Fastest Mainsails for Overlapping Headsail Driven / High Aspect Main Boats - speed bubble?

Lost in Translation

Super Anarchist
1,243
59
Atlanta, GA
Pics preferred but not required.  What have people found is best for boats that regularly sail with overlapping headsails?  

Rounded main with lots of shape for other points of sail - live with the bubble upwind - or flat main that minimizes backwinding upwind and relies on the kite or jib to power the boat up enough downwind / reaching?

Think 70s / 80s keelboats.  Boats like this have stiff masts that are not very tunable to adjust main draft.

 

Parma

Super Anarchist
2,905
367
here
Pics preferred but not required.  What have people found is best for boats that regularly sail with overlapping headsails?  

Rounded main with lots of shape for other points of sail - live with the bubble upwind - or flat main that minimizes backwinding upwind and relies on the kite or jib to power the boat up enough downwind / reaching?

Think 70s / 80s keelboats.  Boats like this have stiff masts that are not very tunable to adjust main draft.
A powerful, easy (hah!) to adjust outhaul & cunningham.

I'd go with a very flat mainsail and opt to let the outhaul go off the wind to get the draft you seek. A baggy main upwind = less point and getting pitched over on your ear in gusts.

We used to run a 140 which caused a speed bubble due to backwinding, but a tapered mast & flat main allowed us to keep the boom pretty high towards centerline & avoid too much backwind w/o adding to the heeling moment too much.

 

JPD

Anarchist
509
22
LIS
Pics preferred but not required.  What have people found is best for boats that regularly sail with overlapping headsails?  

Rounded main with lots of shape for other points of sail - live with the bubble upwind - or flat main that minimizes backwinding upwind and relies on the kite or jib to power the boat up enough downwind / reaching?

Think 70s / 80s keelboats.  Boats like this have stiff masts that are not very tunable to adjust main draft.
I have a 73 Ranger with overlapping sails. A moderately deep main works best on our boat. A flat main really hurts in anything under about 12 true.

0.jpeg

 

Lost in Translation

Super Anarchist
1,243
59
Atlanta, GA
@JPD Your Ranger looks great and well trimmed.  Thank you for the post.  I sail in light air and flat water often as well.  How do you avoid substantial backwinding in a main with depth like that?

 

JPD

Anarchist
509
22
LIS
Thanks for that. She's been pretty much restored from the keel up in the 34 years since I bought her.

 I keep the traveler up and that keeps the front of the main out of the way.  The mast  on these boats is not exactly bendy. I flatten the main with the usual controls.....halyard, outhaul and cunningham. 

I would absolutely not go with a flat main in the conditions you describe. 

 

Parma

Super Anarchist
2,905
367
here
I have a 73 Ranger with overlapping sails. A moderately deep main works best on our boat. A flat main really hurts in anything under about 12 true.
I'm curious as to why that works for your boat. Could you explain (readers digest version) what you think is going on with the sails, rig, sheeting angles, point & overall VMG to make that setup work for you? 

 
Last edited by a moderator:

climenuts

Anarchist
662
251
PNW
Not too sure where my main ranks in terms of full vs. flat but here's full & flat photos taken ~30 minutes apart. Outhaul, Cunningham, Babystay, and Backstay cranked to flatten but the two top battens weren't adjusted.

6daJIdYIFW_FA_hhUvrG-V-19f7YY6fAbwf9bXfpnXX2TJFvhx95YZsHq02aTrEKFy8YqmtR-luxjhHoEXNuWpBqfymrov1_8QnBmfFnboFY2H40V4hnMv2DO-PCzGgka063odrb-ssNyrPVCNrW0oJW4UrOgwiD61DqGMh0FouLEla97YI1JWdzTtPLf9l0LFF9YFLq1k3fYsAPaZYBCEefQmM78B0rv8iDbRQHc9iuZeS4BkfvArHtRw_zxfccA2bNtx00F7DQLihRtHgrniuhR4Rf6nCfrX8yV2-F4zmASgYtuAIO9GAoizUWbRzUldhHjI36BKbzeEpxX_9Pd4Ul6p8-1Iv5i8D9p9H8yOs2-ODnAIVFCjNzBlAO7IYcs-PUiBQ7wRZz0joPCnSwkMGhiuT7lWeknQDmN_HpSHPj3hCb35CCXxFYH2R9RReFbI7xT_S7tpXGOsje3znsMLqNTVAJ4YfJ05x73DE7TJZB49wwxO5Ktqq0dO0l-9qr4iH5zIR3Lsej3zZJAPX6LCuqDOMeFdK6gojIIcFz14xLBZkfyOai6RJdVVwigUauCULiC3srt0mIQmaR0uWWBuJ8c0JUCxFAh-qEKBebxodeyA0TFD7fGqIv_50dIBY0mB0Wc2LJpLuza8gkp1YtfeL0ip4hZFSio0RyPx3rLFvEDkovBtCGNxFnaH7Qtt4xdSDCFhPN5JeoqsvrPUBok3sQ=w1345-h1009-no


pFvwDOZnRmPEb-pa7czE2KkaT_hF1vl3YatyAbyUCe4q8pp-Lu9tncWhsRB0VBr8OZhj4XIEutzL9vFOus72_p-pZOzaAQyWPEeJlhXg-kM6qyd1JNhHSt0qBpiNYH_mQtdWJ9hk7ny4ao9-_3yIkFv4Twv-EwhGlthTO6J05Vg22cRwEV7ac10os9CbgACmJF_Zjtp8dHD6P1eo72HGA5e_VyZFGHCz_PmZcPlPeW4lT2PwCJdq50fIUSrj7PFiv-6FcO4MmQT6kZMErfrU-WpP437CCv37L1Xr0bYxnZtfr_KqSRF88msn1RqT5MqBWy4wMLK_u9FyWFZvW-PuoBSlsvoFY2PqEdUOgRIY7IpK5FTm_tUFpDURls0-jb0yky7DIbUXFGfcDNdzuSSkBOSMvsnQVz2aR8NSQw7Gr8cYOgFQT6E4g2R-itA2Kn7tpL2U6YaGOsg0RXrMa89X2_JiRWcHAJKSkVX8-4MujvsNF8nAtk4vWJiifzmatgyFuGeiBdm1lIBy_j3s-QDhup4hVdfANY_Y28nw3uBFtUkU63r_hQ0jXCTu9ReuPgNStKAT1Zxuvk0xDYAu9nHPR0Z7aeQ_t1c3Y-Q8jvlqofrunpJ4KV0lGdO_3BPZ84qISDzfnuMH_y-VSqINdzYB_A3NBqUbHQ3mdSpDSVoan6PLuwsCMaZJS7ebFjwFaWmmX6UqdPYkZRTlEnkUXKtS5apT=w1345-h1009-no


 

blunted

Super Anarchist
1,500
326
Toronto
Some people may go insane over what I have to offer here.

Backwinding isn't always a bad thing.

It's ugly and has a bit of drag but its not the part of the sail plan doing anything very useful.

The luff of the jib is doing the most work in the whole sail plan and everything after that is just trying to hang onto flow. If you have a big overlap you just have an oversized slot which is there to accelerate flow on the lee of the main behind the end of the slot and help keep flow stuck to that part of the total sail plan. The bubble in the main is just the sail trying to get out of it's own way in the slot.

Downwind, is your main doing anything useful? Does it actually have flow over it or are you doing W/L courses sailing deep and relying on your pretty sail up front with the main there as a billboard? If so, I'd just go with a flatter main. If you are doing a bunch of reaching or VMG sailing and your main actually has flow downhill, I'd be inclined to get something with some more depth and then use the tools you do have to flatten it out going upwind.

Note, I grew up racing 8 Meters with massively overlapping headsails and constantly backwinded mains with fairly narrow sheeting angles. I moved on to sailing boats with wings where we control the slot to the millimeter. What did I learn? SLOT IS EVERYTHING and the individual sails don't matter, only how the sail plan works as a whole matters, just consider it as one aerofoil with a slot in it like a big plane with flaps down at takeoff. Goal is to bend air as much as you need or dare matched to heeling moment for the lowest drag you can get. To bend air a long way you need it stuck to the lee side of the foil (Main and Jib) from front to back without it detaching. The slot injects additional energy into the boundary layer which keeps the flow stuck to the main to the end of the leech without stagnation. That's the goal.

 

Lost in Translation

Super Anarchist
1,243
59
Atlanta, GA
Responses from excellent folks so far, thanks. @climenuts, I can't see the pics you have attached.  Just large white space with a question mark.  Would very much like to check out.

@blunted I've been thinking slot is everything too and that kind of thinking is what is pushing me to go very flat on the next main even for the light air lake I sail on but I know got a ribbon main on this boat with main sail foot under 12 feet and jib often with a foot of 24 feet on a J dimension of 15 feet.  My other boat is an A-Class catamaran and adjusting the mast rotation and other controls to keep flow on the leeward side of the main is the most important aspect of the sail performance.  I've gotten comfortable thinking of the jib and main working together on the big boat and understand there can be circulation between the two as well.  

I never see people really worrying about backwinded mains which seems counterintuitive but maybe this is because it only really happens when the boat is getting overpowered?

 

Raz'r

Super Anarchist
59,426
4,438
De Nile
Responses from excellent folks so far, thanks. @climenuts, I can't see the pics you have attached.  Just large white space with a question mark.  Would very much like to check out.

@blunted I've been thinking slot is everything too and that kind of thinking is what is pushing me to go very flat on the next main even for the light air lake I sail on but I know got a ribbon main on this boat with main sail foot under 12 feet and jib often with a foot of 24 feet on a J dimension of 15 feet.  My other boat is an A-Class catamaran and adjusting the mast rotation and other controls to keep flow on the leeward side of the main is the most important aspect of the sail performance.  I've gotten comfortable thinking of the jib and main working together on the big boat and understand there can be circulation between the two as well.  

I never see people really worrying about backwinded mains which seems counterintuitive but maybe this is because it only really happens when the boat is getting overpowered?
We get the speed bubble with either of our big headsails, and I pretty much ignore it and focus on making sure the jib leech is breaking even, and match my main leech to that. The main leech is a little flatter of course as I've got more mechanical advantage there but I don't mind a little twist if needed, which means boom might even be a tad above centerline. If I've got too much twist, the bubble shows up, but then i know I have too much twist.

 

Jeff K

Member
On the last IOR that we raced (won KWRW 03) with it, a Farr Dickerson 37. We used an outboard track and a flat main. Set the backstay to the average wind speed, then dump traveler and then the mainsheet. Pretty easy upwind really, it liked the slot.

 

RATM

Anarchist
852
45
.....SLOT IS EVERYTHING and the individual sails don't matter, only how the sail plan works as a whole matters.......
This is so, so true even on those new-fangled boats with 100% jibs. On a J/105, you want your jib leach tell-tales always streaming so that you can deliver more wind to your main.

Look at those F-1 cars with those 5 bladed front foils. If the rules required them to keep the same surface area but make them solid, you would get 1/10 the aggregate downforce .

 
Last edited by a moderator:

JPD

Anarchist
509
22
LIS
I'm curious as to why that works for your boat. Could you explain (readers digest version) what you think is going on with the sails, rig, sheeting angles, point & overall VMG to make that setup work for you? 
The rig is pretty inflexible so thats a starting point . I'm  left trimming sails to make a difference and the boat seems especially sensitive to main trim. I prefer to sail with a smaller jib with less overlap...say about 140 lp, and a moderately deep main. This seems to be a good compromise on our boat. I would much rather work on flattening out vs. not being able to power up no matter what because the sail is flat. Years ago I had that type of main which was fine  above a certain tws  but the  boat just won't have the same drive in light air. VMG aside, I know the flatter sail kills us under 8 - 10 true.

On the other hand, if I raced in a venue with 15+ all day I would probably want a sail with less depth. 

 

r.finn

Super Anarchist
1,957
502
Whatever keeps your helm balanced. Depower as much as possible until the main is providing nothing, then do a sail change.  There is a point that you're just dragging it through the air, which is slow. I often see people trimming their mainsails to look pretty, like in the sail trim books, at the expense of too much heel and helm.  As a rule of thumb, that's also very slow.  Don't over think it, just pay attention to your helm and respond accordingly.

 
Top