Both those accident rates are higher than the UK, whose
population is
around 25% of the USA. Boating deaths appear vastly higher in
the USA. I
wonder why?

Nice to see a rational approach!

Partly, US has a far more rigorous reporting system. Nearly half
boat deaths occur in small rowboats and motorised fishing boats
pottering around without lifejackets. These don't interest the
MAIB. Additionally, UK appears to have more sail and auxiliary
sail boats active compared to these small vessels. In US the
safety of these sail vessels is *much* higher - so that could be
an equaliser.

Your RoSPA data included only drownings in UK. Dig into their
leisure industry reports (LASS) and you'll find they report
typically 5,000 to 6,000 injuries over about 11 categories of
vessel (which is confusing!). However, the likely ratio of
injury/death will be around 1/5 (the US boating rate) to 1/10 (US
and UK car rate). This implies around 500 to 600 deaths from
boating in UK per year. I know - heroic assumption!

UK road deaths around 3200 in 2005 with 30M registered cars.

Boat-related deaths:

http://www.dft.gov.uk/stellent/group.../page/dft_foi_
610522.pdf shows numbers reported to the Marine Accident
Investigation
Board. Incidents involving deaths, maybe half a dozen a year.

http://www.rospa.com/waterandleisure...atersafety.htm
lists 22 boating drownings in the UK in 2004.

There is no legal requirement to register small craft in the UK
so
nobody knows how many there are. Also certainly several million.

Estimates from consumer market surveys around 1995 put the numbers
of people who regard themselves as participating regularly in
sailing activites around 3,000,000. Not a very useful stat, but
it's the best I've got!

--
JimB
http://www.jimbaerselman.f2s.com/
Describing some Greek and Spanish cruising areas