How The Body Loses Heat when Fishing.

In order to purchase appropriate Warm clothing you must first understand how the body loses heat.

The Body loses heat through:
Conduction - Convection - Evaporation - Radiation

  • Conduction:
    Conduction is the transfer of heat from a warm object to a cold object when the two objects are in contact with each other. This can include rods, reels, dip nets (hands), sunglasses or goggles (face).

    Fishermen experience conductive heat loss when the body is in direct contact with a cold surface, sitting or standing. (through the feet)

    Conduction is also a major source of heat loss in wet clothing.

    Conductive heat loss through the hands is well documented. This occurs when the blood vessels in the hand constrict while gripping an already cold objects.
     
    • Conductive heat loss can be minimized by:
      Using an insulated cushion or seat when sitting. Heat cushions that maximize dead air entrapment by minimizing passive convection within the pad are very effective.

      For the Hands the best prevention against conductive heat loss is the use of minimally compressible insulation in the palms of your gloves or mitts with easily compressible insulation for the back of the hand (to minimize weight and maximize warmth). Mitts are the better choice.

      Heat loss through the feet (and specifically, through the soles of your shoes or boots) simply requires a barrier between your bare feet and the surface.

      This barrier should include socks, insoles, and the sole of your shoe or boot.

      Thin poly-pro or silk socks under a minimal compressible sock made with a high-density merino wool, combined with insoles made of closed cell foam or loden (felted) wool provide good in-shoe protection.
      Shoes with thick mid-soles and those with lugged soles (which minimize direct contact with the cold surface) provide the basis for good winter footwear.

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  • Convection:
    Convective heat loss occurs in response to movement of a fluid or gas.
    The two types of Convection Loss are Active and Passive.

    In outdoor clothing, convective heat loss occurs when warm air next to the body and in the clothing is displaced by cool air from the outside environment.
    Windproof clothing, worn over insulating clothing capable of trapping dead air air in its thickness, provides reasonable insurance against convective heat loss.
     
    • Active Convection:
      The biggest factor contributing to convective heat loss is wind, especially when the boat is moving.
      Consequently, a wind proof jacket should be standard ware.
       
    • Passive Convection:
      This occurs by the “chimney effect” that draws cool, dense air into our clothing system from pants cuffs and waist hems, displacing warm, light air that exits out of our neck and cuffs.

      Passive convection can be better controlled with garments that includes plenty of ventilation options.  Clothing with a hood and adjustable cuffs and hems that can be fully opened or fully closed provides the most versatility – tighten the cuffs and hems to preserve heat and loosen them up to vent heat and cool down and minimize overheating.

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  • Evaporation
    Evaporation occurs when a liquid (such as sweat) changes phase to a vapor (sweat vapor). This phase change requires heat. Unfortunately, your body heat drives this phase change. Evaporative heat loss may be most noticeable in context of the “flash-off” effect, which occurs after a period of intense physical activity and sweating in cold conditions, followed by rapid evaporation and chill after stopping to rest.

    Evaporative heat loss from perspiration can occur in one of two ways.
     
    • Sensible (or “active”) perspiration is caused by the formation of liquid sweat droplets at the skin surface in response to excess heat. This excess heat is usually a result of being dressed too warmly for a given activity level.
    • Insensible (or “passive”) perspiration is the direct emission of sweat vapor from the skin in response to a humidity gradient (i.e., your skin is “drying out”). Insensible perspiration is most significant while at rest, or while sleeping, while sensible perspiration is most significant during periods of activity.

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  • Respiration
    Technically, respiration combines the processes of evaporation (of moisture in the lungs) and convection (displacement of warm air in the lungs by cold air from the outside environment). Because humidity in the lungs is 100%, respiration is an important heat sink in cold, dry conditions. Significant moisture (and thus, body heat) can be lost when that moist air is exchanged with much drier outside air. In addition, some body heat is lost to the process of warming the cold air entering your lungs.
     
    • Minimizing Respiratory Heat Loss
      Respiratory heat loss can be significant in cold, dry conditions.  Respiratory heat losses can be minimized by breathing air that has been pre-warmed and/or pre-humidified prior to taking it into the lungs. Breathing through a fleece balaclava or face mask can improve respiratory comfort by increasing the humidity and warmth of air being breathed prior to its entry to the lungs.

      Innovative products are appearing in the market specifically designed to magnify this effect, and are informally known as “heat exchange face masks.”

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  • Radiation
    Radiation heat loss occurs primarily on cold, clear nights, and is readily noticeable after sunset. Radiation heat loss from the body occurs primarily due to infrared emission. Cloud cover dampens the effects of Radiation heat loss somewhat, by reflecting a significant portion of radiant heat back to the earth’s surface.
     
    • Radiation heat loss is most significant between sunset and sunrise, when the atmosphere loses tremendous amounts of heat that was absorbed by sunlight throughout the day. The best defense against Radiation heat loss is thick insulation.
       
      • Minimizing Radiation Heat Loss:
        Unless you fish well into a starlight cold night don't worry too much about Radiation heat loss.
        But if you do or if you are spending the night beneath the cold stars read on.

        Radiation heat loss is assumed by many to be negligible relative to other heat loss (wind-induced convective, respiration and evaporative). However in windless conditions when the body is not active it can be significant, especially at night.
         
        Radiation heat loss can be minimized by one of two methods.
        The first is by wearing a reflective barrier (such as aluminized nylon or mylar) near the skin capable of reflecting infrared radiation back to the body.

        The second is by wearing thick clothing (down or high-loft synthetic fill garments). The latter strategy is effective because infrared radiation cannot travel through thick insulation, and thus, most of the infrared radiation lost by the body can remain entrapped in the clothing system rather than exiting out to the environment.

        Stay Warm On the Water, and always wear your life vest.

      Warm in Wet Clothes?

      Back to Conduction Heat Loss.

      The presence of water in any insulating material results in:

      (1) A rapid conduction of heat from the body over dry material.
      (2) Displacement of air volume that is normally used for effective insulation (dead air).
      (3) Faster evaporative cooling resulting from the use of body heat to induce a phase change from liquid to vapor.

      In addition, the absorption of water into a knit, woven, or high-loft insulation results in a reduction in insulation resiliency caused by fiber structure collapse.

      This effect reduces the thickness of the insulation further and magnifies the effects of (1,2 and 3. )

      Plus the body loses heat 20-25 times faster when wet.
       

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