4 blade vs 3 blade prop

JohnB · #1 01-12-2003, 01:36 AM

I have a 23' 89 Sceptre with a 250 Merc EFI on it. I currently am running a 3 blade prop and have heard alot of good things about 4 blades.
Does anyone have any experiance good or bad going to or from a 3 to 4 blade prop?
Supposedly, it will get better milage in the cruise (3500-4500rpm) range, and lose a little top end which is no problem for me.
Let me know what you think,

[ January 11, 2003, 12:37 PM: Message edited by: JohnB ]

FELLOW-SHIP · #2 01-13-2003, 05:11 PM

I HAD A 18’ HYDRASPORT THAT HAD A CAVITATION PROBLEM AND WAS TOLD BY OMC THAT I SHOULD GO TO A 4 BLADED PROP WHICH I DID. IT FIXED MY CAVITATION PROBLEM BUT I FOUND THAT IT HAD SOME GOOD THINGS AND SOME THINGS I DIDN’T LIKE AS MUCH AS THE 3 BLADDER I HAD ON IT. GOOD WAS IT GOT UP ON A PLANE FASTER AND I COULD EVEN RAZE THE ENGINE UP ONE OR TWO NOTCHES WITH NO CAVITATION (LESS DRAG) BUT THE RPM’S WERE HIGHER AND THE TOP UN LOWER. IF I WAS GOING THE SAME SPEED I WOULD SEE ABOUT 300 HIGHER RPM’S TO DO IT.
FELLOW-SHIP

ltdan · #3 01-13-2003, 11:17 PM

HEY JOHN, LT HERE. AS YOU KNOW I'M IN THE MIDDLE OF MY 23CC REDO. I KNOW THIS DOESN'T HAVE ANYTHING TO DO WITH THE 3-4 BLADE QUESTION, BUT I NEED TO KNOW HOW HAPPY YOU ARE WITH THE 250 EFI MERC? WHAT YEAR IS IT,HOW'S THE HOLE SHOT,WHAT'S THE TOP END,@ 36 MPH WHERE'S SHE TACH, HOW'S IT ON GAS????? I'VE BEEN THINKING YAMAHA 250 HPDI ALL ALONG, BUT, I CAN GET AN UNREAL DEAL ON A 2001 LEFT OVER NEW 250 EFI MERC, WITH AN EXTRA 2 YEAR'S OF WARRANTY(3YRS TOTAL)FOR $5000 LESS THAN THE VERY BEST PRICE TO BE FOUND ON THE YAMAHA.THAT'S A LOT OF ICE,BEER,BAIT AND FUEL. THE 4 MAJOR NECESSITIES IN OUR LIVE'S. OH YEA, AND SOMETHING TO PUT ALL THAT STUFF IN [img]images/icons/grin.gif[/img] PLEASE GET BACK TO ME. I NEED TO TALK TO SOMEONE THAT'S USING ONE OF THOSE THING'S INSTEAD OF THE SALESMAN. TAKE'ER EASY LT DAN

Billybob · #4 01-14-2003, 09:25 AM

I've never actually run a 4 blade prop on mine, but there has been a lot of discussion over the years on this topic over on the wmi boating board, you might want to do a search over there.But the consensus seems to be that the Stilleto props(3-blade) run the best on our boats.

JohnB · #5 01-14-2003, 09:30 AM

I am putting a 15 1/4" diameter 15 pitch Mirage Offshore prop on the boat. I will post back the results. I am replacing a Michigan Prop, Rapture, that was a 14 1/4 diameter with a 17 pitch. I will report the results.
As far a the EFI, I just finished putting a new transmission in the beast. A gear cracked and blew the thing up when it came apart. That is the only failure I have had on it. This may have been an operator problem, and not a Merc problem. It is a 1998 engine. The engine runs very good, easy starts, uses a little more oil then some. Performance/power is excellent. If it has a week spot, it is in the gas milage department. It tends to be a little thirsty, but is very reliable. The gas milage may be due to the prop configuration, and I will post back the results of the change. The main advantage of the HPDI/FICHT type motors is gas milage. I don't think they are any stronger, and use less gas. If money was no object, I would go for the Yamaha.

bob20544 · #6 01-17-2003, 11:55 PM

I went from a 18D24P cupped 3 blade to a 18D20P Supercup 4 Blade and saw less cavitation, slightly higher speed and would do it again. Cost is higher but worth it. This is a 23 Inboard with a Cummins 250HP Diesel with 2800RPM top and 1.5/1 trans. Placed my faith in the San Diego dealer and he picked the perfect match. Drive seems a little quieter but may be suggestive thinking.