50’ Jib-Schooner Sail Plan, aero analysis

[beiland]

50’ Jib-Schooner Sail Plan, Aero Analysis
Dear forum members,
I’ve recently been sent a proposal for a jib-schooner sail plan for potential use on a new 50’ catamaran, …and asked to comment on its feasibility and attributes.

Along with this request there was included a CFD analysis that had been performed by Doyle Sailmakers. (attached)
jib schooner catamaran.jpg Views: 472 Size: 55.1 KB ID: 126814" style="margin: 2px" />
Sloop and Jib-Schooner.jpg Views: 1051 Size: 94.7 KB ID: 126815" style="margin: 2px" />

Not being that knowledgeable myself about these CFD techniques and interpretations, I thought I might post this info on these forums for some comments by those knowledgeable members of this forum.

[beiland]

...oops the CFD file is a bit larger than allowed so I guess you will have to visit this posting to see that test report by Doyle sailmakers.
sail aerodynamics - Page 57 - Boat Design Forums

[Steadman Uhlich]

Howdy!

I enjoy seeing your posts here on CF and on BoatDesign.net too.
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How does the sail area compare?

What is the expected cost comparison of the two rigs and all related rigging and sails?

[FSMike]

Looks like a variation on Chris White's MastFoil(tm) rig,minus the foils and plus a fisherman.
Lots more info about that on his website chriswhitedesigns.com.

[Seaslug Caravan]

WHY.

I take it you did a CFD analysis knowing full well that the down sides of headsails would not be taken into account.

IE as wind speed increases head stay sag increase and the sail gets fuller, which is exactly the opposite of what you want.

A mainsail can be easily engineered to automatically flatten through mast bend
as wind speed increases.

The ability to motor-sail with a fully battened main sheeted close is taken away by going the flogging headsail route.

The ability to present efficient reefed sail area via a slab reefed main instead of the aero dynamically inefficient roller furled headsail is also taken away.

Can't believe you are wasting everyones time. If this was an efficient way to present sail area then the racing fleets would be all over it.No need for a CFD. There is no conspiracy. Time to take the foil hat off.

[beiland]

Originally Posted by Steady Hand

How does the sail area compare?

The Doyle test reports 37% less sail area for the 2 jib configuration without the fisherman sail.

What is the expected cost comparison of the two rigs and all related rigging and sails?

I haven't seen nor contemplated this factor. I was just asked to comment on its sailing capabilities.

[beiland]

Originally Posted by FSMike

Looks like a variation on Chris White's MastFoil(tm) rig,minus the foils and plus a fisherman.
Lots more info about that on his website chriswhitedesigns.com.

Does has similarities, but I do not think that was the intention.
In the past that potential owner had a large wingmasted cat with a big mainsail. I think his advancing age is dictating a lower aspect rig without a big mainsail.

[beiland]

Originally Posted by Seaslug Caravan

WHY.

I take it you did a CFD analysis knowing full well that the down sides of headsails would not be taken into account.

If you bother to read my initial posting correctly you might discover that I did NOT commission that test, but rather another designer and the potential owner sought out that info. The owner sent it to me for my comments.

Can't believe you are wasting everyones time. If this was an efficient way to present sail area then the racing fleets would be all over it.No need for a CFD. There is no conspiracy. Time to take the foil hat off.

BTW did you even bother to read the Doyle test study that I am also questioning?? We might just learn something from such experimentation

[beiland]

I might add a couple of my initial impressions.

1) This jib-schooner’s rig with its two parallel ‘headsails’ is somewhat analogous to the two parallel headsails* of my aft-mast rig,…and/or the twin headsail rig of this CFD/Windtunnel study carried out in Italy. The Italian test rig with two overlapping headsails proved to be pretty productive upwind, even besting the standard sloop rig.
Wind tunnel and CFD investigation of unconventional aftmast rigs

Doyle’s test on this jib schooner rig is hinting at the same.

Originally Posted by Doyle report

Upwind at low AWA’s the schooner has a slightly lower drive coefficient, however by 40 degree AWA the schooner has the same drive coefficient and by 60 degrees a much better drive coefficient than the sloop

….and this is accomplished with 37% less sail area than the sloop utilized in the comparison study,…interesting

But I also noted that this comparison was made at 20 knots AWS. I’m pretty sure at much lower AWS this jib-schooner would NOT fair so well,…just not quite enough sail area for those lighter winds. This presents their need for that fisherman sail.

Originally Posted by Doyle report

The biggest difference in power between these two rigs will be seen upwind in light to moderate breeze at the AWA’s too low for the fisherman to work effectively.

2) Aero drag of 2 bare mast. I am particularly sensitive about this issue, seeing as to the number of persons who have questioned me about this issue with my single bare mast on the aftmast rig. This jib-schooner has TWO such bare masts in its ‘non-fisherman’ configuration. This would seem to product a lot of drag force, particularly in relation to its relatively small sail area of just two abbreviated jibs.

And I would ask the experts if this CFD analysis by Doyle properly accounted for this extra drag of the 2 bare masts.




* PS: Two parallel headstays on aft mast rig
Aftmast rigs???

[Steadman Uhlich]

Brian,

I recall seeing mono schooners with all sails on roller furling systems.

Given the original objective of this study (aging sailor wants easier to manage rig), I would think the tradeoffs would be balanced and "ease of use" would outweigh the possibly less efficient (not fully battened) sail plan etc.

I also recall seeing another cat that had two Lug or Junk Sail rig (one mast on each hull), but I wonder about two masts in centerline, as shown in this drawing.

How do you think a two mast (Junk Schooner) would compare to the shown (Marconi Schooner)? Any opinion? (I know that Junk rigged boats are favored by some for ease of use, ease of shortening sail, and effectiveness in trade wind reach sailing.)

[Snowpetrel]

Originally Posted by beiland

Does has similarities, but I do not think that was the intention.
In the past that potential owner had a large wingmasted cat with a big mainsail. I think his advancing age is dictating a lower aspect rig without a big mainsail.

I sailed on a big 64 foot staysail schooner across from Hobart to South America. The rig was a modern one with equal mast heights and a large main staysail.


Whist a more complex rig, with a conventional mainsail we occasionally sailed without the main, just the yankee, staysail and mainstaysail. This was a nice, fast easily handled combination with minimal chafe. I can't really comment on how she would compare to a sloop rigged version, though I think the sloop probably would be slightly faster overall, certainly the vessel was not powerful to windward, but the narrow beam and shallow draft probably had a lot to do with this.

A big factor on a rig like this is going to be the sheeting arangement for the headsails. Being able to ease them without them bagging up too much would be critical. Blizard had a boom on her mainstaysl that enabled it to be sheeted well out and kept flat. Maybe barbourhaulers or wide curved tracks would be needed?

The fisherman is going to be an awkward sail to use and sheet. A wishbone or batten might work to sheet it well, but it has big issues witb handling and safety. Sheeting it to the main masthead causes a poor shape. Saying that in light airs it steadys the roll and provides quite a bit of power on a reach.

One thing that I wonder about the report, I am assuming the coefficients are based on the area of the sails? So although the rig has a high coefficient in many wind angles it may still developed less power due to its smaller size?

Sent from my SM-G930F using Cruisers Sailing Forum mobile app

[beiland]

Originally Posted by Snowpetrel

I sailed on a big 64 foot staysail schooner across from Hobart to South America. The rig was a modern one with equal mast heights and a large main staysail.


Whist a more complex rig, with a conventional mainsail we occasionally sailed without the main, just the yankee, staysail and mainstaysail. This was a nice, fast easily handled combination with minimal chafe. I can't really comment on how she would compare to a sloop rigged version, though I think the sloop probably would be slightly faster overall, certainly the vessel was not powerful to windward, but the narrow beam and shallow draft probably had a lot to do with this.

Here is a posting I had made with a similar rig on a Tayana 55.
Aftmast rigs??? - Page 3 - Boat Design Forums



My subsequent question of you Snowpetrel is how did you arrive at the names for your sails, particularly the 'main staysail' as it is behind the second mast?? I termed it a mizzen sail?

[ZULU40]

seems somewhat similar to Carters 'Luna Rig'

CARTER 35 (LUNA RIG) sailboat specifications and details on sailboatdata.com

[Snowpetrel]

Originally Posted by beiland

Here is a posting I had made with a similar rig on a Tayana 55.
Aftmast rigs??? - Page 3 - Boat Design Forums
Attachment 126847
Attachment 126848

My subsequent question of you Snowpetrel is how did you arrive at the names for your sails, particularly the 'main staysail' as it is behind the second mast?? I termed it a mizzen sail?

Thats a very interesting boat, thanks for the pic's I am not sure I like the two furlers in the middle of the boat, too much windage, and I don't think a genoa would work well there, but who knows? Maybe it does help, and is worth the weight and windage penalty. The two furlers fwd work well. The big genoa does great duty as a light weather sail to windward and a great downwindsail. Interesting that both use booms. Thats the way Id go. Vanging the booms out is an issue. Ideally something like the hoyts boom would be good.

On the naming. Since both masts are the same height by common convention its a schooner. So the aft mast is the main mast. Hence the mainstaysail. The fwd one would be the forestaysail. But its really a bit arbitrary in these cases. You could call it a ketch if you wanted to, just make the foremast an inch taller...

[beiland]

Kind of interesting sidetrack,...this naming of sails.

I just googled 'staysail' and arrived at what I often thought was a basis for calling a sail a staysail.

Staysail

A stay is a piece of rope or wire that supports the mast forward, to prevent it from falling backwards. In the 16th century it was discovered that you could set a triangular sail on such a stay, and this turned out to be an important breakthrough in the development of sailing ships.
Soon every sailing ship carried staysails on every possible stay, and still today staysails are in use on every kind of sailing vessel, from small sloops to full-rigged ships. A staysail has three corners; the highest one is called the head, the lowest one is the tack, and the remaining one is the clew. The edge that is bent to the stay is called the luff, the bottom edge is called the foot, and the remaining edge is the leech.
The sail is set by hoisting it up along the stay by hauling the halyard that is fastened to the head. The sail is then trimmed for the current winds by adjusting the sheet that is attached to the clew.

So that's one reason I questioned the use of the term staysail for that schooner's aft mast mounted sail.

I also adopted the term 'mainstaysail' for that single middle forestay mounted sail I utilized to replace the conventional mainsail on my aftmast rig.
Sail Propulsion - Revisiting a Mast-Aft Sailing Rig

The inner main-staysail will replace the Bermudian mainsail and perform a similar function in a more efficient manner, as its leading edge is not fouled by a mast and its foot not misformed by a boom. The wind slot between the two headsails has been made larger than on a conventional cutter rig, which increases the effectiveness of the mainstaysail itself, and very importantly, the parallel nature of this slot produces a much more favorable interaction between these two sails than the ever-variable, triangular slot between the traditional main & jib. Equally important the draft pockets on these two headsails are both in harmony, lifting and driving ahead as opposed to the old Bermudian mainsail which drove downward on a reach.