a ultimate MotorSailer idea, Dynarig motorsailer

Dear HTMO9,……..my curve ball pitch


That is a REALLY BIG MAINSAIL. I have trouble imaging handling such a big sail, particularly short handed,...raising it, reefing it, storing it away, etc, etc


It was for these reasons that I sought out an attempt to eliminate the tradition mainsail, and develop my aft-mast or mast-aft rig, which I eventually termed a ‘single-masted ketch’. A look thru this brief page of my old website is still very applicable,.. https://www.runningtideyachts.com/sail/


For years I tried promoting this idea, and found many supporting documents and test touting its significant aerodynamic qualities. BUT I had one major item of resistance, the significant backstay loading. And I had suggested a faulty backstay item that I thought would solve the problem, but it turned out to be an error on my part. I believe I have now corrected that problem with a slight redesign which I will talk about later.


There are thousands of attempts to explain the aerodynamic interactions of headsails with the mainsail. The fellow who really got it correct is Arvel Gentry. His many papers can be found here in a PDF form,… https://arvelgentry.jimdofree.com/articles/

He also explains the correct interaction between multiple headsails. I followed his knowledge, particularly with respect to dumping velocities of overlapping headsails.


An interesting wind tunnel test,...




http://www.cruisersforum.com/forums/...ml#post1903468
Wind tunnel and CFD investigation of unconventional aftmast rigs

.....CONCLUSIONS
In the present paper an unconventional rig has been investigated in comparison with a standard sloop rig by means of wind tunnel tests. The traditional sloop yacht rig used as a reference is a Comet 51’a Vallicelli Yacht Design & Co 51 feet IMS cruiser-racer. Several unconventional configurations have been tested, all characterised by an “A” shaped stern mast without mainsail in single-jib and double-jib configurations. Aerodynamic data available from experiments have been used to perform some performance prediction at full scale by means of a VPP code.

Both experimental tests and VPP calculation show that the double jib
configuration with overlap gives the best performance and also the same configuration without overlap gives better results in comparison with the standard sloop solution.

Numerical investigation have been carried out using RANS simulation in order to better understand the aerodynamic differences resulting from the experimental tests. Simulation results put in evidence a slat effect in the overlapping jibs configuration leading to more attached flow on the aft jib allowing for an higher pressure drop on the sailplan.







Here are several other postings I made to justify this rig. I think you will find them interesting,..


https://www.boatdesign.net/threads/aftmast-rigs.623/page-80#post-953010


https://www.boatdesign.net/threads/aftmast-rigs.623/page-80#post-953011

Backstaying your new rig?

How do you intend to add backstays to this rig of your new design?,...to counter that BIG genoa and avoid that BIG main? …..like Hemisphere ??


Hemisphere is rigged like many other cruising cats with shrouds acting doubly as partial backstays, AND the sheeted-in-tight mainsail acting as a backstay. That’s a BIG main to keep sheeted in so tightly to try and keep a reasonably tight forestay in a good breeze, …..another item I was not so fond of on short-handed cruising cats.


I once posted,...
No wonder we see so much headstay sag. No wonder these boats can not carry a nice masthead genoa. Added to this equation, the shrouds are attached at a ‘shallow angle’ (half that of the forestay), so their aft-pulling capability is limited by both this shallow angle and the 3 point (tri-angled) configuration. Then at their point of attachment to hull sides (skins) there is likely no firm bulkhead backing, just skin. The shell of the hull is being asked to absorb the load, which it does in a ‘forgiving manner’ resulting in more forestay sag. It’s no wonder these vessels can’t carry a decent size headsail.


So now back to my aft-mast concept. I am now suggesting the mast be canted forward by only 5-6 degrees rather than the original 10 degrees. It could even be stood up straight, but that begins to interfere with my beloved self-tacking inner staysail, and even spreader interference with upper portions of the genoa.


I took that aft-jumper strut off the rig, and attached the mizzen sail to the mast itself. This attachment might be in a slot form, or maybe could be made a roller furling mizzen (remember I had been shooting for all 3 sails to be roller furling !). At any rate this style mizzen attachment defuses those folks that complained about the drag of the previous bare mast. I’ve retained the wishbone boom and loose -footed aspect of the mizzen,..better sail shape, lighter in weight, and easier on bashed heads?



THE BACKSTAYS
I’ve long been a fan of sailing any multihull boat right up to windward with the best monohulls. I use to get particular joy out of overtaking many of them to windward. Our little Firefly trimaran would surprise many a monohuller.


Generally we quested for good headstay tension and good headsail shape. I think I have provided some proof of value of the twin headsail rig, and now we need good headstay tensions,..and that means good backstay tensions.


My rig makes use of 4 backstays,...to divide up the loads in the stays themselves, and to divide up the loads to their attachment points on the hull. These 4 backstays might better be described as 2 continuous line stays,...they run from their attachments on the hull up thru a turning device on or near the mast, then back down to the hull on the opposite side,..a continuous line. The ‘turning devices’ might be some sort of stand-alone sheeve or a sheeve attached to mast. One primary point is that both legs of the backstay are in near equal load even while the masthead might be leaning to one side or the other. One set runs to the masthead to counter the genoa loads, while the other runs to the inner forestay point to counter the staysail loads.


The beam of the boat might be a little extra to allow for mizzen sail to set properly between these backstays,.. even on a reaching point of sail.


(pictures coming)

I'm going to use my old model of the boat to show the rigging, but please remember I have not modified this model of the boat to reflect the new cant of the mast to 5--6 degrees. It still has the old 10 degree cant.

I'm not sure what went wrong with my posting the images,...some were full size, others were NOT?

I was trying to show how with a little bit of extra beam on the boat,... those backstays could be attached inboard of where I have them, while still providing plenty of room for the mizzen sail to swing out even on a broad reach. It is also possible that the mizzen sail could be hosted higher.

The mizzen and the staysail can both be self-tacking, and both be made to roller furl. In fact all 3 sails can be roller furling, thus no hosting of BIG (and heavy sails).

This rig adapted to Kajan's vessel design could be made to look real acceptable.

I wrote this in jest back when I was 73,...I just turned 81, and not so sure I could do it now

You know I can still imagine sailing a big 65-foot catamaran with this rig right off the mooring, and back to the mooring, without the engine, by myself, with so little effort that I might take it out having only a few spare hours to kill or just a daysail.

And I would rig mine with tiller steering rather than a wheel and get a really good balanced helm. I wouldn’t have to uncover any sails, nor recover them when I returned to port. And I would be less concerned with reefing by myself if the wind were to really come up. If I were short-handed at sea, I would have many of the benefits of a ketch rig, without the necessity of slab reefing the main and mizzen sails of the traditional ketch rig.

That about sums it up. I would like a 65 foot cat that I could take sailing by myself, and that might even be easier than a beach cat. Try hoisting a full batten mainsail on a 65 footer by yourself, or even a 40 footer. Most folks over 50 will have second thoughts, or will just unfurl the jib and forget about hoisting the MAINsail.

I'm 73 now, and I could sail this 65 foot cat by myself with this aft mast rig. And with the balance and low power afforded by the smaller 'mainstaysail' I could sail this vessel right off the mooring or maybe right off a side-to-dock slip.


Here's a challenge (whoever)..... Le Mans start. I'll be out sailing before you get the covers off your mainsail, and when we return for the day, I'll be at the bar sipping on a Margarita watching you put away your vessel for the day.

HA,....Ha

Rather surprisingly I just recently happened to have received a private message from a gentleman asking about helping him understand a mast aft monohull he was (had) considered buying. He sent along 2 pictures (attached).

I vaguely recall hearing of this vessel a few years ago, but seeing that it appeared to be Finnish owned, I could never establish a conversation with the owners.

In looking at the design I would guess that they considered some of the results of that wind tunnel testing I mentioned above, (posting #22 above)

Nice looking rendition Kajan!

PS: It even looks fast, just sitting still