Plywood Boat Plans | Star 45 R C model sail boat Keels and keel ballast bulbs

Plywood Boat Plans

AMYA Star 45 Class Rules, 2006, KEELS AND BALLAST BULBS


7.1 Keel will be of the style known as drop, and will be of the FIN and BULB type.

7.2 Keel fins may be solid or hollow and constructed of reinforced plastic, plastic laminates, fiberglass, wood or metal. (Note: Strength and integrity of the keel fins must be maintained whether built solid or hollow.) Keel fin shape is not specified but must follow the general shapes outlined on the reference drawing. However, keels will not be less than 6 inches nor more than 8 inches long (Fore and Aft) at the keel/hull junction, nor less than 4 inches nor more than 6 inches long (Fore and Aft) at the keel/ballast bulb junction.

7.3 Keels, keel fins and ballast bulbs may be removable, however, they may not be changed, interchanged, substituted or otherwise manipulated once any heat or series of heats in which scores will be compiled, has started. Mechanically movable keels or ballast bulbs are specifically prohibited from use in Star 45 Class Yachts.

7.4 Ballast bulbs may be constructed of any material not prohibited by the AMYA. The actual shape is left to the builders discretion, but will not exceed 9.75 (9 3/4) inches from the front of the keel bulb to the rearmost point of the keel or bulb.

7.5 Total drop (length) of the keel fin/ballast bulb combination will not exceed 11.5 (11 1/2) inches when measured from the keel/hull junction, before any fillers or streamlining is added.

7.6 Ballast may be made from any readily available material, such as poured lead, lead shot, etc. (Note: When using material such as lead shot, the mass must be solidified through the use of a bonding agent such as fiberglass or epoxy resin, plaster of paris, poured over and through in order to create a solid mass.)

7.7 Race directors may elect to use a template based on the construction plans to determine the keel length (depth).

7.8 Keel depth shall be measured from the center of the keel fin at the hull to the bottom of the ballast bulb. This measurement is from the edge of the bottom of the hull as it meets the side of the keel and should be determined during construction and before any fillet or fairing is added.

7.9 The Star 45 Class specifically excludes radio equipment, sail controls and batteries (power cells) from being considered ballast. This specification defines ballast as anything carried aboard the model for the main purpose of changing the weight distribution of the model and/or weight of the model. Ballast shall be fixed in place by gluing, fiberglassing, or bolting (bolts and screws).

7.9.1 Ballast may not be removed or relocated during any one regatta. The use of Velcro or similar quick release fasteners is prohibited as methods of mounting ballast.

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Boat Plans Pdf | Stability with Water Ballast

Boat Plans Pdf

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.

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Dinghy Boat Plans | More on Stability with Water Ballast

Dinghy Boat Plans

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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Pontoon Boat Plans | Didi 950 in Australia

Pontoon Boat Plans

Fred Grimminck in Queensland, Australia, has previously built a boat to our Didi Mini design. Now he is building a Didi 950. In contrast to the boat of Mike Vermeersch that I showed yesterday, Fred is building his boat from scratch, marking and cutting the plywood panels himself from our drawings.

Today I have received photos from Fred of his project. He is at the same stage as Mike but the different perspective of his photos shows the details from different angles to help visualise how it all goes together. Click on the photos to enlarge.

Bottom panels fitted, bow view

In this photo you can see how the bottom panels are slightly Veed aft but the V increases toward the bow and the flat panels become very fine, both features to soften the ride when the boat is planing fast in lumpy water and slamming over short waves can become uncomfortable. The edges of the panels land on the doublers of the tangent stringers at the intersections of flat and radiused skin panels. The edges are rebated to half-thickness, with the first layer of radius plywood landing on the doubler and the second layer landing on the rebate, forming a Z-shape joint detail.

Ready for side panels to start

 In the photo above, the doubler at the upper tangent is in place and part of the lower side panel is clamped in place, seen at bottom right. The left edge of this panel has been planed to form the sloping surface for the scarph joint to the next piece, the main difference from the jigsaw joints of Mikes kit. Also visible in this photo, are scarph joints in some of the stringers. These appear to have been glued in place on the hull. The alternative is to pre-glue them into long lengths before installing in the boat.

Interior view of transom and cockpit area

The photo above shows some of the interior detail. The transom is 9mm plywood but has doublers to strengthen it around the perimeter, at the backbone and at the rudder hardware. You can see the plywood backbone passing through the bulkhead ahead of the transom. These intersections are self-locating egg-crate detailing to assist with accuracy during setting up the skeleton. The backbone is on centreline in bow and stern but changes to a pair of backbones offset from centreline from forward of the mast through to the cockpit.

A major difference between the two boats of Mike and Fred is in the keel detailing. Mikes boat has a fixed bulb keel that hangs from an internal support box that is bolted between the two components of the double backbone. The support box also holds the engine beds and bearers, sited directly over the keel. Freds boat will have a lifting keel. It will be housed in a modified keel support box of identical footprint but with integrated casing for the lifting keel and without the engine beds. Freds engine will be a saildrive unit located under the companionway and front of the cockpit.

There are also boats to the Didi 950 design beign built in Greece and Latvia. Watch this blog for news on all of them.

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Boat Plans Aluminium Australia | Started ballast

Boat Plans Aluminium Australia

Anyone whos thinking about building a boat, take some advice from me and dont wait until a few weeks before your anticipated launch to start pouring your ballast.

I dont think I could have picked a worse day to start pouring lead ingots. At noon today the temperature in the shade was 94, and the dew points seem to be in the 70s making for oppressive humidity. I consider myself a pretty tough guy regarding manual work as Im in decent shape, and Ive been doing physical work all my life. I have  no problem admitting that todays task of pouring lead ingots kicked  my ass.
 
The design of the boat calls for 4300 lbs of ballast  under the forward sole. For our ballast, Im using lead that came from the demolition of an MRI machine. The material is as clean as can be, and with each lead shingle weighing 30 lbs, its relatively easy to handle.  I must have messed up somewhere at some point, because I only have 3000 lbs of lead on my site. I could have sworn I had 4500 lbs, but I now know for a fact that Im going to be lite.

Having a skid steer loader at our place made this nasty job a wee bit easier. Moving the lead from the storage area to the melting area was made easier with the loader as was handling the fire wood and moving the freshly pour ingots in to the shop for cleaning up and weighing.

I made a melting pot out of a piece of 12" pipe and framed a stand for it to sit on giving me room for the fire. Lead melts fairly easily, but it helped immensely by using my back pack blower to force feed the fire. The melting pot comfortably handles 200 lbs of lead.  The pour spout is a 1" nipple welded into the melting pot with a 1" 90 and a short length of pipe to get the material to the molds. Before I pour, I have to use a propane torch to heat the pour spout so the lead from the previous pour can be melted in the spout.   I made two molds to try to  help speed things up. Each mold contains six ingots, and once the mold is full, it weighs about 100 lbs. After a pour is made and the lead has set up enough to pick up the mold, I drop the mold forcefully into a spare bucket for the loader to part the ingots from the mold. The problem is that if the lead doesnt part on the first throw, picking up the 100 lbs mold a few times gets tiresome.

Using a circular saw to cut the thin piece of lead between each ingot is how I process the ingots prior to weighing each ingot. I write the weight on each ingot so I can keep track of how much lead is going into each ballasts compartment.

I  now know Im going to be  lite on the ballast, so the question is how will this effect my launch. Out of the 4300 lbs designed, I think Im going to end up with 2700 - 3200 lbs installed for launch. Because the boat is going to spend the rest of the season on the Ohio River ( about as tame a mill pond as one can find), I think Im going to be OK. If I was launching at the Ocean or Gulf, Id feel a lot less comfortable being lite, and for sure would not try to go off shore without the designed ballast.  Im going to run this scenario past the naval architect and see what  he says.

For some reason, I thought Id get all this ballast poured in one day. Todays pour netted me 1300 lbs of ingots.  

Cheers

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Kayak Boat Plans | Didi 950 Hulls Taking Shape

Kayak Boat Plans

The Didi 950 projects of Fred Grimminck in Australia and Mike Vermeersch in USA continue in parallel. Freds build is from plans only and Mikes is from a kit that was cut by CNC router. Both have completed the flat sheet panels of the sides and bottom and are now skinning the radiused parts of their hulls. This is the stage that the hull shape really starts to show.

Some of the photos that I show of these two projects show minor differences, due to building from a pre-cut kit or with the builder cutting all components. Both produce the same boat at the end of the process but they may look a little different at times while being built.

Side and bottom panels all completed, ready for radius to start.

The photo above is of Mikes kit boat, with neat edges at the sheer (where hull and deck will meet). The photo below is of Freds boat with irregular edges at the sheer. This is because the kit panels are supplied with a uniform strip of waste to be trimmed off to the final line after turning the hull over, while the boat built without a kit has the panels inividually cut by the builder and the waste width may vary.

Same stage, Freds boat. Backbone still to be trimmed at forefoot.

The radius is skinned in two layers, made with narrow transverse strips. The first layer lies on the stringers and the doublers of the tangent stringers, fitted between the edges of the side and bottom panels. These edges have rebates pre-cut into them and onto which the second layer will be laid.

First layer of radius being fitted to Mikes boat.

The rebate along the edge of the side panel can be seen in this photo.

Final hull shape starting to become clear.

Construction of the boat in Latvia has now started and the boat in Greece will soon follow. To see more of this design and others in our stock design range, please visit http://dixdesign.com.

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