Square Top Main vs Roachy Main

[Barra]

Square tops seem to be all the rage on new cats these days and i was wondering just how much gain in square footage (as a %) these actually achieved roughly?

Yes the gain is up top where it matters but just eyeballing a decent roach main vs a square top it doesnt look like there is a significant gain...

Anyone got any real world comparisons in area gained and any noticable improved performance?

[Bash]

Originally Posted by Barra

Yes the gain is up top where it matters but just eyeballing a decent roach main vs a square top it doesnt look like there is a significant gain...

Anyone got any real world comparisons in area gained and any noticable improved performance?

It's not just about getting more sail higher up, which is great in light air but not the whole picture. It's more about getting great flow higher up. It's also a matter of being able to do more with twist.

Think of the square top as being far less efficient an airfoil than the tip of a triangle. On most conventional triangular sails, the top 5% isn't accomplishing a thing, except to induce drag. On a square-topper, the top of the sail is finally getting some work done.

[downunder]

Have a talk to a couple of the big sailmakers that supply a lot of cats. They should have the answer. Norths for example. Good question.

[markpierce]

Saw this cat several weeks ago going to windward. Mainsail appears to be reefed.

[Barra]

That shows it nicely markpierce on the seawind 1160 you pictured - not a lot of area gained from this roachy main to a squaretop.

Good point Bash on the efficiency gained but just look at the seawind main and tell me it can really be a 10% gain in performance is ive heard claimed. I mean in light winds thats gonna take me from 6 knots to over 6.5 and thats a pretty big gain from what looks like just a few square feet of canvas....

[Bash]

Originally Posted by Barra

Good point Bash on the efficiency gained but just look at the seawind main and tell me it can really be a 10% gain in performance is ive heard claimed. I mean in light winds thats gonna take me from 6 knots to over 6.5 and thats a pretty big gain from what looks like just a few square feet of canvas....

In the racing world, a 10% gain is HUGE.

But let's do the math here. If you increase speed from 6 knots to 6.5, then you've only gained 8.3%

(That's still huge, BTW.)

[Barra]

exactly huge gain well beyond the physics it seems to me. and yes i was being a little conservative at "over 6.5" knots but im allowing for some marketing puffery from the sail makers...

anyone with real world improvements that they have seen from a changeover?

[Palarran]

My understanding is that the downside is stowing it in a stackpack. From what I've read, they are great for racing cats and just for show on cruising cats. By far the sail I want is a roller furling gennaker.

[Bash]

Originally Posted by Barra

exactly huge gain well beyond the physics it seems to me.

Exactly what physics are you talking about here? (Or are you just being dismissive because you don't understand the physics?) Seriously, the aerodynamic advantages of fat-head sails are not at all controversial to anyone with an above-Fox-News understanding of science.

("Fat head," btw, is the common nickname for square-topped sails within the racing community. Have you noticed how top developmental racers are all using this type of sail recently?)

[Barra]

Originally Posted by Bash

Exactly what physics are you talking about here? (Or are you just being dismissive because you don't understand the physics?) Seriously, the aerodynamic advantages of fat-head sails are not at all controversial to anyone with an above-Fox-News understanding of science.

("Fat head," btw, is the common nickname for square-topped sails within the racing community. Have you noticed how top developmental racers are all using this type of sail recently?)

No bash im not being dismissive - but ill happily dismiss your crappy attitude and views about my education levels....

the physics im talking about are SA/diplacement, bruce numbers etc ie if its just about those numbers then its a 1% odd improvement in sail area for a supposed 10% improvement in performance. as you say theres more at work.

I didnt say they are controversial Bash (good name for ya) im just questioning if the numbers stack up and what real world crusing results have been. Sure ive noticed the racer trends just like anyone else with an "above fox news" understanding of sailing but as you sound like you probably already know they will spend big bucks for a 1% improvement in performance.

either way sounds like you have no actual experience to add on this topic...

[Bash]

Originally Posted by Barra

the physics im talking about are SA/diplacement, bruce numbers etc ie if its just about those numbers then its a 1% odd improvement in sail area for a supposed 10% improvement in performance.

SA/displacement ratios have nothing to do with it. A transition to a square-top sail design compared to what you've termed a "roachy" main does not necessarily change sail area. What it changes is the shape of the airfoil. A square wing tip is more efficient than a pointed tip because of how it promotes air flow. We know this from studying bird wings, and know this from studying the development of aircraft wings. Now we're able to translate that understanding to the development of sails, especially mainsails.

"Bruce numbers" deal with the power-to-weight ratios of multihulls. These numbers are not contingent upon sail shape in any way. Simply put, a Bruce number is the square root of the sail area divided by the cube root of displacement. Nothing more.

[Barra]

Originally Posted by Bash

"Bruce numbers" deal with the power-to-weight ratios of multihulls. These numbers are not contingent upon sail shape in any way. Simply put, a Bruce number is the square root of the sail area divided by the cube root of displacement. Nothing more.

Lord of the bleeding obvious. even fox news types can rehash formulae.

Technically (and i can tell you love being technical) the interpretation of a bruce number IS CONTINGENT ON A SAIL SHAPE ie the indicated performance from the bruce number is going to be based on some basic sail shape for the main.

[Bash]

Originally Posted by Barra

Technically (and i can tell you love being technical) the interpretation of a bruce number IS CONTINGENT ON A SAIL SHAPE ie the indicated performance from the bruce number is going to be based on some basic sail shape for the main.

Nope. The formula only admits two variables: sail area and displacement. It's quite a simple formula. Sail shape would involved far more advanced physics.

[waikikin]

Originally Posted by Barra

That shows it nicely markpierce on the seawind 1160 you pictured - not a lot of area gained from this roachy main to a squaretop.

Good point Bash on the efficiency gained but just look at the seawind main and tell me it can really be a 10% gain in performance is ive heard claimed. I mean in light winds thats gonna take me from 6 knots to over 6.5 and thats a pretty big gain from what looks like just a few square feet of canvas....

I think thats a pretty telling picture your referencing there, that seawind sail is most of a square top & the difference sfa. I think theres some fuzzy physics offered around sail design/marketing & sometimes uneven comparisons rather than "all things being equal" except the marketed factor, also not all sailors/teams are equal in skill. The skill of the sailmaker is matching the sails to the vessel & rig as a package & also interpreting the needs & skills of the sailors of that vessel. I think the main(bad pun) advantage of these style of sails is in the "auto trimming"/gust response whatever you want to call it ability designed into them... when the sail can respond to a gust or puffage as I sometimes like to say by letting the head ease/lay off/exhaust on the hit of some extra puff & trim as the vessel accelerates or puffage eases much quicker & more reliably than a self appointed hot shot ocean hero sailor(I can say that) you can effectively carry more sail & power for longer, if your into that kind of thing.

[daddle]

Ask the sailmaker about longevity of the square-top. There are some large loads up there that might affect life. Plus, as maybe someone hinted above, diagonal battens lend themselves better to race crews than cruisers - who like to store sails on the boom rather than pull battens and roll up large sails during cocktail hour.