i550 construction guide

I 5 5 0 S P O R T B O A T

CONSTRUCTION GUIDE

WRITTEN BY:

Christopher Beckwith, N.A.

i 5 5 0 S p o r t b o a t C o n s t r u c t i o n Gu i d e

1

Table of Contents

Table of Contents

Preface

How it all began.........................................................................................................................................................................4

iBoat..........................................................................................................................................................................................4

Tokyo Trash Baby......................................................................................................................................................................5

Designing the i550

Requirements for Micro Class....................................................................................................................................................6

Wire frame model of the i550 hull.............................................................................................................................................7

Sharpie Hulls ............................................................................................................................................................................7

E-mails from Down Under.........................................................................................................................................................9

Construction

Versions and Options................................................................................................................................................................11

Lofting.....................................................................................................................................................................................13

Cutting.....................................................................................................................................................................................14

Stitching...................................................................................................................................................................................16

Stern, Stem and Symmetry ......................................................................................................................................................17

Fillets and Taping hull..............................................................................................................................................................18

Fillets and Taping frames.........................................................................................................................................................20

Stringers and Bunk Supports....................................................................................................................................................21

Interior Fixtures.......................................................................................................................................................................22

Decking and Cabin Trunk........................................................................................................................................................24

Finishing the Hull....................................................................................................................................................................26

Finishing the Deck...................................................................................................................................................................27

Outfitting

Versions and Options...............................................................................................................................................................28

Keel and Rudder


Rig



2


3

Preface

How it all began

The i550 was born of the Micro Ton Class in Europe. I was looking for a “little” big boat. Ideal-ly, something as fun as a J/24 but without the need for five crew, an army of people to launch and rig, but still have a little bit of space down below to store some gear, pass out on at a regatta par-ty, and possibly slap together on a limited budget. The Micro Class seemed to satisfy that need, however, it was not an established class in North America. Thus I began a broader mission, to not only design and build a boat for myself, but try to build a class in North America to compete against.

Micro Class Boats racing at 2008 Toyota World Championships

iBoat

I had created back in 1999 a company called iBoat. Boats designed under this name included a Mount Gay 30, Mount Gay 25, Open 6.50 (Mini Transat), and a ballasted skiff. iBoat welcomed a new boat that year with a Micro Ton Class boat. We had some other offshoot projects, includ-ing some 1/12 scale America’s Cup model racing yachts, some International One Meter yachts, and other low budget projects. iBoat was not a full time job, nor was it a job at all really. On a good month, it might pay some regatta expenses, but never paid the bills. As I immersed myself in my current boat of choice of the time, the Thistle Class, I sort of let iBoat fade away. Slowly but surely, the website expired, plans were lost as computers were upgraded, general interest just diminished.


4

Tokyo Trash Baby

One night, I received an e-mail regarding the i550. Seemed there was some interest in Australia with souping the boat up, bigger rig, more ballast in the keel, etc. Trick the boat out as a sport-boat. A little redrawing here and there, and we had a semi-finished product. Albeit though, if you ask that Australian, Andrew Clauson, about the plans, they were a bit crude compared to what comes in the plans pack today. Through countless e-mails with Andrew, and based on informa-tion from another boat that was built to the original plans, the design was tweaked, and Tokyo Trash Baby was born. The first i550 of the “turbo” variety.

Original line drawing of the i550 “Micro Ton Class” design


5

Designing the i550

Requirements for Micro Class

The requirements for the Micro Class were fairly straightforward. Simply put, it’s a box rule, with interior accommodation requirements, and safety requirements. This is where the mind starts clicking away... what would be faster, a “bare minimums” boat, or a “maximums boat”? I explored both options extensively. Keeping in mind that I wanted to build in plywood, for cost, and speed of construction, different thoughts on actual design concepts were creeping through my head as well. I need an aspirin just thinking about it, let alone going back and forth with con-cepts and balsa models at the time.

I thought a narrow hull, would prove to be fastest, however, I wanted to exploit the beam rule at the same time. This took me down an interesting path of, in one rendition, six chines. Needless to say, I just wasn’t getting what I was after. A few versions had the chine at the waterline, and the hull below shaped, and some were shaped as with the current i550 design. Nothing was working, and the project got scrapped for awhile. After all, there were no boats to compete with in the US yet, and no one interested in what I was babbling about at the yacht club.

I revisited the project some months later, with a refreshed perspective. It hit me to start over, but start from a different angle. Start from inside the boat. I took the minimum interior accommoda-tions, and then worked backwards. I ended up with an interior “pod” that I could insert into any hull, and see what worked best. There was a specific look I was after, and I really wanted it to be “Mini-Transat” styled. So many of the Micro Ton boats had strange looking cabin trunks that had odd square shapes to them just to conform to the rule. I was after something that looked good as well as serving it’s purpose.

The accommodations “pod” as dictated by the Micro Class rules

I finally thought I had it. I had a “Micro-Ton” class legal design. It was a single chine hull. Nar-row at the waterline, with a massive flair at the deck. The cabin trunk was a bit large for looks, but, all in all it looked like what I was going after. The plumb bow required the boat be 5.25 me-ters long. (Micro Class requires a waterline length of max 5.25). Conventional rig, and all the i 5 5 0 S p o r t b o a t C o n s t r u c t i o n Gu i d e

6

bells and whistles one could throw at it. I posted the boat on the web, and had a few takers. In the end, the boat looked like a fun dinghy if you removed the cabin trunk. This was done in an early version of the boat. All in all, I was happy with the direction the project had gone.

Wire frame model of the i550 hull

Sharpie Hulls

I had spent a good amount of time reading up on sharpie style hulls. These boats were common in the late 1800’s. Amazing really. Narrow, single chine, plank on frame boats that were used in the shallows of Long Island Sound for oystering. As the boats progressed, they began to be fitted out for racing. Over 100 years ago, some of these boats were achieving speeds over 20 knots. I thought, maybe I should build one of these for fun. A thirty-five foot open dinghy, built with modern materials and sails. Surely we could hit 30 knots!

Traditional New Haven Sharpie

These boats fascinated me. I purchased plans, I purchased countless books, scoured the internet. The only thing I think in the end that kept me from building one, was the sheer amount of work that would have to go into something that large, combined with the fact I probably wouldn’t be allowed to race it anywhere, unless of course, I could talk some other nut job into building one with me.


7

The sharpie’s design is quit unique. If you think of the sharpie, as a class rule, over time, it was maximized to the perfect hull form. The boats were actually only limited by the length and num-ber of masts. Two major groups evolved, a 27 foot version with a single mast, and a larger 35 foot version with two masts. This winning “formula” included things such as dead rise, rocker, flair, etc. What’s more amazing to think, without the aid of computers and mathematics, these boats had to be built, to be tested. Wow.

With the i550, I utilized some of the knowledge of these sharpie techniques. I mean, after all, if you are going to build a hard chine boat, it seems these things would be it. If they can give me 20 knots out of the gate, I’ll take it. One area, where I stuck to the sharpie “formula” was in rocker. I kept the rocker in line with traditional sharpie designs. This is an element of the design that can be tough to work out properly, and as such, I started with something proven as my basis. This would be changed as the design evolved, but gave me a proven starting point. I pretty much built the whole design around the sharpie, scaled to 20 feet. Twenty feet, because I would be lobbing the aft two feet off the boat, which on a sharpie, is all overhang anyway.

As the design progressed and it was apparent through VPP software that it would perform best heeled, and as all history on the designs indicated. I started playing with taking my design, and splitting it down the middle. Then, widening the stern. Almost like opening the boat up from the back, but leaving the bow fixed together. As I did this strange things happened to the VPP soft-ware. I would get numbers that would go up, and go down.

I lobbed the two feet off the stern and concentrated on one half of the hull, heeled at 15 degrees. Ironically, this became a very easy task, and as I progressed, I would mirror my project from time to time to see how they matched up, and ensure it looked ok. Every minor change, for aes-thetics and trying to exploit the rules, and trailering laws, had to be checked in VPP. I was most concerned about the numbers going down, and if I could, try to get the numbers to be more fa-vorable.

After a couple months of long nights, early mornings, and weekends that gave me an idea of what it might be like to lock myself in a cabin in the deep woods in Idaho, and write a fanatical manifesto. I had a sharpie hull. Two of them actually, that could be joined together to present a finished product. Although changed significantly from the first rendition, it looked like the boat I was after.

What had changed? just about everything except the profile view. The deck was at max legal trai-lering limit in the US. The waterline, while being beamier wasn’t as wide in relationship to the deck. As the boat was designed at a 15 degree angle, the rocker shape changed as well. All these


8

changes, however, presented a new set of problems. I now had to go back and check righting mo-ments and ensure I met the Micro Class safety and interior requirements. Luckily, everything checked out. I just had to convince a small group of fanatical sailors to build this thing.

i550 righting moment cb, cg and righting moment at 15 deg. heel

E-mails from Down Under

It wasn’t long after the design went public, that I received an e-mail with no fewer than one mil-lion questions about the design and the boat. The e-mail had an accent, it was Australian. It seemed Andrew, an aspiring builder in Australia was interested in the design, and wanted to take a look. I gladly sent a set of plans, and got no fewer than two million more questions. Don’t think I am joking. I am dead serious.

It seems he wanted to build the boat, but “turbo” it. He and I were in the same boat, we liked the design, but had no Micro Class to race with. Although, looking back, I believe his intention was to race other similarly sized sportboats. Sounded fun. Lengthen the boat, a few tweaks here and there. Recommendations as to what to do to reinforce this or that for the added keel and rig loads, and what could be stripped and what should be left in the interior for reinforcement, and a “turbo” i550 was born.

Tokyo Trash Baby under construction in Australia

Pictures would trickle in from time to time, I moved to a new town, upgraded computers, forgot about the project at one point. Assumed he scrapped it, etc. One day I got an e-mail telling me it


9

was going to finally be splashed. A few years after it started, it seemed the turbo version was ready to go. Tokyo Trash Baby hit the water.

This peaked my interest. Could it perform with other sportboats? Would the turbo’d version be worth it? It seemed to be peaking other peoples interest as well, and e-mails started coming in slowly. Discussion continued as to performance, self righting, speed potential, pole articulation. The big questions... “What should change?”

Self righting tests of Tokyo Trash Baby

I hastily redrew the boat, adding much needed detail for the average builder. I incorporated some of Andrews recommendations, and some that seemed, without the need to adhere to the Micro Class rules, should be made. The cockpit was extended as an option. A bulb keel was incorporat-ed into the plan set, panel details were added. A more complete package was put together, and a serious project came into existence.

No doubt, Tokyo Trash Baby put the boat on the map. I hastily put a website up with photos and information, Sailing Anarchy picked up on it and ran a headline article. If TTB put the boat on the map, Sailing Anarchy put it out to the universe. I was bombarded with hundreds of e-mails, I think the first week the article ran, I sold about 30 sets of plans. I made my move, and decided it was time to start my own i550 build. I convinced my wife it would be good, and got on the band wagon at hull 36.


1 0

Construction

Versions and Options

The first thing that you will need to decide is will you be purchasing a kit, or lofting and cutting on your own. I highly recommend the kit, as it will save a significant amount of time in the build process. The time saved, more than pays for the cost of a kit boat. If you want to scrape together cash to build over time, Tyvek patterns are the way to go. It minimizes the time to loft the hull and reduces the chance for error drastically.

kit templates from Watershed Sailboats

Along these same lines, you will need to decide what type of ply you will be using. While any 1/4 inch ply will work, and I have full faith in even 1/4 inch luan ply from the local lumber yard if carefully hand selected, it would never hurt, if money allows, for Meranti or Okoume ply. There is some significant difference between the latter two. Many will argue you must use Ok-oume to save weight in the boat. However, we’re talking about the difference of maybe 40lbs over the whole boat. This 40lbs. difference can be made up for elsewhere with the use of a lighter cloth, as explained below. Okoume being the lighter material, however, structurally, it is not the strongest. If you went with the stronger, heavier Meranti or Luan, you could lessen your cloth weight, from 10oz. to about 6 oz. this will give you a boat of the same strength and weight as a 10oz glassed boat, in Okoume, at a significant cost savings in both ply and fabric. Bare in mind, that the ply panels will be completely encapsulated in epoxy on the inside and out, and will be completely covered on the outside with cloth as well. All edges and seams will be taped, which is why one could get away with the 1/4 inch Luan from the local lumber yard.

It’s important to note, all ply, in North America at least, has been created with waterproof adhe-sives. What we’re really looking for, is number of ply’s and voids. You have the possibility of


11

getting more voids with a luan plywood, but again, everything will be encapsulated in epoxy and cloth, so we shouldn’t worry ‘too’ much. The more ply’s that make up a sheet, the less chance we have of voids inside, or of the adverse affect of voids. The more ply’s the thinner the veneers that go into the sheet, and the better chance we have of the voids being filled with a glue. Ideally, we’re looking for panels comprised of four or more ply veneers making up the sheet.

Comparison of a bad quality ply on the left, and an exceptional quality ply on the right

Many will argue the Meranti, Okuome, Luan issue to the grave, but in the end, it really doesn’t matter if you build the boat properly, and use the appropriate materials. Meranti and Luan will save you almost half the cost of Okoume.

If you really want the most “Gucci” boat out there, and really maximize the advantages of avail-able materials, you could build the hull from Meranti, and the frames and deck from Okuome. This would give you a nice stiff hull, and a slightly lighter deck and internal structure. However, I truly believe the advantage in doing this, would be more of a head game, than an actual advan-tage. However, there’s something to be said about the mental game...

The next big decision will be Carbon, S-Glass or E-glass. What we are shooting for here is to make the boat as stiff as possible. A boat made of plain old E-glass will be fine, and will last as long, if not longer than any polyester resin glass boat out there. But if you are building this boat to race, you want to minimize the effects of loading and stress on the hull. You want the boat to be stiff. If you can find it, and if you can afford it, S-Glass would be the ideal way to go. At 3 times of the cost of standard E-glass, it has 40% more tensile strength, and 20% higher modules for the same weight. Thus you could use a lighter cloth. In this application, there is no gain in us-ing Carbon. You will not save any weight in the build of the boat, as 6oz carbon weighs the same as 6oz glass. 6oz is 6oz. The bigger problem you will run into with Carbon and S-Glass is find-ing a suitable quantity. When you do, it won’t be cheap. E-Glass can be utilized with just as much faith as S-Glass and Carbon for most of the hull structure.

For the “Gucci” builder, you’ll want to incorporate kevlar tape at high impact areas for abra-sion resistance, and isn’t an expensive addition to the build along with carbon stringers. More on this later...


1 2

For 1/4” Luan and Meranti, I would use the 6oz cloth. For Okoume I would use 10oz. For an Okuome/meranti build, the 6oz will be fine. While we are on the topic of cloth weight, I would-n’t use anything less than 6oz cloth of Carbon or S-Glass either, as you start to work with pretty small layers of material, and then abrasion resistance might be something of an issue.

If you are really experienced, and KNOW you will be building an underweight boat, you can beef up the fabric on the hull and use lighter fabric in other areas (deck, tapes, etc). This is a great way to increase boat weight uniformly without messing with corrector weights later.

Next, you need to decide which version of the boat you intend to build? Long cockpit or short? It really depends on the type of sailing and what you will use the cabin for, if at all. If you plan on spending any amount of time down below, go with the short cockpit. If you are mostly day sail-ing or actively racing, long cockpit is the way to go. All versions will leave you with an identical hull, and rig setup. The long cockpit will be the more competitive version of the boat, as it will give you far more options with crew weight placement, rigging layouts, and freedom of move-ment around the cockpit.

One other option, is the cabin-less hull. This is a boat built to the plans, with the cockpit extend-ed forward to the mast, and some access hatches for gear storage. This is a simple modification of the plans, and will be a future option of the plans and kits.

There are some other decisions that need to be made, but we can wait on those until we get to them. Until then, it’s off to lofting out the panels and cutting.

Lofting

The old saying, measure twice cut once applies here. I would say, measure at least three times, cut once. Lofting is the process of transcribing the plans, to the plywood. For hull panels, utilize the baseline method, measuring all points from the baseline and marking them out on the ply. Connect all the dots with straight edges and splines. BEFORE cutting, butt join the hull panels together, so that you can verify they match up, and it’s yet another way of ensuring accuracy. Go ahead and cut out panels.

A lot of time can be saved in the lofting process by purchasing full sized Tyvek® templates. In this case, the templates are laid over the ply panels and you spray paint the edges, giving you a nice fine inner edge where the cuts need to be made. It saves considerable time for the money.

Hull bulkheads, interior pieces and frames are much easier. Plot them out on the panels and cut out. Save all scrap as this will come in handy later for some odds and ends used in the construc-tion, or for reinforcement pieces below hardware and fittings.


1 3

Lofting will be more than half of the pre-assembly hurdle. Actually, about 40 hours of the build is dedicated to lofting. While this process seems like it might go on forever, when you are finally done, you will have accomplished something significant. You drew the entire boat, and should be intimately knowledgeable with every component and dimension.

Frame 169.5

Cutting

Cutting the panels will prove to be a little more rewarding than lofting. You’ll want to ensure you have a good quality jig saw and a good quality finishing wood blade for this job. All straight edges, such as frames and such, should be cut with a circular saw along a straight edge. Cut pieces carefully. It’s best to develop a method of cutting. For example, always cutting on the in-side of the hull panels or always cutting on the forward edge of the frames, to the outside of lines, etc. As long as the method stays the same throughout the cutting process so you end up with a symmetrical hull. It’s funny, but little deviations in cutting style over the course of the build, will give you slightly unsymmetrical hulls. I like to cut to the inside of all lines. I also like to cut with the inside of the hull panels down, so the saw is on the outside face. Typically, a jig saw can tear up the bottom side of the wood a little bit. I would rather have this rough edge, on the inside where it will be covered by a fillet, than on the outside where I might have to do some work to clean it up. I also always cut on the forward face of all frames. This is just personal pref-erence. Some people like Coke®, some like Pepsi®.


1 4

All frames cutout and ready for assembly

Assembling the panels

I use a simple epoxy/glass butt joint on all my panels that need to be joined. This is pretty sim-ple, and is only needed to hold the ply together until the outer glass shell is in place. Butt the panels to be joined together, saturate with epoxy where they meet. Layup a six inch piece of glass tape over the joint and epoxy. Repeat on the other side. This will create a bit of a “bump” on the outside of the hull that will need to be faired in smooth to the overall hull shape.

Another method of butt joining the panels, is to use a six inch wide piece of 1/4” ply on the in-side of the hull panels. This is much stronger than the glass method mentioned above. However adds more weight and requires a little more planning. These “plates” used to form the butt joint, can be lightened up by cutting lightening holes in them, just as you would a frame section. These


1 5

are only placed on the inside of the hull, leaving the outside of the hull panels nice and smooth for the final glassing.

The Gucci builder will incorporate a combination of these methods, glassing the seam, and us-ing smaller strips of wood to add structural integrity to the build. Another variation on this is taping the joints, and following up with stringers in the hull.

An example of using strips of wood to butt join panels.

For a really speedy build process, you should saturate all panels and frames before putting them in the boat/assembly. This will allow you to lay them flat, and saturate with epoxy to get a nice even finish. Then, flip the panels over and repeat the process.

Stitching

Now the fun begins. You’ll really start to feel like you are accomplishing something at this stage, and things will come together pretty quickly. I like to start with the center/hull bottom. About the forward half of this component needs to be stitched together. I drill a hole every six inches, about 1/2 inch in from the edge, and zip tie the split center seem together. It’s important that NOTHING be epoxied at this point. We won’t epoxy until we are 100% sure everything is symmetrical, and the hull structure is 100% together.

Bottom panel, joined and stitched


1 6

Once the center seem is joined, I now take one hull side, and start drilling and zip tying every six inches. Some pre-drilling here makes things go much smoother. I like to pre drill the hull bottom, and as I pull the side to it, I drill the hole in the hull sides, drilling and zip tying as I go. This en-sures two things. One, I am not working at an awkward angle from underneath or inside the hull to get to the hull bottom panel. Two, my holes will all line up ok.

The zip ties are only needed to hold the hull together until the epoxy fillet and tape dry. I like to work front to back on the chine seams. This seems to be the easiest way of doing it. One thing that works really well when joining the hull seems is to put a 1/2” piece of PVC pipe into the in-side of the hull, and zip tie around this. This ensures the zip ties put equal force on the hull panel, and line up perfectly on the outside. It’s also important that the “eye” in the zip tie be outside the hull. Thus, when the zip tie is tight, and we apply the fillet, we have a smooth piece of zip tie in-side the boat.

Stern, Stem and Symmetry

The stern can be laminated out of two pieces of 1/4” ply. The innermost ply panel of this layup can, and should have lightening holes cut into it. Our goal here is to add strength, and rigidity, but not weight. You’ll also want to add reinforcing where there is going to be a motor mount, or rudder fittings. This is simple enough to do with scrap pieces of ply that might be on hand. Once the stern is ready to be installed in the boat, It should be placed in the back, and lined up with the aftermost edge of the hull sides and bottom. It can, and should be zip tied in place at the sheer line, the chine, once in between those two points, and a couple times across the hull bottom. The same applies for the stem piece. Once this piece is assembled and in place, it should be zip tied to hold it until it has been epoxied. The stem should be 1” in thickness minimum.

Sides, stern and stem in place ready for epoxy


1 7

Now, the boat needs to be put into symmetry. The easiest way to do this is to run a string from the center of the stem, to the center of the transom. The hull should be propped up level at the bow and at the stern. Measure from the bow to a point on the shear line that is about 1/4 of the distance back. Do this on each side of the boat, and make a mark at this point. Repeat this for 1/2 of the boat, and 3/4 of the boat. Now, run a string across the boat connecting the two points at the forward, middle, and aft points. These are the points we will align the hull with before gluing.

Measure along each string to from the shear line to the center string. The distance on each side should be the same. If it is not, gently twist the hull until it is. This process is not nearly as hard or complicated as it may seem. Paying careful attention here, ensures your hull is nice and square. A symmetrical hull will be less than an 1/8th of an inch off at each one of these points. This is also where your cutting technique can make a big difference. If you utilize a kit, full size patterns, or computer or professionally cut components, you should have a perfectly symmetrical hull as soon as it's zip tied.

Fillets and Taping hull

Now the challenging part. We need to fillet the hull joints without altering the shape of the hull as we have it set. I would suggest using a slow cure epoxy, so that if there is a problem, there is enough working time to straighten and remeasure the hull. The easiest way to apply the fillet is to work up some thickened epoxy to peanut butter consistency, and use a large paint stirrer or tongue depressor and apply to the inside joint. Be sure to go back and remove the excess above and below the fillet to allow for a nice smooth transition for your glass tape to go over later. Once you have the center seem, the chine, the bow, and the stern filleted in place, allow it to cure thoroughly. This is the bond that will ultimately give your hull the strength it needs, so rushing this step, or skimping in any way, is not what you should do in this step.

It should be safe to cut away your zip ties once the fillet cures. Ensure the inside seam is nice and smooth. Be careful, as the hull is still very fragile here. Everything should still line up in your string jig laid out over the top of the boat. You should still be able to do some minor twisting at this point. But only very minor. We’ll need the aid of the frames to finish any final tweaking to the hull shape. So we can finish this tweaking in a later step.


1 8

Fillets on the left and taped seams on the right.

Take a 6 inch wide 6oz. tape, and run it down the center chine on the inside of the hull. Ensure it is saturated with epoxy, and squeegee out any excess. The squeegee will become your most im-portant tool in the build process if you intend on building a strong, and light weight boat. It will ensure your cloth is fully saturated, and that you don’t use too much epoxy on your cloth, pulling the excess out, and keeping weight down. Extra epoxy lobbed on when it doesn’t need to be, re-ally will add up fast and won’t contribute to your structure. Ideally we want the cloth to be touch-ing the wood, and not “floating” in the epoxy.

Ideally you’ll want to use a biaxial tape for the center/chine seems, as these will have all sorts of load forces on them. You can get by with standard glass tape, however if you intend to push the boat to the limits and/or sail in heavy seas and wind, the extra money on the biaxial tape on the chine seams will really give you longevity and added strength in your hull.

Now, repeat the taping process for the chine seams. If possible, make sure all tape seems are sin-gle pieces that run the length of the hull. This will provide the most strength. If you do have to use multiple pieces of tape, ensure they overlap each other.

Finally, we want to tape the stem and stern panels in place. This can be done with a 6 inch wide, 6oz. plain weave tape. Allow these joints to cure fully before proceeding.


1 9

Fillets and Taping frames

On your string that runs down the centerline of the hull, you should be able to mark out distances back from the stem, for each frame location. This is important, as the hull is still very fragile, and rather flimsy. If you insert a frame at the wrong location, you could easily distort the hull, and end up with something next to impossible to fair. You could also end up with something quit op-posite, and end up with a hull that is a bit too weak, and unsupported.

Frame spacing should be within 1/2 inch of the intended location. Start with frame 018, and work your way back. Ensure the centerline of the frame, matches the centerline created by the string. Place the frame in the hull, and force it tight against the hull sides and bottom. To force it into place and create the correct hull shape, you’ll want to push it down into the hull, and zip tie it in place at the top, where it meets the shear line. Once you have it secured in place, we’ll go ahead and fillet the seams on the front and back sides of the frame, and then tape the front and backs , as we did above. However, it’s only necessary to use a 4 inch wide, 6 oz., plain weave tape here. Repeat this process for all frames. The lower edges of the frames, along the chine, will need to be trimmed to fit the newly created fillets, to allow for a proper fit. If the corners aren’t trimmed off, you’ll not get the frames in place.

Lower edge of frame showing notch for chine fillets

Frames 110 and 124 should be carefully measured to ensure there is at least 14 inches between them to allow for the keel trunk housing. One ideal solution here, might be to build the keel trunk before installing the frames, and ensure proper fit to the keel, then install the frames, using the keel trunk as a spacer. Once all the frames have been installed, filleted and taped, it’s easiest to finish up the remainder of the interior components before continuing on or adding decking. It’s important as you install the hull frames, that you keep the “V” in the bow sections and the arc in the aft sections, These give the hull added rigidity along the bottom, and are much stronger than flat ply, with far less flexing. Part of the design process with the i550 was in determining the maximum distance between frames and stringers material could be unsupported, and the arc


2 0

needed, to give a solid hull. Without this curve, and center chine in the bow, the hull will be prone to flexing, so it’s important, that the frames be forced into the correct positions.

You should really be seeing the boat starting to come together now. You’re almost home free. Things should be pretty stiff now, and you should be able to work in the boat, without serious fear of damage or distortion. Just ensure the bottom is supported about 1/3 back, the middle, and 2/3rds back in the hull.

Frames installed, filleted, and taped. Sheer clamp shown in place.

Stringers and Bunk Supports

As we insert the bunk supports, we’ll use the process for installing them, that we did for the frames. It’s also the point, where we want to double coat the interior surfaces with epoxy. The first coat should be a regular mix of epoxy to saturate the ply components. The second coat, could be tinted, if desired to add a color of your choosing to the interior appearance. If you aren’t too worried about weight, and your epoxy work is good, you could lay a 6oz. plain weave cloth in the cabin area, where there will be high traffic, and things being tossed into and out of the cab-in. Even if you area being weight conscious, this isn’t a bad idea, as it will prevent dings and nicks from occurring in this portion of the hull.

Bunk supports shown in place with mast compression tube at frame 89.5


2 1

We’ll insert the stringers/bunk supports in the same manner as with the frames. Position them in place, fillet and tape. Those really looking for the extra edge, will benefit from using a biaxial tape on each side. 4 inch, 60z. biaxial, in the same manner as with the chines. Aside from giving the bunks support, these stringers give the hull fore/aft support when the rig is loaded up, they also transfer loads from the keel outward and fore/aft along the hull.

The “Gucci” builder will benefit from using carbon uni tape on the stringers. This will help pre-vent fore and aft flexing up and down of the hull, or the ends wanting to come together as the rig loads up.

Interior Fixtures

As we fit out the remainder of the interior, this is the perfect time to watch for potential sharp edges and corners that sails might get caught up on. All edges should be rounded. What works re-ally well on the interior berths, is to route all interior edges with a router.

Placing the berth tops in the boat is easiest at this stage as well. Any completely sealed compart-ment should be fitted out with an inspection port to allow air to circulate and the boat to breath and dry out. An option with the interior, would be to include a forward berth platform between station 053.5 and 089. This should be easy enough to fabricate for someone that would like the added space. Additionally, you could go as far forward as frame 018. It would give the potential for three to sleep in the boat, and was a feature of the original i550 (as designed for the micro-class) however it will add about 20lbs. to the overall weight of the boat. For boats built exces-sively light, this might be an option, rather than adding corrector weights.

Bunks installed inside cabin

The section on each side of the keel trunk, should be made from 1/2 inch ply, or two pieces of 1/4 inch ply laminated together. Lightening holes could be made on the lower piece of the 1/4


2 2

laminated version, and retain the same strength, with lighter weight. Ideally, the whole piece on each side would be made from one piece of 1/4 inch ply, with an additional 1/4 inch backing on the underside, at the thwart area of the keel trunk. This will create the most solid keel trunk as-sembly possible and when tied into the stringers will really add side support and help with load transfers.

If you really want to make your boat bombproof, and give it some added strength with very little weight gain, add stringers to the underside of the cockpit floor. This is simply a 4 inch piece of 1/4 inch ply, run down the centerline of the hull from frame 110, or 124 (depending on what ver-sion of the boat you are building) all the way to the stern. Cut a 4 inch deep notch, 1/4 inch wide in the center of each frame, and slide the support piece in like a puzzle. Variations on this are fine as well, with two or three stringers running fore and aft smaller in dimension. Epoxy in place. The weight gain will be only about two pounds, and it will really give a solid cockpit floor be-neath your feet.

Cockpit stringers added to notched frames. Interior filleted, taped and saturated with epoxy.

The interior should now be finished to suit, and prep work should be made for any rigging items that might be hard to get at once the decking is on. The bow is an area that is tight to work in, so any recessed furler, or bowsprit should be planned, as well as any reinforcement to the bow area. Also, the stern, and the rudder mount, as well as a possible motor mount location should be rein-forced, and glassed over. This will prevent washers or backing plates from digging into the wood structure, and compromising the epoxy coating protecting the wood core.

The last step, and realistically this could be done sooner, is to install the sheer clamp. This is a 1” x 1/2” hardwood that runs around the sheer line of the boat. This should be a solid piece or scarfed together from no more than two pieces, and epoxied in place. I like to do this last, be-cause I can use notches in the frames to hold it in place while the epoxy cures. I also drive


2 3

screws in from the outside to hold it in place. It also gives you something solid to screw the edges of the deck down onto.

Sheer clamp shown installed ready for decking

Decking and Cabin Trunk

Fitting the deck will prove to be more challenging than one might think. The deck should be cut out slightly oversized, and cut to fit when you are ready to install. This will ensure any deviation, doesn’t leave gaps, where structural integrity is needed along the shear line.

We should begin however, by assembling the cabin trunk, just as we did the hull. Stitch the com-ponents together, and trial fit over the hull. Ensure proper fit. Once you have everything lined up, You can glass the outside of the cabin trunk so that the components are no longer dependent on the zip ties. DO NOT epoxy it to the hull or frames yet. Once this cures in place, pull it off the hull, and fillet and tape the inside seams of the cabin trunk. Once this cures, we can bond it back in place, on the boat. We’ll fillet and tape the joints to the frames just as we would anywhere else. We can then allow that to cure as we begin installing the deck structure.

As we add the deck, it’s easiest to work front to back. The underside of the deck should have been precoated and sealed with epoxy, as it will be hard to reach once construction starts. Also, any area requiring reinforcement, that we won’t be able to get to easily later, should be rein-forced at this time with ply backing plates, and glass patches over the ply. Starting at the front, we’ll mix up some thickened epoxy, and apply it to the top of the frames. It won’t take much. It helps in this step to have someone in the boat, under the deck. The goal here is to lay the deck on, ensure it is lined up, and weight the piece down to give it a good bond with the thickened epoxy. The person under the deck, will spread the excess epoxy in a nice fillet, and apply tape to the seam. This can be tricky work in the bow, and in the stern.


2 4

Decking fixed in place, edges are cut slightly large to allow for perfect trimming

Care should be taken to ensure the pieces fit correctly before any epoxy is applied to the frames for bonding. In the cockpit area, we’ll do the deck sides first, as this will make access easiest to the underside where they meet the frames. Next we’ll do the sides of the cockpit, and then the cockpit sole. All seams should be filleted and taped. Once the deck has been trimmed, and edges faired, routed, rounded, etc... we’ll want to glass over the entire deck structure., including the cabin trunk, the back of frame 110 or 124 (depending on the version being built), and the stern of the boat.

This leaves us with a finished deck structure.

Cockpit floor in place awaiting side panels.


2 5

Finishing the Hull

This part can be a bit daunting, but in the end, should be manageable for most. The hull needs to be flipped over upside down, and supported at the 1/3 and 2/3 length point. The bottom of the hull, and the sides, should be filled and faired, edges rounded to suit, and then the entire structure glassed over. Glass is per the first section of the construction guide. Obviously, the more you can afford the better. However, E-glass will suffice for even the picky builders. 6oz or 10oz depend-ing on the ply you used, and if you can obtain biaxial fabric, this would be the fabric of choice.

You’ll want to ensure the correct amount of epoxy to fabric is used, and this is where a squeegee comes in handy. As you squeegee across the fabric, it will pull epoxy across the top of the cloth, and fill the weave. This technique should also give you a pretty fair surface to work with for fin-ishing, as it doesn’t allow much epoxy for the material to “float” in. You’ll need to go back and fair the hull once this dries, and fill in any exposed weave, but, this process will go quick. The sides of the hull are a bit trickier, but still more manageable upside down than right side up.

Hull 36 upside down, glassed and faired.

If you really want to protect your hull and really make it durable. While the boat is upside down, add a piece of 4 inch wide kevlar tape from the bow, to the keel slot. If you hit something, or while trailering, the boat hits debris, it will be in the front half of the boat. I run the kevlar from the top of the bow, all the way down the bow, and continue back to the keel slot. I also add it along the rail at the shear line where I know I will be prone to hitting things, docks, boats, hoists, etc.


2 6

First of many coats of perfection paint on the bottom of hull 36

This will obviously need to be faired in into the finished project. Fairing is a matter of will pow-er. When is fair fair ? When is enough enough ? Once the hull is faired though, you are ready to apply the finish coat of your choosing. I prefer a two part paint such as Awlgrip or Interlux Per-fection. You'll want to apply your finish coat, go back and sand, and reapply your finish coat, probably three or four coats to get it perfect. Once this is done, we can now roll the hull over to finish the deck and begin outfitting the boat.

Hull, finished, ready to flip and complete the deck.

Finishing the Deck

Fill and fair like the hull. It's not so important that it be perfectly fair. Anything you do here will be purely cosmetic. You want to get transitions smooth, and ensure that you have a finished prod-uct to your liking. Once the deck has been sanded, filled and is prepped for paint, paint as you would the hull, and let dry. You'll now want to plan out your non-skid areas, and how you'll work this out. I like to use the Interlux non-skid additive with flattening agent in the perfection paint.


2 7

It's a nice tough finish that will really hold up well to the abuse of a racing boat and the workout a deck gets on a boat of this size.

photo of paint

photo of non skid

OutfittingVersions and Options

Coming soon.

Keel and RudderVersions and Options

Coming soon.

RigVersions and Options

Coming soon.


2 8

i550 construction guide

Documents

s p o r t b o

t c o n s t r u c t

taping hull

i550 hull

taping frames

tconstruction guidewritten

d e1table of contentstable

christopher beckwith