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Drilling and cutting the boom

 
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beaglebuddy



Joined: 10 Feb 2012
Posts: 501

PostPosted: Mon Dec 17, 2012 8:16 pm    Post subject: Drilling and cutting the boom Reply with quote

I have the Chinook 185 to 247 aluminum boom, If I can get it down to 179 I can fit it on two more sails I have. I suppose I could tie off a line to both sides of the boom to secure it but I'm not too handy with knots.
It seems that there is room to drill three more holes on the clew end to get to 179 but the rear end of the boom will not slide any further into the front end it seems because that is where the tube changes to a smaller diameter on the front end.
So if I cut 6 cm off the front of the rear piece it should slide in far enough but I will then potentially reduce the max recommended extension by 6 cm which would be ok because my largest sail will potentially be 239.
Boom is over a year old so I assume it's out of warranty?
There are rubber plugs inserted into the ends of the rear piece apparently to keep water out, not sure if they are salvageable but I could just put some silicone rubber caulk in the ends instead.
Opinions?
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mark



Joined: 10 Apr 2000
Posts: 102

PostPosted: Mon Dec 17, 2012 9:16 pm    Post subject: Reply with quote

If you are planning to use the boom at 239cm I would not cut off any of the extension. While in theory you would have sufficient length most booms are a bit stiffer when not fully extended. The extra overlap gives you a bit more margin. Have you rigged your sail that requires a 179 cm length? It may be that the suggested length is only close and you actually may need more. If you have an adjustable outhaul with blocks you will probably use up most of the extra 6 cm. Unless the sail is one that requires very little outhaul tension I would doubt the extra 6 cm space between the clew and the end of the boom will matter.

Another thing to consider is that the edges of the holes you drill will not be anodized and will corrode easier. Also if you go down the drilling path you may only want to drill one set of holes to fit your existing sail rather than 3 sets. Also to consider is how you can accurately drill the pairs of holes. I am not sure what equipment you have but accurately hand drilling them may be a bit difficult.

You should be able to remove the plugs. If they are damaged either wine or champagne corks make good replacements depending on the required diameter.
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isobars



Joined: 12 Dec 1999
Posts: 13267

PostPosted: Tue Dec 18, 2012 9:33 am    Post subject: Reply with quote

I've drilled and/or shortened many metal and carbon booms over the years without ever encountering any durability problems. You and BagelBuddy have covered the pitfalls pretty well; just drill no more holes than necessary, drill pilot holes, be careful, precise, and thoughtful, and the biggest short or long term hassle should be the plug. Some are glued in place quite securely, others free to move. The former can be a real beyatch if they need to be shifted; plastic pipe and a mallet can be our friend then. However, they can fall freely out once the glue is torn loose, in which case you'll have to install new plugs. I cut them from blocks of dense polyethylene foam using a sharpened section of old metal boom arm as a plug-cutter.

You'll probably hear some water trapped in the boom. Since an ounce sounds like a quart, don't waste much effort getting it out. The last boom I sold sounded bad, and I spent a frustrating hour or two removing what turned out to be an ounce, if that.

Mike \m/
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yvanboniec



Joined: 08 Mar 2012
Posts: 100

PostPosted: Mon Dec 31, 2012 4:39 am    Post subject: Oops I did it again Reply with quote

I drilled the boom (gore pic below).


At first, my electric drill would just slip on the carbon area and was not powerful enough to make a hole (so don't try this at home).

I had a friendly pakistani worker from a nearby hardware store do it for me with heavy duty tools that maintained the boom under the drill while drilling

I realised - a bit too late - that drilling was easier when the sliding part is on the boom.

After 7 holes, it went fine, so I decided to reward myself with a double serving of kebabs.



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isobars



Joined: 12 Dec 1999
Posts: 13267

PostPosted: Mon Dec 31, 2012 12:34 pm    Post subject: Reply with quote

What do you plan to use all those holes for? They do weaken the boom.
You were asking about shortening the boom, yet appear to have lengthened it by reducing its overlap with the outer arm. Risky business, especially with all those holes. That 50 cm extension mark is underlined for a reason; it means, "This boom is not engineered to withstand the stresses generated by less overlap".

Mike \m/
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swchandler



Joined: 08 Nov 1993
Posts: 5435

PostPosted: Mon Dec 31, 2012 2:37 pm    Post subject: Reply with quote

Yikes, that guy at the hardware store really did a screwball job lining up the holes.
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slinky



Joined: 24 Aug 2007
Posts: 395
Location: Old Saybrook Ct.

PostPosted: Mon Dec 31, 2012 2:43 pm    Post subject: Reply with quote

beaglebuddy, 6cm is 2.36". I would try rigging those sails on the boom as is, just outhaul so the clew is a few inches shy of the boom end. The clew will move slightly side to side, but not enough to make much difference. I have a friend who rigs his small sails on a boom that is about 6" or 15cm. too long. It will work. Also mark raises a good point, that the boom is stronger, and stiffer when it is not fully extended. Leave well enough alone.
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rich1



Joined: 10 Apr 2000
Posts: 156

PostPosted: Tue Jan 01, 2013 12:05 pm    Post subject: Reply with quote

I'm with Slinky on this one. 2.5" is nothing. Rig it, and if you really want to, you can use the excess out haul line to tie the clew to one side of the boom, but I wouldn't bother.

Definitely not worth shortening the booms for. I've done all kinds of boom mods, extensions, shortenings splices etc, and I wouldn't bother with this myself for the sake of a couple of inches.

Chris
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isobars



Joined: 12 Dec 1999
Posts: 13267

PostPosted: Wed Jan 02, 2013 4:58 pm    Post subject: Reply with quote

I don't like slop at the end, as it lets the sail pop and jerk during sheeting transitions. I live with an inch or two if I slack off my outhaul offshore, but if I expect to keep the outhaul loose for a while, I'll shorten the boom. It's not a BIG deal, but its nuisance factor increases with gustier winds and maneuvering. 3" is very obvious, distracting, and sloppy every time I change my sheeting load (in vs out), which is many times per reach and often pretty rigorous.

Mike \m/
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