We are going to buy a spare prop, we currently have 2 blade 15 X 11 fixed. I am wondering what the pros/cons are 3 blade vs 2 blade. I searched the site and can't find anything dealing with this specific comparison.
Things I am wondering about are:
Drag - I expect the 3 blade will have more but how much more? One prop guy claims it would be like "dragging your hand in the water". I would have thought it would be more than that but maybe not.
Prop walk - I am told 3 blade causes a lot less prop walk in reverse than 2 blade which is a big bonus if it's true.
Efficiency - I read a claim from a prop mfg that the 2 blade should never be on a sailboat because half the prop is directly in the keel wake all the time and obviously with a 3 blade it would only be 1/3. But generally, is a 3 blade prop any more efficient than a 2 blade?
Balance - above place also says 3 blade props balance better and are less likely to cause harmonics or vibration than 2 blade ones.
Comments? Advice? Thoughts? Anybody go from 2 blade to 3 or vice versa?
I can't give you a direct comparison; I had a factory 2 blade prop on my '88 C30 and a factory 3 blade on my current '7 C36. Both Michigan Wheel I believe.
On the C30, I got caught in a sudden squall on a couple occasions, where, even at full throttle, I could not keep the boat moving or the bow into the wind. Once was off a lee shore and I had to pitch the anchor and ride it out. The engine was screaming at full throttle, but the prop just did not have enough 'bite' to put the power to the water. Several boats were beached, and I thanked my Bruce anchor many times for setting quickly and holding in that blow..!
With the 3 blade prop on my C36, this has never been a problem. I got caught in a squall that had my inflatable spinning and flapping in the breeze like a flag on the end of it's painter; no problem whatever controlling the boat under power.
So I feel that for motoring at least, the 3 blade is far superior, though again, I did not compare on the same boat. The C30 was more difficult to back up, but it also has the engine/prop mounted much further forward. I could rarely get it to turn to starboard in reverse. The C36 is no problem.
Can't comment on drag. I know I look longingly at some of those beautiful feathering props walking around the marina. But my wallet says no.
Gary and Cathy Price
1997 C36 Mk II Tall Rig/Wing Keel Imagine...
Hull # 1617
Worton Creek, Md.
Northern Chesapeake Bay
Hi Bud,
Use this link, and scroll down to Maine Sail's remarks, it is a good summary.
[url]http://www.cruisersforum.com/forums/f114/two-blade-vs-three-blade-prop-2...
Cheers,
Graham Mackey
SV Nostromo
1989 C36 908
Tall Rig/Wing Keel
Toronto, Canada
Seems like drag increase is pretty minimal. Really, our biggest issue is prop walk, really would like to minimize that as much as possible.
Bud, I just went through that decision myself and selected the two-blade. But first, let me say that the prop is a 15x10, not a 15x11 as you state. I called Ken in the parts dept at Catalina in Largo, FL, and he confirmed that the prop should be a 5x10, and I purchased the new one from him. Could it be that you have the wrong prop? If so, perhaps your excessive prop walk is a result of that. I frankly love the prop walk on my boat...I would call it a 'moderate' amount of prop walk, but it is absolutely predictable and reliable. It is a great tool for close quarter handling, and I use it that way and count on it. BTW, I would think a 15x10 would have less vibration than a 15x11.
For what it is worth, here are my replies to your concerns...
Drag - "I expect the 3 blade will have more but how much more? One prop guy claims it would be like dragging your hand in the water." Yep, probably right...I used to sell airplanes and can tell you from personal experience that a two-bladed Beech Bonanza is faster than a three-bladed same airplane.
Prop walk - "I am told 3 blade causes a lot less prop walk in reverse than 2 blade which is a big bonus if it's true." No comment; don't know. Except that your prop walk ought to be moderate, desirable and cherished, as described above.
Efficiency - "I read a claim from a prop mfg that the 2 blade should never be on a sailboat because half the prop is directly in the keel wake all the time and obviously with a 3 blade it would only be 1/3. But generally, is a 3 blade prop any more efficient than a 2 blade?" I think that statement is pure BS. Under motor, rather than wake from the keel being a problem, I suspect disturbed flow from the strut would be an issue, but a small one. And under sail, I would bet that the keel wake doesn't even come near the prop. While HF was on the hard last week I considered drilling and tapping a hole on the side of the strut and mounting a zinc there, but I chose to not do this in order to keep the flow over the strut as undisturbed as possible.
Balance - "above place also says 3 blade props balance better and are less likely to cause harmonics or vibration than 2 blade ones." No comment; don't know. But if you have a 15x11 your vibration issue may be a result of that.
I have been very satisfied with the stock two-blade 15x10 on High Flight, and I have needed to motor in some very demanding waters (a rough Columbia River Bar, for example).
Larry Brandt
S/V High Flight #2109
Pacific Northwest, PDX-based
2002 C-36 mkII SR/FK M35B
[QUOTE=bstreet;7116]Seems like drag increase is pretty minimal. Really, our biggest issue is prop walk, really would like to minimize that as much as possible.[/QUOTE]
Bud, you might want to rethink the prop walk idea as a "problem." Altogether too many folks do that. And most because they fail to give the throttle enough oomph when backing.
I've had a three blade fixed on [I]Aquavite [/I]since we've owned her, while the PO also gave us the OEM 2 blade.
We leave our slip backing out (always go bow in) and find that if there is NO wind and I just click the gear shift into to reverse, the stern walks to port and scrapes the side of the boat on the dock. No water over the rudder, no directional stability. So I "goose it" and the boat slides only a tiny bit sideways and then starts going where I want it: backwards.
I've also practiced, practiced, practiced, and can turn our boat on its keel. Literally. Back and fill, back and fill.
It's also great for coming alongside docks port side to, as well as leaving if you're tied starboard side to.
I've discussed this on many forums over the years. Learn to use prop walk properly, and you'll wonder why anyone ever takes issue with it.
Stu Jackson, C34IA Secretary, C34 #224, 1986, SR/FK, M25 engine, Rocna 10 (22#)
Thanks for the input guys. Larry, we don't have a vibration problem, we actually don't have any problems with the 2 blade prop, except the prop walk. Other than that we find it totally satisfactory and never feel like we don't have enough grunt under power. I'll recheck the stampings on the prop next time I'm at the boat, I could be mistaken on the 11.
I use prop walk to my advantage, on port side docking I can park the boat with one shot every time with zero help from shore. Starboard is a totally different story, even using a variety of methods to deal with the issue it is never fun. We were stuck on a starboard dock this year so I got lots of practice, what made it worse was having to make a starboard turn into a starboard dock from a very narrow fairway. Easier to do if you can make a port turn into a starboard dock but we can't. The marina we're in was made for 30' boats max so it's tight and so are the slips.
I would prefer to split the difference because with no prop walk to deal with I can just use the rudder to position the boat and the prop to stop it. But that's likely a pipe dream there's always going to be some prop walk just from rotation alone.
Bottom line here is we don't have any huge issues to address, we are just buying a spare prop and thought from what I'd read that there may be some advantage to a 3 blade.
Funny that the Campbell Sailor prop recommended by Maine Sail in the link Graham provided is from West by North Enterprises, and it was that site that I got the above quotes from. They are death on 2 bladed props it seems.