Square top mains?

Climb back into you hole Paul and get back on your medication.....................

 

Here are photos of the V70s. No "Lazy Jack" leech control systems, whatever they are. I've sailed on quite a few boats with big head mains. None had any strange leech control systems.

 

The reason it is a problem is the angle of the upper battens on some sails. They are not parallel to the other battens, not perpendicular to the luff. Sometimes they are at very different angles, even 45 degrees.

So when you drop the sail and the batten is still attached to the mast track it can't lay flat on top of the stack. The solution is to have quick pins for the upper battens on this type of set up. After detaching the quick pins you can wrap the head of the sail around the stack with the battens lining up. Sometimes this requires 4 or more quick pins.

Of course you could simply opt for a big head with less drastic top, and have all the battens somewhat parallel. Then you could forgo the need for the quick pins.

Be aware that on some thin like a 50 footer you'll have the boom height above deck, plus the height of the stack. That can be difficult to negotiate when needing to pull pins or remove the halyard shackle.

 

Yes, or one could spend more money and get one of these auto stow thingys.

Here,,,,,,http://www.doylesails.com/anomaly/

And add more weight and complication right where you don't want it.

Regards

 

Ah now I see. Angled battens would be a big problem.

Michael: an example of what i was talking about with apparent wind would be a vespa. If you are doing 30 kph on a vespa, what direction does the wind come from 90% of the time?

Or... If one boat is doing 7 knots on a beam reach and the one next to it on a parallel course is doing 14 knots, which will have the sails more tightly sheeted at proper trim?

I suppose it's sort of like the theory of special relativity...

 

CatBuilder, the issue is the one that Paul and Bruce described. As they said, there are ways around the issue, but those ways involve cost, weight and complication - as do heavily loaded full battens on most offshore-size boats in my experience, even when they aren't used for squaretops.

The figures that Mikko introduces may indicate that just sticking on a taller mast with a narrower head (which is more efficient according to aerodynamic theory) is less trendy but perhaps more effective, cheaper and simpler - depending of course on the boat.

Of course, it doesn't take a huge amount of time to pull the battens out, or unclip the cars, but then again the squaretop may also not save a huge amount of time on the racecourse or day or overnight cruise. YMMV.

I'm not trying to attack squaretops, which can be great for the right people and boat, just musing on the fact that while they may be trendy, they also may not suit most craft.

 

The sail won't go into the stack pack because of the diagonal top batten preventing the sail from being lowered all the way... the top of the sail will stop about the square top's width above the boom, unless you take the diagonal batten (which is needed to support the top) out or release the headboard from the mast.

 

This is an interesting topic.

My micro-cruiser sports a Hobie 16 mainsail with full-length battens. The top batten is definitely diagonal. I'm considering a new mast: the existing is bent and I'd like to try a different section shape.

So before I invest in the new mast, I'm considering getting my sailmaker to cut the top of the Hobie sail to make it a flat-top. Trendy, yes.

I'd be giving up about 1% of the boat's sailplan but reducing the mast height by 8%. Reducing the mast weight by 2 lbs would be the same as increasing the keel weight by 10 lbs.

As argued on this thread, the boat may sail better with the square-top, but it may not all be for aerodynamic reasons.

 

Would you point to some method on how to calculate the loads from square top main on the mast?
My search in Classification Societies Rules was not successful so far.

 

Surprised at all the interested in big topped mains when it means the loss of a standing backstay and having to resort in either no backstay or having to tack twin backstays. No backstay seems a compromise in rig adjustability and having to tack backstays seems like a lot of work.

 

Well, some fractional rigs with swept spreaders and large mainsail do NOT need a backstay so dearly.
For pure racers, tacking a backstay is not that different from tacking the runners...

 

If I do cut the Hobie sail, are there any special considerations for the headboard? Is the halyard cringle in the same location relative to the mast groove? Or does the halyard cringle need to be moved more outboard?

I imagine that the stresses are still radiating down and and aft from the halyard and that the square-top is supported only by the battern. I'm expecting that there is no need for layers upon layers of sail material across the entire flat-top.

Any advice on this cut? Does anyone have experience with the details for this modification?

 

Well, the headboard will have to take a fair amount of horizontal pull away from the mast...

 

Hi all, very new here and a long term catamaran sailor. After reading most of the threads here, few mention the disruption created by the mast and seem to treat the issues as if the mast is not attached to the sail. To my mind, at the minimum, the square top section provides sail surface area away from mast influnce and allow some lift to be generated instead of drag.

Perhaps the solution to making a given sail area effective is to have a horizontal structure at the mast head that the head of the luff is attached to and similar at the foot, horizontal cables from the luff to cars on mast leaving a gap between the mast and the luff of the sail equivelent to the area of disruptive influences of the mast. However it is done, placeing the sail outside of the supporting mast structure removes many complicated variables from the equation.

Most aerodinamic theory and discussion does not include the complications of an external support structure(mast).

Bob

 

To be honest, I don't know many (if any) significant articles or books on sailing aerodynamics that DON'T treat the issue of the interaction between the mast and sail seriously.

The gap idea has been tried, by the French AC team. It has also been tried, in effect, by the old external vertical mainsail reefing systems which were terribly inefficient.

Some new CFD work apparently indicates that the mast actually creates much less disturbance to the airflow than previously thought.