Beefing up the insides for JSD

bilbobaggins

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This is a Harken hi load Special padeye. The fasteners are 10mm 12mm The pitch distance between the 2 fasteners in line with the load is 33mm 44mm.

This is not enough.

The general rule of thumb for bolted fittings in composite is 4x-5x fastener diameter spacing. 

When they get closer together (3.33x) then the bolts start tearing out.....

Here is what I am talking about (this is a well thought out chainplate). For a JSD I think a metal plate makes a lot of sense. Most people's composite skills are not good enough to make a really good uni carbon or glass chainplate. They are good enough to add a lot of glass on the inside of the hull......


Damn!

Back to the drawing board.... :angry:

Inked40773532463_1b24f77072_c_LI.jpg

 
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estarzinger

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Composite chainplates are great (and easy to calculate) if the load is all in one direction, like, uh a chainplate. You always know the load direction because the rigging loads are a constant direction.
I have seen a whole bunch of composite rudder gudgeons, which have a wider range of load angles.  And composite tack points for asym's - which had a decent arc of potential load angles.  This just seems like a question of proper design.  (I might comment in my own use of drogues I agree with the yaw angles, but would comment that the fully loaded pitch angles were pretty steady)

regarding diy skills . . .yea probably . . . when you are building to high load requirements often diy comes up short . . . but he did hire a pro to make the soft shackle so ....

 
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Zonker

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Re the padeye bolt spacing. Yes that's why I assumed only 2 bolts are working. It doesn't mean you can't use them - just that failure mode will be tear our rather than bearing stress. If you make the glass thick enough it's a moot point. You're only dealing with a 5000 lb design load! Leave the fwd most bolts slightly looser and the aft bolts will take most of the stress :)   
 

Evans you're right about people making rudder gudgeons and tack fittings like that. Probably they get away with it because (if done in carbon) the bloody things are so strong when made to "look right" then there is a huge SF.  And they are incorporating more off-axis fibers (biaxial stitched cloth).

I have seen rudder gudgeons with the angle of the carbon straps well spread out (about 90 degrees to each other) so they do line up with the +/- 45 degree rudder load cases. Haven't really looked at assymetric tacks but again, I think it's just so much material (and lower loads) that it's ok. Or again, they are using lots of off axis cloth.

By the way - here is why you try to load up carbon uni in the direction of load. At 10 degrees off axis, you only get 1/3 the strength of 0 degrees. At 30 degrees you're really in trouble.

image.png

 

CaptainAhab

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Autonomous,

You are making a big point of Structural Fillets. If I were doing this layup I would mix a thick batch of high density and do a larger than normal fillet in the corners. Then run the reinforcing fabric on top of the fillet. Is that what you going on about?

 

estarzinger

Super Anarchist
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Evans you're right about people making rudder gudgeons and tack fittings like that. Probably they get away with it because (if done in carbon) the bloody things are so strong when made to "look right" then there is a huge SF.  And they are incorporating more off-axis fibers (biaxial stitched cloth).

I have seen rudder gudgeons with the angle of the carbon straps well spread out (about 90 degrees to each other) so they do line up with the +/- 45 degree rudder load cases.
most of the strong point carbon constructions I have seen splay the uni's - which I imagine is both to get bonded surface area and also to make sure that you have sufficient fiber alignment to the range of load angles.

The bonded areas requirements are surprisingly pretty low - even with a 4:1 safety factor - bilbo's would seem to need only 9 sq inches per brible arm (sorry for the imperial measurement).  

load    5040.0    lbs per bridle
bond strength    2200.0    psi
minimum bond area    2.3    sq inches
safety factor    4.0    
safety bond area    9.2    sq inches  (EDIT: since he would be bonding to polyester I presume, you could double this - still not huge)

The fiber splay angles vary quite a bit between the different applications I have seen but I have seen ones for wide load yaw angles using upto 60 degree splays.  Obviously you have to add fibers to compensate for the ones at any moment that are off load angle.  But carbon is so f&*king strong that is not hard to do and still have it 'look right'.  Bilbo has mentioned s-glass, and if he has some (or access to some) it might be (you would be a much better judge than I about that) a better material than carbon here, but everyone seems to use carbon.

strongpoint.JPG

I'm surely not suggesting anything you dont already know, just laying out some thinking.

 
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Zonker

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To do those splayed laminated are tricky. I've seen the "folded over a tube/pin style at an angle" before but never like your picture. It's cool but at a very high skill level versus flat laminates. 

Uni S or even E glass is fine too. Uni E glass is very strong so by the time you get to the "that looks about right" thickness you could do it in E glass as well. 

Yes, bonding areas areas for lapping onto a surface are always smaller than you think reasonable. As long as you never have a Peel load! I.e.straight aft load or inboard toward the vessel centerline is fine but outward of the transom is a very bad thing (tm) 

If I was doing this I would make them on a bench (flat, temp controlled), cure, trim, then take to the boat and bond them with Spabond. S3 Gelmagic or any one of the rubber toughened epoxies. Working with wet laminate on a vertical edge surface can be done but has high degree of difficulty. About 7-8/10 from the judges. 

 

estarzinger

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 I've seen the "folded over a tube/pin style at an angle" before but never like your picture. It's cool but at a very high skill level versus flat laminates. 
 The guys doing those specific pieces are actually in Bilbo's neck of the woods: 

FLiNK Limited
Rosemary
Jubilee Road
Totnes
TQ9 5BW
UK

 

Autonomous

Turgid Member
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Autonomous,

You are making a big point of Structural Fillets. If I were doing this layup I would mix a thick batch of high density and do a larger than normal fillet in the corners. Then run the reinforcing fabric on top of the fillet. Is that what you going on about?
I'm not the guy to engineer laminates but that sounds close. My experience is mostly with wracking forces on corners of heavy equipment and also small stitch and glue boats. Without adequate gussets materials joined at angles can too quickly become hinges. That's my point. 

 

longy

Overlord of Anarchy
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San Diego
My understanding: the filler doesn't add much strength, it is to allow the cloth fibers to bend around that inside corner without crimping or forming too tight a bend. Is there any guide for fillet size vs laminate thickness?

 

bilbobaggins

Member
65
5
 The guys doing those specific pieces are actually in Bilbo's neck of the woods: FLiNK Limited.....
 
I've followed up on Evans' helpful pointer to FLiNK Ltd, and had a lengthy 'consult' with Julian S. their top specialist. He certainly has the background and the 'hands on'.... or pro CV.... and understood exactly the objectives and the constraints. He endorsed much of what was raised here/above and I'll be incorporating - insh'allah - his suggestions for a hand layup that is likely to have enough 'redundancy' to accommodate this ould fule's clumsy handiwork.

That includes about 10 layers of multiaxis quadriaxial 1200gsm, thicker than the 9mm titanium plate of the pad eyes, laid up as a sort of 'fat tadpole'.... and the aft 'edges' of these layers carried around the insides of the hull/transom corner - with a fillet - as suggested above. He didn't seem overly concerned about the bolt spacing. There is support for running a reinforcing structure across the transom, underneath the stern hull/deck join, as encouraged here-above. And a couple of other thoughts, including a thinner s/s plate inside acting as a v. large washer, and a 200mm wide tape of uni-carbon run horizontally forward from the bolts area, in the centre of the layup.

I had considered some 'great big' s/steel chainplates - but would still need a similar 'beefing up' inside.

The issue of maintaining bonding pressure/support on essentially vertical surfaces i.e. against gravity is still open, but the idea of using multiple small powerful 'rare earth magnets' ( wrapped in release film ) inside and out to hold a 'wrapped' support mat vertically in place.... has some traction and will be trialled.

We agreed there are no guarantees and, as it's my decision and only my sorry pink ass that's at risk, there's no issue of 'Liability'. I'm at ease with that.

 

Zonker

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No need to get fancy on vertical laminations. Wet out your fabric, then sprinkle a light dusting of colloidal silica into the resin to thicken it. Squeegee/roll it a bit more. No more than 3x1200 layers at a time until the resin gets tacky. Then add more layers. 

 

bilbobaggins

Member
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5
No need to get fancy on vertical laminations. Wet out your fabric, then sprinkle a light dusting of colloidal silica into the resin to thicken it. Squeegee/roll it a bit more. No more than 3x1200 layers at a time until the resin gets tacky. Then add more layers. 
I'll do 'zackly that, thanks, Zonker. You're a star! ( You don't do 'housecalls', do you? :rolleyes: )
I'll also grab a couple of those IR heat-lamps used in pig hatcheries/incubators to keep me warm while the glue goes off.

 

Zonker

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In case I wasn't clear: wet out the fabric on a plastic covered horizontal table. Then sprinkle a bit of silica and roll/squeegee it into the fabric. This thickens the resin and prevents vertical drain out (and makes it more sticky. Roll it up into an easy to handle piece.

Now apply to the vertical surface a bit at a time, squeegeeing it into place. If you have a helper, have them in the cockpit wetting them and out and passing the rolls to you. Given that it is probably pretty cold right now, you can likely wet out the pieces yourself and then climb into the tight spot with a handful.

You can also write on glass with a Sharpie to make sure you have the layers tapered in sequence.

 

bilbobaggins

Member
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5
Yes, thank you, 'Z'.  I already have a 2' square plastic-covered 'table' I made up which clamps into a 'Workmate' portable bench ( https://www.youtube.com/watch?v=MtdblY_ChV8 ), which I've used effectively for smaller jobs. I think I'll make up a larger table to fit across the cockpit, rimmed around as a 'bund'.

I'll also do a trial run....

As for the 'Sharpie', yes, I'd planned to use 'strike up marks' for positioning, as clear line of sight may be challenging at times. I'll probably use some polyester release film between iterations, too. I'm wondering if I can source some veterinarian elbow gloves I could coat with release agent, so I don't have to spend the night 'on the job'....

 

Zonker

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I would not use release film. It is smooth. I'd use peel ply which leaves a micro textured surface, ideal for following laminations.

 
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