Masthead, or Fractional Sloop?

[Jackdaw]

Sorry jackdaw, but I happen to believe science should always be in question. Our history of what we claim, believe, accept as scientifically sound supports a more sceptical approach.
I had a retired chemist/atheist tell me the origins of the universe was settled science. That was his argument.
Im this case, I'm incline tip believe you. That doesn't mean I know what the science is and I always need more than just a statement that is akin to "because it is", I need understanding.
From what little I know, looking at those images, a larger leading edged headsail is going to make more difference than a more efficient main.
I'll agree with you that I'm wrong but, I still don't know why I'm wrong.
- Will (Dragonfly)

I agree science always has to be in question. But you have to start from a place where you are asking reasonable questions. If you don't, you can go down the totally wrong path. Like that picture you posted. Looking at that isolation could do that.

OK I'll give it to you straight. ;^)

For any given sail area, models and real-life testing has shown that a non-overlapping fractional sailplan provides the best lift/area ratio. Working together as one foil maximizes the given area.

Truth be told, the people at the deep end of the science are not totally clear on all the 'whys', so AFAICT there is no absolute 'proof' for this. But the same is true for gravity, but I'm not walking off any buildings anytime soon either!

 

[Jackdaw]

Just to clarify this discussion a bit, are we only talking about upwind sailing or all points of sail? I would really like to see the same graphical representation that Jackdaw just posted from North Sails comparing a masthead rig to a fractional rig to see how different they really are in identical conditions. It would also be interesting to see how forces change as the wind direction changes. I believe that the common consensus is that a masthead rig would do better downwind but how about close, beam and broad reaching? If two identical boats were rigged with a masthead and fractional rig, both having the same sail area, would one rig be better than the other sailing in all points of sail? I suspect not, but where does the advantage end assuming a spinnaker isn't used? Curious!

Mostly upwind. Because off wind spinnakers and code sails come into play. But again, for the same amount of area, the differences will be small to none.

Downwind, masthead rigs used to do better against fract spin boats because they where fractional spin hoist as well, because old (IRC and PHRF) rules dumbly penalized them for a hoist bigger than J. They had smaller downwind sail area. Now, most fract boats are masthead spin hoists, and the advantage has turned the other way.

Here's an empirical data-point. Now absent of any artificial rates rule, have you seen ANY masthead performance boat designed in the last 20 years? I cannot think of one. People want a fast boat or a fast OD, they design it non-overlapping fractional. All of them.

 

[Head Sail]

For any given sail area, models and real-life testing has shown that a non-overlapping fractional sailplan provides the best lift/area ratio. Working together as one foil maximizes the given area.

Therein lies the rub. For any single masthead boat, if it was converted to a fractional rig, the sail area would be less assuming the mainsail is unchanged. For any given boat a masthead rig's sail area will be larger than a fractional rig. That's why it's called "fractional".

 

[shemandr]

... For any single masthead boat, if it was converted to a fractional rig, the sail area would be less assuming the mainsail is unchanged. For any given boat a masthead rig's sail area will be larger than a fractional rig. That's why it's called "fractional".

Not really. "Assuming the mainsail is unchanged" is a non-sequitur. The masthead boats of the 70's had a very small main. Modern fractional rigs have a large main and as Jackdaw sail the air draft of the sailplane is larger. You can't compare rig types with the main remaining constant. I'm not sure you can just put a fractional rig on a hull that was designed for a Masthead rig. Although I think it has been done. My Mark 25 was likely such a boat. Taller mast could bend the hull with ease.

 

[Head Sail]

Not really. "Assuming the mainsail is unchanged" is a non-sequitur.

Ok, change it to "all things being equal". It comes down to simple geometry. You can get more sail on a masthead rig however, a fractional rig may be preferable given a set of X and Y axis of the headsail to work with.

 

[Franklin]

My take is this...if you want to do the coconut milk run, it is better to have a masthead rig. At times you will be able to pole out the large Genoa and do hull speed dead down wind to reach your destination quicker. I have a fractional rig of course so when I pole out the jib, I need 15 knots true wind just to make 5 knots. Sure, spinnakers are made for that but most cruisers do not like to fly those at night and rarely mess with them on short trips and you can't go DDW with a spinnaker made for a fractional rig...Asym spin.

If you want to go north/south, then fractional rig is better due to a lot of close reaching or beating.

 

[Ted]

It's interesting to note that the old J29 was offered with a fractional or masthead rig. The IJPE dimensions were different but the sail area remained essentially the same with the fractional rig having slightly more sail area (3 square feet more) than the masthead rig. The masthead rig was more desirable in predomidently lighter wind areas. I would assume because they carried a masthead spinnaker also. I fail to understand why J Boats would go through all that trouble to make two rigs for the same boat instead of just adding a masthead spinnaker to the fractional rig. According to the J Boats PHRF analysis comparing of all their models, the J29 masthead rig has a rating of 111 and the fractional rig a rating of 114. This seems to be a fair example of comparing two identical hulls with different rigs. There doesn't seem to be much of a performance difference here. Wouldn't it be great if Rod Johnstone could jump into this discussion?

 

[topcat0399]

Mostly upwind. Because off wind spinnakers and code sails come into play. But again, for the same amount of area, the differences will be small to none.

Downwind, masthead rigs used to do better against fract spin boats because they where fractional spin hoist as well, because old (IRC and PHRF) rules dumbly penalized them for a hoist bigger than J. They had smaller downwind sail area. Now, most fract boats are masthead spin hoists, and the advantage has turned the other way.

Here's an empirical data-point. Now absent of any artificial rates rule, have you seen ANY masthead performance boat designed in the last 20 years? I cannot think of one. People want a fast boat or a fast OD, they design it non-overlapping fractional. All of them.

You are making me regret that I just dropped a boat buck on a brand new 120!!!! darn it!

 

[Will Gilmore]

The J121 is listed on sailboatdata.com as a fractional but, that doesn't look like a fractional rig.
- Will (Dragonfly)

 

[Ted]

Will, the drawings that you posted are of a C&C 121 not a J121.

 

[Jackdaw]

I fail to understand why J Boats would go through all that trouble to make two rigs for the same boat instead of just adding a masthead spinnaker to the fractional rig. According to the J Boats PHRF analysis comparing of all their models, the J29 masthead rig has a rating of 111 and the fractional rig a rating of 114. This seems to be a fair example of comparing two identical hulls with different rigs. There doesn't seem to be much of a performance difference here. Wouldn't it be great if Rod Johnstone could jump into this discussion?

Because under PHRF a spin with a hoist greater than .95 of the 'I' measurement carries a prohibitive penalty. So no masthead spin for the fract boat. The bigger spin on the masthead more than generates the 3 seconds.

 

[Will Gilmore]

Will, the drawings that you posted are of a C&C 121 not a J121.

So it is. It came up under my search for the J121. I thought it said J121 on the link.
C&C 121 was first produced in 1999.
Guess that's too old to count.
- Will (Dragonfly)

 

[Jackdaw]

a spinnaker made for a fractional rig...Asym spin.

I agree with your other points. But there is nothing about a fractional or masthead rig that makes one type of kite better (or worse)

 

[Gunni]

It’s like nobody has ever heard of the Solent rig!

 

[BarryL]

Hey,
In all honesty, I don't think it makes that much of a difference. Decide what features you want in a boat, come up with a budget, and see what boats best meet your needs. Unless you have a VERY large budget, you will have to compromise somewhere, and I would not let a fractional or masthead rig be the ultimate decision maker.

I have sailed and raced both kinds of rigs, I don't ever recall thinking "Damn, I wish this boat had a masthead (or fractional) rig." I agree that the factional rig is in favor today. For example. my boat, the C&C 110, was first delivered in 1999 and has a masthead rig. The next boat released, the 115, was delivered in 2005, and has a fractional rig. The two boats are very similar, but the 115 is significantly faster. While it would be nice to have the 115 instead of the 110, the 115 is significantly more money.

Barry

 

[smokey73]

It is always nice to know how to maximize the performance of your boat. Great discussion and I like to keep informed. However, I would guess (and its only a guess) that the vast majority of us, Jackdaw and a few other excluded, cruise more than we race. I would also guess that many of us, like me, have an admiral who is a part of the discussion about the boat we bought, have or want. With that being said, I can't imagine her saying "boy, I wish this was a (fill in the blank) rig". Just isn't in her wheelhouse. She might say, "can you handle the sails without me?" Do I race? Not formally but you bet, when I am on a near parallel course with a sailboat of approximately the same length as mine I'm always thinking, "I'm gaining on him" or "he's going faster than me, I need to adjust the sails." Be honest, don't you do that too? Still, all in all, my admiral is more interested in the cabin layout, heads, galley, etc. As we say here in South Carolina "If Mama ain't happy, ain't nobody happy". If I ever enter a formal race I'll let the PHRF make the adjustments for differences in boat performance, flawed as it may be.

Now for a simple question. I 1994 Hunter 40.5, standard sized battened main, non furling, solid foot, overlapping Genoa (not sure of how much, probably 130%). From what I'm reading if I intend to do a lot of beating to windward, I'd be better off with a non-overlapping Jib, Is that correct?

 

[Scott T-Bird]

Well, you wouldn't change a masthead rig for a fractional because isn't it true that a boat with fractional rig has the mast stepped further forward to increase the size of the main? Even all mastheads aren't designed exactly similar. I think if you compared my Starwind 27 to a Catalina 27, you would find that Starwind has a larger Main and smaller Fore sail while the combined sail area is almost exactly the same. Evidently, the Starwind mast is placed slightly more forward than the Catalina mast in a relative comparison.

It seems to me that the advantage of fractional is almost strictly in upwind sailing, i.e. pointing, with the ability to sail closer angles. Is it logical to improve pointing on a masthead simply by utilizing a non-overlapping head sail with the tracks inboard from the shrouds? In my case, it seems logical as wind speeds regularly climb above 20 knots in summer thermals. So the smaller head sail size is not a limitation with higher wind speed, no? Or is there something about the fractional configuration that improves speed?

On another note, am I wrong in noticing that fractional rigged boats have evolved from 3/4 fractional to more like 7/8 or even 15/16? If that is the case, it seems that if the trend is to move the head of the fore sail up the mast, why doesn't the evolution stop at a masthead rig?

 

[Crazy Dave Condon]

trying to figure this out with masthead or fractional

 

[Will Gilmore]

on a near parallel course with a sailboat of approximately the same length as mine I'm always thinking, "I'm gaining on him" or "he's going faster than me, I need to adjust the sails." Be honest, don't you do that too?

I think I can honestly say that I have never been in that situation when that wasn't exactly what every "sailor" on board was thinking AND doing.
No matter who's boat it was.
The only exception would be if the other boat were so far out of our league as to practically be a different class boat, like a power boat or atomic submarine. We had no hope of keeping up with the submarine we watched fly past at the entrance to Chesapeake Bay. I blinked and it was gone, must have dove in an instant. No one ever thought, "I can out sail that." It would be the same if a big old 90' AC catamaran sailed past. Completely different class.
Anyhow, this discussion is about learning about sail dynamics for me. I'll buy whatever fits my budget and use, when it comes time to buy another boat. If I'm designing my own boat, its rig will be based, in part, on what I learn here.
I'm going to go lookup performance data on the delta rig now. I think it might be pertinent. Be back to report.
- Will (Dragonfly)

 

[Jackdaw]

C&C 121 was first produced in 1999.
Guess that's too old to count.

Didn't find one, did you?? ;^)