there is some advice on the RYA site that covers this;
http://www.rya.org.uk/Activities/PowerboatRacing/competitorsinfo/travelinsuranceadviceforforeignevents.htm
If you had one from the previous Worlds it should still be valid – as I recall they last 5 years
I have always had an SSR when travelling abroad (in the EC) – but never been asked for it. But for what it costs – £25, and the ease in applying…. anyway here’s the link to apply online.
https://mcanet.mcga.gov.uk/ssr/ssr/