Well Dressed for Maine

©2010 Jeffrey E. Isaac, PA-C

In the classroom discussion of hypothermia, I like to introduce the mechanisms of heat transfer by asking the students to grasp a metal table leg with one hand, and place the other hand on a book or the wooden tabletop. When asked which one is colder, they immediately respond, “the metal”. Someone usually then points out that both objects are really the same temperature, its just that the metal feels colder because it conducts heat energy away from our hands much faster than the less dense wood or paper. Likewise, the tabletop is not really warm; it just conducts heat energy much more slowly.

Conduction, that is the movement of heat energy between objects in contact with one another, is just one form of heat transfer. When dealing with cold weather, we also must consider convection, radiation, and evaporation. Convection refers to heat transfer by moving air. Your convection oven, humming quietly down in the galley, is transferring heat energy from the electric coils to the swirling air in the oven box and then to your cinnamon buns. You feel the heat of the sun on your shoulders by way of long-wave radiation. No direct contact or air is necessary. Evaporation takes advantage of the need for water to absorb a tremendous amount of heat energy as it turns into a gas.

Heat energy moves from warmer objects to less warm objects. Sitting in your cockpit on a cool Maine morning, you are the warm object. Some heat energy is radiating from your exposed skin into the surrounding environment while a lot of heat is being conducted directly into the stainless steel winch you’re sitting on. This probably feels pretty good right now, since you were a little warm in your cocoon in the forward cabin and you have a fresh bun in your belly. You appreciate the delicious chill of the light southeast breeze scuffing the still water around your Grand Behemoth 65 Luxury Motorsailer. Live is good.

As you take another sip of coffee, you are mildly annoyed by a sudden shout and splash from across the anchorage. The instructor aboard an Outward Bound open sailing ketch has just jumped into 50-degree water to demonstrate that life is even better with a little morning discomfort. She is on a completely different boat, having been a little chilled all night in the fog and then immersed in cold, dense water. Emerging from her dip, evaporation takes hold with billions of molecules of water absorbing hundreds of calories of heat energy from her skin as it vaporizes in the morning air. The light wind increases the rate of evaporation, and adds to convective heat loss. The heat transfer is so efficient that she has already begun to shiver. So, why is this woman smiling?

First, she is being paid to look tough. Second, her duffel if packed with the right clothing to deal with the environment she’s sailing in. She knows how to control conduction, convection, radiation, and evaporation, and will soon be as warm and comfortable as you are.

Effective insulation protects you from direct contact with cold, dense substances like water and steel, restricts the movement of air, and minimizes the effects of evaporation. It works by trapping air between you and the cold. It will be versatile, allowing you to vent heat when necessary to avoid the need for sweat. Finally, it will be easy and comfortable to wear and pack, or you won’t use it.

You can’t see it from where you are, but madam instructor is sitting on a small closed-cell foam pad as she’s toweling off. This type of low-density insulation won’t compress under her weight, keeping her a comfortable distance from the cold deck. Her first layer of clothing will be thin polypropylene, essentially soft-spun plastic. She’s not relying on this for insulation, but to wick moisture away from her skin to the outer layers where it can evaporate without cooling her. Her brand is Patagonia Capilene, but there are lots of others.

Suddenly, she’s looking right at you, causing you to drop your binoculars in embarrassment. You then realize she’s actually studying the clouds beyond you as she selects her next fashion statement. Out comes a loose, synthetic pile pullover. This is the fluffy loose-spun polypropylene insulation layer designed specifically to put distance (loft) between her and the cold rain and wind. Its fabric will also trap most of the radiant heat leaving her skin. It is loose fitting with a large neck opening to ease installation and removal. There are no heavy rayon or cotton cuffs, waistbands, collars, or elbow patches to get soaked and cold. The garment is 100% polypro – which will absorb less than 0.5% of its weight in water.

In the “old days” she would have worn wool for this purpose, maybe over silk long underwear. But even these historic fabrics don’t compare. Wool will retain about 17% of its weight in water, and silk about 6%. Cotton has no place in protective clothing in a wet environment. When kept absolutely dry, cotton is a fine insulator, but when wet it is absolutely useless. It works best as a bar towel.

The instructor’s pullover, being of very low density, offers good loft but no wind protection – it’s not meant to. The lightweight nylon shell she puts on over it will control the conductive heat loss to the wind. This jacket has a drawstring waist and a collar with a hood, and Velcro closures over wide cuffs allowing her to almost completely trap warmed air in the insulation layer beneath. There is even a small patch of polypro to protect her chin from contact with the metal zipper-pull. The full front zipper and zippers in each armpit, along with the loose cuffs and draw strings openings, will allow her to easily vent heat through conduction from the insulation layer when needed.

By virtue of her profession, this woman has access to pro-deals on every imaginable type of outdoor equipment. But, what you see her using is simple and task-specific. Her jacket does not sport anything in the way of spiffy but dysfunctional extras like absorbent material in the cuffs, collar, waistband, or even logo patches. She also knows that the more expensive combination garments like fleece with a wind block layer, or pile jackets with a heavy cordura shell, will absorb and hold more water, aren’t as versatile, and certainly don’t pack as well.

Her bottom layers are similar, with nylon pants over wicking and insulation layers. The outer shell pants do not have an elastic cuff on the bottom. Instead they are full width cuffs zippered to the knee. This allows her to vent when necessary, and put them on or off over her sea boots.

Only when the rain starts will she go to full foul weather gear to keep dry. Even if she gets completely soaked, as she did during her capsize drill last month, this outfit will keep her warm. You, on the other hand, with your cotton sweatshirt and canvass shorts will have to stay below and watch movies on your iphone until the rain stops.

To learn more that you ever wanted to know about the science of clothing, try Secrets of Warmth by Hal Weiss, Cloudcap, Seattle, 1992. ISBN 0-938567-32-2. The book is a bit old now, but the principles are timeless.