New extreme roach flat top main?

[tomfl]

Originally Posted by geoff326

Presumably a square top main has the advantage of being able to twist off in the gusts, which I would have thought on a catamaran would be a desirable feature re safety.

What you say is true of what I will term cruising square tops which seem to open up even more when a gust hits, so much so that a square top can be cut to function as the first reef.

If you look at what I will term high tech racing square tops the sail is cut so it does not twist nearly as much as a cruising square top.

If you look at the racing square tops in this video there is not a lot of twist off. When I look up from my steering station my square top opens up at least twice and probably three times as much as these racing square tops.

One thing I notice is I spend a lot more time adjusting the traveler than the sheet and traveler adjustment seems to affect how much or little the top third of the sail opens up compared to adjusting the main sheet, not to mention boat speed and balance. In fact in a steady wind I often forget to turn on the auto pilot once I am happy with how the traveler is adjusted. I would also note how travelers on racing boats are normally curved and tend to be larger than on cruising boats, which allows better control of how the sail is shaped.

https://www.youtube.com/watch?v=Q4peE1uPmr8

[SVNeko]

Originally Posted by SVI

The only downside I see is have to reef earlier.
Currently I take the first reed at AWA 28-30.

But 100m2 main will be lots of fun in light wind...

I want to reuse 2-3 lower battens. Where do I get the new, longer ones?

You can probably use the extra sail area. Sounds to me like you are extremely undercanvassed if you don't take in a reef until 28-30 kn.

[Barra]

Originally Posted by SVNeko

You can probably use the extra sail area. Sounds to me like you are extremely undercanvassed if you don't take in a reef until 28-30 kn.

+1

[Barra]

Originally Posted by tomfl

Traveler and preventer.

Im not sure I follow? Both of these are pulling down on the boom effectively just like the twin mainsheets (two sides to the traingle). the topping lift is providing a triangulating opposite force to hold the boom in place in light air...

[UNCIVILIZED]

Originally Posted by SVNeko

You can probably use the extra sail area. Sounds to me like you are extremely undercanvassed if you don't take in a reef until 28-30 kn.

My Point EXACTLY!
Such relates directly to my reference regarding filling up the holes in one's sail inventory.
It's simple enough to just fit a short sprit, add a structural furler, & fit a well shaped, full sized genoa. Ditto on adding a Screecher & or Code 0. All, likely for less $ than a new, racy mainsail, plus the beefed up deck & spar hardware needed to handle it.

Ah, & not to sound harsh. But it might also be prudent to try putting the boat on a diet. Specifically, off load literally everything onboard. And take note of how much your WL rises. Then, only put back on what's Truly necessary. And I guarantee you'll notice the difference.

Back to the vang thing. One can just bite the bullet, & have a custom one fabricated, or create a DIY unit.
Were it me, I might manufactuer one with some curvature pre-built in to the fiberglass/kicker rods. So that it would fit in the "normal" location. This, due to the cabin house obstructing the movement & mounting of a conventional, straight one. And have the rest of the system be much akin to the Boomkicker, described below.

That, or even have a unit designed & fabricated so that it's lower end terminates at a structural hard point, on top of the cabin house. With or without the ability of one end of the vang, to articulate as needed: So as to accomoate the changing angles of things, as the boom swings though it's arc.

Note, that when I say structural hard point. One could be built to be much akin to how the forward ends of the booms on some OPEN 60's are attached.
And for some visuals of what I'm describing regarding vangs with curved rods, there are some approximations of such vangs here www.boomkicker.com Albeit, you'd need more initial prebend built into the rods.

On the rods for the kicker, you could have a set of curved, custom, composite rods made up. With their lower ends fitted to the traditional location for a vang's attachment on the mast.
Their purpose being exactly the same as the springs, or fiberglass rods in a conventional vang (kicker). Or the gas pressure built into a standard hydraulic vang.
So that with no force acting to compress them, their natural tendency will be to lift up the boom.

Then, have their attachment to the boom, be to a sliding car, mounted to a track on the boom's underside. To which a hydraulic cylinder is also connected. One which runs between this car & the mast.

Thus, in normal operation, with no load being applied to the hydraulic cylinder, the composite rods will lift the boom up. And then, when pressuere is applied to things via the cylinder, it pulls on the vang's rods on the boom's underside, further bending them. Resulting in the boom being pulled downwards. Just as a conventional vang would do.



Or a different approach for a custom/DIY vang option is this:
Make up 2 beams/plates. With the lower one affixed to the mast in the standard location, via a gooseneck. And the 2nd beam is affixed to a car on a track, on the boom's underside.
Then, have the 2 beams bolted together with a structural pivot pin, so that they form an "L" where they meet., underneath of the boom. Thus avoiding having them hit the cabin house.

Along with the beams, you'll need to attach a large spring/shock setup. From both sides of the boom, to the more horizontally oriented beam (or the beams connecting pivot pin). And hook up a hydraulic cylinder to this same beam, where it's attached to the car on the boom's underside.

So that when you crank up the hydraulic cylinder, it pulls the upper beam's connection on it's track, towards the mast. Thus compressing the springs in the system. Which will subsequently pull the boom downwards.

Or, you could even mount the hydraulic cylinder with one of it's ends at the connecting hinge pin of the 2 beams. And have it's other end affixed to the mast just below the gooseneck.
So that when activated, the cylinder would again, compress the springs attached to the upper beam, thus pulling the boom downwards.
Also, the springs in the system could be connected instead, to the more vertically oriented beam, in order to achieve the same effect.

- Pretty much, if one spends half an hour studying the various suspension setups on mountain bikes, you'll come up with loads of (proven) ideas.
That, & or, take a look at some of the custom hardware setups on Dennis Conner's soft sail catamaran. The one which is the twin to the hard sailed version which sailed circles around the old Kiwi monstrosity back in the late '80's. Said cat has Lots of neat toys

[davecalvert]

It is true that one of the benefits of a square top main is the twist in the upper part of the sail. This does release pressure in the top, moving the power and center of effort down in the puffs. We don't intentionally design the cruising square top mains to twist off sooner than racing mains. I think this is more a factor of differences in mainsail trim. Racers pay more attention to sail trim than cruisers. I often see cruisers sailing with excessive mainsail twist, even when going upwind. This is mainly a function of too little main sheet tension.
Most catamarans have a long main traveler. This, in addition to the main sheet, are all you need to trim twist in or out. No vangs needed.
I use the upper tell tails to indicate main sheet tension and twist and the lower tell tails to indicate traveler positions.
For up wind in light air, the traveler should be above center. In moderate winds, centered, and in strong winds a bit below center. Use the boom as a sight and look up at the top batten, or second batten, on a square top main.
The back half of the first horizontal batten should be roughly parallel to the boom. This is a good starting point in determining leech twist. This setting is best for up wind. As the sheet and traveler are eased for reaching, the top will begin to twist off more and it will be more difficult to get the top batten parallel to the boom. In this case, the additional twist can be a benefit. But, using the boom as a sight, can help make one realize when there is too much upper twist.

[geoff326]

Originally Posted by davecalvert

It is true that one of the benefits of a square top main is the twist in the upper part of the sail. This does release pressure in the top, moving the power and center of effort down in the puffs. We don't intentionally design the cruising square top mains to twist off sooner than racing mains. I think this is more a factor of differences in mainsail trim. Racers pay more attention to sail trim than cruisers. I often see cruisers sailing with excessive mainsail twist, even when going upwind. This is mainly a function of too little main sheet tension.
Most catamarans have a long main traveler. This, in addition to the main sheet, are all you need to trim twist in or out. No vangs needed.
I use the upper tell tails to indicate main sheet tension and twist and the lower tell tails to indicate traveler positions.
For up wind in light air, the traveler should be above center. In moderate winds, centered, and in strong winds a bit below center. Use the boom as a sight and look up at the top batten, or second batten, on a square top main.
The back half of the first horizontal batten should be roughly parallel to the boom. This is a good starting point in determining leech twist. This setting is best for up wind. As the sheet and traveler are eased for reaching, the top will begin to twist off more and it will be more difficult to get the top batten parallel to the boom. In this case, the additional twist can be a benefit. But, using the boom as a sight, can help make one realize when there is too much upper twist.

So, basically to reduce twist increase leach tension?

[davecalvert]

Yes, increase in main sheet tension reduces twist.
A lot of cruisers do not use enough main sheet tension, especially when sailing upwind.

[geoff326]

Originally Posted by davecalvert

Yes, increase in main sheet tension reduces twist.
A lot of cruisers do not use enough main sheet tension, especially when sailing upwind.

Coming from a windsurfing background, when flat top sails first appeared on the scene it wasn't simply a case on plonking this type of sail on a typical windsurfing mast. 'Flexi-Top' masts were part of the package. Essentially this type of mast could flick off in the gusts and so open up the leach.
Therefore I do wonder how much thought has has gone into mast design for a flat top main on your average cruising boat.

[tomfl]

Originally Posted by davecalvert

It is true that one of the benefits of a square top main is the twist in the upper part of the sail. This does release pressure in the top, moving the power and center of effort down in the puffs. We don't intentionally design the cruising square top mains to twist off sooner than racing mains. I think this is more a factor of differences in mainsail trim. Racers pay more attention to sail trim than cruisers. I often see cruisers sailing with excessive mainsail twist, even when going upwind. This is mainly a function of too little main sheet tension.
Most catamarans have a long main traveler. This, in addition to the main sheet, are all you need to trim twist in or out. No vangs needed.
I use the upper tell tails to indicate main sheet tension and twist and the lower tell tails to indicate traveler positions.
For up wind in light air, the traveler should be above center. In moderate winds, centered, and in strong winds a bit below center. Use the boom as a sight and look up at the top batten, or second batten, on a square top main.
The back half of the first horizontal batten should be roughly parallel to the boom. This is a good starting point in determining leech twist. This setting is best for up wind. As the sheet and traveler are eased for reaching, the top will begin to twist off more and it will be more difficult to get the top batten parallel to the boom. In this case, the additional twist can be a benefit. But, using the boom as a sight, can help make one realize when there is too much upper twist.

Not disagreeing with anything in your post. But I would note everything you posted was related to boat speed. I normally trim to balance the boat so the auto pilot is not needed, or at least not needed as much.

I tend to look at the top 1/3 of the main from my steering station and often it is very open. I also have bench seats at the back of the cockpit and when the boat is balanced and sailing on its own I will sit on the shady side and look up, again the top 1/3 of the sail seems very open. My guess would be this is very boat dependent.

If I am more interested in boat speed I tend to pay more attention to how the slot between the working jib and the main and the slot between the screecher and the working jib look like. If they are dialed in I seem to get a bigger boost in boat speed than any other adjustment I make.

Once I get the slot between the screecher and working jib right I use the traveler to adjust the slot between the main and the working jib. I see lots of folks who seem to set the traveler in the middle and never change it at all. Spending time playing around with the traveler was well worth my time and I suggest it is something others should do if they have not already.

I agree any benefit from a vang is not worth the cost/effort/complexity involved.

[tomfl]

Originally Posted by geoff326

Coming from a windsurfing background, when flat top sails first appeared on the scene it wasn't simply a case on plonking this type of sail on a typical windsurfing mast. 'Flexi-Top' masts were part of the package. Essentially this type of mast could flick off in the gusts and so open up the leach.
Therefore I do wonder how much thought has has gone into mast design for a flat top main on your average cruising boat.

Good point.

I spent a lot of time on my F2 boards. Not only did the mast (really the sleeve on the sail) rotate (few big boats have rotating masts) but the mast also could slide fore and aft in a track and be articulated to change the rake. Part of the flexibility of a windsurfer mast was due to no stays, spreaders, or shrouds; something almost all big boats have. Not to mention it was common to have windsurfer sails ranging from three square meters to twelve square meters. I have never seen a big boat that had that range of sail area available.

Another consideration is related to the idea that for every three feet in boat length the forces doubles (put in any numbers you like but the concept is viable). Once a boat reaches a certain size unstayed masts become a real design problem. Stuff like a NoSuch have multiple masts on boats that normally would be sloop rigged.

Stepping a mast on a big boat is also a consideration. You need to have a solid place step a mast on a big boat which may affect the interior of the boat while on a windsurfer it is not really a consideration.

So there is a lot that goes into mast design on a big boat, and how flexible the top of the mast is winds way down on the priority list.

[geoff326]

So there is a lot that goes into mast design on a big boat, and how flexible the top of the mast is winds way down on the priority list.[/QUOTE]

Interesting points.

However, I think you'll find these days most competent windsurfers have no need to go below 4.5 sq metres, and where as short boarders used to be maxed out at 6 sq metres they can now easily carry 7 sq meters- all down to mast and sail design.
So, while mast flexibility may not be at the top of the priority list for big boats for now, perhaps if mast designers took a leaf out of windsurfing technology, then maybe they could make their fortune by coming up with a design that would make the the first two reefs redundant. After all, the flat top sail originated through windsurfing.

[AD28]

Originally Posted by geoff326

After all, the flat top sail originated through windsurfing.

That statement is incorrect. Flat tops are as old as gaff rigs, which effectively a flat-topped main is, just doesn't have the controls as a 'true' gaff-rigger (peak and throat halyards)

[tomfl]

Originally Posted by AD28

That statement is incorrect. Flat tops are as old as gaff rigs, which effectively a flat-topped main is, just doesn't have the controls as a 'true' gaff-rigger (peak and throat halyards)

Not everyone has the same definition of a flat top, but to say a gaff rig is effectively the same as a flat top is just wrong.

While a gaff rig may look something like a flat top there are real differences. As I posted earlier perhaps the biggest advantage of a flat top is turbulence reduction at the top of the sail. There is significantly more turbulence with a gaff rig, even if you discount the turbulence added from the peak and throat halyards which greatly disrupt the air flow. Another big difference is sail shape. A well designed flat top has a much better sail shape part due to the number of battens while a gaff rig looks baggy in comparison. A gaff rig also has a lot more weight aloft than a flat top

No way to sugar coat it a gaff rig is much different than a square top.

[geoff326]

[. Another big difference is sail shape. A well designed flat top has a much better sail shape part due to the number of battens while a gaff rig looks baggy in comparison. A gaff rig also has a lot more weight aloft than a flat top

No way to sugar coat it a gaff rig is much different than a square top.[/QUOTE]


The other point I forgot to mention was a lot of effort in windsurfing sails has gone into batten design - in particular that it is tapered correctly.
Although a gaff rig may look similar, can it actually twist off?