single layer poly?

Hello friends,

I’m set on purchasing a Necky Manitou 14 with the skeg, however I am a little concerned about the boat’s construction. From what I gathered, Necky is now owned by Johnson. I called the customer service line and they told me that the Manitou 14 is made of single layer poly. Should I be concerned about stiffness or durability? thanks for any input.


– Last Updated: Dec-19-12 4:08 PM EST –

Virtually all whitewater kayaks are made of rotomolded single layer polyethylene. Multi-layer poly is actually also rotomolded, but the polyethylene powder is loaded in stages, and the second load is formulated is such a way that it forms a foam core which adds stiffness.

The only problem with single layer polyethylene (solid polyethylene) is that poly is rather flexible. Until recently, few canoes were made of single layer poly for that reason but since kayaks have decks they are essentially tubular and that geometry adds inherent stiffness. Many poly kayaks also have internal foam pillars or bulkheads, which add additional rigidity.

agree - no
Single layer poly is the norm, and what Necky was using before being bought by Johnson Outdoors (which was done many years back).

the three layer plastic boats, like what is used by Valley and P&H, is stiffer, so has some very slight efficiency advantage. Not something which you or I would notice. But being stiffer, the three layer also does not take hard hits as well (likely the reason that P&H came out with a single layer surf spec Delphin).

if it were a canoe …
… like a Coleman RamX , then it would be ridiculed as a junk boat . But since it’s a kayak it’s ok .

There’s a world of difference between an Old Town 3 layer poly canoe and single layer other brand canoes .

I wasan’t aware there are 3 layer kayaks on the market , if so I’d imagine them something more on the line of the Old Town canoes .

many modern high-end whitewater canoes designed for creeking are now made of solid polyethylene.

These include the Blackfly Option, Ion, and Octane and the Esquif L’Edge, Spanish Fly, and Prelude.

Solid poly works quite well for these boats since they are relatively short and most of them are partially decked.

The foam core of three layer poly construction does add stiffness, but the inner and outer solid layers are pretty thin and it is quite possible to wear into the foam core with the repeated abrasion that comes with hard use.

Boats made from solid high density linear polyethylene can also be repaired when cracked using thermal welding. Repair of three layer poly boats is more problematical, so there are trade-offs with either construction method.

learned something today, and feel much better and more confident now. I paddle in Alberta and every shore line is beach deprived here. happy holidays to all and thanks again.

other than design (shape) …
… what would be the difference in the HDPE used in a Coleman RamX compared to the single layer high end (HDPE) creekers you’ve mentined ??

Is it the thickness of the HDPE maybe ??

Is there any way of knowing the HDPE thickness of a given boat , short of personally measuring it . Say if someone wanted to know a Coleman RamX thickness , compared to the Old Towns int. and/or ext. layers , compared to the high end creekers mentioned ??

I know design and performance are part of what makes for the so called high end boats … but is there more to be said about the single layer HDPE used in the high end boats than the single layer HDPE used in the cheap boats ??

Some folks like those Colemans
Coleman made 17 foot long canoes out of Ram-X. Because of the inherent flexibility of non-foam cored poly those boats required extensive aluminum structural supports for bracing including a keelson, multiple aluminum thwarts, aluminum seat frames, and upright aluminum braces extending from the bottom of each thwart and seat frame to the keelson.

With all that aluminum and a boat of that length, the poly had to be necessarily pretty thin to keep the weight down to a non-obscene level. As a result, the sides and bottoms of those boats flex quite a bit.

I understand that linear polyethylene varies quite a bit in density. Some has a specific gravity less than 1 and some greater than 1. I haven’t seen boat makers publish maximum and minimum thickness values for their solid poly boats. All of them tend to claim their material is “the best” without publishing any real scientific information.

Molded polyethylene boats are generally not of uniform thickness. The mold is constructed such that the finished boat is thicker on the bottom and at the stems than the deck, for example. Furthermore, the rotomolding process does not always distribute the molten poly as uniformly as intended so thin spots and voids can result. I know that some makers used to do quality control by measuring the thickness of the poly in various locations using a hand-held ultrasound probe. I don’t know if they still do that.

Some folks think that the blow molding process for constructing solid poly boats results in a more uniform and stronger product. I know that the general consensus was that Prijon whitewater kayaks (which were blow molded) were significantly tougher than similar rotomolded contemporary models made by other manufacturers back in the late 1980s and early 1990s, but they also seemed a bit heavier so maybe it was just a matter of using more material.