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1979 Nacra 5.2 Rebuild  Bottom

  • Just punched the same boat I sold 15 years ago. This boat is in great shape for being 40+ years old. I am in the process of stripping the boat down and plan to repair some minor hull damage and re-install new items that are worn out. I have spent a lot of time on “The Beach Cats” and am impressed with all the great advice everyone is willing to offer. My first big project is to fix the hull damage where the dolphins striker bar meets the hull. I have included the image and am looking for; 1. Advise on epoxy repair and Gel Coat 2. Identifying the part that is attached to the hull where the damage is. For Item 1 I plan to grind out the damage, sand, prep, epoxy, glass, fill and gelcoat. Does anyone have advice on which brand of Gel Coat is the best. I will be using West System 105 epoxy resin with 205 hardener and investigate which glass and filler to use. I will be looking to roll and tip the area with Gel Coat. I also have some worn Gel Coat spots on the hulls and want to apply a new coat over the entire hull area. I don’t mind sanding and polishing but want to know how much work over spraying as an alternative it will be. I think the mixing, thinning and spraying may be difficult for a novice although I have a compressor. If anyone has a feed on those #2 items for purchase I would appreciate it. Thanks

    https://www.thebeachcats.…ictures?g2_itemId=132991
  • In case you want to look at additional photo’s I have started an album on the technical page titled. 1979 Nacra 5.2 rebuild.

    https://www.thebeachcats.…ictures?g2_itemId=132916
  • Looking forward to following this one. I picked up a Nac 5.2 years ago for $400 with no trampoline, sails, or jib blocks. The plan at the time was to pick up another one for $300 that the owner had wrecked when the trailer became detached from his car while driving, but that one got sold before I got to look at it. (I should have rolled the dice and bought them both over the phone). Anyway, it's sitting under a cover, under some trees on a rental property I have in Santa Maria. Never got the time to mess with it, and it's been a bit denominational to know most of the money I would put into it, I would never get back, unlike the original two boat plan.

    Maybe you'll inspire me to take the project on.

    --
    Bill Mattson
    Prindle 19 "Gelli Bean"
    Prindle 19 "Cat's Pajamas"
    --
  • Found the answer to my own question from the Nacra 5.2 Assembly Manual. The part is called a “Bearing Tang” which is riveted to the inside of the hull. It seems this spot can be critical if the beam straps are loose because the hull can then be forced into the dolphin striker support strap. This is obviously what has happened to the hulls on the boat. Probably another reason to make sure you periodically check your beam strap bolts and be cautious when putting your boat on its side to do any work.

    https://www.thebeachcats.…ictures?g2_itemId=133015



    Edited by leadbetter on Apr 29, 2020 - 12:33 PM.
  • leadbetterFound the answer to my own question from the Nacra 5.2 Assembly Manual. The part is called a “Bearing Tang” which is riveted to the inside of the hull. It seems this spot can be critical if the beam straps are loose because the hull can then be forced into the dolphin striker support strap. This is obviously what has happened to the hulls on the boat. Probably another reason to make sure you periodically check your beam strap bolts and be cautious when putting your boat on its side to do any work.

    https://www.thebeachcats.…ictures?g2_itemId=133015Edited by leadbetter on Apr 29, 2020 - 12:33 PM.


    Bolted rather than riveted
    https://www.murrays.com/product/56-2511/

    Visible here in page 2
    https://www.nautic-sport.…/eclate-ancien-nacra.pdf
    You can search those codes in Murrays.

    If I understand correctly, if you add this part you could take off the tube at the center between both beams. I think what is does is to avoid that the beams rotate on its ow axis, especially the front one.



    Edited by Andinista on Apr 29, 2020 - 03:15 PM.
  • Looked at the “Internal Beam Casting” but this boat, (1979) does not have the hole to accept the part. I think it may. Have been on previous models. Also no looking to get rid of the center beam, its original and is a good foot brace. The damage is into the hull and is a must fix. Otherwise I’m very impressed with the removal of all parts, (Nothing Broke)! Beams look in great shape, a low profile track on ream beam would be a nice improvement. Any advice on what type of glass I should use to fix the hull Bearing Tang Damage would be helpful. Also looked at the Beam Straps and although I have not measured them it looks like the front and rear Beam Straps are the same length and shape, very odd! Per the owners manual the front and back are 1/2” difference in length. Here are the hulls separated and the tang damage.

    https://www.thebeachcats.…ictures?g2_itemId=133019

    https://www.thebeachcats.…ictures?g2_itemId=133022



    Edited by leadbetter on Apr 29, 2020 - 09:34 PM.
  • Leadbetter, I just sent you a message. Give me a call to discuss fiberglass and gelcoat methods.

    --
    David
    Inter 20
    Southern Maine
    --
  • Removed more items off the hulls and almost done. Ground out the Bearing Tang damage. The Tang rivets are on either side of the forward bulkhead so another reason to think about a third inspection port if repairing damage to hulls in front of it. While pulling off the inspection port outer rings it became handy to pry with a large putty knife after I drilled out the rivets. The silicone causes a great adhesion and I’m wondering if too much applied for any part causes more headaches when trying to remove something, especially when you don’t want to pry against a hull!! Thanks “David” for the advise on the hulls this morning!! I’m still deciding what to do about the hulls?? Sail sooner or work on it more!!

    Hull inspection and cleaning
    https://www.thebeachcats.…ictures?g2_itemId=133031



    Edited by leadbetter on Apr 30, 2020 - 10:11 PM.
  • Looking at the photo after grinding; and your hatch location, I would do this repair from inside the hull. You should have the fiberglass repair go around the corner (under the beam pocket to be a structural repair you never have to worry about again). The corner that is now an open hole- takes a fair amount of load.

    Here's a strategy I would use:
    1. Sand the fiberglass inside the hull. If you can hand sand the hole from the inside to create a knife-edge scarfe, this is ideal for load transfer with the repair patch. I know this is a pain in the ass, but will be much less work than an exterior cosmetic repair. If you can't get a knife-edge, there will be more of a stress concentration and more fiberglass should be used.
    2. Acetone wipe fiberglass for bond prep after sanding
    3. Apply flashbreaker tape (or packing tape) to the outside of the hull damage as a dam
    4. Flip Hull so hole is facing down. Resin and glass will be pressed to the tape dam.
    5. Mask deck area so wet fiberglass does not drip on the hull as you reach through the port with your wet glass patches
    6. Assuming knife edge is achieved- Apply fiberglass repair (inches larger than hole in all directions- including around the corner). Layers should be different sizes so the plys drop off and spread the load distribution from the beam. You can dart or cut the glass so it bends around the corner well. The cuts or darts need to be in a different location on each ply. Inspect with a mirror and flashlight. Use slow hardener so you can take your time with this- fast hardener will not give you enough time. The total repair laminate thickness should match or exceed the original laminate thickness.
    7. Trial fit some of the fiberglass pieces before you wet them out. This will help you define what size and geometry you will cut and fit this specific area of the hull.

    There will be very little aesthetic work after tape removal, just minimal fairing and a small area to gelcoat/paint (brush, roller, or spray) where the hole is.

    I can discuss laminate details when you share the specific thickness (prior to sanding) of the hole and what glass you will use.

    --
    David
    Inter 20
    Southern Maine
    --
  • Sounds like a much better plan!! Because the hatched area I drew with a pencil is bent into the hull I’m thinking of opening it up so that I have a bigger hole to sand the inside. What do you think? Otherwise I can’t get to the area in front of the bulkhead. If I open up to about 1” then I can get inside but its a very tight space as I have not only the bulkhead but a rib also running lengthwise on the hull. Other option is to grind away some bulkhead and lay the repair while reinforcing the bulkhead I removed. It’s not going to be pretty but I want to get it done right. Thanks

    https://www.thebeachcats.…ictures?g2_itemId=133039

    Not a great picture, but inside of hull.
    https://www.thebeachcats.…ictures?g2_itemId=133042

    Peter
    Nacra 5.2



    Edited by leadbetter on May 01, 2020 - 11:33 AM.
  • You can absolutely cut to your hatched area. That "Tab" is nothing but a spacer now. May as well give yourself room for sanding. If the resulting hole is too big for tape to cover smoothly (I don't think it will be), you tape a flat backer panel (called caul plate) over the hole. Wax paper taped over the caul will make sure the caul plate can be removed after the fiberglass is cured.

    Sandpaper glued to a paint stir stick with 3M77 can do wonders when sanding this type of hole.

    --
    David
    Inter 20
    Southern Maine
    --
  • I would cut away the bulkhead (as small as possible). Do the repair described above, then wet layup the missing piece of bulkhead.

    An oscillating saw with a diamond cutter can act like a scalpel to surgically cut pieces of bulkhead rather than grind (see links). You may even be able to re-install the piece of bulkhead you cut away and only have to wet tab the cutline? Let me know if the bulkhead has core or if it is solid fiberglass after it is out?

    https://www.harborfreight…q=oscillating+multi+tool

    https://www.harborfreight…g-multi-tools-64967.html

    --
    David
    Inter 20
    Southern Maine
    --
  • I agree and will open the area up to see what can be accomplished. By that time I will look at the bulkhead and figure out how and where to cut. It’s interesting to see how the boat was built. This spot is critical and has numerous converging angles. Obviously important for a proper build up. I noticed the thickness of the cradle is not a beefy as I thought it would be. I’m hoping the outside edge of the hull is better reinforced. As always I appreciate the advice!!! Thanks.

    Peter
    Nacra 5.2
  • Just ground out the bent in tab part of the damage. The hull and cradle are about 4.5 to 5mm thick. The hole is 1” by 2 1/2”. The bulkhead does not feel very thick, maybe 1.5 to 2mm thick and I don’t think it has a core but will find out. I’ll probably cut about a 4” diameter hole and try to reinstall. What type and weight of cloth should I use for the repair. I was thinking Matt because of all the contours. Would Peelply be better on the outside of the repair as I need to order some more products from West System and have seen how easy and productive it is to use?

    Opened up damage
    https://www.thebeachcats.…ictures?g2_itemId=133047

    Bulkhead
    https://www.thebeachcats.…ictures?g2_itemId=133050



    Edited by leadbetter on May 03, 2020 - 02:44 PM.
  • In your thickness measurement, are you including the gelcoat and fairing thickness? It looks like there is gray primer or filler under the white gelcoat or paint? We want to boil down to the laminate thickness only- ignoring gelcoat, resin richness and wrinkles.

    Matt has a binder specifically for polyester resin and should not be used with epoxy. If you want to use epoxy, do not use chop strand matt. The binder is the fiber coating that holds the fibers together and helps the resin permeate the fibers. Chop strand matt binder chemistry will not react as intended with epoxy. See note on the link mentioning this.
    https://www.fibreglast.com/category/Fiberglass_Mat

    4 oz per yard (400gram per square meter) glass will go around the corner best, as it is thin and conforms well. It will require the most layers for the repair, because it is 0.20mm, 0.008" thick for a single layer. Assuming the original laminate is 4mm, then 20 plys would be the right number (4mm total/.20mm per layer)

    6oz is typical, can be bought locally, and is 0.01" thick (.25mm). This would be a 16 layer repair.

    I prefer 400gram per square meter 45 stitched biax glass. The stiched glass does not fall apart as much as the woven glass after you wet it and attempt to reach and precisely place it inside the hull. https://www.fibreglast.co…2806/Stitched_Fiberglass

    Have a look at this link. This is the cross section you are trying to achieve for the hull (from the inside of the hull) https://www.westsystem.co…ning-laminate-thickness/



    Balance the laminate. Here is an example 16 ply laminate: 8 ply should be installed 0/90 and 8 at 45. Notice symmetry about the middle (layer 8/9)

    Layer 1 0/90
    Layer 2 45
    Layer 3 0/90
    Layer 4 45
    Layer 5 0/90
    Layer 6 45
    Layer 7 0/90
    Layer 8 45
    Layer 9 45
    Layer 10 0/90
    Layer 11 45
    Layer 12 0/90
    Layer 13 45
    Layer 14 0/90
    Layer 15 45
    Layer 16 0/90


    Peel ply will be fine. If your buying it, you can apply it both outside the hull (this will give you a smoother surface that is closer to paint or gelcoat prep) and after the laminate (inside the hull). It will absorb excess resin from the hand layup process and leave a clean/professional laminate with no glass splinters.

    As your plan gets closer to happening- let's have another discussion to talk through details, such as resin batch planning, temperature, alone versus help, etc.

    Cheers

    --
    David
    Inter 20
    Southern Maine
    --
  • Yes the measurement was a total, not just the laminate. I will remeasure but its probably about 4mm. Looked at the video and understand the chop strand matt is not compatible with epoxy. I will get the cloth and other supplies while I wait for the oscillating saw to be delivered. So if I understand I will sand and bevel the inside. Apply Peelply to the outside and layer the cloth after wetting the area in the layers you describe. I assume the 0/90 and 45 mean laying it at different angles each layer except for the 8th & 9th layer? I cant thank you enough for the advise and will talk when all is ready to go.
    Peter
    5.2
  • Yes, Sand and bevel the inside. Using the West System link above and your sanded hole geometry and thickness, this will help you define the repair patch geometry. 4mm thickness x 12:1 ratio means the largest glass needs to be 48mm (4*12) larger (for each side) x 2 sides = 96mm larger than hole. Rounding this to 100mm or 4 inches.

    --
    David
    Inter 20
    Southern Maine
    --
  • Looking to buy a random orbital sander to sand and polish the gelcoat when I get to it. I have an air compressor to drive it. Does anyone have a good recommendation on a brand and model of sander? There are way to many options out there. I’m looking for a 5” with dust collection. I’m also confused, does “Duel Action” mean random orbital and the ability to switch to just orbital? Thanks

    Also looking for a longboard sander and a half piece 3M organic vapor face mask. Can’t find anyone who has the mask in stock for around $40 due to the COVID-19 issue.



    Edited by leadbetter on May 14, 2020 - 10:42 AM.

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