Engineered Carbon Fibre Beams for a Tiki 26

[Robert Hughes]

I've just mounted a pair of new main crossbeams on my Tiki 26, and thought some of you might like to see what was involved.  Zest is one of the Imagine Multihulls Tiki's, built in GRP/foam sandwich construction, and she's 26 years old.  She was designed and built very well, but 1990 was a long time ago.  I've been doing a full refit, and taking the approach that I want everything to last at least as long as I'm likely to...  As an example I've replaced all the gunwale rails and beam lashing points using iroko.  My original beams look ok, but I know a similar boat had one crack a year or so ago due to hidden rot in a plywood web.  I may do some serious cruising in a few years time and want to have complete confidence my beams are ok.

I looked into the various options, such as stripping down and renovating the existing beams, or replacing in aluminium, or glass/carbon over a foam core.  In the end I decided to spend the money and go with engineered carbon fibre tubes.  The advantages are that they have a known strength, should last longer than the rest of the boat, not involve too much work on my part, and give a significant weight saving.  The only disadvantage is that they're not cheap, in fact they're b***dy expensive, and I would never get the cost back if I sold the boat.

Finding a company willing to look at a one-off job such as this proved very difficult, all the companies around here would only do production runs.  Luckily I found C-Tech in New Zealand, who were extremely helpful.  I did the basic load calculations for a number of scenarios myself, to get an idea how strong the beams needed to be, then C-Tech came up with carbon structures to suit.

The tubes were too long to send by air, so I had a long wait while they travelled half way round the world by ship, but eventually the big day arrived, as did a huge box.  The carbon tubes cost about £2400 plus the dreaded VAT (UK tax).  The packing crate was £175, and shipping came to £440.  Shipping was arranged from this end; it would have cost twice as much if arranged from New Zealand, so that was a useful lesson for next time (probably when I order a carbon mast...)

Like any kid, the first thing I did was sit the new toys in place to see how they would look!

The grey part in the middle of the forward beam is the reinforcement to carry the mast.  The idea is that the loads are shared efficiently between the top and bottom of the beam so that there is no tendency to crush the tube.

This is achieved by inserting a thick-walled carbon tube of about 40mm diameter, then adding extra reinforcement to the top and bottom faces.

The reinforcement on the bottom is tapered out carefully to ensure there is no stress concentration due to a sudden change in thickness.  This picture was taken after I had sanded the tubes and started applying lightweight filler ready for painting.  Another lesson learned for next time is to order the tubes machine-sanded.  It's amazing how much harder the resin is compared to the West epoxy I'm used to.  These tubes are made from pre-preg carbon which is cured in a huge oven.  They're amazingly hard and if you tap them they sound more like steel than fibreglass.I wanted to use the old mounting points rather than make changes to the decks, so I fabricated feet for the beams that would mate to the existing upstands.  This was done by moulding fibreglass shells on the beams to make the top halves of the feet, and making the bottom halves from plywood with hardwood locating blocks.  In the picture you can see release film to protect the beams, held on with double sided sticky tape.  After laminating the glass a layer of peel ply was used, to help get tight consolidation and a good surface for bonding.

The beams were accurately jigged in position and thickened epoxy used to fix the upper and lower halves of the feet together.

Back in the shed, the feet are ready for finishing.  First they were drilled and screwed to the beams so they could be refixed accurately.  Then they were taken off and more filler etc applied to form solid shapes, before trimming.  Another lesson - Note the markings on the foot, "SIA" stands for "Starboard Inner Aft"...  With eight similar but different feet there's plenty of scope for confusion.

One final trial fitting with the feet screwed in place to make absolutely sure everything is right before epoxy bonding them to the tubes, and carefully blending all the edges and joins.

Upstands for the tufnol cleats were made in a similar way to the beam feet.  I used Jotun paints, applying four coats of Penguard HB primer followed by four of their Hardtop two-part polyurethane.

Although the beams are painted for protection and to stop them getting uncomfortably hot, I did want to show off the the carbon fibre.  The answer was to get C-Tech to make a set of carbon end-caps, which are clear finished.

The lashings are easier to tighten than on the old beams, I think because there are no corners.  The load is also spread very evenly around the surface of the beam.

One big advantage of carbon fibre, and I can guarantee I'm no muscle-man!  This is the mast beam, which weighs 19kg including the feet, cleats, end caps and paint.  The aft one is much lighter.  I've not yet weighed the originals accurately as they're stored away, but I couldn't lift the heavier one without serious risk to my back...

If anyone else is interested in making similar beams I can let you have more details of the spec we came up with, and I'd recommend C-Tech.  I'll be ordering a carbon mast, and am also thinking about other bits to get at the same time, such as components for a "goal post" structure for the stern, and a new forward netting beam.

[Robert Hughes]

Here's a sketch showing roughly how the cockpit will be hung from the new beams:-

In practice it will be a little different because the cockpit is actually a bit lower, but the principle is the same.  I've moulded glassfibre shells from the beams like I did for the upper halves of the feet, but with a sheet of 2mm rubber under the release film to give the required clearance.  The cradles will be bonded on as an integral part of the cockpit structure.  The cockpit will be trapped between the beams, so the assembly routine will be to secure the mast beam first, put the cockpit into place, then secure the aft beam.

Jerry S said:

Robert,  That is a magnificent project and you have done an excellent job with the fitting and finishing.  I would love to have a carbon mast but cannot find a suitable excuse.  How do you plan to hang the cockpit?  Jerry 

[Robert Hughes]

Hi Ian,

Thanks for your comments, you raise some interesting points.

Regarding the Wharram philosophy and low costs, the way I look at it is that Wharrams provide the opportunity to get afloat very cheaply and simply, but from that starting point you can move as far as you wish, if you wish.  These new beams have cost about 60% of what I originally paid for the boat, and they've not increased the value by anything like that, so they're not an economic proposition, but they're something I wanted to try doing and by my own criteria I'm glad I have.  There are people who buy or build a boat because they want to sail, and there are people who build or rebuild boats because they love building boats.  I'm one of the latter, and one of the many reasons my starting point this time was a Wharram is that they're cheap, robust, and easy to work on (obviously as well as being seaworthy and incredibly beautiful).  The great thing about the Wharram community is that these boats attract a huge variety of people from lots of different backgrounds, all with different outlooks and motivations.

Another way of looking at it is that I could have spent money trading up to a bigger boat, and that's what a lot of people do.  I haven't, instead I'm trying to make my 26 footer as good as I can get it.  I've sailed big boats and little ones, and I'm a firm believer in the saying that "the smaller your boat the bigger your adventure".

Regarding the weight advantage etc from this project, the main benefit as far as I'm concerned is in loading capacity, and to offset the weight of other things I plan to add.  An example would be a goal-post structure across the sterrns to carry solar panels, antennae, and possibly a small wind vane.  A limiting factor for small Wharrams undertaking long voyages is their ability to carry sufficient stores and I don't want to adversely affect that.  I'm not concerned about loss of speed as I don't think it would be too significant, but these boats can give a very wet ride (even wetter than normal..) when heavily loaded.  I once did a long trip on a Pahi 52 that was carrying a huge amount of stores, fuel and water.  It still sailed well, but a lot of water came over the deck as soon as it got a bit rough.  These boats with their fine bows need to be able to rise to the waves as easily as possible.

Low mainetance is a big advantage as far as I'm concerned, but this could have been achieved almost as well with aluminium at a lower cost.  Aesthetically though, they wouldn't have been anything like as good, and I suppose I wanted to try working with carbon fibre as I've never done it before!  I've also had a great deal of fun working on the design aspects of the project, and working out how to fabricate all the various components.  I'm now turning my mind to the cockpit...

All the best,

Rob

[Jerry S]

Robert,  I am with you.  I did not choose a Wharram for the philosophy rather was is the boat that suited my requirements of ease of transportation, storage, maintenance, launching and sailing ability.  I went to Australia whilst it went into a barn in deepest Dorset for three years. I have road moved it twice on a car trailer and another two times with a lorry plus HIAB.I sailed it to the Netherlands and will sail it back to either Liverpool or Portsmouth.  It also provides an endless opportunity to fiddle, tweak and customise.  My mast goes up today and I have replaced all the standing rigging which needs to be re-set, so the mast has to go up and own a few times with the launch.  If it were carbon I could do it alone rather than messing with a crane. My first project this season is the electrical system and I have gone for a small petrol battery generator (www.thesupercharger.co.uk)  Good luck with the cockpit and I hope you get out on the water in reasonable time.

[sailorjoy]

Hi modern folks,

I´m a  traditional sailor grow up on big traditionel sailingships and find the philosophy of wharram to keep it simple and cheap very good. But I agree with Robert to save weight and make the handling easier. The handling includes also the maintenaces like sanding and painting every season. When you add up the money for painting and the time for sanding of wooden beams over the years than are the costs for carbon beams not so high especially when you build them by yourself.

Best regards

Jan

[Ian Bamsey]

Robert, Thanks for your well thought out answers to the points I raised. Like you I really like the building / design part of these boats and I can understand why you've gone for the carbon beams. Very interesting and a great result. 

I'm intrigued by the composites approach. Of course, ply and epoxy is a composite and ply can be thought of as a structure core. I feel there might be a possible design at a low(er) cost that might confirm the weight advantages. Kevlar is a possible material for beams as it has high tensile strength but is a bit cheaper than carbon. Carbon is particularly good for creating stiff structures, but this is not a big factor for Tiki beams. I'm interested in beams from a foam core with vacuum bagging etc. Low temperature prepregs and more and more available.

Your comment about small-boat-big-adventure really resonates. I've really enjoyed my small trips on my Tiki 21 - only a few nights so far but great fun. I'm a kayaker and this boat feels like a pair of oversized WWRs with sails. I'm tempted by a Tiki 30 for the family, but fear loosing the urge to go for a blast after work.

There have been some other good reactions to the comments from others. I look forward to some more.

Ian

[sailorjoy]

I´ve bought carbon very cheap at "hp-textiles.com". They offer short ends and second choice layers at "ebay". I paid for the carbon for my three beams 250,- Euro. I find it not so expensive.

Jan

[Robert Hughes]

Hi folks,

I'm doing some experiments at the moment, comparing glass vs carbon fibre and epoxy vs polyester resin, over PVC foam cores.  I'll start a new thread when I've reached some conclusions.  The reason for the tests is that I've decided to build a new cockpit rather than adapt the old one to fit my new beams.  As well as saving quite a bit of weight I want to add lockers and cut down on the places where water can come up.  I may also use Kevlar or another aramid in selected areas where it's properties are advantageous.  I have heard that Kevlar can be difficult to work with, so I'm checking that out as well...

All the best

Rob

[Ian Bamsey]

I've built kevlar kayaks. It's much like other cloth to lay up. It's just very difficult to trim when wetted out.

[Robert Hughes]

Thanks Ian.  I'm thinking of adding it over the carbon on the cockpit floor, to protect against things like the steg of an outboard, or an anchor being dropped on it.  I'll be laminating a full 8x4 sheet, then trimming it, so I need to check how my tools deal with cutting it.

Ian Bamsey said:

I've built kevlar kayaks. It's much like other cloth to lay up. It's just very difficult to trim when wetted out.

[Ian Bamsey]

When you lay up in a mold and you overrun an edge you normally trim with a sharp knife against the mold edge just as the layup goes off. With kevlar, the knife will cut, but then it catches and drags the cloth breaking up the structure. Once it's gone right off, you need a grinder or jigsaw with plenty of blades!

Why not make a big one piece mold and layup a carbon kevlar structure. There would be little point in using epoxy as polyester is strong and it's not below the water line. 

What a great project, take me back 35yrs to my school days when our teacher was designing slalom kayaks, carving clay plugs and making molds. All great fun.