Define Blend. Mobil 1 sued Castrol in 1998 because they marketed Syntec as synthetic. They lost. Blend is a very misinterpreted word. So is synthetic. Oil in an engine has do do many things, one of which is to protect against pressure. Pressure protection only happens when the engine is running. Oil MUST do more than just that, and in boats, many are stored for a period of time in the off season. Synthetic oils do NOT cling as well as mineral oil. Period. During the off season, your engines are exposed to dramatically changing temperatures and humidities. You want all the protection you can get in terms of corrosion and moisture protection. Fully synthetic oils are great at what they are designed for, but long term storage is not their strong suit. This is a multi faceted issue and there is no silver bullet. Fully synthetic motor oils will not always put you in a superior position, but they do have advantages over some mineral oils, when the engine is running. Long term storage is not one of its advantages. There are many studies that say engine damages occur in the first 15 seconds of startup. Consider that many Yamaha owners, not wanting to add fogging oil, go out in the middle of winter, and crank over their engines for 15 seconds every few months. Most measuring sticks say that an "in-service" engine gets 30 minutes of run time per week! Some of the things we do to prevent one issues, cause more concern on many other issues.
Again, there is nothing wrong with using iridium spark plugs or fully synthetic oils...but you can NOT extend the manufacturers recommended change intervals on either. However, the strong suits of some of these products only work when the engines are running, not during storage, and paying much more for a product your going to change annually with low hours is a little self defeating. As a matter of fact, you would serve yourself and your engine better to change the oil twice a year if you store your boat for longer than 2 months. That way, you don't leave moisture and contaminants in the oil over the winter.
There is no right or wrong here. I just want to point out that one size does not fit all. Since about 1995, ZDDP and other additives have been reduced in oils to levels that do not provide adequate protections. For that reason, engine manufacturers and enthusiasts alike, have been recommending other additives besides just oil in the engine and fuel in the tank. Knowing what your cutting out when you make a change is important. Because it may be significant protection your cutting out. In my boat, I run Yamalube 4M 10W40, Yamaha Ring Free, Marine Grade Stabil, and Yamaha Fogging Oil using the Yamaha Tech service bulletin WCA2011-003. In closing, Yamalube is not superior to other oils, and you may find better oil at Walmart. But if your intent is to run a PAO based oil, then your only choices (in the US) are Mobil 1, Amzoil, Red Line, or Royal Purple, that I know of. Just be aware that PAO is designed to protect a running engine, not long term storage of engines.
