Under-Propped ?

[ndutton]

My blade width is 25% of diameter. I think 33% would be more normal.

Michigan Propeller's Sailor 2 is 36%.

You know those Aussies, probably works better spinning backwards.

Correction:
The 36% is E.A.R. or Expanded Area Ratio. It's the ratio between the area of the blades to the area of the circle described by the diameter of the propeller. There's another ratio that compares the projection of the blades to the circle, takes blade pitch or blade twist into account. I can't remember right now what the other is called, the B.A.R. or the D.A.R., something like that. The E.A.R. is usually higher than the other.

[Marian Claire]

Some good, some ???. I had the new prop installed today. It is a 14 X 9 three blade. It was bored for 1.25" and my prop shaft is 1" so we used a sleeve to make up the differance. The vac #s look good from my dock testing. I seem to have lost about 2 "s from the old prop. That is right at what I was looking for. Will try to do open water tests in the AM but more SCA here so who knows how good they will be.
I do have a whine/chirp that was not there with the old prop. It kicks in around 1300 RPM and maxs at 1500 RPM and drops off from there. At 2000/2200 RPM I can still hear it but it is faint. It is not in the A-4, reversing gear or 2 to 1 reduction gear. There is no movement in the drive shaft to prop shaft coupling. No vibration that was not there before. Just noise.
Any advice?
Will post pics of the old and new prop when I get home, land home that is.
Dan S/V Marian Claire

[sastanley]

Dan, My chirp was the shaft on the shaft log...Harmonics mean something is out of whack. Mine chirped for 33 years at certain RPMs before it was a big enough problem that I had to rectify it.

YMMV.

[edwardc]

Originally Posted by Marian Claire

...
I do have a wine/chirp that was not there with the old prop. It kicks in around 1300 RPM and maxs at 1500 RPM and drops off from there. At 2000/2200 RPM I can still hear it but it is faint. It is not in the A-4, reversing gear or 2 to 1 reduction gear. There is no movement in the drive shaft to prop shaft coupling. No vibration that was not there before. Just noise.
Any advice?...

We had a lot of discussion on this thread last year about "prop singing" at certain rpms.

Coincidentally, I just had my boat "short hauled" yesterday to clean the bottom and scrape & repaint the prop. I took that opportunity to put a small bevel on the trailing edges to try and cure it, but haven't taken it out yet. As soon as I do, I'll bump the thread with the results.

[Marian Claire]

Thanks guys. Very good thread Ed. The pic of RobH2's prop is just like mine. What do you call the part that is attached to the hull? SCA thru tonight but should be calm enough Friday to do some test runs. Will keep an eye and ear on the whine. Dan S/V Marian Claire

[edwardc]

Don't know what it's called, but it sure looks like it's a holder for the cutless bearing. That looks like a set screw on the side.

I've read that many here have the bearing directly installed in the "deadwood" directly ahead of the prop, with the setscrew set in the fiberglass. This looks like a much more robust solution, less likely to let the bearing slip.

[Dave Neptune]

Dan et all, there is a good pic of a prop on another thread that you can "see" the grind used to rduce prop singing. Look at the outside edges of the prop all the way around the blade there is a "counter swirl" of grind marks you can see. Those are ground and a very very very slight angle on the drive face and a bit more of an angle on the back side. The slight strain put on the blade from the "angle" is not perfect and eliminates the harmonic vibration that is the singing. The chirp can also be cavitation as the blades pass through the deadwood restriction.
The pic is post #60 in CalebD,'s thread Shaft removal~~~~~~11/29/11 in the Driveline threads. When I first saw the pic I thought of I think it was Edwards singing prop last year, not sure it was Edward though.

Dave Neptune

[sastanley]

Now you don't have to go look for it.

--> link to that post #60 <--

And here is the pic re-posted here..

Caleb, I am still amazed with the work. That looks nothing like the piece of garbage prop I sent you..

[Marian Claire]

The mechanic stopped by the marina and I snagged him for a listen. Same results. No vibration, max whine at 1500 rpm. He suggested I loosen the stuffing box to a heavy flow and test. That produced no change so a lack of water in the cutless does not seem to be an issue. After he left I ran it in reverse at 1500 rpm and no whine!!! The new prop did not have any of the grinding or edge angle as best as I could tell. The leading edge was also much sharper than my old prop. Consensus seems to be run it and see what happens. Dan S/V Marian Claire
PS. If Hanley and PT are out in the Albermarle and it is blowing like it is here they are in for a exciting ride.

[Dave Neptune]

Dan, the whine should change as the prop dirties up and becomes less symetric, at which point it should begin to quiet. Not uncommon especially on a fresh prop. Any compitent prop guy should be able to "fix" easily but you will have to get it to him or get busy with a file yourself. If you do don't take much especially on the thrust side facing aft.
I recomend you use it as is until you either want to rid it of the whine and/or you are sure you don't want to give it another tweak.
The whine will not hurt anything unless you are of the Ulysses type, then tie yourself to the stick within reach of liquid bread, a video in hand and send us vids of the lovelies.

Dave Neptune

[Marian Claire]

Results from first open water test are very positive. I will spare you all the #s but here are a few.
2300 RPM 6.3 MPH 12" vac
2600 RPM 6.8 MPH 9" vac
2800 RPM 7.1 MPH 8" vac
There is less variation in the tail wind, head wind, beam wind #s. The MC actually "squats" and puts out that rolling wake like other boats. This is all new. The whine is much less in open water.
Look forward to seeing how she does in current and head winds.
Thanks to all. This has been a long process but worth the effort.
Dan S/V Marian Claire

[Dave Neptune]

Dan, those numbers look good for using all available from the A-4. Did you try a WOT at all, I'm guessing 3200 is about where it will max out. This is a rarity form what I have seen on this forum for the most part. At your 2800 with 8" your cylinder load is pretty low, just more burns in the same time frame so you have reduced a great deal of preassure on the rod bearings and the crank bearings will be happier too! You even have room to possibly add a bit more pitch.
The whine is less noticeable underway because the harmonics with water flowing past the hull will change the pitch and range of the "song" your prop is singing. Like is said don't worry to much about it as it has a good chance of going away once a lil growth starts. Your so close to "perfect" now any changes should be slight and patiently thought over from experiencing this prop for a while. If the "song" drives you nuts oor it is easy to get the prop removed go-4-it.

Fair winds my friend _/) _/)
Dave Neptune (\_

[Marian Claire]

Had a chance to take the MC out in less than ideal conditions for motoring. 15 to 20 and gusting higher, 2' to 3' breaking waves of very short period. With the old prop in these conditions I could not maintain speed and would always fall off when I hit a bigger set of waves. Ended up spending a lot of time regaining speed and getting back on course. With the new prop I lose a little speed when I hit a bigger set of waves but was able to push thru and not fall off. Much easier on the helmsman.Stopping power is unreal and reverse actually works and is controllable. I do agree I could bump up a little more in pitch but will run this for awhile.
While the prop was of I pulled the rudder, removed the temporary repairs and do a more permanent repair. The rudder is two large pieces of mahogany and one of the original rods had corroded allowing the upper area to separate. Pics of the props and what got sucked in the RW intake during a dock test. That is some kind of grass. Dan S/V Marian Claire

[Dave Neptune]

Dan, good to hear the power is getting to the water! That's how it should work. When you were running hard aginst the wind and sea what were you reading RPM vs vac? Did the vac values go up a bit out on the water compared to being tied to the dock?
Excellent choice to run the prop for a while before making any further adjustments! You may still have some available power left and be able to cruise a bit faster at lower RPM's yet~but wait my friend and see how it works when a bit dirty!!! Then decide.

Dave Neptune

[Marian Claire]

[QUOTE= When you were running hard aginst the wind and sea what were you reading RPM vs vac? Did the vac values go up a bit out on the water compared to being tied to the dock?


? 1. I did not get any vac #s during the "rough" conditions test. Just to awkward to do single-handed with the vac gauge in its present location. IIRC Somewhere around 2000 rpm gave me good steady forward progress without excessive pounding. My GPS speed was all over the place so any guess at speed is just that, a guess. Say 4 mph???
? 2. Yes. Checking my notes the vac # was 2"s+- higher on the open water test than the dock test at the same rpm.
Dan S/V Marian Claire

[Skywalker]

Over propped...I think this is my problem.

I have the original 13 inch prop (1966 direct drive tartan 27). I am not sure of the pitch, but Caleb (1967 tartan 27) noted 8 inch. Prior to his season, my friend ooh my prop to his shop. I asked for a reduction to gain some RPMs. He reportedly reduced he pitch an inch.

Well, my A4 is running beautifully. But, I'm only spinning her at 1500 rpm. I get to hull speed even prior to that in flat water. I'm also singing at 1300 or so.im also getting a lot, and I mean a lot, of noise. I'm thinking it's pressure waves from the prop on the hull.

In my prior ownership, I spun the indigo, but I want to race a little, so I went back to the two blade. The Indio performed beautifully.

So, I'm going to a different sop this offseason, old and very respected. I don't trust the work done this year. I'm thinking he increased pitch, not decreased! I'm also thinking of cutting down the diameter an inch.

So, if I reduce diameter and inch, and get the pitch down to 7 (based on Caleb) maybe I can get some RPMs.

Any thoughts?

Thanks

Chris

[Dave Neptune]

Chris what RPM's are you turning? I would not touch the dia on the Indigo or are you talking of the 2 blade.

You will not be using much POWER to achieve your hull speed and with the Indigo I'd guess you would achieve it at around 1800 and 10" of vac which is about 10~12 HP.

Get back with a few more details.

Dave Neptune

[romantic comedy]

It takes the same amount of horsepower to reach hull speed, regardless of prop or engine speed.

[Skywalker]

I'm turning 1500 rpm, two blade.

I'm pretty sure it's 13x8.

[Marian Claire]

One of the many things I learned during my re-propping was the value of good data.
RPM #s, and it may be wise to verify your tach with an optical tach, BTDT.
Vacuum gauge #s, I had no clue about this when I started the process but now, thanks to the folks here, I rely on it.
GPS for speed over ground. With the added knowledge of local conditions, current, head wind etc.
This type of info will tell you how well your existing prop fits your boat and your needs. What is most important to you cruising speed, sailing speed, reverse control, stopping power, more ummph to get thru adverse conditions? The pros and cons of a two blade/three blade prop.Then it is a matter of understanding your boats set up and how adjustments to the props pitch and diameter effect RPM. Then you just have to test it in the real world. No magic bullet but info and understanding may save you $$$ and avoid multiple prop changes. Dan S/V Marian Claire

[Skywalker]

Excellent approach, as always.

My tach is new from MMI this season. I don't know the accuracy, but I'll see about checking it.

I meaure my speed with my gps, flat water, back of the harbor, basically still water.

I haven't had opportunity to motor in adverse conditions. When it's been snotty, I've been sailing! Wind direction allowed me to sail in and out.

I achieve 5 kts in calm conditions at 1200 rpm or so. six kts 1400-1500.

Back in the day when I had he indigo, I didn't have a tach, so I don't know RPMs to compare.

I'm going to dive under and get the diameter for sure, 12 or 13 inches. It is the original prop, narrow blades. It wasn't stamped by he prop shop after they worked on it. Not good to use a friends "guy" sometimes.

I would bag this whole thing and buy another indigo if it weren't for my enjoyment of racing. Maybe I'll just take the 3 seconds on my PHRF and bite the bullet. I do remember how smoothly and powerfully the boat moved with it.

Chris

[CalebD]

Chris,
I am looking at my spare 13" x 8" bronze 2 blade prop. This was Shawn's 12" x 6" that I had a reputable prop shop in Newburgh, NY alter into a 13" x 8". Yes, they stamped it "13 x 8".
I bought Shawn's as I was considering the whole prop size conundrum when we replaced our prop shaft a few years ago. I was considering trying a 12" x 6" prop like all the Catalina 30' guys seem to use. Someone (I think it was Marian Claire or Hanley) suggested that when the prop sits in an aperture (as it does on a T27) that the larger prop size helps to overcome the reduced flow from the dead wood of the keel. With the C30 the prop sits in clean water under the hull, supported by a strut so the 12" x 6" gives plenty of thrust with unrestricted water flow.
I'm pretty certain that we do not run our engine at as high revs as some here recommend but I do find we get plenty of thrust from our 13" x 8" prop. I never got a chance to try out a 12" x 6" though.

[Skywalker]

You are right, Caleb. I haven't had a performance problem, but a theoretical problem! I'm not getting enough RPMs, but I haven't had too, either.

As one T27 to another, do you think the indigo would produce too much drag for racing with the three seconds I'll get?

Also, when it's gets snotty, do you think the 13x8 will have enough thrust?

Luckily, I have the fall to experiment. The winds will blow, and I'll see how Skywalker responds!

Btw, I just picked up a sym chute and pole. Free! So I have another project! Have to rig a guy, cut the pole to length. Isn't life great?

Chris

[CalebD]

Skywalker/Chris,

I also like the idea of the Indigo prop for the A4 but have not tried it out. I suspect if you allowed the Indigo prop to free wheel in the tranny (neutral) while sailing it would cause less drag. I'm not sure how the tranny would feel about that though. Gaining 3 phrf points will probably help your corrected finish times though! I think we are currently carrying a phrf of ~248 which hasn't helped us much this season. We are back in the middle of the pack.

As to snotty weather and the 13" x 8" two blade prop delivering enough thrust, I haven't had any problems so far (knocks wood). I'd guess that the most efficient propeller would be best in snotty weather; which might be the Indigo. As you might guess, the Hudson River where we race is more protected than the LI Sound outside Mt. Sinai/Port Jeff so we don't usually get really large swells like you might (6' swells on LI Sound is pretty rough if they are close together!). We do get to contend with a current in the Hudson of <= 2 knots though.

I sometimes worry that the lower rpm's we normally use may help cause our spark plugs to get dirty faster. It is probably a good idea to give our engines a good workout so they get well warmed up before winter layup. I seem to recall getting our T27 up to hull speed on flat water at about 2400 rpms.

I also like being able to "tuck" the 2 blade prop vertically behind the dead wood for racing.

[Skywalker]

If my PHRF was 248, they'd run me out of be club! I race with a 234 and they are bitching about that!

I do tuck my two blade.

I haven't had any issues, but I think I will reduce the pitch and see.

This forum keeps me thinking...

Chris