Small sailboat Design - advice requested

It's always reassuring when they don't flop over on their sides on launch day. Congratulations Terry.

A few notes; the silver tarps are the heaviest of all the tarps. You'll want to get the lightest you can find. I'm sure that was just one you had around the garage. Try to access her sailing abilities in winds from 5 to 10 knots. Under this wind strength and you'll just be testing you patients and over this wind strength you're sailing ability. Your attempt at a "Ljungstrom" rig is notable, don't give up quickly, but don't be surprised if you find the same things everyone else has about the rig. During setup of the booms, make them angle down at their after ends (several degrees). This will cause them to be self "vanging" which is an ideal thing on a small boat and the whole point to using a sprit boom. It also appears your mast is in the aft hole. It needs to be in the forward most hole or the helm will be "lee" on you.

 

------------
You deserve congratulations as well,Paul! Damn fine design!

 

- now you tell me! It is my own fault as I selected them for the color. I should have known they would be extra heavy-duty, as I bought them at the farmers' store. Still, one day I may appreciate having a cow-proof sail.

 

Terry....

See this patent.....http://www.google.com/patents/about?id=7A8zAAAAEBAJ&dq=bruce+king

It's a double-sided sail on twin independent booms with a rotating mast. To windward the sails fold around the mast and lie alongside each other. Off the wind the sails unfold....wing-n-wing style (as you tried) and the mast rotates taking the head forward and becoming more spinnaker shaped.

In practice it works quite well, downside is there are lots of bits to keep track of. Carbon spars keep it very light. It's just never been commercially developed.

 

Tad: I saw that one recently, and it also references this one which is even closer to my design http://www.google.com/patents?id=tbMsAAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q=&f=false

The main difference is, I only propose to use it downwind. Naturally I'll experiment with it inother directions but I expect it will require large amounts of lee helm. Paul tells me my double sail is called the Ljungstrom rig.

 

Here you see a good example of the Ljngström rig:
(http://3.bp.blogspot.com/_jM-1EKCHjJU/R6tfZVl0pRI/AAAAAAAAACI/QC3rN7iTBqQ/s1600-h/DSCF1072.JPG)

 

Some info here,
http://dobrakusa.blogspot.com/2006/12/rig.html

 

Thanks for the info Raggi! I wondered if it would work with a loose-footed sail, now I can see that it does, at least downwind. The simplicity of the boomless design is offset by the need to manually rotate the mast, however the mast-furling system is nice. This will give me a lot to think about during the hard-water season!

Afterthought: according to the Oxford online dictionary the term "Ljungstrom rig" describes a loose-footed sail set on a rotating mast; the double sail is an optional feature. This older thread discussed it http://www.boatdesign.net/forums/sailboats/split-mainsail-has-been-tried-before-20229.html which I hadn't seen before. Search tools work much better when the correct term or name is used.

 

Statistics

I was going over my building log yesterday. I can't remember if I undertook to provide building time data but here it is for those interested. For comparison, I usually complete a small canoe in a little over 30 hours fully finished. There was a bit more to this boat.

Hull construction 80 hours
Hull finishing 20 hours
Rig* 40 hours
Total 140 hours.

Times include temporary frames and jigs specific to this boat. I expected about 100 hours total when I started, but I had no idea the rig would take so long. The time-consumers in hull construction were the bulkhead, daggerboard trunk, buoyancy tanks/seats and transom, only 12% of the hull weight but 50% of the time. I don't have to have to deal with those in a canoe.

Interesting statistic: my canoes weigh about 20 lb/9 kg: that's 1.75 hours/lb for for the sailboat and the canoes.

* Rig in this context comprises everything except the hull, i.e., mast, booms, sail, rigging, daggerboard, rudder and tiller.

There was a fair amount of design time involved because I did not follow the designer's plans exactly; that time is not included. Also there were mistakes and repeated work: I excluded that where it was to fix one of my design errors and included the rest, so for a builder working from a detailed construction plan these times are honest. However, for a first-timer there would be extra time for nail-chewing before cutting expensive wood (I'm over that phase), time to build useful general purpose jigs I already had, and setting up a workshop; probably 200 hours.

Calender time was 3 months, May to Oct less about a month vacations and sick leave. Total days worked 61; Longest working day 6 hours, average hours per day only 2.3! Lazy *******!

The total weight of the boat is 60 lb (hull) + 20 (rig -as defined above) or 80 lb, 36 kg. Construction is 4 mm okoume marine ply throughut except bottom which was 6 mm, some hardwood ply, plus cedar, oak, pine, spruce and what they call "mahogany" these days. Epoxy used on joints exposed to water or where gap-filling was needed, and Titebond III glue used for well-fitted joints elsewhere.

Hull is 10 ft/3 m LOA, mast 14 ft/4.3 m (2 piece telescopic wood), sail area is 33 sq ft/3 m2, which can be doubled for downwind. Of course, she will acquire several bigger sails to play with over the Winter. It never stops!

 

Thanks, interesting numbers.
Would cnc precut also cut the total hours significantly?

 

I believe those figures were within the estimates we discussed at one point or another in the process, Terry. 65 square feet of sail area will be about right for this little boat, for best performance without gymnastics. 2.3 hours per day production time is very respectable as a part time project. That's over 5 hours a day actual time at the boat, including butt scratching, tool finding, cigarette smoking and fetching fresh beer breaks.

The actual panel cutting time wouldn't really affect the overall build time by a significant amount I don't suspect. CNC panels are a wonderful marketing tool and do offer class racer and one design options, but don't save much in build time. They can improve hull shape compliance considerably as well as assembly ease on a well thought out kit, at the cost of considerably more in machine cut materials and it's shipping to your location.

 

Ragnar: my best estimate, since I did not always record cutting and assembly time separately for all components, is the time spent cutting and rough shaping totalled about 32 hours. That was more than I expected.

Paul: Yes, those numbers are about right. My approach to the mast and booms was a bit more complex. The precut parts of a kit save significant time as well as reducing worry and perhaps providing a better selection of material, but I enjoy cutting the ply and lumber.