Catamaran Sailing
Catamaran Pictures

Vol 3 - Issue 1 October 1998

Hobie 16 Frame Epoxy Project
Increasing the Performance of Your Boat

By Gary Willcox

    This article will explain the step-by-step method of epoxying the frame of a Hobie 16 together to achieve a stiff, well sailing boat.  The techniques will be very similar and can be applied to a Hobie 14.  This article does not pertain to other Hobies since they do not have the elevated 3 corner casting design.


    Why would you ever want to "permanently" glue your H14/16 frame together?  It sounds a little absurd and extreme at first.  It is said that besides the helmsman (which is the major part), the four things that help make an H16 fast are:  minimum boat weight (320 lbs.); minimum skipper and crew weight (as close to 285 as possible); decent sails/sail shape; and a stiff boat.

    A stiff boat helps the boat go fast by not absorbing energy as the waves cause the hulls to act as independent suspension arms.  It also keeps the hulls forming a consistent plane to each other as they slice through the water.

    There are several ways to achieve a stiff boat.  One is to buy a new one.  Hobie 16's built in the last couple of years have a new corner casting and pylon design that achieves a much tighter fit.  These new models are very stiff without having to epoxy the frame together.

    If this $7,000 (US) solution is not satisfactory, another method is to use shims.  These fill the voids in the castings and mating parts.  Some good materials are cut up plastic milk jugs, thin flexible kitchen cutting "boards," mast chips, etc.  You will probably still need to do quite a bit of disassembly and re-reviting just as the epoxy method.  The advantage is that a shimmed boat is easier to take apart, although I believe it would be less stiff than a boat that has been epoxied together.

    The easiest and still somewhat effective method is just to tighten the trampoline.  You can tighten the tramp lacing until the crossbars bend in about 1 to 1-1/2 inches.  Don't forget to tighten the rear laces too.  The main trampoline should be about 2.5 to 3 inches from the rear tramp strip. 

    If you worry about not getting your boat apart after epoxying, the folks at Gougeon Brothers (West System Epoxy) tell me that heating up the casting to 140 degrees F. with a torch will melt the epoxy.  Gougeon Brothers were very helpful during my telephone calls before this project.  Not only do they know epoxy and boats, but they are very familiar with Hobies.  The gentleman that I spoke with has owned a H16 and knew exactly what I was up against.

    Some people swear by turning the boat upside down and pouring epoxy in the casting to pylon joint.   While it may appear easier not having to take the boat apart, take out rivets, etc., it does have some drawbacks.  First, the epoxy without the filler is very brittle.  I have heard reports of the epoxy cracking and falling out.  Second, the pylon to corner casting is already the tighter joint.  The cross and sidebar to corner casting joints seem to always have the most play in them. 

       I performed this project on a 1982 Hobie 16.  While it may be questionable whether this 1982 boat will ever be super competitive, I did the epoxy frame job on it for several reasons.  This boat was very worn.  The joint of the rear corner casting to sidebar joint was so worn that I could rotate the sidebar in the casting a good quarter inch in either direction.

    My daughter commented after one long distance race on Lake Erie that "at least the boat didn't fall apart."  I asked her what she was talking about.  She informed me that when she was on the trapeze in about 2 foot swells, she could see the hulls moving up and down independently.

    Other racers in Division 10 swore by epoxying their Hobie 16's.   I figured that this would be a good boat to try the procedure.  I also thought that the boat would be safer and stronger.  Last, I needed a new trampoline and thought this would be a good time to do the job.

    I encourage you to read the West System literature either in paper or on-line form.  The link is listed below.  It will help you understand the characteristics of epoxy if you have never worked with it before.  Let's get started!

Supplies needed

  • West System 105 Epoxy Resin
  • West System 205 or 206 Epoxy Hardener
  • West System High Density 404 Filler
  • West System measuring pumps
  • West System Aluminum Etch Kit (optional)
  • 24 Stainless steel rivets - size 6-8 (3/16" diameter x 1/2" grip length -- unpulled rivet length is about 0.7")
  • Acetone
  • 2 Small paint or tooth brushes
  • 2 Mixing pots
  • 2 Mixing sticks

Tools Needed

  • Rivet puller
  • 1/8" punch
  • Electric Drill (preferably variable speed)
  • 3/8" Drill bit
  • Eye protection
  • Gloves (the West System gloves are very good)
  • Standard toolbox wrenches/sockets
  • Measuring tape
  • Level
  • Rubber mallet
  • Straight 8 foot 2x4
  • Emory paper - coarse
  • Mainsheet and blocks
  • Tramp tightening device

Other Requirements

  • At least two people
  • Approximately level garage or surface
  • Decent weather, not overly humid, preferably between 70-80 degrees F

Time Requirements

  • Labor -- 4-6 hours
  • Epoxy curing -- 48 hours

Approximate Costs Involved

  • 1 quart 105 epoxy and .44 pint hardener - $34
  • 404 high density filler -- $8.50
  • Mini measuring pumps - $7.50
  • Gloves, mixing pots, mixing sticks -- $5
  • Rivets - $16
  • Optional aluminum etch kit -- $11

Relevant Web Sites (with dealer locators)


   Start by removing the shrouds and trapeze wires.  Remember to take note how the rigging is attached to the mast tang -- it's not intuitive 6 hours later.  Neatly coil all rigging.  Remove the mast from the boat and set aside.  Remove the rudders by disconnecting the rudder crossbar and removing the rudder pins.  Remove the jib sheet, traveler lines, righting lines, etc.

    Let's see how much play there is in your boat with the trampoline still tight.  With the boat still on the trailer, tie down one hull and leave the other untied.  Measure the distance to the floor on the tied down hull at the tip of the bow.  Lift the boat up by the untied bow and measure the distance to the floor at the point that it starts to lift the trailer.  You will be amazed at the several inches of flex between the two hulls.  Write down the difference and we will compare it to the post epoxy state.

    Another test to determine the amount of play is to have the boat off the trailer and grab one bow and rock it up and down.  Feel the amount of flex in the boat and how long it takes the other bow to follow the lead of the driven bow.

    Now that you are down to two hulls, a frame, and a laced tramp, remove the boat from the trailer if you haven't already.  Let's take the time to get some hull alignment measurements.  Measure the distance between the front two pylons, then between the two rear pylons.  Take the measurement on the aft side of the pylons and where the pylon connects to the hull.  The following measurements are the distance between the pylons (center to center).  Measure on the back side, close to the hulls.

    FORWARD pylon distance:  78 1/2"

    REAR pylon distance:  77 1/4"

    These are dimensions to a stock Hobie 16.  Even though the forward distance is greater than the rear doesn't mean that the hull centerline is toed out, just that the pylons are not on the same axis.  If your hulls are way off of the dimensions above, stop here and compare it to another boat that is close to these numbers.  Do some more measuring between the two boats and determine if crossbars are the same length, etc.   You don't want to "permanently" glue the boat back together with some weird geometry.  I found that my boat was within a quarter of an inch of each dimension.

Remove Trampoline

    The next step is to unlace the trampoline.  Slide out the trampoline from the front crossbar.  You can aid this process by spraying the trampoline track (both above and below the trampoline) with silicone.  Then remove the trampoline from the sidebars.

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    Note that the trampoline opening on the sidebar is located by the front casting.  This is done for safety reasons.  If it were swapped and mounted close to the rear casting, the opening would not be covered by the trampoline.   There would be the potential to insert a finger or two into the opening, and once side pressure is applied, pose the danger of seriously damaging a finger.  However, when the opening is by the front casting, the tramp has a tendency to pull out of the track.  When we replaced the sidebars prior to the epoxy, we chose to mount them in the rear.  We took the precaution of jamming the exposed flared opening with about a 4" length of 5/16" or 3/8" line.

How much slop?

    Now that the boat is without trampoline, let's examine it some more.   While one person moves one hull up and down, examine the amount of slop in the casting joints.  We found that on our 1982 H16 there was the most slop between the sidebar and the rear casting.  We also noted that the front crossbar to front casting joint was incredibly solid -- such that it did not move at all.  We made the call to not epoxy that joint.  It appeared that the dolphin striker had kept that joint from loosening over the years.  It also meant that we wouldn't have to disassemble the dolphin striker, and deal with the front set of 6 rivets on each of the two forward castings.  It was a big time and work saver, without compromising the stiffness of the boat.  We still epoxied the other two joints on the forward casting as well as the three joints in the rear.

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Removing Rivets

    The next step is to drill out all of the corner casting rivets.   Use about a 3/8" drill bit to knock off the old rivet heads.  If the rivet starts to spin, switch to a smaller diameter drill bit and secure the head of the rivet with a pair of needle nose pliers or vise grips. Do not

be tempted to use a 3/16" drill bit and drill out the center of the rivet -- you will enlarge the hole in the casting too much.  Once the rivet head is knocked off, use a 1/8" punch to drive the rivet into the casting.  Don't use a punch that will fit inside the rivet.   Otherwise you will just expand and jam the rivet.  A variable speed drill is very useful here so that you do not accidentally drill out casting material once you knock off the rivet head.

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Dolphin Striker

    If you are epoxying the front crossbar joint of the pylons, you will need to remove the dolphin striker nuts.  Take note the position of the nuts on the dolphin striker threads.  You will want to replace the nuts with about the same amount of torque.  Use an open end wrench instead of an adjustable wrench -- there is little room for an adjustable wrench.  Be careful not to strip the outside of the nut.  Take your time and be patient.  The thread is fine and will take quite a few turns to remove.  If you choose to replace this nut, double check the threads before you bring them home from the hardware store.  Most general hardware stores don't carry fine thread in this size of nylock nut in stainless.  You may have to get the correct nut at a Hobie dealer.

Remove Frame from Hulls

    With socket and wrench, remove the pylon nut from the pylon bolt in each of the corner castings.  You may have to use Liquid Wrench, WD40, or the like, to free the bond between the stainless steel nut and the aluminum casting.  Drive out the pylon bolt from the corner castings.  If the threads on the pylon bolts or nuts are stripped, badly corroded, or worn, you may want to replace them.

    Ease the castings off the hull pylons.  Keep them as even as you can so that the frame does not bind.  You may have to use a rubber mallet or dead blow hammer to get them started.  If they are really seized, you may have to heat the casting with a propane torch (don't get it too hot) so that it will expand more than the pylon.

    Once the frame is apart, disassemble all side and crossbars and set them aside.  Secure the mainsheet traveler to the rear crossbar by tying a line or a bungee cord around it and the traveler eye.  This will keep it in place and help you not forget it when you are rushing to re-assemble the boat.  Remember the open "L" side of the traveler car faces the rear of the boat.

Weigh the Hulls

    While the boat is apart, let's take advantage and weigh the hulls.   Place a bathroom scale on the floor and balance the center of the hull bottom on the scale.  New boats are about 65-70 lbs. each hull.  Mine weighed in at a hefty 82 and 85 lbs.

New Traveler?

    You may want to inspect the rollers or needle bearings on the mainsheet traveler.  If the traveler doesn't have the zing that it used to, you may want to replace the lower portion now for about $35 (or the entire car for $55).   Remember that to replace it later you will have to remove and replace several countersunk rivets on one side of the traveler track. 

Vent Tubes

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    Take note that the pylon vent tubes, shown at left, are in place and not clogged.  Make sure you can blow some air through them.  These will only be on the front pylons and allow the air in the hulls to expand without causing damage to the hulls.  It is also a good time to remove any old dried up silicon that is in the triangular shaped extrusion on the aft side of the pylon (shown to the right of the vent tube below).  You can replace the silicon later when the boat is together.

Surface Preparation

    We now need to clean every male and female part of the crossbars, sidebars, and castings.  Use a rough grade emery cloth and remove all oxidation, dirt, etc. from the three

joints in each casting as well as the end of every cross and sidebar.  Wash with soap and water, rinse, and allow to dry or use compressed air to dry.  Wipe down the male and female joints with lacquer thinner or acetone.   Wipe the surface dry with a cloth before the solvent has time to dry on its own.   Caution:  use thinners and acetone only outside in a well ventilated area.

glue17.jpg (28324 bytes)

    The technical support people at West System recommended cleaning the castings and bar ends with their aluminum etch kit.  Theory is that by super cleaning and creating scores in the aluminum will create a superior bond.  I liked the idea, special ordered the etch kit, then left it home 300 miles away from where I performed the project.  My resultant epoxy frame seemed strong without it, but I still liked the idea and pass it on as a suggestion.

Epoxy Decisions and Tips

    I can't recommend enough to read the West System User Manual before this project.  That 15 minutes could save you hours of disaster later.  You can skip over the fairing and other non-relevant topics.  While I have tried to relay much of the important items, there are still important tips and techniques to help your project be successful.  For convenience, here is the link again:

    Below is a chart to help you decide whether to use West System 205 or 206 hardener.   It depends on the outside temperature.  If the temp is above 60 degrees F (and will stay above 60 at night), I would choose the 206 hardener.  It will give you the most pot life and working life.  Don't think that you only have 9-12 minutes to get your boat back together with the 205 hardener.  That is the pot life.  You have that many minutes to spread it out.  Once it is thin and on the casting and bar surfaces, it will take a couple of hours to cure.

  205 Hardener 206 Hardener
Pot life at 72F (22C) 9 to 12 minutes 20 to 25 minutes
Cure to a solid state 6 to 8 hours 9 to 12 hours
Cure to maximum strength 1 to 4 days 1 to 4 days
Minimum recommended temperature 40F (4C) 60F (16C)

 glue05.jpg (11090 bytes)

    I did this project in Tennessee in August, so I chose the 206 hardener.  The smallest container sold is one quart of 105 resin and .44 pint of hardener.  You will have most of it left over.  For the cost of the rivets only, you could easily epoxy another 4 boats with just the quart of resin.  Go in on this with a friend or two and share the labor and supplies.

    I also chose to use the West System mini measuring pumps and the West System mixing pots.  Whether you choose the 205 or 206 hardener you still use the same 105 resin.  The measuring pumps shown below always deliver a 5:1 ratio for each pump.  Make sure that you prime the pump into a different throwaway container before measuring.  You could measure by weight or volume, but it is well worth the $7.50 to have these pumps.  Do not be tempted to alter the 5:1 ratio because of the temperature or humidity.  You will either have a mess with uncured epoxy, the epoxy setting too fast, or insufficient epoxy strength.

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    You want to make sure that you don't use a glass or a foam container to mix in.  The epoxy mixing generates heat and could easily melt the foam or get the glass to hot to hold.  Also the amount of surface area and mass of the epoxy determines the pot life (the time the epoxy is workable in the mixing pot).  The West System containers work well for this job.

Two Step Bonding Method

    So that all the surfaces get coated and adhere well, we will first wet out all of the surfaces with an epoxy mixture without filler.  Pump about 3 pumps of resin and hardener into your mixing pot.  Stir with a mixing stick for at least 1 minute.  If you stir less, you may not start the hardener chemical reaction.   Caution:  if the mixture starts to smoke (because of too much heat/stirring or too much mass in the container), set down container and do not breathe fumes. 

    Apply a moderate coat of this mixture to all male and female joints -- pylons, castings, side, and crossbars.  Discard the mixing container.  Note in the picture below that we have applied 2" masking tape to the hulls so that we don't have to worry about cleanup.  We are also sure to wear gloves and protective eyewear.

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    Go ahead and let this first wet out coat sit for 20-30 minutes.   Epoxy dries faster the thicker it is, so don't worry about this thin epoxy drying too fast.  Go ahead and put the trampoline on the side rails and the rear strip on the rear crossbar.  This will save time and hassle trying to thread it in the side rail slot later when the casting is in the way.  By now you have decided on whether to mount the side rails in their normal position or with the tramp slot opening in the rear.

    Mix up another batch of epoxy in a new container.  Use about 7 strokes of each pump.  Stir the mixture for at least 1 minute.  Add in 404 high density filler about a tablespoon at a time until the mixture is the consistency of mayonnaise (it won't be as smooth).  This filler is what gives the epoxy its strength.

    Liberally apply this thickened epoxy mixture to all male and female surfaces.  Apply more to the female casting joints than the pylons and bars.  A toothbrush works well to apply the thickened mixture to the casting joints.  Take care to avoid the area around the aft part of the front pylon and casting joint.   Leave about a 3/4" gap.  This will allow the vent tube to not be sealed off by the epoxy.


   Insert the front crossbar into the front castings and start the dolphin striker nuts.  Stand up each hull and insert the pylons into the front castings.  As you insert parts together, you should get a reasonable amount of thickened epoxy mixture to ooze from the joint.  If not, you may need more epoxy in the joint.  Wipe off any extra with a paper towel.

    Insert the sidebars into the front castings.  Insert the rear crossbar into the rear pylons.  Insert the the sidebars into the rear castings.   Slide the rear castings on the rear pylons.  You may have to lift the forward castings up on the forward pylons so that the rear pylons

don't bind.  Insert the forward edge of the trampoline into the front crossbar.

    Go around to all of the rivet holes in the castings and insert a rivet as a place holder.  Do not set them yet.  If the rivet hole on the casting and the crossbar do not line up, insert the 1/8" punch into both holes and line up the two pieces.  If the rivet head does not sit flush on the casting, place a small deep socket (one large enough for the nail, but smaller than the rivet head) over the rivet nail and tap the socket with a hammer.

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Lace the Trampoline

     Start by tying a bowline at the front of the trampoline on the port side.  Lace by threading up through all holes.  This will help a whittled keeper dowel to stay jammed into the grommet. Use a pair of pliers, a large open end wrench, a commercial tramp tightener, or a homemade tool shown below (a 2x4 with two lag bolts) to spaghetti wrap each

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section of the web.  Use a whittled dowel jammed into a grommet hole to hold the line.  Use the traveler cam cleat to "tail" the line.

    Moderately tighten the center lacing.  Do the same for the rear lacing.  Use a piece of line for each side of the rear lacing.  To start the rear lacing, put one end through the hole in the rear casting and tie a figure eight knot on the other side. 

    Go back and re-tighten the center section, then re-tighten the rear.   Tie off all three pieces of line at the center rear intersection with half hitches.   Even though the corners of the tramp frame will be epoxied solid, we still want the trampoline moderately tight.  This will reduce the whole frame from flexing.

    Tighten the dolphin striker nuts.  Adjust so that when hitting the dolphin striker with a metal object, it is tighter than a thud but less than a ping.   If you grab the dolphin striker rod and shake it, it should not move very much.   Do not over tighten, now is not the time to break the front corner castings.

Measurement Time

    Let's start by making the boat level.  Insert the rudder pins in the gudgeons.  Place a straight 2x4 across the tips of the bows.  Check with a level.  Shim the bottom of the hulls with wood or cardboard to make level.  Double check the sterns the same way.

    Place the 2x4 on the floor, under the bow tips, stretching from one bow to the other.  Using the level, shim until level.  Check the following measurements and adjust to make boat even and symmetrical:

  • Vertical distance from level 2x4 on floor to level bow tip -- compare to other bow.
  • Bow tang bolt to opposite rudder pin center -- compare to other cross direction.
  • Vertical distance from level 2x4 on floor to level stern lip -- compare to other stern.

    If the cross measurements are off, use the mainsheet to adjust.   Attach upper block to bridle wire thimble.  Tie a large bowline on a separate line and loop around stern hull/deck

lip.  Attach this line to a shackle on the lower mainsheet block.  Take it easy adjusting this line.  Each click on the mainsheet block will make about a 1/4" inch adjustment in the cross measurement.

    An alternative way to ensure that the boat is square and level for the frame epoxy job, some have built a

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fixture for the Hobie 16.  Before taking the boat apart, create a crude cradle frame out of wood to hold each hull in position.  Fasten the two cradles together.  Make sure the boat has the desired dimensions, then disassemble it.  This would be helpful if your floor surface was not very level.

Set the new Rivets

    Use a rivet puller to set all of the new rivets.  If the face of the rivet is not flush with the casting, use the deep socket as described earlier.   With a hand riveter such as the Marson HP-2 shown in the illustration, you will need 3, maybe 4 strokes to pull the rivet.  You will also need two hands.  To avoid the rivet nail from dropping into the casting on the upswing of each stroke, place a slight amount of sideways pressure on the rivet puller.  This will bind the nail in the hole so that it does not fall through during the upstroke when no jaw force is applied to the rivet nail. 

    Pulling 24 rivets with a hand riveter will tire you.  Take turns with your assistants.  If you have access to a larger riveter, such as the Marson Big Daddy, use it.  The HP-2 is capable, but your hands will get tired before it does.  Do not attempt this with a garden variety rivet puller from the hardware store, even if it looks like the HP-2.  The jaws are probably not capable to pull 3/16" stainless steel rivets.

    Note that Hobie uses Monel rivets in the factory.  These will have a less corrosive reaction to the aluminum castings, and are more difficult to obtain.   I am told that the stainless steel variety are stronger than the original Monel.   The choice is yours.

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Recheck all Measurements

   After setting the rivets, recheck all measurements.  As you adjust one measurement, it will have a tendency to throw others out of adjustment.  Also, check the front and rear pylon distances that you measured before taking the boat apart.  They should be close to your original measurements.

Epoxy Cure

    Once the measurements are all even, leave the boat shimmed and mainsheet attached.  Wipe off any excess epoxy from the joints and pylons.   After about an hour, the epoxy may want to ooze out the bottom of the castings.   Use a putty knife to pack the semi-cured epoxy back in the joint. Remove the masking tape from the hulls.  Let the epoxy cure overnight.  Reassemble the boat.  If the temperature is cool, you may want to wait another day or two before moving and taking the boat out for a sail.

Check for Flex

   Now that the frame has cured, perform the same pre-epoxy flex tests.  Grab one hull and move it up and down and watch and feel the other hull follow.  You can also secure one hull to the trailer and lift the other hull and compare it to before the epoxy.  You will be amazed at the difference.

Post Epoxy Sail

    Since this project, I had the chance to race this boat locally.   All I can say is, "what a difference!"  As the boat tackled motor boat chop, it just cut right through it instead of slowing down and absorbing the shock.   It felt like a totally different boat.  Flying a hull was precise and controlled.  I had only wished that I had done this on my previous Hobie 16's.   A must recommend project for anyone wanting to get more out of their H16.  An absolute must for the occasional or serious racer.  Now is the time to perform this job.  You don't want to wait until the nights are too cold for the epoxy to set properly.

Acknowledgements:  Special thanks to my Father-in-law, W.R. McCarter, for the labor and second opinion help on this project; Jamie Diamond for H16 frame epoxy tips and encouragement; Matt Miller of Hobie Cat USA for the pylon dimensions; Strictly Sail of Cinn, OH for carrying the Hobie line of boats and parts and West System Epoxy; and my wife, Mary, for supporting me in my boat tinkering projects.

Disclaimer (sad, but have to say this):  Attempt this project at your own risk.  Every boat is different and poses different problems when attempting a project such as this.  The author or OTW in no way assumes responsibility, express or implied, in the outcome of this project.  Always wear eye protection when working with drills, punches, epoxy, riveters, etc.  Perform in well ventilated area.   Do not breathe dust from 404 filler.  Follow all precautions, warnings, and directions on all tools, supplies, epoxy, and hardeners.

Gary Willcox

Hannah Banana

Cincinnati, Ohio

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