Hi Henry, If I do all the geometry, it works out that measuring from the forestay/deck intersection to the front of the mast is off from the true J measurement by about 1.5 inches on a Montgomery 17. As a sailmakers, we send out a form that instructs the customer how to measure their rig for new sails, with enough measurements for us to calculate all the measurements we need to fit sails accurately. The customer doesn't need to understand the geometry behind the forms. It's high-school trig and geometry, with a geodesic twist thrown in for fun because sails are 3D shapes, not 2D. Good think I loved geometry and trig in school. :-) The 3D twist is why a 2D drawing showing the three edges of the sail don't accurately foretell what the LP of the sail truly is. As a result, Jerry's sailplan drawings, in 2D, which shows the geodesic edges of the sails, inaccurately the LP. Don't worry about it.... you sailmaker will take care of it for you. :-) Judywww.hydesailsdirect.com From: Henry Rodriguez <heinzir@gmail.com> To: "Judith Blumhorst, DC" <drjudyb@blumhorst.com>; For and about Montgomery Sailboats <montgomery_boats@mailman.xmission.com> Sent: Sunday, May 29, 2016 3:03 PM Subject: M_Boats: Genoa size... Thanks, Judy, for the great information. I OWE YOU A BEER! I went out and measured and sure enough it is 6'7"! I guess I was overthinking it. I thought that with the cabin in the way I couldn't get a true right angle to the mast and so the measurement wouldn't be accurate. But I moved my tape measure around and found that at the most I might be off an Inch or so but nowhere near the 6+ inches difference suggested by the 7.16 J posted on the MSOG site. Tim's response below seems to indicate that that is the measurement for the tall rig. He just measured his at 7'1-3/4" which is right on. Tim, thanks for the response and for helping clear this up in my mind. Once again science and technology overcame fear and superstition! Henry On Saturday, May 28, 2016, Judith Blumhorst, DC <drjudyb@blumhorst.com> wrote: Henry, if you want to know what the J dimension is on your boat, just measure it! I'd be willing to bet you a beer that it's within an inch or two of 6'7" , based on my experience with measurements taken from a bunch of M17's. I have a copy of Jerry's original sailplan drawings, probably the same ones that Gary has. A couple of years ago, Jerry made copies and sent them to a folks who needed them in order to support the Montgomery owners community . As a sailmaker, I was lucky enough to be one of the recipients. The plans indicate that the J dimension is 6'7". All good sailmakers build sails to the actual measurements of the rig. My customers have confirmed the "J" dimension several times, +or - an inch. So I'm placing my bet on 6' 7" = 6.58' . The other number is probably just plain erroneous. For hank on headsails, the most popular headsails are the 109% and 150%, but a 130 or 35 works fine too. The toe rail tracks on the boats built by Jerry can accommodate any size you want, with whatever clew height your sailmaker recommends for your particular purposes (ie, windward-leeward racing vs cruising including reaching). The genoa tracks on the more recently built Bob E built boats are long enough to accommodate just about any size genoa as well. For cruising boats with roller furlers, 135-ish is the most versatile for most cruisers, because it still has a good shape when reefed to about a 110%. But if you typically sail in very light winds, then a 150% might be better. If you sail in heavier winds, maybe a 109% is the best. For super light winds, a Cruising Code Zero (on an itty bitty free-flying furler like the Ronstan Series 80) and tacked to the bow pulpit would be awesome. It's much bigger and more powerful than a 170 drifter - it's about twice as big as a 150% genoa! It will sail as high as 55 degrees true wind angle (30 degrees apparent), so you can go to weather with it. For sailing downind in light air, a Cruising Zero won't sail as deep as a Cruising Asymm, but you can still jibe your way downwind sailing as deep as maybe 135 or 140 degrees, depending on wind strength. It's so big and powerful that you can get the boat going 2.5 kts at a true wind angle of 135%, in 3 knots of wind. A drifter can't do that. You can play around with apparent wind angles and boat speeds at http://www.hydesailsdirect.com/Articles.asp?ID=278 . The take home message is this: If the boats is fast enough, the apparent wind angle is going to be a beat, even if the true wind is aft of your beam. Judy Bwww.hydesailsdirect.com From: GILASAILR--- via montgomery_boats <montgomery_boats@mailman.xmission.com> To: montgomery_boats@mailman.xmission.com Sent: Thursday, May 26, 2016 10:40 PM Subject: Re: M_Boats: Genoa size... Henry, I have a rigging drawing dated '1973' that shows the 'J' dimension as 6'-7" - you are fine at that number - that is approx. .04" less than 'J' - as my grandson likes to say (20 mo) "OOhh myy! We can ask Jerry if the 7.16' is for the flush deck?? Have Fun Go sailing. GO In a message dated 5/26/2016 8:33:50 P.M. US Mountain Standard Time, heinzir@gmail.com writes: I have seen two different figures published for the "J" measurement of the M17: 6.58 ft and 7.16 ft. I'm guessing that the longer one is for the original (and newest?) boats that have the forestay pinned at the tip of the bow and the shorter is for the newer style boats that have the forestay pinned back from the bow about 6". I think I ordered sails using the shorter "J" measurement and shortchanged myself! My 150 is actually 137 and my 135 is closer to 125! Henry On Thursday, May 26, 2016, <swwheatley@comcast.net> wrote:
Genoa size is luff perpendicular (LP) expressed a percentage of the J measurement. LP is the length of a line drawn from the clew to the forestay intersecting the forestay at a 90 degree angle. The J measurement is the length of a line from the forestay pin back to the mast intersecting the mast at a 90 degree angle. On an M17 it is an imaginary line because the mast doesn't actually extend down that far down. There is some conflicting info out there but I believe the J measurement on an M17 is approximately 6 1/2'. Maybe someone else can chime in with the exact number. Measure your LP and compare it to that to determine what you have. For example, an LP of 10' corresponds roughly to a 150 genoa.
If your genoa is an older hank-on, it is probably a 150. If it is on a roller-furler, it might be a little smaller. I run a 135, which is a popular size for a roller furling genoa.
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From: "Jazzy" <jazzydaze@gmail.com <javascript:;>> To: "For and about Montgomery Sailboats" < montgomery_boats@mailman.xmission.com <javascript:;>> Sent: Thursday, May 26, 2016 2:41:37 PM Subject: M_Boats: Genoa size...
Hi all, was just pondering my tired sails. How does one know what size Genoa is installed? Thanks!
Couple of updates...
Stoked for Mem Day...trailering to Pleasant Harbor Marina where we have a slot for a night, full amenities and a motor couple coming to join the festivities. Should be good pirate fun.
Last week I took my friends son out. He's 18 and had never been in a sailboat, we spent a few hours tooling around the harbor, I worked him hard on terminology, parking, stopping at random buoys, starting and stopping the motor, approaching objects slowly... boy was he surprised when I hopped off and told him to take a solo lap at the end of the day! Hahaha. Reminded me of flight instructor days. His dad told me afterward he couldn't stop talking about it. Now dad wants to go. Maybe got us two new sailors... do share your boats and teach some youngsters! What's a dock ding or two compared to passing the torch?? Hahaha. A bonus was that I got to see my boat cruising around. They are quite graceful and salty looking when off their trailer aren't they ? ;) Much sexier than the Harbor 20 that was buzzing around.
Found a slip for 110 a month 8 minutes from home...sooo tempted. Comments? Is the bottom going to hell in a hand basket?
Jazz
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