Anyone know what the design considerations are for sails that connect at the clew directly to the blocks, around the boom, vs the older style that connect to the boom, with the outhaul connected to the piece that holds the clew, and blocks on a separate tang?
It seems that the length of the foot would be more important with the newer style -- too short and none of it would work at all, but too long and you're going to break something by fighting the mast rotation/outhaul w/ an 8:1.
It also seems that with the semi-fixed outhaul on the newer style that the usage of the downhaul changes to include more of the function of the outhaul.
So are the sails designed differently overall? ..or is it still just specific to the characteristics of the boat as a whole without any one overall consideration for the different style connection to the boom?
Hopefully that makes sense, any insight is appreciated.
I've sailed quite a few boats, but of the more modern ones I'm limited to an I17, an I20, and an SL16. The SL16 is the only one that has the 'new style', but I'm not familiar enough with that boat to pick up any nuances...probably not smart enough to pick up any nuances on any boat, which is why I'm asking.
Thanks
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Rob
OKC
Pile of Nacra parts..
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Sail design for boom styles
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Posted: Apr 17, 2013 - 02:00 PM
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Posted: Apr 18, 2013 - 11:24 AM
I spoke with Randy Smyth briefly about the subject last year. He didn't seem to think there was any reason to change the shape of the sail for either boom.
I have not looked closely at the infusion but I know the AHPC products are adjustable, its just normally done on the beach. There is a small cleat on the end of the boom that allows adjustment.
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Greenville SC
Offering sails and other go fast parts for A-class catamarans
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Posted: Apr 18, 2013 - 02:28 PM
Rob, the short answer is there are none. The sail don't care. The angle that you pull on the clew can be achieved with both designs.
All the current designs and brands are using tubular booms with a simple turning block on the end to manage outhaul. The older style booms are pain and don't adjust easily with a load, or at all. Usually you have to let off the mainsheet to adjust. They create larger loads of compression making mast rotation more difficult. They are a thing of the past. The newer design is better in ever way, less compression, easier to adjust on the fly, and much less expensive to replace when you crew lands on it.
The sails are designed for the platform, not the boom.
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Philip
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Posted: Apr 18, 2013 - 03:02 PM
So, to set up a main sail with the newer style boom really only requires that the foot length is correct for the distance between the beams -- ie just a bit longer, so that when traveled out a bit the blocks aren't pulling the clew aft and flattening the sail. Right?
Thanks
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Rob
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Posted: Apr 18, 2013 - 04:10 PM
I'm not sure if you're confusing me or yourself . . .
Did you mean foot length (as in main sail) or boom length?
Sail trim is dynamic. All that you mentioned is controlled via outhaul, mainsheet, rotation, traveler, and downhaul. We agree and understand that. Likewise, most beachcats have straight travelers, except for a few unirigs (i.e. A-cat). So the condition you mentioned when traveled out comes into play, and the boom length is set up for the design of that particular platform. Are you looking to a get longer footed main? If the additional foot is excessive you will need to adjust the boom length, but then you throw the platform out of balance. Are you only looking to change the length of the boom? I would not mess with the geometry of that boom length. Remember Rob, we are only moving the outhaul a few inches on a modern spin rig platform. You mentioned I17, I20. Not sure what yours were but both rigs have both style booms, and perform the same based on that dynamic trim. You just don't experience sailing conditions or induce trim in a way where the mainsheet is forcing slack in the outhaul.
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Philip
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Posted: Apr 18, 2013 - 06:02 PM
To me the length of the boom is essentially irrelevant, provided it's long enough.
To add a little perspective -- I'm curious about fitting a sail to my 5.5 that wasn't designed for it, which would require adding a boom. I'm also curious about the difference in the I17/F17 sails as it relates (if it exists) to the different boom styles. I don't believe they changed the boom at the same time they went from Carbon to Alum. but I could be wrong...which would mean the sail is a different cut for a different mast (at least it should mean that....)
I'm not asking b/c I want to change the dynamics of my I17, though.
I didn't know the I20 switched booms as well.
The way the clew lines up with the traveler on the I17 I could see it being an identical main (if ep made mains for the carbon stick and round boom)...it's that close. However, with the older cats w/ booms, it's no where close at all, as they were much lower aspect.
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Rob
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Posted: Apr 19, 2013 - 04:52 PM
Rob,
The type of boom is completely irrelevant to the how the sail is made. Changing to the tubular boom was simple a change in production for all boats. Cheaper, easier, lighter, less parts, and more profitable for Nacra.
Regarding alum vs. carbon stick, the sail cut was unique and specific for the alum stick.
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Philip
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Posted: Apr 20, 2013 - 01:07 PM
I asked someone very familiar w/ the F17s and was told that the aluminum stick came out in 2008, and the round boom was added 2005.
So, assuming (as you've told me to do) that they made no concessions in the sail design for the new boom:
I could theoretically find a used sail from 2006-2007 or so and it would fit perfectly, or
I could switch to a newer style clew connection if, theoretically of course, my boom was such a corroded POS that I've already replaced it with something I made myself.
IIRC, the clew of my main lines up almost directly over the track, which would mean I couldn't travel out too far and have any pocket in the sail...considering that it's a spin boat, though, no harm no foul.
However, for an older boat, such as a 5.5, to use a boom w/ the main connected directly to the blocks, I think I'd need a slightly longer foot.
I'll tinker w/ this 5.5 nonsense in a few weeks and report back.
Thanks
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Rob
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Posted: Apr 20, 2013 - 01:09 PM
To add to this, it seems like the new ones only need to have real strength in compression loads, although with a composite tube this small I'm not sure how much you can vary the layup.
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Rob
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Pile of Nacra parts..
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Posted: Apr 20, 2013 - 01:16 PM
I'm not totally on board with what sail you want to put on what boat, but . . .
and you already know this, the 5.5 is boomless and by design, pulls the clew, and rotation is induced, where as a sail or boat designed for a boom, the opposite is true. Let's clarify, the tubular booms are aluminum.
I might be less confused if you would mention what sail you want to put on what boat . . . is it a 5.5?
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Philip
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Posted: Apr 20, 2013 - 01:37 PM
Philip
Bang head here until unconscious. X
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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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Posted: Apr 20, 2013 - 05:11 PM
The sail to go on a 5.5 isn't really designed for any particular boat imo...more of a 'shoe fits' situation.
I thought the round ones were carbon, not aluminum, but that's obviously not a big deal either way.
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Rob
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Pile of Nacra parts..
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