design for light airs

My light air experience comes from a Siren 17 I used to own.

One Summer, when I was on my two week vacation, I decided to sail down to the south end of Lake St. Clair. I started early in the morning with some decent wind. By early afternoon, when I was in the midle of the lake, the wind all but quit. I had only a pint of fuel in the outboard, giving me a motoring range of three miles, tops.

I gave up my goal and headed for home. It took me all day to reach the mouth of the Clinton river where I kept my boat. Once there, I was feeling whoosy and prickly. I motored up the river, pulled into my slip, dropped one loop around a piling, then let myself fall into the muddy Clinton.

The next day, be for the effects of the major sunburn I had caught up with me, I went to the local sail maker with the Siren's fore triangle measurements. My request was simple. The biggest light wind jib he could make for it.

It was early the next season that I got around to mounting the new sail track I was goining to need to make the new sail operational.

I was out on the lake one evening and the wind dropped down to between 3 to 5 kts. So I pulled the standard spool furling jib off and hanked on my new toy. It was like I had fired up the outboard, except for the lack of noise. In fact, the only noise I heard was the bow cleeving through the still water. The boat was going at least 3kts but less than 4. (At 4kt, the centerboard pennant would moan.)

I inadvertantly sailed into a fleet of racing keel boats. In my efforts to stay out of their way, I passed them all.

With the new sail, the boat went from 145 sft to about 180. But that is only part of the story. The new jib was cut for light winds and, for that purpose, probably delivered more power than its extra sqare footage may indicate. And all of this was quite inexpensive. The sail cost me about $300 1981 dollars, The boat w/trailer cost about 6,000.

I would suggest that you become good pals with your sailmaker and make the boat you already have into a light wind rocket. Or consider some poor old, beat up, centerboarder.

Bob

 

A very cogent argument, Vega. Thanks.

Questions to all: Is there a website that lets me compute the SA/D ratio backwards? That is to say, if I know working sail area (say 610 sq ft), but don't know displacement, what displacement do I need in order to have a SA/D ratio of 16?

I suppose I could setup a spreadsheet to calcute this, but I never seem to get it right.

And does adding the stay sail on a cutter really help at all in light airs? Thanks.

 

With 610 sq ft of sail, to have a SA/D of 16 you need a 6.7T boat.

What really helps in light winds is an asymmetric spinnaker. There are some, designed for cruisers, that are effective since 50º or so. They can be mounted with a simple furling system and are easy to use.

 

Thanks, very much.

See, this is what confounds me about this boat I'm considering. It's on the hard. True displacement is unknown. Original design call for 6 tons. I think this makes sense given 4mm plates below waterline and 3mm above. But cabin and spars were originally wood. Today the cabin is steel and spars are alloy. Documented displacement is gross 12 and net 10 tons. Not sure what to make of all this. Ballast is nearly 4900 lbs, lead.

Owner is professional mariner and swears the boat sails like a witch. But of course he's gonna say that.

Price is right because she's a preverbial white elephant. And we're boatless right now, not counting the Flying Scot and Sunfish.

Kind of like jumping off a cliff. Do I feel lucky?????

The biggest problem is that my first boat was a Holman & Pye design, and it did sail like a witch, IOR notwithstanding. Allen Buchanan was a well-regarded designer also from England. I'm a big believer in good designers. The potential for this not to be a dog is there, I think.

 

What is the draft?

 

Draft is 5.5 feet. (Sorry for non-metric dimensions--I'm so American.) Keel is cutaway forefoot with raked attached rudder.

Correction: working sail area is 519 sq ft, but with genoa is 610 sq ft. With stay sail add another 221 sq ft. Not sure, however, the stay sail counts for much. I never used one before. Still has chainplates for yawl rig, but it's a cutter now.

1964 construction; upgraded engine, spars, rigging, interior, etc., in 1991. I suspect the boat has been on the hard for awhile.

Thanks for your interest.

 

Method for calculating S/D backwards.

Hi Hiracer:

Here is a step by step process for determening Displacement Based on available Sail Area and desired S/D:

1.) divide available sail area by desired S/D ______,
2.) find the square root of the answer to 1.) _______, and
3.) now cube the answer to 2.) _______

This gives you the displacement of your boat in cubic feet. You now either multiply this number by 64 to get pounds, or divide it by 35 to get long tons.

Bob

 

Hiracer, I have to go...sleeping time. But I have something for you. I guess you are going to like it. See if you can find that boat.

( I guess you mean Alan Buchanan and not Allen, and yes he was a great Architect )

http://www.yachtingmonthly.com/ym/100/images/pdfs/1950s.pdf

 

I own an old Rhodes design of the form you describe. She is a joy to sail. Low wetted area gives good light air speed. She draws right out when sailing fast and is a freight train to windward. I describe her as easily driven. I counter somewhat the wide form stability position which permits more sail area. I would say this form 'requires' more sail area to move well. A hull which is nicely balanced moves well with moderate sail. We sail with a asymmetrical for light conditions. She is very comfortable in a seaway.

 

To properly compare things we have to keep the rest of data constant. So for the same sail area, displacement, etc, my statement is true, of course.

On your statement "...the short waterline is always a no no, especially in light winds" I would like to kknow your reasons.

 

Congratulations, you have a very nice sail boat; about comfort, you are absolutely right. This kind of boat is a lot more comfortable in a seaway, compared with a modern light cruiser.

Comparing traditional small beam cruisers with modern broader beam cruisers, regarding capacity to carry sail (initial stability) it is like this:

An old traditional narrow cruiser has very little form stability, and the boat stability comes almost all from the Ballast. Typically a boat like this has near 50% of its weight in Ballast.

The beamier hull of a modern cruiser permits that a significant part of its initial stability comes from the resistance that the shape of the hull offers to being rolled. This stability is called form stability. This permits that a modern cruiser, for having the same initial stability (or to carry the same amount of sail) of the traditional sailboat, will only need to have a ballast of about 30% of its weight, sometimes even less.

For the same size, this typically makes the beamier boat a lighter boat and even if it is broader it has in fact a smaller wetted surface than the narrow traditional boat. This happens because, being heavier, the narrow boat will sit more deeply in the water and typically it will have a large area long keel, while the beamier boat will sit very lightly in the water and typically will have a small area fin keel.

For the same size, a traditional cruising boat, with more wetted surface, more weight, same area of sail and (by design) with a smaller LWL will not be a match for a light modern cruiser in small winds.

The only situation when your boat could be faster than a modern lighter cruiser is probably against the wind in strong winds and heavy short seas. In this situation the modern boat would sail badly, jumping in every wave, crashing on the next one, with such violence that it is possible that the heavier boat, with a much smoother movement, slicing through the waves, can be faster.

Faster or not, in these conditions, I would rather be in a traditional boat than in a modern one; the traditional one would be a lot more comfortable to ride, and I mean a LOT.

Of course, speed is not everything and for the same initial stability your boat would have a better final stability (also called safety stability), a better AVS and a better resistance to capsizing (mainly because of its superior weight and typically lower CG). It is a more seaworthy boat.

 

This particular boat, as many others of her type are actually not narrow, as dimensions on the waterline are what counts.

Same long overhangs that makes them appear narrower also makes sail area look smaller (in proportions to the hull) then it is. Take a look at the attached simple drawing which illustrates what I mean.

Many boats of that type were built in The Netherlands in those years. They were built well, by professional yards. These are good sea boats, will not break any speed records but they are good choice for cruising, especially if money is tight. Just check her condition thoroughly to avoid nasty suprizes. Give a special attention to engine and other expensive stuff. Measure thickness of the plating!

Milan

 

No, as I have said in the previous post, a traditional cruiser (narrow hull, long keel) to be capable of carrying the same sail area, has to be heavier than a modern light cruiser (beamier and with a fin keel). One needs 50% of its weight in ballast, the other can do with less than 30%.

 

They can also be very beautiful and seaworthy boats and Alan Buchanan was a fine architect, known for his seaworthy and good looking boats. I am sure it will be a very agreeable boat to sail…and pleasure is what counts most…or do you want to race the boat?
As Bntii has pointed out, it will also be a comfortable boat in a seaway.

About the quality beauty and seaworthiness of Alan Buchanan designs, do you know that the personal boat of Dick Durham one of the editors of Yachting Monthly is an Alan Buchanan Yeoman Junior? (the yeoman is the black and white picture)
http://www.ybw.com/ym/meet.htm
Yachting Monthly has been reported by several members of this forum as one of the best sailing magazines and you can bet that those guys know a lot about sailboats


Can you post some pictures of that boat?


Have a look at some of the Buchanan boats. True classics!

 

Sorry. You are correct; it's Alan, not Allen.

Yes, the boat under consideration is very much like the Yeoman Junior. I couldn't read the dimensions post with the Yeoman, so I'm not sure about size.

Wow, have you ever perfectly described the one thing I didn't like about my first boat. As a coastal cruiser in Alaska, I would run into these steep, rough seas. The pinched stern on the Wauquiez would do nothing to stop to hobbyhorsing. That was it's one big failing.

* * *
I spoke with the owner today about light air sailing. He hasn't sailed it much, and most of that has been offshore sailing. He claims not to know how it sails in light airs. Don't know what to make of this.

Anybody ever hear of a dumb fool buying a boat on the hard without a test sail?? Don't say it. I know I'm crazy for even thinking of it. But . . . we could pay cash for it now. I keep coming back to the designer and location of build. Two good combinations. How bad can it be?