My boat calls for a 2 blade 15+12 prop.What are the advantages/disadvantages of a 2blade or 3 blade propeler
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slower under sail, faster in rough water.
Steve: Generally you will see that the 3 blade prop will slow you down under sail and give you more punch in strong currents or heavy seas. Are you having some specific problems that you are trying to correct?
Steve: Generally you will see that the 3 blade prop will slow you down under sail and give you more punch in strong currents or heavy seas. Are you having some specific problems that you are trying to correct?
3 Blade For Me
I just put a three blade on my 2001 320. Best $350 I ever spent. Increased speed, manuverability, and all of my vibration is gone. Go for it!!!
I just put a three blade on my 2001 320. Best $350 I ever spent. Increased speed, manuverability, and all of my vibration is gone. Go for it!!!
Vibration Change
Bob - if the vibration changed as much as you indicated when the prop was changed then it appears the old prop wasn't balanced. To minimize vibration the prop should be balanced for weight and pitch (so all blades have the same pitch). Steve - A fixed blade two-blade prop will cost you around a half-knot in lost speed and a three blade will be even worse, something to factor in. A feathering or folding prop will help you sail faster and eliminate the prop shaft turning while under sail saving wear and tear on the transmission and cutlass.
Bob - if the vibration changed as much as you indicated when the prop was changed then it appears the old prop wasn't balanced. To minimize vibration the prop should be balanced for weight and pitch (so all blades have the same pitch). Steve - A fixed blade two-blade prop will cost you around a half-knot in lost speed and a three blade will be even worse, something to factor in. A feathering or folding prop will help you sail faster and eliminate the prop shaft turning while under sail saving wear and tear on the transmission and cutlass.
props
Steve; It depends on what you want. As other posts have said, 3-blade powers better but costs sail speed. I have a Max-Prop now and love it, but on my previous boat, a C-30, I had a folding 2-blade turned by a Uni 5411 that worked fine. To save a few bucks, a fixed 2-blade can be aligned vertically behind the keel, with a marked prop shaft and locked in place with the trans in reverse. Your priorities and budget will determine your choice.
Steve; It depends on what you want. As other posts have said, 3-blade powers better but costs sail speed. I have a Max-Prop now and love it, but on my previous boat, a C-30, I had a folding 2-blade turned by a Uni 5411 that worked fine. To save a few bucks, a fixed 2-blade can be aligned vertically behind the keel, with a marked prop shaft and locked in place with the trans in reverse. Your priorities and budget will determine your choice.
three
Hello Steve, Both the two and three blade will help propel the vessel in flat calm water at apx. the same speed. The three blade however, will help to maintain the speed when the vessel is confronted with adverse conditions like heavy winds or seas, towing a dink or additional weight added to the boat. You will also see a reduction in noise being created by the prop using the three blade. Hope this helps. Kevin
Hello Steve, Both the two and three blade will help propel the vessel in flat calm water at apx. the same speed. The three blade however, will help to maintain the speed when the vessel is confronted with adverse conditions like heavy winds or seas, towing a dink or additional weight added to the boat. You will also see a reduction in noise being created by the prop using the three blade. Hope this helps. Kevin
If drag is your concern, go folding
Feathering props have usually more drag than folding props. Also, some feathering props like the Max Prop or the Auto stream, have flat blades that make them less efficient during motoring. Autoprop does have a nice twist in its blades and is claimed to have better efficiency than all other props including fix props. The problmes I saw with Autoprop were its cost, the complex and delicate set of bearings in mechanisms, and the fact that all three blades adjust their pitch independently acording to local hydrodinamic forces. One could imagine how a little barnicle in one of them can affect that blade's pitch and cause a good amount of vibration. The draw back with the folding props is the need for centrifugal force to open up and such a force is small when they are folded (Force~mass*RPM*radious^2. As a result, it may take you to rev up the engine before they open and as they suddenly open you get a big slam on the shaft. Also, as fixed blade props they are not great in reverse as the leading edge of the blade becomes the trailing edge in reverse plus the force of the water tends to fold the blades back. I personally went Gori 3 blades to replace the 2-blade fix that came with my 361. It folds nicely, it has twist in the blades and it uses the force of the water to start opening up the blades and therefore it does not slam the shaft. Also, it has a very clever mechanism to flip the leading edge in reverse, giving it as good grab in reverse as in forward. I tested it for the past two weeks and it has worked like a charm both sailing and motoring. Very smooth ride and excellent reverse during docking. Last, but not least, it is easy to service and it cost a lot less than an equivalent MaxProp. The web site below has all kind of prop links.
Feathering props have usually more drag than folding props. Also, some feathering props like the Max Prop or the Auto stream, have flat blades that make them less efficient during motoring. Autoprop does have a nice twist in its blades and is claimed to have better efficiency than all other props including fix props. The problmes I saw with Autoprop were its cost, the complex and delicate set of bearings in mechanisms, and the fact that all three blades adjust their pitch independently acording to local hydrodinamic forces. One could imagine how a little barnicle in one of them can affect that blade's pitch and cause a good amount of vibration. The draw back with the folding props is the need for centrifugal force to open up and such a force is small when they are folded (Force~mass*RPM*radious^2. As a result, it may take you to rev up the engine before they open and as they suddenly open you get a big slam on the shaft. Also, as fixed blade props they are not great in reverse as the leading edge of the blade becomes the trailing edge in reverse plus the force of the water tends to fold the blades back. I personally went Gori 3 blades to replace the 2-blade fix that came with my 361. It folds nicely, it has twist in the blades and it uses the force of the water to start opening up the blades and therefore it does not slam the shaft. Also, it has a very clever mechanism to flip the leading edge in reverse, giving it as good grab in reverse as in forward. I tested it for the past two weeks and it has worked like a charm both sailing and motoring. Very smooth ride and excellent reverse during docking. Last, but not least, it is easy to service and it cost a lot less than an equivalent MaxProp. The web site below has all kind of prop links.
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