Material Observations

[OKreally]

There have been a few question recently about materials recently so....

 

I thought I'd endeavour to give a general description of the various materials that kayaks are made from - a couple of posts have raised questions about strength, durability etc. Before I start let me say that we (Johnson Outdoors) make canoes, kayaks or both out of all these so I have no particular axe to grind for one material or the other. The adage horses for courses has never been so appropriate & there is also the cost factor to take in to the equation.

 

1) Polyethylene - the most common material for kayaks & canoes (US definition would be Eskimoes use kayaks, ethnic North American Indian use canoes. I'll talk mostly re the sit-on-top kayaks that are most used by the kayak anglers

 

Polyethylene is usually roto moulded - that is a measured amount of the material (most regularly monolink polyethylene) is placed inside two halves of a female mould that make up the shape of the boat, heated to a melting point in an oven then rotated & tilted to coat the inside to create a one-piece seamless shell with the thickness computer controlled to dictate greater or lesser thickness where required. Fittings such as the inserts for attaching accessories can be placed inside the mould before moulding begins to allow them to be encapsulated so that there are minimal holes needed to attach further toys later. A controlled cooling process ensures that the boat retains it's shape & thickness & fittings are added when it has cooled & been freed from the mould.

 

It has the advantages of being one-piece having no hull to deck join, very strong in that it bounces off most obstructions (Rolls Royces are an exception I believe!) & can be supplied in most colours. Once the tooling has been paid for the high number that can be produced from this ensures that the cost per boat is lower than most of the other materials available...certainly in terms of years of use they're probably the best value for money around - also reflected in high second hand values!

Downsides are it's a little heavy & not as stiff as some other alternatives but the fact that virtually all the world's manufacturers use it would indicate it does most things for most people. Other derivatives are triple or multilayer set ups - we use these in the open (Canadian style) canoes. This has a hard-wearing layer on the outside, a foam layer in the middle & another layer of polyethylene on the inside. This creates a stiffer, lighter shell that has good sound deadening qualities (we also use it in some of the Old Town sit in kayaks) but is more expensive & more difficult to mould intricate shapes in to. It's also, in common with rotomoulding generally, a less exact science. Each year manufacturers learn more about rotomoulding but there will always be small vagaries caused by temperature, humidity etc on the day...I'd add that this applies to all plastic moulding.

 

2) Thermoformed polyethylene - as used by Bic or by ourselves in our Waterquest canoes, pedal boats, fishing tenders etc etc - sometimes called twin-sheet construction. These are made by taking a rigid sheet of polyethylene, softening it by heat in to a mould that makes up the top or the bottom moulding of the kayak. These two halves when cooled are joined by a number of methods...they can be welded as in the Bic or Pelican kayaks or flanged then stapled & shrunk on to a mastic bed & encapsulated by a fender plastic as we do with the Waterquest Dinghies, Basstenders etc. Both work...backings for fittings can be attached to the inside of the mould before top & bottom are joined together.

 

Advantages are it's quick & cheap to make, quite stiff (on a par with rotomoulding) & a little cheaper to tool for.

 

Downsides - It suffers from being more brittle & less bounceable. It's also difficult to get a variety of colour in to - you're generally restricted to the colour of the sheet you buy & there is always a small danger that what started as two pieces can become so again. Again it's difficult to get sophisticated shaping in to the moulds so the designs are generally quite simplistic.

 

3) Fibreglass - I use the term loosely as there are many forms of this material varying in sophistication & content but all use essentially two female moulds for top & bottom that are laid up seperately & then hull & deck are joined together. Some are 'vacuum bagged' where the resin is drawn through the woven fibres that make up the material portion of the glass by creating a vacuum that the resin then fills - this should ensure that the roving has an even & fully saturated spread of the resin allowing the minimum amount to be used so as to save weight. Fibreglass generally achieves all it's waterproofing qualities from the 'gelcoat' that is the first coat applied to the moulds - the skill of the laminator/sprayer will again dictate the evenness & weight of this coat...again it's usually one colour - often white as pigment adds weight to gelcoat. Exotic materials can add strength & stiffness & also save some weight - carbon & kevlar are among the most commonly used but add a large percentage to the cost. We build Necky sea kayaks in excess of 22ft long in various combinations of the above & various canoes in the numerically lower selling ranges.

 

Advantages - a mould is by far the cheapest of these discussed to make so in line changes can be done quickly & cheaply.You can ask for custom alterations as the boat is being built. The boats are stiffer than the polyethylene so feel positive to paddle but the BIG sacrifice is ability to take abuse. Gelcoat chips easily (we've played recently with a two part baked on paint to see if it's any better) & the stiffness that makes it nice in the water means you have to take a lot more care beaching, crossing rocks, loading & unloading etc - if the gelcoat chips that's the only waterproof bit of the lay up so water can add weight & take a while to dry out before repair. Weight is less but to get anywhere near the strength of the poly boats it could be laid up to be a lot thicker but probably heavier so defeating the object

It's not great to attach things to but as long as you get inside & reinforce with glass or load spreading washers or plates it can be done. I should add that it's the most repairable of the materials - cosmetics & strength are down to the skill of the repairer who gets a fair bit of practise! The cost of boats in this material appears (& is) high largely down to the high portion of labour content in manufacture & fitting out.

 

Which leaves...Royalex - a very light, stiff heat formed sheet that is vacuum formed in to a mould when hot. It's very stiff & arguably about five to ten times stronger than fibreglass (a derivative is used in US army helmets) It's also very expensive as the company that owns it has a monopoly & it is expensive to tool for & difficult to work with. We make top of the market canoes & kayaks in it - no sit-on-tops yet!!

 

Aluminium- mostly used in canoes..not much to add as it's not really relevant here.

 

Wood...looks lovely...again see above for relevance!

 

Birch Bark & canvas...yep - we still can make them but it's usually for film companies these days.

 

Hypalon, cordura, nylon, rubber etc inflatables!.....answers the question that none of the others can - 'Will it go in my boot, locker, cupboard etc. They're much better these days but you buy them to answer the question above - you don't buy for performance or durability!

 

There are others but not really relevant in this market. I'm sure that some people will add to this or take issue but it's supposed to be a general overview - I've already declared that we make in most of these materials so any criticism I make is equally applicable to our own products. My own background has always been in boats & a boatyard building wood, fibreglass & steel boats was first stop when I left (navy) school so I hope the opinions are based on a bit of experience.

 

Cheers

 

Andrew

(Johnson Outdoors UK)

[SpeciMan]

Excellent post Andrew.

 

Only yesterday I was reading up on kayak design and materials and came across another good article. It also covers the pros and cons of different materials (about 2/3rds down the page) and the rest of the article talks about kayak design, stability etc.

 

Rogue Paddler - How to choose the right kayak

 

Simon

Edited July 15, 2007 by SpeciMan

[Mark Crame]

I found that absolutely fascinating - thanks for that.

[GB]

Plastic is great for rough and tumble stuff but you gotta love a composite for performance and feel. Maybe one day someone will come up with a wonder material that gives the best of both.

[Simon Everett]

Rough and tumble and feel together - you been playing with your missus again?

[GB]

Rough and tumble and feel together - you been playing with your missus again?

 

 

STEADY, Down boy

[*Blaze*]

Good post thanks for taking the time to write it