Although I'm pretty sure 99% of the population will figure it out, I just have to clarify.
Pre-dive
When stating "put hot water" into your suit, only put hot (basically anything over 55 celsius, 131 Fahrenheit) water in if you are NOT wearing your suit. If wearing your suit, I would recommend around 45 celsius or below. Also be aware that if you put in hot water, all your blood will rush to the surface of your skin. When you jump into the cold water all the heat in that blood will be lost to the external environment. You will effectively kill your body's warmth at the beginning of the dive.
My recommendations would be:
Start your first dive in a DRY wet suit. This way, the blood will be kept in the core of your body, and thus you won't lose more heat than is normal for being submerged in cold water.
When finishing your first dive, add WARM water to your wet-suit to begin the warm-up process of your body. As soon as possible, remove the wet suit, store in a warm, dry (well this is debatable - the suit is wet and you are a scuba diver) location. Put yourself in a heated location out of the wind and get your body temperature up. Dress warmly (not in wet garments) for your surface interval.
2nd dive - ensure dive partner understands turn around signals, too cold signals etc.
Jump in wet suit as quickly as possible. Gear up as quickly as possible. Try to do all this in a heated location (if possible) out of the wind (if possible - excuse me as I laugh as this just never happened for me). Jump in water, do a quick 20 - 30 minute dive, run back out and repeat end of dive performance. Jump in car/truck, turn on heater, and scream in agony as the pins and needles of returning blood to hands grips you. Laugh about at bar later that night.
Another piece of advice... do not drink or exercise rigorously right after a cold dive, as due to the decreased blood flow to the peripheries, you are at a higher risk of having nitrogen still absorbed in your tissues for the peripheral areas. The alcohol/exercise will increase this off-gassing (due to dilation of blood vessels) and could possibly (while minimal it is possible) increase your DCS risk. Always dive conservatively, even if using the "10 feet deeper than actual" rule.
I did my first 80 dives in 40 - 48 Fahrenheit (~4 - 8 celsius) water in a wet suit, by following the above I found I was much warmer at the end of the dives (unfortunately it took me 20 - 30 dives to really figure it all out).
Below you can find a table that I found interesting in relation to this discussion:
Table 1: Exposure time at given temperatures that
causes deep second-degree burn injury in adults
Temperature,°C (°F) / Exposure time
44 (111) / 6 h
49 (120) 9 min
51 (124) 26 min
52 (125) 2 min
55 (131) 2030 s
60* (140) 56 s
66 (151) 2 s
70 (151)
*Usual temperature of home water heaters.
Pre-dive
When stating "put hot water" into your suit, only put hot (basically anything over 55 celsius, 131 Fahrenheit) water in if you are NOT wearing your suit. If wearing your suit, I would recommend around 45 celsius or below. Also be aware that if you put in hot water, all your blood will rush to the surface of your skin. When you jump into the cold water all the heat in that blood will be lost to the external environment. You will effectively kill your body's warmth at the beginning of the dive.
My recommendations would be:
Start your first dive in a DRY wet suit. This way, the blood will be kept in the core of your body, and thus you won't lose more heat than is normal for being submerged in cold water.
When finishing your first dive, add WARM water to your wet-suit to begin the warm-up process of your body. As soon as possible, remove the wet suit, store in a warm, dry (well this is debatable - the suit is wet and you are a scuba diver) location. Put yourself in a heated location out of the wind and get your body temperature up. Dress warmly (not in wet garments) for your surface interval.
2nd dive - ensure dive partner understands turn around signals, too cold signals etc.
Jump in wet suit as quickly as possible. Gear up as quickly as possible. Try to do all this in a heated location (if possible) out of the wind (if possible - excuse me as I laugh as this just never happened for me). Jump in water, do a quick 20 - 30 minute dive, run back out and repeat end of dive performance. Jump in car/truck, turn on heater, and scream in agony as the pins and needles of returning blood to hands grips you. Laugh about at bar later that night.
Another piece of advice... do not drink or exercise rigorously right after a cold dive, as due to the decreased blood flow to the peripheries, you are at a higher risk of having nitrogen still absorbed in your tissues for the peripheral areas. The alcohol/exercise will increase this off-gassing (due to dilation of blood vessels) and could possibly (while minimal it is possible) increase your DCS risk. Always dive conservatively, even if using the "10 feet deeper than actual" rule.
I did my first 80 dives in 40 - 48 Fahrenheit (~4 - 8 celsius) water in a wet suit, by following the above I found I was much warmer at the end of the dives (unfortunately it took me 20 - 30 dives to really figure it all out).
Below you can find a table that I found interesting in relation to this discussion:
Table 1: Exposure time at given temperatures that
causes deep second-degree burn injury in adults
Temperature,°C (°F) / Exposure time
44 (111) / 6 h
49 (120) 9 min
51 (124) 26 min
52 (125) 2 min
55 (131) 2030 s
60* (140) 56 s
66 (151) 2 s
70 (151)
*Usual temperature of home water heaters.
