what size grp tube for my stackpack?

[BlueChip]

My stack pack is fitted with s/s tubes about 22mm diameter, I'm thinking of replacing the stainless tubes - which are very heavy, with GRP or carbon fibre tubes but I don't know what diameter to use.
The stack pack is about 4m long, can anyone who's got one this sort of size and who uses GRP or carbon rod for support let me know what diameter rod they have and whether it's stiff enough or they wish they had a larger size?
Thanks

 

[prv]

For what it's worth, ours has fibreglass battens, about an inch and a half wide and maybe 3mm thick.

Pete

 

[BlueChip]

I want something which is rigid, I don't think battens will do it.

 

[alahol2]

I can tell you that my stack pack has 3m battens. They are 10mm solid GRP rod and are about the correct stiffness. I suspect, as they will be supported in 3 or 4 places along their length, that 10mm would be sufficient for 4m battens. I guess they are not very light weight if you compared them to carbon tube.

 

[BlueChip]

This site is interesting.
http://www.allproppedup.co.uk/
They say in their FAQ that tubes are stiffer and lighter than solid rod, so a tubes sounds best for this purpose.
Carbon is stiffer and lighter.

10mm GRP tube - £10.40 for 5m
10mm Carbon - £18.00 for 5m

so not a huge difference in price.

 

[vyv_cox]

My Kemp stackpack, new last year, has battens. They are flexible enough to roll up for transport, we took them as hold luggage to Greece in a coil of about 2 feet diameter and they were delivered to us the same way. Plenty rigid enough for their job.

 

[Billjratt]

Battens. They will bend to follow the stack taper but not sag, and lie nice and flat against the sail.
Seems tubes are used by DIYers, battens by pros.

 

[reeac]

It had never occurred to me that some stack packs used tubes rather than battens. I remove my stack pack from the boom every Autumn for dry storage at home. I find the lateral flexibility of the battens (and the bolt rope) very handy as I install it from the mast end of the boom with the boom in place and the whole thing slides past the mast and into place. It's a single handed job. The battens give rigidity in the vertical direction which is useful as the stack pack sides are suspended at intervals from the lazy jacks but I see no need for much lateral rigidity.

 

[lpdsn]

Like most people, my stack pack has fibre glass battens. Boom is over 6m but the stack pack itself is probably only about 5.5 metres.

Never thought of using tubing, but maybe it has advantages. I'd think carefully about how much abuse your stack pack gets. Carbon tube will shatter if overstressed.

 

[alahol2]

It had never occurred to me that some stack packs used tubes rather than battens.

Having had both flat battens and rods on two different incarnations of the stackpack (both professionally designed and made) I can only say I prefer the rods. The flat battens tended to swing around and bend in the horizontal plane when dropping the sail sometimes swinging under the falling sail so that they had to be pulled out. The rods keep a nice straight line in all planes and, to my mind, look neater both when stowed and when raised.
I guess it is down to the overall design of the 'package'. For example, my lazyjacks are attached directly to the rods through small cutouts in the pocket for the rod. So no stitched on tabs to tear cloth/fray/stitching getting UV pox etc.

 

[lpdsn]

Having had both flat battens and rods on two different incarnations of the stackpack (both professionally designed and made) I can only say I prefer the rods.

They do sound tempting. I'm just wary of the forces on the rods given the size of boom and sail. Battens seem to be far more forgiving.