Three-blades or not to Three-blades...thats the question! I'll be pulling my Catalina 30 out this spring to paint the bottom and thought about uprading from my two-blade prop. Thoughts?
Props
- Thread starter thubbard84
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I can't tell
about prop walk but I can back better with the three blade. I have enough thrust that I can put the rudder hard over and run full astern for a few seconds and kick the stern sideways. Put the rudder over the other way and repeat the effort without moving forward or backward more than five or ten feet. Very helpful when backing into a slip.
about prop walk but I can back better with the three blade. I have enough thrust that I can put the rudder hard over and run full astern for a few seconds and kick the stern sideways. Put the rudder over the other way and repeat the effort without moving forward or backward more than five or ten feet. Very helpful when backing into a slip.
3 blade will actually create more prop walk
Franklin: If you have two prop with the same diameter, the 3 blade is going to create more prop walk. If you check out most prop upgrades the owners have gone down 1" in diameter. Prop walk is the effect of water pushing against the hull (in reverse). The recommended MINIMUM prop tip to hull clearance is 15% of the prop diameter. The more clearance the better. Consequently reducing the diameter increases the clearance.
Franklin: If you have two prop with the same diameter, the 3 blade is going to create more prop walk. If you check out most prop upgrades the owners have gone down 1" in diameter. Prop walk is the effect of water pushing against the hull (in reverse). The recommended MINIMUM prop tip to hull clearance is 15% of the prop diameter. The more clearance the better. Consequently reducing the diameter increases the clearance.
Backing In
Ever tried to pass your slip up and give yourself a little room to back in? That's how I back...yes...I think only two of us at my marina does it, but it really does help. I've watched a guy go forward, backwards, forwards, backwards many time trying to line himself up right in front of his slip. Crazy...I never have that problem because I pass my slip up about 3-4 slips and then start backing slowly. I have plenty of room to get my boat moving and enough time to get the timing and speed down just right before I make my turn. The turn is easy once you got those two down. No matter what the winds are, it's a piece of cake docking my 37' boat into my 38' slip all by myself. The cool thing about this approach is that you come to a full stop in the middle of the dock channel and you get a feel for how the wind is affecting the boat and the minimum speed needed to control steering for the given wind speed and direct, all in an area where you have plenty of room for error. That is good info to have when docking because we all know it's best to approach the dock with at least speed as possible. Don't want to have to rely on throwing the transmission into another gear because sometimes that doesn't work (seen it happen), so as they say...don't enter a slip faster then you would want to hit it at
sorry I rambled...I just don't understand why people try to back into a slip like they back a car into a parking spot. I feel one should back in the same way one goes in bow first.
Ever tried to pass your slip up and give yourself a little room to back in? That's how I back...yes...I think only two of us at my marina does it, but it really does help. I've watched a guy go forward, backwards, forwards, backwards many time trying to line himself up right in front of his slip. Crazy...I never have that problem because I pass my slip up about 3-4 slips and then start backing slowly. I have plenty of room to get my boat moving and enough time to get the timing and speed down just right before I make my turn. The turn is easy once you got those two down. No matter what the winds are, it's a piece of cake docking my 37' boat into my 38' slip all by myself. The cool thing about this approach is that you come to a full stop in the middle of the dock channel and you get a feel for how the wind is affecting the boat and the minimum speed needed to control steering for the given wind speed and direct, all in an area where you have plenty of room for error. That is good info to have when docking because we all know it's best to approach the dock with at least speed as possible. Don't want to have to rely on throwing the transmission into another gear because sometimes that doesn't work (seen it happen), so as they say...don't enter a slip faster then you would want to hit it at
sorry I rambled...I just don't understand why people try to back into a slip like they back a car into a parking spot. I feel one should back in the same way one goes in bow first.
Each boat handles differently
some don't back in a straight line no matter how skillful your are. And some will back just as well controlled as when they are driven forward. Some times I have wind and current to deal with and with a noth wind and and ebb tide I had best make my turn with good timing, going four slips past would just mean turning and trying another approach. Been there, done that.
some don't back in a straight line no matter how skillful your are. And some will back just as well controlled as when they are driven forward. Some times I have wind and current to deal with and with a noth wind and and ebb tide I had best make my turn with good timing, going four slips past would just mean turning and trying another approach. Been there, done that.
more than just prop walk
do you race your boat?? Or do you at least want to sail it as best you can?? A 3 blade prop WILL ( I know I have one) slow your boat down under sail by as much as 1/2 kt. in light air. no big deal if you're only going a short distance away from your slip ,but a weekend trip can take as much as 2-3 hrs. longer to get to your destination. Have you though about getting a folding prop??? or Feathering prop???
do you race your boat?? Or do you at least want to sail it as best you can?? A 3 blade prop WILL ( I know I have one) slow your boat down under sail by as much as 1/2 kt. in light air. no big deal if you're only going a short distance away from your slip ,but a weekend trip can take as much as 2-3 hrs. longer to get to your destination. Have you though about getting a folding prop??? or Feathering prop???
If you are
concerned about the added drag of a third blade, you can calculate the added blade area that you will get with a three blade prop and find a tin can with a cross sectional area equal to the difference and rig a threepoint harness on the can. Then when you are sailing with the two blade prop and with an accurate knot log determine your boat speed, then drop the can into the water and tow that and note the change in boat speed. This is an accurate and low cost method to sort fact from fiction.
concerned about the added drag of a third blade, you can calculate the added blade area that you will get with a three blade prop and find a tin can with a cross sectional area equal to the difference and rig a threepoint harness on the can. Then when you are sailing with the two blade prop and with an accurate knot log determine your boat speed, then drop the can into the water and tow that and note the change in boat speed. This is an accurate and low cost method to sort fact from fiction.
Prop walk is a Good thing!!!
I love the prop walk on my pearson 323. It enables me to back into my slip. I set up so that in forward the rudder pushes me to the starboard and in reverse the prop walk pulls to the port. So a slow backup then a burst of forward works well unless there is a lot of wind. There is a lot of drag!!!! With the catalina's spade rudder the prop walk may not help you much but my pearson has a skeg and the rudder doesn't help much in reverse. You might consider an upgrade to a feathering prop. A lot depends upon your style of sailing. When the wind drops do you ghost along under sail or fire up the beast in the bilge??? When the wind builds do you put in a reef or drop the sails and fire up the beast in the bilge??? Seriously I know some sailers that seem to only sail when the wind is between 10-12 knots anything more or less they fire up the beast.
I love the prop walk on my pearson 323. It enables me to back into my slip. I set up so that in forward the rudder pushes me to the starboard and in reverse the prop walk pulls to the port. So a slow backup then a burst of forward works well unless there is a lot of wind. There is a lot of drag!!!! With the catalina's spade rudder the prop walk may not help you much but my pearson has a skeg and the rudder doesn't help much in reverse. You might consider an upgrade to a feathering prop. A lot depends upon your style of sailing. When the wind drops do you ghost along under sail or fire up the beast in the bilge??? When the wind builds do you put in a reef or drop the sails and fire up the beast in the bilge??? Seriously I know some sailers that seem to only sail when the wind is between 10-12 knots anything more or less they fire up the beast.
Save Your Money
The overall net effect of making this change will be NEGATIVE since it will make the boat sail slower and have very little effect on motoring. You didn;t indicate which motor you have but if it does hull speed under power now, IT AIN'T BROKE SO DON'T FIX IT
The overall net effect of making this change will be NEGATIVE since it will make the boat sail slower and have very little effect on motoring. You didn;t indicate which motor you have but if it does hull speed under power now, IT AIN'T BROKE SO DON'T FIX IT
Same experience as Ross
My 3 blade experience (all good)is the same as what Ross encountered. Also, I have less prop walk with my 3 blade. I switched to a 3 blade to solve some problems. You don't mention what you are trying to fix or improve on your boat. Last, I can't believe how negative some folks are about 3 blades and how many generalizations are made about them. Just as no two boats handle the same, I'd think the same applies to props. Once you know what you want to fix, buy the prop type that will do it. Kevin
My 3 blade experience (all good)is the same as what Ross encountered. Also, I have less prop walk with my 3 blade. I switched to a 3 blade to solve some problems. You don't mention what you are trying to fix or improve on your boat. Last, I can't believe how negative some folks are about 3 blades and how many generalizations are made about them. Just as no two boats handle the same, I'd think the same applies to props. Once you know what you want to fix, buy the prop type that will do it. Kevin
3 blade
With a three blade you will have much more thrust. My guess is that, unless you are racing, you will not notice any difference in sailing speed. The blade on a prop for your size boat is about as big as the palm of your hand. If your 10,000 pound boat were moving at 6 knots and you stuck your hand in the water, how much do you think that you would slow down? Kind of like dragging your foot to slow down a dump truck.
With a three blade you will have much more thrust. My guess is that, unless you are racing, you will not notice any difference in sailing speed. The blade on a prop for your size boat is about as big as the palm of your hand. If your 10,000 pound boat were moving at 6 knots and you stuck your hand in the water, how much do you think that you would slow down? Kind of like dragging your foot to slow down a dump truck.
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