My engine was rebuilt end of last year. Pulls 13-14 inches of vacum at idle. Putting my hand over the breathers on the valve covers i dont feel any blow by. But every time i run my boat i have to add at least a qt of oil. i figure its burning somewhere around a qt every 10 hours or so. I am running Royal Purple 20w50 HPS. Does this seem too high or is is normal for a synthetic motor oil.

That is quite a bit for a 525SC. Mine with 475hrs only used a qt every 25hrs or so.
My 502mpi's use a quart about 15hrs.

one thing i havent checked yet is the pcv valve the sits in the intake that attaches to the top of the blower. wonder if that is sucking too much oil back into the motor

Do a leakdown test, if numbers are high will tell you everything. I ran my blown 502 175 hard hours with run of the mill rings ( J/E plasma) and that thing was eating oil and had crazy leaakdown numbers towards the end, funny thing was it only lost 1-2 mph. Smitty

Did you have the problem prior to using Royal Purple ? I went on a RP binge and put it in my truck , mc and boat . It seems to break down very quick and boat - truck are eating it . More expensive junk in my book , i'm going back to Mobile I which i never had a problem with !!!!!

I did a cold leakdown test earlier this year and was 20-25%. Engine dead cold, i havent done one with the engine warmed up. It doesnt ever seem to smoke or anything either. Before i had the engine gone thru last year i used valvoline racing 20w50 and never had a problem. I used a break in engine oil on the dyno. and have been using royal purple since. I thought about trying a different brand to see if that would make a difference.

I had a similar experience using Brad Penn, motors ate it up. Switched to Valvoline Racing and no more oil consumption.

I had a pick up years ago that when I would run Quaker state oil in the truck would just eat the oil up...switched to another brand and the problem went away...might be worth a try switching brands..

I use Rotella 15w/40 in my 502 MPI. Have never added a drop.

20-25 leakage is 2 much,something is wrong,you should be able to hear the air leaking threw the rings into the crankcase.