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Re: Blade's strengths and weakness? [Re: tshan] #120515
10/21/07 11:56 AM
10/21/07 11:56 AM
Joined: Mar 2006
Posts: 1,246
Orlando, FL
tback Offline
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Orlando, FL
I had a delamination problem with one rudder (an original carbon fibre rudder--not being produced any longer), VectorWorks replaced both rudders without question.


USA 777
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Re: Blade's strengths and weakness? [Re: ] #120516
10/22/07 08:42 AM
10/22/07 08:42 AM
Joined: Sep 2005
Posts: 1,187
38.912, -95.37
_flatlander_ Offline
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_flatlander_  Offline
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Quote
Hi all,

as suggested I would agree that Kevlar makes no difference when it comes to dents, the amount of denting that occurs in a Glass or Kevlar outer skin is a result of the core stiffness, as was said, solid glass boats had little trouble with this but they are to heavy and flexible for a F16 hull.

So the amount of denting is reliant on the density of the foam core on boats like Taipans and Blades and then it is still a balancing act between weight and dent resistance,along with thickness for overall stiffness. I have certainly seen some Mosquito's in OZ that dent to easily. Can not comment on those in the US, it may be worth asking the manafacturer if he has altered foam core density at all, as that is what they did with the Mossies in OZ.

and from Bobcat
Quote
My boat isn't Kevlar. Kevlar may be something to look for.

and from PTP
Quote
Not sure kevlar would makes much of a difference.

and from Tom (tshan)
Quote
1. Make sure the hulls are kevlar (almost all are).

So is there a consensus here? Are you saying kevlar reduces, but does not eliminate dimpling?

Are there other attributes or drawbacks of a kevlar outer skin?
For instance, added resistance to puncture wounds?
More difficult to repair?

Thanks


John H16, H14
Re: Blade's strengths and weakness? [Re: _flatlander_] #120517
10/22/07 08:45 AM
10/22/07 08:45 AM
Joined: Dec 2005
Posts: 443
Edmonton, Alberta, Canada
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I am probably in the same boat as you actually. I know little about Kevlar but what has been written here. I think that it is more puncture resistant and I guess I extended that to more dent resistant.

Re: Blade's strengths and weakness? [Re: _flatlander_] #120518
10/22/07 10:23 AM
10/22/07 10:23 AM
Joined: Feb 2006
Posts: 3,348
F
fin. Offline
Carpal Tunnel
fin.  Offline
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F

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I think Kevlars greatest virtue is puncture resistance.

Re: Blade's strengths and weakness? [Re: fin.] #120519
10/22/07 03:16 PM
10/22/07 03:16 PM
Joined: Jul 2004
Posts: 2,718
St Petersburg FL
Robi Offline
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Bulletproof baby!

Re: Blade's strengths and weakness? [Re: fin.] #120520
10/22/07 03:42 PM
10/22/07 03:42 PM
Joined: May 2002
Posts: 1,037
Central California
ejpoulsen Offline
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I have an AHPC Kevlar Taipan that seems to be very strong and I have not seen any dimpling, leaking, daggerboard well issues, delamination, etc. I have no idea about the Blade.


Eric Poulsen
A-class USA 203
Ultimate 20
Central California
Re: Blade's strengths and weakness? [Re: _flatlander_] #120521
10/22/07 04:38 PM
10/22/07 04:38 PM
Joined: Jun 2005
Posts: 61
Northwest-Germany Hamburg
Holger Offline
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Northwest-Germany Hamburg
The outer layer of a sandwich composite has to withstand tensile loads and the inner layer compression loads in case of an impact.
When we compare the different laminate materials:
Tensile strength [MPa] E-glass 2400, Kevlar 3000, Carbon 4000,
we see that carbon is the strongest material, but in case of an accident Kevlar has it's large advantage over the other materials.
Strain at break point E-Glass 4.5%, Kevlar 2%, Carbon 1.2%.
The 1.2% figure for carbon fibre indicates that though very strong it is also very brittle and will break shortly after the load stress passes yield point.

So the advantage of Kevlar as outer layer is, that it is lighter than glass, stronger in tensile strenght and not brittle.

In case of repair Kevlar will fuzz at the surface if you want to sand it, and it is hard to cut. It must be covered with glass or gel coat.

Here the source for the above mentioned with more technical background:
http://oneoceankayaks.com/Sandcore.htm
http://www.auf.asn.au/scratchbuilder/composites.html


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Dynautic Blade F16-GER 001
Re: Blade's strengths and weakness? [Re: Holger] #120522
10/23/07 03:13 AM
10/23/07 03:13 AM
Joined: Nov 2006
Posts: 435
Finland
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Finland
There are only two small drawbacks with Kevlar. It's sensitive to light (UV) and absorbs a lot of humidity???
Two good reasons why not to use it in boatbuilding.

Re: Blade's strengths and weakness? [Re: Gato] #120523
10/23/07 03:19 AM
10/23/07 03:19 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
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Those are not good reasons to discard Kevlar as Carbon is at least as sensitive to UV when untreated and glass is at least as hydrophile as Kevlar can ever be. Both other materials are used extensively so why not Kevlar.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Blade's strengths and weakness? [Re: Wouter] #120524
10/23/07 03:47 AM
10/23/07 03:47 AM
Joined: Nov 2006
Posts: 435
Finland
Gato Offline
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Still the reason why the aircraft industry has almost abandoned Kevlar is the problem with waterabsorbing...

Re: Blade's strengths and weakness? [Re: Wouter] #120525
10/23/07 09:23 AM
10/23/07 09:23 AM
Joined: Sep 2005
Posts: 893
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waynemarlow Offline
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Farrier will not allow Kevlar on the outer skin, not sure why, can anyone enlighten me, he also is quite open that you can use carbon on the outer skin but to get dramatic weight savings, the skins become so thin that they cannot withstand the impact loadings of crashing into things. He advocates glass and a good layer of it as it is very resillient to dings etc ?, easy to repair, cheap to manufacture and does the job, any weight savings can be saved elsewhere. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

Re: Blade's strengths and weakness? [Re: waynemarlow] #120526
10/23/07 11:25 AM
10/23/07 11:25 AM
Joined: Sep 2005
Posts: 1,187
38.912, -95.37
_flatlander_ Offline
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Quote
Farrier will not allow Kevlar on the outer skin, not sure why, can anyone enlighten me,
Back to what Holger said
Quote
In case of repair Kevlar will fuzz at the surface if you want to sand it, and it is hard to cut. It must be covered with glass or gel coat.
Concured by extensive search of "kevlar" on this forum (after I asked) seems the common layering is gelcoat, glass, then kevlar.

The common theme for kevlar use is not structural strength, but improved dent resistance


John H16, H14
Re: Blade's strengths and weakness? [Re: Gato] #120527
10/23/07 11:30 AM
10/23/07 11:30 AM
Joined: Jun 2005
Posts: 61
Northwest-Germany Hamburg
Holger Offline
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Northwest-Germany Hamburg
How does the water come to the Kevlar strands as long as it is bedded in the epoxy matrix? Epoxy does not absorb water, like polyester or vinylester. So when the Kevlar is stored dry prior the laminating process, everything would be ok? And most builders use a gelcoat or painted surface which inhibits UV.


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Dynautic Blade F16-GER 001
Re: Blade's strengths and weakness? [Re: Wouter] #120528
10/23/07 11:36 AM
10/23/07 11:36 AM
Joined: Jul 2001
Posts: 953
Western Australia
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its the epoxy that is UV sensitive and heat sensitive... Maybe heat isn't an issue where you are.. It is here, so those in the know just paint the hulls...

Re: Blade's strengths and weakness? [Re: _flatlander_] #120529
10/23/07 05:55 PM
10/23/07 05:55 PM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline
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dent resistance comes predominantly from the core density, particularly with the very light skins; carbon, kevlar or glass; used on our size boats. The thickness of skins on our size boats range from 0.25-0.5mm. That's why hard points are de-cored or have the core replaced by a harder core.

Re: Blade's strengths and weakness? [Re: ncik] #120530
10/23/07 08:11 PM
10/23/07 08:11 PM
Joined: Jun 2004
Posts: 1,479
Thailand
Buccaneer Offline
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Thailand
The Kevlar is stiffer and doesn’t dent (just be sure to leave the car/house keys at home and not in your back pocket)... <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />


"House prices have risen by nearly 25 percent over the past two years. Although speculative activity has increased in some areas, at a national level these price increases largely reflect strong economic fundamentals." – Ben Bernanke – 2005
Re: Blade's strengths and weakness? [Re: Buccaneer] #120531
10/23/07 08:41 PM
10/23/07 08:41 PM
Joined: Sep 2003
Posts: 264
Long Island, NY
gregP19 Offline
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Long Island, NY
I'm changing from the "hook" system to the "keyhole" system for my harness. To me that is a good way to be proactive in the interest of minimizing holes in the hulls of my fragile Blade.


G Gove Blade #728 Long Island, New Yawk
Re: Blade's strengths and weakness? [Re: davefarmer] #120532
10/24/07 03:19 PM
10/24/07 03:19 PM
Joined: Jun 2005
Posts: 61
Northwest-Germany Hamburg
Holger Offline
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Northwest-Germany Hamburg
I found that the round 80x2mm alu beams are not so stiff as expected. I think these are the recommended ones which most homebuilders use. In choppy waves i can see and feel some vibration in the platform. Compared from memory to my former Nacra 500 it is noticeable more.
Would a replacement with 80x3mm carbon tubes for example bring effectively more stiffness?
How far does a little more flexible platform suffer in speed compared to a optimized platform with more rigid beams? Probably working on my sailing skills has more effect than new beams, but it is always nice to have optimal material for the beloved sport.


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Dynautic Blade F16-GER 001
Re: Blade's strengths and weakness? [Re: Holger] #120533
10/25/07 04:28 AM
10/25/07 04:28 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
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80x2 beams are in the homebuilding plans because these are universally availbable the world over while having a good ration between weight and stiffness.

Not all stiffness comes from the beams, the stiffness of the beams landings and torsional stiffness of the hulls between the beams is important as well. Basically, we need to find out first what the case of your problem is and adress that.

Going for 80x3 mm beams will give you 50% more beam stiffness but this will not translate directly into 50% stiffness increase of the whole platform because of the other factors named above.

Weight increase (for 2 beams) will be about 4 kg.

It is worth a try, but I don't expect more then 25% stifness increase.

How much does the boat flex now ?

Measuring this involved laying the platform up on its sterns (without mast etc) and seeing how far one bow needs to be lifted before the other bow is lifted clear of its support as well.

By the way the nacra 500 (and nacra 5.0) used the beams of the larger boats like the Nacra 6.0 and F18's and that makes them very stiff for the Nacra 500. Of course this comes at a cost, in the case of the Nacra 500 this cost is roughly 50 kg additional boat weight and 20% slower performance.

Stiffness of a platform is important but certainly not all important. More stiffness is mostly better in the way of feel in very choppy conditions. In the way of all-out speed I'm not sure how important is really is.

Wouter

Last edited by Wouter; 10/25/07 04:31 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Blade's strengths and weakness? [Re: Wouter] #120534
10/25/07 03:11 PM
10/25/07 03:11 PM
Joined: Jun 2005
Posts: 61
Northwest-Germany Hamburg
Holger Offline
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Northwest-Germany Hamburg
Quote

How much does the boat flex now ?
Measuring this involved laying the platform up on its sterns (without mast etc) and seeing how far one bow needs to be lifted before the other bow is lifted clear of its support as well.
Wouter


For a exact measurement in this manner I'll wait till the season is over, and I have to take the mast down. Probably beginning of the november. So far I enjoy the last sailing days with cold feet


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Dynautic Blade F16-GER 001
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