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Old 16-10-2014, 08:49   #61
bmz
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Re: Main Sail Runner (or not)

"Lift, by definition, is perpendicular to the direction of the air flow."
I am happy that you understand that; because it means that a windward leech will slow a boat down.
"You shouldn't try to make your main look like your genoa in a beam reach. You should try to make your genoa look like your main. This is why people Barber haul or use reaching struts."
You have it backwards again; both baber hauls and whisker poles are used to widen the leech of the head sail off the wind to make it look far less like the mainsail, not more like it.
BTW, rather than argue this, why don't you empirically test it. Why don't you put telltales on both your main and genoa running from the luffs to the leeches and see which ones stall. I have; and therefore made my subsequent mainsail loose footed with extended outhaul travel--to mimic my genoa. BTW, I also gained 20 seconds per mile.
Additionally, as far as who is arguing with professionals, I would note again that sailboat manufacturers are eliminating travelers altogether because of the negative affect of windward leeches.
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Old 16-10-2014, 09:13   #62
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Re: Main Sail Runner (or not)

Quote:
Originally Posted by bmz View Post
"Lift, by definition, is perpendicular to the direction of the air flow."
I am happy that you understand that; because it means that a windward leech will slow a boat down.
"You shouldn't try to make your main look like your genoa in a beam reach. You should try to make your genoa look like your main. This is why people Barber haul or use reaching struts."
You have it backwards again; both baber hauls and whisker poles are used to widen the leech of the head sail off the wind to make it look far less like the mainsail, not more like it.
BTW, rather than argue this, why don't you empirically test it. Why don't you put telltales on both your main and genoa running from the luffs to the leeches and see which ones stall. I have; and therefore made my subsequent mainsail loose footed with extended outhaul travel--to mimic my genoa. BTW, I also gained 20 seconds per mile.
Additionally, as far as who is arguing with professionals, I would note again that sailboat manufacturers are eliminating travelers altogether because of the negative affect of windward leeches.
I am desperately trying to avoid using emoticons.

I can't even follow your arguments anymore. Lift of a wing is defined as perpendicular to the undisturbed airflow far from the wing. Is that better? The direction of the boat and the direction of the wind are different, obviously.

Please name 5 racing boats made in the last decade that don't have a traveler. How about one? Some cruising boat manufacturers are eliminating them because people think that they take up too much room and don't know how to use them anyways.
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Old 16-10-2014, 09:38   #63
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Re: Main sail Runner (or not)

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Originally Posted by cwyckham View Post
Lift, by definition, is perpendicular to the direction of the air flow.
I really don't wanna get into this dogfight but technically lift is perpendicular to the chord. Chord is defined by airfoil shape.

An airplane has a fixed shape therefore a fixed chord.

A sail can have many adjustments to change the shape of the chord. It can also have variable twist of the trailing edge.

You are predominantly correct in your explanations but I felt it necessary to point this minor anomaly out.

@bmz - While you obviously have a passoin about how this stuff works, and you have convinced yourself of your theories and opinions much of what you are saying is incorrect.

For example earlier you stated outhaul impacts twist. Outhaul impacts lower 3rd sail shape predominantly belly but it has almost zero impact on twist.

I honestly don't want to get into a prolonged fur fight but I think you should do some reading - maybe the aforementioned symmetry book or at least a few sail trimming guides.
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Old 16-10-2014, 09:46   #64
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Re: Main Sail Runner (or not)

There are plenty of 505s with no traveler.

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Old 16-10-2014, 10:03   #65
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Re: Main Sail Runner (or not)

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There are plenty of 505s with no traveler.
Perhaps I should have specified over 30'?
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Old 16-10-2014, 10:13   #66
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Re: Main sail Runner (or not)

Quote:
Originally Posted by Ex-Calif View Post
I really don't wanna get into this dogfight but technically lift is perpendicular to the chord. Chord is defined by airfoil shape.

An airplane has a fixed shape therefore a fixed chord.

A sail can have many adjustments to change the shape of the chord. It can also have variable twist of the trailing edge.

You are predominantly correct in your explanations but I felt it necessary to point this minor anomaly out.

@bmz - While you obviously have a passoin about how this stuff works, and you have convinced yourself of your theories and opinions much of what you are saying is incorrect.

For example earlier you stated outhaul impacts twist. Outhaul impacts lower 3rd sail shape predominantly belly but it has almost zero impact on twist.

I honestly don't want to get into a prolonged fur fight but I think you should do some reading - maybe the aforementioned symmetry book or at least a few sail trimming guides.
Hi Ex-Calif. I'm very glad to have you join. I desperately want to shake my head and walk away, but I'm afraid that other users might read some of this stuff and believe it... So I find myself stuck in an endless fight between two people, neither of whom are going to budge an inch.

I'm trying not to pull out credentials, because ideas should stand on their own and I'm just a manager now, but I was a practicing aerospace engineer not too many years ago. How lift actually works isn't as easy as it seems and 90% of people who think they know how it works don't. It is also really hard to explain on a forum (I spent years on a pilot's forum and even there it was no easier!).

Lift is perpendicular to the undisturbed airflow, not the chord. See here: Lift (force) - Wikipedia, the free encyclopedia)

Chord is actually the line from the leading edge to the trailing edge. At the base of the sail, the chord is therefore the line along the boom. As you work up the sail, the cord twists to leeward, usually (aircraft wings are also usually twisted in this way). This degree of twist is a large part of what this thread has been discussing.

When you say that we can adjust the chord of the sail, I think you actually mean camber. The chord is always a straight line from one edge to the other and the "belly" of the sail which we adjust with outhaul, Cunningham, etc. is the camber.
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Old 16-10-2014, 10:42   #67
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Re: Main Sail Runner (or not)

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Originally Posted by savoir View Post
There are plenty of 505s with no traveler.

Attachment 89822

Attachment 89823
You're like me, you've got a stick and just like poking things.

505 has a bridle and vang sheeting. Leech twist entirely controlled by vang and
bridle allows the boom to be pulled to the centerline.

An earlier post, which I'm not going to look for, someone said the boom should be on the centerline. That person has never sailed a wide cruising boat where the genoa is sheeted to a block on the bulwark/toerail. If the jib is sheeted wide, not much point in stalling the main.
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Old 16-10-2014, 14:58   #68
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Re: Main Sail Runner (or not)

"I am desperately trying to avoid using emoticons.
I can't even follow your arguments anymore. Lift of a wing is defined as perpendicular to the undisturbed airflow far from the wing. Is that better? The direction of the boat and the direction of the wind are different, obviously."
Unfortunately when you resort to ad hominem rather than substantive response, useful discussion is over.
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Old 16-10-2014, 15:13   #69
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Re: Main sail Runner (or not)

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Originally Posted by cwyckham View Post
Hi Ex-Calif. I'm very glad to have you join. I desperately want to shake my head and walk away, but I'm afraid that other users might read some of this stuff and believe it...
not much chance of that. I have no friggin idea what you are all talking about. Im an armature pilot, but I just fly the thing, the same as my sailing. Wind in the sails and it goes forward and I go sailing good for me.

I did pick up in the comment that travelers are being dispensed with on new sail boats and that gives me confidence that I'm not loosing that much.
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Old 16-10-2014, 15:19   #70
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Re: Main Sail Runner (or not)

"much of what you are saying is incorrect.
For example earlier you stated outhaul impacts twist. Outhaul impacts lower 3rd sail shape predominantly belly but it has almost zero impact on twist."
Actually, I did not say what you allege; what I said was: "the only way your top batten would be parallel to the boom, is when you have no twist in your sail."
However, if your outhaul is tight and your top batten is parallel to the boom, loosening your outhaul will open up your leech and your top batten will no longer be parallel to the boom.
"I honestly don't want to get into a prolonged fur fight but I think you should do some reading - maybe the aforementioned symmetry book or at least a few sail trimming guides."
Isn't there anyone here who wants to deal with the substance of these issues? I am not alleging that reference to books or sailing guides is improper; but the proper way to reference them is to quote a specific reference which you allege refutes the substance of my position, not an ad hominem suggestion that I need to read them.
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Old 16-10-2014, 16:34   #71
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Re: Main sail Runner (or not)

Quote:
Originally Posted by cwyckham View Post
<snip>

Lift is perpendicular to the undisturbed airflow, not the chord. See here: Lift (force) - Wikipedia, the free encyclopedia)

Chord is actually the line from the leading edge to the trailing edge. At the base of the sail, the chord is therefore the line along the boom. As you work up the sail, the cord twists to leeward, usually (aircraft wings are also usually twisted in this way). This degree of twist is a large part of what this thread has been discussing.

When you say that we can adjust the chord of the sail, I think you actually mean camber. The chord is always a straight line from one edge to the other and the "belly" of the sail which we adjust with outhaul, Cunningham, etc. is the camber.

Sorry for my errors. It was late last night when I got home. My brain wa in neutral.
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Old 16-10-2014, 19:11   #72
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Re: Main Sail Runner (or not)

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Hi LadyM,
I'm anchored off Fleming Key, right next to Key West. Tomorrow evening, the first of a couple months of vacationing family and friends will arrive, and if weather allows we'll probably sail over to visit Fort Jefferson in the Tortugas.

Do you sail out of Miami? Do you sail?
Don't apologize! We needed a fresh voice or two

Sent from my SGH-I337M using Cruisers Sailing Forum mobile app
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