Sorry for the long post… I have a Catalina 27 with Evinrude 9.9 moored on the Columbia River. Our slip is crows-wise to the current, which can be quite strong. Backing out of the slip can be harrowing at times. I need a new prop, and am thinking about using more ‘pitch’ to hopefully increase low-rpm thrust and make backing out easier. So, does anyone know the pitch of the stock prop on this OB? And Any recommendations on a pitch that will offer better low-rpm performance? Thanks
more low-rpm thrust?
- Thread starter chabala
- Start date
- Status
Try this
Pitch is changeable on shafts with inboard engines, and it's pretty tricky. Fortunately with an outboard all you have to do is change the angle or tilt of the entire engine to achieve your objective. You can do that by moving the pins or putting a chock wedge in there temporarily until you're happy with the results.
Pitch is changeable on shafts with inboard engines, and it's pretty tricky. Fortunately with an outboard all you have to do is change the angle or tilt of the entire engine to achieve your objective. You can do that by moving the pins or putting a chock wedge in there temporarily until you're happy with the results.
I am Confused
If you increase the pitch to noticably increase low rpm thrust you will decrease the maximum rpm the engine can achieve and in turn lug it down which will cause carbon build up and cause running problem down the road. If you need more thrust why does it have to be at low rpm's why not rev the engine?
If you increase the pitch to noticably increase low rpm thrust you will decrease the maximum rpm the engine can achieve and in turn lug it down which will cause carbon build up and cause running problem down the road. If you need more thrust why does it have to be at low rpm's why not rev the engine?
Outboard Pitch and Thrust
For 1-year I had an 1998 Evinrude 9.9 2-stroke on my O'Day 240 -- 23 ft., Wing Keel, 3600 lbs. The 9.9 replaced a 10-yr. old 8 Hp. 4-stroke Honda that was getting hard to start. I recall that the Evinrude prop had a 9" pitch, and it had absolutely NO reverse thrust. Evinrude swapped the prop to a 7" pitch to alleviate the problem. The 7" did help. [Reverse thrust improved from nothing to mediocre.] Of course fuel economy deteriorated as did high-end speed. Bottom Line: after 1-yr with the 9.9 I traded it for another 8-Hp Honda. Result: nite vs. day improvement in forward and reverse thrust, plus almost double the fuel economy, and quieter and cleaner. Lessons Learned: 1. Less pitch improves low-end thrust. 2. You can't make a silk purse out of a sow's ear.
For 1-year I had an 1998 Evinrude 9.9 2-stroke on my O'Day 240 -- 23 ft., Wing Keel, 3600 lbs. The 9.9 replaced a 10-yr. old 8 Hp. 4-stroke Honda that was getting hard to start. I recall that the Evinrude prop had a 9" pitch, and it had absolutely NO reverse thrust. Evinrude swapped the prop to a 7" pitch to alleviate the problem. The 7" did help. [Reverse thrust improved from nothing to mediocre.] Of course fuel economy deteriorated as did high-end speed. Bottom Line: after 1-yr with the 9.9 I traded it for another 8-Hp Honda. Result: nite vs. day improvement in forward and reverse thrust, plus almost double the fuel economy, and quieter and cleaner. Lessons Learned: 1. Less pitch improves low-end thrust. 2. You can't make a silk purse out of a sow's ear.
pitch is matched to
the engine horsepower and load. Load is the size of your boat and its resistance in the water. When the pitch of the prop is properly matched to these conditions, the engine will run at rated peak RPM at full throttle. If the pitch is too low, the engine will over rev at full throttle. If the pitch is too high, the engine will never reach peak operating RPM. A case in point, a 50 foot houseboat using 2 70 HP outboards will run a pitch of around 11. The boat goes about 9 knots at full throttle engines turning 4400RPM. A 16 foot runabout w/ 70HP outboard will run a 19 to 21 pitch and go 35+ knots. If you want more thrust, try a 4 blade prop or a prop shroud.
the engine horsepower and load. Load is the size of your boat and its resistance in the water. When the pitch of the prop is properly matched to these conditions, the engine will run at rated peak RPM at full throttle. If the pitch is too low, the engine will over rev at full throttle. If the pitch is too high, the engine will never reach peak operating RPM. A case in point, a 50 foot houseboat using 2 70 HP outboards will run a pitch of around 11. The boat goes about 9 knots at full throttle engines turning 4400RPM. A 16 foot runabout w/ 70HP outboard will run a 19 to 21 pitch and go 35+ knots. If you want more thrust, try a 4 blade prop or a prop shroud.
Pitch is the designed forward movement
A propeller is designed to move the boat forward a given distance/ rev. A 7 pitch prop moves the boat forward 7"/ rev. A 9 pitch prop moves forward 9" / rev. If you over power a 9 pitch prop, you get what is known as prop slipand the prop becomes ineffective. If you lower the pitch to 7 pitch, the prop bites the water better at lower speeds. Mercury used to make a dog eared prop (cir 1978)that had a lower pitch and bigger blades for low speed. r.w.landau
A propeller is designed to move the boat forward a given distance/ rev. A 7 pitch prop moves the boat forward 7"/ rev. A 9 pitch prop moves forward 9" / rev. If you over power a 9 pitch prop, you get what is known as prop slipand the prop becomes ineffective. If you lower the pitch to 7 pitch, the prop bites the water better at lower speeds. Mercury used to make a dog eared prop (cir 1978)that had a lower pitch and bigger blades for low speed. r.w.landau
chabala, another thought ...
If you are trying to move your stern upstream as soon as you put it in reverse, the bow will pivot around the keel and swing downsteam right away. Try backing the stean straight out or even aiming the stern down stream abit to gain some stearnway. Remember the boat will have a tendance to pivot on the keel. Use this to your advantage. As soon as you have sternway (moving backwards with some speed) then turn the stern up stream. Try this in an area that is not congested if you can find a place with similar conditions and less boats. r.w.landau
If you are trying to move your stern upstream as soon as you put it in reverse, the bow will pivot around the keel and swing downsteam right away. Try backing the stean straight out or even aiming the stern down stream abit to gain some stearnway. Remember the boat will have a tendance to pivot on the keel. Use this to your advantage. As soon as you have sternway (moving backwards with some speed) then turn the stern up stream. Try this in an area that is not congested if you can find a place with similar conditions and less boats. r.w.landau
Thanks 
Thanks for all the info. Revving the engine causes the boat to rabbit into the narrow channel between mooring piers which results in much panick while running around to prevent smacking neighboring boats. I'm not worried about fuel economy or top end, as we only motor to get into the channel to get the sails up. I'll look into a 7" pitch 4 blader, and practice pivoting.
Thanks for all the info. Revving the engine causes the boat to rabbit into the narrow channel between mooring piers which results in much panick while running around to prevent smacking neighboring boats. I'm not worried about fuel economy or top end, as we only motor to get into the channel to get the sails up. I'll look into a 7" pitch 4 blader, and practice pivoting.
- Status