Sail trim quiz question

Apr 16, 2017
841
Federation NCC-1701 Riverside
Lots of questions here!

With three sails, each one will be trimmed tighter than the one in front of it. Your picture shows them in equal trim.

Your picture of upwind trim shows the boom really far off the centerline. That’s never the case for optimal trim.

Yes, when Reaching with the jib clew has to move outboard for proper trim. Most modern boats now have a mechanism to allow this, either with out haulers or with three-dimensional clew rings.

Yes the Volvo boats use reaching poles to Hold the spin sheet outboard, to allow the clew to stay outboard. Greatly improves sail shape with the code 0.
Was watching some mini transat and vendee globe videos. I suspect the clews pull in tighter due to attachent points back to the hull, but ill never be able to test that. Turbofans in jets seem to be parallel.

Its hard to get that boom over centerline

Ive got to find a way to pole out the jib on my 170. Like i said earlier the jib is cut so that the foot is a full naca. For exaple the chord is based on "j" the jib foot, but i would like to maybe recut as if j was jib plus boom. But stop the chord at j. If that make any sense.
 
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
Turbofans in jets seem to be parallel.
Jet engines are also circular, so each fan blade has just as many blades before it as the next one. Each blade is affected by the one before it, but all of the influences are common across the circumference. That's not true of sails linearly placed along a boat.
Its hard to get that boom over centerline
That's what travelers are good for. Otherwise it's basically impossible to really be on centerline.
 

walt

.
Jun 1, 2007
3,511
Macgregor 26S Hobie TI Ridgway Colorado
Pressure travels at the speed of sound in air which is way faster than any sails travel at. Another interesting thing about how the pressures created by the sail in the back (wind wise) can influence the pressures created by the sail in front.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Ive got to find a way to pole out the jib on my 170. Like i said earlier the jib is cut so that the foot is a full naca. For exaple the chord is based on "j" the jib foot, but i would like to maybe recut as if j was jib plus boom. But stop the chord at j. If that make any sense.
Indeed. I think I mentioned this earlier, but boats with non-overlapping rigs HAVE to have a way to move the clew outboard once you start reaching. If you don't, the great sheeting angle that makes for good upwind sailing destroys your sail shape. On BlueJ we use an outhauler, mounted 2 feet outboard from the track on the gunnel (near the shrouds) to allow up to pull the sheet (thereby the clew and leech of the sail) outward when jib reaching. Good for at least an extra 1/2 a knot. Here we go, 7.9 knots on a jib reach!

reaching sheet.jpg
 
  • Like
Likes: Will Gilmore

RussC

.
Sep 11, 2015
1,578
Merit 22- Oregon lakes
On BlueJ we use an outhauler, mounted 2 feet outboard from the track on the gunnel (near the shrouds) to allow up to pull the sheet (thereby the clew and leech of the sail) outward when jib reaching. Good for at least an extra 1/2 a knot. Here we go, 7.9 knots on a jib reach!
What's the difference between an outhauler and a barber-hauler? or is it just a different name for the same thing?
 
Last edited:
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
What's the difference between an outhauler and a barber-hauler? or is it just a different name for the same thing?
So-called ‘haulers’ are a collection of controls designed to deflect control lines (usually sheets) after they leave their last deck block. Inhaulers pull jib sheets IN towards the centerline for better upwind performance. Outhaulers pull OUT for reaching. The first setup of inhaulers were called barberhaulers, named for the person who invented them.

Some boats can take advantage of both, some just one or the other, depending on the location of the jib track. Due to the critical nature of the clew placement, inhaulers are much more common on jibs then genoas. Most headsails will benefit fron outhauling when reaching.

Twings are related, they pull down on spin sheets and guys.
 
Last edited:
Jun 3, 2004
890
Hunter 34 Toronto, Ontario Canada
I would think it has a lot to do with balance between the two sails- when the main is eased off, the wind doesn't force the front half the boat into the force of the wind. When we race the San Juan 24, we often have the main traveler almost up to the windward end. I think this is especially true of non fractional rigs because the head sail provides so much of the force?
 
Apr 16, 2017
841
Federation NCC-1701 Riverside
In the spirit of Christmas I placed some tinsel on the mylar sails of my remote controlled sailboat. A wind tunnel was set up in my laboratory using an air mover fan set on a cooler. The sailboat was placed in various orientations.

I am trying to load some videos but not having great luck.

The wind was surprisingly flat and well redirected. By 15 feet away the air had only spread out from a 6 inch nozzel to about 2 feet. This was measured with tinsel 3M'd to a kabob stick.

The tinsel was about 6 inches long glued on both sides of the luff and 6 inches of tinsel glued to the leech. I got to see air moving from the luff to about twice the foot out.

Some interesting observations.
1. On average, as air flows around the jib it leaves the jib at pretty much the direction as it is trimmed, for a long distance out. If the jib is trimmed to 45 degrees it leaves 45 degrees, if it is trimmed in 80 degrees it leaves at 80 degrees. This lookes like a true deflection/redirection.

2. Upwind. I started out with the boom on centerline. It was sort of stalled. Lee telltale looked great with the boom to lee a little. This is boat specific, but a start position. I centered the boom again and accepted poor telltales.
The jib is slowly trimmed in. As it is pulled in the trailing airflow comes with it. At some point the airflow trailing the jib is directed to the lee draft of the main. The main lee telltales pick right up. This must be the "slot". There is no veturi or anything like that. Trimming the jib simply redirects more moving air over the lee main(lift surface). With more trimming the jib redirects the airflow right into the leading edge of main. The telltales and main flop. This is the backwind. Over trimming the jib has the same effect as decreasing the angle of attack on the main.

3. On a broad reach. The main sail splits the wind up in a stall. Much like a bird coming in for a landing. There is a cool effect where the air flow does a 80 ish degree turn between the mast and the jib. Its really noticable mid jib. the air then deflects out past the jib as if on a beam reach/close reaching, at whatever the jib is trimmed at, boosting the main lee telltales some. Main luff windward telltales are sucked up around the mast to lee.

Take-a-ways (from a noob point-of-view). Assuption is flowing telltales equal best sail performance.
The headsail is magical. The jib affects the main. The best trim is when the airflow from the headsail is directed to the deepest camber of main. When the jib is trimmed right the main can be trimmed to a lower angle of attack. Adjust main to take advantage of this.

A well trimmed and cut jib increases pointing AND a poorly trimmed/cut jib devastates upwind pointing.

Jib helps main even downwind. It redurects main turbulence to back over main lift surface.

The well trimmed/cut headsail isnt just extra sail, its a mainsail force multiplier.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
In the spirit of Christmas I placed some tinsel on the mylar sails of my remote controlled sailboat. A wind tunnel was set up in my laboratory using an air mover fan set on a cooler. The sailboat was placed in various orientations.

I am trying to load some videos but not having great luck.

The wind was surprisingly flat and well redirected. By 15 feet away the air had only spread out from a 6 inch nozzel to about 2 feet. This was measured with tinsel 3M'd to a kabob stick.

The tinsel was about 6 inches long glued on both sides of the luff and 6 inches of tinsel glued to the leech. I got to see air moving from the luff to about twice the foot out.

Some interesting observations.
1. On average, as air flows around the jib it leaves the jib at pretty much the direction as it is trimmed, for a long distance out. If the jib is trimmed to 45 degrees it leaves 45 degrees, if it is trimmed in 80 degrees it leaves at 80 degrees. This lookes like a true deflection/redirection.

2. Upwind. I started out with the boom on centerline. It was sort of stalled. Lee telltale looked great with the boom to lee a little. This is boat specific, but a start position. I centered the boom again and accepted poor telltales.
The jib is slowly trimmed in. As it is pulled in the trailing airflow comes with it. At some point the airflow trailing the jib is directed to the lee draft of the main. The main lee telltales pick right up. This must be the "slot". There is no veturi or anything like that. Trimming the jib simply redirects more moving air over the lee main(lift surface). With more trimming the jib redirects the airflow right into the leading edge of main. The telltales and main flop. This is the backwind. Over trimming the jib has the same effect as decreasing the angle of attack on the main.

3. On a broad reach. The main sail splits the wind up in a stall. Much like a bird coming in for a landing. There is a cool effect where the air flow does a 80 ish degree turn between the mast and the jib. Its really noticable mid jib. the air then deflects out past the jib as if on a beam reach/close reaching, at whatever the jib is trimmed at, boosting the main lee telltales some. Main luff windward telltales are sucked up around the mast to lee.

Take-a-ways (from a noob point-of-view). Assuption is flowing telltales equal best sail performance.
The headsail is magical. The jib affects the main. The best trim is when the airflow from the headsail is directed to the deepest camber of main. When the jib is trimmed right the main can be trimmed to a lower angle of attack. Adjust main to take advantage of this.

A well trimmed and cut jib increases pointing AND a poorly trimmed/cut jib devastates upwind pointing.

Jib helps main even downwind. It redurects main turbulence to back over main lift surface.

The well trimmed/cut headsail isnt just extra sail, its a mainsail force multiplier.
That's very cool!
 
Oct 19, 2017
7,733
O'Day 19 Littleton, NH
It is apparent and consistent with theory that the headsail trimmed correctly to the main will improve flow over the leeward surface of the main and improve lift. My question is, where are the forces directed on the main? The models clearly show a strong forward driving force from the headsail but, I see more heeling force than driving force from the main. Is there a significant advantage to having the second sail other than to balance the helm? Is this a more efficient setup than something like a delta rig where the overall design balances around just a larger staysail?
Are Marconi rigs more efficient than staysail rigs or are we just interested in the most efficient way to set the sails for a Marconi rigged boat?
- Will (Dragonfly)
 

Joe

.
Jun 1, 2004
7,999
Catalina 27 Mission Bay, San Diego
It is apparent and consistent with theory that the headsail trimmed correctly to the main will improve flow over the leeward surface of the main and improve lift. My question is, where are the forces directed on the main? The models clearly show a strong forward driving force from the headsail but, I see more heeling force than driving force from the main. Is there a significant advantage to having the second sail other than to balance the helm? Is this a more efficient setup than something like a delta rig where the overall design balances around just a larger staysail?
Are Marconi rigs more efficient than staysail rigs or are we just interested in the most efficient way to set the sails for a Marconi rigged boat?
- Will (Dragonfly)
I suggest you get a copy of the new revised "The Art and Science of Sails: Revised Edition" by Tom Whidden and Michael Levitt.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Are Marconi rigs more efficient than staysail rigs or are we just interested in the most efficient way to set the sails for a Marconi rigged boat?
- Will (Dragonfly)
For upwind performance, a Marconi sloop is MUCH more efficient than a staysail rig.
 
Apr 16, 2017
841
Federation NCC-1701 Riverside
@BobbyFunn I would love to see the video on your test but don't see a link?
I am adding some industrial techno pop to the audio and am waiting for the licensing. :laugh:

I hear ya. The videos are about a minute each and are over 100mb. I need to figure a way to post them while keeping my secret identity.

Screen shots of tinsel telltales in a 15 knot breeze dont look great. Chaos is measured in averages so you need to see everything.
 
  • Like
Likes: Will Gilmore

DaveJ

.
Apr 2, 2013
449
Catalina 310 Niagara-on-the-Lake
I'm not seeing the video either. :(
Very well described, but a video is worth.... a lot of words....
 
  • Like
Likes: Will Gilmore
Apr 16, 2017
841
Federation NCC-1701 Riverside
Is there a significant advantage to having the second sail other than to balance the helm? Is this a more efficient setup than something like a delta rig where the overall design balances around just a larger staysail?
Looks like based on my research that most lift is acting on first quarter of lifting surface. The rest is drag. Long chords are not as good as short chords. Its better to have a very long wing with a short chord than it is to have a very short wing with a long chord. Think sailplane and u2 spyplanes versus vintage hanggliders. Problem on sailboats is the longer higher up the sail goes the more rotational force (rounding up & heeling) there is so the advantage is wasted on submarining the bow.

For sails its better to break ip the long sail into slots so that there is the headsail quarter lift and then a second mainsail quarter lift. Both sails are deflecting wind.
 
  • Like
Likes: Will Gilmore
Apr 16, 2017
841
Federation NCC-1701 Riverside
Looks like based on my research that most lift is acting on first quarter of lifting surface. The rest is drag. Long chords are not as good as short chords. Its better to have a very long wing with a short chord than it is to have a very short wing with a long chord. Think sailplane and u2 spyplanes versus vintage hanggliders. Problem on sailboats is the longer higher up the sail goes the more rotational force (rounding up & heeling) there is so the advantage is wasted on submarining the bow.

For sails its better to break ip the long sail into slots so that there is the headsail quarter lift and then a second mainsail quarter lift. Both sails are deflecting wind.
 

Attachments