Planing My MacGregor 26D

[Dan McGuire]

Haven't Learned Anything New

I have looked in every sailboat book I have and the dictionary. The best I can come up with is that surfing is a form of planing. The boat has lifted up on top of the water so that there is little bow or stern wave. When you see a power boat planing, there is virtually no wake or waves. I understand why the MAC Classic 26 is difficult to plane. The hull is not shaped correctly plus when when the sails are pushing hard enough to get the speed they are pushing bow down too much. That is true of most sailboats. When planing due to surfing, the boat is moving downhill similar to surfing and less force is needed to get the boat up to planing speed.BTW. Your last paragraph to be patronizing, but maybe it was not intentional.

 

[John Dawson]

makes SIMPLE sense

You don't often get to experience serious surfing on a lake. The term surfing usually means forces added from outside the boat, including the danger of being out of control. Surfing hazards include broaching (accelerating boat overpowers rudder and turns sideways before knockdown) and diving (boat accelerates into trough, buries bow and pitchpoles). It implies sea conditions that can produce acceleration from mild rides to extreme dangers.Planing is the term generally used for boats designed to achieve higher speeds at will, under control. The dangers a hydrofoil faces are voluntarily self-inflicted.You may argue that the fluid dynamics of both have similarities, but the mariner is using these terms to distinguish very different circumstances and possible consequences. To argue that it is the same phenomena only neuters those words and makes us invent more words to identify and discuss these matters. The savy helmsman may not be an engineer, but he has a practical understanding of his task. Surfing is a specific, tangible sailboat action for Rod and others, and implies a great deal more than the innocuous word 'planing'.For more information on surfing strategies and excess speed, you could read about streaming warps, etc. in 'Heavy Weather Sailing' by Adlard Coles, or other such manuals. Interestingly, Adlard uses both the terms planing and surfing on page 45. In his index, however, he does not include any reference to 'planing'. He does refer to 'surfing' on pages 45, 168, 186, 193, 194-7, 202, 207-10, 219-20, 228, 230-1, 279-81, 285-6, 353, 356-60, 365, 399-400, and 402-3.

 

[Dan McGuire]

Interesting and Descriptive

We don't get anything like that on our lake. I was visulizing something similar to surfing (on a surf board), which is clearly planing.From your description it looks like the boat may actually may be moving slower than the water, since you imply loss of rudder control. I will describe what I think is happening based on your description. Correct me if I am wrong. Unfortunately I will be out of town for a few days and will not be able to respond.The boat is on the forward face of a large fast moving wave. Locally within that wave the water is moving the same direction as the boat. Since the boat is travelling in that local environment, its forward speed is fairly high, in excess of hull speed. However, the boat's speed relative to the water next to the boat is slower. Therefore with what may be fairly large sail forces, the boat is in danger of losing rudder control. Additionally, if the boat moves too far forward, it gets into the trough and pitchpoles.

 

[Ramblin' Rod - Mac 26D - SeaQuell]

Nope, on many accounts

When a displacement hulled boat is in motion, it creates a bow and stern wave.Below hull speed, the bow wave is at the bow, and the stern wave is some distance back on the hull, relative to speed.At hull speed the bow wave is at the bow, and the stern wave is exactly at the transom. In essence, the boat is in a valley.If more power is applied, the displacement hull simply pushes more water, the bow wave and stern wave become higher, and hence the valley becomes deeper.No amount of additional power will enable the displacement hull to climb up over the bow wave.This is the prime difference between a displacement and planing hull. A planing hull is designed so that it can climb up and over the bow wave, and then speed is limited pretty much only by power and drag.The Macgregor 26 classics have displacement, NOT planing, hulls. They CANNOT plane.As a completely seperate issue, when a following wave (lets call it a wind wave but it could be generated by something else) overtakes a displacement hull, the wind wave modulates with the bow and stern wave.With sufficient power (from sail or motor) up to a certain wave height, the displacement hull will tend to move at the speed of the overtaking wave. This IS surfing. When just the right amount of power is maintained, you can hold it and ride the wave for some time or distance. I have done this many, many times on waves from 2 to 4 feet, for as long as 5 minutes, sustaining 8.5 mph by GPS, with no current. With too little power, you "lose" the wave and it overtakes you and continues on. At that precise moment, the vessel will tend to wallow and be difficult to control.In very high and steep waves, when a wave begins to overtake, the hull created bow wave falls away below the boat. Now boat speed is limited by gravity, power, and drag. The boat races down the forward face of the wave until the bow drops into the water and a new speed limiting bow wave is developed, or until you plunge into the back of the preceding wave.When the latter occurs, the sudden deceleration of the vessel, and then the stern lifting action of the overtaking wave, can cause loss of control, broach (suddenly thrown sideways, which is different than "rounding up" but also commonly confused)and possibly cause you to pitch-pole (flip end over end, real nasty.) I have experienced a few broaches, but fortunately have never experienced a pitch-pole.One tactic to keep the boat from broaching or pitch-poling is to trail warps, and another is to traverse the forward face of the wave. We have done both, for hours on end, on many occasions.>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>My last post was not intended to be patronizing. Your prior comment implied that because you did not already know the distinction between planing and surfing, that I must be in error. I attempted to point out the alternative possibility, that perhaps you simply had not learned the distinction yet. Sorry if that offended you.

 

[Jeff M21319]

A slightly different explanation...

I'm hoping that maybe I can add to this discussion and help explain away a bit of the confusion. Here is how I have had the two terms explained to me by a friend who is a long-time sailor and engineer: SURFING is essentially a condition where the boat is sliding down the leading edge of a wave. In conditions where boat speed through the water is close to the speed of the wave, the boat can often 'ride the wave' and gain a bit of speed. PLANING is a condition where, due to hull design, at a certain speed the boat is essentially no longer going THROUGH the water, but is going OVER the water. The bow wave is pushed astern and basically lifts the forward section of the hull out of the water, thus decreasing drag and allowing for even greater hull speed. This process is easy to see and feel on any ski boat. Let's say you are sitting in the water with the engine idling. Push the throttle forward and the boat begins to accelerate. At a certain speed, you will feel the boat start to 'rise-up' out of the water. (this is often referred to as 'getting on the step')Now the boat will accelerate even more and begin to 'skim' along the surface. At this point the bow wave is nearly amidships and a good portion of the hull is no longer actually touching the water. Because this leaves less wetted area, there is less drag and the boat can go faster. Pull the throttle back to idle and the boat will begin to decelerate. At some point the boat will begin to settle back into the water and decelerate rapidly. That is the point where the boat no longer has sufficient speed to stay on top of the water and gravity takes over. (this is often referred to as 'coming off the step') The planing hull has now reverted to displacement to remain afloat. Because a displacement hull does not have the ability to 'get on the step', it will never actually get into a planing mode. Even if you are surfing down a wave and the bow is out of the water, you're not actually planing, as the stern of the boat is still in displacement mode. One of the main differences between a displacement hull and a planing hull is that with a displacement hull more engine power will not increase boat speed significantly. For instance, you could put a 50 HP outboard on a 26D and the boat would still not do better than about 8 kts through the water. If you tried to push it too hard, the bow and stern waves will increase in height until the middle of the hull would no longer be in contact with the water and the boat would likely break-up. With a planing hull, the more power you give it the farther it will come out of the water until the boat completely looses contact with the water. At that point you will have little, if any, directional stability and the boat will likely 'spin-out' or flip over. (ever see a hydroplane go nose-up and flip?)Anyhow, hope this explanation helps.Jeff

 

[Bryan Ricks]

How about this

When your travelling down a wave hence, surfing; the water is moving in the same direction. You may be going faster than rated hull speed, but your not exceeding that maximum hull speed realtive to the water, just like going faster downstream. Gravity and water let you go faster. This is what Jeff was saying.When you're planing, you've stepped up and now have less surface area, and faster speed. This is what Jeff was saying. Cars hydroplane when the tires actually ride on the surface of the wet road--not a good thing.When I was a kid, I used to bodysurf, and never planed. Those guys on the boards surfed and planed and went like bat's out of he**Sorry I reiterated what you said Jeff

 

[Dana M26D]

When an S/V becomes a M/V.

I thought we enjoyed sailing. Who cares about planing hulls and the big horse power required to hold planing speeds. The M26X and M26M are nice boats but sacrifice a bit of sail-ability to get their pseudo semi-planing hulls up and away. My 26D holds hull speed with an 8 HP O/B. The 26X needs over six times the HP to reach three times the speed. (On a good day.) True, some have gotten their 26X to plane under sail, but it's not an every day event. I'd rather do without the heavy engine and stability concerns. Whenever I need to use the O/B I may be 1/3 as fast but a gallon of gas will last a long time. Of course the 50 HP engine would come in handy in several situations, and I think MacGregor forsees the future needs of the market extremely well. The displacement hull formula is:Hull Speed = 1.34 times the square root of the waterline length. My 26D has a waterline length of 23.5' so it's hull speed is ~6.5 knots.Taking into account all the +/- of water temp, salinity, marine growth, etc., the average displacement hull will vary only slightly from this figure. This is the maximum effective hull speed. A great deal more power will only push a displacement hull slightly faster. It would soon become ineffective to carry the greater HP and poor fuel economy for the slight gain in speed. If you must go faster it's much more effective to buy a longer hull.A displacement hull can exceed it's hull speed with additional power. In RAMBOAT's case he powers up with a spinnaker. He's likely more than doubled the effective sail power, yet only gained a slight increase beyond hull speed. Still, every knot counts.Some sailors are skilled at telling speed by the point where the crest of the bow wave hits the hull. (near the cockpit) A bit of sail trim will shift the bow wave crest forward or aft. Keep trimming until the crest is as far aft as possible for every point of sail.Can a displacement hull plane? No.Can it exceed hull speed? Yes, but only slightly.Until the lottery win (retirement planning) I'll keep enjoying sailing as it should be... In a displacement hull at hull speed. Let the M/V'ers enjoy the true co$ts of planing.

 

[Ramblin' Rod - Mac 26D - SeaQuell]

Not so Brian

Your theory that water in a wave moves laterally significantly, and that is what allows you to move faster than hull speed, is false. When a non-breaking wave passes, the majority of the water motion is vertical, and very little if any is lateral.If you watch a floating tennis ball, as the wave approaches the ball raises on the crest, the wave passes and the ball lowers into the trough, but if there is no current, the ball's lateral position is virtually stationary at all times.

 

[Dan McGuire]

Question

Rod. I thought I was beginning to understand surfing until your last post.I assume by lateral, that you mean in the direction the wave is traveling as opposed to at right angles to the wave movement. If the water is not travelling at a significant lateral speed and the boat is not planing, how do you account for the speed of the boat exceeding hull speed?

 

[Bryan22217]

Why can't anyone spell my name right?

The reason the tennis ball doesn't move is because it isn't surfing. The action we're trying to describe harmonizes with the momentum of the energy of the wave, and doesn't occur with every wave.  When surfing, one of the elements is catching the internal motion of the water which the tennis ball doesn't because it's displacement isn't enough. The ball does react to the internal wave by actually drifting behind as it passes. That's why it gets sucked out to sea. There are a lot of other factors involved to achieve surfing.http://www.galleryoffluidmechanics.com/waves/intlab.htmBryan

 

[Ramblin' Rod - Mac 26D - SeaQuell]

Dan

RE: Lateral - You are correct. By lateral I mean on a horizontal plane, (in the direction of the wave is implied as that is what we've been talking about all along.)Another good analogy is a rope held tight at one end, and raised and lowered sharply at the other end. This generates a wave that travels its length. The wave travels in the horizontal plane, but at any given point on the rope, the rope itself only moves in the vertical plane. You can put a piece of black electrical tape anywhere on the rope, to verify this.RE: Surfing - Read my prior post titled "Nope, on many counts". About half way down it talks about wind waves modulating with the hull speed limiting bow and stern wave. This means that the hull created waves, normally moving 7.4 mph at hull speed, combine with the wind waves in such a way that the resultant moves at a higher speed than the hull created waves alone. As these waves overtake you, you will consistently see the GPS peg about 8 mph or a little better. You can definitely feel the acceleration as the wave combines with the stern wave, and feel the deceleration as it pulls ahead of the bow wave.On steep waves, when the bow wave drops away from contacting the hull, it no longer holds the boat back. That's when true surfing takes place, and exceptionally high speeds (9 and 10 mph) can be maintained for as long as you "hold" the wave. Take your boat out on a good size lake with lots of open fetch. In about 12-15 knots, head on a broad reach under jib and full main. You should maintain 7.4 mph pretty easily. The average wave height will be 2 to 3 feet, but on occassion, one about 4 feet high will happen along. You'll definitely feel the boat take off when these waves catch up to the transom. That's surfing. Shortly, you'll feel the boat decelerate and "wallow" when you lose that wave. Note this same thing doesn't happen in flat water, same wind speed, same boat speed, when you then get hit with a gust (more power). That would be planing, and the Mac26 classics can't plane. Instead, you'll just heel excessively and round-up.

 

[John Dawson]

Broader description

I think there is some misconception here about the term 'surfing' meaning going faster than hull speed, or riding a wave, or planing along in a sustained way.I consider it surfing when going downwind and getting a little push/slide as waves lift the stern, all at a moderate pace. Its certainly surfing when doing hull speed and staying on a crest for awhile. You don't need to ask your GPS when you feel the boat take off.In the large waves, some of the accelerating force is simple gravity; you are falling down the side of a hill of water. I take the term surfing to apply to both following seas and head seas, in that getting down from a crest can be an exercise in rapid descent. Don't 'fall off' the crest and don't dig in at the bottom. Your stern is higher than your bow, and instead of a bow wave to slow you down, there is a valley in front of you. In a following sea, you may feel like you are standing still while waves lift you. Surfing is sometimes more about maintaining control in a washing machine environment than planing along at high speeds. Hope this subject is getting clearer, Dan.

 

[Ramblin' Rod - Mac 26D - SeaQuell]

Bryan

Sorry, I mispelled your name. One out of every 10 people I meet confuse my first (Rod) and last (Brandon) to call me Brad. The executive assistant at a previous employer did this for about 10 years, and new it every time immediately after she did it. It's amazing how your brain can play tricks on you.From your most recent post...RE: The reason... Absolutely correct, the ball is not surfing. But this shows that the water in every wave (non-breaking) only moves vertically. No lateral water movement (to speak of).RE: When surfing, one of the elements is catching the internal motion of the water...Incorrect. What enables surfing is when the object shifts its relative position in the water. (See above, the water doesn't move laterally, again any amount to speak of.) In other words, the object slides on the surface of the water, not with the body of the water. RE: That's why it gets sucked out to sea.Incorrect. When an object gets "sucked" out to sea, it is due to current caused by a rip tide. Lastly, up to this point, I've specified non-breaking waves. Breaking waves are a different story, lots of lateral movement. Toward the wind at the base, and with the wind at the top.(That's why these babies of just the wrong height, when taken broadside, can roll the most seaworthy sailboat.)Then again, not too many of us are out sailing our Mac26 classics in breaking waves. (White caps are not breaking waves.)

 

[Ramblin Rod - Mac 26D - SeaQuell]

John

Excellent point about surfing below hull speed.I absolutely concur. When you are only sailing along at say 4 mph, if a good enough wave catches up to you from astern going 5 mph, you can hold the wave (and the 5 mph it is moving) for quite some time.Up until now, I have only discussed the condition at hull speed to show that surfing is not the same thing as planing.

 

[Dan McGuire]

A few Comments

Reference water motion within the wave. I served 20 years in the air force as a meteorologist. During that period I was TDY to the navy in support some of their operations. I went to a school at Norfolk NAS for a course on polar meteorology and a little oceanography. I also took several courses offered by the navy over the years. None of this even remotely qualifies me as an oceanographer. I remember some of the wave models. They showed a rotary motion within the wave with a horizontal axis perpendicular to the wave movement. I don’t remember any quanitative description of the speed of the water motion within the wave, but it was not just vertical. I have also seen wave machines and the same kind of rotary motion is apparent.My sailing experience is limited. I started sailing in 1997. All of my sailing has been on inland waterways and lakes. I tend to be somewhat skeptical when someone states that something is impossible. I am not convinced that it is impossible to plane a MAC 26D. Difficult, but not impossible. I have a MAC 23. I believe the hull shape is similar to the MAC 26D. I have experienced 8k speeds for a few seconds according to the GPS. There have been numerous other sailors who have experienced similar bursts of speed for a few seconds and some for several minutes. It is questionable whether we were planing, but I believe there was a fairly strong gust and the boat picked up its speed prior to establishing the bow and stern wave. It then settles back down to something under hull speed. According to the descriptions others have given, it may be possible that during that interim period, the boat lifted and planed and may have maintained that condition for a few minutes.From what I have read in the forum and from my own experience and education, I believe that the surfing speeds are aided by several factors. I believe the speed is aided by the forward motion of the water. I also believe that some help is provided by sliding downhill and there is a small benefit because the sails don’t have to provide as much forward force. This helps prevent rounding up and the bow from digging in.For Rod and the others who have contributed, thank you. I have learned a lot about surfing. I don’t believe by any means, that I am 100% correct or have learned it all.

 

[Kevin C 26S]

White caps are not breaking waves! Oh no...

here we go again!(Actually, I agree with you, but still this could add another 100 replies to this silly thread!)

 

[John Dawson]

It wouldn't surprise me

if you could get a Mac 22 to plane with a ridiculous amount of force, the rear section is so flat and shallow. My interest here was to convince you that surfing is a familiar sail term and not synonymous with planing. Always fun when you stir things up and demand the facts, Dan et all.

 

[mrbill]

against my better judgment.....

I will post this photo link.....no idea if statemst are true...http://groups.msn.com/ToolManBoatContest/toolmancontest.msnw?action=ShowPhoto&PhotoID=106

 

[John Dawson]

Shut my mouth

As I said, the Mac22 (and Mac25) are very light and have very flat bilges, but I would have thought it would take more than 25hp to do it. I wonder if its true and if so, what GPS speed is achieved?

 

[Ramblin' Rod - Mac 26D - SeaQuell]

Dan, Re: circular/elliptical motion

Absolutely correct!I was trying to avoid this level of complication while explaining the reason surfing boats moved faster is NOT due to the horizontal motion of water within the wave.Here's a link to an excellent explanation of the elliptical water particle motion in a deep water wave.http://www.onr.navy.mil/focus/ocean/motion/waves1.htm Note that this elliptical motion does not induce any horizontal motion in the bottle (or vessel). The bottle moves up and down quite a bit, but there is no significant horizontal movement. Here's an even better simulation of the circular motion in a shallow water wave that shows that no matter at which point you look at on the wave, after one complete cycle, the water has moved zero lateral distance.http://www.esam.northwestern.edu/research/about_waves.htmlI can't find any simulation of a wave overtaking another, to show the modulating effect. I guess y'all are just gonna have to watch the transon waves on your boats.Regarding acceleration during gusts, I think it may certainly feel like the boat is moving faster than hull speed, and a GPS may erroneously report a higher speed for a few seconds (due to the algorithms used to calculate speed) but unless the boat is surfing on waves approaching from astern, a dsiplacmenet hull cannot be driven significantly over hull speed. In closing, a Mac26 classic has a displacement hull, and can surf very easily. However, no matter how much power is applied under sail or motor, it cannot plane.