Hitting the Nail on the Head with CC19

We all know what it means to "hit the nail on the head". Taken literally, it is so satisfying to hit a nail so square and hard that it drives a long way into the timber. Just a few such blows and it is home, securing whatever its destiny in life was to hold in its given place. Taken figuratively it means that we have expressed an idea very clearly and in a way that resonates with others.

In just the same way, it is possible to design something that is just perfect, that we would not like to do any differently if we were to start again from the beginning, even if armed with the experience that came from the use of that product. A designer can and should get tremendous satisfaction from his/her involvement in the process whenever that nail is so squarely struck on the head. I have been lucky enough to find that nail a few times.

The Cape Cutter 19 is just such a design. I really would not change anything at all about that little boat. I have not sailed them enough and hope that I will get many more opportunities to sail them. The sailing that I have done has always impressed me with the extraordinary speed, handling and ability of this little boat.

Two Cape Cutter 19s drying out in UK.

 It is not a racing boat, so dont expect it to plane downwind like a sportboat. It is a little cruiser that can sometimes make you feel like you can take on the sportboats. Take it out in light conditions and it will sail past virtually any other cruiser or cruiser/racer of similar size, as well as taking out many much larger boats that should be a whole lot faster. It is oh so satisfying to sail past a boat that looks much faster but isnt.

It is not only a light-weather boat though. Remember, I grew up sailing the waters of the Cape of Good Hope and spent most of my life sailing there. Most circumnavigators tackle the Southern tip of Africa with great trepidation because of the often violent wind and sea conditions. For those who live there, those are the conditions that are given, so they have to be dealt with. I designed the Cape Cutter 19 to sail those waters safely, with due diligence by the skipper, of course.

There is a really nice independent review of the CC19 and its bigger sisters on the SA Yacht Blog . It includes observations by the author of boats to these designs that he has seen in action around the Cape of Good Hope and how they have managed in those conditions.

These boats are loved by their owners and they are very sad to part with them. One such owner is Russell Eden in UK, who sold his CC19 this past weekend. I received these messages from Russell, repeated with his permission.

"I sold my Cape Cutter 19 today after three years of ownership.

She was number 47, built in SA. I wanted to personally thank you for creating such a beautiful craft. Each and every day I sailed her I had people approach me to talk. People would sail/motor over to take photos and video. People offered me money for her, there, on the spot.

Ive only sold her because my wife says she will come sailing with me more often if we had a boat with full standing room and a heads. I would have kept her forever otherwise.

Im sitting here now wondering what Ive done; Ive let go perhaps the most wonderful piece of property Ive ever owned. No doubt Ill get over it in time, but I doubt Ill ever own anything quite so easy on the eye, or so wonderful on the water.

Thank you for designing her."

Russell followed up with:-

"I really meant it too. You designed something which grown men cry after.

 That said, it was only ever the white ones I lusted after. I think you need to be able to see the lapstrake, which you cant always do on the darker hulls."

Russell Eden sailing his CC19 "Zephyr".

Thank you Russell, for your kind words. I get great satisfaction from them.

The Cape Cutter 19 is a GRP production boat built in UK by Honnor Marine . It can also be built from plywood from plans that we supply at http://dixdesign.com/ . There you can see our wide range of other designs as well.

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More on Stability with Water Ballast

John Gilbert asked a question in response to my recent post, Stability with Water Ballast.

I do not get why the red and blue curves do not meet up at 180 degrees. Inverted the boat has no windward side as you point out, so you have water ballast on one side and none on the other side. As you have drawn the curves you have powerful stability in the  inverted position with the water on one side (red), but actually a righting moment if you have water on the other side(blue). What is the difference?

To help with understanding this I thought it better to write a new post that expands on the dynamics of stability than to try to answer it in the comments section after that post.

This will be more easily understood by seeing a diagram showing the stability graph expanded through a full 360 degrees rather than all conditions overlaid on top of each other in a 0-180 degree range. This is exactly the same stability info for the Didi 950 as shown in the graph of my earlier post but shown in a different manner.

Diagram of Stability through 360 Degrees

I will start with the green curve. This shows the stability without water ballast. The centre of gravity (CG) is on centreline. The stability curve intersects with the horizontal grid line at 0 degrees heel and increases identically both to left and right of the 0 degree line, so the boat will float without any heel to either side when right way up. The boat will stay that way in the absence of any wind, wave action or crew movement on the boat.

Follow the green curve until it comes down past 130 degrees to again intersect with the horizontal line at the Angle of Vanishing Stability (AVS). Then it enters a range of negative stability where it will proceed toward upside-down. At 170 degrees it crosses to above the horizontal line again. This indicates that the superstructure volume is trying to turn it back upright and doesnt want the boat to lie totally inverted. It will easily flop back and forth between the 170 and 190 degree points. The boat can return to upright along either green curve.

This all depends on a totally waterproof superstructure, of course. In practice water is likely to enter the boat at a rate that depends on what is open at the time, which will affect the inverted stability. 

Moving on to the stability with water ballast, in my earlier post I said that the boat will capsize along the red curve and recover along the blue curve. I explained the relationship between the two curves but that relationship is not easy to visualise if only seen across the 180 degree range.

In the diagram above you can see that the red and blue curves only meet in two places and both are on the horizontal line. These are the two points at which the boat will rest when there are no outside influences from wind, waves or crew movement.

The boat cannot rest totally upright nor totally upside-down because the weight of the water to one side is heeling it toward that side. It will rest at approximately -5 degrees heel instead of upright and at 200 degrees instead of upside-down when inverted.

Bearing in mind that the areas of the curves below the horizontal line indicate how much energy it needs for the boat to get past the AVS points so that it can right itself when in that 200 degree situation, it is now easy to see that it will take a large amount of wave energy to get past the AVS of the red curve but a very small amount of wave action to get past the AVS of the blue curve.

This graphic shows that if a water ballasted boat capsizes it will do so along the red curve but it is very unlikely to return along that same path, nor is it likely to stay capsized for long. Once past the AVS of the red curve the negative stability will push it to 20 degrees past upside-down. After that the blue curve will take over and almost guarantee that the boat returns to right-way-up pronto.

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Winter on Beaver Creek with Wild Rose

As promised, photo evidence from the Oregon coast on the first day of 2014.

The group of hardy individuals who brave mid-winter weather to drift quietly on local coastal rivers grows weekly. The last time we did this, temperatures were below freezing, but yesterday the most challenging problem was having worn too many layers.

From some of the shots, you can see the brilliant, low-angle winter sun played havoc with picture exposure.


May all lifes difficulties be so taxing.

Beaver Creek empties directly into the Pacific Ocean just south of Seal Rock, Oregon. The estuary is protected by recent acquisition of property by the State of Oregon Fish and Wildlife Department and is quickly becoming a popular kayak destination.

The creek meanders through a marshy estuary and upstream, soon narrows to a trickle. There is a sandbar across the mouth that prohibits salt water intrusion and limits the current flow. You can see the bar in this photo. Yes, those gulls are standing on the sand. To get this picture, I was in a narrow channel in about a foot of water, with a swift current threatening to wash me up on the sand, or out to sea. Just time for a quick shot, then paddle like mad!

Exploring this creek was the initial motivation for building Wild Rose. A row boat just takes too much width to get very far upstream, as can be seen with Lazy Duck. Wild Rose will open a whole new navigational experience for me. Im looking forward to it!




As always, more photos can be found on Dorymans Flickr site.

All the best to you and yours for the new year.

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Boatbuilding with the Shopsmith

If you have a small shop, as many of us do, how do you cram in a table saw, a drill press, a lathe, a disk sander, a jointer, a band saw, a horizontal boring machine, an over-table router, and a thickness planer and still have room to breathe?

The answer is, with a Shopsmith

The Shopsmith multi-purpose tool can do all that, and a whole lot more, for a lot less than buying all of those tools seperately. Not only that, but you can buy a used Shopsmith for about the cost of only one of those tools, fix it up, use it for years, and pass it down to your grandkids someday for them to use.

The Shopsmith has been around, in various forms, since the first model 10ER built by Magna was sold by Montgomery Ward in 1947. An improved Mark II was introduced in the 1950s, followed by the Mark VII with lots of extras including the ability to tilt in both directions and included a built in vacuum. But the most popular and most versitile model is the current Mark V. Production ceased in the early 1960s due to a variety of changes within the company and the buying public, but production resumed in 1973 under a new company - Shopsmith Inc. Over 1,000,000 Shopsmiths have been sold.

The Shopsmith is built to last - essentially forever. Every part, down to the individual screws, can be ordered as replacement parts directly from Shopsmith. The entire machine is made of cast aluminum and steel. Its difficult to find a plastic part on the machine anywhere. Service manuals, operation manuals, videos, even instructions on how to refurbish a used machine are all available from Shopsmith.  Compare that to most other power tools sold today.  When something breaks on them, their next destination is usually the landfill.

New Shopsmiths are not cheap - not surprising for a machine built to last a lifetime. They start out at about $3,300 for the base model, but used Shopsmiths can be found, sometimes very inexpensively. I purchased my Shopsmith model 510 complete with the bandsaw and jointer accesories, for $350 from a gentleman on Craigslist. The machine was about 12 years old. It had only been used a few times before it was stored unused in a barn for about 10 years. The machine was missing some parts and parts of the machine were rusty. I paid another $150 to replace the parts that were missing or that needed replacement, and spent several days cleaning off the rust. I overhauled the headstock, following the instructional videos provided by Shopsmith. The headstock was in great shape except for one part in the speed controller. The rust on the way tubes came off pretty easily with fine sandpaper. After the overhaul I spent several hours adjusting the machine so that it cut square and true. I now have a Shopsmith which is as good as new, for $500 and about a weeks worth of elbow grease.

The machine is about the size of a bicycle. It has casters which enable the machine to be rolled around the shop to where ever it is needed. When done, I roll it over to its parking spot next to the wall. Foot levers on the casters allow you to lower the machine to the floor so it rests solidly when in use.

Here I have my Shopsmith set up as a table saw.You can add table extensions to make the surface larger for cutting big stock, like sheets of plywood, or simply use the main table for smaller items. To cut angles, the table is rotated, not the blade as on most table saws.

Boatbuilding involves quite a bit of ripping of long stock. For that, you need an outfeed table. I built this home-made outfeed table from a piece of plywood and some scraps. It attaches quickly with no tools required. It use it frequently and it works great.

When Im not using the outfeed table, I usually just let it hang like this.

The bottom of the outfeed tables support leg has an eyebolt in a slot.  The eyebolt simply slips into a hole that I drilled in the table upright.  There are a nut on the eyebolt to adjust the table so its level, but that only needs to be done once.  The upper end of the leg has a "ball and socket" joint.  I made the leg this way so that the table can be raised, lowered and tilted, along with the main table without any adjustments.

Next function: the disk sander. The sanding disk can be attached at either side of the headstock. It makes quick work of sanding all those flat edges of your Navigator bulkheads straight. It can also be used like a grinder to sharpen tools. If you had a very large part to sand, you could assemble a large table using the table extensions (like I did for the table saw). The versatility of this machine seems endless.

Id be lost without my bandsaw. It drops into two mounting holes on the left side of the machine, and then you attach it to the headstock with a coupler and youre in business. The bandsaw is powerful. It will resaw lumber up to 6" thick without a hint of bogging down. It will cut metal too, with the proper blade. When cutting long stock, again, the table extensions can be set up to provide a very long outfeed table. This is one of my favorite setups.  Ideal for cutting planking!

Next, the jointer. Like the bandsaw, it drops in on the left side of the Shopsmith and connects to the headstock using the same coupler, except it connects to the high-speed port. I use the jointer to plane boards perfectly flat, such as those strips used to make the centerboard and rudder. It will plane a board about 3 1/2" wide laser straight.

I forgot to mention, the table saw, band saw, and jointer all have ports where you can attach a shop-vac to collect the shavings and sawdust as you cut.

I havent used the lathe very much yet, but its there when I need it. Too bad Navigator doesnt use belaying pins, they would be fun to make.  I did use it to make all the nice wooden handles that you see on the machine.

To use the Shopsmith as a drill press, you first lock the headstock in place, install the table, turn it vertically and lock it, then release a locking handle and flip the headstock up vertically. This creates a far better drill press than your typical drill press.  Table extensions can be used to create a very large horizontal surface for drilling large items. The table can be tilted to drill holes at precise angles.  The rip fence can be used to align and clamp workpieces.  I used this to drill the pivot hole through my centerboard case and centerboard perfectly straight and perfectly aligned. I also use the machine in this mode, with a Wagner Safe-T-Planer to thickness plane stock. Its not as fast as a thickness planer, but it works just about as well plus you can plane at an angle. Here is a video demonstrating the Safe-T-Planer
I also use Forstner bits to hollow out the hole for the lead in the centerboard, and the hole in the mast steps, and of course for countless routine drilling operations. I also mount a drum sander to sand interior curves.  I even mounted various router bits with the large table to "machine" my rudder.

If you ever need to drill a hole in the end of something very long, or a piece that wont sit flat vertically, the horizontal boring function will come in handy. Here I am drilling a hole through the Navigators stem for the towing eye.

I should state that, no, I dont work for Shopsmith Inc. Im just a very satisfied customer.  The thing that impresses me most about this machine is its versatility.  Ive even found crazy and effective ways to use the machine that its designers probably never dreamed of.

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Sailing with Andrews Navigator Wren

Sailing Ellie alongside my friend Andrews beautiful Navigator Wren at the Port Townsend Pocket Yacht Palooza Crooza around Marrowstone Island, Washington was a real treat.

 

Andrew did a magnificent job building Wren. Her beautifully varnished seat tops and laminated tiller are especially beautiful.  I love her colors, and envy the batten arrangement in her mainsail, which allows the main to be dropped without removing the battens, unlike mine.  Comparing boats was a learning experience for us both, as we pondered  each others ideas.  There are more photos of Wren here.

The Palooza and followup cruise were both fantastic.  We had every kind of weather, which made the trip quite interesting.  It was great meeting John Welsford again, albeit briefly, as John was quite busy tending to his Scamp Camp.

For more photos of the Pocket Yacht Palooza and Cruise, click this link.

Cant wait to do this again next year!

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Reconecting with my past Thanks !

One of the reasons I started to write my thoughts and life experiences down here is to share with my daughters and others what could be done in life with very humble beginnings, a bare bones education, some common sense and lots of work. I have been mostly self taught because I never really liked being in school and the time it took out of my day. I have always just wanted to study what interests me and pass up on the rest. This approach has worked out ok for me but I have explained many times to my daughters that it will not work for them as they are not like me. The world has changed in my short lifetime and is not as simple as it once was. Plus they are way smarter than I ever was so a good education will do them well in life. 

I have had more time lately as my kids are gone from home . My wife has a summer job up north , rain squalls interrupt my day for short periods so here I sit trying to exercise my mind while waiting for the rain to pass. Our place is small 12x16 with 10 porch . I work outside so when it rains its break time.

 Since posting my Flats boat building history I have received many nice emails and photos of past boats from old clients and new second owners. Its been very nice to reconnect and to meet the new owners. When I started this blog we were on the move all the time, internet was very slow in the places we were sailing. I did not have the time or inclination to sit and ponder. Today is another matter. Now I connect every where and with this new iPad contraption my daughters gave me for Christmas its so fun and fast. Two weeks ago Lillian asks me if I know how to see who and how many people are reading my blog. What you can do this !!!? She shows me why and how its done. Amazing . 23,000 views to date on this blog from all over the world. I had no idea. Now I understand why all those ads know whats on my mind. Kinda scary. 

A nice picture of a Whipray posted on the Tribenwaters sight telling me how much fun he has enjoyed  his skiff.

Latest email has this picture from an early client in HBBWs time when I actually was doing the glass work trying to train people. Back then I was still not comfortable backing up in my new F150 so on the delivery day sea trial I asked the owner to back her in for me. This is the first big engine we put on one of these skiffs . He says he just sold it to a good friend after 17 years of using it. 

Thanks for the memories

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Finished with the interior firing

As the title says, Im finished with the interior firing, and await the insulator. While the firing job is neither sexy nor that much fun, it sure is nice to walk into the shop and smell fresh sawdust vs acrylic urethane, epoxy and thinner.

Theres really not a whole lot one can say to dress this job up and towards the end it just felt like work. Looking at whats left of the 1000 count box of bolts, nuts, and washers, I have to conclude that I installed over 600 of those little rascals. My ten year old 3/8 air ratchet took a dive on me during this project, so that got replaced. I used a case of polyurethane adhesive, and a fair amount of lacquer thinner cleaning the adhesive off of my hands.

I had a few people ask me what I meant when I stated I held the firing proud of the steel frames, so I thought Id include a picture showing how the lumber sticks past the framing vs explaining it. Installing it this way will allow me to use the lumber as a screed when trimming the foam, and will insure all the metal is covered with foam. Any metal not covered with foam has a high probability of sweating condensation then dripping on to the liner and creating a stain or damage. I know boats are a compromise, but having the lumber 5/16" proud of the steel does not mean squat in regard to head room or taking away from square footage. 6 10" of head room or 6 9-11/16"... who cares.

Wherever possible, I also held the firing off of the cabin sides. I pretty much stuck with 5/16" everywhere I could. My plan was to get as much of the metal covered with insulation. I used blocks vs continuous firing wherever possible, and once insulated, Ill pad things out to the finished wall surface with finished trim.

Im going to go ahead and install the blocking for soffit   that creates the overhang on the salon. Since there are no side decks, once the super  structure is welded in place, that job will then need a ladder 16 above grade. Ill bring the soffit to a finished state including finish paint and the wiring need for accent lighting over each of the salon windows.

I have a bit of work to do before the insulator shows up in regard to taping off any finish paint I dont want to get spray foam on. Because all the window openings are finish painted now, I think Im going to fasten some 1/8" plywood in the window openings. There is no way paper is going to hold up to the force of the commercial foam gun, and I dont want to pay the foam contractor to stand around while I fix a screw up.

Im going to foam the roof over the aft deck with a  half inch or so to stop any condensation. Ill also be installing a ceiling in this roof to hide the framing. One thing that bothers me with this ceiling is that the designer changed the height of the trim piece as it goes from the sides to the aft elevation. The trim is more narrow on the aft elevation vs the side elevations. Because of the way the roof is framed, in order to make the ceiling line constant, youll see the edge of the ceiling material protruding below the trim piece on the aft elevation. Im not into welding any fix in place now that everything is finished painted and Im about ready to foam. A drip edge of some sorts might be an alternative or a slight change in the ceiling profile as it passes the last frame. Theres more than one way to skin a cat, so its not that big of a deal, just some more detail work. I can deal with the actual ceiling at the boat yard, but I have to deal with the blocking before the foam guy shows up.

As I sit typing this post on Sunday night, Im listening to a Neil Young song with the lyrics "dont let it bring you down, its only castles burning" drifting from my speakers. That lyric sort of seems appropriate in that sweating the small stuff gets us nowhere. In the end, getting there is half the fun.

Cheers,

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Howdy Bailey Boatbuilder with a Difference

Howdy Bailey is a long-time friend, from long before we moved to USA. Howdy had bought plans from me for the Pratique 35 and we visited him in Norfolk, Virginia, on our first trip to USA in 1983. I was a young designer, not yet through with my studies at Westlawn School of Yacht Design (now named Westlawn Institute of Marine Technology) and was totally unknown. Yet, based solely on the design that he had bought from me and a few hours chatting over dinner, Howdy Bailey had the confidence in me to commission the design of a 64ft charter yacht that was to be built for a consortium in Norfolk. That design is the Dix 64 and the boat was launched and went into the St Thomas charter trade as "Rising Sun".

Dix 64 "Rising Sun" shows off her exquisite finish.Howdy Bailey in the red shirt.

"Rising Sun" was beautifully built in steel, finished in flag blue Awlgrip that displayed her blemish-free surfaces to perfection. Rigged as a staysail schooner for ease of handling by a small crew, she surprised all who sailed on her with her speed under sail and characteristics.

Over the years and on opposite sides of the Atlantic, Howdy Bailey and I maintained a lasting friendship and worked together on many projects. They included the Echo 38 cruising tug "Echo" and the Little Creek 47 "Flutterby", now owned by Howdys son Dylan Bailey.

"Echo" at home on a backwater of Chesapeake Bay.

Little Creek 47 "Flutterby" waiting to start a Chesapeake Bay Schooner Race

Howdy was instrumental also in me receiving the commission to design "Sabbatical II" as a custom design for a local businessman and friend. Howdy and his very capable crew turned her into a work of art, with beautiful detailing of a complicated boat.

The ketch-rigged "Sabbatical II" sailing in sloop configuration.

I have always thought of "Howdy" as a nickname, maybe short for Howard or some other name. Not so long ago I asked him what his real name is and he replied "Howdy". He was named Howdy at birth. Howdys interesting name carries through to him being one of the most interesting people that I have had the pleasure of knowing in the boating industry. He no longer builds boats and instead works in the marine service industry. He and his small crew take on service work of all types, from rebuilding joinery to rerigging and new plumbing or mechanicals. Whatever you need done to bring your boat back to pristine condition, Howdy and his guys can do it. Custom metalwork is their specialty, able to produce aluminium and stainless items to a very high standard. They are currently completing the keel/engine support structure in steel for the Didi 950 being built in Ohio.

Howdy also has great community spirit. He introduced me to some surfing friends a year or two after we arrived in Virginia Beach and I joined their very informal Iguana Surf Club. Every year this club hosts a fun day on the beach as a fundraiser for the Norfolk-based Childrens Hospital of the Kings Daughters, with surf contest, fun events and a big party afterwards. The past few years Howdy Bailey has really come through with large amounts of cash that has been donated by his customers and local businesses toward the fundraiser. Howdy has a big heart.

Ever since we met, he has done business from various buildings near to Cobbs Marina at Little Creek, an inlet off the mouth of Chesapeake Bay. It was always an interesting place to visit, with all kinds of fascinating bits and pieces hung on the walls or suspended from the roof. Howdy is a collector, not of "stuff" but of "interesting stuff". His workshop just wasnt big enough to display all of his eclectic collection.

City codes have now forced a relocation and Howdy Bailey Yacht Services has moved into a larger shop at 7527 Avenue J, Norfolk. This has much more open space and it has been put to good use to show off Howdys collection of toys, bicycles, boats, signs, classic cars, old tools and a host of other things. The heavy items are on the floor and lighter items are hanging from the roof or along the walls. Even if you have no interest in boats or quality metalwork, Howdy Bailey Yacht Services is an interesting place to visit.

Main entrance to Howdy Bailey Yacht Services

Howdy in red shirt and Larry Foster, long-time colleague.

View of the shop from the front entrance.

Lots to look at, in every direction.

Howdy and I go back a long way and I look forward to continuing that way for many years to come. If you have some boat work that needs doing by competent people, visit Howdys shop or call him on 757-480-0058.

To see more of our designs, please visit http://dixdesign.com/.

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Stability with Water Ballast

A potential builder of the Didi 950 asked me a question about stability with water ballast. He could not find an explanation on the Internet describing the effects of water ballast on a boat when capsized, so here it is.

After looking at the stability curve, he was concerned that the stability curve with water ballast to windward, the normal position for sailing in strong winds, has a very large area of negative stability. He wanted to know how that affects the time that the boat will take to right itself if capsized. This is a natural question following the amount of discussion that has been happening after our recent capsize in the Didi 38 "Black Cat" and the very rapid manner in which she returned to upright.

Shown below is the stability graph of the Didi 950 in fully loaded condition; click on the diagram to enlarge it. This is the condition of lowest stability due to the inclusion of crew, stores, liquids and many other weights that are above the centre of gravity (CG) of the boat. There are three curves shown. When looking at the graph, consider that the area enclosed by each curve above the horizontal 0 line is a measure of the energy that is required to take the boat from upright to the point of vanishing stability (AVS) where the curve crosses the 0 line. Until the AVS is reached, the boat will return to upright if no additional heeling force is applied to it.  Beyond the AVS the boat will continue to full capsize unless there is another force being applied that will return it to the positive side of the AVS.

The green curve is with ballast tanks empty, so akin to sailing a boat that has no water ballast. This curve is very similar in form to that of "Black Cat", with the area enclosed by the curve above the 0 line many times greater than the area enclosed by the curve below the 0 line. She would right herself very quickly with no water ballast. The red curve is with the windward ballast tanks filled, good for powering to windward or power-reaching in strong conditions. The blue curve is with the leeward ballast tanks filled. One would not sail her like this but it is a situation that could result from an accidental gybe in strong winds.

Didi 950 Stability Graph. Click to enlarge.

With no wind or waves and the ballast tanks on one side filled, the boat will not rest upright. It will heel over until it stabilises at a heel angle that places the CG vertically in line with the centre of buoyancy (CB). That will be the nearest crossing of the curve with the 0 line, which is at 5 degrees in this case, seen on the blue curve. Add some wind to bring the boat to 0 degrees heel and the righting moment that is working is the point where the red curve hits the left edge of the graph. Without water ballast the boat must heel to 6 degrees to reach the same righting moment. That is where the power benefit is coming from with water ballast, the boat will sail more upright than with empty tanks, in the same wind strength.

Note that all three curves are closely bunched when the boat is heeled 90 degrees. This is a knock-down situation, probably from losing control when driving hard downwind under spinnaker. The mast is horizontal but not in the water. This bunching of the curves at 90 degrees is because of the position of the ballast tanks in this design, low in the boat fairly close to the vertical CG. There would be a bigger spread if the tanks were located high up under the deck.

The red curve shows the benefit of increased righting moment when the windward tank is filled. There is considerably greater gain in stability shown by the red curve than lost stability, shown by the blue curve, when ballast is on the wrong side.

All three curves show that the wind alone cant capsize the boat. When the mast hits the water there is still considerable righting moment available for all three situations. If the boat is in large waves and hit by a big one while knocked flat, the added energy from the wave can capsize the boat in all three situations. 

It seems counter-intuitive but the condition most likely to invert the boat under wave action after a knock-down is with the water ballast to windward (red), i.e. the condition in which the boat will be sailed in strong winds. This is because after the water ballast passes beyond the point where it is vertically above the overall CG of the boat that extra weight is on the wrong side of the CG and is helping to capsize the boat rather than to bring it back to upright. It pulls the red curve below the green curve and reduces the AVS from 133 degrees to 122 degrees. 

Overall it takes more energy to capsize the boat from upright with water ballast than without, evaluated by comparing the area enclosed by the red curve with the area enclosed by the green curve. When the area enclosed by the blue curve is compared with the green curve, there is very little difference. It will take a similar amount of energy to capsize the boat without water ballast and with water ballast on the wrong side, when going from upright. Ironically, the wrong side has the greatest amount of reserve stability after a knock-down and has the greatest angle of AVS, so it is the condition least likely to capsize after a knock-down.

Back to our capsizing boat. Once past 122 degrees it is into a big range of negative stability that shows as the area enclosed by the red curve below the 0 line, taking it all the way to 180 degrees, i.e. totally upside-down. But see that the curve does not return to 0 at 180 degrees, which means that it is unstable at that angle. Same as happens when the boat is upright, the water ballast off to one side prevents the boat from resting at the 180 degree position. It has to rotate to where the CG is vertically aligned with the inverted CB. That is at the point where the curve crosses the 0 line. If the red curve is extended to the zero line it will be to the same angle that the blue curve crosses,  i.e. 160 degrees.
 

There is no windward or leeward when the boat is upside-down, the sails are under water. The boat is stable in the 160 degree position, so leaning 20 degrees to one side of upside-down. It needs to get past the nearest zero crossing to come back to upright. The boat doesnt care which way it goes. It needs a lot of energy to go back the way that it came along the red curve but very little energy to get to the 140 degree AVS crossing of the blue curve. With the motion from just a small wave it will continue past that 140 degree point. Once that point is passed, the righting moment of the blue curve takes control and will return her to upright. If the rig is still standing then the sails will fill and she will be back into the stability situation shown by the red curve. She has capsized along the red curve and righted herself along the blue curve.

In essence, it will take a lot less energy for the boat to right itself with water ballast than without, so she should right herself more quickly with the water ballast. The difference is that without water ballast she can go either way from inverted to upright but with water ballast she has to go full circle.

To visit our website, go to http://dixdesign.com/

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Didi Sport 15 A Family Boat with Juice

Some of my supporters have been waiting for this boat for a long time. I have posted sneak previews of the Didi Sport 15 (or DS15) but the design was taking its time to reach completion. It was leap-frogged in the design queue by designs that were much more demanding of my time.

Now the plans are complete aside from some minor details and the prototype is into the final stages of build. This boat is looking very good, with interesting finishes and excellent standard of finish. The builder is creating a work of art of which he will be justifiably very proud.

This design, like the Didi 950 that I introduced last week, is a development from the Didi Mini Mk3. It has a modern hull shape with topside chine aft, built from plywood.

Didi Sport 15 hull, radius chine with topside chine.

The concept of the DS15 is a boat that can be stable and safe for family sailing and raid type racing, exciting as a little ballasted sportboat and super-fast as an unballasted trapeze dinghy. Choose your style of sailing or switch back-and-forth depending on conditions or who will be sailing with you.

Didi Sport 15 rig

The rig combines a reefable square-top mainsail with self-tacking jib, as working sails, with an asymmetrical spinnaker on retracting bowsprit to supercharge it downwind. It also has a light drifter/reacher Genoa for light airs when your wife is aboard and doesnt want the excitement of the asymmetrical.

Didi Sport 15 Prototype, round bilge from plywood.

Didi Sport 15 plywood framework ready for stringers.

It can be built by amateur or professional builders, from plans and offsets, from plans and full-size Mylar patterns or from plans and a CNC plywood kit. Go to our pricelist to order plans or plans and patterns. Go to our USA kits page to order a kit of all plywood components, accurately cut by CNC router.

Please visit our website at http://dixdesign.com/ for more info on this and our other designs.

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A lovely little daysail with my Daughter

Blake Island is a lovely little Marine State Park located 8 miles West of downtown Seattle.  The island has an interesting history.  It was an ancestral camping ground of the Suquamish Indian tribe.  Legend has it that Chief Seattle was born there. Capt George Vancouver noted the small round island in his journal in 1792 during his exploration of the area, but didnt bother naming it. It was later surveyed and named Blake Island in 1841, but local settlers referred to it as Smugglers Island. Shortly thereafter the island was logged until its timber was exhausted, abandoned, and neglected until the banks foreclosed on the loggers.  Around the turn of the century it was sold to the wealthy Trimble family who renamed it Trimble island. They built a mansion and a beautiful estate where they lived until 1923, when Mrs Trimble died in a freak accident. The Trimble family abandoned the estate. Once again, smugglers, this time in the form of bootleggers and rumrunners, used the island during Prohibition.  It was rumored to be used as an ammo dump and a unit of the Coastal Artillery of the US Army was garrisoned in the Trimble mansion.  After they left, the mansion was gradually plundered, vandalized and finally burned down in the 40s by two High School students who camped there in a home-made 16 boat.  The neglected island was traded to an investment company. After the war, developers expressed an interest in building a luxury resort hotel on the island, but it was traded for timber instead to Washington State where it was turned into a State park. Tillicum Village, a popular tourist attraction featuring Indian arts, culture and food , was added in 1962.  Today, about 100,000 people visit this lovely little island every year.

Last Saturday my Daughter Heather and I were two of those visitors.  We launched Ellie and headed for Blake under beautiful blue skies and 5-10kt winds. We knew we couldnt linger long on Blake because the forecast was for bad weather to move in that evening.

Heathers little dog "Spud" was very excited to come along. He enjoyed every minute of the hour long sail across the Sound.

Nearing Blake Island

The Indian longhouse of Tillicum Village behind the breakwater.

We tied up in the marina and went ashore. Blake Island was buzzing with activity. The entire shoreline was covered with dozens of tents belonging to Cub Scout Pack 144, there for a three day campout.  They were having a blast building driftwood forts and fishing off the docks for pile perch.

The tour boat Argosy dropped off tourists at Tillicum Village while we ate lunch and a steady stream of pleasure boaters filled the marina for the weekend.


After lunch we set out to explore the island.

We were only able to stay for a few hours.  Storm clouds were starting to gather so we headed back towards Seattle.  With the wind picking up, this was a great opportunity for Heather to do some sailing.

The Space Needle served as a great navigational aid

Meanwhile, Spud found a nice cozy spot to take a nap.

 

It was a wonderful little daysail to one of our favorite local spots. We hope to do it again soon.

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