Return to the home page...

Go Back   Moyer Marine Atomic 4 Community - Home of the Afourians > Discussion Topics > Drive Train / Propellers

Reply
 
Thread Tools Display Modes
  #1   IP: 205.211.168.100
Old 09-05-2012, 11:22 AM
smp smp is offline
Senior Member
 
Join Date: Dec 2011
Posts: 54
Thanks: 0
Thanked 0 Times in 0 Posts
What size prop?

I don't know anything about props. I know that I have a two blade fixed on my C&C 32 and I think it's right hand drive and I think that because I read that right hand drive has prop walk to port and that's what I have! Lots. Right now backing up is really difficult. Would a folding prop make this harder or easier? Probably a tough question to answer as there are different designs. What size should I be looking for? There's a guy locally selling a folding prop it's 15" diameter with a 12" pitch and 1" shaft, is this right for my boat?

I want to go faster
And if it improves reversing that's great. If it makes it worse that's bad. If reverse remains tricky but the boat goes faster that's still a win.

Thanks for any and all input.
Steve
__________________
-Steve

Suhana, C&C 32
Toronto
Reply With Quote
  #2   IP: 24.224.206.117
Old 09-05-2012, 11:32 AM
Mo's Avatar
Mo Mo is offline
Afourian MVP
 
Join Date: Jun 2007
Location: Halifax NS,
Posts: 4,401
Thanks: 202
Thanked 318 Times in 220 Posts
Folding prop is good for racing your 32....will have a considerably less performance than your two blade in reverse. I see you are in Toronto so docking might not be as horrendous there as here some days. I have a 3 blade and it's staying on just for the reverse....I'll take the hit on speed. Some days I can have 30 kts of wind on the stern coming into dock...I can lay her there.

Mine is 12/6 (pretty sure). The stamp is hard to read...either a 6 or a 9 but I don't think it's a 9....performs very well with my 30.

Hope that helps you out.
__________________
Mo

"Odyssey"
1976 C&C 30 MKI

The pessimist complains about the wind.
The optimist expects it to change.
The realist adjusts the sails.
...Sir William Arthur Ward.
Reply With Quote
  #3   IP: 71.118.13.238
Old 09-05-2012, 11:56 AM
Dave Neptune Dave Neptune is offline
Afourian MVP, Professor Emeritus
 
Join Date: Jan 2007
Location: Lake Arrowhead Ca.
Posts: 4,466
Thanks: 543
Thanked 720 Times in 490 Posts
Angry Walking!

Steve, the only way to really reduce prop walk is to get away from a 2 blade and go to 3. I did so for the same reason as Mo. Now I can back out of my slip and I have more power forward. I went with a small 3 blade and it actually has less drag than the 2 blade I removed. I went from a 13 X 7 to the Indigo and have been happier and faster ever since, that's sailing and motoring.
My boat is 35' and really works the lil' beastie below.

Dave Neptune
Reply With Quote
  #4   IP: 206.125.176.5
Old 09-05-2012, 12:48 PM
sastanley's Avatar
sastanley sastanley is offline
Afourian MVP
 
Join Date: Sep 2008
Location: Solomons, MD
Posts: 6,810
Thanks: 832
Thanked 458 Times in 345 Posts
Steve, that prop is WAY TOO BIG for your boat, probably even with a reduction drive Atomic4. (edit, thanks Mo..I think you're right..15" too big even with reduction. )

One major difference between most Atomic 4's and their diesel counterparts is most diesels have transmissions that reduce the prop speed as compared to engine speed by typically 50% (2:1 reduction) - most Atomic4's are direct drive..the 'detent' you feel when shifting into forward locks the clutch plates so your 'transmission' (reversing gear) and prop spins the same speed as the engine...Slower prop speeds allow you to swing a bigger prop..faster prop speeds require a smaller prop. This presents some challenges for efficient motoring and it is easy to overprop an Atomic4.

You probably want a smaller prop..the Atomic4 does not make enough power at typical cruising RPMs to spin a big prop. The Indigo prop mentioned by Dave is a 10" diameter x 7.4" pitch 3 blade prop specifically designed for the Atomic 4.

As Dave & Mo commented a two blade will walk more than a 3-blade, generally speaking, and also generally have less sailing drag (Dave's huge old prop being an exception). Total blade area (i.e. drag when sailing) is a factor, and there is a trade-off...a better prop for motoring will result in some trade-off for sailing...a prop that is good for sailing (folding) will result in reduced motoring performance, as they typically don't back real well. A 2-blade folding or feathering prop would provide the least sailing drag. A fixed 2-blade prop can be stored vertically to hide it behind the keel/deadwood/strut to some degree..a 3-blade does none of the above, but probably performs the best under power.

There are other props for Atomic4's...i.e. the CDI prop..which has flexible blades that flatten out at higher RPMs to unload the motor...they are a type of plastic though, so conventional wisdom would indicate they are more prone to damage (I have no personal knowledge of this, my own theory). There are prop companies ($$) that will make a prop that you can adjust the pitch on so you can find the perfect match for your boat & sailing conditions..these may feather or fold, but are likely pretty expensive..a company like MaxProp or Kiwi Props comes to mind here.

One more thing about backing up with an Atomic 4 boat. The reversing gear assembly provides a slight reduction to create "reverse"...about 1.3:1...so 2,000 engine & prop RPM in forward (w/ direct drive) does not equal 2,000 prop RPM in reverse. I can run WOT about 2,250 RPM in forward, but spin the engine over 2,600 RPM in reverse at WOT...and it scares you at first because the reversing gear screams and howls, but I think the engine loves it since they generally run in a lugging condition under 2,000 RPM.

So, now you know a little more about props...don't buy that huge 15" prop unless you are certain you have enough tip clearance (distance between prop tip & hull), a 2:1 reduction drive on your Atomic 4, etc.. - The absolute largest prop I could spin on my C-30 is 12" diameter, due to tip clearance, unless I moved the strut aft and a longer shaft to get it away from the hull. I have the 10" Indigo and took the slight sailing performance hit, for the happier engine and motoring advantages. If I raced my boat, I'd have a reasonably priced Martec 12" x 6" 2-blade folding prop and deal with the middle-of-the-road motoring performance.

edit - Steve, after my long dissertation on props, I have some questions for you.."you want to go faster"...motoring or sailing? The boat will only go to hull speed, and a larger sailboat (i.e. over 30' or so) will never get there with the size motor that is in them..you can get close, but there is simply too big a trade-off between HP & prop size to get a boat to theoretical hull speed under power. With a super clean bottom & clean prop and good running engine, I am in the 6.05-6.1 knot range at WOT in perfect conditions. One week's worth of bottom growth knocks this to 5.8-5.9, so the conditions have to be perfect all of the time..flat water, clean bottom, clean prop, strong engine, no wind, etc... It does not take long to knock the performance off, and as you can see, there are many factors. Therefore, all that being said, I like to cruise about 5-ish to 5.2 knots...That is about 1,850-1,950 RPM and the motor is happy and I am happy. Motor sailing helps a lot too, and I usually have the mainsail up in 95% of my "under way conditions" and it can give me anywhere from 0.1 knot of help to a knot & a half sometimes.

So - several questions for you -
1. What do you have now?
2. Do you want to motor or sail faster? (How much faster?)
3. Do you want to motor faster at the engine's expense?
__________________
-Shawn
"Twice Around" - '77 Catalina 30, #511 with original A-4 & MMI manifold.
She is even happier with fresh paint on the topsides!

http://www.moyermarine.com/forums/signaturepics/sigpic3231_6.gif

Last edited by sastanley; 09-05-2012 at 01:10 PM. Reason: more questions for Steve & a few edits
Reply With Quote
  #5   IP: 24.224.206.117
Old 09-05-2012, 12:54 PM
Mo's Avatar
Mo Mo is offline
Afourian MVP
 
Join Date: Jun 2007
Location: Halifax NS,
Posts: 4,401
Thanks: 202
Thanked 318 Times in 220 Posts
Shawn is right. Over looked the size of the prop you were looking at....forget it even with a reduction drive...too much for her. The engine won't turn it and then you will get off the dock in a breeze and the boat can't get going fast enough....then you blow into someone.

There is sweet spot with props...go outside that range and boat control, in various situations, is gone out the window.
__________________
Mo

"Odyssey"
1976 C&C 30 MKI

The pessimist complains about the wind.
The optimist expects it to change.
The realist adjusts the sails.
...Sir William Arthur Ward.
Reply With Quote
  #6   IP: 205.211.168.100
Old 09-10-2012, 10:51 AM
smp smp is offline
Senior Member
 
Join Date: Dec 2011
Posts: 54
Thanks: 0
Thanked 0 Times in 0 Posts
Thanks for all the input guys, much appreciated.
To answer your question Sastanley, I want to go faster under sail and I would like to reverse better. I'm on the C&C mailing list and I was following a thread about folding props and I read a few comments about IMPROVED reversing performance with folding or feathering, can't remember which. Anyway, on the long list of projects that require large inputs of boat bucks I think that a new prop is very low on the list. You guys have shed light on the subject for me and I thank you
__________________
-Steve

Suhana, C&C 32
Toronto
Reply With Quote
  #7   IP: 138.88.71.210
Old 09-10-2012, 10:31 PM
sastanley's Avatar
sastanley sastanley is offline
Afourian MVP
 
Join Date: Sep 2008
Location: Solomons, MD
Posts: 6,810
Thanks: 832
Thanked 458 Times in 345 Posts
Steve,

From my understanding, a feathering prop is better for motoring performance (especially in reverse compared to a folding), and will give you the best 'under sail' performance as well in terms of the least amount of drag. The compromise in this case is $$$, as feathering props tend to be expensive.

I know a guy on Sailing Anarchy, by the name of "RockHead"...he is a US dealer for a good feathering prop company. I think it is Flex-o-Fold.
__________________
-Shawn
"Twice Around" - '77 Catalina 30, #511 with original A-4 & MMI manifold.
She is even happier with fresh paint on the topsides!

http://www.moyermarine.com/forums/signaturepics/sigpic3231_6.gif
Reply With Quote
  #8   IP: 24.188.39.151
Old 09-10-2012, 11:28 PM
Skywalker's Avatar
Skywalker Skywalker is offline
 
Join Date: Jan 2012
Location: Stony Brook, NY
Posts: 621
Thanks: 0
Thanked 17 Times in 12 Posts
Neptune

Did you really gain boat speed with the Indigo?

On my Tartan 27, I started with the original two blade 13 x 7, switched to the Indigo to deal with he very strong current in my harbor, then switched to a Vari prop two blade feather when racing became more important.

If I did not race, I'd stick with the Indigo. Unfortunately, I sold the Vari prop (long story), so now i have to chose between the two blade 13x7 and the Indigo.

I'm still racing...

I'm leaning to the two blade and hiding it behind the deadwood.
Reply With Quote
  #9   IP: 96.229.18.9
Old 09-11-2012, 08:43 AM
Dave Neptune Dave Neptune is offline
Afourian MVP, Professor Emeritus
 
Join Date: Jan 2007
Location: Lake Arrowhead Ca.
Posts: 4,466
Thanks: 543
Thanked 720 Times in 490 Posts
Lightbulb Choice

Skywalker, I did not loose any speed with the Indigo when changing from a 13 X 8", which has about the same "area" exposed. My prop runs in the open not behind anything. If you can tuck the 2 blade behind it is less drag. Remember the Indigo is quite small at 10" diameter and with the "seconds" you gain with a 3 blade rating may just offset the speed and make a gain for you, it did in my case.

Dave Neptune
Reply With Quote
  #10   IP: 24.188.39.151
Old 09-11-2012, 07:38 PM
Skywalker's Avatar
Skywalker Skywalker is offline
 
Join Date: Jan 2012
Location: Stony Brook, NY
Posts: 621
Thanks: 0
Thanked 17 Times in 12 Posts
Thanks for the feedback.

I'm torn. I love the performance of the Indigo but I get a little crazy with the racing.

I'm planning on entering the Around Long Island Regatta again, a 190 mile ocean race.

Weekly beer can, local regattas, too.

I don't know.
Reply With Quote
  #11   IP: 74.108.24.222
Old 09-11-2012, 08:06 PM
Loki9's Avatar
Loki9 Loki9 is offline
 
Join Date: Jul 2011
Location: Long Island, NY
Posts: 379
Thanks: 0
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by Skywalker View Post
Thanks for the feedback.

I'm torn. I love the performance of the Indigo but I get a little crazy with the racing.

I'm planning on entering the Around Long Island Regatta again, a 190 mile ocean race.

Weekly beer can, local regattas, too.

I don't know.
I was in the same boat, so to speak, and I went with a Martec 12x7 folding prop. I'm very happy with it, easiest 1/2 knot you can get, and I don't feel like I gave up anything to get it (other than $$$).
__________________
Jeff Taylor
Baltic 38DP
Reply With Quote
  #12   IP: 24.188.39.151
Old 09-11-2012, 08:32 PM
Skywalker's Avatar
Skywalker Skywalker is offline
 
Join Date: Jan 2012
Location: Stony Brook, NY
Posts: 621
Thanks: 0
Thanked 17 Times in 12 Posts
Unfortunately, my T 27 has an aperture - no room for folding and don't have two grand for feather!
Reply With Quote
  #13   IP: 74.108.24.222
Old 09-11-2012, 10:27 PM
Loki9's Avatar
Loki9 Loki9 is offline
 
Join Date: Jul 2011
Location: Long Island, NY
Posts: 379
Thanks: 0
Thanked 3 Times in 3 Posts
Oh well, hiding a 2 blade is probably the best option then.
__________________
Jeff Taylor
Baltic 38DP
Reply With Quote
  #14   IP: 138.88.71.210
Old 09-11-2012, 11:24 PM
sastanley's Avatar
sastanley sastanley is offline
Afourian MVP
 
Join Date: Sep 2008
Location: Solomons, MD
Posts: 6,810
Thanks: 832
Thanked 458 Times in 345 Posts
Question

Skywalker...do they give you a 6 second PHRF credit where you are for a fixed prop?
__________________
-Shawn
"Twice Around" - '77 Catalina 30, #511 with original A-4 & MMI manifold.
She is even happier with fresh paint on the topsides!

http://www.moyermarine.com/forums/signaturepics/sigpic3231_6.gif
Reply With Quote
  #15   IP: 24.188.39.151
Old 09-12-2012, 06:02 AM
Skywalker's Avatar
Skywalker Skywalker is offline
 
Join Date: Jan 2012
Location: Stony Brook, NY
Posts: 621
Thanks: 0
Thanked 17 Times in 12 Posts
I've gotta dig out my old PHRF certificate. I think it's only 3 seconds.
Reply With Quote
  #16   IP: 206.125.176.5
Old 09-12-2012, 08:35 AM
sastanley's Avatar
sastanley sastanley is offline
Afourian MVP
 
Join Date: Sep 2008
Location: Solomons, MD
Posts: 6,810
Thanks: 832
Thanked 458 Times in 345 Posts
Lightbulb

Hmmm..OK..I was just curious.

I only do one "race" per year in my boat, and it is a fun double-handed one. I use a 6 second credit here on the Chesapeake, but my boat hasn't had a real PHRF cert for 20+ years.

In reality, none of that matters much..6 seconds per mile is something like 2 boatlengths (too early to do the math)..

New sails, a clean relatively smooth bottom, not carrying 500 lbs. of junk on board and no bad crew work is really what wins the race.
__________________
-Shawn
"Twice Around" - '77 Catalina 30, #511 with original A-4 & MMI manifold.
She is even happier with fresh paint on the topsides!

http://www.moyermarine.com/forums/signaturepics/sigpic3231_6.gif
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
bolt size for prop shaft coupling tartansailboat Drive Train / Propellers 34 09-27-2011 11:08 PM
Proper size and pitch prop for 74 C&C33 MkI kwalters Drive Train / Propellers 6 10-16-2008 05:24 PM
prop performance baileyem General Interest 3 06-07-2007 09:30 PM
Prop size Sailwood Drive Train / Propellers 8 05-06-2005 02:55 PM
Prop effect on A4 Performance raleighm Drive Train / Propellers 2 04-29-2005 11:47 AM


All times are GMT -4. The time now is 08:05 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2021, vBulletin Solutions, Inc.


Universal® is a registered trademark of Westerbeke Corporation

Copyright © 2004-2021 Moyer Marine Inc.

All Rights Reserved