foam block reset

last fall I bit the bullet and cut 2 holes in my Sunfish.  I was pretty disappointed, as the foam bedding was severely deteriorated, in some places the foam flotation blocks were no longer rigidly attached to the hull at the bottom and the deck at the top of the foam blocks.  especially where this occurred at the bottom of the blocks, it meant the hull could be flexing up and down as I sailed, which could lead to stress cracks in the fiberglass. I decided that since I had the boat opened up with the new holes for inspection ports, I should try to get the foam blocks reset before I actually installed the inspection ports, and made the opening just that much smaller to be able to work with.  there is a good tutorial by Wind Line Sails on how to reset the foam blocks here.  there is also a more thorough one at the Yahoo Sunfish Sailor Group.  it’s in the “Files” section, titled “Block_Reset” by John Howard, and it’s a “fantastic photo essay to accompany the Wind Line Sails repair sheet”.  I strongly recommend joining the Yahoo Sunfish Sailor Group and downloading that .pdf file to review before starting this task – it is very helpful.

I used the same method as John, and hung my Sunfish from the rafters in my garage using 2 ratcheting tow straps.  I also set a sawhorse at each end, just to keep the Sunfish steady as I was working on it.

it was a pretty hot day in mid-June, and I didn’t particularly want to wear a long-sleeved shirt, but did want to protect my arms as I was reaching in and out of the hole cut in the fiberglass.  I ended up cutting the ends off of a pair of socks, and wearing them as “sleeves”.  I also put masking taped around the hole – this helped probably just as much as the sleeves (see picture below).  then I proceeded to just use my hands to break out some of the old chunks of loose bedding foam.  I tried (unsuccessfully) to use the drywall saw method to cut out the bedding foam along the bottom of the hull.  I couldn’t get the saw to bend enough, and the loose foam was breaking out easily by hand so I just proceeded that way.  I removed as much of the bedding foam as I could that was loose, especially in the areas where a foam block was loose.  after sweeping out the inside of the hull, I was ready to start replacing the expanding foam to reset the foam blocks.

again, I mostly followed John Howard’s “Block Reset” method, but I will outline most of it here for you as well.  I put down an old plastic drop cloth to catch any drips.  I then used 2″ blue painters masking tape and some painter’s paper (newspaper would work) to protect the areas of the boat around the inspection ports.

I purchased the 2-part expanding foam from US Composites (much cheaper than a few other places I had looked).  it is generally suggested to use the 4-lb density kit – I bought the smallest kit (FOAM-0404). (also – US Composites is pretty competitively priced for West System epoxy as well).  I bought 2 measuring cups (99 cents each at Harbor Freight), and then just used plastic cups to mix the expanding foam.  I wore a pair of the blue vinyl disposable gloves to keep the stuff off my hands.  I also grabbed some scraps from my woodshop to use as mixing sticks.

mixing the foam was pretty straight-forward.  the foam is a 2-part system, requiring equal parts of “part A” and “part B”. I used the measuring cups to get equal amounts, and then mixed it together in the blue plastic cups.  prior to starting, though, I used a utility knife to cut the lip off the plastic cup – it shortened the cup just enough to fit easier in the inspection port holes, but just as importantly, allowed me to squeeze the cup, making it easier to direct the pouring of the expanding foam.

John Howard described the 2 parts nicely: “Part A is dark amber like maple syrup; Part B is clear and thicker like corn syrup.” after the 2 parts are combined, I would stir/mix them together for maybe 30 seconds or so, and you can feel it starting to thicken.  I would then reach into the holes in the Sunfish, stretch my arm as much as possible to get deep into the hull, and pour the expanding foam out right where the foam block meets up with the fiberglass hull.  if you are doing a complete re-do, I would probably try to use the cup-on-a-stick method that Dan shows at Windline.  but since my foam blocks were mostly just loose near the daggerboard trunk, I think I could reach by hand enough to do an adequate job.

I then basically just made several very small batches – maybe 2 oz of each part.  I found it was easier to control the pouring of the foam when I made the small batches, especially since I was pouring “blind” inside the boat.  it also gave me time to let the previous batch set up some, so I could easily tell where I left off, and what spots needed to be hit with a little bit more expanding foam.  I finished the forward and aft blocks from one side, and then flipped the boat over to the other side and did the same there.  I used the expanding foam at the top and bottom of each of the foam blocks as well – so at the end of the day, pretty much every foam block joint with the fiberglass had been reinforced with a new chunk of the expanding foam.

I ended up having a small amount of the 2-part foam left over, so I think that the small kit would probably be adequate for most repairs.  one thing I did notice, though, was that if you poured the foam too early, it was still too runny(?), and if the gap between the hull and the foam flotation block was large, the 2-part foam would slide right through the gap, and then pool down in the bottom of the boat!  I solved this by doing 2 things: I stuffed a scrap piece of the old bedding foam down in the bottom of the gap, and waited just a little longer on the next pour, so that the 2-part foam was a little bit thicker.

in the picture above, you can see the new expanding foam (the lighter yellow color).  at the top of the foam block, you can see I left a portion of the old foam there – but added expanding foam behind it to re-seat everything. you can also see I could only reach so far forward by hand.

the 2-part expanding foam sets up pretty hard in maybe 30 minutes or so.  I can now reach in and push on the flotation blocks, and they don’t budge at all.  I will admit – the very 1st batch of the 2-part foam was (how shall I say this…) interesting.  but after I figured out the timing and how it all worked, it was a very easy (but messy) task, and I think my Sunfish is now much improved, with solid bedding at each of the foam flotation blocks.

final thoughts: having sailed the boat a few times after this repair, I do think I should have been maybe a bit more diligent in removing the old bedding foam, especially at the bottom of the boat.  I noticed that the old bedding foam that is still in there does soak up any water that gets in pretty quick – whereas the new bedding foam seemed to stay dry.

of course, I could just get around to fixing the leaks in the boat and that would solve that problem, too.

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9 Responses to “foam block reset”


  1. 1 Port Clinton Docks August 29, 2010 at 10:11 am

    So, you’re recommending us to use that too? 🙂
    Actually, someone already suggested me to use that for my boat but I didn’t take his suggestion. But now, I think i’ll use it.
    If I’m going to have an another damaged boat.

  2. 2 Alexander Thompson June 20, 2014 at 9:21 pm

    I just got myself what is being described as a pre-72 model, and though it is dry as a bone and the hull is very much intact, there’s a foam block shifting forward. Probably port side or center, I can’t tell. I want to go sailing, and not spend summer repairing it. What are the chances anything terrible may happen in one season. As a friend said of the potential repair: ‘that’s what October is for.” Thanks

    • 3 my2fish June 20, 2014 at 9:30 pm

      Alexander, at this point, I’d probably just go sailing! If the boat is that old, chances are it has already been sailed quite a bit with the loose block. I don’t think one more season is going to make it any worse.

  3. 4 Alexander June 23, 2014 at 10:33 am

    Thanks! We’re putting in tomorrow then. I an inclined to make it right when I get the time this fall using your inspection port process. It gets WINDY here, so am looking at a 53sq. Ft. Sail I see on line that I might hank onto a spare boom set I have for blowy days. Thanks for the advice!

  4. 6 Jonathan Smith April 20, 2016 at 8:19 am

    Getting ready to refurb 1976 Sunfish #49939. This post is my #Motivation. Pics to follow.


  1. 1 sailing log: 2010-06-26 « my2fish: a blog about sunfish sailing Trackback on September 8, 2010 at 10:02 pm
  2. 2 sailing supplies | my2fish: a blog about sunfish sailing Trackback on May 17, 2014 at 8:03 am

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