This past weekend on a Catalina 30 std rig,new 135 genoa, good mainsail, 3 blade fixed prop. Winds at 8-10knts(gusts to 12+), beam reach, all tell tales streaming(thanks Don G.!)I was typically at 5.8 to 6.0 knts (max was 6.2)per my handheld GPS (inland lake, so no current). Is this what I should expect? Theoretical hull speed is 6.7. At what wind speed should I expect to reach hull speed if ever? Does the 3 blade fixed prop cost .5kt in speed?
Hull Speed
- Thread starter Stephen K
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...thought I mentioned...
I was mostly on a beam reach...Don's trim guide and my new genoa have really made a big difference. The wind was from a good direction that allowed a long beam reach down the lake instead of the usual Lanier two step tacking drill. This allowed me to play around with sail trim and I was finaly able to get the mainsail's top tell tale flowing well. I am lucky to be able to get out of my slip and to the "main body" of the lake without to much danger...we have not encountered problems sailing in the main part of the lake, but you do have to be paying attention...there is a lot of visible land that is usually not there. It was a beautiful Saturday with about 20 boats out there.
I was mostly on a beam reach...Don's trim guide and my new genoa have really made a big difference. The wind was from a good direction that allowed a long beam reach down the lake instead of the usual Lanier two step tacking drill. This allowed me to play around with sail trim and I was finaly able to get the mainsail's top tell tale flowing well. I am lucky to be able to get out of my slip and to the "main body" of the lake without to much danger...we have not encountered problems sailing in the main part of the lake, but you do have to be paying attention...there is a lot of visible land that is usually not there. It was a beautiful Saturday with about 20 boats out there.
Prop Drag
IMHO, typically comparing a fixed two blade prop to a two blade folder or feathering prop there would be a 1/2 knot difference. Moving to a three blade, I'd expect more than a 1/2 knot loss. At those wind speeds, a larger Genoa would typically produce higher speeds. In any case, I'd trade in the three blade if you are serriously interested in performance. There might be an advantage to a three blade prop for punching thru waves and headwinds or for long distance motor sailing, but why on Lake Lanier?
IMHO, typically comparing a fixed two blade prop to a two blade folder or feathering prop there would be a 1/2 knot difference. Moving to a three blade, I'd expect more than a 1/2 knot loss. At those wind speeds, a larger Genoa would typically produce higher speeds. In any case, I'd trade in the three blade if you are serriously interested in performance. There might be an advantage to a three blade prop for punching thru waves and headwinds or for long distance motor sailing, but why on Lake Lanier?
You are probably aware
that your GPS speed was speed over ground and not speed through the water, as indicated by a knotmeter. I sometimes see as much as a one knot difference between the two instruments. While this would not work with a 3-blade prop, I sometimes align my fixed 2-blade prop to be lined up vertically with the keel. I do this by marking the trans coupler and then turning the shaft by hand to line up the marks before locking it in reverse. This sometimes produces a half knot more speed when I'm racing. Speed can also be impacted, sometimes severly, by what you are dragging along on the bottom of your boat. Any hard or soft growth there will slow you down. Not sure what grows on boats in Lanier, but it's just a thought. I think you should be quite happy with your boat, your sail trim, and your skill, to be doing 6 kts in winds blowing 8-10 kts. Sounds like some great sailing to me.
that your GPS speed was speed over ground and not speed through the water, as indicated by a knotmeter. I sometimes see as much as a one knot difference between the two instruments. While this would not work with a 3-blade prop, I sometimes align my fixed 2-blade prop to be lined up vertically with the keel. I do this by marking the trans coupler and then turning the shaft by hand to line up the marks before locking it in reverse. This sometimes produces a half knot more speed when I'm racing. Speed can also be impacted, sometimes severly, by what you are dragging along on the bottom of your boat. Any hard or soft growth there will slow you down. Not sure what grows on boats in Lanier, but it's just a thought. I think you should be quite happy with your boat, your sail trim, and your skill, to be doing 6 kts in winds blowing 8-10 kts. Sounds like some great sailing to me.
Does anyone have a reference for making a chart of "polars" for a cruising boat? I have seen some complicated methods but would like to create a basic chart.
Speed
Steve: As Warren M has indicated, 6 knots boat speed in 10 - 12 knots of wind ain't bad. In fact, it is very good. There is no question the 3 blade prop is a drag on the boat speed. In most cases a 3 blade is over kill. I'd want a 3 blade if I was crossing the Columbia Bar but in most other situations a 2 blade will get the job done. If a mate is boating in conditions where he really needs a 3 blade he had better know his onions about sailing and seamanship. I assume you have the prop locked in reverse. If you wanted more speed you'd have to replace the prop with a folder or feathering prop BUT as we discussed yesterday on the phone regarding the Garhauer rigid vang or the Garhauer adjsutable fairlead system. You didn't mention the prop but had you my answer would be the same. First I'd get the adjustable fairlead system and the reason for that is the jib is the engine of the boat and you just can't tweek the jib with the pin type fairlead system as easily and efficiently as you can with an adjustable system. Sailors will do what is easy and not what is hard and it is hard to adjust the pin type system. That is why on the boats I go on that I see most of the pin system frozen in place. Sailors don't bother with it and that means the setting is like a broken clock - it is only right for a certain wind condition and point of sail and WRONG for all others. After I purchase the adjustable fairlead system, I get the rigid vang and last I'd deal with the prop. If my boat was sailing at 5 to 6 knots in 10 to 12 knots of wind I'd forget the prop!! Did your brother receive his book and chart? How long do you think it will take for him to catch up to you from a sail trim standpoint!!
Steve: As Warren M has indicated, 6 knots boat speed in 10 - 12 knots of wind ain't bad. In fact, it is very good. There is no question the 3 blade prop is a drag on the boat speed. In most cases a 3 blade is over kill. I'd want a 3 blade if I was crossing the Columbia Bar but in most other situations a 2 blade will get the job done. If a mate is boating in conditions where he really needs a 3 blade he had better know his onions about sailing and seamanship. I assume you have the prop locked in reverse. If you wanted more speed you'd have to replace the prop with a folder or feathering prop BUT as we discussed yesterday on the phone regarding the Garhauer rigid vang or the Garhauer adjsutable fairlead system. You didn't mention the prop but had you my answer would be the same. First I'd get the adjustable fairlead system and the reason for that is the jib is the engine of the boat and you just can't tweek the jib with the pin type fairlead system as easily and efficiently as you can with an adjustable system. Sailors will do what is easy and not what is hard and it is hard to adjust the pin type system. That is why on the boats I go on that I see most of the pin system frozen in place. Sailors don't bother with it and that means the setting is like a broken clock - it is only right for a certain wind condition and point of sail and WRONG for all others. After I purchase the adjustable fairlead system, I get the rigid vang and last I'd deal with the prop. If my boat was sailing at 5 to 6 knots in 10 to 12 knots of wind I'd forget the prop!! Did your brother receive his book and chart? How long do you think it will take for him to catch up to you from a sail trim standpoint!!
let me set...
the record straight. We did hit the high 5's and low 6's in the strong puff's and approx 70-80 degrees off the wind. We had plenty of 4-5kt time. I bought the boat in 2006 and it came with the original 3 blade prop...obviously not needed for the lake, but I'd rather not spend a chunk of money on swithching at that this if I'm not racing. Don, my brother was with me and we had a blast. I had him at the helm and I did all the trim. Next time out, we will switch roles. He is catching on quick. I moved the jib fairlead a few times before getting it right...I was lucky to be able to play around with that on a long tack which is not common at Lanier. Yes, I probably would get the most benefit from the adjusatble fairlead system given short tacks and variable winds at Lanier. Conditions were such that we really did not start to flatten the main. I did play around with the traveller and mainsheet combination to finally get the top telltale to flow. I sailed with the transmission in neutral and swithced to reverse some of the time to compare spped. I noticed a slightly higher speed with the prop freewheeling in neutral vs. being locked in reverse. Is "R" preferred vs "N"? I know NOT to sail with it in "F". My only other observation is that the soft vang is a real bugger to get any leverage / movement on the boom. I guess that would be solved with the rigid vang. Many thanks for the continued advice!
the record straight. We did hit the high 5's and low 6's in the strong puff's and approx 70-80 degrees off the wind. We had plenty of 4-5kt time. I bought the boat in 2006 and it came with the original 3 blade prop...obviously not needed for the lake, but I'd rather not spend a chunk of money on swithching at that this if I'm not racing. Don, my brother was with me and we had a blast. I had him at the helm and I did all the trim. Next time out, we will switch roles. He is catching on quick. I moved the jib fairlead a few times before getting it right...I was lucky to be able to play around with that on a long tack which is not common at Lanier. Yes, I probably would get the most benefit from the adjusatble fairlead system given short tacks and variable winds at Lanier. Conditions were such that we really did not start to flatten the main. I did play around with the traveller and mainsheet combination to finally get the top telltale to flow. I sailed with the transmission in neutral and swithced to reverse some of the time to compare spped. I noticed a slightly higher speed with the prop freewheeling in neutral vs. being locked in reverse. Is "R" preferred vs "N"? I know NOT to sail with it in "F". My only other observation is that the soft vang is a real bugger to get any leverage / movement on the boom. I guess that would be solved with the rigid vang. Many thanks for the continued advice!
Free Wheeling Prop
Steve: It is not a good idea to have the prop freewheeling. The tranny does not like that situation. Lock the tranny in reverse. For those that have a 2 blade prop the same applies but you should take it one step further. You want the prop blades to be straight up and down. How do you know where that position is? Next time you have the hull cleaned have the diver set the prop in that position. Then you merely mark the shaft with paint or whatever so when you shut down the engine and begin sailing you merely shift to nuetral, set the shaft according to your mark and then shift to reverse. The end result is your minimizing prop drag - your not eliminating drag but your cutting it down as much as possible. See the little bits and pieces of info you learn from this forum!!!
Steve: It is not a good idea to have the prop freewheeling. The tranny does not like that situation. Lock the tranny in reverse. For those that have a 2 blade prop the same applies but you should take it one step further. You want the prop blades to be straight up and down. How do you know where that position is? Next time you have the hull cleaned have the diver set the prop in that position. Then you merely mark the shaft with paint or whatever so when you shut down the engine and begin sailing you merely shift to nuetral, set the shaft according to your mark and then shift to reverse. The end result is your minimizing prop drag - your not eliminating drag but your cutting it down as much as possible. See the little bits and pieces of info you learn from this forum!!!
Polars - Ken
Thanks for the offer - yes, I would like that software. I can't locate your email address in the site directory. Can you please click on my name and email me?
Thanks for the offer - yes, I would like that software. I can't locate your email address in the site directory. Can you please click on my name and email me?
GPS Speed
On a lake GPS speed is water speed, only if a current is present will GPS speed differ from speed over the water. Knotmeters are not very accurate and a GPS can be used to calibrate them, but my experience with Knotmeters is that they are not linear in accuracy, and not repeatable either. The GPS speed on any heading will definately show the effects of sail trim far better than anything you get from a Knotmeter.
On a lake GPS speed is water speed, only if a current is present will GPS speed differ from speed over the water. Knotmeters are not very accurate and a GPS can be used to calibrate them, but my experience with Knotmeters is that they are not linear in accuracy, and not repeatable either. The GPS speed on any heading will definately show the effects of sail trim far better than anything you get from a Knotmeter.
Follow the manufacturers recommendation
whether to allow prop freewheling or not. Yanmar indicates the bearings and gears on their transmissions are receiving adequate lubrication when freewheeling in neutral. They also allow for the transmission to be placed in gear but recommend reverse, not forward. What they do not mention is that in order to get the transmission out of gear with minimum stress you should slow the boat to under 1 knot. A freewheeling transmission is accumulating hours of wear and tear, but a stopped in gear transmission is receiving stress forces in the gears, shafts and clutch. Which is the worse of the two evils? It's your call. My personal preference has been to let it freewheel but if you are racing and need every bit of speed don't see a problem in stopping the prop. There is a gadget out there that manually locks the shaft which would seem to take care of either issue but I do not know how well it works or how convenient it may be to use.
whether to allow prop freewheling or not. Yanmar indicates the bearings and gears on their transmissions are receiving adequate lubrication when freewheeling in neutral. They also allow for the transmission to be placed in gear but recommend reverse, not forward. What they do not mention is that in order to get the transmission out of gear with minimum stress you should slow the boat to under 1 knot. A freewheeling transmission is accumulating hours of wear and tear, but a stopped in gear transmission is receiving stress forces in the gears, shafts and clutch. Which is the worse of the two evils? It's your call. My personal preference has been to let it freewheel but if you are racing and need every bit of speed don't see a problem in stopping the prop. There is a gadget out there that manually locks the shaft which would seem to take care of either issue but I do not know how well it works or how convenient it may be to use.
Congratulations, Stephen
It's nice to see someone who actually tried both free-wheeling and fixed prop, and is open to basing his choice on data - rather than the endless theorizing on this issue that often fills sailing forums. Your 0.5kt speed reduction from dragging a fixed prop through the water is exactly what I get on my Hunter 36 with its 3-blade prop (whose acceleration I dearly love when the Merrimac River entrance bar is breaking). My previous boat had a 2-blade prop, and lost 0.25-to-0.3kts when freeewheeling. Needless-to-say I was mystified by the apparent reversal from the 2-blade to the 3-blade, uintil I found that the Navy (David Taylor Model Basin, as I recall) had done a study of the effect of a dead prop on drag. The study apparently concluded that minimum drag for a 2-blade prop did, indeed occur when it was fixed - especially if fixed in vertical alignment with the keel. It also showed, however, that a 3-blade prop gave minimum drag when free-wheeling. You'll often hear advice from sailors who are also pilots that you should always fix a prop, since a freewheeling (airplane) prop has more drag than a fixed one. This is certainly sound advice for airplanes, but apparently boats are more complicated <g> . My grad school fluid dynamics was a long time ago, but I do remember that the mathematics of incompressible fluids (like water) is very different than that of compressible fluids (like air), so that's probably where the differences in applicable models come in. In any case, it's a delight to see someone actually "count the number of teeth in the horse's mouth," rather than conducting theological arguments. One Caution: The advice given above about checking your transmission manufacturer's recommendation on wear is also well-founded - I have Yanmar's cone clutch in mine, which is very happy. There are other types of Yanmar transmissions that can suffer extensive clutch wear in freewheeling. When you stop dragging the prop along you seem to be doing pretty well on getting speed from your sails. Fair winds, Al
It's nice to see someone who actually tried both free-wheeling and fixed prop, and is open to basing his choice on data - rather than the endless theorizing on this issue that often fills sailing forums. Your 0.5kt speed reduction from dragging a fixed prop through the water is exactly what I get on my Hunter 36 with its 3-blade prop (whose acceleration I dearly love when the Merrimac River entrance bar is breaking). My previous boat had a 2-blade prop, and lost 0.25-to-0.3kts when freeewheeling. Needless-to-say I was mystified by the apparent reversal from the 2-blade to the 3-blade, uintil I found that the Navy (David Taylor Model Basin, as I recall) had done a study of the effect of a dead prop on drag. The study apparently concluded that minimum drag for a 2-blade prop did, indeed occur when it was fixed - especially if fixed in vertical alignment with the keel. It also showed, however, that a 3-blade prop gave minimum drag when free-wheeling. You'll often hear advice from sailors who are also pilots that you should always fix a prop, since a freewheeling (airplane) prop has more drag than a fixed one. This is certainly sound advice for airplanes, but apparently boats are more complicated <g> . My grad school fluid dynamics was a long time ago, but I do remember that the mathematics of incompressible fluids (like water) is very different than that of compressible fluids (like air), so that's probably where the differences in applicable models come in. In any case, it's a delight to see someone actually "count the number of teeth in the horse's mouth," rather than conducting theological arguments. One Caution: The advice given above about checking your transmission manufacturer's recommendation on wear is also well-founded - I have Yanmar's cone clutch in mine, which is very happy. There are other types of Yanmar transmissions that can suffer extensive clutch wear in freewheeling. When you stop dragging the prop along you seem to be doing pretty well on getting speed from your sails. Fair winds, Al
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