Moderated ECO 6 Build - rudder blade failure
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Recently I made my first attempt to build the rudder blades for my ECO 6, and met with a big failure. Advice, comments, suggestions are invited before I make my second attempt. The photos show what happened. The ?Meranti is very stiff, almost brittle. ?It appears to me I put too much epoxy mix in the V. The building plan diagram for the ECO 6 specifies filling to ?a line drawn at 13mm from the leading edge. The directions call for the line to be drawn at 15mm. I was aiming for the 13mm line but I expect I added too much - it was difficult to tell. It was also difficult to keep two pieces of plywood so that they meet only on the corners - i expect the join looked more like the one in the left of my rough drawing. I am not sure how significant that might be. If that is critical, perhaps someone might suggest how to achieve that.
In one photo of the end of the blade, the epoxy appears to have failed. In my impatience, I tried bending things the morning after the pour and the epoxy was set but had not fully cured. I heard a loud crack and stopped bending and left it for 48 yours before trying again. I used a combination of ratchet straps and then clamps to close the V. Even with the trailing edges completely closed, there was still a large gap between one side of the blade and th 20X20mm spacer.. I left it over night like that to see if it would close any but it would not. To see what would happen I ?applied another clamp and of course, the plywood failed. On my next attempt I will make the line much darker, and I will use a refillable calking cartridge (which I have and didn't think to use) to place the epoxy mix more carefully. A friend suggested that the V needs be closed some but I am not convinced that is the best solution. I look forward to hearing other's experience. |
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Hi Rod
What a pity for all the work.? Meranti is not usable for the rudders, as you know by now.? I specify Ocume for the whole boat. Ocume is a lot more flexible and lighter, by the way. The start V on the bow has to be as shown in the drawing. In your sketch, the left solution. Do not fill the bow area for more than 12 mm. A bit less is no problem. When you can not get Ocume ply., use Birch. Birch is very flexible. For sufficient strength, use one more layer of glass cloth. On the main stringer, use on each side one layer more of UD carbon. Success Bernd |
¿ªÔÆÌåÓýI have been using a similar fold up method for dagger boards and rudder blades over the last 40 years except instead of using plywood I use a Sheetmetal mold to lay up a composite part. The most recent ones I did were a pair of dagger board rudder blades about 300mm chord x 2m length. The system involves having a Sheetmetal shop fold up a simple mold out of 16 gauge steel, an appropriate die is used for ?the leading edge radius and it is folded to about 45 degrees then I have them do a 90 degree fold at the trailing edge to create a flange that I can screw a strip of wood to so I can use clamps to pull the two sides together if that makes sense. Basically you are making a Vee shaped mold with a flange at the trailing edge to stiffen it. You need to make a simple wooden jig to support it leading edge down while you apply mold release and do the fiberglass layup (or carbon). After it has cured you fold it up around a beam at the thickest point and glue the trailing edge together. I use predominantly uni glass and double bias in the laminate to make a structural skin so there is no extra glasswork done after releasing from the mold and the blade is perfectly fair and is ready to sand and apply paint. You do need to of course, plug the ends and I now use Coosa board for this. I have used various foams to fill the blade in the past but have settled on leaving them hollow as there is no chance of exotherm causing fairness problems and also if you sustain damage and get water in the blade you can just drill a hole and drain it out with no risk of waterlogged foam. With this method you do have the cost of the mold but it is not very much, I believe it cost me about 160 usd for my current mold which can be reused. My current blades are on a 31ft 7000lb Gemini cat. For the beam that you fold around I have settled on a diy fiberglass I beam that I make by making 2 channels glued together back to back so the web is twice the thickness of the flanges. ? ? Steve ? ? ? ? ? ? ? ? ? ? ? Sent from for Windows ? From: christopher gent
Sent: Sunday, March 19, 2023 5:55 AM To: [email protected] Subject: Re: [K-Designs-Multihull-Sailboats] ECO 6 Build - rudder blade failure ? Hi Rod. I built an Eco7.5. My rudders were laminated wood. But my dagger board used Bernd¡¯s V system. I had problem because I could only get 6mm plywood instead of recommended 4mm.? ? Bernd¡¯s advice to me was to use a router for 1-2 mm along the whole ?length of the inside faces (spaced about 5 cms apart.) This again was straining the ply a bit so I ended up repeating the router groves as deep as 3mm. It worked out fine. I used some slightly thickened epoxy on the inside of all the grooves before closing it all up.? ? I hope you get some success?with this method. ? ? Best regards ? Chris Gent.? ? On Sat, 18 Mar 2023 at 23.01 Rod McLaren <nkosuohene@...> wrote:
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Hi Rod
In my blog pages for my Duo 480 I reccomended making up a shorter test panel of rudder minus the inside carbon. I used the jig that Rodney gave me from his KD650. The angle is the same. I passed the jig on to David so I assumed he used it also on his Eco 6. Rodney had closed the angle up a tiny bit after his own earlier failures. On my blog you can seee the angle of the jig panel sitting on the table of my drop saw. Further hints were: dont over fill the epoxy in the bottom. Dont screw and glue on the interior batten or coat the insides of the blades with epoxy in advance. Do them wet on wet, which retains the the original flexibility of the plywood . I definately found it helpful to make up a practise piece first. The quality of the plywood these days probably isnt the same, and also the type of ply used may also be important (as again Bernd mentioned) cheers Bryan |
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Thank you , all, for the suggestions and advice. I am working on the cockpit coamings at the moment, which gives me time to consider the options being suggested. Clearly, as the saying goes, there are more than one way to skin a cat. (in this case, an ECO 6 cat :-) ) I will update you once I have something to report.
Bernard, I knew Okoume was specified throughout the boat and I would much have preferred to build the boat with it. ?However I was not able to source it locally. Only one lumber yard in our province offers marine plywood, and the only type they are able to get is Meranti. Now that I have worked with Meranti and know more about its characteristics, I would consider paying the extra cost of freighting in Okoume from a distance if I were to build another boat.? As for birch plywood, the only birch plywood available in Canada that I am familiar with is used in cabinetry and does not use waterproof glue. It is not suitable for this application.?I learned this the hard way many years ?ago . There is a story to go along with that - it was my first boat building experience, building a Tiki 21. I used exterior grade, good-one-side Douglas Fir for the hulls and had no difficulty. In fact the boat is still in use in West Africa. The plans specified 5/8 inch marine plywood (which I could not get locally where I lived at the time) or 3/4 inch birch plywood (which I could get) for the rudders, skegs and a few other small parts. I sailed the boat 3 summers in Canada, with the boat moored in a small lake and had no problems. At the end of the third season, the boat was loaded into a container and shipped to Ghana where I was moving to build a hotel on the coast. The boat was set up on the beach where I was building and from time to time I took people out for short day charters. On the fifth time, we came in over the surf onto the beach. I quickly realized the skews and rudder had folded over on impact - they were completely water logged and delaminated. That was Canadian birch plywood!! |
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I will provide a proper update in a few days. I decided to go with Dominic's approach. Thank you, Dominic, your photos were very helpful. ?This second attempt has been successful, enabling me to use the Meranti plywood. I will attach one photo today with others to follow after I have shaped and then fibreglassed both rudders. This was earlier today after gluing up the second one.
Now I have another question. I have puzzled over the drawings for the rudder housing off and on all winter. I sort of understand them but I don't. It is not clear to me where the bungee cord goes and how it is routed. Also, with this set up, is it possible to sail with the rudders partially down, as might be the case if a boat was in a shallow waters? Or is it all down or nothing? Have other builders adopted other approaches?? |
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Hi Rod
The rudder automatic is very simple. You can fasten the bungee cord in many ways.? Example sketch attached. The elasticity of the bungee cords differs from type to type. You have to test it. If the rudder jumps off at too low a speed, tighten the cord. The rudder jumps up but settles down to a given extent. Mostly this is enough to have rudder in the boat.? Have fun Bernd? |
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Thank you, Bernd. That helps. Now I understand where the bungee cord goes. ?Figure 17 ? says "The drawing is to scale. Print it out" What size paper is it being printed to in order to get "full size" and "to scale"? Also, I see the rudder is at an angle to vertical. What is that angle? How is that angle determined?
I apologize for all these questions. Perhaps all of this is clear to others but it is not clear to me and I don't want to do a bunch of work and then learn I have done it wrong. |
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Hi Ron
Watch it. Drawing 17 is to scale, meaning 1 :1. The sort of sketch is a JPG file and not to scale. The wooden "eye" is only an example. You can also use a bull's eye on each side. The angle is automatic determined by the position of the plastic tupe and the distance of the rudder to the lower corner of the rudder housing. It is a triangulation ;-)) Cheers Bernd ? |
Rod McLaren
Bernd Kohler
bryanandmarycox
