Cold weather/cracks in plastic

[ronaultmtd]

I broke one of my kayak loaders made from schedule 40 PVC 1 1/2" pipe with the weight of my kayak on it-something I built it specifically to do and have used this loader for a full summer-but this time it was brittle due to the cold- that got me thinking about our kayaks and the nature of plastic- linear poly used by the majority of manufactures of kayaks is tough, durable (but heavy) plastic. To cut down on the weight of the kayak, they roto-mould it thin in some places and thicker in stress areas. The kayak was designed to be used in the water when most folks fish- hence warm weather- see where I am going here?

Think about the folks who are reporting cracks- hard-core, fish all the time warrior types- they wring out their equipment to the max- add three basic conditions- prolonged heavy use, cold weather, waves and stress from bouncing around on the water- the loss of elasticity in the plastic combined with the stress factors could be the reason these kayaks develop cracks when exact same models used by other anglers never develop cracks-

...or I could just be full of beans and be completely off base-

[J.A. Veil]

Most plastic kayaks are built pretty tough. That doesn't mean they are fail-proof however. Ron makes a good point about cold weather stress. I don't think that water temperatures in the 30s (the lowest water temps we are likely to experience) should cause much problem. But if you store your kayak outdoors in very cold air (like we get most winters), then bump or drop the kayak, it could result in some small cracks.

Most plastic compounds contain phthalate esters, which serve as plasticizers and give plastic some degree of flexibility and bendability. Prolonged exposure to sunlight cause plasticizers to move out of the plastic and vaporize (for example, new cars often get a film on the inside of their windshields after sitting in the sun for while. The esters vaporize from the dashboard and create a film on the inside of the windshield).

Repeated flexing of certain areas can introduce cracks or other openings. Last summer I reported on a hairline crack that developed near one of the scupper holes on my Native Manta Ray. In retrospect, I think the stress was caused by my entering and exiting the boat with one end on the beach and the other in the water. For those short periods, the middle part of the boat was supported by neither water or land, allowing the kayak to flex slightly in the middle when my large mass pushed against the hull while getting in and out. Even a hairline crack that is not obvious unless you go looking for it can allow several gallons of water to enter the bilge area during a 2-4 hour trip.
I have since modified my entry and exit moves to allow the boat to be fully supported.

[ictalurus]

A lot of polyethylene plastics have lower temperature use ranges around -20 to -60*F (based on some of our lab equipment), but I don't know how that lower range changes with time. I think UV damage may be a more critical factor for affecting brittleness, which may also affect the lower temp range as well.

The cracks developed during the summer for all the hulls I had crack except the last one, and I store my yaks in a shed so they're protected from UV damage. I didn't fish in the winter with most of them, but I did push hard into waves. I think it was primarily a design flaw in the mold combined with some issues with certain colors, at least for the Hobies. The plastic in the front of the drive well was so thin in the ones that broke that the outline of my finger was clearly visible through the plastic when I put my hand in the front hatch and reached to the drive well.

You're right about the hardcore types, though. The defect probably took a certain number of hours to fail, and the avid anglers hit that threshold faster.

I think Hobie now puts brass inserts in the crack-prone areas to attract more plastic during the rotomolding process and may even weld in extra plastic after the yak cools.

[DOGFISH]

That would probably be a good question to pose to a kayak manufacturer. In years past, I had a roto moulded canoe. On one cold spring morning we were going crappie fishing. The canoe slid and fell onto the tailgate of my pickup. It punched an almost perfect round hole into the bottom of the canoe. At the time we also thought about the cold.

I know UV does take its toll. I keep my kayaks in the garage. However, even with the sun exposure from fishing outings, one can see the difference in color of the plastic. I know with certain plactics, the darker the color the more UV resistant they are said to be. Anyone around here a plastics engineer?

[Southerly]

i agree on everything above. in WindSurf gear, weight was very critical and some gear was prone to breakage, some seemed overweight etc.

what i discovered was that design of consumer gear pivoted around the need to achieve an acceptable warranty liability. paying for local repair could be disastrous for the mfr depending on the particular amt of time/quality of work done there, and shipping cost for return to some central repair would also be disastrous.

i expect it's similar with kayaks. they would like to sell very lightweight gear, but must balance that with required toughness.

otherwise, i spoke to a hobie rep regarding drive-well cracks prior to purchase of my outback. his 1st question was 'what year and what color was the yak?'. the plastic is some sort of PE but it's likely to be a propietary blend of new/recycle PE along with colorants, and who knows what else. more virgin PE is stronger, but costs more. a high ratio of some colorants or other 'fillers' may also reduce strength.

from what i was told, i think the 'whiter' colors have more of something added to make them opaque and that may have aggravated hobie's particular problem (now solved for all colors as i understand it).

in any case, i would try not to throw yaks around, particularly in winter, or sit in them on dry land etc.

[Meadeo]

Hmmm..

Makes me want to rethink my outside storage of kayaks atleast to a location in the shade... I would hate to weaken my gear just by leaving it on racks outside in cold weather and in partial sun..

For those of you who don't have space in doors for storage of yacks what sort of storage have you come up with to protect from excessive UV damage?

I was thinking about building something this spring as a more secure and light protecting storage compartment for my boats..

So far i have yet to get any cracks in the cold weather or warm weather otherwise but i would like to do my best to avoid any as well.

Meadeo

[Southerly]

my old sit-in kayak is at least 10 yrs old and always stored under the deck upside down. seems fine and not 'bleached'. the outback is generally kept outside, but under a piece of tarp. i wanted to add a couple grommets to make the cover easier/better to use but haven't made the ffort so far.

but currently, the outback is in the house in my playroom getting custom work. crate tie-down, battery securement, new x-ducer mtg,...

[Yak Fish]

I had an orange 2007 outback that developed the drive well crack. I now have a 2011 in the ivory dune color. Because I'm now paranoid about it happening again, I wrapped the tips of the mirage drive where it presses on the drive well with a foam rubber bumper. It seems that no matter what Hobie does in that location, short of filling the whole thing with plastic, that the constant rubbing of plastic on plastic will cause some fretting and cracking over time, especially when you use them hard and in all conditions like most of us.