Aftmast rigs???

I'd do a bit more research on those squaretop mains. I've run across a lot of questionable posting on the true advantages of them, even aerodynamically. They do seem to be the latest 'fade'.

 

Good point.

I guess I could try to incorporated a 'squaretop mizzen', but then it would not roller furl,....and it just doesn't make sense.

The squaretop mainsails are trying to get better production out of that upper tip of their triangular shape that falls behind a relatively big mast leading edge, and working in a free stream.

I would hope the upper triangular tips of my two headsails would be more productive sail area as a result of the mast at their trailing edges. And the tip on my mizzen sail might be more productive as a result of having a 'wire' leading edge.

 

Err, No.

Its mostly about pressure distribution and induced drag, and partly about twist control and mast bend/depowering characteristics, especially in the smaller classes.

 

You'd be surprised. Next time you think you're on a dead run, flick the sail across and see if you're just as happy on the other gybe. If you're not you're probably not on a dead run. An absolute dead run is a very slow point of sailing on almost everything, and most sailors naturally sail a few degrees off without realising it. And yes, I'd even expect that with the classic twin headsail cruising setup.

Even in the big heavy Americas Cup 12 metres they didn't sail dead downwind, as can be appreciated if you read a description of the famous last run of the 83 Cup. The difference with the very high performance boats is only in degree: that they go so fast that the apparent wind is forward of the beam, so when they get below the magic angle the apparent wind bleeds off and they really slow down. With slower boats the effect is much more subtle, and so is the angle required.

 

"I'd do a bit more research on those squaretop mains."

Research such as actually buying one, fitting it to my boat and being very happy with it?

In the pic below the wind is about 7k (direct downwind to our destination) we are doing about 7-8K. Apparent wind is a beam reach by sailing higher than downwind, but still very deep to maintain speed and use all the available sail area. This only works when your boat is reasonably quick. So the main still does not hit the shrouds in this situation even when the destination is direct downwind. The sail area up high helps here in the light wind.

 

SquareTop Mains

Please note that i did say "better production" which would include such things as reducing the induced drag, etc.

I don't have time to go back thru the subject of squaretop mains at the moment, but I think you might find some interesting negatives if you did a thorough search. Here is just one discussion on this forum,...there are many more mentions
http://www.boatdesign.net/forums/sailboats/squaretop-mains-46803.html

 

Racing downwind

Let me clarify my experiences here. I've raced hi-perf 'beach catamarans' (Prindle & NACRA), and had experiences with Formula 40 cats in the early days in France. In a number of these instances I have learned directly from Tornado Silver Medalist and sailmaker Randy Smyth about competitive racing.

Even with these hi-perf cats if is often more productive to sail dead down wind to the mark in two conditions,....very light winds and very heavy winds. Yes, it can seem painstaking slow, but most often you arrive first at that downwind mark while the other guy is sailing off at tangents.

Now remember also that here I am talking of sailing to a mark dead downwind, which on a race course should be set dead downwind.

Per cruising boats (particularly cruising catamarans), they are very often underpowered sail wise, and overloaded weight wise to really be able to really bring their apparent wind forward enough to take advantage of tacking downwind.

 

You are lucky you boat can do that.
My Salina 48 in full livaboard trim would need at least 12kn to be able to take advantage of that sail trim.
Any AWA over 125 would result in the Genoa blanketed and loosing drive.
Eeven with the boom locked in position by the preventer, any beam sea would cause the main to flog wildly from side to side, do that for a few hours and the though of damage creeps in and down she comes. Enduring that for day upon days in the trades is frustrating to say the least.
Add to that the complication associated with the hoisting and lowering of a square top, it makes me wander if it is a wise solution for a "cruiser".

On the other hand, many times I set the Parasailor and never looked at the trim for days. Similarly with twin head sails.

Different story tacking upwind, but I detest that.....

 

Downwind Sailing & Rigs for Cruising Cats

On this subject of downwind sailing for CRUISING cats, there is an interesting subject thread over here by some vessel owners:
http://www.cruisersforum.com/forums/f48/what-downwind-sail-for-a-cruising-cat-158251.html

 

Great threads. After reading them ages ago it made sense to fit a square top main. The info in them made it seem favorable to me. IMO you would have to have a bad preconceived idea about squaretops to begin with to read those threads and come to the conclusion they don't have many performance benefits. It would require a heavy dose of cherrypicking to ignore it all and stick to the few negative points, most of which did not even apply in my case. The most obvious benefit being the performance increase with limited mast size, which is exactly what aft mast rigs have, and is exactly what a person with an existing mast has when all they require is a new main and not a whole new rig. The extra drive up high may not be the best for tender boats with low RM, but we are talking about cruising cats here.

Seems the cons just dont apply to cruising cats when it comes to performance. As for ease of use and cost? Well I can tell you from direct experience...

Spiv

Raising and lowering a squaretop main: Its easier to lower and store than a usual main. You just pull a string and the headboard disconnects. Then the most bulky part of the sail falls back into the bag and the top of the bag is about one foot lower making it easier to reach the zip.

Raising, well you pull that same string to pull the spring loaded pin down and lock the headboard in after the main is raised about 4 feet. So the effort you won when packing the sail up is made back up here. Over all the effort is the same. But the device to do this costs $300, the sail it self costs only slightly more because its bigger. Not much when you just spent $18,000 on sails.

The rig I was describing for my "one day" boat has the mast fairly well back and is a masthead rig with large headsails. The squaretop main is simply not used at all in situations where blanketing/shroud contact might occur on passages. The headsail/s will be much bigger so it wont do much for speed. If you can bring the apparent forward in the lighter stuff, well the benefit of the main is still there downwind. The boat I am talking about is very light and has much less space than a charter cat.

 

I know Dennis, I had that system for 3.5y, trying to hook the headboard of my 18m tall sail on my own was always a big effort, to the point that at times I just could not be bothered raising it.
Then, I installed a system with spectra line that made it all automatic, no more connecting and disconnecting the headboard manually, drop the sail in 2 seconds, raise it perhaps 1 min. See pic.

My next boat will not have a main with battens on a track, but on a furler.
Love furlers, see my twin downwind sailing pic. and love the Parasailor.
Most purist will be horrified, but I am not a purist, I am a cruiser... Arrrr

 

Looks awesome Spiv. When you mean a furling main I assume boom furling so you can still have battens and roach? I am also a cruiser, but I am one who will trade some space and load for performance and windward ability. For me sailing has to be fun, and IMO fast is fun and motoring is not. My favorite part of cruising is the actual sailing.

The difference with mine is that the headboard is positively captive via a pin, which makes it a little more tricky. The part is a prototype and has a few issues but I will be getting the updates.

I like the pic with the screecher is it? and the jib wing on wing. No main needed. The dream boat I am talking about with a more aft mast and smaller main would have a large masthead genoa with a real furler (as big as my screecher), and a staysail on a furler for heavier winds. With both of these out and no main down wind it will move with ease. But as I say a lighter boat should be sailing at least on an apparent beam reach down wind, so the main will still be usefull most of the time. When its strong, well you just don't need the main downwind and the deeper angles will suit the headsails. But you do then have an efficient high aspect, high area squaretop main for windward work in stronger wind when sailing upwind with the staysail.

 

Prout Style Rig

Sounds to me like both of you gentleman would prefer a more aft placed mast with a smaller mainsail and bigger headsails,.....shades of the old Prout rig concept.
Elsewhere in this subject thread I have mentioned this Prout subject as well.

 

Kind of Brian, but it would look more like this (but smaller).



Than this.



The idea is just to reduce the size of the main (to make it easier to raise etc) and increase the size of headails to reduce the time you even need to use the main for single handed sailing. The larger headsail could be a high tech dacron and the inner would be laminate as only the smaller one would be expected to be sheeted hard in strong wind.

I'm talking a main and head sail of similar size rather than the main being about 40/50% larger.

 

I agree that its not a performance idea, but a cruising one. That, done well could well be faster for cruising reasons. The main reason being that cruisers often sail under headsails only because they could not be bothered raising their large mainsails. They might not raise them because they are single handing and have a large boat, or they are only sailing a shorter distance where its just not worth the time and effort to raise the main.

The "moot point" about not needing the main anyway when cruising is not moot at all. Passage speed is important. When the main is smaller and the headsails are larger, you will be going faster under headsails alone. BUT, the important part is the mainsail (I am saying still use a decent size and high performance main) is that bit smaller so is easier to raise anyway. So for cruising reasons I think it could be faster, even if for racing reasons its not.

I'm just using my own boat as an example, 70m2 main. 40m2 genoa. And a 70m2 screecher which is a fragile setup on a 2.5m pole and endless line furler (pic in this thread). Its not to be left up in strong winds (even furled) and certainly not for use single handed. Setting up is a PITA with the pole etc, and you would want a decent helmsman to get it down if the **** hit the fan rather than an auto pilot.

The main is a PITA to raise and pack up alone. I think the boat would still have very good performance with say a 55m2 high aspect square top main (same height as now), and 35m2 heavy jib for windward work. I think this setup would be as fast or faster to windward than what I have now once the wind got to the point where I would have to reef my current setup (which happens fairly quickly) thanks to the higher aspect ratio. Sure in lighter winds, it will have less power.

However, I now also have room for a larger headsail (say 70m2) on a real furler (single handed safe) so the power will be the same or even greater than before, but with this up it might not point quite as high (not as good for racing). Downwind, speed will be comparable, as sail area will be similar (the cutter rig means I can use both headsails), but it will be much faster with headsails only as the headsail area will be much larger.

So its not fastest for racing, but for cruising its probably faster unless you cruise your boat like a race boat.

I would just like to add, I am usually the one flying thier mainsail when everyone else is just using thier jibs (when I'm not alone anyway). Seems a normal affair in Moreton bay for the weekend cruisers to not even bother with unpacking their mainsail bag, even in light winds. For them, the main is a waste.