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Old 16-06-2015, 12:21   #61
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Newer Rig dwg & Force review

That rig dwg I posted above has been modified to a newer version. In particular note that the forward jumper struts are now directly in line with the long aft facing one. This also changes the angles involved with those diamond wires on these struts, and those diamond wires wrap around the mast tube rather than individual terminations at each end.
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Here is a force review posting:
Aftmast rigs??? - Page 23 - Boat Design Forums
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Old 21-06-2015, 16:41   #62
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Re: Don't use the Main?

Quote:
Originally Posted by eyschulman View Post
If you want easy the gaff schooner rig using modern light materials would give a low center of gravity simple rigging and a fair spread of sail easy to raise and lower. With lazy jacks and jiffy reefing not to hard to manage. Since big cruising cats tend to sail off the wind a gaff schooner would be just fine and the sails would always come down fast and easy for quick change to motor mode or motor sailing with a reduced sail area jib and fore sail. To keep the weight down lots of carbon fiber in the rig.

Back in the day my Dad had a gaff rigged schooner and some of my best memories are on that boat.

If the truth be known the battened big square top on my Seawind comes down like a guillotine. Something I have heard from many other multihull guys with big square tops. But I do try and keep the cars and track well acquainted with Maclube.
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Old 21-06-2015, 17:15   #63
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Re: Don't use the Main?

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Originally Posted by RichandHelen View Post
The latest issue of "Sail" awards the Lagoon 39 as "Boat of the year" in its class. A lot of the credit goes to the farther aft-placed mast. This give the boat a smaller, more manageable mainsail. The magazine states that many multihull captains frequently don't use their main for just that reason - it's just too large and difficult to handle.

Is this true in your experience?
I am going to take heat for this opinion. I think many who don't use the main are either lazy or in poor shape physically. I think there are a lot of new breed push button sailors(raised on electronic games) out there. I think a lot of the motor boat mentality has moved into sailing. I am in my late 70s so I grew up with the concept that a sail boat had to be worked. So when I single handed my J/35 or J/44 and the wind was right it was jenny time and no electric winch. When the wind picked up down with the jenny and up with the working sail(lots of hanks) This kept me in good shape and my boat really moved along. With roller furling lazy jacks and jiffy reefing things are so easy that there is little reason not to use the main even if it is not RF but jib is.
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Old 21-06-2015, 18:59   #64
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Sail Aerodynamics

...interesting presentation with some illustrations

Advances in sail aerodynamics - part two
http://cdn2.hubspot.net/hub/209338/news/Ad_aerodynamics/index2.htm

....a couple of quotes...
Quote:
Jib head vortex on the main
As always at the tips of airfoils, there is a vortex forming behind the leech of the jib towards the head. When this vortex travels behind the leeward side of the main, it bends streamlines above itself away from the surface of the main, effectively "ripping off" the flow from the main surface at the hounds level and a little above it. This can be seen on the simulation as a triangular, disturbed air area. Above this area, closer to the top the flow can still be attached. Lower fractional rigs (7/8-rigs) suffer more from this than masthead or high fractional rigs. This could be one reason that 9/10-rigs have grown in popularity lately.
Quote:
Think one
To understand how the mainsail and the jib work together, it may be useful to think of them as one wing with a slot in the middle. The jib forms the front part of the wing (leading edge in aircraft terminology) and the mainsail forms the back part (trailing edge). The jib is the curved, smooth shaped front part of the wing, the main is the more straight, flat part. When you adjust the main sheet or traveler, you adjust the camber of the whole wing in a very smooth way, around the hinge that the mast forms.

When you keep in mind that pressure always acts perpendicular to the surface, it is easy to see why the jib usually is in charge of most of the forward driving force, while the main causes most only heel. When sailing upwind most of the surface of the jib is oriented in the direction of the motion, while most of the surface of the main is oriented perpendicular to it, the leech often even pulling back. But it would be wrong to think that the jib is more important for that. The mainsail is bending the air in front of the jib, allowing the boat to point higher than with the jib alone, and also helping the jib bear more loading without stalling.
Quote:

Air in the slot - accelerated or not?
The old question about the slot effect seems to have a different answer depending on how you define "slot", and also how you define to accelerate:

If you consider the slot as the area between the mast and forestay, in front of the mast, then the air is slowing down. But if you define the slot as the area between the mainsail and the genoa behind the mast (like I would), then air is definitely accelerating in the slot, as witnessed by the colors turning from yellow to orange and red, when the air moves from the mast towards the leech of the genoa. You can try this yourself: When you stand of the fore-deck, the wind is lame, but when you walk back into the slot between the main an the genoa, you really feel the wind blowing in your face by the time you reach the genoa leech.

This acceleration is relative, however, the airspeed is not faster in the slot area than in case the mainsail were alone, without any jib at all. The main effect of the genoa or jib is to slow down the air speed in the front part of the main, no Ventura-effect there.
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Old 21-06-2015, 20:02   #65
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Re: Don't use the Main?

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Originally Posted by eyschulman View Post
I am going to take heat for this opinion. I think many who don't use the main are either lazy or in poor shape physically. I think there are a lot of new breed push button sailors(raised on electronic games) out there. I think a lot of the motor boat mentality has moved into sailing. I am in my late 70s so I grew up with the concept that a sail boat had to be worked. So when I single handed my J/35 or J/44 and the wind was right it was jenny time and no electric winch. When the wind picked up down with the jenny and up with the working sail(lots of hanks) This kept me in good shape and my boat really moved along. With roller furling lazy jacks and jiffy reefing things are so easy that there is little reason not to use the main even if it is not RF but jib is.
EY,

Sure, there's no doubt that there are those out there cruising, or want to be, who are not experienced sailors in adverse conditions. Maybe they've just been lucky enough to charter a cat for holiday times in good sailing conditions under non-challenging conditions.

But so be it. The point is, there is no question that a large, roachy, full batten mainsail can be a handful under certain wind and sea conditions. So this becomes a safety issue. Sailing off the breeze with the main up a non-rotating mast; wind comes up fast & strong; want to drop the main but it won't; wife is on-watch or you are sick.....stuff happens to the best of us.

We are just discussing that, aside from needing the highest efficiency working to windward (either racing or needing to work to close reaching to windward alot when cruising), maybe having a headsail driven boat rather than a mainsail driven boat is not a bad idea as a cruising boat. Physically easier hoisting and reefing, lower cost, not a huge drop in performance on most points of sail, more friendly to older sailors or newbies...etc. That's all.
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Old 21-06-2015, 21:11   #66
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Re: Don't use the Main?

This is a very odd thread....don't get it at all....if a main sail is too much trouble? That's just way too much convenience...too much stability...whats the point?
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Old 21-06-2015, 21:53   #67
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Re: Don't use the Main?

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Originally Posted by IdoraKeeper View Post
This is a very odd thread....don't get it at all....if a main sail is too much trouble? That's just way too much convenience...too much stability...whats the point?
Idora,

I'm not certain what you mean? Why is it an odd thread? Could you clarify?

Do you mean the question of relative size/area (and/or aft mast placement?) of mainsail to foresails for cruising cats is a foregone conclusion? If so, I for one am someone who is interested in other's opinions on this topic that might be contrary to the more conventional view.

Also, I see there have been over 7,000 views of this thread in the last few days as well, so besides some very reputable designers who feel smaller mains have real merit for cruisers, obviously a few others on CF are interested enough to have a look at the thread.
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Old 21-06-2015, 22:42   #68
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Re: Don't use the Main?

When I was located at the visitors wharf in Noumea there were 17 monos. 16 of them had in mast furling - the main was battonless. It occurred to me that clearly there is a distinct advantage for the real cruiser here otherwise why would it be this way.

They do not give a sh$t about pointing - they just want to be safe.

Cats are a little different due to balance, but having just journeyed from NC to Vanuatu at 30+ knots in 4 m seas and having to reef the main twice I would seriously consider an in mast furling system should one present itself for cats in the future.

Further, >90 AWS, the main does not add any significant benefit compared to any one of my three headsails.

It all depends on your priorities - getting speed out of your boat or travelling comfortably and safely.
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Old 21-06-2015, 22:57   #69
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Re: Don't use the Main?

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Originally Posted by cwjohm View Post
When I was located at the visitors wharf in Noumea there were 17 monos. 16 of them had in mast furling - the main was battonless. It occurred to me that clearly there is a distinct advantage for the real cruiser here otherwise why would it be this way.

They do not give a sh$t about pointing - they just want to be safe.

Cats are a little different due to balance, but having just journeyed from NC to Vanuatu at 30+ knots in 4 m seas and having to reef the main twice I would seriously consider an in mast furling system should one present itself for cats in the future.

Further, >90 AWS, the main does not add any significant benefit compared to any one of my three headsails.

It all depends on your priorities - getting speed out of your boat or travelling comfortably and safely.
Hi Chris, exactly! Good feedback. 16 out of 17 boats is almost a...trend?

Great to hear you're having a good sail in South Pac. Sorry to hear your solar is a bit disappointing in output.

I looked at a boom furling system that would allow battens, but getting the angle of the boom to mast exactly right seemed to be the weak link. If it wasn't perfect it seemed it would jam.
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Old 22-06-2015, 01:08   #70
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Re: Don't use the Main?

Hi Rob


Actually my solar panels are working well, but most of the time it is either thick cloud cover or raining so no output to speak of.


It just seems to be the norm here.
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Old 22-06-2015, 06:05   #71
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Re: Don't use the Main?

Quote:
Originally Posted by cwjohm View Post
When I was located at the visitors wharf in Noumea there were 17 monos. 16 of them had in mast furling - the main was battonless. It occurred to me that clearly there is a distinct advantage for the real cruiser here otherwise why would it be this way.

They do not give a sh$t about pointing - they just want to be safe.

Cats are a little different due to balance, but having just journeyed from NC to Vanuatu at 30+ knots in 4 m seas and having to reef the main twice I would seriously consider an in mast furling system should one present itself for cats in the future.

Further, >90 AWS, the main does not add any significant benefit compared to any one of my three headsails.

It all depends on your priorities - getting speed out of your boat or travelling comfortably and safely.

Cats are already out there with inmast furling. Fountaine Pajot offers it on new cats. What I see as the biggest negative is the loss of sail area. Many cats have a large roach or a square top main. Neither of those are possible with inmast furling. I've sailed two identical boats, except for the main sail, and noted immediately in winds under 20kts the square top main is about a knot faster on most points of sail. In really light wind, say under 5kts, the small main on the inmast boat really struggles to move. The big advantage to the inmast is the ease of reefing and simplicity of tweaking the out haul from the helm.

Also the inmast sail can't be made as heavy since it must be thin enough to roll up. No battens.




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Old 22-06-2015, 14:02   #72
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Re: Don't use the Main?

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Originally Posted by cwjohm View Post

It all depends on your priorities - getting speed out of your boat or travelling comfortably and safely.
Is there some law that says you can't do both?
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Old 22-06-2015, 15:29   #73
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Re: Don't use the Main?

Perhaps we need to take another 'tack' at the reasoning here.

The subject thread is titled 'don't use the main'sail... that is. The problem with that solution is it doesn't take into account the interdependence of the headsail and the mainsail. A headsail can be a more effective sail than the mainsail, BUT it can only do so with the HELP of the mainsail.

Lets go back to this link,
http://cdn2.hubspot.net/hub/209338/news/Ad_aerodynamics/index2.htm
and look at the text in the middle of the sail.
Click image for larger version

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Quote:
the jib may contribute up to 90% of the total drive of the sails, but without the mainsail it loses its magic
Then have a look at this flow illustration. Which sail has the greatest pressure differential across it, and which one has that differential in the direction of the boat's travel,...obliviously the headsail
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The sailboats illustrated here are fractional rigged boats, much like most of our catamarans are rigged,....our headsails are much smaller than the mainsails. So if we reduce the size of the mainsails (by making them roller furling, or eliminating their roach, or eliminating their fat-heads, etc, we are going to significantly cut the boat's performance, because we don't have headsails large enough to make up the difference !! We have potentials to make the rigs more effective by increasing the size of the sails that we can make more effective, but we continue down the path of making the following sail (the mainsail) ever bigger and the headsail ever smaller.

It's this reasoning that lead me to the twin headsail rig on my mast-aft configuation. I wanted a nice big headsail that could be helped by its following sail (my mainstaysail). And I wanted it to occur in a more 'parallel manor' than the traditional configuration (a more consistent slot).

Here are a few illustrations (rough draft) that I made of 3 style rigs, fractional jib, masthead jib, and then aft-mast rig.
Note that the horizontal lines in each of the illustrations represent the centerline of the vessel when viewed from above, so you see the overlap of each of the two sails at each elevation in the rig.
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Look how consistent that slot is for the aft-mast configuration.
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Old 22-06-2015, 15:38   #74
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Re: Don't use the Main?

Andrew


Yes, it is called the law of physics.


In the case of a significant swell which if you are lucky is 6-8 seconds apart in peaks and if you are unlucky is confused and the peaks come from anywhere, if you push an object through that swell at anything close to wind angle, comfort for the occupants and safety for the boat will be directly proportional to speed through the water. This applies to both a bathtub and a gunboat. Even on the Queen Mary this is the case. That is why they have stabilisers.


Yes the degree of discomfort will vary from boat to boat, but from my experience the heavier the boat the more comfortable the ride.


Some may obtain some perverse pleasure in travelling at 10 knots in these conditions and the boat being thrashed to death and waves of seawater coming over the boat from in front and behind. Those that are more sensible will slow the boat to 8 knots thereby improving comfort and safety for boat and passengers. In order to achieve this the main needs to be reefed or in the worst case bought down. This is not a trivial task in those conditions.
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Old 22-06-2015, 18:00   #75
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Re: Don't use the Main?

Just wanted to say that I thought the last 2 posts by Brian and Chris beautifully summarise why aft mast/smaller mainsails are attractive to me for our FreeFlow cruising cat.

Thanks guys
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