Vincent DePillis

How big a square top?

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Posted this query in F-boat list, with no response.  Thinking about a new main for my F31rR

 Ian Farrier always advised against large roach sails, because it screws up center of effort.   I have seen this effect personally, with a friends F31 that had been modified to have a larger boom and foot.   The boat was unmanageable.

But I see that more and more boats (multis and Class 40s in particular) are moving to mains with very straight leeches and very large heads.  One experienced multi sailor here in the PNW has recently moved to such a sail, and has explained to me that the new sail has made his cat easier to sail-- that the big top twists so easily that it takes the punch out of the gusts, and he is doing less helming, and less trimming, with the new sail.   He also emphasized the benefit of carbon battens, which keep the head flat and help pull depth out of the mid section of the sail as the head twists.   

Have any of you had experience with this?  For reference, stock sail plan calls for a 38" head on a 14.3' foot.  My existing sail increased head by 4", and decreased foot by 4", which works well.  I have one proposal that calls for a 6 foot head (which seems pretty wild, TBH).

Appreciate any thoughts and advice.

Vince DePillis.

 

 

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I just saw Russ's new main for his G32 and it occurred to me how fat his (sail) head was but then saw how much the foot was shortened in what I can only imagine was an effort to maintain the center of area and henceforth the balance of the boat. Would that be the same cat sail that you are referring to? It would seem that if you make an effort to maintain the original center of effort (in such a manner as shortening foot) you could use the fatter head. 

Sorry Russ I had to edit above since it sounded like I was calling you a Fat Head! Nice job on the boat, main looks great! Pedal unit ditto.

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A lot depends on conditions and a number of other factors, including the materials used. A big square top can develop a soft leech quickly if you aren't using higher end materials and fully supported battens, and on a boat like the F31r the carbon battens are a big weight savings.

An experienced sail maker is going to be key. I can't speak for the big cat/tri market as I simply don't have enough experience to, but I relay what is going on in the small boat world at the moment. I'd be talking to Doyle NZ, Incidence Sails in France and probably North Sails France. I'd also give Jay Glaser and Randy Smyth a ring.

Square tops started small, went big, then went back small in an effort to lower the center of effort (that is the whole DS principal, sorry, end plating is a few % on paper at best). This is all happening within area limited rules. Mischa explained this well at the last U.S A Cat nationals, basically there is a minimum head size to get the sail to twist, where that limit lies for an F31R I couldn't say. The downside to the small square top is your center of effort is now low enough that getting a hull to fly on a high performance cat is tougher downwind in the medium range, so that is a balancing act and something we are sorting out on the F18 at the moment (closer to your F31R I would say than the A Cat for example). What we have noticed is the DS sail we are using is very cambered up at the bottom, which gives you a lot of power upwind and reaching down low which is fast in a pretty wide range of conditions, but once hull flying steadily it can be a touch draggy, fortunately our particular sail flattens nicely. If sailing in a breezy area, I would personally opt for a similar design if it could be made to work, but I suspect there are a number of more complicated issues with boom and rotation that prevent that, so I would go back to the last generation F18 mains for inspiration:

image.png.1ce6743c15113e293fb806abf3068770.png

As you can see, the foot and head size are pretty close. You will need a deeper cut I suspect to get more power and you are also not running the same apparent wind angles as an all-out racing cat, which also translates to a sail with more camber.

I also personally wouldn't deviate too far from tried and true, but again, talk to an experienced sail builder.

 

 

 

image.png

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Suggest you have a conversation with Kame Richards of Pineapple sails in Alameda (near San Francisco).  He designed a Very Large square top that works very well on a local F24Mk1.  Of course, the F241 does not have a rotating rig and that makes a big difference when it comes to supporting the square top (and yah, the F31 would need a much bigger sail).  I am actually surprised by how well the sail works in the heavy winds we get here-I would expect it to be better in the lighter stuff vs. the heavy.

And you should know that the COE is not necessarily at the centroid of the triangle.  The sailmaker designs the max camber placement which has an effect on the COE of the sail and the COE of the sailplan. 

You also will have to deal with your local rating committee who will be suspicious of any sailplan changes.

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2 hours ago, Vincent DePillis said:

Posted this query in F-boat list, with no response.  Thinking about a new main for my F31rR

 Ian Farrier always advised against large roach sails, because it screws up center of effort.   I have seen this effect personally, with a friends F31 that had been modified to have a larger boom and foot.   The boat was unmanageable.

But I see that more and more boats (multis and Class 40s in particular) are moving to mains with very straight leeches and very large heads.  One experienced multi sailor here in the PNW has recently moved to such a sail, and has explained to me that the new sail has made his cat easier to sail-- that the big top twists so easily that it takes the punch out of the gusts, and he is doing less helming, and less trimming, with the new sail.   He also emphasized the benefit of carbon battens, which keep the head flat and help pull depth out of the mid section of the sail as the head twists.   

Have any of you had experience with this?  For reference, stock sail plan calls for a 38" head on a 14.3' foot.  My existing sail increased head by 4", and decreased foot by 4", which works well.  I have one proposal that calls for a 6 foot head (which seems pretty wild, TBH).

Appreciate any thoughts and advice.

Vince DePillis.

 

 

Just put a new main on an 8.5m catamaran, 4m foot, 11ish m leach and a 40% square top against a rotating mast

The barn door is driven slightly by the class rule limiting air draft, but the sail twists nicely when needed.

Built by Evolution sails in NZ,  who have done the last 4 mains for this size racing multi, 3 cats and a F82R

upwind trim small wrinkles below 3rd batten and small crease coming up from outhaul.JPG

cracked sheets 2 sail reaching.JPG

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23 minutes ago, Dead air said:

Just put a new main on an 8.5m catamaran, 4m foot, 11ish m leach and a 40% square top against a rotating mast

The barn door is driven slightly by the class rule limiting air draft, but the sail twists nicely when needed.

Built by Evolution sails in NZ,  who have done the last 4 mains for this size racing multi, 3 cats and a F82R

upwind trim small wrinkles below 3rd batten and small crease coming up from outhaul.JPG

cracked sheets 2 sail reaching.JPG

Which 8.5 is this...?

 

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6 hours ago, Rasputin22 said:

I just saw Russ's new main for his G32 and it occurred to me how fat his (sail) head was but then saw how much the foot was shortened in what I can only imagine was an effort to maintain the center of area and henceforth the balance of the boat. Would that be the same cat sail that you are referring to? It would seem that if you make an effort to maintain the original center of effort (in such a manner as shortening foot) you could use the fatter head. 

Sorry Russ I had to edit above since it sounded like I was calling you a Fat Head! Nice job on the boat, main looks great! Pedal unit ditto.

My main has a head about 45% of the foot length (I think) and that's because that is what the sail designer, Magnus Doole thought would work. The foot length is dictated by the traveler location. I would have a longer foot, but the main is around-the-boom furling and reefing, which means that the boom can't go past the traveler. It doesn't have anything to do with me being a Fat Head.

The reason my working sails are a different color this year is that North replaced last year's sails because there were issues with them. The new sails seem really good.

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5 hours ago, Vincent DePillis said:

Man.  Looks flat.  And interesting to see close together shallow battens.

Fast boats need flat sails..... Don’t forget that the chord depth the wind sees includes the over rotated wing mast.....

Closely spaced and shallow angled battens help to spread upper batten load, gives better support to the head and might mean that you don’t have to disconnect as many (any?) upper hanks to get the mainsail head to lay flat on the boom when stowed?

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5 hours ago, PIL007 said:

Which 8.5 is this...?

 

I smell a new main for a new boat??? hmmm? :D

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2 hours ago, Rasputin22 said:

Nice rig. What track and sliders are you using? 

Ronstan Series 19

21 minutes ago, Sidecar said:

Fast boats need flat sails..... Don’t forget that the chord depth the wind sees includes the over rotated wing mast.....

Closely spaced and shallow angled battens help to spread upper batten load, gives better support to the head and might mean that you don’t have to disconnect as many (any?) upper hanks to get the mainsail head to lay flat on the boom when stowed?

I did think it looked flat, but the old main was likely blown out, and we are still a little light on batten tension

The head of the sail is lashed on, and the next two battens on quick release cars so its relatively easy to get the sail flat on the boom (easier than inserting and tensioning two battens which is what we used to do

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You need to remember with the exception of his last couple of designs, the F boats all have quite small rudders.  Ian might have objected to the big head based upon the fact it would move the centre of effort too far back and cause weather helm.

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10 hours ago, PIL007 said:

Which 8.5 is this...?

 

The 8.5m rule limits mast height to basically what would have been installed on 70s cats.  The result is to be fast in this class you need wide low aspect ratio mains and headsails.  What is best on an 8.5m isn’t necessarily a good option on other platforms.

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In your original post, you said that a 6 ft fat head seemed extreme.... 18 ft skiffs have had fat heads around that size for years... Jonathan Witty’s LUMIX certainly did, because I measured it...

In the link below, Colour 7 looks to have around 2/3rds of boom fat head:

http://www.mysailing.com.au/news/square-top-jibs-and-other-sail-innovations

Do you need more sail area?.... Can you and your boat take the extra power?

if yes and can still maintain helm balance, then a fathead is a cheap and effective way of doing it....

 

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3 hours ago, Sidecar said:

In your original post, you said that a 6 ft fat head seemed extreme.... 18 ft skiffs have had fat heads around that size for years... Jonathan Witty’s LUMIX certainly did, because I measured it...

In the link below, Colour 7 looks to have around 2/3rds of boom fat head:

http://www.mysailing.com.au/news/square-top-jibs-and-other-sail-innovations

Do you need more sail area?.... Can you and your boat take the extra power?

if yes and can still maintain helm balance, then a fathead is a cheap and effective way of doing it....

 

Like my old boat

2 meter head to a 4.1 meter foot.  Awesome sailplan

 

 

Wanda 20090624-3.jpg

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56 minutes ago, Christian said:

......2 meter head to a 4.1 meter foot.  Awesome sailplan.....

Mine’s bigger than yours !!!!!.... 2.36m on 3.9m boom and the boom is counterbalanced...  The leech is vertical, aft of the pivot, it is 100% head/foot ratio.

i have balance problems (resolvable without touching the rig)...... photo below is with 2 reefs in on the main. The windward jib is also almost 100%.

Early days yet... proas are a weird world......

9E0CF9B8-B8C4-4A53-8EFA-35951F9BEF09.jpeg

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6 hours ago, Vincent DePillis said:

That was a boat from south Africa, right?  on race to Saint Helena or some such?    Got a name for me?

Yep, Banjo. Start of 2014 Governors Cup.

The owner told me he is very happy with the sail and balance.

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@Vincent DePillis for a big square top, and twist control you'll want more power on your mainsheet. Traveler track + cart upgrade, 12:1 or whatever. Also a good downhaul setup.

The F31Rs I've seen are not setup for a laminate sail with good twist control.

Maybe you already know all this, but it hasn't been mentioned yet in the thread.

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Martin, I agree, stock main controls are undersized.

 My mainsheet is a custom Harken 12:1 ratchet fiddle block which I lead to a winch in heavy air, and I changed out the traveler for a Harken big boat traveler with 6:1  end controls.   Not concerned about controlling the main. 

The mast is another issue.  The F31r Omohundro mast section is a little undersized , and the unsupported top mast bends more than I would like.  I do wonder if a 40% head will add a lot of stress to the mast .  I could add shrouds to the mast head, at the cost of increased windage.

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Evil Gnome F85sr

Main about 12m luff and quite flat

Mast 12.8 m double spreader 190 aluminium wing with reinforcing stiffener in mast from bottom spreader up from Alyachts.

Running backstays 

3.0 metre foot 

1.8 metre square top head

Mainsheet 7;1 but run through 40:1 Harken winch and give it heaps

24:1 downhaul

Had to reinforce the traveller support beam and have a Harken 3:1 traveller about 1 metre long as we are nearly always creating apparent wind.

Then chase the loads and reinforce what needs it.

It all depends on how hard you want to push.

Evil

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Thx gnome.  Any of your friends sailing f9/f31s?  Would love to know their thoughts on mainsail plans.  Looking for pix too.

There are a couple of things I am wondering about – one is whether a big square top would increase the tendency of the boat to sail bow up.   The F31s are a bit short on float buoyancy in the aft part of the float. I put on new larger floats but most of the volume is in the front of the float, increasing the bow up attitude when the wind increases.   This is potentially  helpful from a safety standpoint downwind, but increases transom drag upwind.

( I have been contemplating an setting up the mast dead vertical, eliminating  the existing rake,  as an experiment to see whether this would lessen the tendency to sail bow up.)

 

 

 

 

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@Vincent DePillis

I forgot, I should have mentioned it before. Apologies. You can also check what other F31 (ish) tris have as headboards by checking some of the rating sites:

http://www.mycq.org.au/documents/omr/omr.xls

https://sites.google.com/site/mocrarating/home

A quick glance at OMR gives:

Carbon Credit, a well known F31SRC, headboard: 1.69m

Crosshair, another F31SRC, headboard: 1.48m

Wilparina 2, an F9, headboard: 2.00m

A quick look at MOCRA website:

Ottodrei, an F9A, headboard: 2.40m

Morticia, a Seacart 30, headboard: 1.80m (1.77m in OMR)

The CE shift aft from going bigger square headed isn’t much and should be more than compensated by standing your mast more vertical, as you were already contemplating.

How is you current helm balance BTW?

 

 

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Thx sidecar,  that looks super useful.  Will review in detail. 

Helm balance is nice in existing set up.  I have the farrier marine deep F 32 rudder.  So plenty of rudder to work with.

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So raking your mast less should mean less weather/more leehelm?

Which could be (partially) balanced by the CE shift aft of bigger square head?

Good Luck....

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Yeah that is the thought.

just today I did a rough measurement of the mainsail head on a brand new Corsair 970 sport:  67”!

i suspect that the main hull, mast location, and daggerboard location are v similar to f31.  

Hope to sail on the boat tomorrow.  Should be interesting.

 

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On 5/31/2018 at 6:01 AM, Vincent DePillis said:

  I have one proposal that calls for a 6 foot head

Works well on my boat.

 

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F85SR, 

Carbon Mast of 41.5 ft  , Main has 6 foot head and 10ft foot. So head  is 60%of the foot and works really well.

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Any reason why a big square top wouldn’t work well on wishbone boom rig/freestanding masts? 

Pretty low aspect sails. Could use more power in light air  

 

5BD72469-E822-4A66-B98A-76D29AC9F75F.jpeg

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Not sure how your skinny mast tops would stand up to more area up there. Might just bend away and make things worse. You already have a pretty long top batten.

If you're slow in light winds you need a big code zero... uh the freestanding mast rotates doesn't it. Never mind.

Maybe a topmast like an old style gaff rig that you hoist above the mast! 

1797856279_cat2foldbighead.thumb.jpeg.29d19cf194c87aa5c72efdb231550a59.jpegst

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1 hour ago, Zonker said:

Not sure how your skinny mast tops would stand up to more area up there. Might just bend away and make things worse. You already have a pretty long top batten.

If you're slow in light winds you need a big code zero... uh the freestanding mast rotates doesn't it. Never mind.

Maybe a topmast like an old style gaff rig that you hoist above the mast! 

1797856279_cat2foldbighead.thumb.jpeg.29d19cf194c87aa5c72efdb231550a59.jpegst

I’ve got something like a code zero, but my continuous line roller fuller needs to be top down to work correctly, and it’s not, so it does not furl properly. I can still use the sail, and it works great on certain angles, but it’s a pain compared to sailing with just the two mains. 

Having loaded up the masts with this added on, top of the mast mounted “Genoa”, pretty hard while racing, I doubt the mast top would bend off much more than 6-8” with a larger square top. But I’m curious if the “vanging”  of the wishbone boom would be sufficient to keep the leech of a squaretop sail sufficiently tight. 

Especially say when reaching, or sailing deep downwind. There is basically no sheet tension pulling down, only back. 

Would the top of the sail bend off too easily with a wishbone boom setup?

35335292-DA86-43AB-9C97-140C1EEE80C5.jpeg

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  WylieCat 30's in SF have moved to fat head sails with good results. Moving the front of the wishbones higher up the mast will help add the needed leech tension.

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Vince,  I've got a 6' sq top on a 17' foot.  Electric mainsheet winch to crank 'er in.  (probably don't do what I should even so)  Mainecat 38.  Next main will have a 16' foot.

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