can anybody tell me what would acceptable leak down on a marine blower motor

They should be within 10% of each other. I like to see under 15% with some time on it, around 6-8% new. Just a guide. a blower motor should have the same leakdown numbers of a N/A. The rings should still seal, and so should the valves.
What problems are you having, blow by, low compression?

no problems but leak down is 9-11% did'nt know if that is bad or good 300 hrs.

I would say that is good for 300 Hrs. Could you tell where the air was leaking? Rings, intake valve or exhaust valve?

<10% is good.

Was the motor cold or hot? If it was cold even better.

+2 good to go! my question is,blower motors+300 hours..alot of stress on the lower end..may be time to check things out so you have no future problems..

300 hours on a blower motor, it's not bad. but yes where it is leaking is important. With 300 hours I would not feel bad freshening it. Cheap insurance.

i did run the motor but it does not get real warn with the muffs and the hose because it has an open cooling system with no thermastat. it has 125- 130 compresson in all cyl at 5000 feet

The numbers sound good to me, especially with 300hrs on it.