Stretchy Stays

Would the springy stays that Bill Korsgard brought to our attention in the RC landyacht video (in Forums > Other > Gallery) be useful on RC yachts for water?

Seems like an inovative idea here, or maybe its just that I haven’t seen it before.

yar

I will jump in YAR with my two penneth worth.:stuck_out_tongue:

The reason the “stretchy stays” work so well on the land yachts ( LY) is that because there is no flex (or very little) in the axle mechanism , the stretch helps to absorb the gust and prevent capsize as the LY accelerates with the gust.
Whereas, the water yacht heels over with the gust and is dampened by the keel weight being shifted outboard until pressures are equalized and the resultant forward drive becomes the force vector most useful to us.:graduate:

That is not to say that having a bendy rig on a yacht is necessarly a bad thing.
On the contrary, a number of full size and model yachts use the bendy mast system to advantage.
The idea is to have the correct amount of flex in the top section of the mast so that the sail leech is allowed to free off enough, to depower the top of the sail and keep full power on the rest of the sail.
The main becoms self adjusting and the boat climbs to weather with out any further input from the driver.
When set up properly it works a treat. But that is another thread.:devil3:

To answer your question directly; YES, Stretchy Stays on a yacht could work great.:scared:

Whereas, the water yacht heels over with the gust and is dampened by the keel weight being shifted outboard until pressures are equalized and the resultant forward drive becomes the force vector most useful to us.
Would keeping the hull flat in the water in a puff, as the landyachts frame stays on the tarmack, be advantageous?

yar

The stretch in the rig absorbs some of the wind energy that should have been used to accelerate the boat.

Could be useful for the multihulls in keeping them from flipping.

I would have some concern in allowing a rig to fall off that much and then “snap back” to vertical. The land yachts to a lesser degree and ice boats have little if no (relative) rolling/sliding resistance, so they can make use of acceleration. Multihulls on the other hand have a lot more comparable friction. I would wonder if downwind, a “stretchy” shorud would let the mast tilt forward too much and help induce “tripping/pitchpole” ?

If a multihull tips to the side, you can control via rudder and sheeting if necessary, but downwind there aren’t a lot of options if the bows start down the mine shaft.

Yar,
To answer your earlier question, yes this has been done before. Kris Seluga has been selling his kits ( http://www.rclandsailing.com ) for several years using this system. Also, iceboats & landyachts have slacked off their side stays for decades as a means of spilling air in gusty conditions. We call it “slop”. My personal opinion is that it works fine in this application, but I’m not sure if you would be gaining alot of advantage on a monohull keelboat where the righting moment offered by the keel is serving the same purpose. It would be interesting to see it tried however, perhaps in conjunction with a lighter or shorter keel.

Ian,
Another way to achieve the same result on a landyacht or iceboat is to allow a fair amount of flex in the plank (axel/crossbeam). Compression load from the mast pushes the hull down, which changes the geometry of the rig enough to allow decent slop. When the gust subsides, the deflection springs back & the mast returns to vertical. In fact, I’ve been planing down the thickness of the plank on my full sized “Renegade” class iceboat to make it bend easier. I’ve reduced the load needed to deflect it to “flat” from 600# down to 475# & it makes quite a difference. I can feel the boat squatting down before it goes into a hike. On my models, I find the flexing platform to be more controllable than the stretchy stays.

Dick,
You have a valid concern about stretchy stays possibly causing a forward leaning rake when running downwind, increasing pitchpole potential. Not to mention forestay sag & loss of control of headsail shape. However, if one holds to broad reaches downwind & keeps apparant wind forward, this might not happen. Also, it should be possible to design a pivot/hinge mechanism which would allow lateral mast movement but not fore-aft.

Also, it should be possible to design a pivot/hinge mechanism which would allow lateral mast movement but not fore-aft

And here it is, or at least my friend Paul Dodge`s version of such a mechanism.

I am fascinated by the notion that letting the rig go forward on a land/ice yacht increases the tendency to pitchpole. Geometry suggests that this is the correct analysis.

However, the mythology of ‘water’ yachts is that letting the rig go forward over the bow has the reverse effect. I’ve aleways been very sceptical about this. Anyone have any comments?

Angus -

Land/ice yachts allow the mast to bow to the sides, not forward, although they do carry a huge amount of mast rake as well and thus any forward movement might not be as critical as when there is only an initial mast rake of just 3 degrees.

At 3 degrees of rake on an r/c multihull however, a bow down situation plus “stretchy” side shrouds - we don’t use backstays so mast can pivot - can translate very quickly into 10-15 degrees of forward rake. Pitchpole on a multihull is influenced (in part) by the mast moving (or trying to) forward faster than the hulls can keep up - similar to a monohull that pitchpoles and then broaches. Once the “lever” mast starts forward, it’s length and wind pressure generally overcomes the ability of bow buoyancy to keep up due to hull friction. On a land/ice yacht, rolling/sliding friction is so much less. The pitchpole also seems evident when a hull uses a high aspect ratio rig/sails. Also a factor in multihulls is we don’t count on a lead bulb to keep our hulls in the water and upright.

:smiley: This is because anything weighing a lot (like lead) seems to have strange impact on top speed! :stuck_out_tongue:

Cheers and have a good holiday season.

Ian,
I’m not sure how that would work. It clearly would allow sideways swing, but I’m not sure it would be able to withstand much forward bending moment. I was sort of envisioning a pivot point at deck level (similar to Paul’s), but with the spar extending below deck into a transverse slot that would only allow lateral movement. Or instead of a slot, perhaps a below deck tensioned cable would have less friction. The spar would still need to be quite strong (CF??) to be able to handle the leverage.
Bill