After-market jib-boom

[zoidberg]

I'm mulling over a 'mod' to my li'l old Cutlass 27 and invite views and opinions.... I cannot easily mount a furling asymmetric spi 'as is' but have the Bartel furling gear already - don't want a conventional spi with pole and strings - and am considering copying the 'Arkema' scow arrangement, with no bobstay ( shallow angle ).
Thoughts?

 

[flaming]

I'm mulling over a 'mod' to my li'l old Cutlass 27 and invite views and opinions.... I cannot easily mount a furling asymmetric spi 'as is' but have the Bartel furling gear already - don't want a conventional spi with pole and strings - and am considering copying the 'Arkema' scow arrangement, with no bobstay ( shallow angle ).
Thoughts?

View attachment 99093

If you have strong enough pole and a robust enough mounting point then you can easily fly a normal asymetric from it without a bobstay. The likes of J etc have been doing this for decades.

The strength issue comes when you want to use a code zero or similar which requires significant halyard tension. If that's your aim you will need a bobstay. One way of getting better geometry for the bobstay with a very "rakish" bow profile is to angle the bowsprit down. Another is to use a dolphin striker, but that does not easily lend itself to a retractable sprit.

 

[zoidberg]

Yes, 'flaming, thanks. That's what I want to do - but not with a Code Zero. And neither bobstay nor dolphin striker.

I'm hunting for a 'strong enough pole'..... of about 2 metres by about 85-90mm. 'Thick-wall'.

This is what I'm trying to do....

I have the FRP moulding ( shown 'white' above ) - and the SK99.....

 

[flaming]

Then I see no reason why that wouldn't work.

You'll have to get really rather lucky to find such a pole second hand though...

 

[zoidberg]

Yes......

Once again, we are 'on the same page'.


Peeps may be wondering about the pair of Hi-Load shackles.

My deck fitting for the forestay is set back from the bows and the bronze open fairlead there. It is of 'T- section ', about 18cm long, with 4 holes for shackles/toggles - and substantially through-bolted.
I could 'feed' SK99 ( near-zero 'creep' ) through those holes, but the sharp edges would concern me. Simpler by far to mount one or more Hi-Load shackles as shown. Yes, i could manage with just the one, but using two gives a far better 'D:d ratio' and consequent improvement on the weakening by being bent around a tight radius.

And, as shackles-and-chains guru Jonathan Reeves writes in his latest published article in Practical Sailor, loading shackles at odd angles reduces their load-bearing capacity. Using two in such a situation may be 'belt and braces, but it is a win:win solution in every sense, except for the 'angina of the wallet'.....

 

[TernVI]

If you have strong enough pole and a robust enough mounting point then you can easily fly a normal asymetric from it without a bobstay. The likes of J etc have been doing this for decades.

....

But the structure of the front end of a J-120 was probably designed around the pole.
In some ways the upward force on the bow is the easy bit, the downward force on the inner end of the pole is bigger and perhaps less easy when retro-fitting an existing structure. Even in a simple asy dinghy it takes some thought.

Of course it all depends how much wind you want to use it in. You might get a lot of benefit for sailing in F2-3, from a system which wouldn't survive F5.

 

[TLouth7]

There have been several threads on these fora over the last few years of members describing their approach to doing exactly this. It is possible to whack a sleeve down inside an aluminium tube to increase stiffness at the bow fitting (where bending moment is greatest). You may have better luck finding the threads by searching "asymmetric spinnaker pole" or similar on the PBO furum.

The downward force on the inboard end is a function of the inboard and outboard lengths of the pole, so keep this ratio as high as possible. Presumably you only need the outbaord section to be long enough to clear the forestay and pulpit, not some enormous skiff pole.

 

[zoidberg]

The downward force on the inboard end is a function of the inboard and outboard lengths of the pole, so keep this ratio as high as possible. Presumably you only need the outbaord section to be long enough to clear the forestay and pulpit, not some enormous skiff pole.

'Zackly!

 

[TernVI]

There have been several threads on these fora over the last few years of members describing their approach to doing exactly this. It is possible to whack a sleeve down inside an aluminium tube to increase stiffness at the bow fitting (where bending moment is greatest). You may have better luck finding the threads by searching "asymmetric spinnaker pole" or similar on the PBO furum.

The downward force on the inboard end is a function of the inboard and outboard lengths of the pole, so keep this ratio as high as possible. Presumably you only need the outbaord section to be long enough to clear the forestay and pulpit, not some enormous skiff pole.

As a retrofit, it's an awkward point load on a balsa cored deck, whereas if you were starting from a clean sheet of paper you'd design the inboard end to be supported by a bulkhead. One neat solution I saw was a gybing pole which sat on bits of deck which were reinforced for the bow cleats.

Once you poke the tack of the kite forwards, you tend to think of gybing with the sheets 'inside', which works better if the pole has a little bit of length about it. Having done a few races in, and a few more against, RS400s, the idea of gybing the pole has a lot of appeal if you want to head deep downwind. Might also let you open the anchor locker....