DPV Power Rankings

Formula H2O tested each DPV prior to the 2011 Weeki Wachee Warrior Challenge using a scale to determine it’s race class.  A full description of the methods used to record the thrust data can be found below, the following spreadsheet contains thrust data collected from the DPV’s and the race results:

Pull Test Procedure for Determining Race Class Assignments:

Underwater thrust being measured on Gavin DPV

Intent and purpose for testing

            The purpose of the pull test is twofold, first is to allow to fairly set race divisions so that everyone who races has a fair competitive chance and the second is to provide a method for verifying divisions after each race.

Every DPV not being raced in the “Unlimited” division should be tested prior to racing and may be tested immediately after the race if they place.

Pull scales are used to measure the thrust of DPV's to determine their race class.

Reasoning behind using a pull test to set divisions

            Using a pull scale to determine how strongly a DPV can pull is a basic test that has been used to evaluate DPV performance for a very long time. Because this is a simple test that anyone can do with just a length of rope and a pull scale, like those commonly used by fishermen, this is both easy for us to do at the event, and easy for people to do themselves with  closely repeatable results.

The testing that maps thrust to overall diver speed, however, has only recently become available to the diving community and this is due to the dedicated group of divers who conduct the “Tahoe Benchmark”. These individuals have done extensive testing on a wide variety of DPV’s and published both their methods and findings for all to see.  From The Tahoe Benchmark we now know that thrust is a very reliable predictor of speed and we have a good understanding of what thrust levels will produce what range of speeds. Divisions are setup to keep racers’ DPV’s within about fifty feet per minute speed of each other. This is within a range that makes the racers’ performance a predominant factor in the outcome.

Another finding from the Tahoe Benchmark is that not all DPV’s of the same make and model will perform the same. Age, how they have been maintained, and battery performance all contribute to overall performance. By using this test each racer will compete in a division appropriate to the DPV and battery that they have, in the condition that it is in.

For the curious, it should be noted that although smaller people with less drag are faster than larger people, real world results, while wearing SCUBA gear, point to this equating to only ten to twenty feet per minute in the slower divisions and twenty to thirty feet per minute in the fastest one. Considering that a strong SCUBA diver can swim one hundred feet per minute or more, and that buoyancy, trim and riding technique can reduce forward speed by as much as half, there are no certain combinations of DPV and racer size to win.

Pull Test Rules for Determining Division

  1. Divisions will be classified by the maximum allowed measured thrust for each division. At this time those divisions are:
    1. Recreational Class – 20 pounds or less before the race
    2. Expedition B Class – 39 pounds or less before the race
    3. Expedition A Class – 59 pounds or less before the race
    4. Unlimited Class – 59 pounds or greater before the race
  2. Races will be conducted in order from the slowest to the fastest division, when possible, although multiple divisions may be run simultaneously.
  3. Divisions will be set in advance of each race event and published on the Wreck Racing Leagues web site prior to the race.
  4. The same scale will be used throughout the entire race event for same division testing whenever possible. Multiple scales may be used for different divisions, but all DPV’s competing within the same division, will be tested using the same scale. For example a one hundred pound scale may test all of the DPV’s competing in the 55lb division, but a second fifty pound scale may be used to test all of the DPV’s in the 30lb division and 15lb division.
  5. The scale will be of common variety and need not be calibrated or certified. Once the first test has been recorded, no alterations to the scale are allowed. The purpose of the scale is to provide a common standard that each DPV can be compared to, and does not need to match any other standard itself. It is understood that each division’s standard is the appropriate marking on the scale which is provided, and not any other measurement.
  6. All racers will be given the chance to have their DPV tested prior to racing, on the official race scale. Racers can choose to compete in any reasonable division they wish, but risk disqualification at the end of the race if their DPV exceeds the allowed limit for the division they have chosen. For example if a DPV tests at 31lbs that racer could choose to race in the 30lbs division, the 55lbs division or the unlimited division. They could not race in the 15lbs division, because that is unreasonable. Staff will try to allow racers to test their DPV’s several times if desired. Competing in the 30lbs division is reasonable, because many DPV’s slow down notably after just a few minutes of running. A wise racer would confirm this with a second test after several minutes of running and make an informed decision.
  7. WWL staff has the final say as to what is considered reasonable.
  8. All races must be validated upon completion, either through group acceptance or testing.
  9. If after a race, every single racer within that division and presiding WWL staff agree to validate the race without testing, no testing is required.
  10. If after a race, any racer within that division or a presiding WWL staff member wishes to have the race validated by testing, all placing racers will have their DPV’s tested immediately. The after race test is used to validate the race and all previous tests are considered void. It is important for racers to know their DPV’s and how they perform with different levels of battery charge and after use. If a placing racer exceeds the pull test limit for their division, they are disqualified from that division. If they exceed the division limit by five pounds or less, they are eligible to race in the next higher division or be considered for placement if both divisions ran simultaneously.
  11. When reasonable WWL staff will not start the next division’s race before the previous division’s race has been validated.

 

Pull Test Procedures

To a reasonable extent, the process of pull testing DPV’s will be made consistent, transparent and public. All test results will be publicly stated at the time of testing, recorded and made available for all racers to review while at the event.

  1. When possible, the same area will be used for testing throughout the event.
  2. When possible, the area will allow for at least five feet in front of, behind and to both sides of the DPV while testing.
  3. Each DPV will be attached to the pull rope by either its tow cord or a similarly attached bridle that allows an even pull away from the rope.
  4. WWL staff or the racer at the direction of WWL staff will hold the DPV at arm’s length perpendicular to the DPV and trigger it.
  5. All testing will be performed for maximum thrust possible. This will usually be the highest pitch of an adjustable propeller and maximum RPM.
  6. The DPV will be held far enough under the surface so as not to pull in air, but reasonably close to horizontal.
  7. A relaxed hold on the DPV will be used so as not to influence the results of the test or give the appearance of influencing the results of the test.
  8. Once the DPV is at full thrust and all slack is out of the rope, the person holding the DPV will announce “Full Thrust” to signal the person checking the scale to take a measurement.
  9. Once at “Full Thrust” a constant pull measurement will be noted. If a constant pull value is not obvious, official value will be measured at ten seconds from “Full Thrust” declaration.
  10. If a racer will be using multiple DPV’s not attached to each other, each unit will be measured independently and their sum used to determine division. If some or all of the DPV’s being raced are attached to each other in a rigid frame, and will remain attached during the race, those DPV’s can be tested as a single unit.

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