I should have made my initial question clearer, I'm an experienced mono and cat sailor, I'm totally familiar with the all the downwind sail options available, I'm looking technical opinions and observations concerning using the combination of topping lift and main sheet to offer support to the upper, un-stayed, mast section. Clearly I can fit runners, I'm just interested to here thought on the topping lift/main sheet combo.
That combo will provide a force in the aft direction. If the centre of effort of the sail were to swing sideways - as they can do if not hauled down fairly hard- they will pull from the side. This may result in a frequency situation, whereby the motion rocks from side to side working on the mast tip. The amount of side pull depends on the amount the sail is allowed to swing. It can be made worse by the boats motion over the wave, even though it may seem in line with the centre of the yacht.
Absolutely.
good point on the side loads, the traveller is 5m long so, say te wind is 170-160 on the port quarter I can move the traveller to port to compensate. The cats roll motion limited and very slow, the sail will use guys to both bows and sheets to both stern quarters so there should be good stability
DD had just answered that and I had agreed with. Only provides some support in a single dimension (aft if traveller centred). Zero benefit for lateral loads. And if pulled on tight enough to help fore and aft, will increase tension load on mast.
YES! hadn't thought of using the main halyard for addition support, many thanks for that!!
mast compression load?
That got me thinking, better still I could use the topping lift to one quarter strong point and the main halyard to the other, that would also avoid compression on the boom/gooseneck
You did say you wanted a low hassle solution I thought. I think the main thing opinions have thrown up is that it’s going to require a bit of setting up each time, and that setup isn’t going to be guaranteed bullet proof. Which is what I'd want for long distance/ocean crossing. There is going to be a risk from doing this, setting aside my own misgivings about kite flying and recovery. Setting up your topping lift and main halyard every time is going to be more hassle than running backstays, surely.
many thanks for your detailed and constructive comments
running backstays need to be detached from the quarters and attached to the chain plates when not in use so that they do not get in the way of the boom. They also require tensioning tackles and create windage when they are not in use. Using the topping lift and main halyard is arguably no more complicated to deploy and by using existing gear, more efficient.
The norm is just to slack them off. Will that not work on your boat? You won’t have chafe on your main if you’ve dropped it.
Sorry if you feel offended by my reply but my experience on this forum, besides my sailing experience, I made the assumption that the question you posed was from someone inexperienced in handling a spinnaker. I did note you joined the forum in 2009, but you have hardly posted on the forum over the past 14 years. I also know there are lots of "experienced" sailors who have one years experience multiple times. Thank you for clarifying your question with information that should have been included in the original question.
Running back stays are generally used to support the lower section of the mast - eg for a spinnaker or jib set BELOW the masthead. They don’t go to the masthead, where there are usually fixed backstays. Except for more modern / racy rigs with square topped mainsails - in which case flying a kite from the wrong place is likely to be even more risky as any modern rig is likely to be optimised for the designed rig (not just over specced as was often done in the past as too difficult to do calculations manually).