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  #11  
Old 12-09-2013
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Re: masthead versus fractional rig?

So my masthead sucks with no apparent advantages, I'd better go sink her
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Last edited by PaulinVictoria; 12-09-2013 at 12:56 PM.
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Old 12-09-2013
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Re: masthead versus fractional rig?

Last week weekend While flying the %155 we managed to pull both the spreadder boots off. Its the first time flying that sail. Is it normal to lose the boots? I installed them with white tape from west marine?

maybe wrong thread but for the head sail ?

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Old 12-09-2013
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Re: masthead versus fractional rig?

Nicely done Jeff.
Not sure I agree with your very last statement though. Why do cutters fly smaller spins?
Or, did I misunderstand you? I would think the larger "J" of the cutter would lead to larger chutes.

I have no idea what a "fractional cutter" is.
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Old 12-09-2013
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Re: masthead versus fractional rig?

Quote:
Originally Posted by bobperry View Post
Nicely done Jeff.
Not sure I agree with your very last statement though. Why do cutters fly smaller spins?
Or, did I misunderstand you? I would think the larger "J" of the cutter would lead to larger chutes.

I have no idea what a "fractional cutter" is.
Bob,

When I was writing the above several years back, I compared the sail area of the 100% foretriangle on a number of masthead sloops vs. cutters. It was a bit of an artificial calculation, because I then calculated an SA/D but only using the 100% foretriangle and disregarding the mainsail. The thinking was to get a sense of the size of the chute vs. weight of the boat, with the assumption that the proportion of the sail area of the chute to the size of the 100% foretriange would remain similar between the different rigs. In that calculation, the sloop spinnakers had considerably larger SA/D's than the cutters, and that is where that statement came from. To be more accurate, that should probablty have read, "Cutters generally fly smaller spinnakers relative to their displacement as well".

In hindsight, with your comment, I can see several issues in the thought process, and so consequently with my corrected statement as well. Your point about the bigger J is very valid. [For those who are unfamiliar with the way that sails are measured, in a general way, J is the dimension from the tack of the jib to the base of the mast. In racing rules, and more loosely for cruising sails, the girths (horizontal width measurement limits) of a spinnaker are derived as a multple of the boat's J measurement.] When you look at cutter rig, it generally has a very large J as compared to a sloop with a similar area 100% foretriangle. Consequently, since the centerline length of a spinnaker does not increase above length of a jib luff, but the width is a multiple of the J, the cutter would be expected to have a larger area in its spinnaker for any given 100% foretriangle area, albeit at a lower aspect ratio, making a cutter's chute better for sailing dead downwind but not as effective for reaching.

Somewhat mitigating against the larger area implied by the larger J, is the fact that cutters generally have less SA/D's if calculated as only the 100% foretriangle area (i.e. without the area of the jibstaysail). But even that is not true in all cases. Boats like Bob's Tayana 37, which has a proportionately high aspect ratio rig for a cutter, and the large J typical of cutters, could carry a very large chute even when compared on a SA/D basis.

I have no idea what a 'fractional cutter' is either. If I typed 'fractional cutter' and it appears in my write up, I apologize. 'Fractional cutter' strikes me as even worse than my other pet peeve term, the insidious and lubberly term "Cutter Ketch".

PaulinVictoria:
I did not say that a masthead rig sucks. In my mind, it is one of the better rigs out there for small boats. But as compared to a fractional rig, absent some racing rule that favors masthead rigs, a masthead rig has no real advantage over a fractional rig, while fractional rigs tend to be more efficient, easier to handle, and less expensive to construct and maintain. While this may sound a subtle distinction, the comparison to a fractional sloop does not make masthead sloop rig a bad rig. It just makes it an inferior rig as compared to a fractional rig. Sail on....

Jeff
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Re: masthead versus fractional rig?

I know Jeff I like my honking great headsails and tree trunk mast, they look fantastic compared to those prissy little fractional jibs with their spindly bendy masts.
Actually, coming to think of it, pretty much all the photos I see of broken masts seem to be on fractional rigs, whether that is a weakness in the rig, or simply because most racers are fractional now, cameras out on the water are more common and generally it's only those idiot racers that are pushing it like that (I'm still waiting to blow up the spinnaker on our J24).
As ever though Jeff, very interesting posts from you.
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Re: masthead versus fractional rig?

Quote:
Originally Posted by PaulinVictoria View Post
I know Jeff I like my honking great headsails and tree trunk mast, they look fantastic compared to those prissy little fractional jibs with their spindly bendy masts.
As you point out, I'd have thought a masthead rig has at least one major advantage over a fractional one - sheer additional headsail area. Sure, the main might not be as "efficient", but with a honking great genoa and 20% bigger spinnaker to drive you along at top speed, who cares really?

For this reason, a not very uncommon sight around here is people flying an enormous masthead spinnaker on a fractional-rigged boat - just to get that extra few knots downwind in the light stuff.

Quote:
Originally Posted by PaulinVictoria View Post
Actually, coming to think of it, pretty much all the photos I see of broken masts seem to be on fractional rigs, whether that is a weakness in the rig, or simply because most racers are fractional now, cameras out on the water are more common and generally it's only those idiot racers that are pushing it like that (I'm still waiting to blow up the spinnaker on our J24).
If twilight racing in these parts is anything to go by, if there really is a trend there, it might be amongst those who crank their backstays on really hard and chinese gybe in the next big gust. That must put far more stress on the mast than I'd have realistically thought it should handle...
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Last edited by Classic30; 12-10-2013 at 01:35 AM.
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Re: masthead versus fractional rig?

Thanks to Jeff, as always there is a lot to learn from his thorough and well-explained posts!

This time, though, there seems to me to be one point he skipped, that to my mind is an advantage of the masthead rig. On a fractional rig without runners, the spreaders will be aft-swept in order to counteract the force of the forestay on the mast. This means you cannot let the mainsail as far out as on a boat with straight spreaders. The effect this has on effective sail area going dead downwind is quite small. But it means that when sailing in waves, the chances of an involuntary gybe will be larger. (Since the sail is not let out all the way, there is a reduced angle for sailing by the lee before the sail gybes.)

Moreover, while I can't quite explain why, I have the feeling that when the mainsail is not all the way out, there is a need for more counter-rudder and active steering to prevent broaching (perhaps due to increased healing with the mainsail closer to the center line?), and greater difficulty for a wind vane to maintain the course without reducing the area of the mainsail.

These points are perhaps most relevant for offshore sailing.
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Re: masthead versus fractional rig?

Quote:
Originally Posted by axel View Post
Thanks to Jeff, as always there is a lot to learn from his thorough and well-explained posts!

This time, though, there seems to me to be one point he skipped, that to my mind is an advantage of the masthead rig. On a fractional rig without runners, the spreaders will be aft-swept in order to counteract the force of the forestay on the mast. This means you cannot let the mainsail as far out as on a boat with straight spreaders. The effect this has on effective sail area going dead downwind is quite small. But it means that when sailing in waves, the chances of an involuntary gybe will be larger. (Since the sail is not let out all the way, there is a reduced angle for sailing by the lee before the sail gybes.)

Moreover, while I can't quite explain why, I have the feeling that when the mainsail is not all the way out, there is a need for more counter-rudder and active steering to prevent broaching (perhaps due to increased healing with the mainsail closer to the center line?), and greater difficulty for a wind vane to maintain the course without reducing the area of the mainsail.

These points are perhaps most relevant for offshore sailing.
On ourfractional-rigged boat, the mast is still held back by the backstay, and the spreaders are not swept aft much, if at all. Boats rigged WITHOUT backstays (Hunter markets several) may have swept spreaders and suffer from the loss of mainsail projection you mention. My main problem downwind is that a fractional spinnaker gives me perhaps 20% less sail area than a masthead spinnaker would. I keep thinking about attaching a block at the masthead and borrowing the spinnaker from a 45' masthead-rigged boat, but I worry about turning the top 1/4 of my mast into a pretzel if I flew it in too much breeze.
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Re: masthead versus fractional rig?

No Jeff, it, "fractional cutter" wasn't in your post. I read it in another post.
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Re: masthead versus fractional rig?

I think on some rigs with minimal support for the upper panel (above the forestay) flying a masthead kite could end up in some trouble.. but I've often seen a spinn halyard tang 2 or 3 feet above the forestay, could be a decent compromise without excessively loading that unsupported panel.

Jumper struts should help a bit, but I think one should add some runners to support the loads, esp for an 'afterthought' masthead kite.

We have a swept spreader rig, no runners, but still a backstay (dyneema on a whip to accommodate a largish roach main - something you can't do with in line spreaders and a masthead rig) Our mast is setup for runners, and our pointing would improve but we don't race anymore and can't be bothered...

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