Boat engines should run a similar oil ratio as far engines. 70% castor/30% synthetic!! I run 20% total content at a 70/30 castor/synthetic blend and 20-30% nitro. This is the most ideal fuel I’ve used in my K&B and OS marine engines thus far. I wouldn’t run an OS on anything less than 50% castor 50% synthetic. The liner plating is very fragile. My Nova and Picco truck engines get 11% oil at a 70/30 castor/synthetic blend and I couldn’t be happier. Even a friend with Traxxas fuel noticed within 5 seconds of starting his engine on my fuel brew to notice how different it is compared to the swill he had been using.