prop size for Ericson 32-3

Just finished my first summer with an 1985 Ericson 32-3. Great boat. Lots of fun sailing. Different story under power where speed is slow. Getting the proper rpms under load and no load. Cruising 2400 rpm I get 4.5-5.0 kts. Engine is a Universal diesel M25. Prop is a two blade fixed 12LH10. I sense this is not the correct prop size. Any examples of what is working out there is greatly appreciated.

Prop Experiences

Hi! We have a "87 32-3. We've owned the boat 9 years and have had three props on the boat. She came with a fixed two blade. We changed to a three blade fixed in 2001. This increased propulsion and improved reverse in spite of port torque. Normal cruising is 5.5 -6.0. Four months ago we changed to a 2 blade Flex O Fold prop. Propulsion is as good or better and reverse is better with no port torque. We normally cruise at 1800 RPM. The 3 blade fixed was a 14X9. The 2 Blade fixed is a 15X10.

More Prop Wash....

Chris,
There are some applicable threads on this site, too.
Here's a recent one:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=7444&referrerid=28

Or this:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=7040&referrerid=28

For something that seems, at first blush, to be a simple physics or engineering question, prop selection actually is rather complex.

I sometimes wonder if, behind the scenes, the experts actually do have to read tea leaves or throw the bones.....


Best,
Loren

props

Gulfcoaster, thanks for the reality check. Nice to hear an example that matches my situation. How do you find the folding prop under sail compared to the fixed two blade...does it contribute to better speed under sail? I hesitate at a fixed three blade.

prop wash

Loren:
Thanks for the insight. You are correct, it seems more black magic than science. I'm happy to get some help before making the investment though.

Still more prop stuff

We went with the 2 blade because it has less drag and allows better boat speed. There is a great article in the Yacht magazine about props a few months ago. They equated a three blade prop locked to dragging to buckets behind the boat. Lots of drag. These gizmos are expensive and unless you want to race.. I'd just get a bigger prop with more prop pitch. The thing cost 1015.00 and it didn't fit when folded back. It cost another 1100.00 to pull the shaft and rudder and have the shaft shortened. I got a good dent in the wallet, but am very satisfied with the prop. If you just get a bigger prop with more pitch you will get better boat speed at a lower RPM.

Chris, You certainly not getting the kind of boat speed when motoring you should be. Our 1986 32-3 with an M25 easily motors at 6.4 kts (2500 rpm)and peaks out at 6.9 (2950 rpm) when the bottom is squeaky clean. A nice all day motor speed is 6.1 at about 2000 rpm. You will get the benefit of lots of experience and advice on this site. I would recommend you get accurate full power data for boat speed, rpm, gear ratio and existing prop geometry and talk to a propeller shop. The balance of prop diameter, pitch and blade area is almost an art. They will set you up with recommendations for prop application. There is also lots of info on this site you will find by searching. Keep at it. It is worth it if you motor much at all.

newgringo:
Since looking into this, I've talked with a prop guy. Based on boat size, weight, engine, gear ratio, etc he has spec'd a 14x11, 2 blade or a 15x11 if it fits with enough clearance under the skeg (3" clearance is recommended). I'll have to inspect when the boat is pulled for the season. For reference, what is your prop size and # of blades? I like the speed you are getting. Thanks, Chris.

Chris,
Our boat is fitted with a 14" dia by 8" pitch Michigan Sailer 3 blade. The 14 " dia gives us 1 3/4 " clearance from tip to hull for 12 1/2% clearance. Very smooth operation. It is important to note that we have Hurth HBW100 1.8:1 gearbox and not the original HBW 50 which had a 2.0:1 gearbox. Of interest is you state you now have a LH prop. That means you have some other kind of gearbox or you are running the HBW 50 tranny in reverse. Very interesting. Important to nail that down.
When all is said and done the prop guys will want you to peak out at 3000 rpm or close when at full power which should push you to hull speed.

Newgringo:
Thanks for the heads up on the transmission. I am unaware that the boat has anything but original. Could the HBW50 transmission run an LH prop? You are correct that transmission and gear ratio is key for the prop sizing so I'll take a closer look at it tomorrow and try to find some model info. Absolutely that needs to be correct.

Chris,
I had a few moments so thought I offer some thoughts. I think most of the E32-3s came with HBW50 tyranny's. In my service manual the most common one is the HBW50-2 but there is also an HBW50-3 with different ratios and power capacity. For the "-2" the normal installs used Shift Position "A" for forward which is the reversing position. The ratios are:
HBW50-2
A 2.05:1 Reversing Action for RH Prop Boat going Forward
B 1.86:1 Same direction for RH Prop Boat going Back wards

It is easy to tell which way your boat is rigged. Put the boat shift lever if Forward see which way the prop shaft turns compared to the engine. You can do this with the engine off by turning the engine by hand. Turn engine its normal direction, clockwise looking at the front of the engine. All for now.

details, details

Newgringo: Wow, the devil is in the details. I definitely have a LH prop. For whatever reason a previous owner decided to configure the boat this way because I don't think it came from the factory this way. However, I've learned many important details. First the Hurth HBW50 transmission is a "full power reversing" transmission, meaning that you can use forward and reverse either way and still get the same rpms. The shift cable determines the rotation. Second, my prop shaft spins CW in forward, the same direction as the engine (CW when looking aft) so my transmission is operating position "B" and therefore operates a LH prop (just a confirmation but nice to know). The big find here is that the transmission ratio is different for each rotation direction. My LH prop needs to be sized to a 1.86:1 gear ratio not the 2.05:1 for a RH prop. Had I not known this, I could not size the correct prop. Thanks for your help. BTW, great day on the water in Narragansett Bay today. 15-20kts steady wind building to 20-25kts late in the afternoon...great fall sailing.