Spinnaker Topping Lift Routing?

[Baddox]

I have recently bought a spinnaker and instead of flying it free, I would like to use a spinnaker pole.

The 30ft boat already had a sheave box half way up the mast which would be ideal for a topping lift for the pole, however the previous owner fitter radar on a bracket a couple of feet below the sheave box so the topping lift would foul the radar.

I’d prefer not to move the radar or cut a hole in the mast for another sheave box, so wondered if a halyard lead could be used to route the topping lift down the mast to below the radar. Would a halyard lead be up to the job of surviving the angled pull when supporting the spinnaker pole? Is there a better way of doing things? Does a spinnaker pole exert much force on the topping lift – I’ll have a downhaul below the pole?

 

[johnalison]

Sounds a reasonable option but God didn't invent masts to put radar on, they're supposed to be for sails.

 

[PaulRainbow]

Sounds a reasonable option but God didn't invent masts to put radar on, they're supposed to be for sails.

Don't be silly, you can't mount radar on the sails.

 

[lpdsn]

I’d prefer not to move the radar or cut a hole in the mast for another sheave box, so wondered if a halyard lead could be used to route the topping lift down the mast to below the radar. Would a halyard lead be up to the job of surviving the angled pull when supporting the spinnaker pole? Is there a better way of doing things? Does a spinnaker pole exert much force on the topping lift – I’ll have a downhaul below the pole?

You should be able to adjust the uphaul by hand so that should give you a feel for the forces involved. Can be more force on the downhaul if the kite wants to sky. If you can get a suitable lead then it should be strong enough. You sometimes get fractional halyards for spinnakers that come out of the top of the mast and are led down to just above the forestay and the loads there would be considerably higher.

That said, I think I'd just move the radar and use the original arrangement.

 

[William_H]

Yes run the topping lift down the mast to a sheave attached to the bottom of the radar mount. A topping lift typically emrges from the mast midway up. So a bit lower will not be too much of a concern. Initially the load on topping lift is just the weight of the pole. However when shy you might find topping lift takes more load against down haul. Pretty hard to adjust the topping lift with that load. My pole (a wind surfer cf mast section takes a decided bend) It is desirable to raise the pole a little when shy to free off the luff. Hence topping lift pressure. I had better explain that olewill loves to race (every Sunday) and typical winds give us a very shy run in one area when winds are usually around 15 to 18 knots. I do run a smaller spinnaker for these days but do delight in flying it when all other people have more sense. (don't fly spin.)
Mostly just to show off a brilliant crew. I also like to watch others with their big spins get into real trouble trying to follow. (show us your keel is the cry) olewill (the crazy)

 

[[70521]]

Sounds a reasonable option but God didn't invent masts to put radar on, they're supposed to be for sails.

But masts are really useful for putting radars on, unless you only want a visible horizon of 1 nm.

 

[lw395]

How much load the topping lift sees depends on the configuration of the pole downhual/foreguy and guys. If you move the guys well forwards, they can turn the sideways/forwards force of the kite into a lot of downforce.
I haven't explained that very well have I?

Look at the vectors. To prevent the pole ever skying, the guys/foreguy/downhaul can put a lot of downforce on the pole sometimes, the pole-up has to resist that.
But the force on a pulley below the radar won't be a big fraction of the pole-up load, if it's only deflecting the pole-up through a small angle.

As ever it depends on how much wind you fly the kite in. If you're going to surf with the big boys in RORC, it's a lot more serious than a cruiser who only uses his kite for progress in force 2.

 

[johnalison]

But masts are really useful for putting radars on, unless you only want a visible horizon of 1 nm.

I find 12-20 miles for picking up ships from my pole more than adequate, though I appreciate that moving a radar is a major job that the OP won't want to do. No sea-clutter from a lower position is another bonus, and I know that sailorman would agree.

 

[Baddox]

Thanks for all the feedback. Moving the radar isn’t out of the question but I’d really rather not as the sheave box is just above it and a radar reflector is above that. Putting the radar any further up the mast will move it progressively close to the forestay.
Overall, I think I’ll go for the halyard lead first and consider moving things around next time the mast is unstepped. We're not racers and so far have only had the spinnaker out in winds up to about 12knots.