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PostPosted: Sun Nov 10, 2013 1:23 pm 
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I've been working on reinforcing the hulls on my 1985 redline 18 and figured I'd share with the forum. As many folks know, the mid '80s H18s are known for having issues with hull failure. The hulls have a tendency to crack near the front crossbar where the deck meets the hull. When this happens the side of the hull can buckle and fail. I figured some preventative work couldn't hurt as the boat is getting up there in age.

The objective is to reinforce the bond between the inside of the hull and the inside of the deck. I chose to use epoxy resin and carbon fiber cloth. Before the carbon can be laminated to the hull surface, a large glob of red glue must be ground down and the hull seam filled with resin to form a fillet for the carbon cloth. I chose to completely disassemble the boat so that the hulls could be flipped and positioned as necessary. I also removed the access port assemblies to allow as much room for working as possible.

Here is the red glob of glue that needs to be ground down. I used a rotary tool with a coarse sanding drum.
Image

After sanding the glue, I filled the voids along the hull seam with thickened resin. This is where having the boat apart comes in handy as you can position the seam as the low point and let gravity create your fillet.
Image

Then the rotary tool and coarse sand paper were used to grind everything fair. This process creates a huge amount of dust, so a dust mask and shop vac are necessary. A mirror is used to see areas hidden behind the crossbar saddle.
Image

After creating a smooth fillet, the surfaces are thoroughly sanded and wiped with acetone. FIrst I laminated three plys of 6" wide tape, 10" long and each ply was overlapped by 3". First I wet out the carbon with resin on a sheet of wood. I painted a thin layer of epoxy inside the hull, and then carefully placed the plys inside the hull and removed all pleats and voids with a brush. Excess resin was pulled out of the cloth with the brush as well.
Image

The carbon wraps around the hull and extends onto the deck several inches.
Image

I then laminated several larger plys over top of one another.
Image

The largest outer ply is 20" x 14".
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Image

Image

The thickness of the hull sidewall was increased by up to 1/16" in some areas (increased from 1/4" to 5/16" thick) and feels very stiff. Hopefully this reinforcement in conjunction with the updated crossbar anchor plates will keep these hulls going. I am also looking into adding stringers to the interior hull sidewalls.

Hope this helps anyone considering taking on this project.

sm


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PostPosted: Sun Nov 10, 2013 4:02 pm 
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Does Lauren let you do epoxy work in the living room? :)

Jim


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PostPosted: Sun Nov 10, 2013 4:08 pm 
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Not a chance. Probably better off that way.

This was started a couple months ago when it was warm enough to do epoxy in the garage. Probably won't be able to finish it up until spring.

sm


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PostPosted: Sun Nov 10, 2013 4:19 pm 
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Nice work. Thanks for sharing.

Jim


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PostPosted: Tue Dec 10, 2013 6:23 pm 
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First of all...... Nice camera work.

Second, Why carbon? Do you feel the fiberglass and Poly wasn't strong enough? Explain your stinger ideas and why you feel you (we) need them. I am just beginning a 1985 referb and I am starting with the reinforcements. I have done this reinforcement in the past but I am open to your changes.

Third, how critical is the removal of the glue if you use epoxy? I believe the epoxy will bond with the glue (not sure tho)

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H18 '85
H18 '89 "Knotty Passion"
H20 '96 "20/20 Vision"
Fleet 259 Central Coast California


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PostPosted: Tue Dec 10, 2013 7:56 pm 
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wscotterwin wrote:

Second, Why carbon? Do you feel the fiberglass and Poly wasn't strong enough?


Well carbon is a bit stronger than standard E-Glass, so that's a definite benefit and was one of the reasons I chose to use it. But of course you can get equivalent strength by simply adding a couple more plys of glass. Carbon is stiffer, so that's another benefit I think. One of the biggest benefits I found using the carbon was in handling during layup. Getting the reinforcing fabric (carbon or glass) in through the access port and laid up on the hull side wall/deck is very challenging. For the larger patches, I had to fold them in half to get through the port. In the past, when I've worked with glass, if it folds over onto itself or develops wrinkles, etc., it usually ends up becoming just a sticky blob of fibers and a total mess. With the carbon, this was not the case. Since the carbon is stiff, it stays together much better and getting the lifts and voids worked out was a lot easier. It could be moved around and re-positioned in the hull without falling apart. I chose to use epoxy over polyester because it has higher strength and better bonding properties. Since sanding and prepping the inside of the hull is difficult, I figured better to err towards a resin system that has a stronger bond.

wscotterwin wrote:
Explain your stinger ideas and why you feel you (we) need them.


My stringer idea is to add half round stringers about 48" long to the inside of the hull on both sides. I made up a mold using 1-1/2" PVC pipe cut in half. The stringers have a flange that would allow them to be bonded to the inside of the hull and then additional glass laminated over top. They would be located maybe 2" below the crossbar anchor plate mounting holes and extend about 2.5 to 3 feet forward of the crossbar. The idea being to stiffen up the flat section of the hull and add even more strength to the hull sidewall in the area where these hulls are known to fail. Here's a pic of a prototype stringer.

Image[/URL]

wscotterwin wrote:
Third, how critical is the removal of the glue if you use epoxy? I believe the epoxy will bond with the glue (not sure tho)


Are you talking about the removal of the "red glue"? The reason I removed much of the glue is because the large blob of glue at the crossbar saddle bulges outward. There's no way to lay the cloth along the hull/deck joint unless a large amount of the glue is removed to create a fillet/smooth transition. The first and third pics in my post show how the glue was transformed from a "blob" to a "fillet". I don't think bonding to the glue with epoxy is a problem.

sm


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PostPosted: Wed Dec 11, 2013 9:03 am 
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I am going to use the carbon as well as I purchased it yesterday at TAP Plastics. Not cheap I will say but it looks fun to work with. I see your point on the glue and I will not fully remove as I have in the past and only create a smooth transition.

Your stinger idea looks interesting but trying to get the 3 ft ahead of the cross bar looks very difficult. That port hole is a little small and my arms a lot short. :-)

My last red line boat started coming apart at the rear cross beam after Mohave last year and I had to repeat the process in the back. Ugh!!!

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H18 '85
H18 '89 "Knotty Passion"
H20 '96 "20/20 Vision"
Fleet 259 Central Coast California


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PostPosted: Wed Dec 11, 2013 11:58 am 
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wscotterwin wrote:
Your stinger idea looks interesting but trying to get the 3 ft ahead of the cross bar looks very difficult. That port hole is a little small and my arms a lot short. :-)


I'll try to remember to post about the stringer installation when I get around to it. Unfortunately, it's 30 degrees here now, so fiberglass work isn't happening for at least a couple months....

sm


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PostPosted: Thu Dec 12, 2013 2:42 pm 
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Steve,
Your stringer solution sounds like a good idea for an admitted weak spot in the hull. However it does add a structural member to the hull assembly that was not there during manufacture. You are not concerned about a rules challenge to what might now be considered a non class hull? Is there a predecent for it?
Food for thought.

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'88 H18SE Arís


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PostPosted: Thu Dec 12, 2013 3:34 pm 
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The "standard" reinforcement of adding glass patches to the hull/deck joint is a hull modification that wasn't there during manufacture. I would view the partial stringer as a similar modification in that it increases hull strength without changing hull shape or altering performance. There was also a Hotline article that discussed adding bulkheads to the hulls to reinforce damaged decks. In all cases, no portion of the existing hull structure is removed or modified and if anything, these changes add weight to the hull. I suppose if someone really had a bug up their butt, it could be a protestable change, but I think it would have a tough time sticking. In any case, this boat is currently my beach boat, so not really an issue. Just trying to keep the old girl on the water safely at this point.

sm


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PostPosted: Fri Dec 13, 2013 7:26 am 
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That was my question, whether there was a demonstrated history of hull reinforcements over the years that did not affect rating or performance. Thank you.

I know something about keeping her in good shape. I have the common 'butt drop' damage to the port hull on my '88, just in front of the rear crossbar. After two attempts at filling the deck sandwich from the top with Git Rot, it is now apparent the lower glass layer is split. I'll have to bite the bullet and install a rear deck port to reach the area for a glass or carbon fix.

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PostPosted: Wed Dec 18, 2013 11:11 pm 
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That bulkhead article looked interesting... I've got a set of 85 hulls with some separation issues that I've gotta get into myself. Some cracking at the seam between the deck and the hull that I can slide my pocket knife all the way into... I let the project sit as I had some concerns about other weak areas that I couldn't see as easily. Someone's gotta come up with a drone for laying glass way inside these things...

Tom

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Fleet 259, Central Coast CA
H18 ('81)
H18 ('85)
H20 ('97)
H18 ('78)


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PostPosted: Mon Dec 30, 2013 10:13 pm 
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What's with the carpet foam padding?

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H18 ('85)
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PostPosted: Tue Dec 31, 2013 5:24 am 
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moncasta wrote:
What's with the carpet foam padding?


I used it (along with wood blocks and some other stuff to help prop up my mirror on the inside of the hull so I could see while I worked in front of the crossbar saddle. The inside of the hull is slippery, especially when it's tilted at an angle, so the carpet/foam just helped to provide some friction.

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 Post subject: Hull Reinforcement
PostPosted: Mon Jan 20, 2014 3:17 pm 
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Greetings. I have issues with the stern of the Starboard Hull on an 18' Hobie where someone pulled the boat on shore without releasing the rudder. The back of the hull cracked and a body shop was not able to repair the leaking hull. Is there a source just for the back of a hull that I could buy or do you have any other suggestions for repair? The body shop guy was a hack and just coated the back with all sorts of fiber Glass and it's a heavy mess.


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