Rating Sea Conditions

Sea Conditions Rating System

by Eric Soares

When scouting a river, kayakers will duck into an eddy or climb out and take a look at what lies ahead in the next set of rapids. They note hazards and lay out a route. What they see is what they get. River conditions remain constant during a short time period. But the ocean changes quickly, all the time. You can scout from on the water or from on land. But what you see is not necessarily what you get. So scouting becomes more difficult and complex. What is needed is a way to classify general danger and difficulty on the sea, so you know whether it’s too extreme for you to kayak that day.

River Difficulty System

River runners have devised an international classification system to rate the difficulty and danger of a river section or rapid, based on factors such as flow and gradient. It works like this: Class I is moving water with only a few riffles, waves and obstructions. Class II has small rapids, waves up to three feet, wide and clear channels with some maneuvering needed. Class III has rapids with high, irregular waves, and narrow passages with complex maneuvering. Class IV has long and difficult rapids with constricted passages requiring precise maneuvering and Eskimo rolls, and dangerous conditions which make rescue difficult. Class V has extremely long, difficult and very violent rapids which require very precise techniques, and loss of life is possible in a mishap. Class VI is Class V taken to an extreme; conditions are nearly impossible, suitable for a team of experts only, and loss of life is probable in a mishap. The rating system is subjective, but an indicator of what a boater is getting into. For example, if you don’t have a reliable roll, you should stay out of water rated Class III or above. Also, a river’s rating may go up in the winter when it’s cold outside or if the river flow increases.

Sailors use the Beaufort Wind Scale to rate conditions caused by wind while in a sail boat at sea in navigable waters. The Beaufort scale is useful but does not account for being in a small kayak in surf or rock gardens. We sea kayakers need our own rating system which accounts for wind and other relevant variables, yet can be converted to a class system akin to the one river runners use, so you can decide if sea conditions are classed too high for your skill level.

Scouting the Sea

Since the sea is jazzy, complex, and changes over time, you should really take your time when scouting before setting out. First, check weather reports for an approaching storm or big swells. Assuming the weather doesn’t scare you off, assess the conditions when you reach the water’s edge. Get with your partners, and go through the Sea Conditions Rating Scale (SCRS) point by point. Discuss each factor until you reach consensus. Then move on to the next item. When finished, tally the score, convert to a class I-VI system, and determine whether everyone in your group can safely partake that day.

When using the scale, be sure to account for the worst conditions likely to be experienced on your outing. For example, it may be breezy and flat and safe at the put-in, but the wind may be howling around the point with big swells and no safe place to take out. If you intend to paddle to the point, those potential conditions must be given their due. Account for the passage of time. For example, if the tidal current is slack when departing but will rage at six knots when you reach the shoals in two hours, factor that in.

Note that the scale rates general conditions and does not account for freak occurrences such as rogue waves, waterspouts, and the like. Should you suspect inclement weather (such as a lightning storm), even though the weather report states otherwise, don’t go out.

We recommend you practice with the scale and assist beginners who use it, since they are less skilled at reading conditions. Eventually, you should be able to calculate the factors in your head, and not need to have the SCRS in hand. As you peruse the SCRS, take a minute and recall the conditions on your last outing; or better, on your most harrowing outing. What was the Class rating, and were you within your skill level?

Sea Conditions Rating System (SCRS)

Factor Computation Method Maximum Points Score

1-Water Temperature 1 point for each degree below 72F 40 ____

2-Wind Speed 1 point per mph of wind speed 50+ ____

3-Wave Height 2 points per vertical wave foot 40+ ____

4-Swim Distance to Safety 1 point per 100 meters 20 ____

5-Breaking Waves 30 points if waves are breaking 30 ____

6-Rock Garden 20 points if paddling in rocks 20 ____

7-Sea Cave 20 points if entering sea caves 20 ____

8-Night 20 points if it is night 20 ____

9-Fog Up to 20 points if fog is dense 20 ____

10-Miscellaneous 10 points or more for other danger 10+ ____


Divide total points by 20 to obtain CLASS LEVEL = ______

Scoring Directions: Scope out the sea using instruments or conservative estimates, and rate each of the 10 factors. Add scores and divide the sum by 20. Scores up to 1.9 are Class I–easy to moderate difficulty, danger, and skills required; Class II (2.0 to 2.9)–intermediate difficulty, danger, and skills required; Class III (3.0 to 3.9)–advanced difficulty, danger, and skills (e.g., a reliable roll and self-rescues a must); Class IV (4.0 to 4.9)–extreme conditions, advanced techniques required, loss of life possible; Class V (5.0 to 5.9)–very extreme, life threatening conditions ; Class VI (6.0+)–nearly impossible conditions, suitable only for a team of experts, loss of life probable in a mishap.

Descriptions of Factors

Each of the 10 factors has been weighted depending upon its difficulty and/or danger. Before first using the scale, read factor descriptions to better understand the variable’s importance and calculation method. Note that the first four factors always apply to any sea kayaking endeavor, even in a protected harbor.

Factor 1, water temperature, starts at 72F, because that is a temperature most people can swim comfortably in, and it happens to be 40F above freezing. Remember, cold water is the number one kayak killer, so it receives a lot of weight in the algorithm. However, it takes no skill, only the proper nutrition and clothing (wetsuits, drysuits) to compensate for cold water. Also, air temperature is usually not that important, since cold water takes away body heat 20 times faster than the same air temperature. To calculate factor 1, subtract the water temperature from 72 and the remainder is the score. Using a thermometer to measure the actual water temperature is superior to an imprecise, subjective estimate.

Factor 2, wind speed, is similar to flow rate in rivers. The more wind, the more difficult and dangerous conditions become. Wind is also fickle; it may increase or decrease at a moment’s notice. That’s why we give it so many potential points. Windspeed can be observed using the Beaufort scale or measured with an anemometer. Remember to assess it in an exposed area (not in a lee). Calculation of wind speed score is simple; the score is the same as the high mean wind speed in statute mph. If the wind is blowing at 15 mph but gusting frequently at 25 mph, then record 25 mph for factor 2.

Wave height, factor 3, like wind speed, is measured in actual vertical feet. Watch the waves for a few minutes to make sure you see the biggest waves, then estimate the high mean vertical wave height from trough to crest, not the slope (face) of the wave, and multiply by two to obtain factor 3. Wave height is measured separately from whether the wave is breaking (factor 5).

Factor 4 is the “how long can you tread water?” variable. It represents an estimate of how far you would have to swim to reach a safe shore or safe place should you lose your boat. Each interval of 100 meters is represented by 1 point, up to 2,000 meters or more, over a mile, at which point, assume you will be awaiting rescue (20 points). If anyone in your party cannot swim 100 meters to safety, or there is no safe place to take out even if you could swim (say up against a cliff), or a combination of factors would make self-rescue improbable, assign 20 points to factor 4. If you will be making a long crossing (20 points), bring communication devices so you can be located and rescued.

Factor 5 is breaking waves. If waves over two feet are breaking , add 30 points. We give factor 5 a lot of weight because waves become much more powerful when they break on the sea floor. If special circumstances are operating in the surf zone, such as a strong rip current or extra steep beach break, add more points when you compute factor 10, miscellaneous conditions.

Factor 6 is a rock garden. If you intend to paddle into it, add 20 points. Do the same for Factor 7, a sea cave. If waves (factor 5) are breaking onto a rock garden (factor 6) and you go through it to get into a sea cave (factor 7), add 30+20+20 to get a combined factor of 70, divide by 20 to obtain 3.5 (Class III)–and that’s before you add in the first four required factors!

Factors 8 and 9, night and dense fog conditions, reduce visibility and each rate an automatic 20 points (one class increase). If they appear together, add 40 points to your total which increases the risk two whole classes.

Factor 10 is a hodgepodge category to score unusual, temporary, or local hazards such as ship traffic 10 or more points. An area noted for shark attacks, dumping waves, or a strong rip current would each receive an extra 10 points. Other miscellaneous factors to consider include strong rip tides, significant tidal currents, extremely cold air, intense rain or hail, icebergs, and flotsam.

Sample Situations Using the SCRS

Here are typical examples for each Class. For Class I, say Princeton Harbor in the summer, the water temperature is 52F (20 points), wind speed is 10 mph (10 points), wave height is one foot (1 point), swim distance to safety is 400 meters (4 points), and there are no other factors. Points total 35, divide by 20 = 1.75. Just about any kayaker wearing proper clothes who can swim can safely paddle here. If we add dense fog (20 points) to this equation, we’d total 55, divide by 20 = 2.75. Now it’s Class II+, still doable, but more dangerous. So you see, even a small, protected harbor on a calm day may rate higher than Class I.

If you wanted to kayak surf at a break on a typical day at Montara Beach, you would calculate the difficulty like this. Water temperature is 52F (20), wind speed is 8 mph (8), wave height is five feet (10), maximum swimming distance to safety is 200 meters (2), and you are in a surf zone (30). Your point total is 70, divided by 20 = 3.5, so it’s Class III. Since it is Class III, you know you are paddling in rough conditions and must have a good roll and rescue skills. If you observe local factors operating, such as an exceptionally steep beach break, dumping surf, and/or a strong rip current, you might add 10 or more points and recompute your score.

Say you wanted to play in the rock garden just south of Montara Beach on the same day. You add 20 points because of the rock garden (everything else remains the same) and achieve a new total score of 90, divided by 20 = 4.5–Class IV. This is extreme sea kayaking and requires advanced navigation and paddling skills. This is best attempted with a competent team, never alone.

Say you wanted to explore the nearby Montara sea cave in the same conditions. You are still in six-foot surf and rocks. So, the cave adds yet another 20 points for a total of 110, divide by 20 = 5.5–Class V. This cave, in these conditions, should only be explored by a team of experts, because even though the waves aren’t that high, they compress in caves and you could be entrapped or smashed.

Needless to say, Class VI should not be attempted, unless you and your team of experts are prepared for possible death. What constitutes a Class VI in sea kayaking with no surfzones, rocks or caves? How about a 12-mile storm kayaking trip across San Francisco Bay like I took several years ago (read the complete story on pages 88-93 in Sea Kayaker’s DEEP TROUBLE by Matt Broze and George Gronseth). On that day, water temperature was 55F (17 points), the wind was predicted to be 40 mph (40 points) in the middle of the bay, the waves were eight feet high (X2 = 16) and breaking (30) due to the interaction of the 6-knot ebb current with the incoming wind and waves, and it was too far and difficult to swim to safety (20). The score that day was 123 points, divided by 20 = 6–Class VI. Sound dangerous? It was. Read the story to find out why one should not kayak alone in Class VI conditions.

SCRS Caveats

Remember that sea state changes rapidly, so don’t be lulled into a week-long paddle in Class IV conditions because the SCRS indicator was only Class II when you set out. To be safe on an expedition, your team should use the SCRS each morning before venturing from camp. On any day in any location, assign points based on the worst conditions likely to be faced. Another consideration: the SCRS only rates sea conditions, not the suitability of your equipment, or mental or physical preparation, or skill levels of each person in your party.

Use the Sea Conditions Rating System (SCRS) to compute the risk factors each time you go sea kayaking. Have everyone in your party compute their estimates, and then compare. If scores differ, discuss this with your teammates. Use your SCRS to help you gauge and improve your scouting and rating ability. Use instruments, weather reports, and your subjective navigational estimates in concert to assign points to each factor. When testing the scale for validity, it is a good idea to practice using it using a challenging kayak outing which has already occurred, so you can compare the actual conditions with the SCRS score and class to see if it matches up.

Don’t underestimate conditions to be macho or sucker people into doing activities beyond their skill. The SCRS is useful but artifical; it only estimates, not guarantees the actual risks you will face. Finally, keep in mind that the SCRS is at best a general guideline, an indicator; it doesn’t account for freak incidents such as williwaws or rogue waves. Its main value is it encourages kayakers to take the time and effort needed to assess the complex factors which comprise the sea.