Read the Steve D article on Engine Survey.
5-10 minutes at WOT
Then 30-mins at 80% Load
"Nearly all engine manufacturers warrant their engines to operate at WOT for 10-minutes, often much longer without encountering problems with overheating, fuel and air starvation, provided the engine has been properly installed and maintained."
If the seller is uncomfortable with this, you may want to find out now before you hire people. Or decide you're okay with a short duration WOT test. Personally, when buying, I always recommend the seller provide the captain as I don't want to be responsible for any helm time (your mechanic, once you find one, will agree). As a seller, I'd be nervous about this and would certainly pre-test to make sure I'd pass. But I do believe it a reasonable test. Like JLeonard , I'd definitely be reluctant too - 8-seconds as in Bull Riding is a long time. 10-minutes would go at glacial pace......
1970 Willard 36 Sedan Trawler
Current Location: Ensenada MX