Aftmast rigs???

[upchurchmr]

There are a few "minor" differences besides the mast position.

They have nothing whatsoever to do with cruising boats typically discussed in this thread.

 

[DennisRB]

Each time those extreme race boats get posted as "aft mast" the same relevant point gets made. Its a case of long bows out of the front rather than masts put at the back. Same thing you say? Well no point in repeating the differences yet again. Scroll back a few pages where it has been discussed in detail.

Not dissing the idea. I like sailing with a main. I just hate raising it, reefing it and storing it. So a little less main and more area in furling sails out the front is a good idea for cruising too. It means less engine hours in the real world where short trips means raising the main just isn't worth the effort.

 

[brian eiland]

"When sailing upwind most of the surface of the jib is oriented in the direction of the motion, while most of the surface of the main is oriented perpendicular to it, the leech often even pulling back."

This is the worst statement of "fact" I have ever seen.
I don't know what kind of a terrible boat or sailor is being represented here, but on my old Tornado catamaran the angle of incedince of both sails is almost equal.

I can't believe this is being quoted by anyone who sails.

Did you manage to look thru a lot of the material presented there by WB Sails,....quite a knowledgeable gentleman & outfit.
http://www.wb-sails.fi/en/contact-us/wb-sails-story

http://www.wb-sails.fi/en/contact-us/wb-sails-crew

http://www.wb-sails.fi/en/sail-technology/technologies---videos

And you did note this image?

 

[brian eiland]

There are a few "minor" differences besides the mast position.

They have nothing whatsoever to do with cruising boats typically discussed in this thread.

A number of these newer boats are moving their rigs back to counter the bow burying tendencies of those tall mainsails, and to take better advantage of their headsail areas.
I chose to eliminate the mainsail.

The racing monohull, Wild Oats, made quite some modes to move her rig back,....mentioned a few here on this page and some photos

 

[upchurchmr]

Brian,

Please discuss the quote I was talking about - which you originally quoted.
Not much of a discussion when you ignore the actual words that I took exception to.

I still have an article of the first time I saw you state your mast aft theory about 20+ years ago (maybe 30 years ago). You still are not making your case by not addressing the issue - skipping to something else as a distraction.

 

[brian eiland]

"When sailing upwind most of the surface of the jib is oriented in the direction of the motion, while most of the surface of the main is oriented perpendicular to it, the leech often even pulling back."

This is the worst statement of "fact" I have ever seen.
I don't know what kind of a terrible boat or sailor is being represented here, but on my old Tornado catamaran the angle of incedince of both sails is almost equal.

Additionally, in heavy weather I easily left the jib off and sailed extremely fast and weatherly.

I can't believe this is being quoted by anyone who sails.

Is this the 'original quote' you speak of,...that I did not respond to??

If so, here is another noted sailor and sailmaker's viewpoint
Sails in Combination

 

[upchurchmr]

Yes that was the statement that I re-quoted.
And you still didn't respond.

 

[tgtony52]

There are a few "minor" differences besides the mast position.

They have nothing whatsoever to do with cruising boats typically discussed in this thread.

I thought this thread was about "Aftmast rigs" which not only includes boats with masts positioned on the transom but any sailing boat (cruising or not) with a mast positioned aft of the middle of the boat.

I also thought that state of the art boats with masts 60 per cent back from the tack of the foremost sail would be not only relevant to this thread but would also be of significant interest to those who believe in aft mast rigs ( for whatever reason).

I believe that these "extreme race boats" are absolutely relevant to all the discussions within this thread as they show that moving the position of the mast further aft is part of the answer to improved performance. Like any other sport, technologies developed in racing have spinoffs beneficial to the rest of us, we just have to recognize it.

 

[DennisRB]

I believe that these "extreme race boats" are absolutely relevant to all the discussions within this thread as they show that moving the position of the mast further aft is part of the answer to improved performance.

Brian's whole idea is to move the mast back to make the main very small if not get rid of it entirely. His assertions are that better aerodynamic performance comes from less main and more headsail.

There is a subtle but major difference which most people seem to understand. When comparing working sails, these boats still have large mainsails compared to the headsails like they have always had, so are aerodynamically similar. The same rig is being moved back to prevent nosediving by way of longer buoyant bows for a hydrostatic/dynamic difference. The mains are not tiny and being replaced by headsails. The longer bows mean similar "flying" sails are now connected to the deck as bow spits are not needed or can be much smaller. Overall there is less nosediving. The rigs are similar, there placement is different. The standard mainsail is a crucial piece of the rig as always, and has no sign of becoming vestigial equipment soon to be phased out.

The racing monohull, Wild Oats, made quite some modes to move her rig back

To allow a more buoyancy at the bow so the boat could carry more sail without nosediving. How much smaller did they make the mainsail Brian?

 

[brian eiland]

Yes that was the statement that I re-quoted.
And you still didn't respond.

As I said before go have a look at similar descriptions of the interaction of the headsail with its trailing sail (albeit a mainsail or maybe my mainstaysail)

http://www.hk.northsails.com/TIPSADVICE/Howdosailswork/tabid/10496/language/en-US/Default.aspx

Sails in Combination

Each sail by itself is much simpler than the
combination of a foresail and mainsail as
in the sloop rig. The sails are operating so
close to each other that they both have
significant interaction with the other. The
most interesting feature of this is that the
two sails together produce more force to
pull the boat than the sum of their forces if
they were each alone.

Earlier, upwash was identified as the
increase in flow angle immediately
upstream of a wing. There is also a
corresponding change in angle, called
downwash, just behind a wing, where the
flow leaving the wing has been turned to
an angle lower than the original flow. This
is the cause of the well known “bad-air”
that a boat just to windward and behind
another boat experiences.

The mainsail of a sloop rig operates in the
downwash of the forward sail, causing the
flow angle approaching the mainsail to be
significantly reduced from what it would
be otherwise. This decreases the amount
of force that the mainsail produces. The
observed affect commonly referred to
as “backwinding” is partially a result of
downwash from the foresail, but is also due
to the higher pressure on the windward
side of the genoa being very close to the
forward, leeward side of the mainsail,
causing the flexible material of the mainsail
to move away from that higher pressure.

The foresail of a sloop rig operates in
the upwash of the mainsail. The wind
as far upstream as the luff of a genoa is
influenced by the upwash created by the
mainsail. Hence, a jib or genoa in front of
a mainsail has a higher flow angle than it
otherwise would have by itself, causing
an increase in the amount of force that
the forward sail produces. So, while the
mainsail is experiencing detrimental
interference from the foresail, the foresail
benefits from the interference of the
mainsail. Notice that more air is directed
around the curved leeward side of the
foresail. This causes higher velocity (lower
pressure) and more force. The net result is
that the total force of the two-sail system
is increased, with the foresail gaining more
than the mainsail loses.

There is a converse affect to a windward
boat receiving “bad air” (downwash) from
a boat ahead and to leeward. A leeward
boat gains additional upwash (“good air”?)
from a boat just to windward and slightly
behind that acts like a lifting windshift
until it moves ahead of the windward boat.
This is the same phenomenon from which
a foresail of a sloop rig benefits.

Another consequence of the difference in
flow angles that the two sails experience in
each others’ presence is that the mainsail
must be trimmed to a much closer
angle with the boat’s centerline than the
foresail, which is able to be trimmed to
a lead position well outboard. This angle
represents the difference in upwash on the
foresail and downwash on the mainsail
due to each other.

 

[CT249]

Brian, isn't the relevant part of Mikko's post the piece where he says "it would be wrong to think that the jib is more important". That demonstrates quite clearly that he does NOT think that the jib is a more important sail.

Secondly, no really good sailor oversheets their mainsail, by most definitions.

 

[CT249]

Current leading yacht in the 2016-7 Vendée Globe yacht race, Hugo Boss, is showing the way in competitive yacht design. The trend in the design of these IMOCA 60 boats over the last couple of decades clearly shows the mast position has moved significantly aft.
View attachment 110824View attachment 110825

And the trend in design in many of the fastest craft has been to get rid of the jib altogether, and just use a mainsail. So we can all pick and choose individual classes to "prove" our points all day long, and in the end it will prove nothing.

There are probably well over 10,000 boats that have been built to the rules of one class I sail in. My boat, as modified by me, may well have its rig further aft than any other boat in the entire class, so I'm not saying that mast forward works better. The point is that (as others have said) mast positions and rig designs are influenced by so many factors that we can't just point to any one design as evidence of broad trends or proof of concept.

 

[brian eiland]

Brian, isn't the relevant part of Mikko's post the piece where he says "it would be wrong to think that the jib is more important". That demonstrates quite clearly that he does NOT think that the jib is a more important sail.

https://cdn2.hubspot.net/hub/209338/news/Ad_aerodynamics/index2.htm

Think one
To understand how the mainsail and the jib work together, it may be useful to think of them as one wing with a slot in the middle. The jib forms the front part of the wing (leading edge in aircraft terminology) and the mainsail forms the back part (trailing edge). The jib is the curved, smooth shaped front part of the wing, the main is the more straight, flat part. When you adjust the main sheet or traveler, you adjust the camber of the whole wing in a very smooth way, around the hinge that the mast forms.

When you keep in mind that pressure always acts perpendicular to the surface, it is easy to see why the jib usually is in charge of most of the forward driving force, while the main causes most only heel. When sailing upwind most of the surface of the jib is oriented in the direction of the motion, while most of the surface of the main is oriented perpendicular to it, the leech often even pulling back. But it would be wrong to think that the jib is more important for that. The mainsail is bending the air in front of the jib, allowing the boat to point higher than with the jib alone, and also helping the jib bear more loading without stalling.

I was NOT trying to say that he thought it was the MORE important of the two sails,...but it certainly is important. "in charge of most of the forward driving force'. And yes, it can not do this on its own, it needs the helping hand of that following sail.

Secondly, no really good sailor oversheets their mainsail, by most definitions.

I was referring to a number of discussions that occurred on the Sail Aerodynamics subject thread (I believe it was), where there was much discussion of sheeting the mainsail up & often over center to provide a 'flap effect' in order to point higher. I call it over-sheeting.

 

[brian eiland]

Current leading yacht in the 2016-7 Vendée Globe yacht race, Hugo Boss, is showing the way in competitive yacht design. The trend in the design of these IMOCA 60 boats over the last couple of decades clearly shows the mast position has moved significantly aft.

WOW, have a look at this latest video
https://www.youtube.com/watch?v=kw-e2k5Ddpo

 

[Spiv]

"When sailing upwind most of the surface of the jib is oriented in the direction of the motion, while most of the surface of the main is oriented perpendicular to it, the leech often even pulling back."

This is the worst statement of "fact" I have ever seen.
I don't know what kind of a terrible boat or sailor is being represented here, but on my old Tornado catamaran the angle of incedince of both sails is almost equal.

Additionally, in heavy weather I easily left the jib off and sailed extremely fast and weatherly.

I can't believe this is being quoted by anyone who sails.

You should go and teach this guy how to sail.
Apparently he prefers to sail with two reefs in the main, staysail and reacher.