Saturday, February 20, 2010

The case for seeded waves...

After completing the Avalon Swim, I was pondering whether seeded waves would work, where swimmers are sent off in times according to their 1km swim times.

Being of the pointy-head variety, I had to satisfy my curiosity with some analysis of the results to see if seeded swims would work, and even out the flow of swimmers around the course.

The chart below shows the numbers of swimmers in 2 minute increments according to their finishing time.  For those fellow pointy headed swimmers, you will note that half of the swimmers have completed the swim by 28 ½ mins time and that the results are skewed, with a tail of slower swimmers.

This info shows that if starts were based on seeded times with equal time classes, then there would be some groups much larger than others.  Seeded starts might work if the times were worked out such that waves were based on achieving equal sizes.

If the organisers were to achieve say, 5 waves of 200 persons each then seeding would have to be based on 1 km swim times as follows:

• < 18 mins per km • 18 – 19 ½ mins per km • 19 ½ to 21 mins per km • 21 to 23 ½ mins per km • >23 ½ mins per km

With age group wave starts, it is near impossible to group waves into equal size classes. The table below shows the number of swimmers by age group category.

This info shows that grouping the swimmers into equal size groups would be very awkward. For example, there were 337 swimmers between 35-45 yrs of age, so you can get a feel for the issue.

In short, I don’t envy organisers of swim events in trying to sort out wave starts. People say, “more waves”, but while the waves are set out in age groups, it will never cut the argy bargy as swimmers’ abilities are not age dependent (if you have raced John Koorey, you will understand what I mean!)

Seeded waves would work but would require honest assessment of one’s swimming abilities and a reasonable analysis of previous events’ results to assess time categories and wave numbers.

John Bamberry


  1. The TamaCloey has seeded waves based on previous ocean swimming history. Come and join us for the 2.5km Cliffside Odyssey between Tamarama and Clovelly on Easter Monday!

  2. Interesting piece. I did the Tama/Cloey swim last year which was seeded by time and to some degree worked, however given that it was over a longer distance and was a point to point swim as averse to a shorter circuit course.
    With circuit courses and shorter distances I don't think you need seeded waves and age groups do work. Although sometimes argy bargy at the starts, with aged groupings you get the wave quickly fanning out/stringing out. In a seeded wave swim over the shorter distances you wont get such a result due to a wave of similar times/ability.
    In short I reckon keep the shorter circuit courses (under 2 km) to aged waves and if you really want to, yet not necessary, make the longer distance point to point swims by seeded waves i.e Palmy-Whale, Little Bay, Tama Cloey

  3. What about simply putting a series of those timing mats (that are at the finish line) and put them at the start also. It would work out when you start and when you finish. With that, people could start whenever they please.

  4. John you are a true swimming tragic, with that statistical analysis and histogram. Good work !!!

    Age groupings should work well for most swims, the organisers have a few options to keep the wave sizes reasonable , eg. 5 year vs. 10 year splits, male/female only or combined. The key is the organisers having good information early on as to how many swimmers will be competing, so they can split the age groups appropriately. There was one swim earlier this season that had 50% more entrants than the previous year, and a large number of late entries on the day, and started with the same wave splits as previous year. Sure enough the race was crowded with a lot of grabbing and bumping at the turns. If this sport continues to grow they may have to look at "no late entries" on some of the larger swims.

    Seeded waves, if done properly and honestly, would actually make for really competitive races and faster times, as you would always be swimming and trying to keep up with or stay ahead of a whole wave of swimmers of equal ability, if not your own age and sex. Every wave would feel like a kind of "elite wave" in its own right, even to average swimmers.

    You would need a reference for event organisers to determine seedings, ideally a national database of all swimmers results, ie "rankings" and average times. And no late entries, unless they create "back of the pack" for late entrants.

  5. Hey Richard, It's hard to give up this addiction; I wonder if they have an ocean swimmers rehab clinic. I appreciate your comments; I did a similar exercise for the Big Swim and came up with a similar result to the article posted on Avalon; I agree that it would make for more competitive races as you are swimming amongst a group of people of like capability. I think this is an exercise in traffic flow; if you start slow moving trucks with speedy sedans, you're always going to have log jams and impatient drivers, with occasional learner drivers (breast-strokers) blocking the lanes. Whereas, if you let the sports cars (of all vintages) go off first, and leave the learner drivers till last, people might find it easier to get round the course (plus waves wouldn't have to be separated by as much time).


    John B

  6. Touché fellas,

    love ya work Bambi. Such a seeding and gridstart system would work a treat as long as the pre-race timing info is empirical and not just guess-work on the part of the entrants. That would be like asking once or twice a year golfers to nominate their handicap. I reckon if you haven't got the runs on the board or you couldn't be bothered to pre-enter, then to the back-o-the-pack it is.

    However you could have a special celebrity wildcard system to lure the odd quick outa the pool or pry a pollie out da house.



  7. I would have though that a lot of the argy bargy starts at the beginning of a race as swimmers take off together and don't have their own space. With age groupings and different abilities, after a couple of hundred metres the field tends to start spreading out fairly quickly. Surely the argy bargy would last longer with seeded waves as a large number of swimmers with similar abilities get stuck amongst each other. As a slower swimmer who likes to get out and just have a good swim, I am more than happy to stand back at the beginning and let everyone else take off into the melee. Sure, I then have to pass those who can't sustain anything like their initial pace, but I like swimming wide (this usually keeps me out of the way of faster swimmers in following waves coming through and I also view the extra distance swum as value for money!). I like swimming in an event out on my own - I would rather take my chances with nature than with the arms and legs of my fellow competitors, especially around the buoys. In the age groupings where the waves are large, it is also possible to split by male and female to make them smaller. The start waves at Bilgola were large because they covered 15 years instead of the usual 5-10 years. A friend swam in the Tama2Cloey last year and found the seeded waves frustrating as it was difficult to find your own swimming space for large parts of the race. I like the current age starts with different abilities, though it can be difficult for organisers to estimate how large the waves will be when sometimes there are huge numbers of late entries on the day.


  8. Hi Sue,
    I appreciate your comments. From my experience, the biggest concern in the argy bargy stakes seems to be faster swimmers swimming over slower swimmers. I guess there's always going to be a clash of sorts. Having said that, I never touched a soul in the Malabar-Little Bay swim. I also swam in Tama2Cloey and also found it hard to find my own space - but I felt I had to push hard to keep up, which I really enjoyed. I don't mind either format but I am finding the short 1.5km swims very frustrating from the disparate abilities in age groups - it's like that feeling that you get when you are driving along the highway, wind blowing in your hair (at least for some!) when you turn the corner to find a slow moving caravan, and no overtaking lane. If organisers went over the number of swimmers in age groups from previous swims (and I am sure some do), they would find a repeated pattern. The most populated age categories in most swims, for example, is the 35-40 and 40-45 age groups (mid-life crisis??). There's a wealth of information in the results recorded on, so it wouldn't be hard for someone to work it out.


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