3 Blade Prop Pitch

[mel low]

I have a 1986 hull #162 and I want to change my two blade 15-10 prop to a three-blade. I have the M-25 21 hp. In the archives I have found many references to people re-pitching their 3 bladed  15-9 to 15-10. Most of these were boats after 1988 with the 25 XP 23 hp. My question: Will I overload my 21 hp with a 15-10 3 blade or would I be safer with a 15-9?

Next question: Does anyone have a 15-9 3 bladed prop that they'd like to sell?

[Ron Hill]

Mel : The original posts were for a M25 engine to repitch (3 blade Sailor prop) to 10 inches.  Another later article (still early 1990's) recommended that the M25XP be repitched to 10.5 inches.  The difference after repitching to 10 inches (M25XP) was absolutely amazing!!!

I don't know your engine hours nor the maintenance done on your engine, but it is 24 years old!!  A few thoughts

[mel low]

Mel : The original posts were for a M25 engine to repitch (3 blade Sailor prop) to 10 inches.  Another later article (still early 1990's) recommended that the M25XP be repitched to 10.5 inches.  The difference after repitching to 10 inches (M25XP) was absolutely amazing!!!

I don't know your engine hours nor the maintenance done on your engine, but it is 24 years old!!  A few thoughts

Ron. I have only owned the boat for 6 months and there was no maintenance log with the boat. The engine has 1750 hours on it.  The boats curses at 5.5 knots at 2200 RPM.I can put it to full throttle at 3000 rpm and it will do 6. Reading what was written in past articles most of the boats were able to cruise at 6 with the three bladed prop. But as you point out the 88 and newer have the M25XP. So maybe staying with the 15x9 3 blade would be safer.

[Roland Gendreau]

I have a 3 blade 15x9 prop in reasonably good condition if you are looking for one.

Contact me off list to discuss

Roland Gendreau
Gratitude #1183

[Hawk]

I shouda bought a lottery ticket because today I hit the only semi-submerged log for miles and now need a new 3 blade prop and shaft. And I was looking out.
Anyway, searching I didn't see any advice on the recomended prop size for the M35 30 hp. I see many people have increased the pitch to 10" for their M25s.

Any thoughts? Thanks
Hawk

[Stu Jackson]

Mel : The original posts were for a M25 engine to repitch (3 blade Sailor prop) to 10 inches.  Another later article (still early 1990's) recommended that the M25XP be repitched to 10.5 inches.  The difference after repitching to 10 inches (M25XP) was absolutely amazing!!!

I don't know your engine hours nor the maintenance done on your engine, but it is 24 years old!!  A few thoughts

Ron. I have only owned the boat for 6 months and there was no maintenance log with the boat. The engine has 1750 hours on it.  The boats curses at 5.5 knots at 2200 RPM.I can put it to full throttle at 3000 rpm and it will do 6. Reading what was written in past articles most of the boats were able to cruise at 6 with the three bladed prop. But as you point out the 88 and newer have the M25XP. So maybe staying with the 15x9 3 blade would be safer.

Mel,

Ours works just fine, has been for the 13 years we've owned our boat.  The PO had replaced the 2 blade that came with the boat.

[Hawk]

Hey Stu,

Are saying above that 15 x 10 ought to work for the M35?

I'm going to check my prop today to see if it's stamped with the size.

Hawk

[Craig Illman]

The reduction ratios on the transmissions MAY be different for the M25 variants, M30 and M35 variants, so the same pitch may not be optimal. Check the plate on your transmission.

Craig

[Stu Jackson]

Hey Stu,

Are saying above that 15 x 10 ought to work for the M35?

I'm going to check my prop today to see if it's stamped with the size.

Hawk

Nope, I was answering (as quoted) Mel's question.  I don't have an M35, so can't tell ya about my personal experiences re: props.

[Jim Hardesty]

My Max-prop is set at 10.3 inches.  Max-props are adjustable but only in set increments.  The engine does build full rpm's, boat speed is 7-7.5 knots, depending on conditions.    
Thats me, my season is about 6 months, so the bottom is always clean.  I think that a pitch of 10 inches would be just about right.
Jim

[sail4dale]

I replaced the fixed three blade prop a 15 x 9 with a Flexifold 15 x 10 three blade.  I cannot get a full 3000 RPM from the engine now but I  motor up to 2700 without smoking.  At that RPM I can motor at 7 to 7.4 Knots with a clean bottom in smooth water.  I've been very happy with the prop and backing up is great also. Cruising, I usually do 2300 RPM and will average about 6.7 knots.
Love the the prop.

[sailaway]

Mel I have a 1986 hull number 95. I have a 15 x 9 x 1 prop It works very well no smoke out of the engine at any speed. I can do 6.8 knots in flat water. Charlie

[Ron Hill]

Guys : I believe that it might be worth your while to reread the Mainsheet article I wrote a few years back on Boat speed/ Prop pitch/ Engine RPM.  I tried to make the article as thourough as I could in laymans terms.

The bottom line is that there is NO way that you can compare prop pitch between differant types(styles) of props, because they are designed differently.

The difference between transmission differentials is negable between 2:1 and 1.86:1 !!

PLEASE READ THAT ARTICLE - so people will stop trying to compare apples to oranges.  A thought

[Hawk]

My 3 blade prop is a Michegan sailor stamped 15 RH 12.......

Hawk

[mel low]

Update:
I obtained a 15-10 3 blade and had it repitched to 9. This took my boat speed from 5.5 to 6 at 2200 RPM. If I was to do this again I would have left it at 10. The 3 blade was a great improvement over the 2 blade.