max prop settigs

[frankies56]

hello everybody I think I posted this on the wrong thread, but I have 37 cutter with a 2 blade max 16 inch max prop I emailed the company and they suggested a 14 pitch after telling them eng hp, lenght at the waterline.and weight , now just had the bottom painted and when I was leaving I was under proped so bad I could rev past to 3800 rpms. what a disapointment. now if any of you are running a two blade prop what diameter and pitch are you running I would like to keep it at 3000 max rpm,s this is the second time now last one I did not have a manual so just looked at it and guessed. it keeped it at 2800 but felt it was loading the eng. any thoughts on this ??

 

[fstbttms]

What do you mean you "looked at it and guessed"? Guessed at what?

 

[frankies56]

I guessed at the pitch. just by looking at it not knowing what the letters meant

 

[fstbttms]

I guessed at the pitch. just by looking at it not knowing what the letters meant

Jeezus. How can you bitch about the prop's performance when you assembled it without using the instructions? You blindly set the pitch, using absolutely nothing to guide you and it's the company's fault that the pitch is incorrect? Unbelievable. I'd be surprised if the blades even feather correctly. In any event, you will need to repitch the prop. The manual is available on the PYI web site, BTW.

I guess I've heard it all now.

 

[Ron20324]

The reason for running the engine to max rpm in neutral then in gear while under way, is so the engine is working at it's proper loading. Like trying to use second gear (not 1st) to get a car going. If you want to limit rpm, back off the throttle, but set the prop properly.

 

[frankies56]

I am not BITCHing about the prop performance, just asking what others with my boat have for there,s boy. fsthttms. you sure got a lot of attitude.who likes to sail with an as#.

 

[fstbttms]

Sure sounded like you were complaining about the pitch settings you got from PYI.

 

[frankies56]

no just asking fellow sailors what they use on there cutter. I do have the manual now.but needed something to start from thats why I asked pyi.there calculation is off. just wondering if I should step up to a 16 or 18 deg, pitch

 

[fstbttms]

no just asking fellow sailors what they use on there cutter. I do have the manual now.but needed something to start from thats why I asked pyi.there calculation is off. just wondering if I should step up to a 16 or 18 deg, pitch

Why would you assume the PYI recommendation wasn't correct? You didn't pitch the prop at the setting they gave you. By your own admission you eyeballed the pitch adjustment. You have no idea what the pitch is currently set at. In fact, it's highly probable that the blades are set at two different pitches.

 

[Blaise]

Midnight Sun uses a 17X16 folding Martec. I have a 3ym 30 28 hp. It turns to 3400 rpm under way which is about perfect. Your engine should be able to turn within 100 rpm under way. You didn't say what engine you had, but if it redlines at 3600 and you can only get 3000 underway you are way overpropped.

 

[frankies56]

Blaise, I have a 3qm30. I will try go to 16 pitch next time out.I like to run at about 2500 rpm. right now it goes at about 4.5 knots at 2500.with the 16x14 max. as for fstbttm. when I did the prop the first time I eyeball it as I said. then ask pyi for recomendation the second time. why do you want confrontation.get over it. it must be hell being around you !!!!

 

[fstbttms]

Blaise, I have a 3qm30. I will try go to 16 pitch next time out.I like to run at about 2500 rpm. right now it goes at about 4.5 knots at 2500.with the 16x14 max. as for fstbttm. when I did the prop the first time I eyeball it as I said. then ask pyi for recomendation the second time. why do you want confrontation.get over it. it must be hell being around you !!!!

No, it's not. But what you posted was that you disregarded PYI's recommendation and pitched the prop by eye with no instructions. You said nothing about pitching it multiple times. Don't blame me for your inability to communicate well.

 

[gettinthere]

he may have been rough, but he was accurate. you clearly stated you "looked at it and guessed".

 

[SG]

Frankies56:
I believe the RPM you want to run the boat at a "full" is under load. It is not running the engine at idle. I'd STOP doing that at full RPM unless you just want to damage something.

If you check the engine specs, or call a knowledgeable mechanic, or the engine manufacturer, then you can find-out what the top-end under load RPM's should be. (Our 85 hp Yanmar is about 3200 RPM.) You shouldn't be running at that unless you're in desperate shape, have little choice, and don't intend to do so for very long (until the engine is shot). On our Yanmar, we can run all day at 2,800 RPM unless the cooling system has an issue.

In flat water with no wind (like on the Intercoastal Waterway on a calm day), your Hunter should be a "hull speed" at say 2300 RPM. If you look-up "hull speed" on the web (https://en.wikipedia.org/wiki/Hull_speed) you'll see that after you reach that speed, you need ever increasing RPM (and fuel consumption) to achieveing ever decreasing incremental additional speed.

The increases in RPM should create more proportional increases in speed below "hull speed". Above "hull speed" your fighting an "uphill" battle.

If you are lugging the engine (i.e., using too great a drive on the prop), then you'll tend to have something similar to trying to start a car off in third gear. If you're under pitched, then you'll be spinning but not driving the boar forward enough.

If boat is in flat water but has a headwind, for example, you will notice that you don't get to hull speed until your RPM is (say) 2700 RPM. When you're in a foul seaway and into a headwind, you may not get to hull speed until the RPM's have "maxed out".

So back to the Max Prop. I'd start with PYI's suggestions for your engine and boat. If you tow a dingy, it may be a little different.

Then, tell us what happens at various RPM's in various sea and wind states. Make yourself a little chart of what is the affect (or is it effect ;^))) ) of increases in RPM's and speed through the water. Be careful with tidal or water currents deceiving you.

 

[Brian D]

If you have no markings on your prop, or they are impossible to dissern, then view this youtube video and see if you make some measurement. I am sure once you get the diameter you can look at all the props of that diameter and see what the pitch is.

 

[All U Get]

St. Augustine has a wicked current, were you at slack? Maybe you want to tune it for a little more power than speed.

All U Get

 

[frankies56]

the marks are on the prop. and well I did start with pyi recommendation but was to to flat a pitch. so I will go up another pitch to 16 deg. the next time I haul it out. I think blaise has it right. as for SG. yes the first time when I got the boat. I set the prop by eye as I did not have a manual. it would top out at 2800 rpms and had terrible prop walk. the p.o. had it so over proped that it would not come out of 1000 rpm,s and black smoke.so I knew I had to do something. I like the prop, just need to dail it in. thanks. ps I would not run the motor more than 3000 till I dail it in. no worries I got time. I sail more than motor

 

[John Nantz]

.... it keeped it at 2800 but felt it was loading the eng. any thoughts on this ??

Frankie - Here are my foggy thoughts ....
I say "foggy" because that was many years ago ... put on a PYI 2-blade 16" prop on the boat. Talked to the then, maybe still is, company owner at the Seattle Boat Show. Spoke some french with him (took a class in high school) and he gave me a discount. Okay, back to the prop.

The problem with the original installation was it caused the transom to get grey due to soot. He said to tie the boat to the dock then the engine (Yanmar 3GM30) should be able to run to redline (3,600 RPM per the manual). [foggy part]: I don't remember what the RPM was but the next time I hauled it was adjusted [don't remember which way]and never had a problem since.

The Cascade distributor mechanic rep for Yanmar in Seattle said that the engine should be run at no less than 80% power (2,850 RPM) to avoid carbon build-up in the cylinders. This was in the early 1990s when he gave Yanmar workshops to the Northwest Hunter Owner Association. However, I do agree that running at a slower RPM results in very little loss of speed and a noticeable increase in fuel efficiency, and, it is quieter, but I am concerned about carbon in the cylinders.

Edit, Epilog: Besides crosswords, this is one of the only, I think, three times in my life that I used French! One of the other times was in Czechoslovakia where we wanted lunch at a restaurant and the menu was in the local language. Overheard a couple speaking French and asked them about the menu. The wife was french and her husband was from Czechoslovakia so we got our lunch. Voulez vous le beof avec petit pois mon amie? Like I said, that was a long time back and a long time since l'ecole et je oubliez trés becoup. Since then, being able to speak some German has been infinitely more helpful for doing construction in Europe, but I'm afraid age takes it's toll on the ability to learn.