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.

[Ian Bamsey]

These look very nice, well done. What diameter / thickness are the basic tubes?

[Robert Hughes]

Thanks Ian.

The inside dimensions of both beams are the same, a streamlined oval of 158mm x 122mm.  The wall thicknesses are 3.3mm for the aft one and 3.9mm for the one under the mast.  There are extra wraps in the highest stress areas, where the beams are fixed to the hulls.  You can just make these out if you zoom in to the big picture of the finished mast beam sitting on the boat.

One of the scenarios I looked at for the design was the force under the mast at the point of lifting a hull due to wind pressure alone, with the boat fully loaded.  As far as I know this has never happened on a 26, although there have been instances on the 21 when lightly loaded (and probably with crew caught on the wrong side when the gust hit).  The load comes out to about 1.25 tons.  This was about what C-Tech would have expected from their experience with various cats.  The deflection of the beam in this situation would be about 8mm.  I did ask about the ultimate strength, in the sense of when should I get concerned if I saw flexing under some unforseen extreme conditions.  The answer was that it would take a load of something like 20 tons under the mast to break the beam.  In practice something else will break before these beams do.  Obviously no dolphin striker is needed!

C-Tech do have smaller oval mandrels, and they said they could make beams that were easily strong enough for the Tiki 26 using the 138mm x 94mm one, but they just wouldn't look right.  Having got them I do agree.

Regards

Rob

[Ian Bamsey]

Thanks rob, a really interesting project. Good luck and I look forward to some more photos.
Ian

[boatsmith]

nice!

[paul anderson]

Excellent,the weight savings will be enormous.thnx for sharing this.

[sailorjoy]

Hi Robert,

gratulations for your new beams. Its funny how light the weight of the beams is. I´ve just finished my carbonbeams and was surprised about the weight.

Can you tell me something more about your carbonmast?

Best regards

Jan

[Robert Hughes]

Hi Folks, thanks for the compliments.

I think one of the reasons these tubes are so light is that they're made of pre-preg carbon, which is wrapped in heat-shrink tape and cured in an oven.  This means the laminate is tightly compressed and there is no excess resin to add extra weight.  Also they're made on a steel mandrel so there's no core, and therefore no resin filling the surface of the foam.

Before I placed the order for the beams I also looked into having a carbon mast and decided at that time to get the beams first as the weight saving was much greater.  For the mast the bare tube would weigh about 60% as much as an aluminium one of the same stiffness, and mine is already aluminium.  The quoted cost was around £1400, so it's a lot more expensive than aluminium.  It would have to be made in two parts joined with an internal sleeve, which was included in that price & weight.  From what I've seen on the forum it's difficult to get aluminium tubing the full length as well.  On reason I'll probably go ahead is that I want to make my mast a bit longer anyway.  I understand C-Tech have previously supplied a mast for a Tiki 30.

Here's a picture taken yesterday, showing the new carbon fibre aft netting beam being trial fitted.  The old one is aluminium and I wanted to increase the strength and resilience without adding extra weight at the end of the boat.  I plan to add a "goal post" structure to carry solar panels, aerials, etc, and it will have to be partly supported on the netting beam so that it clears the tillers and mainsheet.  The tube is 2.8m long, weighs 1.8kg, and feels quite safe with my full weight in the middle of it.

[Axel]

Great job and fascinating. I think of doing something like this every time I have to rig up a pulley to move my beams around! BTW, the price really doesn't seem too crazy to me for CF custom tubes of that size.

[Robert Hughes]

You're absolutely right about the cost.  I compared C-Tech's prices for some standard carbon tubes with those from other suppliers, and C-Tech were very good value, even after adding in the shipping cost.  It's just that carbon fibre is not a cheap option compared to other materials such as aluminium tubing.  I think it's worth it though!

Axel said:

Great job and fascinating. I think of doing something like this every time I have to rig up a pulley to move my beams around! BTW, the price really doesn't seem too crazy to me for CF custom tubes of that size.

[Jerry S]

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 

[paul anderson]

Robert i look forward to a warts and all assessment once she is sailing again,this really intrigues me.

[Ian Bamsey]

Robert, This is a great project and the results look wonderful. I have serious "beam envy", especially after spending some time cutting out bad wood from my Tiki 21 beams.

I have some comments and would enjoy a debate around your project. (Don't get me wrong, this is not criticism but a point of debate).

One of the attractions of the Wharrams is their low(ish) cost and the DIY element. I paid less that your proposed mast for my boat, although I have put in serious hours getting it to a point where it's a pleasure. If one starts to spend this sort of money on beams and masts, might some part of the Wharram philosophy perhaps be lost? 

Secondly, putting aside man-handling and transport, is the weight advantage for speed and how important is this, or is it increasing load carrying capacity? (although there is a wet area interconnection between these two aspects). Or is the low maintenance the a predominant factor? 

It would be great to identify ways to build beams at least, to a high standard perhaps using pre-preg within a much smaller budget. Or perhaps the ply epoxy approach is still optimal - given your priorities / requirements. Clearly one factor, which I most enjoy, is the design and completion of your project. Well done.

Once again, I like what you've done, but am interested in people's comments and input.

Again, great job Robert ...

Regards

Ian