Tried out a bit of sailing upwind,

[KC375]

Originally Posted by Mr B

So you have suddenly become an expert in driving Cats now,
If you knew any thing about it, Cats dont require a main sail to sail,
Except up wind,
I think my sail makers knowledge far exceeds yours in relation to Cat sailing,,
A Genoa is all thats needed,
Plus Im not interested in any comments you may make,

Nuff Said,

Mr B
If you have access to a sailmaker that would probably be your best start for advice on trimming your sails. As another poster suggested time on your boat with your sailmaker coaching you may be the best way to master your equipment.
Internet discussions are not really a great place to cover a wide and nuanced topic like trimming sails or sailing approaches in general. In most cases the answer to a question will be “that depends” Internet discussion of how to sail are about as effective as learning the violin that way...lots of words but not much progress.
It is true you can sail downwind without the main...in fact you can “sail” downwind with no sails and no centerboard just the wind pushing the boat. In most situations you can sail downwind faster and with more control with the main up...the closer to a dead run and the stronger the wind you may be as well off with just a spinnaker or a genoa. On a cat sailing very deep wind angles the value of the main false for a number of reasons. If you are not poling out the genoa or spinnaker then the main will blanked it so effectively only one is doing any work. On most cruising cats the stays are well aft of the mast which limits you ability to let out the main to its optimum angle for deep downwind sailing.
As you start to sail closer to the wind...say above a broad reach then the importance of your centerboard increases...your centerboard is to the water what your sail is to the wind...and as important for your forward progress through the water. Once you are reaching or sailing higher you are being driven not by the wind simply pushing you but by smooth flow of wind over your sail(s) creating aerodynamic lift and smooth flow of water over your centerboard creating hydrodynamic lift. You want to adjust your controls so you generate the maximum lift for the minimum drag created.
As your centerboard moves through the water it creates a force that points back and to windward. While the wind on your sails creates a force forward and to leeward. The leeward force of the sail is mostly cancelled by the windward force of the dagger board...you will have some net leeward force producing “leeway”...moving slightly to leeward of the direction of the boat. Similarly you hope the forward force of the sails exceeds the rearward drag or force of the centerboard (and the rest of the boat being pulled through the water).
Most boats are designed so you can have a “balanced rig” (or slightly windward helm but ignore that for now). A balanced rig means the windward force from the center board lines up directly below the leeward force of the sails (or said otherwise the center of lateral resistance (CoR) of the centerboard is directly below the center of effort (CoE) of the sails).
If you have only the genoa up on a boat designed to also use a main then the center of effort of the sail will be well forward of the center of lateral resistance of the center board...imagine a rope pulling on the middle of your genoa pulling straight to leeward and a rope in the middle of your center board pulling straight to windward...the effect of their not being balanced fore and aft means the wind and the water will be trying to pull your bow to leeward, turn your boat to leeward. Within a certain range you can simply counter act that by steering. Any time you use the rudder you effectively apply a brake...so having to continually to steer to windward to compensate for an unbalanced rig slows you down noticeably and limits how close to the wind you can sail. By hoisting and trimming the main – all else equal, you will line up the CoE and CoR. You will have greater drive. You will eliminate the braking of the helm constantly over. You will find it easier to maintain course. You will get to windward much faster.
As you steer down from a beat the effect of the misalignment of the CoE and CoR diminishes until when you are dead downwind – the CoE and CoR are effectively fully aligned (rope on sail pulling forward rope on centerboard pulling back – no twisting. In fact below a certain angle the drag of the center board exceeds the benefit of lift (if any) so you raise the boards.

[Ken Fry]

Originally Posted by Mr B

The wind beam on, is usually the most I go, Being a Cat, I get slammed under the bridge deck and its not pleasant with the wind on the nose, ,

I couldn't find any polars for your boat, but I'd guess that she'll sail best upwind at about 55-60 degrees off the true wind (with the apparent wind being maybe 40-45 degrees). The leeward board needs to be down all the way to make any reasonable progress to windward.

In a long-distance cruise, you will likely find that you won't have enough fuel on board to avoid having to sail to windward. Also, there will likely be a time when the engine has failed, and you are drifting toward a lee shore. Being able to sail away from the rocks can be a comforting thing.

In less than 10 knots of wind, even a boat that is famous for slamming will not slam, because the waves are not sufficiently high. These light-wind conditions can make for very pleasant sailing, and on a warm light-air day, sailing downwind can be uncomfortably hot, while sailing upwind can be accompanied by a nice breeze on your face.

Given the Gemini's substantial windage above the water and loads of wetted area below the waterline, the power of both sails working together is required for making progress against the wind. Having both sails working also keeps the boat better balanced, so less rudder is used, meaning less drag. So you need to use the main and genoa to sail to windward in any meaningful sense. To reduce sail area, reef (furl, etc) reduce them both.

There are some boats that can sail on either main or genny alone and still sail not too badly, but the Gemini is not one of those. Overloading will make things worse: less progress, more slamming.

Upwind, the main is self-tending, so adds essentially nothing to the workload.

So, I hope you spend some time learning to sail to windward efficiently. It is at least half of what sailing is all about.

[NormanMartin]

Just logged in to this discussion. My pal, John, has a Gemini 105mc as do several other friends of his. Those guys always talk about the Gemini user groups and forums. If you don't know how to find them, PM me.

As a sailing instuctor since 1985, I also suggest plain old sailing school. You will learn a lot and make some sailing friends (or not, your choice). Generally, they more you know going into basic sailing the more you get out of it.

The sail maker sail evaluation is good if you can arrange it.

Off topic, John and I joke that my boat is just one of his hulls. It's all good.

Norm
Cape Cod, MA

[seandepagnier]

I suggest you don't use the genoa for docking. It is more controlled to use only the main on second or third reef.

Just drop the main sail when you have the momentum to reach the dock. It is possible to dock under sail in most cases with many boats in most conditions. Adding oars and "most" becomes "almost all"

[Cadence]

Originally Posted by boat_alexandra

I suggest you don't use the genoa for docking. It is more controlled to use only the main on second or third reef.

Just drop the main sail when you have the momentum to reach the dock. It is possible to dock under sail in most cases with many boats in most conditions. Adding oars and "most" becomes "almost all"

Great. I've had someone drop the main with just the right momentum. Skill or dumb ass luck after two jibs in the marina? Went into the slip and stopped.. Probably the later.