Determining Kayak Classifications

Sound Rower’s Kayak Classifications: Tom Cartmill’s System

The present system was adopted around 1995. The categories are based not on overall dimensions but on waterline length to width ratio:

  • SK or touring Sea Kayaks < 9.25 : 1
  • FSK or Fast Sea Kayaks 9.25 : 1 to 10.99: 1
  • HPK or Hi-Performance Kayaks > 10.99 : 1

How are waterline dimensions determined?

  1. Sea Kayaker magazine reviews of boats- they always measure the waterline dimensions
  2. Canoe & Kayak magazine – annual review of all the models to get overall dimensions as a reference point
  3. Manufacturers information – some supply it (not many unfortunately)
  4. Tape measure – actually very accurate if you read on

The classification list now has some 217 boats listed. Sea Kayaker magazine has been a valuable resource for the boats they review. Some manufacturers give waterline dimensions. A number of older boats or those not evaluated by Sea Kayaker I have personally measured with a tape measure and paddled.

There are still dozens of boats on the market not on the list as there is no ready way to measure them. Most are manufactured on the east coast or Europe and they have not appeared at any races.

Recently (2004) I’ve gone back and listed additional information for every kayak evaluated by Sea Kayaker magazine since 1996 when they began to include a measure of speed vs. resistance measured in pounds based on something called the “Taylor Standard Series”. I looked at the number applied to each boat at 6 knots which is the highest speed they evaluate (some of the slower SK boats have numbers so high as to preclude most paddlers ever reaching 6 knots).

A faster boat should have less resistance, be easier to paddle, at high speed than a slower boat. An interesting fact is that most boats take 50% – 60% more effort to paddle at 6 knots as compared to 5 knots. Which demonstrates how much work it takes to be a good racer. Of the 217 boats we list, Sea Kayaker has provided these Taylor resistance numbers for 71. Less than half, but a reasonably large sample.

I sorted the list from the lowest resistance number (e.g. least pounds of resistance) to the highest. I assumed I would find a couple boats that would overlap between SK and FSK. I was surprised that there was no overlap at all between classes. Some were certainly very close, but every single FSK had a lower number than all SK and the only two HPK came in with the two lowest numbers. So this would seem to support that our classification by waterline dimensions does translate into speed.

The Margins

Ten years ago the breaks between classes were more distinct. No SK boat was over 8.9:1; all FSK were 9.7:1 up to 10.8:1 ; no HPK was under 12:1. There are now a number of FSK down to 9.5:1 or 9.4:1. I would suggest we leave the breaks as is, with some latitude to error up and down for an individual boat that is right on the margin. Maybe have some trusted Sound Rowers members paddle it to compare to known SK or FSK boats and decide where it should go. I guess we just have to agree to be less than perfect. At the 2003 Annual Meeting they decided to go strictly by the numbers, no overlap. Not perfect, but what is?

Tape Measure

Quick note that using a tape measure to determine waterline dimensions is actually fairly accurate. I have in a number of cases measured a boat this way, only to have Sea Kayaker later perform their more sophisticated tank test measures. I often find I’m within 1%; at most I’ve been off by 3.5%. Thus far I’ve not placed a boat in the wrong class.

It is a relatively simple process to measure a boat. You first measure the overall length and width. The widest point is generally at the cockpit. I then assume a draft of 4 inches deep (almost all boats Sea Kayaker tank tested came in from 3.5″ – 4.6″ deep). You “eyeball” where the stern and bow hit the water and deduct that from overall length. This can vary from less than a foot to as much as 3 or 4 feet. For width, I use a yard stick held perpendicular at the cockpit to judge how many inches narrower the hull is at the waterline. Crude but effective.

Race Director Education / Racer Education

I think it’s not to much to ask that the race directors and/or the racers please verify their class from the list we post on our Web site.

The idea that all “long narrow” looking kayaks are FSK and that all shorter “less sleek” looking kayaks are SK is just not true. You can see on the list that some boats (e.g. Nimbus Lootas) almost 19 feet long are SK; while some boats (e.g. Wilderness Systems Epic) only 17 feet long are FSK. The designs vary substantially.

Sorry for rambling on. Unlike rowing shells and most HPK boats designed for racing where overall length and waterline length are almost the same, sea kayaks are not usually designed for the primary purpose of racing and the designs are all over the map. Looks are deceiving. Both race directors and racers should be encouraged to use the classification list. It’s on the Web. It could be posted at each race. Racers are asked to list their make and model when they register. They could verify their class.

I appreciate it is a tough issue.

Tom Cartmill, 2004