bscott wrote:Judy, it's nice to have a professional rigging person aboard--thank you. Thanks for the heads up on the use of hound toggles--any pics?
Also, most of the Macs sold with furlers were CDIs with #6 luff tape. Since all my previous boats had excellent Harken 00 Flex. I chose the CF700 because it was the only high quality flex furler that accepts a #6. I agree the CF500 is more than adequate but by the time I converted my sail(s) to a #5 tape, I was close to the price of the CF700. Maybe you can convince Schaefer to offer the CF500 with a #6 tape.
Bob
Hi Bob,
1.) Here below is a picture of a mast hound (Ronstan), which is a good way to attach a forestay to a mast. (because the fasteners and the mast wall are loaded in shear, rather than stress)
2) Here below is a picture of an "eye and jaw" toggle which should be used at the top of the forestay when a roller furler or luff extrusion is present. Toggles can be eye-jaw, double-jaw, or double-eye -- what ever is needed for your configuration. The important concept is that the toggle functions as a "universal joint" at the top of the forestay, which relieves lateral forces where the wire rope enters the swage or fitting.
With a "universal joint" at both the top and bottom, both enda of the forestay are free to move in translation on three axis, plus rotate on two axis, for 5 degrees of freedom. The only constraint is that it cannot rotate along its long axis -- which is a good thing or else the wires would unwrap.
With so much freedom to move around, the lateral forces on the headstay don't get concentrated on the swage, breaking strands from metal fatigue. Rule of thumb, IIRC, is that each broken strand reduces breaking strength by 5%, multiplicatively.
AHA!
It all makes sense now, doesn't it !?!?! With furlers, we find broken wire strands at the top whenever we cut corners and don't install a toggle. We don't find broken strands at the bottom swage... because all furlers have toggles integrated into the drum at the bottom end!!!
cool. Give yourself an A+ if you got that
3) I wholeheartedly agree with you that it would be *Much* better if Schaefer made the CF500 so we could use a #6 tape. It makes converting to the SnapFurl more expensive than it should. It sure does make sense to me, from a marketing perspective.
But .... putting #5 luff tape on a Mac26 150% genoa shouldn't cost $400 (the difference in cost between a CF-500 and a CF-700). So the CF-500 remains a viable option.
Regarding the cost of converting from #6 to #5 luff tape: I'm making an informed guess here - It shouldn't cost more than $200. I'll double check on that with my local Hyde Sails loft manager; he'll know. 1.5 hours of labor is more than enough to cut the old luff rope off and sew the new tape over it, at $70-$100 per hour, depending on where you live.
Sailrite sells everything you'd need for under $75: #5 tape, UV polyester thread, seam stick (two sided sticky tape), needles, etc.
You could do it yourself with a good sewing machine The labor part is not complicated. Cut the old luff rope off, just aft of the cord, using a heat knife to keep the edge from fraying. (A $20 soldering gun with a $5 hot-knife tip is what a lot of sailmakers use). Put the new luff tape over the old, using seam stick tape to hold it in place, and stitch with zig-zag.
Another very cost effective alternative is to sell your old genoa with the #6 tape for $100 or $200 less than you paid for it (if it's in good shape), and order one with a #5 tape. That's what I usually recommend to my customers who want to upgrade from a CDI to a SnapFurl CF-500.
For example, I sell a roller furling genny with a #5 tape for the 26M in 6 oz High modulus cloth by Challenge, including a UV cover, for under $700, about the same price or less than the lofts who cater to Mac owners. That's not the cheapest price around, but In my professional opinion, all-purpose Roller Furler genoas need a stronger cloth and extra reinforcements than you'd need for a light-air genny. If you roll it up and use in in high winds as a working jib, and it's not built to take the extra strength of the wind, it'll get stretched out of shape after just a couple of hours of use in high winds.
4.) A little sail-design engineering about roller furling genoas follows:
Sailcloth is highly technical stuff. there's a lot more to it than how much it weight. Equally important is how we align the load bearing yarns to bear the stress loads we place on the sail.
Take a look at the Roller Furling Genoa below. It has a large elliptically shaped reinforcement patch along the foot, to spread out the load at the "tack" when you furl it up. The dots are furling marks corresponding to reducing the genny to 70,80, or 90% of the LP dimensions
The reefing area calculations work thusly:
A 150% genoa for a Mac26M has roughly 185 square feet of area.
@ the 1st reef mark: it's reduced to 150 square feet, or 81% as big as the full genny (.9 * .9= .81)
@ the 2nd reef mark: 119 square feet, or 64% as big as the full genny (.8 *.8 = .64)
@ the 3rd reef mark: 91 square feet, or 49% as big as the full genny (.7 *.7* = .49)
A working jib for the Max26M is approximately 125 square feet. Compare that to the genoa when it's reefed to the third mark -- 91 square feet. When you reef the genoa to the third reef mark, it's much smaller than a working jib -- it's being asked to perform in the same conditions as a storm jib.
When you're sailing in winds strong enough to need to furl to the third furling mark, it is down to the size of a storm jib. The sail needs to be very strongly built if you're going to subject it to such high winds. If you use the factory genny, made with a 3.8 oz basic cruising dacron, it's going to get "blown out" in an hour or two..
6.) How much power does a storm sail generate compared to a big genoa? The surprising answer is that the storm sail generates more power than the 150% genoa , when used in typical, appropriate wind conditions.
Example:
Let's assume we have a 26X genoa with 180 square foot genoa in winds of 8 miles per hour. let's assume the force is 10-units per square foot of sail area .
Now, how about a storm jib in winds of 24 miles per hour? The force generated by the wind is is proportional to the velocity of the wind squared. The wind is 3 times stronger. The stress on the sail cloth of the small jib in high winds is 90-units of force per square foot of sail area. that's a lot of power being generated.
But what really matters is how the shape of the sail is distorted by the stresses and where the stresses are transmitted. In part, the stresses on the sail get transmitted to the corners, which causes distortion at the corners. Another part is that the stress causes distortion of the sail in arcs from the corners, along the luff and leech and, to a lesser extent, the foot .
If the sail is reefed to 50% of it's original size, but the lift being generated psf has increased to 9 times the original, the stress on each corner of the sail has been increased by a factor of 4.5. If the furled sail is made of light weight material, the distortion (strain) will be too far past the sail's limitsof resistance, and permanently distort the shape.
Both cloth and high-end construction features add to the sail's capacity to resist stretching. That's why the extra reinforcments along the foot of the reefing genoa are just as important as the choice of cloth.
With 4.5 times as much force on each part of the sail, you need to engineer it so the yarns in the cloth are properly aligned to take the abuse, and the cloth is 4.5 times more able to resist stretching
6. stretch is inversely proportional to the modulus of the material times the cross sectional area of the thread...
sail cloth woven from high modulus yarns stretches far less than sailcloth woven from less expensive yarns.... adjusted for many other factors such as the amount of yarn crimp, thread alignment, tightness of weave, resination, .... etc... etc... whew.... it gets complicated.... yada, yada, yada
Fair winds,
Judy B
PS. It's been about 20 years since my last mechanical course, and I'm sure I've made a few mistakes in terminology, and maybe the math. If I've used the terms wrong, I hope a knowledgeable person will jump in to correct my terminology. Thanks.
that can go fast. I also witness a few 
and the 
Oh, the headsail is now an option whereas when I bought mine in 2003 it was standard fare. The mods section on this board is testament to how unfinished these boats truly are.
And you didn't even get around to the CE of a reefed head sail