Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 22-06-2021, 11:08   #1
Registered User
 
Jerry Woodward's Avatar

Join Date: May 2008
Location: Punta Gorda/Kentucky
Boat: PDQ 32 LRC
Posts: 455
Max prop 2 vs 3 blade

My boat: PDQ 32 LRC catamaran, 2 Yanmar 2GM20F engines, shaft drive.

Folding props won't fit, so I am currently thinking of the Max-prop feathering props. My decision now is whether to go with 2 or 3 blade props. PYI recommends 15" props for either. The difference in cost is $800/prop = $1,600 for two.

The famous Yachtingmonthly test concluded very little difference in forward pull and speed between 2 or 3 blades (pitch being the much more important issue).

However, an email from PYI suggest that the three blade has significantly better power, particularly in heavy winds/seas:

Hi Jerry,
For processing water yes a 2 blade is more efficient than a 3 blade as there is less turbulence created by the fewer blades. Processing water is not the same as moving a displacement vessel. When it comes to moving a boat a 3 blade is much more efficient as it does not have as much slippage per rotation when loaded. When pushing against heavy wind and seas the
2 blade slip increases exponentially, compared to the 3 blade as the third blade fills up more of the rotating circle, limiting its slippage.
The advantage of increased beam and freeboard on a catamaran creates the downside of higher windage and more boat to maneuver. The efficient thrust and immediate power of the Max-Prop will improve the control and safety of the vessel in close quarters. The 3 blade will improve boat handling over the 2 blade by getting the boat moving and stopped faster.
As I stated below the 3 blade will have an advantage when powering into heavy winds and seas it will keep boat speed by up to 30% better than the 2 blade.


I'm wondering what others think about this statement. Is the three blade really that much better?

On the plus side for the 2 blade, it should have less drag when feathered and I believe they will weigh significantly less.
__________________
s/v Terrapin
www.sailingterrapin.com
May the four winds blow you safely home
Jerry Woodward is offline   Reply With Quote
Old 22-06-2021, 11:20   #2
Registered User

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 5,147
Re: Max prop 2 vs 3 blade

I have used both 2 and 3 bladed Max props extensively. I don't notice a big difference in thrust between them. Both are superior to other props in reverse.

We are having a vibration problem on the 2 bladed prop that we didn't have with the 3 bladed. The boat will be hauled in a few weeks to deal with it. I do recall that my two bladed wind generator had significantly more vibration than my 3 bladed, but I put that down to gyroscopic effects.
donradcliffe is offline   Reply With Quote
Old 24-06-2021, 07:10   #3
Sponsoring Vendor
 
EWOL Props's Avatar

Community Sponsor

Join Date: Nov 2015
Posts: 115
Re: Max prop 2 vs 3 blade

A 3 bladed prop is always better than a 2 bladed one, not only for better thrust against sea and wind, but also because it gives less vibration and noise (it's a matter of physics of fluids), that is why you are having vibrations now and that is why we at EWOL Propellers have decided not to manufacture the 2 bladed version.


Quote:
Originally Posted by donradcliffe View Post
I have used both 2 and 3 bladed Max props extensively. I don't notice a big difference in thrust between them. Both are superior to other props in reverse.

We are having a vibration problem on the 2 bladed prop that we didn't have with the 3 bladed. The boat will be hauled in a few weeks to deal with it. I do recall that my two bladed wind generator had significantly more vibration than my 3 bladed, but I put that down to gyroscopic effects.
EWOL Props is offline   Reply With Quote
Old 24-06-2021, 07:20   #4
Moderator
 
Pete7's Avatar

Cruisers Forum Supporter

Join Date: Aug 2009
Location: Solent, England
Boat: Moody 31
Posts: 15,474
Images: 14
Re: Max prop 2 vs 3 blade

Ok, so that's quite interesting, but what is the downside of a 3 bladed prop so we have the complete story enabling the customer to make an informed decision.


Pete
Pete7 is offline   Reply With Quote
Old 24-06-2021, 07:57   #5
Registered User
 
Jerry Woodward's Avatar

Join Date: May 2008
Location: Punta Gorda/Kentucky
Boat: PDQ 32 LRC
Posts: 455
Re: Max prop 2 vs 3 blade

EWOL

I have looked at your props on line and they look pretty good. Can you elaborate on the pros and cons of SS compared to the bronze of the Max prop? I get that SS is less prone to corrosion, but most people don't have corrosion problems on their bronze props assuming appropriate zincs and galvanic protection. One piece of information I'm having trouble finding is the weight of the prop. Is the EWOL significantly different in weight?
Also, the adjustment ring on the EWOL looks like a nice feature, but I worry that it may add unnecessary complexity. What is the maintenance like on these props compared to the Max prop?

Finally, can you quote me a price for two props of a size appropriate for my boat?
__________________
s/v Terrapin
www.sailingterrapin.com
May the four winds blow you safely home
Jerry Woodward is offline   Reply With Quote
Old 24-06-2021, 08:08   #6
Sponsoring Vendor
 
EWOL Props's Avatar

Community Sponsor

Join Date: Nov 2015
Posts: 115
Re: Max prop 2 vs 3 blade

Hi Pete,

we don't see any downside on 3 bladed feathering models, but clearly the price will be higher than a 2 bladed version.
Surely a fixed prop 3 bladed will have even more drag than a 2 bladed, that will not be a problem on feathering props, while drag could be slightly higher on some (not all) 3 bladed folding props.




Quote:
Originally Posted by Pete7 View Post
Ok, so that's quite interesting, but what is the downside of a 3 bladed prop so we have the complete story enabling the customer to make an informed decision.


Pete
EWOL Props is offline   Reply With Quote
Old 24-06-2021, 08:32   #7
Sponsoring Vendor
 
EWOL Props's Avatar

Community Sponsor

Join Date: Nov 2015
Posts: 115
Re: Max prop 2 vs 3 blade

Hi Jerry,

thank you for your comment.
I cannot say on a specific brand but I can tell you that bronze is a good metal and can well resist to corrosion in case it is well protected with sufficient anodes, well installed (a good electrical contact is fundamental), not immersed in too polluted waters and not in presence of stray currents.

In real life, sometimes the anode is too corroded or has been even lost in the water due to excess of corrosion, or not well installed (I have seen some props painted with antifouling on the interface between anode and prop, some with untightened screws, etc).
Also...in polluted waters or in case of stray currents, the anodes might not be sufficient to protect the bronze.
In all these cases having a high grade stainless steel prop is important because it will better defend against corrosion.

If you go on our website you can fill a prop sizing request https://ewol-propellers.com/calculate-propeller/


Quote:
Originally Posted by Jerry Woodward View Post
EWOL

I have looked at your props on line and they look pretty good. Can you elaborate on the pros and cons of SS compared to the bronze of the Max prop? I get that SS is less prone to corrosion, but most people don't have corrosion problems on their bronze props assuming appropriate zincs and galvanic protection. One piece of information I'm having trouble finding is the weight of the prop. Is the EWOL significantly different in weight?
Also, the adjustment ring on the EWOL looks like a nice feature, but I worry that it may add unnecessary complexity. What is the maintenance like on these props compared to the Max prop?

Finally, can you quote me a price for two props of a size appropriate for my boat?
EWOL Props is offline   Reply With Quote
Old 24-06-2021, 09:01   #8
Registered User

Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 2,651
Re: Max prop 2 vs 3 blade

having been down this road myself, here are a few things to ponder.

A standard prop has blades that twist...we are all familiar with this. This is done for a variety of reasons, but mostly due to the fact that outer dia. of the prop moves faster than the hub. e, the circumference of the outer dia. is far larger the hub dia. yet both rotate at the same speed.

A maxprop blade does not twist as they are flat. Maxprop recognizes that this is somewhat less efficient than a twisted blade, so the blade area is increased to overcome this deficiency. The increased blade are is quite substantial. If anyone has looked at a maxprop, you will note, the rather large blades. This extra area also has the advantage of extra thrust.

Intrigued I got Dave Gerr's book..." the propellor handbook" to delve into props. It's a long complicated read for those that are interested.

At the end of the day, I replaced a fixed 3 blade prop with a 2 blade maxprop. I could note no discernible difference in speed or power under varying conditions, and even thought the max prop provided better thrust.

Off course, a maxprop can provide the same thrust in reverse as the blades simply flip over. This, I can tell you, made a noticeable difference, as a standard prop typically has poor reverse functions.

You can, off course, also alter the pitch yourself, should you find you need a bit more speed or thrust.

And no question, not having the drag of a fixed prop, is, without question, very improved.

Hope this provides some insight.

Maxprop sells " re-conditioned" props at about 1/3 the price of a new one. I went this route. My prop looked as good as new when it arrived and has never given a lick of problems..
MicHughV is offline   Reply With Quote
Old 24-06-2021, 10:31   #9
Registered User

Join Date: Jul 2017
Posts: 382
Re: Max prop 2 vs 3 blade

At a high level, PYI statement makes a lot of sense.
When it comes to quantify the 3-blade advantage to 30% in certain conditions, it is hard to say, since none of us has likely done any serious comparison testing.
However, PYI is a serious company, has a very solid technology, and they are authorities in props. It is reasonable to assume that they have done the comparison testing and they are reporting actual data. Also, 30% advantage in terms of trust would be what one would expect, correct?, so it is very credible.
As for the negative side of 3-blades vs. 2-blades, an obvious one is more moving parts, more cost, and more weight.
FabioC is offline   Reply With Quote
Old 24-06-2021, 10:44   #10
Registered User

Join Date: Apr 2013
Posts: 96
Re: Max prop 2 vs 3 blade

u might want to check out kiwiprop.us have had one 7 years and still on my first set of blades
roberthowell is offline   Reply With Quote
Old 24-06-2021, 14:34   #11
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 18,274
Re: Max prop 2 vs 3 blade

Quote:
A maxprop blade does not twist as they are flat. Maxprop recognizes that this is somewhat less efficient than a twisted blade, so the blade area is increased to overcome this deficiency. The increased blade are is quite substantial. If anyone has looked at a maxprop, you will note, the rather large blades. This extra area also has the advantage of extra thrust.
What this ignores is that lower efficiency means that it takes more power to achieve a given thrust, and that means lower fuel economy for your boat and running the engine harder to reach a given speed.

May not matter to you, but when we changed from a two blade Martec Elliptic (a very well developed folding prop) to a three blade feathering Autostream, our average fuel consumption increased nearly 25%. For most folks, fuel costs are a very minor part of overall expense, but for us (long range cruising in sometimes unpopulated areas) it reduced our range and length of time between fuel stops to a noticeable extent.

Bollard pull, especially in reverse, was of course far better, but over the years we found that for us this mattered little. We have chosen to use three blade folding props ever since, and find the Flex-O-Fold's performance to be superb.

Jim
__________________
Jim and Ann s/v Insatiable II, reluctantly incarcerated in the POW marina, Hobart, where shore power is assisting our reluctant solar panels in maintaining our life style.
Jim Cate is online now   Reply With Quote
Old 24-06-2021, 17:42   #12
Registered User

Join Date: Feb 2020
Location: Port adelaide south australia
Boat: Cheoy lee perry 48
Posts: 240
Re: Max prop 2 vs 3 blade

Vote 1 for the kiwi props .⛵️⚓️
Searles is offline   Reply With Quote
Old 25-06-2021, 07:41   #13
Registered User

Join Date: Oct 2012
Location: Guilford, CT
Boat: Bristol 35.5 1978
Posts: 557
Re: Max prop 2 vs 3 blade

What no takers for 4-blade?! Went with Variprop 4 blade feathering as folding would not fit in the aperture space in front of my rudder...assuming not an issue in the design of your cat...what I have discovered, much to my chagrin, is that I cannot install the new prop on my shaft w/o either shortening the shaft or dropping the rudder!! So Spring 2022 project - remove shaft, replace cutlass bearing (just because), shorten shaft, install new 4 blade. thnks
Hoodsail is offline   Reply With Quote
Old 25-06-2021, 08:08   #14
Registered User

Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 2,651
Re: Max prop 2 vs 3 blade

I have not noted that the maxprop consumes more fuel.....a prop should always be matched to the engine via diameter and pitch....regardless of type, to ensure maximum efficiency.

I have not done a like for like comparison, as a fixed 3 blade was replaced by a feathering 2 blade, nor have I done any fuel consumption monitoring, just never noticed any increase in fuel consumption..

The maxprop does have the advantage of being able alter the pitch, should the engine not achieve it's rated rpm or over revs.

However, the entire purpose of maxprop and other feathering/folding props is to reduce drag under sail. Like all things, some compromise has to be made.

All things considered, I'd rather have less drag, than any increase in fuel consumption, if any.

For me, personally, my issue was with the engine transmission, in that it is hydraulic. ie, you can't lock the prop, when the engine is not running. Off course, various and sundry shaft locking mechanism are available, but these options were not feasible for me. I did on occasion, try a a set of vice-grips around the shaft, but this requires a lot of effort to put it on and not forget to take it off.

The sound of a spinning prop while under sail, drove me nuts, which is what prompted me to try the maxprop and I have since become an advocate for it.

It may not suit everybody, but it sure as heck suits me.

I am merely offering my perspective on the maxprop and not trying convince anyone to get one or to compare it to others.
MicHughV is offline   Reply With Quote
Old 25-06-2021, 09:06   #15
Registered User

Join Date: Jun 2010
Location: Mediterranean
Boat: Beneteau Oceanis 50
Posts: 427
Re: Max prop 2 vs 3 blade

Quote:
Originally Posted by Jerry Woodward View Post
My boat: PDQ 32 LRC catamaran, 2 Yanmar 2GM20F engines, shaft drive.

Folding props won't fit, so I am currently thinking of the Max-prop feathering props. My decision now is whether to go with 2 or 3 blade props. PYI recommends 15" props for either. The difference in cost is $800/prop = $1,600 for two.

The famous Yachtingmonthly test concluded very little difference in forward pull and speed between 2 or 3 blades (pitch being the much more important issue).

However, an email from PYI suggest that the three blade has significantly better power, particularly in heavy winds/seas:

Hi Jerry,
For processing water yes a 2 blade is more efficient than a 3 blade as there is less turbulence created by the fewer blades. Processing water is not the same as moving a displacement vessel. When it comes to moving a boat a 3 blade is much more efficient as it does not have as much slippage per rotation when loaded. When pushing against heavy wind and seas the
2 blade slip increases exponentially, compared to the 3 blade as the third blade fills up more of the rotating circle, limiting its slippage.
The advantage of increased beam and freeboard on a catamaran creates the downside of higher windage and more boat to maneuver. The efficient thrust and immediate power of the Max-Prop will improve the control and safety of the vessel in close quarters. The 3 blade will improve boat handling over the 2 blade by getting the boat moving and stopped faster.
As I stated below the 3 blade will have an advantage when powering into heavy winds and seas it will keep boat speed by up to 30% better than the 2 blade.

No substitute fir grunt when motoring. 3 blade every time.

I'm wondering what others think about this statement. Is the three blade really that much better?

On the plus side for the 2 blade, it should have less drag when feathered and I believe they will weigh significantly less.
No substitute for Grunt. 3 Blade every time
lordgeoff is online now   Reply With Quote
Reply

Tags
3 blade

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
3 blade Max prop vs 3 blade fixed? Davidhoy Monohull Sailboats 83 14-12-2016 17:46
Two-Blade vs Three-Blade Prop mikereed100 Propellers & Drive Systems 32 12-11-2013 18:20
Going from a 2-Blade Folding to a 3-Blade Fixed Prop pireality General Sailing Forum 2 05-05-2010 20:00

Advertise Here


All times are GMT -7. The time now is 16:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.