genoa overlap

[matoi]

When sketching a sailplan, how do you know what is the proper amount of genoa overlap on a sloop?

Thanks

Mato

[Crag Cay.]

The 'LP' of the genoa is gauged to be a percentage of the boats 'J' measurement.

Anything over 100 - 110% is thought of as a 'genoa', with the overlap going up to 165% on occasions in the old IOR days.

On a cruising boat a genoa with a LP of 135% and a clew cut off the deck is a very workable sail.

[jehardiman]

On the sail sailplan you should draw several proposed sails, but in real life the owner will buy the sail they feel they need. As a designer you should draw in a couple of headsails and check the balance with the main and main under the reefs. I usually draw in and work the numbers for a #3 storm jib, a #1 Jib, a 110% "Decksweeper", a 135% "High clewed reacher". and a 150% "Drifter".

Clew location is going to depend on deck hardware layout, generally you want the clew to be on the line between the sheetblock and perpendicular to the forestay.

[matoi]

Thank you both! I will put up my schemes when as soon as I get to finish them, and ask for your opinion again.

Best wishes,

Mato

[Stumble]

One of the things you need to adjust for is where the boat will be sailed. Here on the Gulf Coast of the US a 155% is almost a necessity due to the light winds we see 10 months out of the year. Of course moving to the North Atlantic changes this.

My normal sail inventory is

155 -#1 Deep Cut Drifter
148 -H#1 Heavier material / flatter cut
115 -#3 Flat cut
75 - #4

Though we rarely use the 3 or 4 since winds above 20 kn are very rare.

The 'normal' roller furling sail is somewhere around a 135, with a high cut clew to make tacking easier. This of course normally requires a slightly longer track than a deck sweeper 135 to keep properly trimmed.

[matoi]

Hi Stumble!

Here in Adriatic we most often have either too much or too little. The combination I got least to use is full main + genoa. Almost allways when I sail out with the genoa up, I soon need to replace it with the jib, or the wind dies out completely. Some kind of Murphey's law I suppose.

So the idea of having a 150% drifter is quite interesting. Is it possible to sail upwind with such combination? Does it cause a lee helm in your experience?

Thanks, best wishes

Mato

[Stumble]

Well for a true drifter say <2kn of breaze we use a high clew 110% made from .50 oz nylon. Basically this is like a code zero and is just used to try and keep the boat moving when the wind is very light. By keeping the sail so light and the clew higher it makes it easier to keep full in very light air. The downside of course being that at 5kn you just blew out a sail and have to get it replaced.

The light 155 is for winds between 2 and 12kn, and no it doesn't create lee helm. Since the power generated by the sail is so small due to the minimal amount of wind. Sure if we were to try and carry it up into the 20kn range it likely would. That is if the boat didn't just fall over on its ear.

One thing to remember is that most boats will do at least some racing where the rules to some degree determine the size of sail you can carry before taking a penalty. Around here that magic number is a 155% which is why everyone uses that as their largest headsail. Since anything smaller doesn't net you any advantage, and in light air the bigger the sail the better. So I would take at least a passing glance at the rules for where the boat is going to be sailing to make sure there aren't any particular breaks that need to be kept in mind.

For a lot of PHRF fleets for instance the break is one rateing up to a 110, then another break above 135, another at 155, and the last at 168. Though your rules may vary.

[fcfc]

It depends on racing rules.

In the old days of IOR, you could go up to 150% genoa for free, any other way to add sail surface was penalized.

Now, for "open" boats, the current fashion is to use only 110% genoa (solent). The clew of the genoa is inside the shrouds. This allow full width spreaders, and chainplates are directly on the hull plating. Both are a big structural gain. Lighter mast, less hull structure.

The sail surface is gained by other ways. Very tall mast, big mainsail roach etc ...
The SA/D of the nacira is 46. Yes 473 sq ft (44m²) for 2000 lbs (900 kg).

See :
http://nacira650.blogspot.com/2007/1...acira-650.html
http://2.bp.blogspot.com/_XXzUEgkDEx...h/IMGP4885.jpg
http://www.pogostructures.com/photos...lenanLaPie.JPG
http://www.finot.com/bateaux/batmono...n/generali.jpg

Note on the open 60 and nacira the curved lower spreader and the very innward lower shroud designed not to interfere with the solent.
See also the transversal sheeting system for the sheet. ( a track on the open 60, and two blocks system on the nacira).

Now, for very very low wind, all have code 0 / gennakers on a bowsprit.

NB I hope english sailing terms are the right ones.

[Stumble]

FcFc,

Part of the reason for going to the smaller overlapping jibs was the move to fractional rigs with larger mains. This allows more sail area to be carried off the wind with masthead spinnakers. Particularly when doing windward/leeward courses the non-overlapping headsail allows for better pointing ability with less leeward slippage from the leeward forces of the Jib.

I still have doubts about this configuration for long distance sailing, but like you pointed out most of the newer desigs carry a Code 0 for upwind reaching in light air.

[matoi]

Why would non-overlaping headsail allow for better pointing ability?

Thnx

Mato

[Stumble]

Matoi there are two reasons.

The first has to do with the forces generated from the sails themselves. Since a main under load wants to turn the boat into the wind, and a Jib wants to turn the boat off the wind, minimizing the jib help to keep the boat pointed up and reduces the forces acting to keep the bow down.

Secondly is that by moving to a non overlapping, or smaller overlapping jib you can bring the sheeting angle towards the center of the boat, since you no longer have to worry about it wrapping to the outside of the shrouds. This allows a much finer alpha angle than is possible with a larger jib further acting to allow the boat to point higher.

Then there are some adventagious design issues that occur, such as allowing for longer spreaders which increases the effectiveness of the upper shrouds, thus allowing for more weight reduction aloft, reduced weight aloft from the head sail itself, a fractional headstay minimizing the backstay effects on headstay sag and allowing better sail control. I am sure there are some more, but these are the ones that come to mind.