How thick is your boom?

30/07/2009 23:25:55
John
I am thinking that whilst its raining on Saturday I might make a boom out of carbon. I think superspars to boom-end fittins for 70mm ID tube. Drain pipe is 68mm OD, how convenient for a mandrel. So, how thick does it need to be? can anybody tell me how thick the wall is on their (ideally) 70mm ID carbon boom is. Any info would be good!

31/07/2009 08:24:38
Chris M
They are 2mm as i recall.

There is however rather more to it than wrapping carbon around a drainpipe and leaving it for 24 hours! You need the correct weaves of carbon (Unidirectional and twill weave.), some means of warming it up for better consolidation and a better cure (Which could bend your drainpipe) and also some means of vacuum bagging the whole assembly to make sure that the resin has correctly penetrated. Failings on nay of these counts will almost certainly cause it to break.

A new boom is just over £300 for a fitted out superspars or a bare chipstow.

31/07/2009 09:14:13
Andy Hay - Enchantment 3386
John, keep an eye on the Cherub web site for guidance on the laminate (there web site was down) - I am planning to make my own in time too. As mentioned in the previous post, the lay-up and fibre direction is more critical than thickness. You will probably find that a home build boom would end up thinner (if done correctly) as you would not have to build in the same safety margins and can optimise the laminate more than a production facility could.

Also there are some good videos on youtube (honest) from the aforementioned Cherub guys which walk you through making a boom / mast / spi pole.

Good luck.

31/07/2009 09:50:12
Mags
Have a think about how you'd remove the drainpipe too....

31/07/2009 09:53:14
Ben 3634
You would,of course,only have to fashion a wooden mandrel to create an ovoid boom,stronger and lighter than a tube surely...

31/07/2009 10:19:48
Andy Hay - Enchantment 3386
Release - candle wax melted then brushed on the mandrel. To release, warm up (a kettle of hot water should do it) and pull. Just watch your missus love you after getting a puddle of wax on the carpet of the lounge - which is where this will take place of course (i.e. a nice warm dry area).

Oval or elongated would give you a smaller section as this is stiffer in the longer direction, so lighter weight. However, this would require more thought on the lay-up as the round section is better at holding its shape. Another layer of +/- 45 or 0/90 cloth would probably suffice though, which would negate the weight saving due to size. Oval will have less windage though (in the fore & aft sense). You could have a 130mm deep (vertical dimension) section which would give you a bit more unmeasured area on the runs. An oval would look a damn sight cooler than a round section though!!

31/07/2009 11:04:03
Andrew M
Heaven Sent still has its original boom from 1993 when carbon spars were just coming in and masts were still outlawed.  It is a deep section from John Claridge though with Dick Batt's logo on it with a track on the top that has never worked properly.  I'm sure you could make the same section, 4" deep by 2" across, but considerably lighter these days.  It has proved durable!

Anyone else still got one?

31/07/2009 13:47:31
John
I've reasonable success before, making a spinnaker pole. That one was a curtain pole. The lost wax method did seem to work very well at removing the mandrel but I wonder if it deforms slightly during curing ( the finished cross section wasnt perfectly circular).  I used shrink tape, bread wrap and bleed cloth to consolidate, and cured it over a radiator under some polythene. 

I like the idea of a non circular cross section, sure I saw some 112mm gutter in b&q.

As far as layup goes its tricky because I cant find any 300g uni, only 200 or 400. Working with 200 puts the number of layers up and I expect I'll run out of time. My current thinking is
200g twill
400g uni spiral at 30 degrees
400g uni, straight
400g uni spiral at -30 degrees
200g twill

But this seems probably a bit light, I guess it would finish up around 1.6mm. Perhaps another straight layer of 400g uni.

31/07/2009 14:50:18
Andy Hay - Enchantment 3386
Found a web site that supplies carbon socks of around the 300gsm weight, both UD & biaxial. just roll it back and peel on. I was thinking about using this stuff plus they do some nice heat shrink stuff for consolidation.

Time for the garage tinkerers to take the class on!!!

www.solarcomposites.com
31/07/2009 16:34:44
John
Its just a shame braid is so difficult to get in the UK. havent been able to find a local supplier.

Bought my carbon this afternoon. Wish me luck!

01/08/2009 16:43:23
pabs
Andy

If you do make a boom out of the carbon sock could you post an Idiots guide as i would love to make one but unsure of what material and quantity to buy

01/08/2009 21:45:37
Andy Hay - Enchantment 3386
Sounds like I might have to do a "How to build a Merlin" book ...

01/08/2009 23:27:45
John
We did the layup today. All seemed to go to plan. It took just under 3 hours to get the carbon on. Couldnt get any slow hardener, only standard. Very glad I put the epoxy in the fridge last night. The job is now sat between two workmates, covered in blankets and bubble wrap, next to a radiator with the heating on at max chat. The house is like an inferno! The drain pipe mandrel did want to sag by about 5-8mm in the middle, but I was fortunate to have 3meters of aluminium angle  to hand to act as a straight edge during curing. 

Would be happy to write this process up if people are interested, including calcs for cutting widths based on spiral and increased diameter thorugh the layup. Acknowledgments definitely due to the cherus class on the process used.

Of course, I still have to get it off the mandrel and attached to the boat. Need to glue the mast back together first.

02/08/2009 08:20:55
Andy Hay - Enchantment 3386
Cool (well, not in temperature terms). I was planning to knock up a box of polystyrene sheeting to cook the thing rather than relying on the central heating.

I was also thinking of a kevlar / glass outer sheath to protect from the scratches and shroud damage.

02/08/2009 10:38:59
Richard Battey
John,

Sounds brilliant!

Great if you can post details and images.:-)

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