ILL AVOID SUGGESTING THAT Marcuss real name is Chrisoula K. Youd understand the joke only if you were familiar with the wrecks of Shaab Abu Nuhas in the Red Sea - and thats one place where youll have no need of a heated undervest.
Marcus at OThree has developed this vest, or HUV, in response to those people who became chilled during long hangs after deep dives in temperate waters.
In fact, while I was being shown this product, a young man who was off to Antarctica to continue filming killer whales hunting unfortunate seals was picking up a new HUV to take with him.
I confess that I dont do that many dives in colder waters. When we get two invitations, one to dive in Sweden and one to dive in PNG, I always ask whos going to Sweden.
In fact, the last time I used a heated undervest of any sort was during a coldwater regulator test in Swedish waters in winter, and the sight of me strapping on the vest elicited cries of disdain - not for the vest, but for me - from my fellow-divers.
Wearing that heated vest required me to cut a hole in my drysuit to install the connection cable between it and the off-board battery-pack, which was un-nerving to say the least!
This one is different.

Installation
The attractive part of this HUV is that you simply install the special combined inflation valve and connection conduit provided, in place of the Apeks one you probably already have.
Full instructions are provided, but its not as complicated as assembling something from IKEA.
The inner side has a lead and connection that simply plugs into the vest. The outer side has a lead with a wet-connector that is connected to one of a range of Custom Divers battery-packs.
You put the vest over your head like a tabard and fasten it tightly with the two Velcro-covered flaps provided.
The vest is worn over the base-layer undergarment such as OThrees PBB, and connected to the lead on the inside of your drysuit before pulling the suit over your head. The connection is protected against damp from sweat.

Power Supply
It takes four hours to charge fully the smaller of the Custom Divers 12V batteries available, at 3.7A/hr. This battery is promised to run the vest for around 70 minutes, so those on long dives might need to switch it on when they are getting towards the end of the runtime.
A battery twice the size lasts twice as long, but I found that this little battery stowed easily without resorting to mounting it on my tank, and sufficient length of lead was supplied to allow for plenty of options.
The outer connection between battery-pack and HUV is a wet connector, so you dont even need it to be connected to the battery until you want to use it.
This might suit cave-divers, or those long-duration divers happy to leave the battery-pack, or a series of them, en route.

Switching
The centre part of the OThree inflation valve is pressed as normal to allow gas to flow from the suit direct-feed hose. The outer ring is rotated as a switch. It has two clicks to take it to the on position, which avoids confusion as to whether it is on or off as you await the warming effect.

Efficacy
The heat from the HUV is nicely diffused through the base-layer garment, and it certainly is effective. Although the heating elements also cover your shoulders and chest, it noticeably warms those parts of your body containing your liver, kidneys and stomach.
I found that I needed to turn it on only for the occasional five-minute period, although it never seemed to get too hot. However, when I switched it off I soon noticed the difference as I cooled down. If you find yourself getting cold on dives, it could well be the answer.
This said, it is yet another item of kit to have to look after. The battery will need charging every day you dive. You wouldnt use it if it was not strictly necessary, and OThree recommends that you keep your standard inflation valve for use on dives on which you dont need the HUV.
I was surprised to find that I needed as much ballast with this HUV over a single base-layer combination as I did with a thick, duvet-style undersuit. It works out rather expensive, too, when compared to a similar item intended for motorcyclists. But then, motorcyclists dont get quite as wet as a diver who floods his drysuit. n

COMPARABLE UNDERVESTS TO CONSIDER:
Typhoon Icebreaker, £499

SPECS
PRICE £575
BATTERY 12V, 3.7A/hr
BURNTIME 70 min
SIZES One-size
CONTACT www.othree.co.uk
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