s rocking chair—sit facing the right way and it carries you forward; sit the wrong way and it wastes your effort. Learning to read the water is an important evolution from “swimming in the water” to “swimming with the water.” Taiwan’s rich marine environment offers excellent conditions for mastering this skill, and every time you enter the water is a chance to practice reading nature.

Related Reading

• Reading Tidal and Ocean Currents: How to Use Water Flow to Save Energy
• Using Tides in Open Water: The Impact of Taiwan Strait Tides on Open-Water Swims
• Reading Currents in Open Water: How to Use Ocean or River Flow to Your Advantage
• Reading Currents in Open Water: Go with the Flow, Survive Against It