Square top main sheet loads

[TJ D]

Originally Posted by admiralslater

Would it be possible to use another car on the track to reduce point loading or are you concerned about the overall load .In theory and feel free to correct me, the main load would be generated from the end of the boom straight to the mast head so if you are running a big roach now the square head may not increase the load all that much . In fact the biggest load differences may be in lightish winds before the tops falls away.
I love buying new sails

A second car? Well, maybe. I'll give that some thought. Our traveler's about 10-11 feet long, so there's room.

The fact that we managed to destroy some (old, so it may not really indicate anything) balls in the car under heavy load has me not wanting to ask a lot more of that component, so this might be a good answer.

I'm also not convinced that a square top will actually require anything more for tension than what we're flying now either. It already takes a hell of a pull to close the leech up. I don't know how many tons, but the sail's almost 900 square feet.

Thanks, TJ

[TJ D]

And yes, you're right. shopping for new sails is a favorite pastime for this sailing geek too.

We just had a new furling code zero built over here in England. The Brexit has some real advantages to those of us who earn and spend USD. I paid about half of what I would have in the USA. Nice

[admiralslater]

Originally Posted by TJ D

I wonder if I'm missing something here.

I have to go to the headboard to disconnect the halyard anyway, so it's really not a problem to disconnect the headboard from the slider (we have an Antal external track). This would be quite simple. Do I also have to remove a batten to get it to store on the boom, or is that enough? Not that taking a batten out's a big deal anyway.

Thanks, TJ

There a number of cars that feed the halyard through them selves to the mainsail so that the batten lays parallel to the boom when not under tension. Depending on the layout of the boat and size of the batten it can be a bit of a pain

[admiralslater]

Our Outremer 45 has 750 square feet and uses 3 linked harken cars but I suspect theyare smaller than yours.

[TJ D]

Yes, our single car is about 10" long. But, a second car is an intriguing idea. Certainly, there's no harm that can come from distributing the load across more of the traveler and more torlon balls to bear the load to boot.

[admiralslater]

Originally Posted by TJ D

Yes, our single car is about 10" long. But, a second car is an intriguing idea. Certainly, there's no harm that can come from distributing the load across more of the traveler and more torlon balls to bear the load to boot.

I agree especially if it was only the car that was showing strain

[TJ D]

Yes, only the car.

Specifically, just the balls in the car. This car was installed in '07, and the boat has sailed a whole lot of miles since then, so I'm not really sure if there was really an overload happening, or just a case of old, worn out balls. I installed a new set when we arrived in England.

But, it got my attention and it was what prompted me to ask the original question about sheet loads.

I'm probably fretting about nothing, since the sail on there now is so roachy anyway.

TJ

[admiralslater]

fretting also known as planning or forthought

[Stingray576]

I Put up my first square top main in 1988-9 season on a lightweight Australian Catamaran design called a stingray. It is a class that pretty much measures as an F18 without spinnaker but much lighter. It was so Radical they put it on the cover of Catamaran Sailor Magazine. The original idea however belonged to Barry Marmion, an A class catamaran sailor from Victoria in Australia. He put it into 'the wild' at a sailing seminar at the advanced Sailing Association in Adelaide with about 50 people present and it was a concept so compelling that we grabbed it and about a year later they were ubiquitous. He put his up just before we did and immediately jumped to near the front of a world class fleet.
Square head mains reduce handicaps by 1.5 to 2% in off the beach cats (and more once the sailors and sailmakers sort them out).

There are a number of reasons they are an 'obvious' improvement:
The head twists and the 'flag' reduces parasitic drag.

The head is much more responsive to gusts. It makes a fractional rig 'more fractional'. You will see the leech open and close in a gust automatically. The sail does not partly stall as gusts hit. Part of the original reason for using them was to allow straight section masts to be used in catamarans instead of tapered sections.

On our 39ft cat the range before the boat feels 'choked' by too much wind is wider with our Doyle square top. (Kangaroo has crossed the Atlantic and Pacific. it is a lightish cruiser with a biggish rig with 100m2 of working sail)

'Tight' leeches are achieved with sheet tension on roached mains but only to a point. Oversheeting actually bends the mast so the leech opens and the sail flattens with more sheet tension and that would be the case on most boats. We have a low set traveler on the rear beam and not on the cabin top. We sheet our main with the traveller 600 up from the CL to windward in most conditions and 'soft' sheet so leech ribbons stall 30% -50%. The amount of twist to make the boat fast is surprisingly large.

The square top is mostly a more forgiving sail.

[Mal Reynolds]

TJ,

My Open 50 has 2 big Harken cars on the traveler, originally designed for an 1100 sq ft pin head. I'm lucky that she has near end boom sheeting. I ordered a 1300 square top to replace the pin head just a month or so ago - it should arrive in a week or two. I also have the external Antal track on the mast. We're using all the old hardware, including the head which I think is odd as it is a 60 degree head, not a 90 so we'll see. I am expecting to simply remove the top batten when dousing.

Anyway, I think it will provide more power in light air and when reaching & running, and less drag due to the aerodynamics of the head and the straighter leach. Also, most important, the boat will look more bad-ass and modern. Not that Rocket Science has that problem!

Here is an old photo without the mainsheet rigged, but showing the two cars on the traveler. When I get down to the boat I can take a photo of how the tackle is rigged with the mainsheet to the 2 cars - it's a bit complex. Not sure if this is helping at all...

Mal

[TJ D]

Originally Posted by Mal Reynolds

TJ,

My Open 50 has 2 big Harken cars on the traveler, originally designed for an 1100 sq ft pin head. I'm lucky that she has near end boom sheeting. I ordered a 1300 square top to replace the pin head just a month or so ago - it should arrive in a week or two. I also have the external Antal track on the mast. We're using all the old hardware, including the head which I think is odd as it is a 60 degree head, not a 90 so we'll see. I am expecting to simply remove the top batten when dousing.

Anyway, I think it will provide more power in light air and when reaching & running, and less drag due to the aerodynamics of the head and the straighter leach. Also, most important, the boat will look more bad-ass and modern. Not that Rocket Science has that problem!

Here is an old photo without the mainsheet rigged, but showing the two cars on the traveler. When I get down to the boat I can take a photo of how the tackle is rigged with the mainsheet to the 2 cars - it's a bit complex. Not sure if this is helping at all...

Mal

Thanks, Mai. I think that the 2 car idea is a very good one. I'll probably implement this on the current main. It can only do good, particularly with our mid-boom sheeting. The loads are certainly higher with this configuration.

If you get a chance to take a picture of how it's run, I'd appreciate it.
TJ

[UNCIVILIZED]

For your traveler you're probably looking for a car coupler. You can buy them, DIY them, or have custom ones built. As well as assembling one made from Dyneema (lashings mostly), or similar cordage. And their configuration, be they metal, or cordage, depends on how many blocks there are in your sheeting system, where they're located, & the loads on them. But fundamentally they're pretty simple. Harken makes a few.

BTW, those bearings would be pretty ancient. So I doubt that they owe you anything. How big's the main? And I'm guessing that you're running an older Harken Big Boat Traveler Car?

[TJ D]

Hi Uncivilized,

We have an inch and a half track. The car's about 10" wide, If I remember right, there are about 80 torlon balls in there. I also don't really think that the failure of the balls had to do very much with overloading. But, as I said, it got my attention just the same. We really don't need the mainsheet coming off.

For the car coupling, I'm sure we'll just lash them with some dyneema.

Our current main is 890 square feet. I'm actually not sure if a square top will gain us all that much area, to be honest. Maybe 10% at most? The sail is nearly square now, carrying nearly the full luff well past the 3rd reef, about 2/3 up the sail.

I'm mostly wondering if a square sail of roughly the same area needs more sheet tension. I'm gathering that it's probably not all that different than it already is with my current sail.

Thanks, TJ

[Mal Reynolds]

Hi TJ,

Got down to the boat today. Here is a photo of my Open 50 setup. Looks like the high load Harken coupler. I'm guessing there's your answer.

Cheers,

Mal

[Stumble]

The short answer is yes a square top will need more sheet tension than even a bigroach main. How much is going to require a lot more expertise than I can offer. It is going to be heavily dependent on how big the top batten is. On an extreme example, on my A-Class cat with a square top that is about 50% the length of the foot the sheet loads easily top 500lbs of tension. Drop that to ~10% on the decksweeper A-Cats are using about 350lbs max.

Assuming the traveler is mounted properly the loads really shouldn't be an issue. Just one or two of the bolts holding it in place should carry higher loads than the sheet could ever apply. But a double traveler is a good idea anyway. If nothing else it will reduce the traveler loads substantially, particularly if the traveler sometimes doesn't run free.

The bearings btw should be replaced every two years in normal applications. On the A-Cat I replace them every 12 months.