Mercruiser Prop Size

"I have a 1979 EBKO CORBA, 19

"I have a 1979 EBKO CORBA, 19 foot, it has a Merc 228 V8 305. The prop I have on takes forever to plain, it is way to big, I can only get it up to about 3000 RPMS. If I get a smaller prop will I be able to plain faster and higher my RPMS? If so, what size prop will i need? I want to be able to pull Skiiers."

"You don't indicate what p

"You don't indicate what pitch your current prop is. If the boat if fairly heavy, you likely need about a 19" or 17" pitch, depending on your drive ratio. I had a 198 hp 305 in a heavy old Webbcraft a few years back, and it needed a 19" to get her planing.
3000 RPM at WOT is way too low. You should get about 4600-4800 RPM @ WOT with minimal load. You will gain about 150-200 RPM for every inch of pitch you go down.
Also you may want to try something like a High Five prop which will slip more from a dead stop, and thereby allow your engine to rev up more and get into a decent power range. These are a huge improvement over the cheap old black aluminum 3 blade "dumbo ear" prop.
Rod"

"I'm really not sure what

"I'm really not sure what size it is, but it's huge! it is so big that the little fin above it had to be taken off to use it, I bought the new fin and it will not fit with it because it will hit it about an inch."

"Skitch
That little fin is an

"Skitch
That little fin is an important part of your corrosion protection and when adjusted correctly can help compensate some steering issues. They do make half size ones that should clear your large prop (sounds like it may be a monster). So I hope you have some type of anode in the hole where the
fin was bolted.
Depending on who manufactured your prop there may be a series of numbers (unless it is worn off) cast or stamped into your prop rather on the hub area or around the side.
These numbers will help you identify the size and pitch of your prop.
Rods advice is very sound, a high 5 or even a 4 blader in the right diameter and pitch will make a huge difference to the performance of your boat, the right prop is an extreamly good investment.
About a month ago I think someone posted a little excell chart with how to work out the correct prop for an individual application, you may want to scan back through the list of postings for a few weeks and see if you can find it.
Regards
Peter C"

"[url=""]http://www.marineengi

"http://www.marineengine.com/discus/messages/12486/Boat_Speed_Finder-79780.xls

Here is the link to the Excel sheet that Peter referred to. I originally posted it Apr 24th.
Most props have the pitch punched on the side of the hub in between 2 of the blades. It usually has 2 digits, followed by the letter P.
If your prop is that big in diameter, it sounds like you may be trying to turn too much blade area, besides whatever the pitch is. You really don't want much more than 14.5" diameter on an Alpha.
As Peter says, you should invest in a good quality new prop that is better matched to your boat and engine package. Most marinas will allow you to test a couple of props to determine the best pitch, if they think you are going to buy a new prop. Be prepared to spend several hundred dollars for a good stainless prop.
Rod"