Kaimusailing

s/v Kaimu Wharram Catamaran

Vessel Name: Kaimu
Vessel Make/Model: Wharram Custom
Hailing Port: Norwalk, CT
Crew: Andy and the Kaimu Crew
About: Sailors in the Baltimore, Annapolis, DC area.
08 July 2024 | Somers Cove Marina, Crisfield, MD
25 June 2024 | Somers Cove, Crisfield, MD
12 June 2024 | Somers Cove, Crisfield, MD
03 June 2024 | Somers Cove, Crisfield, MD
25 May 2024 | Somers Cove, Crisfield, MD
21 May 2024 | Somers Cove, Crisfield, MD
12 May 2024 | Somers Cove, Crisfield, MD
09 May 2024 | Somers Cove, Crisfield, MD
01 May 2024 | St. Marys, GA
23 April 2024 | St Marys, GA
17 April 2024 | St Marys, GA
07 April 2024 | St. Marys, GA
02 April 2024 | St. Marys, GA
21 March 2024 | St. Marys, GA
01 March 2024 | St. Marys, GA
23 February 2024 | St. Marys, GA
15 February 2024 | St. Marys, GA
11 February 2024 | St. Marys, GA
06 February 2024 | St. Marys, GA
26 January 2024 | St. Marys, GA
Recent Blog Posts
08 July 2024 | Somers Cove Marina, Crisfield, MD

TFH!

I was out of cheese and ham. This meant a grocery trip and then of course, visit the American Legion. Cuddily said she would be there after baking fresh fish that she got from her neighbor fisherman.

25 June 2024 | Somers Cove, Crisfield, MD

June is Too Soon

It is Juneteenth, election day for the City of Crisfield, twenty four hundred voters. Up for election are two city council seats for three candidates. The mayor wants to keep her current city council team.

12 June 2024 | Somers Cove, Crisfield, MD

Raindrops and Rainbows

You can take the Mediterranean diet too far, especially with the wine consumption. The noodles are OK if you are burning up the calories, but otherwise they will put on the pounds. So you are left with antipasto, not much else, salad? Chicken Parm? Yes, the chicken parm is probably in itself pretty [...]

03 June 2024 | Somers Cove, Crisfield, MD

Prejudicial Treatment

The excitement of a new baby in the family had me receiving phone calls from all over. The common denominator is that we talked about the weather and food. That makes me hungry and start planning to cook. Cuddily suggested we go to Sysco in Pocomoke to see what wine selection they had there and also [...]

25 May 2024 | Somers Cove, Crisfield, MD

Cap'n Granpa

The Memorial Day weekend was coming up and it is a big deal in Crisfield as well as most of the rest of the Chesapeake. It is the traditional beginning of the summer season. All the boats are launched or commissioned, lots of activity in the marina, motors started up for the first time in a long time, [...]

21 May 2024 | Somers Cove, Crisfield, MD

Cap'n Overboard

The awful jobs get done last. The Atomic Four was waiting for me to pull off the cylinder head, but there was an emergency job, sort of, the mainsail cover was torn and exposing the sail to U/V, very bad.

Proa Pt. VII

30 December 2013 | Bodkin Inlet/Chesapeake Bay
Capn Andy/winter
The proa project isn't dead, just sitting on a shelf since last winter. The model has been knocked around, almost destroyed, and the idea has faded, smothered by all the work and concern for the big boat. When we last set the proa aside, we had built a model to water test things like sail balance, self balancing a sailing course, and see if the hull would run smoothly if there were any choppy waves.
.
While we wait for the opportunity to test our proa model outdoors, we have to resort to vector math and “mind experiments” to try to determine how the boat will perform. It is useful to read as much as possible about other proa designs that have been built. It's like the internet is taking the place of the old guy down at the docks who knows everything. The fact is the internet only has what is posted there. There is a lot online, though, and some of our design elements have already been tested on full size boats.
.
One of the best resources on outrigger sailing canoes is the book by Gary Dierking, also his blog at: http://outriggersailingcanoes.blogspot.com/ Another is the proafile website by Michael Schacht.
.
While skimming through Dierking's other site, the one on which he sells plans for outriggers, I noticed there were links next to some of the photos of examples of his designs. The links lead to other sites, some with detailed build photos and sailing videos. Every time I think I've exhausted available proa information, I find a new link and new answers to some of my questions.
.
One question is about lining up the sail's driving force with the hull's sideways resistance. The traditional proas were of deep vee hullform with the hulls sideways resistance distributed all along the hull length. The center of this resistance moves forward and aft when crew move forward and aft, because the hull sits deeper in the water at whichever end the crew moves to. The traditional oceanic lateen sail also distributes its pressure along a long low aspect ratio triangle. It is relatively easy to balance the sailplan with the hull. Additionally the hull shape had a fore and aft curve, winglike shape, so that the windward side of the hull, toward the outrigger, would have more curvature, while the lee side of the hull would be flatter. This shape would tend to turn the boat downwind, but the sail plan was balanced to this lee helm tendency and they would balance out. An additional benefit was improved windward lift and improved downwind steering.
.
On a more modern hull, the sail tends to be higher aspect ratio and the hull tends to be more canoe shaped with a centerboard or daggerboard of high aspect ratio. These foils are more precise in the location of their lateral resistance, so the balance of sail and hull requires more precision. Normally this can be determined by careful calculation as well as trial and error over several generations of design. Because there are so few modern proa designs, a new design has little to go on. Dierking's book, which still hasn't arrived here, outlines three of his designs and will hopefully provide hands on experience to help with our new design.
.
Already the question of where to put the leeboard seems to have been answered. Dierking puts the leeboard in the center of the outrigger float or at midship of the main hull. A new design by John Harris at CLCboats.com puts a centerboard in the middle of the main hull, but that is a tacking design similar to the old Malibu Outrigger. Their building crew took just 5 days to make the first two prototypes. They are using an oceanic lateen sail of 162 sq ft. Should be a lively boat.
.
The question of what type of rig seems to settle down to 3 possible rigs, adapting an existing windsurfer rig, the oceanic latteen sail, or the Gibbons-Dierking rig, which looks promising. It looks like providing for any of these rigs would be a good idea in a prototype. The leeboard should also be able to be mounted on either the main hull or the outrigger in whatever position works.
.
Instead of getting the model to sail, it might be better to construct the full size hulls. There is a canoe on Duckworks.com that is constructed in 4.5 hours! The same technique could produce a proa sharpie hull in about the same time. They used polyester resin instead of epoxy, and it cures much faster, enabling work to continue at a faster pace than gluing with epoxy and waiting a day or so for the resin to set up. A prototype made quickly could be a smart way to go, use inexpensive plywood and inexpensive resin that works quickly, and then if the result has design flaws, it is just a prototype, and we can move on to a second generation design.
.
I found some quirks in the design software I had used last winter. The HULLS program doesn't update the table of offsets, or the resultant printable patterns until the x,y,z coordinates are entered from the design program, graphically. Also the “Delete Old Patterns” function has to be clicked. What this means is, entering the numerical values into a loaded design doesn't seem to change the patterns that are printed out for the bulkheads, hull sides, etc. unless the changes are entered from the graphic display of the hull. Click on the point on the hull that is to be changed and the coordinates come up in a series of query entries. When the new values are entered, the point then moves to its correct position on the graphic display, the table of offsets is updated, and printed out patterns reflect the changes. Beware, though, any changes are automatically saved to the default.hul file, so the default now becomes whatever you have just changed, any fooling around with the design now becomes the default when you open the program next time. It is still possible to load a saved .hul file, but even that will not be saved in its own filename, it will be saved in the default file. I'm writing this so that I can sort this out, next time I use it. It's a nifty program that helps with chined hull design and can generate a printout of the flat surfaces that make up the hull. An example would be a lapstrake boat with, let's say, 10 planks along each side. These could be set up in the design and tweaked into a smooth shape, the program will show the waterline at an arbitrary displacement weight entered. Then each plank can be printed out in its exact shape. The designer can accomplish what an experienced builder does with a real life boat, but when it doesn't work out, there isn't an unfinished disaster, the design can be wiped from the computer.
.
There is another valuable asset on the internet in the form of Tom Speer, an aerodynamicist, who actually descends from the world of spaceflight and cutting edge military X planes to spend some time helping us sailing lepers with our foil shapes. The rudders and daggerboards of high performance catamarans have evolved thanks to professional design engineers who have used advanced methods to solve problems of ventilation, drag, and getting boats to fly on hydrofoils. This is the new coming thing. I've downloaded a ton of information provided by Speer, maybe the only one doing serious research on foils that have the same symmetry as a pacific proa. This would be a foil that has both ends symmetric, but each side is not necessarily symmetric. The old foils of the Amateur Yacht Research Society were flat on one side and the other side was curved like the arc of a circle. They wrote then that these foils seemed to work well. Speer finds through his analysis that they didn't work so well. Maybe better than a flat board with a rounded edge, but nowhere near as well as a NACA foil section. The NACA sections were designed to work in one direction of travel, but a proa swaps ends and sails off in the other direction, and its foils might not work so well going backwards. Speer discards those shapes that won't work and shows shapes that will. The boat designer can specify a foil that has to be reset 180 degrees each time the proa shunts (tacks), or use one of these shapes that is good on both tacks.
.
Although proas have narrow constraints on their design, the other outrigger, tacking outrigger, has a lot more activity. I ran across tacking-outriggers.com while reviewing CLCboats.com's outrigger junior design and it's origins in a much earlier design, the Malibu Outrigger. Going there brought me to the genesis of my current daysailer, the Hobie cat. Hobie had Warren Seaman help him with advice about the original Hobie cat. Warren Seaman designed the Malibu Outrigger, a direct attempt by a USA Pacific soldier to replicate the outrigger canoes he saw there. Later he would team up with Rudy Choy and A. Kumaliae (?) to form CSK yachts, one of the first and best catamaran design and construction teams.
.
On the tacking outrigger site I came across a few designs labeled “KIR” and “PNG”. The links lead to a UN program of modern outrigger design for indigenous fishermen in the Pacific, replicating some of their familiar canoes with new designs using modern methods and materials. Modern in the 1980 and 1990 era sense. There are about 30 designs, downloadable, but only worth the trouble because I've been looking for tortured ply designs, also known as compound surface designs. There were two designs there that look like I may be able to use someday. Also some of the other designs had shunting proas and details of crossbeams, rudders, and many sailplans.
.
I found a modern A class design which was also tortured ply and I already have Tornado plans, a larger tortured ply. What is difficult about tortured ply or other compound surfaces, is that most design applications need a table of offsets to input a design, and tortured ply works with a defined edge to the 2D surface which is forced into a 3D shape, so there is no table of offsets, just an accurate profile of the 2D surface. The KIR and PNG designs torture their plywood differently, they bend it over a form which has coordinates similar to a table of offsets. I can input these into a design application and work with that framework to make any other compound surface design. To put it another way, I can input them and tweak them to create a new tortured ply design.
.
Why tortured ply? The traditional plywood designs use chined construction with a long piece of wood at the gunwales, at each chine, and at the keel, to define the shape of the boat. The next revolution was taped seam construction which did away with the chine “logs”, the long pieces of wood. The taped seams were still using an angular shape to mimic what was earlier made with hand carved dugout canoes, or built up round bottom designs using planks of wood to make a curved shape. Tortured ply evolved from some designers twisting and bending plywood planks to try to match a curved shape. The ultimate was a complete hullside made in one piece of plywood, but curved and bent to make a compound shape. The construction was further simplified, just bond the two hull sides together at the keel at a specified angle, then bend the sides together at the gunwales to a rounded shape.
.
The usual design process for compounded shapes is to build a model to exact scale and by trial and error come up with the desired shape. Software can predict if a shape is compoundable, but it can't compound a two dimension shape. So, it is beneficial to have a compounded plywood design with a table of offsets. The shape can be defined in software and modified, and the software will let us know if the modified shape is compoundable. It will also produce the profile of the new hullside.
.
Modifying the existing table of offsets can let us lengthen the design, change its sheerline, attempt to add more volume, change the profile of the keel, and when we're done it will spit out a two dimension shape to cut out of ordinary plywood.
.
Our current design has compounded shape in the deck above the bow(s). I am aware of the problems involved in determining the shape of an internal shelf or stiffener, which the design needs. One way is to start with a known compoundable profile, then build with it, and then take off measurements and shapes that will fit the design. The problem is that the stiffeners help shape the design, so it's another Catch 22, you can't shape without the stiffener, and you can't profile the stiffener until the hull is shaped.
.
I had hopes for DELFTSHIP, a design application that works with almost any kind of data input. Several existing hull design file types can be imported, including the .hul files. Table of Offsets can be input using a comma delimiting text file. Line drawings can be input at jpeg or bitmap files, rescaled to match the scale of the “desktop” and new computer drawn lines can be matched up to the background. The best feature is the ability to flatten the 3D compoundable shapes into 2D cutting patterns. Why does a ship building design program have this feature? Many vessels are built out of compounded flat steel surfaces and shipyards are looking to reduce waste and reduce the amount of welding in construction. For the plywood boatbuilder, it has the same benefits.
.
Now for the downside of DELFTSHIP. It is a professional engineering design program, which costs a lot for the home builder, and the free version we are using has some missing pieces, such as not allowing export of the 2D developed shapes. There are other restraints, but the developed 2D shapes have detailed measurements that would allow the shape to be marked out full size in real life.
.
The picture is the DELFTSHIP lines plan of the KIR-7 proa main hull. The design can be found easily with a google search. The boat is built by cutting out the hull sides from detailed measurements and forming around a couple of bulkheads. The DELFTSHIP app enables this design to be digitized and modified using a computer.
Comments

About & Links

SailBlogs Groups