boom.

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trebor
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boom.

Post by trebor » Fri Jun 22, 2012 5:20 pm

Hi all, I have a section of alloy tubing which I intend to use for an uprated boom ( about 3mm wall thickness ), I have been reading the Harrier topic and wondered about thickness and shape of boom with regards to safety, ( barmy question coming ) I can get access to alloy tubing which is 50mm diameter but is about 6mm wall thickness, would this be too thick with regards to being hit on head in unintentional Gybe? and is box section or triangular more likely to injure you? Sorry in advance if this question is a bit naff.Rob.
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Michael Brigg
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Re: boom.

Post by Michael Brigg » Fri Jun 22, 2012 6:44 pm

To be hit on the head by a dinghy boom hard enough to cause serious damage or endangerment, I would generally reckon you would have to be out in conditions sufficiently extreme to ensure that you spent most of the race with your head below your knees.

I can reccomend a baseball cap or something similar also give adequate protection. I took several knocks from a Contessa 32 boom, one hard enough to draw blood, but a canvas cap was adequate to prevent anything worse than you might expect in an amateur/veterans rugby game.
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Re: boom.

Post by Rupert » Fri Jun 22, 2012 7:01 pm

6mm wall thickness would be far too heavy for a boom.

I've not got one handy to measure, but I'd think that 2mm is more common. The size of the boom offers far more stiffness for weight than wall thickness. Bigger the boom, the stiffer.

As for head bashing, don't worry about it. In nearly 40 years of dinghy sailing, I've been hit on the head dozens or hundreds of times, and can only think of a couple where I saw stars, and half a dozen where I've been let with any sort of lump. And in that time, only known 2 or 3 people who have hurt themselves beyond just going "ouch".

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Re: boom.

Post by trebor » Fri Jun 22, 2012 7:47 pm

Hi Rupert & Michael, thanks for prompt reply. Rob.
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Re: boom.

Post by roger » Fri Jun 22, 2012 8:36 pm

Rupert wrote:As for head bashing, don't worry about it. In nearly 40 years of dinghy sailing, I've been hit on the head dozens or hundreds of times,
!
That could explain quite a lot. :shock: :lol:
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Re: boom.

Post by Nessa » Fri Jun 22, 2012 8:41 pm

Can I start a range of boom bashing horror stories? I broke my nose on my contender boom once. Saw stars, had to wait some time before I could get home. No blood though.
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Re: boom.

Post by MartinH » Fri Jun 22, 2012 9:22 pm

Can I start a range of boom bashing horror stories?
Alright, if you must. :D

The first time my daughter tried a L***r (4.7 rig) she gybed unexpectedly (well it was Shearwater), got a bang on the head that could be heard all around the lake, which knocked her out of the boat. She seemed a bit whoozy when the safety boat picked her up so I took her to A&E and she managed to pass out on me part way there. She was well looked after by doctors and nurses while I stood around trying not to look conspicuous in my wetsuit.

Result: a beautiful pair of black eyes and a great reluctance to sail a L***r again.
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Re: boom.

Post by Nessa » Fri Jun 22, 2012 9:24 pm

knocked some sense into her then! 8)
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Re: boom.

Post by trebor » Fri Jun 22, 2012 9:34 pm

it is a question of what hurts the most the boom hitting some ones head or your ribs from laughing.
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Re: boom.

Post by jpa_wfsc » Fri Jun 22, 2012 9:43 pm

back for a booring moment to the original topic... a lot depends on the grade of aluminium. 6mm naff aluminium e.g gas flue pipe would be nowhere near strong enough to be a boom. With the right grade probably 1.5 to 2mm would be over the top in terms of strength. The weak point is always going to be how and where you attach fittings (e.g. kicker).

Probably cheapest and safest way to make a boom is to buy or be given a broken mast and cut it down to the size you need.

As for head bashing - if its bad its not funny, if its comical we all want to hear about it! Suffice to say my son Matthew crewing for an RS500 last year managed to bend its boom (writing it off, a biggish insurance claim) without noticing any pain at all till his skipper showed the bill to him! But then, Matt is a tight head prop so......
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Re: boom.

Post by trebor » Fri Jun 22, 2012 9:53 pm

the teardrop alloy tubing used on light weight push bikes would be ideal then, very strong and light also only about 1mm thick.
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Re: boom.

Post by Nigel » Sat Jun 23, 2012 8:11 am

Hi Rob

trebor wrote:the teardrop alloy tubing used on light weight push bikes would be ideal then
I would say that depends on the overall size. a Teardrop section 10cm deep by 6cm wide would be massively stronger and less bendy than one 5cm by 3cm. I think this was the point Rupert was making earlier.

Thinner wall and bigger profile is the way to go for best rigidity to weight (and of course the right material)

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Re: boom.

Post by Rupert » Sat Jun 23, 2012 11:14 am

John is right about old masts being a good way to make a boom.

As for the comment about my contact with booms explaining a few things, I think it might have more to do with the after sailing wind down of my earlier years. Mind, a bit tender this morning, too...
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Re: boom.

Post by trebor » Sat Jun 23, 2012 12:53 pm

the word "boom" is probably the most descriptive word in the english language with regards to sailing spars, I suppose clout or bash would also do at a pinch, I sailed a Wayfarer for the first time today, with the reef in the sail you would have to stand on tiptoe to get boomed, aft rigged, but still a lovely boat and fast, kept getting my dagger grip mixed up with my panhandle.
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Re: boom.

Post by fcdbm » Sun Jun 24, 2012 10:34 am

Good source of boom material are broken Laser topmasts. As it is a common failing, there is plenty of source material.

The tube is 50mm diameter about 1.5mm wall thickness.

The Laser boom is stiffened at the kicker with a second tube about 450mm long. You can slice a section out of an offcut a then force it inside the boom.

If the sail area is similar or less this will give you an adequate boom.

Before everyone goes on about the Laser topmast failure it is probably better to lose a topmast, than rip out the hull. ie when you strengthen something, then the next stage in the chain becomes the weak spot.

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