Propeller Selection

[Dave O]

Can anyone refresh suggestions for a new prop?

I have a C&C 29 Mark I with an Atomic 4 and the original 2 blade prop. I am considering a new prop for the following reasons:

1. When leaving the dock and in reverse, the current prop creates so much prop walk that the boat is extremely difficult to handle and predict. In fact it's more an art than a science. I am thankful for rub rails. So are those in neighbouring slips. :-)

2. When returning to the dock reverse is pretty much not effective. I need to "glide" into the dock and judge (and hope) that forward momentum is not too great.

I don't expect the boat to brake like a car, but I have seen many vessels of a similiar size approach a dock and "back off" much more quickly than I can.

I am leaning to Indigo but I have seen reports of others. Any thoughts or suggestions?

[Trysail]

Can anyone refresh suggestions for a new prop?

I have a C&C 29 Mark I with an Atomic 4 and the original 2 blade prop. I am considering a new prop for the following reasons:

1. When leaving the dock and in reverse, the current prop creates so much prop walk that the boat is extremely difficult to handle and predict. In fact it's more an art than a science. I am thankful for rub rails. So are those in neighbouring slips. :-)

2. When returning to the dock reverse is pretty much not effective. I need to "glide" into the dock and judge (and hope) that forward momentum is not too great.

I don't expect the boat to brake like a car, but I have seen many vessels of a similiar size approach a dock and "back off" much more quickly than I can.

I am leaning to Indigo but I have seen reports of others. Any thoughts or suggestions?

I have a C&C 30 with a direct drive and the Indigo prop. Here are my observations;

In forward, cruising I gained a couple of hundred RPM. Up to about 2200+. With the two blade I could barely reach 2000. Motoring in a chop seems better, but that's a tough one to judge with all the current and changing conditions here in New England.

Stopping power using reverse is better, maybe 20%

Stopping power using forward is about the same, but, I don't have the prop walk using forward to stop the boat when going in reverse. Yes, had a little prop walk when going from backwards to stop/forward.

Prop walk in reverse is about 40% reduced.

Then engine vibrates MUCH less.

All in all I have to say that I am very happy with the prop. If I was ever to own another boat with an A-4, the 3 blade prop would be at the top of my list of upgrades.

Just don't expect the prop walk to go away completely.

Hope this helps.

[David Masury]

As an owner of a C&C 27 MK lll I can tell you that prop walk is partially a function of the fact that C&C designed the prop to be off center so you did not have to drop the rudder to install or make fixes to the drive system. The other thing is that most fin keel boats experince prop walk simply because there is not enough lateral resistance in the stern to counter the effect.

Now, changing a prop to get better performance under way is a matter of choice. A friend with and Ericson 32 asked me about my prop which is a 11 inch diameter with a 5 inch pitch.. for my boat it is great. He changed his prop to a 12 X 5 and is quite happy with the performance. Essentially, he increased his rpm, but lowered the loading of the engine. He is getting better economy and more control.

I hope this helps a bit

David

[gregt]

Does anybody have experience with or heard about the CDI PerfectPitch propeller?

[msauntry]

No news on the CDI prop recently. General opinion has Indigo's prop being the one to beat. I put one on my Alberg 35 and am quite happy with it. Full keel boat with prop in an aperature, so I still have plenty of propwalk, but its great in forward.

I used to have a Triton with a 13x8 two-blade that I put on the A35. That never let the rpm's get up to where they need to be to push this large boat.

I do like to get every bit of speed possible out of the old girl, so I'm thinking about repitching 13x8 to 13x6 and see if that makes it useable.

[Dave O]

Hope no one minds but I have refreshed this topic with a new question. Fall haul-out is approaching and I am completing my winter upgrade list.

There have been several responses like this:

"With the two blade I could barely reach 2000 RPM. In forward, cruising, I gained a couple of hundred RPM. Up to about 2200+."

This relates to using the old OEM 2 blade prop 11x7x7/8 versus a new 3 blade upgrade such as Indigo.

Why is it possible to reach a higher RPM and what is the significance?

I understand why a 3 blade prop might deliver more thrust, but what does higher RPM have to do with this? I can create higher RPM with my 2 blade just by opening the throttle, but after a certain point the prop is just trashing around and creating froth with no added power (it is cavitating).

Sorry for the basic question but I want to fully understand before investing in a new prop over the winter.

Dave
C&C 29 Mark I
Port Credit, ON.

[msmith10]

The reason people want to get to a higher RPM is that the horsepower curve goes up at higher RPM. I don't remember the numbers, but they're on this site somewhere. The A-4 is only putting out a fraction of its rated 30 hp at lower RPM, for example, maybe 15 hp at 1800 (these numbers are just an example, not the actual results). This results in working the engine pretty hard. If, however, you're running at 2200 RPM, you may be putting out 20 hp, thus working the engine less. This also gives you more reserve if you're fighting a fast current or driving into big waves. My engine pretty well tops out at 1800-1900 RPM. It would be nice to know that you have 300-400 RPM (as well as HP) in reserve in a pinch. Choosing a prop that allows you to run at a higher RPM will give you more HP, works the engine less, and gives you more reserve. Unfortunately, I race and I don't want the drag penalty of a 3-blade prop. I used to have a folding Martec and the performance was so bad I went back to the original 2 blade. The performance was so much better under power I was willing to sacrifice the drag penalty under sail, but I just can't bring myself to go the next step and go to the Indigo.

Mark Smith
1977 C&C 30 Mark I
Port Clinton, Ohio (Lake Erie)

[tenders]

Running at a higher RPM also enables the alternator to generate more juice.

[wlevin]

cdi and indigo

I have tried both the plastic, (two-blade) cdi and the bronze (three-blade) indigo props on our Tartan 34. I like the cdi a bit better. I can hide it behind the keel by lining it up with a mark on the shaft. I have plenty of reserve rpm over 2000 if I need it. The indigo seems to back a bit better, but this is not a big issue to us. I keep the indigo in reserve because I have broken a blade on the cdi hitting a mooring. cdi replaced it for half the original purchase price.
Bill and Jeanne
T-34 #453
Otter

[Bob.Griffin]

I have the CDI plastic 2-blader on my C&C Corvette (31ft) and am generally happy with it. There is a little prop walk but not enough to worry about. Reverse is never as good as forward, I remember reading the reason why but now I forget, I just need to be careful not to over-power in reverse to avoid cavitation.

Bob (s/v Saga)

[Dave O]

Here is a quick update on the results of installing an Indigo 3 blade prop on my C&C 29 Mark I. The principal reason for doing so was to improve handling near the dock ... esp. backing up with all the associated prop. walk problems. I installed the Indigo last fall after haul out and have left the slip 7or 8 times so far this spring.

With the new prop I can reverse much more strongly (without cavitation) than with the original 2 blade OEM. The increased thrust gives me better control and steerage in reverse. The new prop also reduces prop walk, so I can reverse the boat quite forcefully in pretty much a straight line.

Once the boat in underway (in forward) vibration is noticeably reduced. The boat runs smoother and in a sense more forcefully. So that is an added plus I was not looking for but am glad to get.

The only downside is that I can back up with much more speed leaving the dock and that takes some getting used to. Instead of creeping out of the slip at very low speed to reduce prop walk I can almost shoot out of the slip. If I have the wheel turned too sharply to port or starboard, and do not react quickly to the speed, the boat can almost do a complete circle which is amusing to everyone watching but not great for my peace of mind.

All in I think the Indigo was a good investment for the price.

Dave
C&C 29 Mark I
Port Credit, ON

[rigspelt]

Dave, with the 3-blade, did you notice an increase in RPM at cruising speed, and did you notice a speed drop sailing?

[Dave O]

Hi Rig ...

I anticipated an improvement in RPM cruising and a slight drop in sailing performance from posts by others. However, as I don't have a tach, both are quite subjective so I can't say one way or another.

The new prop did deal with the main issue I had (manuevering around the dock). So if there is a decrease in sailing performance it is not noticeable to me and I'll lve with it. Equally, if there is an improvement in RPM cruising I have not really noticed it but I'll be happy to take the improvement however slight.

I believe others are more discerning about those points and they may wish to comment.

Dave

[Mark S]

Dave,

I'm not familiar with the C&C 29 underwater profile. Is your prop in an aperture or is it in open water? Our Pearson 35 has a two blade in an aperture and I'm ignorant enough about prop issues so as not to know whether our probably bronze two blade gives us the performance we need. Generally, we cruise at 6 knots at 1800 RPM but a good head wind or current slows us down. Powering up further than 1800 results in either clutch slipping or cavitation (issues posted elsewhere in the forum). I'd like to know that I have room to give it more power if necessary. Obviously I have to solve the slipping/cavitating issue first. I'm just trying to cast a big net to gather as much knowledge as I can and aperture vs. open water seems to be an important consideration.

Mark S

[Dave O]

Mark

It's in open water. The photo of the old prop does not show this, but the shaft is at a fairly significant angle or offset from the centerline of the boat.

Dave