I started some work yesterday on a friend’s boat that suffered an altercation with a tow boat during the Tradewinds regatta several weeks ago. It had some pretty bad damage to the bow of the port hull where it was split, crushed, and bent off to the side. In case you’re wondering, you’re not looking at two different boats, this boat has a color scheme where it is white on one side and yellow on the other – it’s a pretty wild optical illusion on the water.Â Appropriately enough, the boat’s name is “Undecided”.
It took me a little while to figure out how to approach this repair as there was undoubtedly pretty extensive damage to the foam core inside each hull half. This damaged structure had to be removed. The tricky part was to figure out how to replicate the bow shape because these hulls are asymmetrical (i.e. I can’t necessarily copy one bow to the other). I tossed around ideas about pulling a mold off the Team Seacats blue I20 port hull but dismissed that as far too time consuming. I decided, instead to cut away the most damaged side (the yellow) and clean up the inside of the other and then figure out how to brace it to hold it’s shape so it can be glassed/reinforced. Once that would be done, then I can clean up the cut away portion and work to get it bonded back in place…that’s the plan anyway.
With my trusty diamond encrusted cutter in my Dremel, I went to town on the bow cutting away a panel of the yellow side of the hull so I could gain access to the damage on the inside half.
I then ground away all the broken fiberglass and delaminated foam and was pretty much left with just the thin outer skin which was still trained to bend in the damaged direction. The remaining foam was tapered gently to avoid a stress point with the repair area.
I then took several measurements and came up with a bracing plan to re-train the skin into the proper shape, placed clear packaging tape on the back of the couple of cracks (to keep the epoxy from running through). With the shape verified to be true, I started laminating about 6 layers of 7oz glass with epoxy around the clamps.
Because it was beginning to drizzle and the temperature was about 50 degrees (you need about 60 degrees for the epoxy to cure properly), I roughed out a cheap plastic tent over the repair area and plugged in a small space heater. I was able to monitor the temperature with a remote digital thermometer / humidity gauge that I keep in my shop and was able to keep the repair at a toasty 75 degrees. One day, I’ll have a garage for doing this stuff in.
A quick spot check this morning before leaving for work this morning was good – the inside bow now holds a very straight and true shape and I only have a few minor areas to touch up and fair on the exterior. A little more glassing where the clamps were and I’ll be ready to move onto the yellow cut-away section for repair. The weather is going to get a little colder this week but fortunately I can do the repair on the cut-away section inside my workshop.
No, this isn’t some sexual inuendo…I’ve recently received several requests for information about performing a bottom (or keel) job on a beach cat. Because our boats are so mobile, occasionally they find themselves sliding up a sandy, shelly, or even rocky beach. If you are really careful, the bottoms of your boat hulls will stay nice and clean but invariably something will happen resulting in some speed robbing scratches and dings. I’ve done a few refinishing jobs on the bottom of catamarans and learned a few things along the way. First, there are some simple, but key, tools you will need:
- Sanding Board – you can purchase one of these from various locations. 3M makes a good one but it’s pricey at about $45-$60. The key to the sanding board is that it be semi flexible on the long axis. A good sanding board will also have handles to make things a little more ergonomic. I scratch built mine using some scraps of plastic and aluminum and the long and tall handles I built allow me to really control the shape of the board when necessary (picture below)
- Filler – There is a “Marine” version of Bondo filler and while it is a nice and easy product to work with, I’ve recently found a “premium” Bondo Brand automotive filler that is wonderful to work with and still much cheaper (anytime they slap “marine” on the name of something, the price goes up 150%). Traditional Bondo leaves a sticky top surface that will generally clog up the first piece or two of sandpaper to touch it. The premium version, while a bit more expensive, doesn’t have this tacky layer and is much easier to work with in this respect. Note that the Bondo brand fillers use a polyester resin base so they are well suited to working with gelcoat (you want to avoid using epoxy whenever possible because of possible bond issues with gelcoat application).
- Sandpaper – if you are keen to save a buck or two, you need to get this out of your head when it comes to sandpaper. The time you spend sanding is directly relative to how long you push a piece of paper to it’s death. Keep fresh sandpaper working and you’ll save yourself a lot of time. I have found that Lowe’s carries rolls of sticky-back sandpaper that are about $12 per roll and it is not only very efficient but works great for any size sanding block or board. Our Lowe’s here carries rolls in three grits – 80, 120, and 240 (I think – I’ll double check and update this post). You will definitely need the 120 and 240 – the 80 can come in handy sometimes in the early stages. You’ll also need wetsandpaper 400 and 600 grit. A trailer supply house (Northern Tool) or paint supply house carries wet sandpaper for sale by the sheet and is generally cheaper than a home center box store. If you have a colored boat (not white) you may want to finish off with some 800 or 1000 grit paper as this will help your boat retain the shine for longer periods of time.
- Side/angle Grinder – not completely necessary but it helps to make short work out of deep soft spots for repair. It can be like doing surgery with a chainsaw but is very effective for damage tear-out if you are careful with it. I use a layered sanding disk (with flaps of sandpaper).
- Electric (or pneumatic) palm sander – good for initial shaping of a repair but not much else.
- Pneumatic Paint Spray Gun – there is no need to go crazy here as a generic “home use” spray gun intended for latex paints will work just fine with gel coat. Although it will work, I don’t recommend the buzz bomb self-contained sprayer as it is very difficult to clean. A $40 suction gun designed for latex paints will do just fine (bigger nozzle the better – I’ll put down a nozzle size reference this evening when I get a chance to reference what I have). Gelcoat is thick and will not lay down flat worth a darn anyway so there’s no need to go spend big bucks on an automotive HLVP sprayer that’s just going to spit and spat it out irregularly anyway. Besides, spraying something that catalyzes into a solid can potentially bring death to a paint gun.
- Sanding Sponge – this is to work with your wet sandpaper and can be found at a home center box store.
- Old Washer hose – cut one end off so you just have an extended soft rubber hose for wetsanding you can attach to a garden hose. You’ll find that if you use a hose with a metal fitting you will frequently ding/scratch the finish you are working on.
- Saw Horses – you need to get the hulls up to an operable height. I have some saw horses constructed from 2×4’s and a simple brace kit – works very well to support the hulls removed from the beams. I did screw end stops on the saw horses to prevent the hulls from slipping off the edge while sanding (the straps shown below constantly got in the way). Not shown below, I also added some diagonal bracing to the horses because the sanding motion was causing them to become increasingly wobbly.
- Rubber Boots – if you’re going to be doing the wet sanding in cool weather, a crappy pair of $12 Wal-Mart rubber galoshes are indispensable.
- 5oz fiberglass – standard weave will work fine…no big need for anything exotic unless you are working on an exotic boat using kevlar or carbon in the hull construction. If you feel the need to do one better, get s-glass as it is a stronger variety of fiberglass than the more standard E-glass. Walmart variety “Bondo” brand fiberglass packs (roughly a 5oz fiberglass) will do but you pay a LOT for those vs. an online supplier.
- Polyester (or vinylester) resin – get a decent resin…check working time, you don’t really want something with an extended working time (like a laminating resin). You don’t need to work with it very long on smaller repairs and a faster cure is nice. Vinylester is the stronger of the ester resins but usually has a reduced shelf life of a month or so – it will turn to gel and slooooowly harden after that. The MEKP liquid that is commonly called an ester resin “hardener” is actually an accelerator. Ester resins will harden on their own if given enough time – polyester resins very slowly and vinylester resins harden pretty fast on their own. Use ester resins if you intend to finish with gelcoat. Use epoxy if you are going to paint. Epoxy bonds better to everything but is not the best substrate for gel coat.
- Fiberglass detail roller – this is a small roller with a ridged small diameter aluminum rod on it. It’s is VERY useful for squeezing air out of a hand laid composite structure before cure. You can find these at US Composites.
- Mixing cups and stir sticks. Graduated mixing cups save a lot of time and a mixing ratio chart is a big time saver (one available at www.fiberglasssupply.com – though I had to make some modifications for smaller amounts). You may also want to invest the $11 in a set of West System metering pumps. While they won’t be ‘metering’ anything for the polyester resin, they make dispensing of the resin very clean – a nice bonus. You can find these at aircraft spruce.
- Baby medicine dropper – you can usually peddle one of these from a local pharmacy for free – grocery stores usually have them near the pharmacy as well. Get the bulb / suction type, not the plunger / syringe type. The plunger will not stand up to the MEKP. You will use this for measuring larger amounts of MEKP for the gel coat batches to avoid counting drops…unless you actually enjoy counting to 132.
- Respirator rated for “organics”. The styrene contained in ester based resins and gel coat melts soft human tissue (like lungs and sinuses) and is very bad for you. Wear a respirator. You can get them with refillable cartridges at Lowe’s or Home Depot for $35 – which is a lot cheaper than chemotherapy. Also pick up a pack of latex or nitril gloves – you’re going to need them.
- Solvents, rags, and paper towels – Generally acetone will do most everything you need it to for cleaning out spray guns, tools, and prepping surfaces. If you have moisture that you need to remove (like in a foam core), use denatured alcohol as it will encapsulate the water molecules and evaporate it away rather quickly. For spraying the gel coat, I’m cautiously recommending the use of Duratec High-Gloss Additive. I haven’t used this product but after the difficulties that I have had and some post-trouble advice from people in the industry, I believe this will make things much easier. It’s available at the Fiberglasssupply.com
- Gel coat – for a bottom job on a 20 foot catamaran, you will use anywhere from 1/2 to 1 Gallon depending on the quality of the gel coat. I sprayed two Nacra 20’s (four hulls) in one day – one blue and one white. The blue one took a little less than 1/2 gallon and the white one took nearly the entire gallon to get the coverage needed. Quality of the gel coat could have been a factor as they came from two different suppliers. Most gel coat suppliers can only mix in quarts or gallons – so get the gallon and you’ll have plenty left over. I was fortunate enough to have the name of the original supplier of the gel coat used on the blue boat AND the color code – it made ordering very easy. The company that I ordered this from is Sher-Fab Unlimited, Inc in California and theirs was the gel coat that had excellent coverage.
- Buffer and a buffing agent. Use a real high-speed rotary buffer with a lambs wool (or synthetic lambs wool) pad. The low-cost random orbiting buffers you can find for $30 at Wal-Mart are NOT what you need. You need raw power to cut the gel coat to a shine. I recommend 3M brand “Perfect-it 3000 Rubbing Compound” to use with your buffer and wool pad.
If you wish to go back through the documented history with the Team Seacats Nacra 20, start Here: http://www.teamseacats.com/category/boat-construction/page/8/ . There are more pictures and reference material that might be useful.
On to the process:
I like to disassemble the hulls, trampoline, and beams so that I’m working only with the hulls. You will be spraying gelcoat so it’s just as easy to remove everything now, avoid the mess, and allow yourself better access. I mount the hulls upside down on saw horses and screw wood blocks (padded) in place to prevent the hulls from moving around while sanding. When working on the bows, I strap the sterns in place to keep from tipping the overhung bow.
Before sanding, you want to remove any waxes / silicones that might be on the hull. Wipe the hulls down vigorously with acetone well past the areas that you intend to gel coat. If you don’t, the sanding action will rub these agents deeper into the surface.
Start sanding with 120 grit and the sanding board. The trick to using a sanding board is to ALWAYS keep the board parallel with the long axis of the hull. You can sand up-down, side to side, angle to angle, round and round, but ALWAYS keep the board parallel to the length of the hull. The sanding board will gently bend and you should understand this and use this to keep it bending to the lengthwise shape of the hull. The job of the sanding board is to bridge the gaps between recesses and dings and if used properly, although learning to use a sanding board is a bit of an artform, makes fairing a hull a relatively straight forward process and making a really nice final result achievable for the novice (like me).
Once cured, use the palm sander and some 120 grit to shape the repair close to the final shape. You don’t want to take this too far – you will use the long board later to get the final shape. Any minor indentations or pin holes can be filled with Bondo filler but if you have a significant recess in the repair, you need to rough up with 80 grit and laminate some more fiberglass.
OK, so now we have fixed any soft spots and the rest can be filled using filler. The next step is to sand all those imperfections that the long board skirted over with 80 grit (make a small roll of sandpaper and sand by hand) so you have a good rough surface for the filler to adhere to. Once sanded, these spots will be difficult to see – this is why you marked around them with a pencil right after scuffing the hull with the long board. It’s time to mix up some filler. Mix up a fair amount and make sure you get enough hardner in the mixture. It’s not something that requires great precision, but if you’ve not worked with Bondo before, you may want to make a test batch to ensure you can get the ratio close. Too much hardner and it cures in minutes. Too little hardner and you end up with a difficult to remove gummy mess. You’ll need a squeegee to apply it – plastic hotel room keys work great (and are cheap! – start collecting) and of course the “Bondo” brand squeegees available at most stores work just fine too although they can be difficult to clean to be reused. When reusing a squeegee you can’t have any trace of hardened filler or it will leave a pattern or trash in the filler you are applying. Applying the correct amount can be tricky but after some time, you’ll get the hang of it. Don’t be afraid to come back for a second pass with the filler – but just be sure to scuff up all the surface for good adhesion. Ideally, no dings should be deep enough to require much filler. Max depth should be about 3/32″. Anything deeper should be initially filled with fiberglass and resin.
Once you feel like you’ve made a pretty good go at it, spend some time to really inspect things before going any further. Note that it is difficult to inspect for low spots now because of the different colors of the hull. If you wish, you can spray a light coat of some cheap automotive primer (be sure it is DRY sandable primer!!!! – not just “wet sandable”…that stuff sucks) over the entire surface and sand it away – places where the primer is left are low and will need a little more work. Personally, I don’t find this necessary and find it perfectly adequate to close my eyes and rub my hands down the hull while muttering “nuh nuh nuh nuh nuh nuh….nuh nuh nuh nuh nuh”.
Now it’s time to clean the dust away. Wash the hulls with water and then rub them down with several clean acetone cloths – nothing tricky here.
I’m working to help a friend revive a 1981 Hobie 16 catamaran and will chronicle some of the success and failures on this boat here over the next couple of weeks. We rigged the boat and made a long list of things that need to be addressed; new lines, trampoline, most of the line hardware, a little fiberglass work, and a rebuild of the trailer lights and bearings. Structurally, the boat is in good shape. After $600, we have a big box of parts and have put on the new trampoline that was made by Mainsail Marine (one of Team Seacats sponsors!). The black mesh trampoline is terrific! Other than pressure wash the boat, installing the trampoline is about all we’ve accomplished to date. Unfortunately, I didn’t take any pictures of the boat before we pressure washed it – it had been sitting under pine trees for at least 10 years.
I just realized that I haven’t sailed my F18 at all this year with all the prep-work of the I20 and sailing on OPB (other people’s boats). I decided to utilize the long weekend to re-fair the bottom of the hulls since she’s had a pretty rough go with the 2005 Steeplechase and all the recent neglection. After a lot of sanding, I’ve got a reasonably good finish…I didn’t quite go far enough with the 320 grit and still have some minor sanding scratches visible but I may go back and fix that later. Fortunately, there was plenty of gelcoat thickness that I didn’t have to shoot any gelcoat. I did leave the filler exposed (but polished) on a few major dings I fixed.
It’s time to really start thinking about some of the big races we have coming up. Last week, I took the cover off and spent an evening inspecting the blue Team Seacats Nacra 20. Everything looks good except that I found one of the shroud tangs (a stainless steel plate that holds up the mast!) was loose in the hull. I could wiggle it back and forth and side to side and lift it up and down almost 3/16″. Not good. I put in a call to Performance Catamarans and after a conversation with Jack, I had a better understanding of how this plate is configured. The plate is t-shaped and has some holes through which some heavy fiberglass tow is run and resined to the hull. Then a cover of some heavy knit fiberglass goes overtop of this to make it watertight. Because the plate is t-shaped, it really shouldn’t be much of a failure concern. However, the fact that it wiggles around means that it can continue to wear to the point that it may be a concern. For repair, my hope was that it was watertight and that I would be able to drill a couple of small holes in the side of the hull through which to apply vacuum and draw in epoxy resin…but I wasn’t quite so lucky.
The recess in the edge of the hull from which the plate protrudes forms a great spot to seal off for vacuum….but I had a problem…the plate was not sealed inside the hull. I took my camera and extended my arm up to my shoulder to get some pictures to see what was happening (thank goodness we added the forward ports last year!). I also trickled some water from the top to see if I could figure out where the leak was.
In the left-most picture you can see a trickle of water coming out from under the bunji tube (this is where the trapeze retention bunji goes through the hull). The leak is not the buji tube but is coming through the tang (this would explain why this hull was taking on a little water while under sail). Above this area, you can see a glassed in plate where one of the spinnaker blocks screws to the deck and the vertical structure to the right in the left picture is the front of the daggerboard trunk. After running some denatured alcohol through the tang to dry up the water, I mixed up some thickened epoxy and smeared it over this leak with a gloved hand.
I did eventually find the other opening in the fiberglass backing – it is definitely sealed now (it was at the top where it mates with the mounting plate for the spinnaker sheet block) and the tang is VERY firm in the hull. I’ll be sailing this boat at Spring Fever next weekend so hopefully we’ll give it a good test.