34' O'Day Engine RPM at WOT

[Windchime2]

What rpm does your 34' O'Day reach at WOT? What engine, gearbox reduction, and prop do you have? I am concerned that my propeller has too high a pitch but I would like to know what other O'Days turn before I order a new prop. My 34' O'Day with the M-30 24 hp engine and a 2:1 reduction gear will only turn 2400 rpm at WOT. The engine seems to struggle at >1700 rpm where it only produces about 16 hp according to the attached Westerbeke rpm vs hp chart. It has the original 16x12 two bladed prop that is in excellent condition and clean (PropSpeed). This propels the boat at about 5.5 kts with no current or wind. Normally this works fine for us as we just use the engine for <10 minutes to get to our sailing area and return to the marina. But...we spent last month in the Abacos (Northern Bahamas) and we could have used more power on numerous occasions when the wind, current (Gulf Stream), and waves were all on the nose where we were often travelling at less than 3 kts.
The engine starts on the first rotation and runs great, although I did notice when we got home from the Bahamas earlier in the week that a lot of black unburned fuel spit out of the exhaust when I revved it up prior to shutdown. I plan on cleaning out the exhaust elbow soon as I would like to eliminate any engine performance problems before I purchase a new prop.
Your help will be greatly appreciated.
Bill in JB

 

[kloudie1]

Make sure that the tachometer is not telling you a story.. An optical tach reading on the crank pulley will verify the tach or not.. After you check the elbow, and make sure there is not an air intake obstruction, and verify the tach, then see what ya have.. does sound a bit over-propped, but ya can't make that determination without some good info.. Happy hunting..
EDIT: Another thing to check is that the valve lash (clearance) is correct.. Lots of folks don't check this as a normal maintenance item.

 

[Windchime2]

Thanks for your input. Our boat did not have a tach installed when I purchased it about 2 years ago. I installed a John Deere tach and verified its accuracy with a digital photo tach. I will proceed with your advice and post again when I make any determinations. The naval architect at Michigan propeller advised that this boat use a 2-blade 16x11 sailor prop or a 3-blade 16x10 sailor prop. Does anyone have any idea of the additional drag that would be caused by the 3-blade prop?

 

[FastOlson]

I cannot imagine that boat not motoring at 6 kts in smooth water with a clean bottom. More like 6.5.
It might be "over propped" i.e. has too much pitch.
As for drag, yup, you will lose a half to 3/4 knot under sail with a 3-blade. In the last 25 years we have used a two blade fixed, two blade feathering, and currently a 3-blade (narrow "sailor" blade shape) fixed. We motor at 7. with a clean bottom.
It may take some trial-n-error to get the pitch right. Do you have a diver available ? -- often that service is cheaper than a haul out.

 

[jssailem]

@Windchime2 If you are lookin at “new” props, I would suggest you include WestbyNorth in your request for a prop. Located on Vancouver Island BC, the owner Kelsey is a good guy and a great prop engineer. They make their own and customize it to your boat.

I am a happy owner of a “Campbell Sailor” prop manufactured to my boat’s specifications. Kelsey and I discussed my boat, my motor and transmission. He did some calculations and provided me with the prop that best fit. It went on easily, and I improved my performance both under power and sailing over the stock 3 blade the boat came with.

Check them out on the internet. They ship to where you have the boat.

Good Luck.

 

[Windchime2]

Jssailem
Thanks, I’ll contact them

 

[njlarry]

Sorry it's taken so long to respond. I did not have the info and then searching to find your post came up with no response.
I am also over proped. I have a Universal m25-XPB which I think is rated at 26 hp but puts out 21 hp at the shaft. Hurth 2.0 to 1 ratio and 2 blade 14x9 prop. She cruises very well at 1900 with 6 ktns but will will only get to 2400 to 2600 rpm wot, if I remember. The manual says it should have 2900 at wot.
Made a table of rpm vs speed. Will post later if I can find it.

 

[Windchime2]

Thanks njlarry for the info. Even though you may be over propped your prop sounds a lot closer to the correct dia and pitch than my 16x12. I'm working on long overdue house projects now so I haven't started troubleshooting the boat. We were on her today for a beer and engine/genset run.

 

[jibes138]

Sorry it's taken so long to respond. I did not have the info and then searching to find your post came up with no response.
I am also over proped. I have a Universal m25-XPB which I think is rated at 26 hp but puts out 21 hp at the shaft. Hurth 2.0 to 1 ratio and 2 blade 14x9 prop. She cruises very well at 1900 with 6 ktns but will will only get to 2400 to 2600 rpm wot, if I remember. The manual says it should have 2900 at wot.
Made a table of rpm vs speed. Will post later if I can find it.

Take your prop to a propeller shop, explain the situation and ask them to adjust the pitch. They can take a half inch or inch off the pitch to give you more RPM's.