Chewy
There is no need to add on a power endorsement.
You can take either the sail or the power course and exam. If you have done one there is the option to later take a conversion exam to the other.
The course / exam you are after is Yachtmaster Offshore Certificate of Competence (Power).
There are various pre requisite, not least
- 2,500 miles logged
- 5 passages of 60 miles or more
- 2 of those as skipper
- 2 of those overnight
- 50 days on board
- SRC Radio or higher
- First Aid
If you have not already I would start by doing the Coastal Skipper / Yachtmaster Offshore Shoreabsed Course, you will need this knowledge for the practical exam.
To add the commercial endorsement all you need is a Sea Survival and a Medical from your doctor and a rubber stamping fee of £25.