MacGregorSailors.com

NiceAft,
Agreed. This is likely much ado about nothing, imo. I haven't been worried at all, really. It's others who posted that the genny could be an issue with the M. Since I'm considering buying a 150, versus a spinnaker, I wanted to chase this thread through a bit. I'm convinced there's no problem.

I haven't seen any proof of accident caused by overpowering a genny on an M, and agree, that in strong winds I'd be furling her in anyway. My issue is more often light winds and I want more sail.

Also, I spend a lot of time running with the wind and would like more sail running wing-&-wing. (Due to wind conditions on Columbia river.) Does anyone use a whisker pole with their genny 150? Does anyone use preventers on their main boom?

On the topic of chainplate location on X vs. M, I just ran out and measured the chainplates on the M are mounted ~20" aft of the mast (measured at center of mast). Note that the chainplates are mounted down on toerail so at a height level with the base of the mast, this measurement would be less. Someone with an X can measure theirs.

I believe the chainplates are 8" aft of the

Bob

Nemo - if you are really worried just bring your topping lift down to an aft cleat and the mast cleat. If you are out in conditions which will bring the mast down with that there, then I would be worried about other things.

using the topping lift as a backspar IMO is futle especially if connected to the centered boom. The topping lift is generally fairly light and will streatch, the boom will flex (I assume you are using the vang and the traveler to provide the counter resistance to its lifting up) and the sum is more than enough to wipe out a spar. Change your topping lift to wire and add a short piece to go to a reenforced hard point on the stern if you want true safety IMO.
And yes some of us do use the vang as a poor man's preventer but you might want to look at this thread http://macgregorsailors.com/phpBB/viewt ... +preventer

KHE and tangentair.

I believe you have may misread this post and it's line of thought.

The phenomenon being addressed is that in heavier air, genny loads will cause the "M" mast to topple forward when sailing under a genny alone.

No one is able to show a case where this has happened.

At first glance, the theory seems to be very logical because of no backstay in the M design.

But, a no backstay design should logically indicate that the swept-back spreaders and stays are stiff enough, as is, to stop a forward falling mast failure when flying the genny alone in heavy air.

If that statement is false and the rig is not strong enough, as some believe, then the question to them becomes: What stops the genny from crashing the mast if the mainsail is also set, and the mast loads have now greatly increased in this heavier air?

If the force of a lone genny can cause a mast crash, then how do we square the results when we add in the force of the main into the mix?

Either the existing rig is strong enough, as is, for two sails, or else the main sail and main sheet act somewhat like a backstay.

If the main sail and main sheet are acting like a backstay, then an adequate topping lift can have the same effect.

No one has offered a case where the main and genny have crashed a mast in heavier air either.

Some of us conclude that the rig is strong enough as is.
The first level of insurance is to use an adequate topping lift as a pseudo backstay in place of a set main sail.
The second level of insurance is to wrap it up and go home.

I understand the offsetting loads of a full or even reefed main Vs 150 Genoa but I was under the inpression you were speaking of sailing with just the Genoa deployed and the main tied off or removed from the boom. And I do not know if the spars are or are not strong enough, my only point was that the topping lift streatch and boom deflection would be so much that it was of negligable value - a non-streach line or wire to a stern hard point would be of more use, something I considered once but as I am trying to get my topping lift to do double duty as a wisker pole line.... - haven't tried it yet but I have a plan I will tie on a second line to retrieve it also

...

Hardcrab, I agree with you on your one sail vs two sails argument. Keep in mind that even with two sails there is a breaking point. A guy in a mac classic on our lake found that point while racing.

Well the mainsail provides an aft-and-down force on the mast (by virtue of being attached to the boom, which is then attached to the mainsheet, which is attached to the boat) which prevents the mast from going forward under both sails...does that make sense??

When you're broad reaching or running isn't the main trying to push the mast forward? I agree there is some backward force due to the boom and main sheet, but I would think that is small in comparison.

BTW, I have heard that sailing with just the genny/jib is unwise on any fractional rigged sailboat (regardless of backstay), but I've taken that with a grain of salt.

Yes, makes total sense. A "phantom backstay" if you will.
Therefore, consider which of your listed items is the weakest link in that chain?
My vote goes to the sewn-seamed dacron sail.

King Kong could pull on the top of the mast and the end of the boom and rip that sail, turning the 90* mast/boom angle to a 180*.

He would have a much harder time if an adequate topping lift was in place. Sorta brings me back to my point.
IMHO.

JustSail,
That seems to be a strange place for the mast to fail. Are there hounds drilled at that height weakening the mast? It looks to be above the mast raising hound and yet below the stays hound on my M mast.

And yes, all designs have a breaking point.

Im not a mechanical but Im guessing it will take a lot of force to break a mainsail in tension - as in well over 300#

Points about mast forces on reach and run are valid - maybe it comes down to the magnitude of the forces after all??

Hardcrab wrote:JustSail,
That seems to be a strange place for the mast to fail. Are there hounds drilled at that height weakening the mast? It looks to be above the mast raising hound and yet below the stays hound on my M mast.

And yes, all designs have a breaking point.

The most common point of mast failure is at the spreaders, which is also where the lower shrouds attach. The aft-swept spreaders are pushing forward, stabilized by the lowers pulling aft, making that the strongest point of mast stability.

Any abnormal forces on the upper mast exert maximum leverage right at that midpoint ... just above the stabilty of the spreaders. Easiest way to view this ... rig forces make that midpoint into an unwitting hinge-point.

I think that the picture is actually a Mac-Non-Such

I sailed with just the genoa in 30 kts wind with gusts to 40+. No problems. To be fair, I have running backstays, but if memory serves me well, the outing I'm referring to, I didn't have the runners engaged at first. When it started blowing really hard, I engaged the windward runner. I suspect the M rig can withstand the genoa only setup with no issues, due to the swept back spreaders as already pointed out. The rig was designed w/o backstay, so one would think that it is adequately strong. But for those who want added protection, runners will do the job. Suppose you can't be overly cautious. Keep in mind, however, that multi-million dollar race boats get dismasted all the time

Leon