Just recently purchased the boat moving up from a smaller craft. Have already changed out the rudder assembly with one from IdaSailor and boat is in great shape. I am curious what kind of maximum speeds can be expected from the boat?
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got shute?
it really depends on your sails..... I think 6-6.5 knts is about it unless you get a spinnaker. with a shute, might get another 2 or 3. but, I'm sure someone will swear they saw 10 on the gps,,, lol
it really depends on your sails..... I think 6-6.5 knts is about it unless you get a spinnaker. with a shute, might get another 2 or 3. but, I'm sure someone will swear they saw 10 on the gps,,, lol
THS = 6.4 knots
Top Speed: With decent sails on a beam ream reach and zero current, you should be able to hit 6.4 knots SOG (speed over ground) in about 10 knots of wind at about a 20 degree heel. Conversely, an 8 HP motor with standard prop will get you up to this speed at about 1/2 to 3/4 throttle. You can hit higher speeds surfing, but in flat conditions or going to weather, this is pretty much the limit. Cruising Speed: If you're reasonably dilligent about making distance, under average conditions, plan on VMG to destination of about 3.5 to 4 knots.
Top Speed: With decent sails on a beam ream reach and zero current, you should be able to hit 6.4 knots SOG (speed over ground) in about 10 knots of wind at about a 20 degree heel. Conversely, an 8 HP motor with standard prop will get you up to this speed at about 1/2 to 3/4 throttle. You can hit higher speeds surfing, but in flat conditions or going to weather, this is pretty much the limit. Cruising Speed: If you're reasonably dilligent about making distance, under average conditions, plan on VMG to destination of about 3.5 to 4 knots.
sails
As mrbill stated, more sail equals faster speeds. I often get 8.5mph (7.4 knots) on the GPS with full sails out, 150 genoa, no spinnaker. You also have to consider the wave conditions (surfing) and how far you are heeled over. Some sailors like to keep the boat flat, and others like more heel. Keep in mind that the more you heel, the less likely the stuff in you cabin will be where you put it!!
As mrbill stated, more sail equals faster speeds. I often get 8.5mph (7.4 knots) on the GPS with full sails out, 150 genoa, no spinnaker. You also have to consider the wave conditions (surfing) and how far you are heeled over. Some sailors like to keep the boat flat, and others like more heel. Keep in mind that the more you heel, the less likely the stuff in you cabin will be where you put it!!
hull speed
Hull speed limits your top end unless you have a planing hull or very high performance racing hull.
Hull speed limits your top end unless you have a planing hull or very high performance racing hull.
6.4kts
I can attest to the 6.4knot max. I had a Mac25 for 3 years and that was my max speed on a lake with no current.
I can attest to the 6.4knot max. I had a Mac25 for 3 years and that was my max speed on a lake with no current.
Some things to ponder about hull speed...
A Mac 25 is pretty much limited to 6.4 knots (through the water), unless surfing. In our Mac 26D we are just slightly faster than a Mac 25, everything else being equal. If one sees 7.4 knots (sustained for over a minute) on a GPS (Speed Over Ground, not through the water) on a Mac 25, and are not surfing, then probably at least 1 knot of speed over ground is due to current. To prove, try this. Next time you're on the beam and doing 7.4 knots by GPS (sustained for more than a minute), turn 180 degrees and trim on the opposite tack. Speed (sustained for more than a minute) will drop to 5.4 knots or less. The additional power required for each 1/10 knot over THS is very large and exponential. That is, if it takes 6HP to achieve 6.3 knots, then it will take something like 8 HP to hit 6.4, 12 HP to hit 6.5, 18 HP to hit 6.6, 28 HP to hit 6.8, 42 HP to hit 6.9, 60 HP to hit 7.0, 100 HP to hit 7.1, 200 HP to hit 7.2, and so on. This is why it just isn't worth it to put much over 6 - 8 HP on a Mac 25. Lots more weight, losts more stress on the transom, little or no more speed. Note that when sailing on the wind, once you approach hull speed, larger sails don't really generate additional power. Instead you just heel more, spill more wind, and don't go any faster. In fact, once you get beyond about 25 to 30 degrees of heel, the boat starts slowing down, due to increased rudder drag (due to more tiller required to keep the boat on course) and unfavourtable wet surface geometry. Throwing considerable meat on the windward rail will have an incremental difference, but we're talking maybe 2/10 of a knot max. Downwind, additional sail area may get you 2/10 or 3/10 of a knot over THS in flat water, but you can go higher by surfing, (up to 8 or 9 knots.)
A Mac 25 is pretty much limited to 6.4 knots (through the water), unless surfing. In our Mac 26D we are just slightly faster than a Mac 25, everything else being equal. If one sees 7.4 knots (sustained for over a minute) on a GPS (Speed Over Ground, not through the water) on a Mac 25, and are not surfing, then probably at least 1 knot of speed over ground is due to current. To prove, try this. Next time you're on the beam and doing 7.4 knots by GPS (sustained for more than a minute), turn 180 degrees and trim on the opposite tack. Speed (sustained for more than a minute) will drop to 5.4 knots or less. The additional power required for each 1/10 knot over THS is very large and exponential. That is, if it takes 6HP to achieve 6.3 knots, then it will take something like 8 HP to hit 6.4, 12 HP to hit 6.5, 18 HP to hit 6.6, 28 HP to hit 6.8, 42 HP to hit 6.9, 60 HP to hit 7.0, 100 HP to hit 7.1, 200 HP to hit 7.2, and so on. This is why it just isn't worth it to put much over 6 - 8 HP on a Mac 25. Lots more weight, losts more stress on the transom, little or no more speed. Note that when sailing on the wind, once you approach hull speed, larger sails don't really generate additional power. Instead you just heel more, spill more wind, and don't go any faster. In fact, once you get beyond about 25 to 30 degrees of heel, the boat starts slowing down, due to increased rudder drag (due to more tiller required to keep the boat on course) and unfavourtable wet surface geometry. Throwing considerable meat on the windward rail will have an incremental difference, but we're talking maybe 2/10 of a knot max. Downwind, additional sail area may get you 2/10 or 3/10 of a knot over THS in flat water, but you can go higher by surfing, (up to 8 or 9 knots.)
Surfing and Current
Rod, my experience with 7.4 knots maintained was on Lake Michigan and smaller waves (no surfing). With full sails out, I have maintained this for miles. Who know, maybe there is a fluke in my GPS and I am not actually going that fast. Chris M25 Chara
Rod, my experience with 7.4 knots maintained was on Lake Michigan and smaller waves (no surfing). With full sails out, I have maintained this for miles. Who know, maybe there is a fluke in my GPS and I am not actually going that fast. Chris M25 Chara
Surfing...
Hi Chris, To hit 7.4 knots on Michigan, you were likely surfing. It only takes waves to be about one foot or slightly more from astern to affect boat speed fairly substantially. You can really see this when you are being regularly overtaken. As the wave approaches the transom, the boat speeds up and carries that speed until the wave reaches about mid ship. Then the boat "loses" the wave and speed falls back to normal quickly. When conditions and course are right, you can hang onto them for several minutes. Under these conditions, you tend to pick up the very next wave and be surfing again within only a few seconds. This enables your speed over ground to exceed THS, even when there is no current. In larger waves its more obvious. We once sailed our Ensenada 20 from Kagawong to Heywood Island in the North Channel of LAke Huron, making well over 6 knots average for 5 hours. (THS for that boat was 5.4 knots.) Waves were about 4 feet average (trough to crest) from directly astern and we could hang on to them for 5 to 10 minutes. The longest we've ever held a wave has been in Georgian Bay on SeaQuell, riding on a leading edge for upwards of a half hour. Those were with very steady speed and high waves, (hanging on a wave downwind was more a matter of survival than trying to go fast).
Hi Chris, To hit 7.4 knots on Michigan, you were likely surfing. It only takes waves to be about one foot or slightly more from astern to affect boat speed fairly substantially. You can really see this when you are being regularly overtaken. As the wave approaches the transom, the boat speeds up and carries that speed until the wave reaches about mid ship. Then the boat "loses" the wave and speed falls back to normal quickly. When conditions and course are right, you can hang onto them for several minutes. Under these conditions, you tend to pick up the very next wave and be surfing again within only a few seconds. This enables your speed over ground to exceed THS, even when there is no current. In larger waves its more obvious. We once sailed our Ensenada 20 from Kagawong to Heywood Island in the North Channel of LAke Huron, making well over 6 knots average for 5 hours. (THS for that boat was 5.4 knots.) Waves were about 4 feet average (trough to crest) from directly astern and we could hang on to them for 5 to 10 minutes. The longest we've ever held a wave has been in Georgian Bay on SeaQuell, riding on a leading edge for upwards of a half hour. Those were with very steady speed and high waves, (hanging on a wave downwind was more a matter of survival than trying to go fast).
Mechanism of Surfing
There was a long discussion of surfing in a previous thread. After considerable effort, I concluded that the boat was being aided by the movement of the water within the wave. This is a description of the water movement within the wave. The arrows in the somewhat crude diagram show the instantaneous movement of the water. If you visualize yourself standing still and the waves moving past you, you will be able to visualize the water rotating in a clockwise direction as the wave moves past you. As long as you are near the crest of the wave, you will be aided by the wave. If you allow yourself to be pushed too far forward, the forward motion of the water is decreased and you will move back towards the crest. If you allow yourself to fall behind the crest, you will lose the wave.
There was a long discussion of surfing in a previous thread. After considerable effort, I concluded that the boat was being aided by the movement of the water within the wave. This is a description of the water movement within the wave. The arrows in the somewhat crude diagram show the instantaneous movement of the water. If you visualize yourself standing still and the waves moving past you, you will be able to visualize the water rotating in a clockwise direction as the wave moves past you. As long as you are near the crest of the wave, you will be aided by the wave. If you allow yourself to be pushed too far forward, the forward motion of the water is decreased and you will move back towards the crest. If you allow yourself to fall behind the crest, you will lose the wave.
Surfing Explanation
There was a long discussion of surfing in a previous thread. After considerable effort, I concluded that the boat was being aided by the movement of the water within the wave. This is a description of the water movement within the wave. The arrows in the somewhat crude diagram show the instantaneous movement of the water. If you visualize yourself standing still and the waves moving past you, you will be able to visualize the water rotating in a clockwise direction as the wave moves past you. As long as you are near the crest of the wave, you will be aided by the wave. If you allow yourself to be pushed too far forward, the forward motion of the water is decreased and you will move back towards the crest. If you allow yourself to fall behind the crest, you will lose the wave.
There was a long discussion of surfing in a previous thread. After considerable effort, I concluded that the boat was being aided by the movement of the water within the wave. This is a description of the water movement within the wave. The arrows in the somewhat crude diagram show the instantaneous movement of the water. If you visualize yourself standing still and the waves moving past you, you will be able to visualize the water rotating in a clockwise direction as the wave moves past you. As long as you are near the crest of the wave, you will be aided by the wave. If you allow yourself to be pushed too far forward, the forward motion of the water is decreased and you will move back towards the crest. If you allow yourself to fall behind the crest, you will lose the wave.
Hull speed
Hull speed is clculated at 6.5 k for a Mac 26D The formula is 1.34 x square root of the waterline. It's improbable that someone could sustained a speed of 7.4 speed through the water on this boat.
Hull speed is clculated at 6.5 k for a Mac 26D The formula is 1.34 x square root of the waterline. It's improbable that someone could sustained a speed of 7.4 speed through the water on this boat.
That's actually not a very good illustration
Here's a link to an animation that really demonstrates how a wave works. Scroll down to "Water Waves". Each particle of water within the wave rotates in a circular motion. The closer to the surface, the greater the movement. However, the increased speed when a vessel is acted upon by a wave, is not really due to the particle imparting a force on the hull, or because of a "flow" of surface water. If this were the case, really light objects would be swept away by even small waves. (They aren't unless the wave is so big that they actually tumble or slide downhill on the leading edge.) Instead, a displacement hull accelerate is due to the wind driven water wave modulating with the hull created bow / stern wave, which basically causes the motion of the two waves (not the motion of the water within the waves) to slide in relation to the actual water surface. This is proven by the fact that if the wind wave length (crest to crest) is equal to the vessel bow/stern wave length (crest to crest), the acceleration is still experienced. Whereas, if the acceleration were due to water particle movement in the wind wave, when the full wave length is in contact with the hull, the net force would be zero, and the vessel wouldn't move any faster. It does. Pretty cool stuff.
Here's a link to an animation that really demonstrates how a wave works. Scroll down to "Water Waves". Each particle of water within the wave rotates in a circular motion. The closer to the surface, the greater the movement. However, the increased speed when a vessel is acted upon by a wave, is not really due to the particle imparting a force on the hull, or because of a "flow" of surface water. If this were the case, really light objects would be swept away by even small waves. (They aren't unless the wave is so big that they actually tumble or slide downhill on the leading edge.) Instead, a displacement hull accelerate is due to the wind driven water wave modulating with the hull created bow / stern wave, which basically causes the motion of the two waves (not the motion of the water within the waves) to slide in relation to the actual water surface. This is proven by the fact that if the wind wave length (crest to crest) is equal to the vessel bow/stern wave length (crest to crest), the acceleration is still experienced. Whereas, if the acceleration were due to water particle movement in the wind wave, when the full wave length is in contact with the hull, the net force would be zero, and the vessel wouldn't move any faster. It does. Pretty cool stuff.
Shoot, double-shoot
For some reason, that link doesn't show when I put it in the link spot. Last attempt, try this... http://www.gmi.edu/~drussell/Demos/waves/wavemotion.html
For some reason, that link doesn't show when I put it in the link spot. Last attempt, try this... http://www.gmi.edu/~drussell/Demos/waves/wavemotion.html
Diagram Same as Your Link
If you will look closely at the dots in your link, you will see that they are doing exactly what is shown in my diagram. The difficulty in seeing it is that the waves are moving in your link. In my diagram, I have held the wave stationary, but am showing the instantaneous movement of the water within the wave. If you will think about it, the diagram exactly matches what you see in reality. If you are standing in the water and a wave comes towards you, you feel pulled towards the wave. As the wave crest approaches you the wave pushes. If you are on a beach, prior to the wave arriving, the water retreats. When the crest moves onto the beach, the water flows up the beach. I realize that a wave breaking on a beach is not the same as water in the open, but the mechanism is the same. When surfing, I have heard about people reporting lack of rudder control. There is a reason for loss of rudder control that is a reduction in the water flow past the rudder. The forward movement of the water in the crest also explains surfing. I have heard of no other valid explanation. The other is that, in spite of there being no net transport of the water, there has to be some movement of the water. In addition I would expect the movement of the water to be uniform in relation to the shape of the wave. In the trough, the water flows opposite to the direction of the wave. That becomes the water that forms the wave. In the crest the water flow is parallel to the wave movement.
If you will look closely at the dots in your link, you will see that they are doing exactly what is shown in my diagram. The difficulty in seeing it is that the waves are moving in your link. In my diagram, I have held the wave stationary, but am showing the instantaneous movement of the water within the wave. If you will think about it, the diagram exactly matches what you see in reality. If you are standing in the water and a wave comes towards you, you feel pulled towards the wave. As the wave crest approaches you the wave pushes. If you are on a beach, prior to the wave arriving, the water retreats. When the crest moves onto the beach, the water flows up the beach. I realize that a wave breaking on a beach is not the same as water in the open, but the mechanism is the same. When surfing, I have heard about people reporting lack of rudder control. There is a reason for loss of rudder control that is a reduction in the water flow past the rudder. The forward movement of the water in the crest also explains surfing. I have heard of no other valid explanation. The other is that, in spite of there being no net transport of the water, there has to be some movement of the water. In addition I would expect the movement of the water to be uniform in relation to the shape of the wave. In the trough, the water flows opposite to the direction of the wave. That becomes the water that forms the wave. In the crest the water flow is parallel to the wave movement.
We ll, I hafta disagree that they are the same...
The animation more clearly illustrates the time vs particle displacement relationship, and that the net displacement of all water particles in the wave = zero, and that's a pretty important part of this discussion. However, both show (clearly or not) that if the vessel is in the trough between the waves, that the net water particle direction is opposite to the direction of the wave, AND surfing vessel. This directly contradicts the theory that the particle motion in the wave is directly causing the vessel to accelerate above THS, because similarly, if the net wave particle motion over the surface of the hull was negative, the vessel would slow down. It doesn't. Addtionally, that the vessel doesn't accelerate dramtically when the vessel and wind driven wave direction is opposite, when the vessel is in the trough (region of the particle motion moving in the positive direction), also contradicts the direct particle motion impact theory. However, that the wind driven and vessel created waves modulate, to a higher net speed than the vessel wave alone, still holds water (sorry for pun), under all conditions, including the loss of rudder control.
The animation more clearly illustrates the time vs particle displacement relationship, and that the net displacement of all water particles in the wave = zero, and that's a pretty important part of this discussion. However, both show (clearly or not) that if the vessel is in the trough between the waves, that the net water particle direction is opposite to the direction of the wave, AND surfing vessel. This directly contradicts the theory that the particle motion in the wave is directly causing the vessel to accelerate above THS, because similarly, if the net wave particle motion over the surface of the hull was negative, the vessel would slow down. It doesn't. Addtionally, that the vessel doesn't accelerate dramtically when the vessel and wind driven wave direction is opposite, when the vessel is in the trough (region of the particle motion moving in the positive direction), also contradicts the direct particle motion impact theory. However, that the wind driven and vessel created waves modulate, to a higher net speed than the vessel wave alone, still holds water (sorry for pun), under all conditions, including the loss of rudder control.
Look Again
Run a copy of my diagram. Put it in front of the computer screen as a reference. Run the water wave simulation. Watch one of the blue dots. Don't watch the movement of the wave itself except as a reference point. What you are looking for is how the blue dot moves in relation to a given point on your computer screen. When the blue dot is at the crest of the wave it is moving forward with the wave. When the blue dot is in the trough, it is moving backwards against the wave. When the blue dot is midway between the following trough and the crest, it is moving straight down. When the blue dot is midway between the crest and the leading trough, it is moving straight up. You can also see the other flows at 45 degrees to the cardinal directions. You can also see the other eight intermediate positions, but you have to be a lot quicker in your viewing. Can't anyone else see this? I will try to come up with a better diagram which illustrates this.
Run a copy of my diagram. Put it in front of the computer screen as a reference. Run the water wave simulation. Watch one of the blue dots. Don't watch the movement of the wave itself except as a reference point. What you are looking for is how the blue dot moves in relation to a given point on your computer screen. When the blue dot is at the crest of the wave it is moving forward with the wave. When the blue dot is in the trough, it is moving backwards against the wave. When the blue dot is midway between the following trough and the crest, it is moving straight down. When the blue dot is midway between the crest and the leading trough, it is moving straight up. You can also see the other flows at 45 degrees to the cardinal directions. You can also see the other eight intermediate positions, but you have to be a lot quicker in your viewing. Can't anyone else see this? I will try to come up with a better diagram which illustrates this.
New Diagram
Rod. I came up with a new diagram. Make a copy of the diagram and pull up your link and compare. The diagram shows the same wave moving across the paper. Time 1 or t1 shows the blue particle of water at the bottom of the trough. t2 shows the particle of water rising vertically midway between the crest and the leading trough. t3 shows the particle at the crest. t4 shows the particle of water falling vertically midway between the following trough and the crest. t5 shows the particle back at the bottom of the trough. t2 and t4 shows the particle moving vertically at the intermediate positions. C and T identify the same crest and trough from t1 through t5. Notice that the particle turns in a clockwise circle just as described in your link. Notice that there is no mass export of water. The water stays within that narrow circle. If I can't convince you with this, then I suggest you do the same type of drawing. Hold the wave stationary and show the movement of the water within that wave. I will then try to see your viewpoint.
Rod. I came up with a new diagram. Make a copy of the diagram and pull up your link and compare. The diagram shows the same wave moving across the paper. Time 1 or t1 shows the blue particle of water at the bottom of the trough. t2 shows the particle of water rising vertically midway between the crest and the leading trough. t3 shows the particle at the crest. t4 shows the particle of water falling vertically midway between the following trough and the crest. t5 shows the particle back at the bottom of the trough. t2 and t4 shows the particle moving vertically at the intermediate positions. C and T identify the same crest and trough from t1 through t5. Notice that the particle turns in a clockwise circle just as described in your link. Notice that there is no mass export of water. The water stays within that narrow circle. If I can't convince you with this, then I suggest you do the same type of drawing. Hold the wave stationary and show the movement of the water within that wave. I will then try to see your viewpoint.
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