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PostPosted: Thu Jan 30, 2014 10:55 am 
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Joined: Sat Nov 23, 2013 12:52 am
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Very nice work for such a tough place to access. I just wanted to add a suggestion for those doing internal hull repairs regarding material choices. I have experimented over the years with layups for molded RC racing planes to creat "hulls" with stiff areas blended to impact resistant zones yet preventing twist and stress failures. While carbon fiber is great for areas you want to be as stiff as steel, it can create stress points at its edges and increase the chance of failure. Blends of S glass carbon and kevlar are available and give you options that are great for hulls. Kevlar is hard to cut but manageable. It provides a highly flexable patch yet with extremely high impact resistant. It is very light as well. Glass is great for bonding and resin up take. For the sides of hulls a blend of the three would likely be superiour to a hard spar. http://shop.fiberglasshawaii.com/ This is just one source of many outlets for fabric mixtures. Your repair above was great for a section that no flex can occur at and your tapering of the carbon thickness is the right idea to avoid focusing stress. If you do use a solid spar I would add a bit of kevlar under it to spread the stress to the hull.
Cheers, Steve


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PostPosted: Thu Jan 30, 2014 11:07 am 
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Joined: Mon May 09, 2005 10:25 am
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Location: Jersey Shore
Thanks for the positive feedback. This repair/reinforcement is a bit of uncharted territory for me. Minimizing edge stress concentrations was definitely a concern and the reason for generously overlapped patches. If I go with the reinforcing stringers/spars I will likewise use a tapered design where the thickness reduces at the ends in order to minimize stress concentrations.

sm


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PostPosted: Sun Jun 15, 2014 1:00 am 
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Joined: Fri Apr 19, 2013 2:15 pm
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Srm

Thanks for sharing your hull reinforcement work.

I'm considering doing the same for my 1983 hulls. I'm seeing some hairline cracks in the gelcoat forward of the front cross beams. They are not redline hulls.

Last year, I added the extra chainplates, and repaired a large deck delamination in the port hull aft of the board trunk. Delamination repair looks ugly, but the deck is stiff again. I was also thinking about adding deck ports here, but reinforcing the rim with carbon fiber.

How many yards of carbon tape and fabric did you end up using?

RR


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PostPosted: Mon Jun 16, 2014 12:36 pm 
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Location: Jersey Shore
I think I ended up using about 1 yard of 50" wide fabric, 2.5 yards of 6" wide tape, and 16 oz of resin.

sm


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PostPosted: Fri Dec 04, 2015 7:34 pm 
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Joined: Wed Nov 06, 2013 2:43 am
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Location: Brisbane, Australia
sm i'm about to undertake a similar repair to an Australian BB coded H18 estimated to be about a 96??? model.

Taking on water on my last sail and not being satisfied with a visual inspection I used the air mattress pump and soap spray to find these cracks which became easier to see with the air pressure pushing out on them. I've removed the channel and bolts here:
Image
And the other side:
Image

The inside layup area looks to be re-enforced with a thin layer of glass and a white glue (instead of red) used by glue gun without even applying pressure to bond it into the corner area. On one of my photos you can see a small opening where the crack is. I've only sailed this H18 twice and i'm sure glad i used a front cross bar as the possibility exists for huge failure.
Image
Image

So i'm keen to get working on a similar repair that you've done sm. Do you feel the anchor plate kit is a must and worthwhile addition here?
I have the anchor plates on the side stay areas but not at the cross bar ends.

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2007 Hobie 16 - 'Slingshot'
1996 Hobie 18 - 'Onrails'
Hobie Bravo - 'Hobie Bites'


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PostPosted: Sat Dec 05, 2015 5:55 am 
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Location: Jersey Shore
I would definitely add the anchor plate kit, especially since you're seeing cracking. It looks like adding the fiberglass/carbon patch to the inside of the hull shouldn't be too bad. Just grind away the white glue, fillet the area if needed, and then laminate in the patches. It's best to take the hulls apart for this project.

sm


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PostPosted: Mon Dec 07, 2015 3:35 am 
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Joined: Wed Nov 06, 2013 2:43 am
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Location: Brisbane, Australia
Cheers sm, i've ordered them today. Still unsure I want to take it all apart - i do have an area i can safely turn my H18 on its side which would help alot.
Thanks again for your advice and of course these detailed pictures of your repair!

_________________
2007 Hobie 16 - 'Slingshot'
1996 Hobie 18 - 'Onrails'
Hobie Bravo - 'Hobie Bites'


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PostPosted: Mon Dec 07, 2015 10:23 am 
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Joined: Mon May 09, 2005 10:25 am
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Location: Jersey Shore
It is much easier if you can take the boat apart - let gravity be your friend. When you pour the resin into the hull/deck joint to create a fillet, you want that to be the low point. Also, when you laminate the glass/carbon, it needs to wrap around the hull/deck joint area, so again, you want that area to be down so the cloth doesn't fall off while you're trying to adhere it to the hull. With the boat apart, you can flip the hulls into whatever orientation works best.

sm


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PostPosted: Mon Dec 07, 2015 11:11 pm 
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Joined: Wed Nov 06, 2013 2:43 am
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Location: Brisbane, Australia
Yeah i think your right and the extra effort will be worth it long term. Today I bought some double bias cloth @ 400gsm and also some Qcell for filling. I'll post back when its done.

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2007 Hobie 16 - 'Slingshot'
1996 Hobie 18 - 'Onrails'
Hobie Bravo - 'Hobie Bites'


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