How much buoyancy do you need?

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Spikeedog
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How much buoyancy do you need?

Post by Spikeedog » Tue Feb 05, 2019 1:15 pm

"Flotation (aka buoyancy) is the force (in pounds) required to keep a person's head and chin afloat above water. Most adults need just an extra seven to 12 pounds of flotation to stay afloat. Any quality PFD will provide more than this amount, so you don't need to spend much time analyzing this number"

I have been looking at low profile 'racing' style buoyancy aids as the standard ones are bulky and act against you when in the water and trying to climb back onto a sea kayak.

50n seems to be the level of buoyancy specified in many BAs. What's the experience of using minimal buoyancy? Does anyone carry an additional life jacket as an emergency back up?[/size]

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Re: How much buoyancy do you need?

Post by Ken_T » Tue Feb 05, 2019 1:30 pm

The main problem if you reduce the buoyancy of your PFD is in very rough water where you will spend extra energy to keep your mouth high enough up to breath.
Ken

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Re: How much buoyancy do you need?

Post by Chris Bolton » Tue Feb 05, 2019 2:11 pm

I agree that a bulky BA can make pulling yourself across the back deck more difficult, but I don't find it acts against me when in the water, quite the opposite. I also find buoyancy helpful if doing a re-entry and roll. A typical sea kayaking BA also has a lot of pockets - which make it more bulky, but also allow you to keep with you all the things you might need if you get separated from your boat. I'm happy to have the extra buoyancy and spend a bit more time practising climbing back in.

The text just after your quote from the REI website says "Keep in mind when comparing buoyancy numbers that a person’s weight, body fat, lung size and clothing, and whether the water is rough or calm, are all factors that affect flotation." The rough or calm bit is the important part for sea kayaking, I think. Floating with your face just above the water is OK if it's calm, but if there are any waves you're going to find them washing over you and affecting your breathing. If the conditions are such that you need to climb back into your boat, there will be waves!

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Re: How much buoyancy do you need?

Post by Spikeedog » Tue Feb 05, 2019 4:11 pm

Yes. I take all of that. However, if I weigh 10 stone (nearly 11 actually) then I need say two thirds of the extra buoyancy for a 15 stone paddler. As I always wear a wetsuit as a first layer - there's probably an additional 4 or 5 lbs buoyancy there. So if a 50n BA gives you about 12 lbs, that could be more than double what is strictly necessary.....? A few of the racing type, slim BAs still give 50n I think....I'll need to check.

The point about the rough conditions is a good one and spending more time on rolling and re-entry is spot on too.

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Re: How much buoyancy do you need?

Post by Chris Bolton » Tue Feb 05, 2019 4:25 pm

I don't think an adult size BA with less than 50N is legal to sell in the EU. The racing ones are probably close to the 50N while sea kayak and white-water BAs will have more - partly because if the water is aerated, it's less dense and nothing floats as well. A wetsuit does give you buoyancy, but not always in the right place - to float the right way up you want more buoyancy in your trunk than your legs. A 15 stone paddler who is all muscle might actually need more buoyancy, but in at lot of people the difference between 11st and 15st is 4st of fat, which is quite buoyant!

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Re: How much buoyancy do you need?

Post by Spikeedog » Tue Feb 05, 2019 5:15 pm

Ha - great point!

I just find the BA tries to put me on my back and treading water in an upright position and swimming or trying to make any progress through the water is a struggle so I wondered if you could have too much buoyancy.

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Re: How much buoyancy do you need?

Post by Chris Bolton » Tue Feb 05, 2019 5:31 pm

I just find the BA tries to put me on my back
so I wondered if you could have too much buoyancy.
Yes, too much buoyancy in your legs from the wetsuit! You need more buoyancy in your BA to compensate!

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Re: How much buoyancy do you need?

Post by Spikeedog » Tue Feb 05, 2019 5:48 pm

Q E D!! This why I love this forum.

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Re: How much buoyancy do you need?

Post by pathbrae » Tue Feb 05, 2019 6:06 pm

You can retrofit a spray hood to most life-jackets. I wonder if it would be possible to design something similar to protect a kayaker's airway in an emergency situation? Without one the advice is to breath trough hands cupped in front of your nose and mouth to prevent inhaling spray.

I've also wondered about a combined BA / Life-Jacket (I believe RNLI use them??) to give us a bit more protection if we do end up away from our boat.

The OP suggests carrying a life jacket but I'm not sure how easy (or even possible) it would be to put it on once in the water, always supposing it hadn't disappeared with the kayak...

I've never measured or calculated the buoyancy of an upturned sea kayak - but I'd guess, even packed for a trip, it would comfortable exceed the 50n of a standard BA so the best defence will always be to hang onto that kayak
So much sea - so little time to see it.

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Re: How much buoyancy do you need?

Post by Jim » Tue Feb 05, 2019 10:02 pm

All buoyancy aids including race types on sale in Europe have to meet ISO 12402-5, in the US they have to meet USCG rules I think as type V (I have one somewhere, GCNPA require you to have a BA with USCG label to run the grand canyon). Most racing rules, where BAs are required, state that they must meet the ISO standard. At ICF races they randomly spot check with a buoyancy cage, which is available beforehand to check your own kit, so I know my race BA passed last May :)

50N is what the regulation requires for most adults, only children can have less.

But how much buoyancy do you need is actually a pretty open ended question.

An overweight person may well be less dense than an underweight person because fat is less dense than most of the rest of what we are made of, that means that although heavier, they may naturally float higher in the water. I like to think that the ISO standard is based on some kind of research and accounts for the most dense people indentified in a survey!

Now, even if you know how high you naturally float there are other factors that come into play as already mentioned by others.

One thing that touring paddlers and white water paddlers seem to like to do is have pockets full of stuff, most of which is more dense than water so effectively decreases your net buoyancy meaning you will want a bit of extra bouyancy in your BA to restore the balance.

Rough water and how you actually want to float is another consideration, and there are 2 aspects to this. Firstly there is the size of the waves that are going to be splashing you, but if you are in particularly turbulent water e.g surf or a tide race, the water can be quite aerated, literally the turbulence mixes air into the water (which you may notice as froth) making it less dense than calm water, which means the uplift force will be reduced, so you will float lower in the water.

Another consideration in tide races etc. is the possibility of undercurrents or vortices which try to dynamically pull you under the surface in addition the to basic hydrostatic issue of floating, again more buoyancy can help lessen such effects.

I have several buoyancy aids or different types. The one I use daily is a minimal 50N racing type (usually designed to still have 50N after about 3 years - it does diminish over time...), although because it is the XL size it has an optional extra bit of foam which I do have installed which takes to I think 60N? (It is at work, I use it on my lunch break). I use this and another race BA at weekends when racing (why 2 BAs - I race in 2 classes and find it easier to leave my bibs attached all day rather than swapping them over between runs...), I sometimes use it for river running because I prefer freedom of movement and am happy to carry my safety kit and camera in the boat rather than in pockets. I have used it in my sea kayak on Loch Lomond, and in my canoe on a few lochs for similar reasons. I have and will again use it for sea kayak racing, and would probably use it sea kayaking in a group where rescue should be fairly close. If sea kayaking on my own I would probably wear one of my higher buoyancy buoyancy aids simply because if I do come out of my boat I could foresee being out of it for long enough to be thankful of a bit more buoyancy.

I have never used a lifejacket as well as a BA, in fact I have never used one in a kayak at all. BUT, if you really want something unobtrusive when paddling, you could swap the BA for an inflatable lifejacket, but I would suggest only if you are very confident that you won't end up swimming often. Inflated they are much more cumbersome than a BA, even uninflated they would make climing back in awkward (and do nothing for you) and the risk of damaging it would be a concern.

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Re: How much buoyancy do you need?

Post by CM2 » Wed Feb 06, 2019 1:01 am

You can get vests with less than 50N they just are not called buoyancy aids for example https://www.absolute-snow.co.uk/V/Jobe_ ... e-(156866), they are often used waterskiing where he skier essentially has their own private rescue boat which will come round ot then in a few seconds and they are nearly always on calm water..

I would not use one for kayaking for the reasons others have mentioned.

Something to bear in mind when you start thinking about life jackets is where as a 50N buoyancy aid has you pulling down against BA with 5kg of force with a 150N jacket if it increased to 15kg. That sort of force could easily be enough to have the life jacket ride up making it very difficult to do anything, and possibly even come off over your head https://www.youtube.com/watch?v=m-CmyKdy3MU .

I have a hybrid BA/life jacket that I use for dinghy sailing, it has leg straps to keep it in place. For kayaking the spray deck prevents the use of leg / crotch straps so I stick t a BA for kayaking (though also because the hybrid jacket doesn't have pockets).

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Re: How much buoyancy do you need?

Post by seawolf856 » Thu Feb 07, 2019 3:28 pm

Chris Bolton wrote:
Tue Feb 05, 2019 4:25 pm
but in at lot of people the difference between 11st and 15st is 4st of fat, which is quite buoyant!
I'm off to eat more pies

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Re: How much buoyancy do you need?

Post by mcgruff » Thu Feb 07, 2019 7:28 pm

PFD's are seen as an essential piece of kit but bobbing around in a buoyancy aid may not always be the best survival strategy.

They certainly provide some protection against cold water shock. If you're gasping and thrashing around, a PFD could help keep your head above the surface and breathing.

Most kayakers are probably wearing drysuits, dry kags etc so cold water shock won't be such an issue.

Still, even with a wetsuit/drysuit survival depends on getting out of the water. It could only be a matter of hours before you succumb to hypothermia. Floating is a very passive survival strategy which relies on someone coming to rescue you in good time. But what if what if no-one is there to help? You'd have to switch strategies: stop floating, start swimming.

If you're far from shore, you're now in a race against time against the cold and swim failure. A PFD (or a drysuit) would be a positive drawback here since it would only slow you down. A nice, streamlined wetsuit and good swimming ability would be your best chance to survive.

Perhaps there could be something else to try: a pocket lifeboat (aka a packraft). It wouldn't be quick or easy to inflate the thing while treading water but if your survival strategy is passively bobbing around in a PFD at least it gives you something to do to pass the time.

Getting out of the water is a big step forward. It might not completely remove the threat of hypothermia but would certainly reduce it. It gives you more time to be rescued.

If you've still got your paddle, you might even be able to make your own way to shore - but if it's windy, you're going wherever the wind takes you (pack a lightweight sea anchor with the packraft?).

A packraft might give groups some useful extra options. If someone is injured or loses their boat maybe you could raft up to inflate your pocket lifeboat then tow them back to shore?

Just an idea. I've never tried inflating a packraft at sea.

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Re: How much buoyancy do you need?

Post by Chris Bolton » Thu Feb 07, 2019 7:51 pm

I've never tried inflating a packraft at sea
Neither have I, but it's an interesting idea.
What I have done is inflate a survival bag - the 8' x 4' orange plastic type. Tread water, hold the bag over your head and let the wind fill it. Pull it over your head and down into the water, bring your knees up, fold the bag round you and tuck it between your feet. You have a spray hood with enough air for 15-20min, a bit of buoyancy holding you a bit higher and to any searching lifeboat or helicopter you look like a big orange buoy. When the air gets stale, you'll know about it, then repeat from the start. It does work, although I've only done it as a practice.

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Re: How much buoyancy do you need?

Post by mcgruff » Fri Feb 08, 2019 1:41 am

In a real emergency, making the best use of whatever is available just might give you a chance to survive.

I guess the hardest part is always psychological: being able to force yourself to think calmly and rationally even when you're freaking out.

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Re: How much buoyancy do you need?

Post by Grian » Fri Feb 08, 2019 2:24 pm

Best of both worlds? https://kokatat.com/product/seao2-pfd-lvusea

Unlike any other PFD, the SeaO2 incorporates a 'hidden' flotation chamber within the body of the vest. In an emergency, the PFD's inherent 7.5 lbs. of flotation can be immediately boosted to 22.5 lbs. by releasing the contents of the CO2 cartridge. An oral inflate/deflate tube allows the user to adjust the amount of flotation on the fly, and the flotation chamber can be inflated, deflated and re-armed without removing the life vest. Swimming while the PFD is fully inflated is also easy and comfortable.

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Re: How much buoyancy do you need?

Post by Spikeedog » Fri Feb 08, 2019 5:00 pm

That's clever!

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Re: How much buoyancy do you need?

Post by Grian » Fri Feb 08, 2019 5:02 pm

Spikeedog wrote:
Fri Feb 08, 2019 5:00 pm
That's clever!
I hope so! I have this pfd but have yet to get the compressed air cartridge as they couldn't ship it from the States. Apparently is the same as used for bicycle tyres.

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Re: How much buoyancy do you need?

Post by JB-NL » Sat Feb 09, 2019 7:31 am

CM2 wrote:
Wed Feb 06, 2019 1:01 am


Something to bear in mind when you start thinking about life jackets is where as a 50N buoyancy aid has you pulling down against BA with 5kg of force with a 150N jacket if it increased to 15kg. That sort of force could easily be enough to have the life jacket ride up making it very difficult to do anything, and possibly even come off over your head https://www.youtube.com/watch?v=m-CmyKdy3MU .

I have a hybrid BA/life jacket that I use for dinghy sailing, it has leg straps to keep it in place. For kayaking the spray deck prevents the use of leg / crotch straps so I stick t a BA for kayaking (though also because the hybrid jacket doesn't have pockets).
Very illustrative movie (and yes, these are not the PFD we are using).

However, several years ago (more then10? ) there was an article in Ocean Paddler Magazine. Several manufacturers of sea-kayak PFD's were invited as well some media,at the RNLI training centre.
The RNLI invited them to test their PDF in the "survival pool" where they simulate all kind of bad situations.
The writer accepted the invite.

Two of the main comments in the article were referring to the lack of a crotch strap for kayak- PFD AND the wide arm pitches. After some 10-15 minutes the writer noticed he started to get tiered and dropping out of the PFD...

And now so many years later we see a variety of PFD's in all kind of colours, but still lacking any kind of device to connect the crotch strap.
The spray deck hinders, but some kind of solution could have been thought of....
By using a kind of strap, the need for more buoyancy is then less relevant...although I see the 50N for somebody with an average weight of 70-80 kgs still as a minimum.

JB
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Re: How much buoyancy do you need?

Post by PlymouthDamo » Sat Feb 09, 2019 9:36 am

Here's another invention that should earn me millions: a little oral-inflate tube fitted somewhere near the neck of your drysuit. (Before anyone gets excited: I'm not proposing this as an alternative to a BA or lifejacket - just as an additional layer of protection.)

After surfacing from a scuba dive, your lead weights and gas tanks will have you floating with your eyes at water level. To allow you to breathe and make you more visible to boats, you inflate your 'buoyancy control device' - either a waistcoat-thing or a doughnut around your gas tanks. This gives you a fair amount of lift, but if you want a whacking great buoyancy boost, you close your drysuit's 'dump valve' and inflate that. Now if you do this without carrying a load of heavy dive kit, you can lie horizontally, right on the surface of the water, like a balloon. If your drysuit and seals are good, this should hold the air for a long time, so you'd only occasionally need to top it up with a few breaths of air into the little tube.

This also has a massive difference in terms of heat loss - an inflated drysuit provides superb insulation.

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Re: How much buoyancy do you need?

Post by Spikeedog » Sat Feb 09, 2019 2:01 pm

The wind would take you for miles though....

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Re: How much buoyancy do you need?

Post by PlymouthDamo » Sat Feb 09, 2019 2:36 pm

Spikeedog wrote:
Sat Feb 09, 2019 2:01 pm
The wind would take you for miles though....
Then you'll be interested in the skeg/rudder kit that I'm selling at a time-limited price of....

The only problem I can think of with the idea is that, unlike diving suits, quality surface drysuits are breathable. When searching for leaks on my Goretex suits I've found you can actually suck air through the fabric. So would they hold the air in?

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Re: How much buoyancy do you need?

Post by Spikeedog » Sat Feb 09, 2019 4:21 pm

Breathable must mean the passage of air through the fabric. I got a cheap Chillcheater top the other day and almost suffocated while trying to get the very tight neck seal over my head so Aquatherm would work!

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Re: How much buoyancy do you need?

Post by Ken_T » Mon Feb 11, 2019 1:59 pm

Hi, If you are considering inflating a drysuit, one problem is that because the BA holds the top close to your body you end up inflating the legs. I have seen people float upside down in a drysuit unable to get their head to the surface because they forgot to purge the dry suit of air. This happened even to people wearing a BA.
Ken

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Re: How much buoyancy do you need?

Post by Jim » Mon Feb 11, 2019 4:08 pm

JB-NL wrote:
Sat Feb 09, 2019 7:31 am
Two of the main comments in the article were referring to the lack of a crotch strap for kayak- PFD AND the wide arm pitches. After some 10-15 minutes the writer noticed he started to get tiered and dropping out of the PFD...

And now so many years later we see a variety of PFD's in all kind of colours, but still lacking any kind of device to connect the crotch strap.
Maybe not everyone gets this point, but you should only be using a buoyancy aid in situations where you expect to be getting out of the water within a couple of minutes, i.e. re-entering your kayak. If you take any longer than that in cold water you won't be able to re-enter anyway and within a few more minutes will have lost the ability to swim and will require a full lifejacket to keep your head the right way up. Anyone expecting to be able to use a kayak buoyancy aid for long term survival needs to re-think their approach to paddling. There is a trade off between a device that has a low enough profile to enable you to re-enter, and one that will support long term if you fail to re-enter.

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Re: How much buoyancy do you need?

Post by PlymouthDamo » Mon Feb 11, 2019 4:53 pm

Ken_T wrote:
Mon Feb 11, 2019 1:59 pm
Hi, If you are considering inflating a drysuit, one problem is that because the BA holds the top close to your body you end up inflating the legs. I have seen people float upside down in a drysuit unable to get their head to the surface because they forgot to purge the dry suit of air. This happened even to people wearing a BA.
Ken
I agree - as Jim describes above, buoyancy aids don't provide the same protection as life jackets. I can't picture someone floating head-down whilst wearing a BA though. Surely that would require the whole 'jacket' to be submerged below the surface, i.e a downward force of 50N or more? I'd have thought that the stable position, even with a tightly fitting BA squeezing your upper body, would be horizontal, albeit with your legs bobbing about in front of you like two Zeppelins,

Dealing with 'going inverted' is one of the key skills in a scuba diver's drysuit training. The solution is to pull yourself into a ball and roll back upright so the air can migrate back up to your top half - it is easier said than done and I can well imagine someone failing/drowning if they haven't got anything to breathe and are panicking.

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Re: How much buoyancy do you need?

Post by Ken_T » Tue Feb 12, 2019 10:26 am

Hi, I have seen this problem happen with someone wearing a BA & an inflated drysuit. The problem appeared to be the area around the buttocks inflating, they are an experienced paddler but could not get their head above water. We prioritised rescuing them over analysing exactly what was preventing them getting their head above water. When we got her out one of the observers said to her 'I didn't realise how big your bum is'.
Ken

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