If you're using epoxy or vinylester the mat that comes on one side of the 1708, 1808 isn't needed. It just adds weight and hardly any strength. You can get the same type of fabrics without the mat, and they also wet out much faster. If you are lapping a compound radius or just want to make the cloth edge lay down smoothly a section of 3/4 oz mat over the heavier glass works well AS LONG AS you aren't using epoxy. Without the styrene that's present in vinylester and polyester resins the sizing that holds the mat together WON'T dissolve. It will just make an unholy mess of things and leave you pulling your hair out!!! In such a case [epoxy] just use some 2-4" strips of light weight glass cloth. For the compound curves, set the piece so that the two axes of the cloth are on the bias to the curves and it will lay like you won't believe.
Fiberglass is pretty easy stuff to work with IF you do what each specific fabric wants to do. Not following this simple truth has lead to MANY a bad project, millions of hours of wasted time and money and probably more than a few trips to jail for DWI or domestic violence after soaking at the local pub from frustration!!!!
You missed your calling and should have been a comedian. But really, when I got into a rudder rebuild a few years ago, I just ground away all the old stuff - and am tempted to do the same again. I can clearly see the pattern of each layer of glass and may just grind one whole layer off and replace with 1708. I'll need to redo the entire length of the leading edge anyway, since there is NO glass there - none. Just foam. Or I can put two light layers of cloth - the first one slightly smaller than the second, fair the first before adding the second and then fair both into the old stuff.
The big repair is the head though, but sometimes it's almost better to redo the whole thing and be sure about it than band-aid approach.
I don't use anything but epoxy, so will have to figure out those sizing issues as well. No rush though, since the foam has to dry first and that provides more time to think about it!
Nothing to figure out, just use the equivalent with the mat.
There's almost NOTHING made stock as far as boat companies go that's built in a two piece mold and has a core where they ALSO take the extra time to grind and glass the halves together, it's just the nature of the industry.
On the layering thingy: the wider layers need to go on the bottom, not the top. This doesn't seem to make since until you start grinding, sanding and fairing. Doing it this way you are only sanding down the edges of the fabric, leaving all of the longer tapered edges intact for the greatest strength. If you put the smaller layers underneath and get larger, the patch winds up looking much nicer on the outside, BUT when you start the fairing out process you will be grinding THROUGH the top few patches where the underlying edges of the smaller pieces are. Then your top, largest sections of glass are no longer that because they will have rings all around where you ground through them and some of the layers underneath to get the whole thing fair.
Looks like it's just going to take time and patience to get this old rudder back into shape. One last question though: Dave, you made several references to the weight - adding layers of glass, etc unnecessarily. Do you know what the approx weight for the rudder alone is?
I suppose one could derive that figure by subtracting the weight of the headboard assembly - but didn't know if there is some kind of target weight for the rudder blade by itself.
Answered my own question - post included under "rules etc" section - rudder assembly max 81 min 54. Looks like Steve Bower had a new rudder made by Phils foils that weighs in light of those figures with a blade @ 25 pounds, and complete assembly of 50 lb.
Has there been a proposal to change the class rules modifying the range of allowable weight?
I don't know about that: this is straight from the class rules on this site:
"2.7.A.1. The minimum weight for the rudder assembly (rudder blade, box, gudgeons, tiller, normal hardware, and corrector
weight, if any) is 61 lbs. Tiller extensions are not part of this assembly. Corrector weights, if any, are to be
permanently affixed to the inside of the tiller box, as far aft as possible."
As always, the class rules are the place to look for such info.
Even if they don't make sense at times they ARE still the class rules!
Having to add any corrector weights as far aft as possible is unreal....................................
The weight should be as close as possible to the pivot point of the blade for maximum sensitivity, and that would mean as far FORWARD as possible in the rudder head assembly. Even IF I consider the fact that the goal on a lighter assembly was to keep the weight centered withing the physical mass so that all boats had similar feel and no perceived "advantage", that would put the corrector weight closer to the MIDDLE of the housing, not "as far aft as possible"!
Got into a grinding frenzy on the rudder on Saturday, and took off gel coat and found a layer of chop strand mat followed by a thin layer of woven cloth - not more than 12 oz (just my opinion). Ordered a few yards of the 1700 as you suggested instead of the 1708 and 2 yards of carbon fiber 6 in tape to lay into the shoulders.
So instead of doing a head/shoulder repair, I've decided to reglass the whole thing. Fair and cover with interlux 2000 - maybe 3 -4 coats. There are no cracks anywhere, but the foam core is damp. Drilled a zig-zag pattern near the leading edge at the thickest part of the blade to dry it out. Lord knows how long that will take!
I reglassed a plywood rudder a few years ago on a larger boat, so this is about the same size job, with the exception of replacing new glass on the head curvature. It's just a dirty messy job and my driveway looks like it snowed (white fiberglass dust).
Will probably have the whoe thing fixed for $100 - vs over $1000, just very time consuming.
Getting ready to glass up the rudder after shaping the foil and grinding off the head warp, then adding foam back, reshaping to spec.
Got some 1700 cloth to wrap the foil and add some layers on the head. Question is this: where in the layering do you think it's best to epoxy in the carbon fiber? Is your preference between layers or on top of the last layer before adding interlux 2000?
The original foam core is a pain and does not release water willingly or quickly. Have been baking it in the sun and still got more wet core exposed when doing a little finish prep-grinding. Drilled some holes too, and now I just have a rudder with lots of holes! Well that should lighten it up some, eh?
If strength is the only point of doing the job and you're using epoxy, you don't need the mat that comes stitched into the 1708. Just use the same thing without the mat.
That was not my question. I was asking you how to apply the carbon fiber tape on the head/blade section of the rudder. Does it matter if the c/f goes on top, bottom or between layers of cloth. I am not using 1708, but am using that without mat attached as you suggested + carbon fiber tape rated at 3K.
OK, but a couple thousandths of an inch doesn't matter much to me.
What I was attempting to resolve was this: bonding the carbon fiber between two layers of cloth would provide adhesion to two surfaces that will absorb and transfer load more uniformly than just one, therefore be a stronger assembly instead of simply using epoxy to make it the outermost layer before applying fairing compound, barrier coat, etc.
Don't know how that moisture is going to finally work its way out, but it really hard to beleive after a few weeks how wet the foam retains water. New rudders are laid up with closed cell foam, and thankfully don't have this problem.
Maybe stick it in a giant microwave!
"What I was attempting to resolve was this: bonding the carbon fiber between two layers of cloth would provide adhesion to two surfaces that will absorb and transfer load more uniformly than just one, therefore be a stronger assembly instead of simply using epoxy to make it the outermost layer before applying fairing compound, barrier coat, etc."
If you already had your mind set on what your plan of action would be........................................................ why ask for an opinion? If what you say was true then there are LOTS of airplanes and boats that are in deep do-do!!!! No high tech carbon fiber airplane relies on the carbon being bonded between layers of something else.................................... what's under the primer and paint is carbon, usually many layers, but the top layer doesn't rely on "encapsulation" for bond strength! Also, depending on how many layers of glass you put back on the rudder there could be way more than "a few thousandths of an inch". Cloth thickness specs are for dry fabric. When resin is applied the fabric swells and becomes thicker.
In such a case [epoxy] just use some 2-4" strips of light weight glass cloth. For the compound curves, set the piece so that the two axes of the cloth are on the bias to the curves and it will lay like you won't believe. 
