From personal experience and advice from lots of people I would
summarise as follows:
1) Each individual is different. If anyone says smugly 'it's all in
the mind, I me my superior self never gets sick' just puke over the
person.
2) Some of these are repeatedly quoted as factors that contribute to
bring it on or make things worse during motion: being cold, being cold
and wet, not enough sleep before boarding, rich food, and other food
incl acidic types (citrus) and poultry, fume and odour, looking down or
reading, thinking about being sick.
3) Some of the things that help some people a good rest and good
food 24 hours before, medication 4-24 hrs before (depending on
medication) such as Scopoderm patch behind ear, Stugeron tablets,
Stemetil and Phenergan combination (consult doctors, some medication
may have side effects such as drowsiness and affected eyesight, and
note patches are generally more effective as medication gets into the
system quite reliably whereas tablets rely on the digestion process,
although some people like me are allergic to the adhesives on the
patches), where possible stay (sleep) aboard 24 hrs before departure
(we try to do this before long distance yacht racing), keep body and
head warm, keep drinking and nibbling non-fatty sugary snacks,
concentrating on an important physical task (helming, when appropriate,
works great for me but moving about-tasks can further deplete energy),
keeping interest and spirit up, fresh air and looking at the horizon,
ginger, Fisherman's Friends or similar menthol, wristbands with
pressure on pressure points. Also keep self-talk of 'I feel well'
'I am well'. If sick just get rid of it and business as usual. If
very sick you have to either be on deck staying vertical or below deck
lying down warm, and must drink water or energy drink that has fizz
shaken out, and nibble on plain food or lollies of own choice.)
4) My latest investigation is.... If the condition is at least partly
in the mind, then surely having a hypnotherapist on board should work
wonders?? They can cure even smoke addiction so this should be a
breeze. We should round up those hypnotherapists and invite them to
come sailing, or to treat people before they step aboard. Incentive for
them is also a booming business! It must be worth a go. Please report
back.

Good luck
Solo Thesailor
http://sailingstoriesandtips.blogspot.com