Centre of gravity. The lower I go on the boat ie slit a fish's neck I start to feel green. Could also be that you're just a pussy 

 Might just be Andy ....... dosent generally take long, have never felt safe standing in the tinnys ive been in.

 Sitting would inhibit your body/feet rolling with the punches more therefore confusing your brain more .. haven’t anything smartarse to say as yet , but I might be back ..

 You're full of surprises  I actually was wondering whether or not it had to do with balance, ie not being able to maintain it while sitting, I guess it's something we do naturally while standing without even thinking about it.

Some interesting comments here but think I will have to agree with Sea-Kem: Your're just a pussy.

lol sorry just joke ...couldn't resist.

Weird that the lower you go the more sick you get cos obviously the lower you are in a boat the less you move. Eg up a tuna tower. (pendulum effect)

What Chris says sounds right....legs absorbing movement and could also be something to do with just mental state: while you are up and moving you think about it less. as soon as you sit you think about it.

 I'm betting on the bigger boats you're on the P155 pretty early? This has the effect similar to a quell or seasick tablet that it inhibits your inner ear from sending balance messages which is what make you seasick.

Chris is probably on the money.  another contributing factor could be a lower line of sight giving a sensation of being more 'closed in' ????

to rerig etc, mind you I'm ok in calm seas,used to go out in anything, bit more cautious now

 Interesting - cant say I ever thought about feeling queezy when sitting down , just happens - even with the old eyes on the horizon trick. Hey ZooM - Im in the minority , not one to get tanked on a boat very rarely drink at all whilst on a boat, probably would feel better if I did in this instance.

 Swear by the ol ginger nuts Randall. Have to try it next time

 Few of the lads that I fish with swear by weed and beers. I find it a little irresponsible so just stick to the weed

Eat plenty of pineapple up to about 6 hours before you head out, its not going to stop you being sick but you get to taste it for a second or third time if you are lucky.

Sitting in the dinghy doesn't give you a clear view of the horizon and the dinghy has a much sharper/ quicker roll to it compared to bigger boats, this accentuates the symptoms

 When standing you are keeping your head level with legs and feet. When sitting you are trying to keep your head level with just your upper body. That may be the difference.

chewed without water 35 - 40 min before stepping onto a boat

no milk product under any circumstances. Bit of toaste with some baked beans if ur starving

if you still get sick then take half a quell the night before too... No more than 1 tab 24hrs

... Now harden up ;)

 I used to find it helpful on a plane , which kinda makes sense with the following, so whos going to

be the first to land a dhuie with theres eyes shut haha.

You get motion sickness when one part of your balance-sensing system (your inner ear , eyes, and sensory nerves) senses that your body is moving, but the other parts don't. For example, if you are in the cabin of a moving ship, your inner ear may sense the motion of waves, but your eyes don't see any movement. This conflict between the senses causes motion sickness.

You may feel sick from the motion of cars, airplanes, trains, amusement park rides, or boats or ships. You could also get sick from video games, flight simulators, or looking through a microscope. In these cases, your eyes see motion, but your body doesn't sense it.

 Thanks again fellas - for the record a quell or similar didnt seem to make any difference. Mr Carnarvon - Ive heard a few stories about the benifits of eating pineapple 

For those that find quells etc do not work the best is Phenergen. It's a antihistamine and will cure sea sickness every time guaranteed!

 Sit under a tree

 no milk! Milk is a real killer for me, and trying to untangle that bloody stinking wrasse that's just swallowed your hook and then needing to re tie that leader....that's claimed a few for me, 

quells work for me, so does beer, I have heard an old salties tale about plugging one ear... Never tried it though,

Most times I'm fine though but sometimes I'll take a quell just incase as to not soil a good day out 

 get some insulation tape and tape together the 2 toes next to your big toe.

 10mg phenergan. Well known Antarctica crossing trick.  

 My dad's really bad with sea sickness but he hasn't got sick once since drinking ginger tea.

Just boil some water and add some slices of fresh ginger (and honey and/or lemon for flavour), tastes ok and works really well 

Apparently Travacalm has an ingredient that thickens the fluid in the inner ear.

Works for me. Been taking it for a year or so now and never even felt like getting sick. That includes one day when I was lying on the floor in 20knots looking up into the gunnel joining wires. That sort of stuff would have made me crook real quick without it.

was to skull 1/2 a cup of saltwater. Worked for him. never sick again... Dunno, never been sick. Used to surf and consume my fair share of saltwater though so could be it?????

 As chris says, if youre standing your legs adjust for the boat's movement; keeping your head more still.  If youre sitting, your whole body moves according to the movement of the boat.  

 I agree with the no milk products. Work on a snapper boat and drank 2 litres of choc milk before we went out, trip out was a bit rough and had a good spew session.

 Touch wood never been sea sick in my life..like above mentioned I follow the motion of boat with my legs

feel sorry for those who get sick... Looks like a  chit house of a time ....its is pretty funny Funny tho 

 I did, I was a shocker for any kind of motion sickness, carsick, you name it. 

So i became a professional fisherman. 

The first ten years were the worst.

 LOL how bout a cup of concrete,just jokes fortunately dont suffer from motion sickness anymore i found that if you kept chewing,eating it was kept under control.

i used to give my kids a kwell the night before just as they went to bed , this worked well for them and stopped the sea sickness
taking it in the morning an hour or so before we left the ramp did not seem to work as well with the kwells

other types of tablets seemed to space them out too much

hezzy

Labyrinthitis means an inflammation of the inner ear structure called the labyrinth. Sometimes the term labyrinthitis refers to other causes of inner ear problems that have no inflammation because those problems produce similar symptoms. You have a labyrinth in each of your inner ears, encased in thick bone near the base of your skull. As the name implies, the labyrinth is a maze of interconnected fluid-filled channels and canals. Half of the labyrinth, the cochlea, is shaped like a snail's shell. It sends information about sounds to the brain. The other half looks something like a gyroscope with 3 semicircular canals connected to an open cavern or vestibule. The vestibule portion of the labyrinth sends information to the brain regarding the position and movement of your head. Any disturbance of the vestibule can lead to faulty information going to your brain. Your eyes also send positioning information to your brain. When information from the labyrinth and the eyes don't match, the brain has trouble interpreting what is happening. This misinterpreting often leads to a sensation that you are spinning (vertigo) or a feeling that you are moving when in fact you are remaining still. Feelings of motion sickness (nausea and vomiting) often follow. Sometimes you will experience hearing loss or abnormal sounds such as a high- or low-pitched ringing (tinnitus).

http://www.emedicinehealth.com/labyrinthitis/article_em.htm#labyrinthitis_overview