Using roller sail to make modern Square Rigged sailing ship?

Same general idea as crappy throw-away roll-up shade in pic, but hopefully much more reliable and without the problematic "yank down to roll-up".

Dyna-rig is nice but seems like it relies on high standard of specialized engineering and fabrication for any application. True old style square rig requires LOTS of brave crew going aloft constantly to fiddle with the sails, so pretty much a non-starter.

Using a roller-rig would require either:
a)stiff and strong roller suspended by cross-beam on either end similar to pic to carry the weight/windforce but not the tension

b)strong yards with curved yardarms to keep line taut similar to roller jib

Would either a) or b) system be cheap, simple and reliable? Estimates of weight VS similar sized Dyna-rig?

 

Look at in mast furling systems. You could make a furling yard that way with off the shelf components. Just needs a mandrel shaped for the specific sail shape. Furling can be electric or you need the furling line routed along the yard and down the mast.

Total weight is not the whole picture, weight distribution is. A Dynarig has its furler in the mast and the mast is unstayed so the weight may be greater but more central.

 

???
I was thinking about plain rectangle sails. This would be for cheesy replica of old sailing galley or man-o-war (with gun-decks used as window-offices or apartments, but still able to sail and look like a real square rigger.

 

You did not say anything about "cheesy replica" in your initial post. But even so, if you want the boat to go under sail anywhere except dead downwind the sails will have to have some shape, and the furling mandrel needs to accommodate that, otherwise you can not roll up the belly of the sail. On shapely genoas this profile is made from foam and sewn in, since you can not shape wire.
If looks is all you desire, make the sails flat and out of spinnaker nylon, the engine will provide actual motive power but the sails will look good enough to the tourists. No need to shape anything.

 

So the furling mandrel in this case would be fatter in the middle and tapered at the ends to roll up a curved rectangle sail?
Are traditional real Square-Rigger sails curved by design or did they just get stretched?, because they always look pretty bowl shaped.

 

No need for a shaped mandrel.
Each sail is either fully furled or fully deployed.
Square riggers have enough individual sails to not have to have any partially deployed.

The old timers definitely had belly sewn into the sails.

 

A yarded topsail once called the poor mans spinnaker, was an inverted triangle. point down.
Yard at top. Not having the thick edge seams of the sail roll UP on top each other, but instead spiral in toward the center, might solve, save you some problems.

 

You are about 150 years behind sailing ship technology. Roller furling in square riggers was already a well developed technology in the late 1800's.

 

... And was originally developed/discovered by the Royal Society after Henry VIII tasked them to build a better post mill. There were mills with roller reefing sails that reefed via a crank run though the main shaft and could be adjusted while the mill was running.


"Cunningham became famous for the invention of the self-reefing topsail, which he manufactured in the Gosport Foundry at The Green. The agent for this invention was William Henry Lapthorn, sail maker, ship chandler, of 29 Broad Street Portsmouth. The self reefing topsail was exhibited in a model of a fully-rigged ship at the Great Exhibition in 1862, amongst the section on Naval architecture and Admiralty models. “They roll up like common blinds, and almost entirely obviate the necessity of sending men aloft.” In the 1862 International Exhibition Cunningham was both a medallist and juror."

Clipper Rigs https://doriccolumns.wordpress.com/industry/shipbuilding/clipper-ships/clipper-plans/clipper-rigs/

 

Royal Clipper uses Furling Squaresails

 

I liked your posting, and put a reference to it over here,
DynaRig MotorSailer, ala Maltese Falcon https://www.boatdesign.net/threads/dynarig-motorsailer-ala-maltese-falcon.16276/page-6#post-952872