Carbon boom size?

Hoy,

For those of you with a carbon boom, what size are you using? Exterior diameter and interior diameter?

My new sail is longer footed than my old one, so my current aluminum boom is a tad too short. I'm just wondering what size to shoot for in carbon to have a boom solid enough to take the loads. For the record, I'm not sure I'm going to go carbon, depends on the price really, aluminum is cheap

I'm also wondering if a simple carbon tube can take the punishment of an internal cascade for the mainsheet if I choose to go this route as this would add quite a lot of compression that's not present when the sail is directly connected to the mainsheet blocks around the boom...

I'm not sure if there is any smartass white on white text in this question but I'll take it on face value and give the best answer I can.

A simple solution would be to add a sleeve to the tack end of your existing boom to get the extra length.

If you want to go to a new boom I guess it depends what type of tube you have available in ali or carbon. The filament wound tubes are strong and what we use in A's. 38mm OD for end boom sheeting and 43mm OD for centre sheeting. That is with a 1.8m foot. For a longer foot you'd need to go stronger.

For internal sheeting you probably need bigger ID than those to fit the blocks comfortably. I used internal cascades on my A's in the 80's (we called it an archemedes system) using a 50mm OD 1.2mm wall ali tube then rolled flat on either side to give it about 55mm x 45mm OD. The beauty of this meant the blocks all ran in one plane because they couldn't fall sideways and the boom was stiff in the vertical plane where needed. I had a local supplier who did this section quite cheaply. The advantage of carbon is you can downsize it over ali and get the same strength. In this situation you need the size to fit the blocks so no real advantage in going carbon. There's probably no weight saving and it will almost certainly be more expensive.

Cheers
AUS9

When I converted from a R sized main to a F16 size main I had a similar problem. However, I found that the boom was just long enough, I think I moved the through boom pulley to the very end of the boom or purchased I different type of pulley. It did work. That was on Stealth 516 and it had a rectangular alloy boom approx dim's 65mm x 45mm.
During the 2008 Global Challenge I bent Stealth's 555 alloy boom beyond repair, instead of making an insurance claim I made a new boom from the bottom section of a Windsurfing mast. It works well 99% of the time but there are the very odd occasions when a big gust hits I feel as if the boom bends slightly.
Way back in 2005 I remember racing behind John Alani who was using a part of a windsurfers mast as a boom and that bent like a Banana. So be careful, if you are willing to go down this route but can't find a suitable mast let me know I should be able to help but you'd still need to source a new goose neck fitting as the old Stealth's had a cast alloy affair.

If you want I can give you the dimensions of 555'S original alloy boom (It's behind the Summer House in the Garden). A phone call to Selden's could then be your best bet for an anodized alloy tube of approx the same size. I think you'd be surprised how reasonable their prices are for bare poles

Eric, Mark's right - when I bought 527 back in '05 it had a carbon boom that was 'self adjusting' - unfortunately it was the wrong way round in that the harder it blew, the fuller the foot of the main became.

IIRC it was about a 45mm dia. I replaced it with an ali boom made from the broken topmast of a Topaz and, to be fair, there was bugger all difference in weight once it was fitted out. If you want to go with internal blocks, go with what ACE suggests - an ali boom large enough to accommodate the system you want. If you go for a round section you'll need to devise a way to prevent the blocks twisting inside the tube.

Nice punch


My current boom is aluminum with a rectangular section. Finding a sleeve and an extension that matches is a challenge I don't want to even consider. It's probably cheaper to buy a new boom length in aluminum.

I found that there is carbon tube and carbon tube. Some are uni-directional fibres along the length of the tube, some are mandrel wrapped, some have extra layers on top. Quite the choice!

Thanks for the info so far. Good food for thought.

If it is of any help then I can state that a 50x1.6 mm alu round tube is up to the abuse and one of the lightest options available.

Wouter

Don't even consider carbon, it is just to brittle and will snap with our 90 odd kilos landing on it. Plus changing from rectangle to round is a lot more hardware than what you first think ( gooseneck for one )

Do what I did and just rivet two small SS rig adjusters to the end of the boom and mount the out haul pulleys through that. The Ali boom itself is long enough to cope with the sail it is just getting enough length to mount the out haul pulley ( I think mine only needed extending by about 30mm ).

In my copious spare Ali tube I have a 50mm x 1.6mm length just suitable for a boom, lets talk when next at Datchet

I forgot I had this in my garage. It's the top section of a RS Feva mast, you'll notice some writing on it, that's the length of my existing boom! If I remember I think it would be a good idea to put this in the trailer prior to Como.

What do you call a "small SS rig adjuster" Wayne? Link?

Sorry I didn't realise the existing section was rectangular. That must mean you have some serious loads on it because of either a lot of angle on your mainsheet to track or the mainsheet is mounted on the boom significantly inboard from the clew. If you're stuck with these things because of he structure of the boat then an over engineered boom is the only way to go. Sounds like some way to extend the boom at the tack end would fix it. A boom that bends under high load isn't good - might break but mainly bags up the bottom of the sail in gusts. Good luck with it.

Cheers
AUS9