8/8/2019 Speaking Good 'Boat'- by John Winters

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Speaking Good Boat

By John Winters

In Partnership With Swift Canoe & Kayak

2394 Highway 11 North RR#1

Gravenhurst, Ontario Canada

P1P1R1

Scribd Online Database Series

December 2010

2010 Swift Canoe & Kayak/John Winters. This document is not to be printed, distributed, sold for profit, or used inany capacity outside the Scribd document database without the expressed written consent of Swift Canoe & Kayakand/or John Winters

8/8/2019 Speaking Good 'Boat'- by John Winters

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Speaking Good Boat

By John Winters

How long is a long kayak? How wide is a wide one? How fast is a fast one? Who cares?

If kayak symposium conversation is an indication, paddlers care. Nevertheless, paddlerspersist in using hopelessly inadequate terminology to describe boat characteristics."Fast", "not fast", "wide", "narrow", "stable", "tippy" are but a few terms that havenebulous or, different meanings to different people. Naval architects long ago recognizedthat something better was needed and devised terminology uniquely suited for talkingabout boats. Unfortunately they kept it to themselves. While the uninitiated weremumbling around in an indefinite verbal haze, naval architects were nattering aboutcoefficients and dimensional ratios. Most canoe and kayak designers avoided the issue byimplying that small boat design was an arcane art form understood by only a few andunintelligible to mere mortals.So, at the risk of being drummed out of the Society of Highly Secretive and Mystical

Kayak Designers, I will break ranks with my brethren and reveal hitherto inviolatesecrets. Master this terminology and you too can speak "Boat" with the most erudite ofpaddling sophists. In fact, you might become better at it than some who came by theirmemberships under dubious circumstances.

Let us start with How long is "long"? Builders like to use overall length because itsounds better to people who want lots for their money. The length that counts is thewaterline length because it is the prime factor in boat performance. For kayaks, this isusually a lot less than the overall length. Some traditional designs have as much as twofeet of skinny boat hanging out over the ocean. It looks pretty but it doesn't do much.people who speak good Boat always say waterline length.That's a good start but waterline length doesn't tell us the whole story. We also need toknow how fine the boat is. For this we need a ratio and the important ratio is between thewaterline length and the displacement. (displacement is the total weight of the boat andits contents). Why displacement? Because boat resistance is heavily influenced by howeasily water is pushed apart and drawn back in to fill the hole left by the passing boat.The longer the boat is relative to its displacement the easier it will be to drive through thewater.To give us a nice neat number for comparative purposes naval architects divide thevolume of displacement by the length (on the water remember) cubed. i.e.

There is something neat about this equation. It doesn't matter what set of units you use(metric, English, or Biblical). So long as the units are consistent the number is always the

same. Such formulas are called non-dimensional formulas and are useful in a world thatcannot agree on how long anything should be or even how to measure it.The number is called the fatness ratio and ranges from .63 for long light boats to 1.8 forshort heavy ones. The average loaded touring kayak is around 1.3 to 1.4.

Now, how "wide" is "wide"? For this we abandon the usual maximum beammeasurement for the same reason we abandoned overall length. The important part is inthe water so the critical measurement is waterline beam. So, is a 24" kayak wide? Well,

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yes, if it is only 12' long. On the other hand, 24" isn't very wide at all for 17' long boat.What we want then is another ratio and this time it's the ratio between length and beamor L/B.

The typical range for kayaks is about 11.0 for sprint racing kayaks to 6.0 for the stubbylittle boats designed for the terminally frightened parent. The higher the number thenarrower the boat.Something we hear a lot from builders is how low the wetted surface is on their boats.This is important because low wetted surface means low resistance. But how low is"low". Here the ratio is the wetted surface area divided by the cube root of volumedisplacement squared. All the mathematical manipulation is to provide a non dimensionalnumber. The formula looks like this;S

2 3

where S is the surface area and is the volume of displacement.A low wetted surface ratio is around 8.0 - a high one is 9.5.We hear a lot about high volume and low volume boats. Here I will step on some toes.The terms are meaningless. What counts is the designed displacement or, how much

weight the boat was designed to carry. A properly designed kayak will have enoughvolume to carry the people and gear without emulating a submarine. Having more is noadvantage and having less is poor design. Unless one is partial to squirt boats, it isdifficult to design a sea kayak that won't have enough room for more gear than any wellheeled paddler should own.

Is there a magic number for this? No there isn't. All one needs to know is the designeddisplacement. If it fits you and your gear then it's right. If it doesn't, it isn't. So the magicwords are "designed displacement" not high or low volume.

Hand-in-hand with volume is "depth". Kayaks with a lot of depth are supposed to be highvolume and those with less are supposed to be low volume. Unfortunately depth is a poormeasure of internal volume. The cross sectional shape of the deck (elliptical, pyramidal,hyperbolic, or parabolic) has a greater influence on volume. In fact, depth doesn't tellmuch about anything. The nice thing about this is that you don't have to know any newwords.

So, master the words and formulas and you are well on your way to being bi-lingual.