In my earlier post above I referred to basically jumping in to a swimming pool wearing a life jacket - A Crewsaver 150N as it happens without the crotch straps. I did the water safety course several times when in the EA, and also put the l/j to practical use on a couple of occasions when taking a tumble while electric fishing. On no occasion did the l/j rise up over my head.
It needs to be correctly worn with the waist belt adjusted so that two fingers together can pass between the belt and the body. That done the l/j does what it says on the tin which is to turn the wearer so that they are on their back with head clear of the water and support their body weight. Seeing as most people's chest measurements are, or were, bigger than their waist measurements the l/j should not be able to rise up significantly. However, as people are now getting bigger, ie fatter, and their chest measurement is often smaller than their waist then the larger 165N jacket with crotch straps is the better bet. Farmoor changed their l/js for that reason as I was told by the ranger staff.
It needs to be correctly worn with the waist belt adjusted so that two fingers together can pass between the belt and the body. That done the l/j does what it says on the tin which is to turn the wearer so that they are on their back with head clear of the water and support their body weight. Seeing as most people's chest measurements are, or were, bigger than their waist measurements the l/j should not be able to rise up significantly. However, as people are now getting bigger, ie fatter, and their chest measurement is often smaller than their waist then the larger 165N jacket with crotch straps is the better bet. Farmoor changed their l/js for that reason as I was told by the ranger staff.