Will the wealth of knowledge please explain the con's of a rigid lower mast and flexible upper mast application to for a catamaran, especially in light of the diminishing needs to travel the boom all out on the spi boats running predominately upwind/downwind courses?

Are you refering to the Hobie comp tip?

Refering to the hp dinghy/skiff's with aluminum bottom and carbon tops.

call me ignorant... but I have seen the term "comp tip" around this forum a decent amount but don't know what it is. Can someone explain what the heck it is?

When Coleman (then Hobie's parent company) was sued regarding a death involving a hobie mast and a power line, part of the settlement was that Hobie, from thence forward, would install non-conductive upper masts on all its boats sold in the US. I don't think the Tigers (a HobieEurope product) have 'em, but most all the 16/17/18/20's do. ALL the 20's; they were introduced after the decision. Essentially, the top 4 or 5 feet of the mast is plastic.

John,
What most small boat rigs (cats, dinghy’s, skiffs) are striving for upwind is to depower the rig in a gust, and to keep boat as powered up as possible for the wind and righting moment of the boat. A powerful rig on a small lightweight boat is great until the wind exceeds your righting effort, then it needs to have some depowering mechanisms or you end up swimming.

Dighy's and cats do this in different ways, dinghy’s (generally) have fixed round-ish masts, and cats (generally) have rotating masts that are teardrop or wing mast shaped.

The mast you are referring to makes the top of the mast more bendy than the bottom, so the top "bends off" in a gust. If you look at an i14, it has double spreaders and control lines for each set of spreaders, so you can control the bend of the top of the mast vs the bottom of the mast. This is a way to control the way the mast bends off in a gust and can help keep the boat powered up in a range of wind conditions. Its overly complicated in my opinion.

A modern catamaran rig, which rotates, has a wingmast shape, a powerful downhaul, and a square head sail and you have lots ways to adjust your rig the wind conditions. Add in a carbon mast which can be customized to your weight and bend characteristics specified by your sail maker and you have one of the most advanced rigs available today. The modern A cat rig is a good example of all of these advanced features. A modern rotating cat rig is a very clean, elegant, and forward thinking way to adjust your rig for a wide range of wind conditions, I am surprised the skiff/dinghy world doesnt embrace it.

Wouter will be able to catalog the current high tech cats and their masts. He posted a discussion on wing masts a while back which speaks to some of this. Maybe a dinghy sailor can help us with the current thinking on dinghy masts.

A comp tip has no redeeming sailing qualities, I've heard discussions that it is too flexible. No other modern catamaran mast has a comp tip. So that should tell you something.

Bill

Complicated, but seems as though all the "latest" designs, 49'er, 59'er, Vector, etc. are using it also.

They have powerful downhauls, without the rotation feature, and like you I'm suprised. Why not? (I probably shouldn't ask this here, in this thread, but what is the origin of the rotating mast) What is the current dinghy thinking?

Being a Hobie owner (one w/o comp-tip) I'm not going there....again.

If my memory serves me right the posts I devoted to this topic back then are still accurate. Catamarans in general are still converting from tear drop shapes masts (hobie, prindle, nacra) to the elliptical wingshaped masts (A-cats, F16's, Capricorn F18). All other mods like different layups of carbon are on a differt level in the way of gains, there are more to be considered refinements. Meaning that changing the layup of a teardrop shape carbon mast wins you less than getting any elliptical wingshape mast.

I have not seen any new fundamental developments in mast design after the upgrade to elliptical wingmasts. I agree with Bill here that these wingmast rigs (as found on A-cats, F16 and Capricorn F18) are pretty darn efficient. It will be difficult to find a new technique that will again be a major improvement.

Do a search on this topic. It has been covered several times now. Also do a search on the F16 forum if you are interested in the specifics of a wingmast. There are some posts that deal with the differences between it and more conventional masts.

In the way of dinghy's I feel that many people forget that the right stay tension (they have alot more of them) is a way they use to change mast behaviour to suit the conditions. Cat rigs allow you to do this mostly on the fly while sailing (with exception of diamonds) In this respect I call cat rigs superior.

In addition a fully automatic rig can only work great in its design conditions and mediocre outside of those. There is a reason why some skiffs and surfboards use different rig in different conditions. I call this a pretty brute force approach. Sort of chancing the gearbox in a race car to suit the track and weather conditions on a given race day. EXPENSIVE.

Wouter

When I was still sailing 49-ers I thought the downhaul was anything but powerful. It had only a 1:2 purchase on it and the travel length was kind of short. I also thoughts its effect to be almost negligiable. In no way does it compare to my own 1;12 system on my own cat. With that I can actually see the mainsail go from full draft to really flat (no draft). On the 49-er you really had to look hard to notice the change.

I feel that the 49-er design gambled that most crews would set mast bend by adjusting the stay/shroud tension on the shore and then only need a little (weak) downhaul to do the last bit of fine-tuning. This requires alot of experience and an excellent feel for trim by just looking at the weather forcast or a quick glance over the water.

I was NOT impressed.

Wouter

In the past (I'm not into dinghies that much anymore) the setup was far more along the lines of alu bottom and GLASS FIBRE tops. Afterall carbon is a very stiff material, something you are not really looking for when making bendy tops.

Wouter

Unless you use the geometry of the mast (tapering from top to bottom) like in windsurfers to change the stiffness instead of the material properties, then all carbon is the right way to go.

Gareth
www.fourhulls.com

A common A cat mast adjustment is diamond tension that can be adjusted while sailing. This is done by terminating the diamonds at a lever and then running a set of pulleys to a block which can be controled while sailing. See picture.

The nice thing about this setup is you can start with diamonds fixed to the bottom of the mast and shorten them later to the adjustable system.

Bill

another example

Colin's Flyer has adjustable diamonds

http://sailwave.com/flyer/

Mostly cribbing this info from Bethwaites book, but modern skiff don't seem to bother with rotation because with their sail carrying power and ability to plane upwind and down, and the fact they always use spinnaker off the wind keeps the apparent wind so far forward that there isn't a benefit. They have evolved in simplicity too, with the primary adjuster on the water being the hydraulic cylinder the mast is mounted on controling the sensitivity of the "automatic" upper section, and the outhaul manually controling the lower half. I wouldn't be suprised to see a move that way in cats too, as downwind speeds increase to where in effect the boat feels like its sailing upwind all the time....

Bill,

I'm not sure what's more impressive, the carbon diamond wire adjuster or the fact that the mast builder signed his work! MMMmmmm...that's perty.

SB,

Skiffs are exciting, but they're slower than cats. Our spinnaker cat apparent wind is more direct than theirs and we still rotate to 90 degrees downwind. Mast rotation is incredibly important in all catamarans (especially in A's) to be faster. It gives incredible control over sail shape and I don't understand why so few mono/dingy/skiffs have explored the idea. I think the rotating mast is terribly simple performance gainer that the monohullers have continued to ignore for some reason. Oh wait...it is heavier aloft and when you have very little righting moment, the gains for adding the weight up high are small - maybe that's it?

Jake, what the heck do you think you're starting here :P

A lot of the Open 50 and Open 60 classes are moving to rotating masts, either with outriggers to widen the shroud base or hinged speaders, but is a cat faster than say an Aussie 18? I personally don't have any head to head experience but would love to hear from those that have...

A big reason why a lot of HP monos do not have wing rigs is because they carry mast head kites and need the support of upper diamonds. To many $$$$ have been invested into developing their rigs to start from scratch with a wing mast.

Some monos have carried wing masts for some time such as the NS14 and MG14 which is an NS with spinnaker.








A wing mast was also tried in the NZ R Class skiff (simular to 12 foot skiff) and showed good speed but I think they strugled to keep it facing skywards.

indeed, but only the A-cat and Formula 16 class rules allow this type of adjustment while racing. As far as I'm aware ALL other catamaran classes forbid this kind of adjustment in their class rules. Certainly the F18, F20 and all one-design classes do so.

I seem to remember that a few A-cats even have linked up their downhaul and diamond wire tension systems so that pulling on the downhaul also adds some tensions to the diamond wires.

I must say however that this system hasn't caught on in the F16 class yet and not too many A-cats seem to be using it either although more so than in the past. I know the boats coming through Peter Saarbergs shop tend to have this system but not many others. At least that was the impression I got when I last checked up on it.

I'm not really sure how good this adjustment is in real life sailing. A guy at my club uses it and he is indeed a very good and fast sailor. He is always scoring a place in the top 3 of our races, he sails an open 15 sq. boat = a rather heavily modified A-cat (wider, more sail area, fully angled boards etc). But he seems to adjust it mostly on the beach dependening on the conditions and only during sailing in large waves where he wants some extra power to punch through. I seem to remember he tightens them while sailing with the waves (flattening the middle of the sail) and loosens them when sailing dead against the large waves. In other conditions I don't think he adjust the system at all. Of course the first (on the beach adjustment) can also be done (and ist done by serious crews) using the turnbuckle adjusters. The adjustment on the waters seems to be pretty rare. In my personal experience the potential to make the wrong adjustment is rather significant so some form of calibrated scale is needed. Meaning that if you don't return to the right amount of tension (high) for the upwind leg can really kill your pointing ability (to flat middle section) or make the boat slow (to full in the middle. Or even a combination of both.

The biggest advantage of the system is however that it allows you to play with it during training and thus learn heaps on the right mast tuning (prebend). This is alot more practical then setting some prebend and spreader rake, go out sailing and then go back to shore, adjust the turnbuckles and do a test sail again. havin said this I know teams that bring a spanner with them while training and adjust the diamond on the water as well till they have the setting they want.

With regard to F16's I don't know wether this system will catch on as it is again another line on board that needs to be lead away with some bungee system and the spinnaker negates pretty much all fine-tuning for downwind legs. This allows you to setup the boat fully for upwind work and just have the spin drag you downwind not wasting time in adjusting the settings. F18 and others (if it were allowed by their class rules) would probably show a similar trend.

A-cats of course don't have this (major) chance of sailing setup and here fine-tuning of the mainsail for downwind sailing has the potential to really pay off.

And that is what I know about this system as of yet.

Wouter