Composite Chainplates

[mikereed100]

I am planning some composite chainplates for my cat and am wondering what would be the best reinforcement? Is carbon really much more preferable to S-glass? From what I recall their tensile strengths are very similar. Carbon is stiffer but this would not be much of a plus in a chainplate where nearly all the load would be linear.

Any thoughts on this and composite chainplates in general would be greatly appreciated. There is precious little on the web apart from this link to a most excellent site:

http://www.boatdesign.net/forums/fiberglass-composite-boat-building/composite-chainplates-13648.html

Thanks,
Mike

[Ad Hoc]

It is not so much the chain plates, rather than the how are the chain plates "attached" to the hull. If you haven't analysed the loads correctly, you will get interlaminar shear failure very quickly, owing to underestimating the loads and not establishing the load paths, and hence, the resins/lay-up required to transmit said loads.

[jmolan]

Mike, see ifyou can send a PM to Gashmore, I know I saw he has already done chainplates like you are talking about.

Gashmore
Junior Member Join Date: Feb 2008
Rep: 32 Posts: 17
Location: Macon, GA

To late for the chain plates. They are carbon composite integrated into the topsides and deck. I didn't want to worry about leaks.

[AndrewK]

Mike,
E-glass, S-glass, CF will do the job. decision comes down to what you are willing to pay to save a bit of weight. Relative to E-glass CF will save approx 40% wt, S-glass only about 15 - 20%. Get advice from a composite engineer, as AdHoc said its important to spread the load into the hull structure and to use high shear cores in this area.
As a guide local builders are using a UD lay up that has a SF of 5-7 times the wire breaking load.
Depending on the resin you are using the shear strength could be between 20 - 40MPa so important to calculate the correct surface area required.
You can position the chain plate on the hull side or on a bulkhead. I have seen the UD strapping applied in two ways.
1. Stainless tube is glued on top of a panel at the same angle as the shroud and a slot is cut at the appropriate distance down from this tube that is exactly parallel and aligned with the tube, this distance will be approx 600mm. Continuous 100mm wide UD tape is then simply wound around the tube and the slot, the fibers remain parallel with this method ie you do not splay out the bottom.
2. Alternative is to use pre cut lengths of UD tape and lay these at +/-6 degrees across the tube. This fanning out of the tapes will increase the contact surface area and be more forgiving with the alignment. There is some DB also interlayed amongst the UD.

Let me know if you want more details and photos how I did mine.

Andrew

[Ad Hoc]

mike

You may be lucky, but the values that AndrewK gave for shear strengths may be just data sheet stuff. (Can you confirm this AndrewK, or are these from actual coupon tests of your own layups?).
I would use a value of 15MPa for interlaminar shear for a basic Glass layup.

PS
Not exactly the same, but I just recently finished a job analysing at the loads from a lifting eye, to lift the whole boat; a steel plate bonded into a Glass layup. No matter how you look at it, 15MPa was about as high as i would go, without any real coupon tests for shear.

[mikereed100]

Thanks to all for the replies. This info is pure gold. I did a quick calculation using 15MPa sheer strength and 7x the rigging wire breaking strength of 33,000lbs (This is 14mm wire on a 46’ cat). Comes out to 106 sq in which is actually less than I was planning. The load is parallel to the hull.

Andrew,
Thanks for the suggestions. I had not considered either of the build methods you describe but they both sound better than what I had planned. I would love to see pictures and details of what you have done and would gratefully welcome any additional comments.

Thanks again,
Mike

[CTMD]

Mike,

check PMs

[AndrewK]

Ad Hoc, the resin shear values I mentioned is from data sheet and not test results for my laminate.
I would like to see data showing the difference between test results and calculated values if anyone would like to share these.

Mike
For option 1, I forgot to mention but as the tape is wound around a section of a panel you get the benefit of mechanically locking into this panel as well.
If you look at the photo in Masalai's thread http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-16.html#post277363, you will see the start of this process.
Personally instead of trying to feed the UD through this slot I would extend the cut out to the edge so that the tape can be simply slotted in and not having to poke it through the slit. This way you can cut the length of tape required wet it out roll it up on to a tube and then wind on to the job.

For the stainless tube you have an option to keep it in one piece or cut into 3 segments, two 50mm segments either side of a small segment which is dimensioned from the gap in the toggle of your rigging screw. These segments are separated with plastic discs say 5mm to suit the toggle thickness. This assembly is held together with a bolt, I used this method and you can see this in one of the photos. Advantage with the segmented approach is that you do not have to cut through the laminate later, you simply knock out the discs.

My chain plates are located on the hull so I used approach #2 as I preferred it for this purpose. You will also see that I used a balsa insert 600 x 900mm in this area for its high shear value, 200kg foam was out of stock at the time. Chain plate is located between a bulkhead and aft edge of the dagger board case, distance between the two is 1300mm, laminate in either side in this area was doubled.
The UD tapes were layed at +/- 6 deg across the tube ranging from 900mm either side down to 300mm. There were 3 layers of 450g DB glass interlayered amongst the UD, each one covering the foot print of the UD plus 50mm more than the previous. Finally there was a 560g triaxial and 450g DB covering the area a bit larger than the balsa.
Internally between the two bulkheads there will be pigeon hole lockers that will also help spread the load.

Andrew

[Ad Hoc]

Hi Andrew

When i don't have actual coupon tests for design values i use this:

Interlaminar Shear = 22.5-17.5Gc MPa

Where Gc = 2.56/ [(3072T/W) + 1.36]

T = nominal laminate thickness, mm
W = total weight of glass in g/m^2.

This is from a very good ref book I have, based upon actual tests of various different layups and all tested.

So, it is iterative.

When i use my own old in-house tests data (of various lay ups, thickness etc etc), and select a layup and hence its tested shear value, it comes out very close. So i now always use this formula.

[Ad Hoc]

Andrew

BTW..how is the boat progressing?
Did you sort out your calculations too?

[AndrewK]

Hi Ad Hoc,

Using your formula for ILS a standard hand laminate with 50%wt glass ILS=14MPa and infused laminate at 70%wt glass =10MPa.
This is a long way short of 20 - 40MPa I have seen on data sheets for epoxy resin systems. I can see how hand laminates can vary from shed to lab, but infused laminates should be the same.
Surly the 22.5 can not be a constant for all types of resin and cure conditions?
I would have expected something more like say ILS corrected= data sheet ILS - 17.5*Gc

Boat progress has been very slow, just had three weeks of very wet and humid weather.
And now that the rain has stopped over night temperatures have crashed down to6-8'C.
Have not finished the calculations, I will send you what I have done so far.

Chears
Andrew

[Ad Hoc]

Andrew

sorry I should have noted that the values are for basic E-Glass lay ups like CSM/WR, not epoxy.

[mikereed100]

Thanks Andrew, that's very helpfull stuff. What are you buillding?

Mike

[AndrewK]

Mike, my boat is a 11.9m foam cruising catamaran.
Are you locating your chainplates on the hull side too? which way are you leaning CF or glass?

[jim lee]

Andrew, lets see more pix of this boat project of yours. I for one would love to check it out.

-jim lee

[AndrewK]

Jim, this is what I am building, its a long way to go.


Andrew

[jim lee]

What a kick! Huge project. Have you built both hulls? Or just the one? Is it usual to build cat hulls on their sides? Did you design this yourself?

-jim lee

[AndrewK]

Hi Jim,
Both hulls done and faired to 400mm above waterline, rest of the hulls and hull decks faired up to the high build stage. Hulls joined with bridgedeck between the rear and mast transverse connecting beams. Rear aft face of the beam in place but not the mast beam. I had a leak some time after infusing the mast beam web, I will use this elsewhere and make a new one.
Building the hulls split down the center line and transverse planking is common enough, I think it is a better alternative to longitudinal planking especially for a single operator.
I did the sketches of what I wanted and Jon Sayer http://www.sayerdesign.com/ did the rest.

Andrew

[mikereed100]

Andrew,

Beautifull boat! Best of luck as the build progresses.

I ended up going with the CF as it was easy to find and for the amount I need, not too expensive. I'm still struggling with how to actually lay up the chainplates as I do not have a flat-sided hull with a hull-deck join but rather a gradual curve, so draping the fiber over both sides of the hull would be difficult. I may have to attach it to one side only with high density core replacing the honeycomb for 1 sq/meter in the vicinity. By the way, did you use a bushing in yours or did you just glass around the bolt?

Mike

[jim lee]

MikeReed, where in the world does one find room to build a boat in Santa Barbara? Last time I was there it seemed that space was at a premium.

-jim lee

[AndrewK]

Mike, I do not see a problem having the CP's on your hulls if that is your preferred placement but I personally would not laminate to the outside skin alone. Also nothing wrong having them on a bulkhead or chain plate knee.
Are your hulls already layed up? my recommendations depend on this.
Yes you must have a bush, that is the tube I was referring to.

Cheers
Andrew