not enough carbon!

[203 0]

well, went out on saturday for a nice sail, 10-14kts? wouldnt of thought any thing would of broken, nice flat water, perfect trapeze reaches, they snap, my rudder blade broke just under the bottom of the rudder stock (blades been pushed down to far in the photo)

 

i ended up going for a swim and drifting dangerously close towards the rocks

 

shows that the last owner of 203, when he built the foils, didnt put enough carbon on, probably 2 layers ?

 

 

now time to find a new rudder stock and blade before the summer season finishes

[Guest]

did you have your dagger board raked aft or were you loading up the rudder with weather helm?

[MuzzaB 14]

I am not a composites engineer, but I have been building my own carbon bits and pieces for a few years now. There are others on these forums far more competent and experienced in this technology than me. I probably over-engineer them, but I get the desired results and acceptable weights. Here are some lightly educated thoughts.

 

If you race and class rules limit the use of carbon, check the rules first.

 

Firstly, it is not possible from the pictures to understand the weight of the cloth used in your application. Nor can I comment on whether the application was completed correctly. Even if the engineering design was appropriate, if it was not properly wetted out it will not have acquired the strength it was capable of.

 

Secondly, it looks like a twill weave was used. I use twill for cosmetic applications (where I want that really cool carbon fiber look). I do not use it where my key objectives are strength and light weight. For blades I always paint them white (for UV protection). Even though the paint is sanded to a thin film, cosmetics are never my objective. So twill is out.

 

Thirdly, I cannot see from the pictures whether the core was one piece or a sandwich. If a sandwich, was there any carbon fiber sandwiched between the halves? I use some unidirectional cloth in a sandwich, usually two sheets laid at angles to each other to provide stiffness down the length of the blade and laterally. If the core is one piece, then use unidirectional cloth on the outside of the core.

 

Next – carbon fiber is brittle. While is it light (if done properly) and strong, it can fail catastrophically. Your application places considerable stress on the blade where it exits the rudder case. So assuming that the wetting out was done properly, the issue is in the engineering. As noted above, you can use unidirectional cloth outside of the core. The load reduces as you reach the tip of the foil and your stress point is where the rudder exits the box – so use an extra layer of unidirectional cloth (or two ) on the upper part of the rudder and taper this as you move down the foil (fewer layers and/or narrower strips). The thickest part of the unidirectional lay up should extend comfortably below the lower edge of the rudder box. 100mm or so is my uneducated guess for a boat of your size but curve or taper the transition between cloth layers. This unidirectional stuff should not be your outer shell, so you need, as a minimum, to apply a layer of woven cloth outside that. I tend to then use fiberglass as a final layer – being far more forgiving and easier to deal with for dings and scratches. Obviously the total weight of your layup needs to be considered in choosing the weights of the various clothes.

 

And if you have access to, or the inclination to build, a vacuum bag system, go for it. You can get the strength without bagging, but you will sacrifice the weight benefits through excess resin.

There is a stack of material online to reference. Where I live, the guys who own the I14s are right into this stuff and have a lot of DIY experience. In the UK, the Cherub sailors have some good resources online. To the extent that people are playing with skiffs where you are, talk to them. One of the things here in the US is that there is an absence of DIY mentality except within a few classes (I14, Moths, 505 are examples). In NZ as a kid, everything was DIY.

[203 0]

First of all, I did not build the foil, or the rudder stock.

If the centerboard is made the same way, that will be the next to go.

 

now, i have not used carbon before, so it is a new cloth to me, but i do believe that it is just twill cloth layed on there, with probably only 2 layers, maybe 3.

The core is if a sandwich method, but when built by the last owner, but there is no uni direction in between.

 

i believe that having 2mm shaved of the core, then 2mm more of carbon would of helped a little bit, but yes, your probably right, it probably did need to start tapering 100mm out of the rudder stock, in the picture,the blade was pushed down more so i could remove the bottom of the blade, but when it did snap, it broke exactly where the blade exits the stock, this would of been a real weak point.

 

I do not have the time, or probably the skill to build a foil at the moment, but will try if I have to.I have fixed up a old spare enough blade and stock to use while I get enough cash to buy a new blade and stock, With the stock being home made, there is not way that i will find another blade with the same profile, so a new stock and blade are on the shopping list

 

Now I am just deciding what foil manufacturer to go to...