Masthead, or Fractional Sloop?

[Simon Sexton]

Hey Guys,

I'm really bored right now and wanted to see another conversation spark up, so here begs the question for today: Masthead or Fractional; which one do you prefer, and why?

 

[Will Gilmore]

Simon, It is a good question that I am not fully equipped to answer but I'm always happy to jump in anyways. The masthead sloop has an advantage in that it can fly a bigger headsail. Headsail are considered to have a better leading edge attack on the wind, in part, because the stay is smaller in profile than a mast, less air is disturbed and laminar flow is better because of it. As per other discussions recently, how the main is set in conjunction, can really improve the jib's performance. The foresail actually becomes the larger driving force of the boat.
The advantages of a fractional are in how you can fine tune a main with regard to flattening the luff and bring her closer to the wind.
I couldn't say which pays better dividends overall but, my inclination is to go with the mast head rig flying a bigger staysail
- Will (Dragonfly)

 

[shemandr]

Put me down for fractional. Easier to adjust power and tack.

 

[Jackdaw]

This question has been settled many years ago, its just inertia and old boats that keep masthead rigs still 'in favor' with some people; mostly by the people that own them. While you'll see people sailing masthead boats prefering fractional, the opposite is almost never true.

For any given sail area size, a non-overlapping fractional rig will generate more power, go to windward better, and be easier to manage (single head-sail and lots of mainsail shaping before needing to reef). Its also easier to see around, and there is much less wear on the headsail.

Only downsides:
Extra air-draft
Lesser off-wind performance without a spinnaker

 

[Scott T-Bird]

Funny how Simon picked photos of the fractional rig sailing upwind and masthead rig sailing downwind! Good illustrations!

 

[David in Sandusky]

I’m with Jackdaw.

I love the masthead girl I’m with, BUT

If I were buying new, it would be a fractional rig, based on our chartering experiences.

 

[Will Gilmore]

I think technically, this is a fractional rig but, I can't see that having mast shaping attributes. Maybe I'm all wet but there isn't enough angle and too far away from center to affect mast shape. Maybe that's not the point of this design. Why not go all the way to the mast head?
- Will (Dragonfly)

 

[Jackdaw]

I think technically, this is a fractional rig but, I can't see that having mast shaping attributes. Maybe I'm all wet but there isn't enough angle and too far away from center to affect mast shape. Maybe that's not the point of this design. Why not go all the way to the mast head?
- Will (Dragonfly)

Its fractional. The whole purpose of the the design is to NOT go all the way to the masthead. By not doing that, it allows the backstay(s) to bend the mast forward (and flatten the mid and lower sections of the main) by using the forestay as a fulcrum. If the forestay was at the masthead, there would be no fulcrum.

 

[Meriachee]

That assumes that you are buying a boat for the sail plan. That item wasn't even on the first page for us.

 

[Jackdaw]

That assumes that you are buying a boat for the sail plan. That item wasn't even on the first page for us.

That's interesting. Its the first thing I look at.

 

[Jackdaw]

I think technically, this is a fractional rig but, I can't see that having mast shaping attributes.

My buddy Alex made this instructional vid a few years ago. Funny I sailed with the kid (his son) driving the boat in Texas last month; he's in college now.

 

[Meriachee]

That's interesting. Its the first thing I look at.

That search becomes geographical at some point. It's not like we're in a hotbed of product availability.

 

[Jackdaw]

That search becomes geographical at some point. It's not like we're in a hotbed of product availability.

I get that. ;^) But then each of my last three boats (24, 26, and 35 feet) where over 1000 miles away from home. What price glory??

 

[Meriachee]

Yep. The 270 came from Denver via Seattle. Way far.

 

[Ted]

There are compromises with each rig design. For many people who do a lot of downwind sailing without a spinnaker, the masthead rig with a large genoa is preferred. There are sailors who might not fly a spinnaker but would set a pole to wing out their genoa. Bending the mast to flatten the main sail on a masthead rig can be done with a baby stay but it does get in the way when tacking. Depending on the size of the boat, some fractional rigs need check stays and or running backstays which can also add complexity to the rig. You can argue sail handling ease on either rig. Which sail is more difficult to hoist or douse, a large main or large genoa? It depends on how you rig your boat and your physical ability. Roller furling for main or headsails, lazy jacks and electric winches are some items that will overcome most of the difficulties associated with large sails. For me, a masthead or fractional rig would not be a deal breaker on a boat I otherwise liked. There just doesn't seem to be enough of a benefit to either rig to tip the scale.

 

[jssailem]

When young and racing was all that sailing should be, I sailed fractional rigged boats. Nothing else mattered.
But now that cruising is the focus, solo sailing the norm, and the boat was designed a Masthead Cutter, I have a recognition of the value. No longer am I focused on the slot and the main performance. I can appreciate the elegance of sailing powered by the foresail.

 

[Will Gilmore]

There just doesn't seem to be enough of a benefit to either rig to tip the scale.

What would be the quantifiable benefits?
Discount sail handling because most boats use roller furling headsails, so let's say, for this thought exercise, both boats have roller furling headsails. The main is the same for both boats but "Lightning" is a fractional sloop and "Thunder" is a masthead sloop with otherwise, similar hull characteristics.
Also, let's confine this study to jibs of no more than 100% (non-overlapping).
I've picked this picture off of jackdaw's thread "sail trim quiz question" to help with the concepts we are working with.

Here, for a close hauled configuration (obviously an overlap but the dynamics are, I think, adequately illustrated) this image shows the airspeed over the two sails. Red is the highest speed, dark blue is the lowest speed. This translates to a pressure gradient where high speed air moving across the outside surface is also low pressure on the sail. The blues represent slow airflow that consequently pushes on the sails with greater pressure.
This picture shows the greatest driving force generated by the largest pressure difference is on the staysail by a huge margin. Most of the driving force appears to come from the staysail.
If this dynamic is, in fact, illustrative of the airflow around our two boats Thunder and Lightning, than the main helps back-pressure the jib but offers only a small addition to the forward motion itself. If this is true, and I am only going by how it appears to me, than what increase in performance does improving the main offer to offset the larger driving force of the bigger headsail over the fractional staysail?
- Will (Dragonfly)

 

[Jackdaw]

That's not a very good picture, because it shows a horizontal slice of the sailplan, and you don't know under what conditions that was was calculated, or what it means to show. You REALLY have to be careful about drawing any conclusions from that image.

Here is an image that North Sails shared from the their Design Suite FLOW application, that shows the entire sailplan in powered up conditions.

You can see a much more balanced pressure (lift) load spread over the entire plan, and how the main contributes. In addition, you can see how well the fractional/non-overlapped setup works as one foil to generate lift. It not a question of which sail does 'more work' , they work together as a team. Squatter, overlapped rigs do not do this, and still have all the downside I listed in my first post.

People may have rig preference based on current boats or personal experience, but the science of what is better is not in question.

 

[Ted]

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!

 

[Will Gilmore]

the science of what is better is not in question.

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)