What is the major purpose of these differences?
Does it make any difference in technical terms?
Is one rig better than the other?
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Posted: Dec 16, 2010 - 01:08 PM
Regarding mainsails, some cats have loose-footed booms where the foot of the mainsail is not secured to the boom, ie Prindle 18, whereas other cats have secure-footed mainsails where the sail is connected to the boom by sliding the foot of the sail up a track on the boom using a bolt-rope, ie Hobie 16.
What is the major purpose of these differences?
Does it make any difference in technical terms?
Is one rig better than the other?
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Posted: Dec 16, 2010 - 03:16 PM
My understanding is the bolt rope foot mainsail is simple. The loose foot mainsail allows for more adjustments. Making the loose foot "better" if you was a performance boat.
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Scott,
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Posted: Dec 16, 2010 - 04:08 PM
I hear you Scott, on my H16 the mainsail was permanently attached to the boom, made for easier rigging/derigging of the mainsail, on the P18, it takes 5 min longer to rig mainsail, then attach boom to mast, then attach mainsail to boom outhaul car, then tension everything up with both outhaul and downhaul. But if I was performance orientated, I would have a performance cat like a F-18, I'm not, I do have the need for speed but want to balance that with setup/breakdown time.
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Posted: Dec 16, 2010 - 04:09 PM
Loos foot sails force you to pay attention to the set and make you a better sailor in my book. The pay off is speed. -
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Posted: Dec 16, 2010 - 04:35 PM
So the big question is does anybody KNOW? I would like to know the answer.
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Posted: Dec 16, 2010 - 05:47 PM
Know what? Which one is better? What do you define "better" as? It appears Turbo was looking for simple, so the fixed foot would be better for him.
If you are talking performance the loose foot rig must be better since every modern performance cat I have seen has a loose foot. All those engineers and designers can't be wrong about which is higher performance.
So:
Performance vs simplicity
Performance
Performance better with loose foot. Simplicity better with fixed foot
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Scott,
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Posted: Dec 16, 2010 - 06:40 PM
i find that with my old sails on my H18, the loose footing provides more adjustment to make up for the age of the sail. making an old sail still quite usable, albeit not for racing. thus i don't need a new set of sails... this is "better" for me... -
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Posted: Dec 16, 2010 - 06:47 PM
Yup! pretty much what I had already figured out even with my limited experience, the H16 mast base had a stopper and limits the amount of mast rotation but most performance cats have the nylon ball sitting on top of a rod and there is no limiter, in fact most performance cats even have a mast rotator bar to manually rotate mast. And then there is the 2:1 downhaul, which most racers upgrade to even 6 or 8:1, I can only imagine the forces exerted on a mast with a 8:1 downhaul; and then you have the 2:1 outhaul, I'm sure that is upgraded as well, all in an effort to stretch the sail as tight as possible to increase airflow over the wing/sail, so as to increase overall boat speed. But unless one is schooled in airflow properties and how to read "telltales" on one's sail, one will reach a plateau with sailing, which can only be overcome with the help of someone more experienced.
I think I have just about reached that stage.
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Posted: Dec 16, 2010 - 09:17 PM
between a full set of teltales and a bridal mounted wind vane, thats your most useful set "gauges" on a cat...i love that hobie bridal mount wind vane, your eyes are already looking that way, no looking up at the masthead all day. i have got three teltales on the main and jib...you get a real clear picture of whats happening that way. yup..take your heading, fly the teltales, and sail the wind...petal to the metal.
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Posted: Dec 16, 2010 - 09:47 PM
Don't con a con man. What makes it simpler? I have had 2 h16's and threading the boom on the mainsail was not simpler than attaching my 5.2 main with a quick release pin. Now as for performance, there has to be a reason for the loose footed main to be better performing. It all has to do with air flow, but I cannot figure out why air flow would be more efficient with loose footing, as a matter of fact I would think the loose foot would be a more disturbed air flow.
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Posted: Dec 17, 2010 - 11:22 AM
With my old H16 I left the boom on the sail all the time, just rolled it up in the sail. So I just slid the front of the boom down into the mast track once the sail was raised and put a little tension on the outhaul and was done. No mast rotator to connect and not much of a downhauler or outhauler to adjust. My H18 has a loose foot and probably takes slightly longer. But personally like the ability to disconnect the boom and let the main flap in the wind without boom attached on the beach, versus having the boom swing around on shore.
Performance wise you are able to make a wing shape in the sail all the way to the foot with a loose foot, or flatten out the sail, depending on conditions by adjusting the outhaul and having that batten at the bottom of the sail, it allows you to shape the bottom of the sail. With a bolt rope bottom you have either a straight foot (boom shaped) or a pocket once your sail is old and blown out. No good way to adjust the foot of your sail as I recall.
With the fixed foot sail, the only thing the outhaul does is determine how tight the foot is pulled, it doesn't really change shape since it is fixed in a track on the boom.
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Posted: Dec 17, 2010 - 12:15 PM
That was very lucid and makes sense. Now my question is why is a wing more efficient because the bottom cannot be shaped or does the rest of the wing make up for the inefficency of the bottom edge.
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Posted: Dec 17, 2010 - 01:34 PM
Guess I don't understand the question. Are you talking about the Americas Cup wing sail?
More efficient because the bottom can't be shaped? I don't follow....
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Scott,
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Posted: Dec 17, 2010 - 03:32 PM
No i meant that a wing sail is more efficient and the bottom cannot be shaped. Now does it follow that a fixed foot is more efficient? I am just trying to keep the conversation lively.
Edited by golfdad75 on Dec 18, 2010 - 07:15 AM.
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Posted: Dec 17, 2010 - 09:08 PM
I get it, with the sail rigged loose-foot, you are able to curve the sail more by easing off on both the downhaul and outhaul, more so than on the fixed-foot sail, but without knowledge of airflow properties, it don't mean squat. I don't know if more curve to the sail is better than less curve, or under what circumstances, ie, more curve on more wind, or less curve on less wind, or vica versa. That is why I said that one would reach a level in sailing which could only be overcome with more knowledge, knowledge gained from a more experienced sailor.
I guess one could educate oneself using the internet...........!
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Posted: Dec 18, 2010 - 08:31 PM
the questions were "What is the major purpose of these differences?
Does it make any difference in technical terms?
Is one rig better than the other?"
The reasons H16's come this way, is this is an old design, and not the most dynamic to fit in different wind ranges.
Modern design include the ability to change the shape of the sail at many different locations (luff, leach, out/downhaul, mast shape effecting sailshape along the mast axis to open or close the pocket, rotation limits or inducement, etc all to get the correct chord, depth, pocket shape, draft, etc)
ok to the wings: how many birds have wings that don't change shape at all? (none, they all can change the shape of their wing / sail depending on its needs).
Look at f-14 (jet), it has adjustable wings for different conditions (speeds). also modern testing in high end wing design include the ability to morph shape
are you kidding me?
The main trim parameters are: master wing rotation (similar to mast rotation on a conventional rig); master camber control (general rotation of the flap element); flap twist control (each flap can have a specific angle of rotation).
it is a lower tech system, it has a simpler out haul, minimal downhaul, jib blocks on the beam, 2 way jib adjuster out of the way (beam), less lines, less fuss, shorter.. lighter mast, no boards, simpler rudder systems, no spinnaker, stock non collapsing tiller extension, simpler design (deck lids), -
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Posted: Dec 18, 2010 - 09:18 PM
Typically, the SIMPLE rule of thumb is, the harder it blows, the tighter she goes
this means as the wind picks up, you want a tighter downhaul, tighter outhaul, restricted rotation, and more mainsheet to flatten the sail (upwind). U will probably need to travel out a little bit or you will capsize with a tighter main.. but if you have ever sailed with a loose main in heavy air... you know that your sail will not behave .. it will invert, flop, pop, fart and burp... never good sounds or sights on a boat. This is even more dramatic on less stable boats (mono's) and inverted sails can lead to inverting masts.... never fun to see and bad things can happen...(snap)
again, the SIMPLE idea is that in lighter air... you want a bigger pocket shape to your sail.
Technically, this will create a more powerful low pressure zone and increase the speed of the air behind your sail (due to the curve in the leeward side of the sail).
completely irrelevant but true is the fact that this low pressure actually sucks you forward, you are not being pushed upwind... but being sucked :) sounds dirty and i like it that way :~p
Downwind is a different creature... typically.. you will want to be traveled out downwind regardless of wind speed, and your down and out haul loose... if you have rotation control... you want to let it rotate all the way. Downwind you are being pushed by the sails, so you want a big pocket in both light and heavy air... however you will want to downhaul to open the top and let some wind/power bleed off if your are overpowered.
Edited by MN3 on Dec 18, 2010 - 07:23 PM. -
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Posted: Dec 18, 2010 - 11:11 PM
oh
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Posted: Dec 19, 2010 - 03:26 PM
Sorry Andrew, you have it mixed up. Nothing is sucked, or pulled. We don't actually "pull" a wagon, it is pushed. If you analyze the loads involved you realize that the palm of your hand is pushing on the rear edge of the wagon handle. This increased pressure forces the wagon forward.
Our shrouds are under tension, follow the loads from the hound to the pin at the hull & you find the same thing happens. There is no sucking that shroud downwards.
A sail is much the same as an aircraft wing, which operates on Bernoullis Therom. Airflow meeting the leading edge of a wing, or sail, is forced to split. To simplify greatly, lets think of two air "packets", "A" is forced to travel around the front side, "B" the rear. The two packets want to meet at the same time at the trailing edge.
A wing generally has a degree of camber,(again simplifying, the greater the camber, the greater the potential lift) this camber results in a greater distance along the top edge. "A" is forced to speed up to go the greater distance in the same time. We never added any energy to packet "A" or "B", so the total energy must not change. To achieve this, the pressure of faster moving packet A decreases. We now have a low pressure on top of the wing, & a relatively higher pressure underneath. You have heard since grade 4 science that Nature abhors a vacumn. The higher pressure area tries to get into the lower pressure & equalize it. Result, the wing is forced upwards,(lift) by this higher pressure. We need the higher pressure to obtain results.
Our cars engine does not "suck" air, it is pushed in by higher outside pressure, hence the decrease in power at higher altitudes as atmospheric pressure decreases. To regain that power we turbo charge, or super charge. TC or SC do not create more "suction", they create more pressure on the intake side. It is important to understand this principle, it is not just a matter of semantics.
This differential of pressure is responsible for quite an amazing repertoire in our everyday lives, carburetors, forcing solvent up the tube (notice I didn't say "suck") of the gizmo we attach to our air compressor for cleaning things, & most importantly breathing. Take a breath, our diaphragm drops creating a lower pressure in the lung cavity. Higher atmospheric pressure pushes air into our lungs. Jump off your Cat with a piece of hose in your mouth, then use it as a snorkel. Floating on the surface it is easy to breathe, about 16" down, you die. At that point the water pressure squeezing your chest cavity has equaled the air pressure trying to push into your lungs. No amount of "sucking" can refute the laws of physics and allow you to draw breath. If you could increase the atmospheric pressure it could overcome water pressure to a greater depth & allow you to breathe. This is one reason a SCUBA tank must be pressurized.
Back to sails, now that we understand it is a higher pressure driving the sail,(and skegs or boards converting this push into forward motion). To get more lift(power)we need greater total pressure,which can be obtained by more area, higher wind velocity, denser air, co efficient of lift that is determined by wing shape (CL), or some combination of these. Air velocity has a "squared" function in the equation, & so has the greatest effect. We can't do much with air density, but we can alter the CL by changing sail shape.
A wing,(aircraft or sail) can increase/decrease camber several ways, flaps being the most common way to increase. As they move rearwards & down, they increase both chord & camber. Same is true for leading edge devices,(slats). Increasing chord results in an increased wing area. If you couple the larger area with an increase in CL ie greater camber, the result is greater lift, (power). Of course nothing comes free, greater lift results in greater induced drag. As long as we increase lift more than the resultant increase in drag, we are ahead of the game. A tall narrow sail results in what is called a high aspect ratio,(chord vs span) very efficient...think of a gliders wing, or any soaring bird. This is where the sail trimmer comes in. Modern rigs allow us to change the sail shape to suit the conditions. A hard wing sail will be more tunable, & powerful, but the cost & complexity will also be greater.
And you thought college physics was a waste of time
Edited by Edchris177 on Dec 19, 2010 - 01:54 PM.
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Posted: Dec 19, 2010 - 08:41 PM
I knew this would happen as soon as the mysterious MN3 mentioned how much he sucked.
This reminds me of the heated arguments among various engineers and scientists we used to have on the old hobielist, awesome stuff!
For anyone following along and is confused, don't worry too much about the theory and whether the wind sucks or blows, just try to understand the sail shape required for various points of sail.
As simplified above:
Loose for downwind.
Tight for upwind.
How tight? How loose? What position should each line and adjustment be for a particular point of sail, with a particular:
crew weight
sail age and condition
wind strength
wave height
etc.
That's what you learn by "time on the water", watching others, and getting coaching.
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