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Masthead rig

Dec 7, 2018
105
C&C 27 Mk V Vancouver
w/a J of 11' and E of 9'. What happens to helm etc. if the E was extended to, say, 10' 6"? Or even 11'?
 
Dec 7, 2018
105
C&C 27 Mk V Vancouver
So, on another forum someone posited that increasing foot length on masthead as opposed to frac rig would have less effect with an increase of ~20% being optimal.
Hit me back.
 
Oct 22, 2014
13,435
CAL 35 Cruiser moored EVERETT WA
It is the Foot and the Leech that get extended on the fore sail. As it grows it goes from a 100% Jib to a 115, 135, 140, maybe even a 155 - Genoa. Depending on the point of sail and the strength of the wind this might enhance your experience or overwhelm the boat.
 
Dec 7, 2018
105
C&C 27 Mk V Vancouver
I'm not talking fors'l, it's the main being discussed here.
Increasing size of main w/concurrent decrease in size of genoa to keep CE relatively same.
 
Oct 22, 2014
13,435
CAL 35 Cruiser moored EVERETT WA
That makes sense. I was considering just the J dimension.
 
May 17, 2004
2,827
Beneteau Oceanis 37 LE Havre de Grace
What exactly are you trying to achieve by lengthening the boom and reducing the jib? If the boat has a backstay you might have problems there. I’d be surprised if adding size to the back of the main gave too much more lift, but it will certainly add to weather helm. And making those changes is going to require a lot of sail recutting and a new boom, which wouldn’t be required simply carrying a larger Genoa.
 

DArcy

.
Feb 11, 2017
881
Islander Freeport 36 Ottawa
Increasing foot length doesn't give you as much gain in performance as increasing luff length. Taller, higher aspect ratio sails are more efficient than shorts sails. We want high lift to drag ratios for efficient sails. This is influenced by sail shape but also by chord length which is proportional to foot length. The longer the chord, the longer the air is attached to the surface as it flows over it. Skin friction drag slows the air down, this increases drag so the lift/drag ratio drops.
If you are racing PHRF they don't take any of this into account for modifications to your base rating but a change in sail area is accounted for. So increasing foot length will lower your rating disproportionately to your increase in performance.
Now if you can increase luff length, you can cheat the system ;)
 
Dec 7, 2018
105
C&C 27 Mk V Vancouver
Can't afford a new mast, even a used one is too much f*ckery. Can afford a longer boom. Will extend crane to facilitate a "fathead" main, which will add area up high and should clear up some room to increase luff slightly. Will go 20% longer on foot. Shouldn't affect helm much if at all but want to reduce heads'l size anyways to max 140 for easier singlehanded tacking.
Bigger main more barndoor d/w.
 
Jun 2, 2007
377
Beneteau First 375 Slidell, LA
Before you go to a lot of trouble, maybe you could talk to your local sailmaker and see what he thinks.
 
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Jun 25, 2004
1,087
Corsair F24 Mk1 003 San Francisco Bay, CA
So, on another forum someone posited that increasing foot length on masthead as opposed to frac rig would have less effect with an increase of ~20% being optimal.
Hit me back.
In general, I don’t agree. Without knowing the specific boat, there’s no way to say that 20% is optimal.

In general, Adding 20% to the foot and just the lower part of the sail won’t have much effect, I think. It’s not very efficient down there. You’re not going to get a lot of bang for the buck there, I fear.

If you want more power and speed downwind, the easiest way to do that is with a spinnaker. That’ll add 500-700 square feet of sail area on a boat with J=11’.

What boat are you talking about? It makes a difference.
And, what problem are you trying to fix on what point of sail?

What percent increase in mainsail area will the proposed changes cause?

Adding a crane would not let you build a “fathead main”. A fathead sail has a much bigger roach factor than what you propose to do. A typical fathead sail is used on a rig without a backstay, and typically adds 20% or to the area of a sail compared to a pinhead. Think Hunter B&R mainsail without a backstay, or Catamaran without backstay. A huge roach with full battens to support it.

Adding a crane and a couple of inches to the head won’t add much sail area to a boat with J=11 and P= 9.

Judy B
Retired sailmaker
.
 
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Dec 7, 2018
105
C&C 27 Mk V Vancouver
So there's some confusion w/vernacular here...
1588535793654.png


I know the airs up high so I posit building a "fathead" as above w/max roach to clear backstay w/overlap.
Will move CE back (and prolly not enough to alter helm dramatically) but I singlehanding & want tacking joy so slightly smaller heads'l moves CE forward.
1588537041983.png

Above is is moar powerful than pinhead, no? Crane could up to 12-15".
20% was a figure some other sailmaker from some other forum said was what they added as a rule of thumb to old IOR boats. That ain't set in stone could be less. Curvature of leech has to be pleasing to the eye.
Here's a drawing of my intended victim...
1588537547769.png

Even just doubling the length of that crane would make lots of room for overlapping roach carried to intersect boom at same angle how much longer would it be?
 

DArcy

.
Feb 11, 2017
881
Islander Freeport 36 Ottawa
I hear you on tacking a big genoa. I used to single hand my C&C 27 a lot and would only hoist the 165% if I was sure I wouldn't be tacking. I normally cruised with the 115% working jib, even in lighter air.
I would suggest you spend your money on an asymmetrical spinnaker with a sock or furler rather than everything involved with fitting a bigger main. Overall you will get a much bigger gain in performance.
Practice in light air, you will probably find you can manage it ok on your own. Once in the sock or furled you can just leave it there unless the wind is going to really blow.
 
Jun 25, 2004
1,087
Corsair F24 Mk1 003 San Francisco Bay, CA
Yes, If the crane you add allows you to fit a mainsail with a head girth that’s 20 to 25% of the foot, then you’re in fathead territory. But consider that you might be limited in your ability to add area by a lack of stiffness of the boat. Without “excess” righting moment to spare, you can’t safely add area at the top of the sailplan. Adding area up high affects heeling much more than area down low. Heeling will definitely load up the helm.

How stiff is the boat? Sailboats with that much area up high in the mainsail tend to have deep bulb keels or be wide-beamed multihull, with oodles of righting moment.

IRC/IMF/ORC/PHRF rules limit the head girth of the main to no more than 4% of the foot.

What is the P of the rig? I’ll run some area calculations for you, with typical roach curves for a cruiser, racer, and fathead mainsail.

But again, what performance are you hoping to improve with the new sailplan?

IMG_0597.JPG
 
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Dec 7, 2018
105
C&C 27 Mk V Vancouver
Adding area up high affects heeling much more than area down low. Heeling will definitely load up the helm.
PNW is a light air venue. Reefing.

What is the P of the rig? I’ll run some area calculations for you, with typical roach curves for a cruiser, racer, and fathead mainsail.
That's very kind of you to offer but, point is moot. After viewing boat's condition & mooring situation, not going forward with purchase.

But again, what performance are you hoping to improve with the new sailplan
Not so much as improve, per se, but change. As in increasing power of main while reducing size of fores'l to facilitate singlehandling of both. Ancillary gain is more projected area from main downwind.