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Do-It-Yourself | Repairs

Do-It-Yourself: Catamaran Soft Deck Repair With Expoxy Injection

Added by DamonLinkous on Apr 17, 2013 - 03:49 PM

Hull Repair on an Old Hobie
By Rob Morse (prindle599), written April 17, 2013

Repair catamaran soft decksSoft decks are not a death sentence for your old boat.  It took me a few hours to re-bond the inner skin of the deck to the foam core to repair the soft decks.  It took longer to refinish the deck than to make that structural repair.  The repair isn't difficult, but it does take some feel to get right.  The old Hobie decks have a thick outer laminate, a foam core, and a light weight inner skin.  In my case, this inner skin came away from the core and I glued it back together.  Here is the short version of how it's done before I give you a full step by step description.

  • Drill holes in the outer skin.
  • Carefully drill through the foam core by hand.
  • Inject thickened epoxy between the inner skin and the core.
  • Pull the cores together with sheet metal screws.
  • Let cure and remove the screws.
  • Fill the holes with thickened epoxy.
  • Sand, fill and refinish the deck.

It sounds easy, and it is if you take it step at a time.  Read through the directions several times.  Do all the preparation work you can before you mix epoxy, and don't forget to chock the trailer wheels if the boat is on a trailer (Free lesson number 1.  Yes, I chased the trailer around the garage.) The size of the hole we drill is determined by the size of the syringe tip we use to inject the epoxy. 

I used a standard syringe with Luer Lock syringe tip.  The screw is a number 8 sheet metal screw (#8 x 1) and the drill is a #17 of .173 inch diameter.

Required repair tools-
drill motor, #17 drill bit, tape, rubber gloves, permanent marker, 20cc syringe, rubber tubing, mixing cups, stirring sticks, paper towels, shop apron, #8x1 sheet metal screws, small instrument screwdriver.

Mark the deck-
(picture- 1 rule)
I wanted the screws to be about 1.8 inches apart so I made a paper guide and marked the deck.  Keep thumping the deck and keep marking until you find hard deck.

Soft hull drill guide

Drill the outer skin-
(picture- 2 drill outer deck)
Using a drill stop, drill holes approximately ¼ inch deep through the top deck.  The drill stop can be a metal tube or a strip of firm tape rolled onto the drill bit.  Use a stop or you will accidently drill through both skins.  (Free lesson number 2)  Drill through the top skin only.  Go ahead and drill all the holes through the outer skin of the deck. (picture- 3 drilled deck)

Drill decks

Drill the core-
(Picture- 4 drill through core)
Remove the drill stop from the drill bit.  By hand, drill through the core by twisting the bit between your fingers.  Do not push. Stop drilling when you feel the resistance of the inner skin against the bit.  Do not drill through the inner skin!  (Free lesson number 3) You can feel the inner skin flex away from the bit and then feel the bit pushed back out of the hull as the skin moves back into place.  Drill all the holes through the core.

Drill through core

Prepare and inject thickened epoxy between the core and skin-
(picture- 5 syringe)
(picture- 6 fill)
I used a 20 cc syringe with a short rubber tube slipped around the tip.  The rubber tube forms a seal between the deck and the syringe body.  Mix up epoxy and thicken it until it has the consistency of honey, catsup or mustard.  A water-thin laminating epoxy will leak through small holes in the inner skin.  A mixture that is too thick will sit as a lump and keep you from pulling the skins back together. 

I injected a few cc of epoxy into each hole until I saw the epoxy squirt out the adjacent holes.  I only injected one row of holes before I installed the clamping screws.  Stop squirting and start screwing once you've put epoxy in the first row of holes.

Inject epoxy

Large Syringe

Pull the cores together with sheet metal screws and let cure-
(Picture- 7 screw)
(Picture- 8 fasten)
Put mold release on the sheet metal screws.  I used bright plated screws and a light coating of release wax to keep the screws from sticking.  Screw through the inner skin.  I used a small electronics screwdriver so I could feel the torque on the screw.  Continue to tighten until the inner skin is pulled against the core.  It is easy to strip the screw in the inner core, so be very gentle.  (Free lesson number 4)

Leave the screw in place and move on if you do strip it because the screw at least seals the hole.  Continue injecting epoxy and pulling the cores together as you work your way along the repair area.

Wipe up any excess epoxy now.  It is easier to wipe up the liquid than sand off the solid epoxy, so wipe up your spills.  Let the epoxy cure before you remove the screws.

Fasten deck with screws

Deck screw

Remove the screws and fill the holes-
(picture- 9 fastend)
You now have a hard decks.  You also have a bunch or rough screws sticking out of the deck that give it an industrial Frankenstein non-skid look.  I prefer a smooth deck.  Back out the screws.  Wipe the area around the screw holes with a solvent soaked towel to remove any mold release.  Fill the screw holes with thickened epoxy.  This epoxy mixture must be thick enough to stand on its own and not drain out of the screw holes. 

You want something that is as firm a mayonnaise or peanut butter.  Fill the holes in the deck.  I wanted to leave a solid plug of filler between the inner and the outer skin, so don't I wasn't skimpy with the filler.

Hard deck with screws


Smooth and finish-
I rasped, sanded and refilled the repair area.  Then I waited until another sailor was having their boat repaired and had a professional shoot on gelcoat.

Please comment with your experience if you use this repair method.


Footnote: Thank you Rob (prindle599) for taking time to document and write this up for the community.


  • Posted on
  • May 20, 2013 - 08:16 PM
are screws needed
i have read a bunch of articles on soft spot repair and this is the first i have seen using screws to bring the two cores together. while this seems like a good idea, it also looks like a bunch of extra work and also puts wholes through the inner core which everyone seems to try and avoid doing. i am about to repair a soft spot on my hobie miracle about 6"x10" just inside the starboard daggerboard trunk and a little foreward. my guess is the previous owner installed a port just aft of front crossbeam and didn t seal it correctly. everything seems structurally sound and solid otherwise. i purchased some git rot as per another article i read and planed on using the same technique as above minus the screws. should this be enought?
  • Posted on
  • May 25, 2013 - 07:17 AM
"are screws needed"
Mike, the screws are not necessary but are a good idea, pulls the inner skin back into it's original position. Also cuts down on the weight factor, if you just fill the void between inner skin and foam core you could end up injecting a ton of epoxy into that pocket. If you concern is the holes through the inner skin, remember that the screws will plug the hole untill epoxy hardens, back the screws out, and fill screw holes with putty-like epoxy. But if your boat is a 79 Hobie and weight is not a factor :-) fill the void without screws.
  • Posted on
  • May 29, 2013 - 02:54 PM
I've found a more cost effective way of repairing the hulls than the epoxy. A friend and I purchased an early 80's h-18 and it had a very large soft spot in the starboard hull. we drilled into the outer skin and filled the void with Loctite PL Premium Polyurethane Construction Adhesive. you can get a 29oz tube of it from Lowes for around 7 bucks. It take a day or 2 to firm up but once it does it has made our soft spots go away! We sail it very hard and have had no trouble from the soft spots!
  • Posted on
  • Aug 10, 2014 - 08:35 AM
mold release
What kind of mold release did you use?
  • Posted on
  • May 14, 2017 - 12:34 PM
mold release
Thanks for the great demonstration and write up. As bdiver2000 mentions though, we are missing details on the spec for the "mold release". Can anyone lend some insight? I'm about to start some experiments.
  • Posted on
  • May 06, 2018 - 03:44 PM
screws and mold release
Hi all. I am going about 25% with the screws. Like some of you have mentioned, most people don't use the screws. However, I found that putting screws in about a forth of the holes worked well to keep the inner core from drooping.

As for mold release on the screws, I used a toilet O-ring (not a used one). I just shoved the screws into the O-ring and got them all waxy. I also used self-drilling screws. It kept me from having to drill through the inner core by hand. So far so good.

I have a blue '81 cat fever, and can't wait to get it back in the water.

Thanks to Rob for putting together this tutorial. It gave me the courage to take a drill to my hulls.
  • Posted on
  • Dec 23, 2020 - 09:50 AM
I used this as a basic template for my repair. As a release agent I used PVA, as I had it around and need it for gelcoat repair. A layer of PVA on the deck before injecting epoxy, was helpful in keeping epoxy off the deck and in the holes. Plan is now to fair out the smooth parts of the deck and spray gelcoat. The holes in the grip pad, will be done by brush- I think. All in all I'm happy with this methodology.
  • Posted on
  • Dec 23, 2020 - 11:36 AM
One additional point. When I drilled holes, I noticed a couple noticable wet. I hung a 250watt bulb over areas for a couple days. The surface temp reached about 160ish at the focus point. I ran this until I was certain I had the areas dried out, before injecting epoxy.
  • Posted on
  • Aug 01, 2021 - 02:06 PM
Used this method on a tired old Hobie 16. Did it to the entire foredeck of a port hull. 100+ holes and total PITA, but it's solid!

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