MacGregorSailors.com

Could it be possible that the geneo(150), while adding some power of its own, actually reduces the mainsail's efficiency instead of improving it?

A very good question, Mad dog, and the answer is yes, this is what happens with any jib or genny.

Amazingly enough, the physics of the mainsail/ jib couple has only recently been understood (since the 1970’s)!

Prior to that, it was thought that a “slot effect” between the two sails, in which the airflow accelerates between them, and the Venturi effect (or according to Bernoulli’s theorem) creates an increased lift on the mainsail. But it was found that, in fact, the airflow actually decreases between the two sails.

It turns out that there is actually a “circulation” of air around a sail (started by initiating vortices that trail from the leech of the sail), that is superimposed onto the airflow of the wind.

Now if you place the mainsail and jib together, the air rotating around the two sails will oppose each other in the space between them, and the airflow there will slow down. You can picture from this that the mainsail efficiency will be hindered by the presence of the jib (less airflow over its lifting surface where more airflow would mean more lift, just like an airplane wing), and it is by a factor of almost half.

But the jib will be benefited by the interaction, the airflow on its windward side (the “underside” of an airplane wing) will slow, improving lift, and the airflow on its lee side (the “upper” part of an airplane wing) will increase, also improving lift, and the two sails together are now functioning as one single large sail.

The mainsail also deflects the airflow so that the jib is able to point more directly into the wind without luffing, a known benefit of the sloop sail arrangement.

So the interaction between the mainsail and jib increases the efficiency of the jib by about half, at the expense of the main which decreases in efficiency by a bit less than half, resulting in a net gain in sailing efficiency.

Hope this answers your query. It is a condensed answer to a complex interaction, so if I haven’t been clear enough on anything, just ask and I will elaborate.

I love this kind of stuff because when you look up at the sails you can visualize and understand things going on that would otherwise be invisible.

- Brian.

mad dog wrote:Thanks contributors,
I think I've heard what I needed to hear and as I said at the start - I have no illusions about the 26M's sailing prowess.I just needed a bit more info beyond what I had read up until recently. But there clearly are bigger reasons for choosing the boat and I am aware of those. Having said that, the sailing experience it offers looks like being enjoyable.

Thanks,

Mad dog

I have no issues with my boat sailing up-wind as seen in this vid
http://s844.photobucket.com/albums/ab1/ ... 0_2494.mp4

J

Brian

I love looking up @ the sails from this point of veiw
http://s844.photobucket.com/albums/ab1/ ... 010093.mp4

J

Yeah John!!!

Seen that video a few times now, never get tired of seeing it again!

(Especially in the winter).

Looks like yer tryin to waterski off the front of the boat- ya crazy Canuck!

See ya in TO. -B.

mad dog wrote:Thanks dlandersson - that is encouraging. Finally, I have something to go on.
Anymore performance data hounds out there with more to tell me?

She's no Blue Nose but i am happy with her & have since added 12ft of genny track on the cabin top deck + alot of other hardware
http://s844.photobucket.com/albums/ab1/ ... 010090.mp4

J

Captain, that clipper rig is one of the most impressive things I have ever seen.

My favourite sail is the spinnaker up to probably 15knots of wind but after that I get yelled at too much, rarely if ever try and sail into the wind or tack unless the motor is down as well, if there is a fast running tide or wind coming from where I want to go will wait with either the sail or motor, especially if the fishings good or I have a book in a nice sheltered spot.
Good thing about the macs is there are options, when we were looking at buying had a test run sailing and after heading up a straight we needed to get to port before dark, there was a motor boat and a yacht trying to get in also againt tide and wind, the yacht was losing ground and the little motor boat? was left in our wake, SOLD, didn't buy that boat because it didn't pass the wife test but bought a new .

It's important to point out that no 26 foot boot has a hull speed higher than 7 knots, and the Mac is one of the very rare boats capable of potentially doing better than hull speed when running.

After two years spent learning to sail the Mac, I can reliably get half of wind speed on any point of sail after 50 degrees to true wind. But its not easy: this is not a "hoist the main, crack a beer" sailboat: it must be actively trimmed to sail well.

Keeping up speed means managing the mainsheet in hand, trimming the mainsheet for the correct belly, keeping heel to 20 degrees, keeping the sheeting correct for windspeed by furling and unfurling the genny, and trimming the daggerboard depth for the point of sail. I also will usually pull up the windward rudder. You have to be on top of the helm, and keep rudder angle below 30 degrees at all times, even while tacking, unless your intent is to stop the boat. When you tack, you have to back wind the jib until the new course is set. Because of the nervous helm, single handing pretty much requires an auto helm--these boats really ought to be tiller steered.

It's a difficult boat sail well, which makes it all the more rewarding when you do.

I guess it's all relitive to your point of view, your way sounds way to much like work to me. I always figure i'm doing some really fine sailing when i don't have to touch anything but a beer for at least an hour or so.But admittedly you'll get there 30 minutes before me for sure(for whatever thats worth).I guess i'll have to remember to bring extra beer to last the slower speed i'll make.

I'm with you Ray but if I'm in a hurry (rarely) the 50hp sail gets me there on time.

Mastreb,
Many sailors, like me, could use detailed guidance how to achieve the best sailing experience with our boat.
Did you ever think of publishing your knowledge as "How-To's" in either single video clips or even a disk to be purchased
I'll buy one

Obelix

Im a fair sailor and have had my M model for almost 2 years and sailed it quite a bit. My average speed real world is around 4-5 knots at 15 degrees heel in nice conditions where its not too bumpy. Real world to me means, conditions and methods that one (me at least) is likely to tolerate day in and day out, for weeks. A mad dash is fine for an afternoon. I am, however, not going to blast around being uncomfortable at an extreme heel or being so picky about sail setting and heading that any crew I have rebels! for any longer then that. The tops I have see from my boat is 6.5, in pretty breezy conditions slightly off the wind. My boat is a few hundred pounds heavier then a stock M, plus I have all my supplies needed for staying on the boat for an extended time (But not fridge, over, pressure water and other heavy stuff) Since I would buy the boat again in a minute, I am happy with this speed, and many other things that you dont know your getting, manner-wise, with this boat.
(It will sail itself happily with just the helm locked, half the boats I have had would not do that, it will sail across shoals reasonably well with NO board down at all if you learn how to do it, it sails fine with just the main, and remains in control though slow, if you have to reef it )
I could probably come up with a boat that would sail and power better, but not that would go on a trailer in all 50 states with no permit.
That extra foot of beam makes a big difference.
Ix

Having gone from a standard jib to 150 Genoa c/w furling....well mmmmmm......now decided thats great but will set up the standard jib again cw furling and move the genoa forward on a bowsprit

Some guys sail to eek every .1 of a knot out of their boats, but I'm the sort of guy who likes to point the boat in the general direction I want to go, put a bungee on the helm and go sit on the foredeck.

Here we are last week, cruising accross the bay with the poor mans autopilot at the helm, I dont think we were going that fast, but who cares, this is our kind of sailing

My last trailer sailer was one of the more popular ones here, but I could not get it to do this very well.


Excuse the cockpit mess. I was too busy lying on the foredeck, and eating the fried egg and cheese samwiches the missus was passing me up for breakfast.

Hey now, I'm not always out there running around on deck like a chimpanzee trying to eek out the last .1 knot of speed and screaming orders at the crew...

That's only upwind

Obelix--I've actually learned (and posted) everything I know about sailing a Mac from various forum posts here. There's an enormous amount of collective wisdom here and I wouldn't dream of representing it as something I've invented or discovered. I'll start a unified thread on it however.

Frankly, there's there's really not all that much to sailing a Mac well, it's more just a bunch of mistakes not to make. I think the difference for me is that I'm a big believer in data and instrumentation, so for example, when I'm stuck at 4 knots, I'm not scratching my head wondering if I'm doing anything wrong, I can look at my wind instrument and tell that there's just not enough apparent wind speed to do any better or that I'm facing a three knot current. For me, knowing why I'm not making speed is critically important, otherwise I'd just start trying different things that didn't work and then give up.

A lot of people are more about the pure experience of sailing, and not worrying about what speed they're making. I think the "no instruments and no worries" approach is just as valid if not more so--it's just doesn't happen to be my thing. The Admiral does order me to relax quite often