A Sail Plan

[Bruce Taylor]

I've drawn up a rig--actually two rigs--for my open sailing dinghy.

One sail, 85 sq. ft, for lightweight recreational sailing:

http://www.imagestation.com/picture/sraid36/p8b2f188d9e7e6ee0c06de529ac2069c9/fd202f50.jpg

and two sails (115.5 sq. ft total) for sailing w/ a load:

http://www.imagestation.com/picture/sraid36/p02d200c78bcbf9edd8f74c315736a576/fd202f4e.jpg

I chose standing lug because I wanted a decent spread of sail w/ a low CE...and also, I'm just fond of the rig. Sprit w/ boom would do as well, I guess. Balanced lug looks less trim (and is it harder to keep the luff taut w/ balanced lug? -- looks like it would be). I tried various leg o' mutton rigs, but kept ending up with an excessively tall main. Lateen kept pushing my CE too far aft.

CLR is at the aft edge of the daggerboard (station 7).

In the single-sail version, I've given the rig a lead of about one foot. The CE is over station 6, at the forward edge of the db. This is just a bit over 7%, which may be on the low side.

In the ketch, which will, ideally, be sailed fairly flat, CE and CLR are superimposed. I put a leg-o'-mutton at the mizzen because I didn't want to pull CE any further aft.

Opinions?

[ 10-25-2002, 11:57 AM: Message edited by: Bruce Taylor ]

[Buddy Sharpton]

Opinion: you should consider a third mast step about the forward end of daggerboard trunk to set the single 85 main for good balance with just the one sail.
Questions. Why does the daggerboard have a curved leading edge? Could it not be straight and set at a trailing angle?
Curious sahpe to rudder to get a balanced rudder in such a small boat? It seems to be oddly shaped. Will it be near as efficient as a constant chord?
Where will mizzen sheet to? Will the boom not ride up and sail twist?

[Bruce Taylor]

Hi, Buddy

As drawn, there are 3 mast steps already (the single sail is stepped a bit aft of station 2). If I put the main back at the db trunk my CE would a couple of feet aft of the CLR. Fierce weather helm, no?

I haven't given any serious thought to the daggerboard and rudder shapes (beyond calculating the location and surface area I need). To tell the truth, I have no idea why I drew the shapes I did! I appreciate your views.

I was wondering if I'd need a short boomkin to sheet the mizzen. If I put a fairlead in the transom, the angles look silly. I think I'll work up a "clip on" boomkin.

[ 10-25-2002, 02:11 PM: Message edited by: Bruce Taylor ]

[Wiley Baggins]

Bruce,

Very saucy! I used a balanced lug some time back, and don't remember it being a problem. I think I chose it based on some comments (in a WB article on lug rigs) that led me to believe it was a handier and more controllable rig than the standing lug.

I think a boomkin would be in order to control this mizzen set-up.

Hopefully Todd will come along and enlighten us all!

[Buddy Sharpton]

Where you are talking about is right. my dinghy has a centerboard trunk and that's about where I would need it, but noy your's. 5% lead on the CLR is about right.

[john welsford]

Bruce these log low rigs need a bit more lead than a taller higher aspect ratio one, try for 10% not including the rudder, you may need to draw a skeg in to get it with the mast in the right place, And the other issue is that an ordinary boom will allow excessive twist in the sail when running which generates a capsizing moment.
I'd suggest a sprit boom on the standing lug, and wouldn't bother with the cat ketch as 85 sq ft is plenty for the boat without complicating it. Even at that you'll need a set of reef points.

"Simplicate and add more lightness" Henry Ford.

JohnW


Originally posted by Bruce Taylor:
I've drawn up a rig--actually two rigs--for my open sailing dinghy.

One sail, 85 sq. ft, for lightweight recreational sailing:

http://www.imagestation.com/picture/sraid36/p8b2f188d9e7e6ee0c06de529ac2069c9/fd202f50.jpg

and two sails (115.5 sq. ft total) for sailing w/ a load:

http://www.imagestation.com/picture/sraid36/p02d200c78bcbf9edd8f74c315736a576/fd202f4e.jpg

I chose standing lug because I wanted a decent spread of sail w/ a low CE...and also, I'm just fond of the rig. Sprit w/ boom would do as well, I guess. Balanced lug looks less trim (and is it harder to keep the luff taut w/ balanced lug? -- looks like it would be). I tried various leg o' mutton rigs, but kept ending up with an excessively tall main. Lateen kept pushing my CE too far aft.

CLR is at the aft edge of the daggerboard (station 7).

In the single-sail version, I've given the rig a lead of about one foot. The CE is over station 6, at the forward edge of the db. This is just a bit over 7%, which may be on the low side.

In the ketch, which will, ideally, be sailed fairly flat, CE and CLR are superimposed. I put a leg-o'-mutton at the mizzen because I didn't want to pull CE any further aft.

Opinions?

[Wiley Baggins]

...and wouldn't bother with the cat ketch as 85 sq ft is plenty for the boat without complicating it. Even at that you'll need a set of reef points.

-John WelsfordJohn,

You're no fun! I am waiting for the arrival of the sailing canoe crew to encourage more sail area and a sliding seat. ;)

[Bruce Taylor]

He he. Yeah, maybe 116.5 sq. ft. is over the top.

Increasing no-rudder lead to 10% should be easy, if I ditch the mizzen. I can move the mast step forward if I need to, but I'll play with different sails and see what else suggests itself.

If I had Todd's "big box o' rigs" I'd just reach in and slap one on.

I wonder what software he uses to do that?

[ 10-25-2002, 04:56 PM: Message edited by: Bruce Taylor ]

[ishmael]

My only comment was going to be on the size of the rig. My Drascombe Lugger weighs about 700, has a beam of six and a half(memory), is just shy of 19 ft. long, and has a sail area of 132. 'Course it won't plane unless its life depends on it ;)

I lied, you need a boomkin if you keep that mizzen.

[Bruce Taylor]

OK, then...here's another rig, w/ the CE moved forward to give 10% lead on the (rudderless) CLR.

As long as I'm dropping the mizzen, I thought I'd change to a battened lug.

http://www.imagestation.com/picture/sraid36/p56496b64459e740ad2ff5a42e8e98d09/fd1f9fbf.jpg

[ 10-25-2002, 10:54 PM: Message edited by: Bruce Taylor ]

[Todd Bradshaw]

That's kind of interesting looking. I was thinking along those same lines.
http://www.imagestation.com/picture/sraid36/pd310981a11a8bc23f5610728ec3f4c52/fd1faa1b.jpg

Getting a ketch or yawl to balance with enough lead on a boat with so little lateral plane aft while trying to keep in mind that it's a pretty small boat to be sticking masts all over is really tough. The single sail idea seems to make more sense.

Of course, most folks don't know that the International 14 and the Aussie skiffs are all decended from high performance Viking raiders very similar to your hull. The boats were only moderately successful however, as it's hard to manufacture a high quality trapeze wire from goat fur...

http://www.imagestation.com/picture/sraid36/p9eac83b644efbb4a3402c0f852bdb0d2/fd1faa27.jpg

[ 10-25-2002, 10:20 PM: Message edited by: Todd Bradshaw ]

[Bruce Taylor]

How do you do that?!

[john welsford]

Ok, I meant a sprit boom on the standing lugsail, works extrememly well, go have a look at my stuff on www.duckworksmagazine (http://www.duckworksmagazine) to see how I set them up, try Rogue or GoldenBay for examples, its a very powerful rig which can be reefed easily, does not twist excessivly when running off and is a lot easier on the scull than a conventional boom.

Sounds picky I know, but I think you should be looking to group your centres as close to midway along the waterline as you can, I like my centreboard trailing edge to be on the CLR just a tad aft of 50%, and 10% lead will put the C oE just forward of the leading edge, your centre of bouyancy should be just aft of amidships.
Now here comes the tricky one, draw a bodyplan with the waterline at 5deg heel and do a curve of areas, do it again at 10 deg, and again at 15. Find the centre of bouyancy for each ( we had that lesson last week ) and plot the movement. It should not move aft noticably at 5deg, should move maybe 6inches at 10deg and 18in at 15 deg when you need the boat to be generating enough weather helm to be rounding you up before you capsize.
What this is really telling you is how much the boat will trim down by the bow as she heels and as a consequence how assymetrical ( this is only one of the indicators and for small boats this and the "eyecrometer" will do) she becomes as she heels.

Yours, John


Originally posted by Bruce Taylor:
He he. Yeah, maybe 116.5 sq. ft. is over the top.

Increasing no-rudder lead to 10% should be easy, if I ditch the mizzen. I can move the mast step forward if I need to, but I'll play with different sails and see what else suggests itself.

If I had Todd's "big box o' rigs" I'd just reach in and slap one on.

I wonder what software he uses to do that?

[Stephen Hutchins]

Hi Bruce,
I was once told by Paul Gartside the CE on boats such as you have drawn should line up vertically 1/3 of the way down the leading edge of the dagger/ center board. Until then I had always sort of guessed CE was between 7 and 12% of lwl ahead of CLR. By the way, if you get a chance to attend Paul's design class at the woodenboat school, I highly recommend it. Alot of info and alot of fun!

[Bruce Taylor]

John W. -- I followed your recommendation and made a curve of areas at 5, 10 and 15 degrees. (At the same time, I drew the curve at zero heel, and recalculated the prismatic coefficient. It now stands at 58.1%, which is a shift in the right direction, I think).

The center of bouyancy moved very little between 0 and 15 degrees of heel. The CBs at various angles of heel are all clustered together slightly aft of station 7.

To see what's going on here, I drew up a waterline at each of these angles of heel. The WL is quite asymmetrical at 15 degrees heel (and much more evenly balanced at 5 degrees) so I trust the immersed shape will pull the boat to weather as the boat heels. How strong that pull will be is difficult for me to guess.

The curves themselves were all nice, neat bell curves with no peculiar lumps or bumps.

So, given that the CB doesn't really shift at heel, should I reduce lead below 10%?

I went to Duckworks and ogled Rogue again -- what a beautifully proportioned boat that is. The sprit lug is interesting (I've never encountered that variation before), and would probably serve my purposes well. I don't see a downhaul on your drawing, though. Is there one?

I use a conventional standing lug on my sailing canoe, but have never had a problem with twist (on a run, I sometimes hook the mainsheet over a fairlead on the inwale, which helps keep things in place).

I've always meant to try Todd's nifty auto-vanging sheet arrangement.

Stephen -- Thanks for passing that along.

[ 10-26-2002, 10:19 PM: Message edited by: Bruce Taylor ]

[Todd Bradshaw]

Rogue probably doesn't need a downhaul as such (multi-part, mechanical system) just a tack line from the tack ring to a cleat on the lower part of the mast. Luff tension is going to be generated by a combination of the halyard pulling up, the weight of the yard's aft end pulling down, the sprit boom pushing down and aft on the clew corner and mainsheet tension. These should put plenty of tension on the luff.

Unless you're talking about building a really high-aspect standing lug (like Ben's Harrier), a mechanical downhaul is usually not needed and may do little more than to stretch the luff fabric out of shape. You want the luff tight, but there is a limit, beyond which you do little more than damage the sail, the same way you can by over-tensioning the halyard on a jib with a roped luff.

The self-tensioning mainsheet system will act to a limited extent like a vang, but is really more of a self-downhauling system - easing luff tension off the wind to make a fuller sail and hardening up the luff when sheeted hard to flatten the sail upwind. It really won't work on a standing lug though, since that kind of sail geometry needs the tack corner to be anchored in place. The self-tensioning system would allow the tack corner to rise and the peak corner to drop every time you eased the sheet. On a standing lug with a normal boom, I'd still suggest a real (though fairly simple) boom vang for twist control.

Since sail twist can be good at times and bad at others, on a standing lug I generally like using a regular boom and a vang, rather than a sprit-boom - but - I really like tweaking sails - probably a lot more than most average folks would consider sane. The nice thing about John's system with the sprit-boom, especially on a boat like this where you're trying to keep weight to a minimum and the systems simple, is that it does more than one job with a minimum of stuff and at the same time gives more headroom. It's also an attractive looking rig to boot. The only thing I wondered about was that my gut instinct would have been to put Rogue's sprit-boom on the opposite side of the mast, theoretically to give a little more clearance between boom and sail on the lug's off tack - but I haven't played with such a set-up and maybe there's something that I haven't thought of.

[Bruce Taylor]

Interesting stuff, Todd. You don't sound insane to me, but I guess I'm pretty tweaky myself.

Here's my boat in a Welsford-style rig:

http://www.imagestation.com/picture/sraid37/p81d1f814346341743d9e6d53c1289cb5/fd1e3504.jpg

[john welsford]

It sounds as though you have the hull shape pretty close if you are getting that sort of curve in the graph, and yes at 15deg of heel the underwater shape will be very assymetrical, helping to generate weather helm and a tendency to round up.
The sprit boomed standing lug is pretty efficient, especially reaching and running as you can maintain your airfoil shape when the sheet is eased instead of teh sail going full as you let the sheet out. Another beefit is a very light sheet loading.
Yes it does have a downhaul, on Rogue I use a four part dinghy vang set , I pull the halyard to a preset mark, then heave down with the downhaul to a set of marks and select the right tension for the weather. I have another one set up at the first reefline so dont have to unhook for reefing.
I also use a 4 part outhaul, with modern sailcloth and this foursided sail I have very effective control over sail shape and have raced this setup successfully in open dinghy classes.
Yes the sprit boom goes on the "other" side of the mast, and you're right it distorts the sail less.

Thanks for the compliments on the boats looks, she's been very popular .

JohnW


Originally posted by Bruce Taylor:
John W. -- I followed your recommendation and made a curve of areas at 5, 10 and 15 degrees. (At the same time, I drew the curve at zero heel, and recalculated the prismatic coefficient. It now stands at 58.1%, which is a shift in the right direction, I think).

The center of bouyancy moved very little between 0 and 15 degrees of heel. The CBs at various angles of heel are all clustered together slightly aft of station 7.

To see what's going on here, I drew up a waterline at each of these angles of heel. The WL is quite asymmetrical at 15 degrees heel (and much more evenly balanced at 5 degrees) so I trust the immersed shape will pull the boat to weather as the boat heels. How strong that pull will be is difficult for me to guess.

The curves themselves were all nice, neat bell curves with no peculiar lumps or bumps.

So, given that the CB doesn't really shift at heel, should I reduce lead below 10%?

I went to Duckworks and ogled Rogue again -- what a beautifully proportioned boat that is. The sprit lug is interesting (I've never encountered that variation before), and would probably serve my purposes well. I don't see a downhaul on your drawing, though. Is there one?

I use a conventional standing lug on my sailing canoe, but have never had a problem with twist (on a run, I sometimes hook the mainsheet over a fairlead on the inwale, which helps keep things in place).

I've always meant to try Todd's nifty auto-vanging sheet arrangement.

Stephen -- Thanks for passing that along.

[Bruce Taylor]

Thanks again, John. I'm looking forward to your next article on Duckworks.

I think I'll stay with the sprit/lug. I rather like the battened lug I drew, but Todd said it "looked kind of interesting", LOL! Faint praise indeed.

Now I have to figure out a shape for the rudder and dagger board. Immersed lateral area, w/out rudder or DB, is about 5 sq. ft at 600 lbs displacement. I figure the rudder should have an area of about, hmm, 1 sq. ft.?

I was considering putting the DB forward a bit and angling it toward the stern. Does anyone have any thoughts concerning DB placement and overall shape? Any rules of thumb I should know?

[john welsford]

Originally posted by Bruce Taylor:
Thanks again, John. I'm looking forward to your next article on Duckworks.

I think I'll stay with the sprit/lug. I rather like the battened lug I drew, but Todd said it "looked kind of interesting", LOL! Faint praise indeed.

Now I have to figure out a shape for the rudder and dagger board. Immersed lateral area, w/out rudder or DB, is about 5 sq. ft at 600 lbs displacement. I figure the rudder should have an area of about, hmm, 1 sq. ft.?

I was considering putting the DB forward a bit and angling it toward the stern. Does anyone have any thoughts concerning DB placement and overall shape? Any rules of thumb I should know?I use a figure of 60% of the lateral plane area of the boat excluding and fins or skeg, this figure based upon an aspect ratio of 3.5/1. I try and place the trailing edge at 45/50 or the w/l back from the fwd end of the static w/l.
You can modify the area, less for higher aspect ratio, and more area for lower. Rudder about 1/3 of the area of the daggerboard.
There are as many exceptions to his rule of mine among my designs as there are inclusions, but its a good place to start.

There are more of my stories coming up from Duckworksmagazine, and some in the newsletter section of www.jwboatdesigns.co.nz (http://www.jwboatdesigns.co.nz) . Thanks for being interested, I know this is not the place to get commercial so when you go there dont read the advertisy bits. ( Its not complete yet and the serious bits are not there anyway)

John

[Bruce Taylor]

Good thing I asked...60% is more than I would have guessed.

I'm running out of fun calculations to perform, and it's too cold to start building.

I can't get through to the website, for some reason. Meerkat?

[Don Olney]

Thanks to Bruce, Todd and others for this thread and the "Quick and Dirty Model" thread. This is the WoodenBoat Forum at its best -- interesting, fun and informative.

[Bruce Taylor]

Don, I've been staggered by the quality of help I've received on this project. I initiated six different threads on this boat, and all are packed with useful info. from people who know what they're talking about. Thanks to all who pitched in.

I started lofting today. I probably won't start construction till next spring, but I hope to have the moulds up before Santa comes.

Help me Design a Camping Boat (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=001925)
A Boat Design -- Critique? (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=002002)
A Revised Design -- Throw a Pie... (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=002011)
A new Sketch -- Better, or Not? (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=002020)
A Quick and Dirty Model (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=002059)
Ultralight or Featherweight? (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=005829)

[ 11-05-2002, 06:02 PM: Message edited by: Bruce Taylor ]