Crowther Shockwave Design

I am looking for a mast as sail plan for my 29ft Crowther Shockwave. I recently purchased the boat without a mast so can’t wait to get on fitted. I would like any information on the design. Thank you in advance.

 

Is this your fine cat?
Used Crowther Shockwave 9 M Catamaran for Sale | Yachts For Sale | Yachthub https://yachthub.com/list/yachts-for-sale/used/sail-catamarans/crowther-shockwave-9-m-catamaran/292391

It looks like she was designed / built specifically as a power cat, as I cannot see fittings for rigging anywhere.
Edit - I just saw this comment in the advert - "Chain-plates, mast step and wiring in place, make it easily converted into a sailing catamaran."

Maybe @oldmulti can provide some more info on a possible rig?

 

Thank you for your reply although The catamaran is ready for a mast all the chain plates, wiring and mast block are in place. Totally ready to add a mast.

 

Hi Letitride,
Congratulations on your new catamaran. Try Allyacht spars in Brisbane for rigging & Uk Halsey Brisbane ( Gary Saxby for sails). It looks like your cat came out of a mould. I would like to build a cat like yours. Is there any information on who built your cat?

 

This a redesign of a cornell catamaran (fountaine pajot before building the current cake apartments)


4 "aerorig" style free-standing masts (Windsurfing sails will do with a reinforced mast), 4 kick up or pivot leeboards and 2 DDS kick up stabiliser foils in the bows

Easy to self build and doesn't create extra loads so you don't need extra reinforcement, and wave or wind capsize-pitchpolling risk is reduced to bare minimum

 

No, the Shockwave WOULD require reinforcement to take that rig, because it's not meant to take the loads of those masts. This is very basic structural engineering. Lock Crowther was not a fan of unstayed masts at all because of their structural problems. The 29 does not have mast step structure build into the hulls.

This is a very, very bad idea.

Aerodynamics 101 is that a low multi-mast rig has much higher induced drag than a comparable single-mast rig so it goes much slower unless you spend a lot more to put on a lot more sail area. Have you ever sailed a fast multi? Do you understand the concept of apparent wind on fast multis?

There is not a chance in hell that windsurfer sails would do. Modern style windsurfer sails are very low lift for their area but also very low in power. The extreme mast bend and batten tension they use means that there is a very high amount of friction when getting the mast up the luff sleeve, and coupled with the very high downhaul tensions they need it would make hoisting them a nightmare. In addition, the luff tube and curve mean that such sails are impossible to drop properly, when you try they form enormous and very awkward bundles (rolling is impossible in this situation) and they break down quickly when crushed into a fold.

Have you ever windsurfed? You clearly don't know about windsurfer sails.

The foil in the bow idea has been tried in multis before, including by Lock Crowther himself. It's a disaster because once the angle of attack goes into negative the boat nosedives so instantly and violently, as Lock himself found out when he tried it on an A Class.

Have you ever sailed a foiler or a fast cat? Do you not know about why they put foils where they do? Can you seriously believe that you know more than the world's best multi designers about where foils should go?

This is a collection of dumb ideas and the fact that you throw so many insults at real designers while making such unrealistic posts is bizarre.

 

I know multi windsurf sail foiler . Freestanding mast reinforcment is neccesary . I also find the front foil position counterintuitive if it's placed in the middle of the ship , eg AC72.
History of engine propelled hydrofoils shows different positions of front foil .
USS Plainview - Wikipedia https://en.wikipedia.org/wiki/USS_Plainview and e.g. USS Tucumcari - Wikipedia https://en.wikipedia.org/wiki/USS_Tucumcari

 

Montrero, there's plenty of issues with bow-mounted foils.

1- A full foiler (ie one that raises the hull from the water) needs a vertical section ("mast" in windfoiling) and if that is at the bow of the boat, it slows tacks and gybes dramatically. Secondly, it moves the CLR forward to make tacking even harder.

2- The bow experiences the greatest amount of vertical movement in waves. That leads to a hull-mounted horizontal foil often breaking clear of the surface and ventilating when the bow pitches up, causing a dramatic and sudden loss in forward lift with all the major problems entailed.

3- When the bow pitches down a bow-mounted foil can experience a negative angle of attack, causing an instant nosedive in fast craft. That's what happened to Lock Crowther, designer of the Shockwave, when he tried it on an A Class. The guy he was sailing against said it happened too fast for him to see, so he asked Lock to do it again....

When the actual designer of the boat has tried something and found out how bad it is, people like Herreshock who doesn't seem to have any practical experience should not say it will work. I knew and sailed with Lock and he was incomparably smarter, more experienced and more knowledgeable than Herreshock.

4- The increased motion at the bow causes unsteady flow over the front foil even when the foil does not ventilate, harming its efficiency.

5- The foil reduces the ability of the bow to lift to waves when the boat is not foiling. This means that, for example, far more of the hull is dragged through each crest, increasing wetted surface and (in boats with flare) reducing the effective bow angle. In some craft this doesn't matter too much but in others you can feel the way the foils prevents the boat lifting to waves is a real killer of speed.

6- It's impractical to mount a wand or other sensing device on bow-mounted foils.

7- The lack of beam and space in the bow can cause structural and housing issues for foils.

8 -Reducing pitch can be done much more effectively by mounting foils at the stern, which eliminate the above issues and still reduce pitch.

The USS hydrofoils were much bigger relative to waves, which cured many of these issues, and also still had poor seakeeping in heavy seas.

Those who have sailed foilers normally intuitively understand why they are like they are. Foilers crash much harder than other types, even when the speeds are no higher, probably because once the foils are at a high angle of attack they cause the craft to stop dramatically instead of skipping over the surface. Foils that generate negative pitch also generate painful impacts!

 

Thank you for comprehensive answer .
Ad6 With small boats and light chop it seems to be ok.

 

Yes i suppose pitching stability foils should be placed in the bow rather than midship as some commercial DSS for sailboats

Probably it damps the sinking and lifting of bow when encountering waves

 

It will be tricky without active angle control.But not impossible.

 

What kind of rig will the best for this 29ft Crowther Shockwave ? Shorthanded.

 

I suppose a pivot horizontal foil on the midship-bow area can have an angle of attack just like common airplanes lifting the boat, that would be enough

 

Shorthanded racing? Shorthanded high performance fun? Shorthanded oceanic crossing? And for who? Is cost a significant factor?

Originally the early Shockwaves had a rotating mast, headsail of about 150% overlap, and fully battened main with a moderate old-style roach. These days one could go for a short overlap jib with a screecher, and move the mainsail roach up. But if you go for a squaretop you get the annoying top batten issue, and unless you have good low-stretch sailcloth and mainsheet the upper leach position can vary too much. Personally I'd just go for a lighter fixed mast of smaller section and use mast bend to depower rather than a wingmast unless you can use top-class fabrics.

I'm not hugely experienced on big multis and I've never sailed a 29, but I've sailed one of the Super Shockwave 37s once, and Lock's own Super Shockwave 37 quite a few times. I've also raced a couple of 31' tris inshore and offshore and done cruising and messing around on other cruising multis, a D Class, and owned a few small cats.

Herreschock likes foils but Herreshock refuses to give information on his experience and from the claims he makes I suspect the closest he's got to a sailing boat is watching one on computer.

 

What is the benefit? Lifting foils can be very difficult to make and the boxes have to be very strong. One of the reasons they were problematic on offshore multis for so long is that while changes in buoyancy, CoG and CLR happen comparatively slowly, foils can lose lift in an instant. If you are relying on that lift and it vanishes due to weed or ventilation, you're in big trouble. Those factors don't effect other forms of stability. If you're not reliant on that lift then it's drag and complexity.

Secondly, the evidence from SCHRF stats, which rely on many races, is pretty clear that even changing a cat into a full foiler normally only increases its speed by about 3-4%. The increase in cost is dramatically more than that. There is a bigger performance increase to be gained by fitting a spinnaker, and probably much less overall hassle.

While some craft do gain speed dramatically by going full foiling, they are classes which already have very low drag hulls, high righting moment, high-tech construction, very efficient flat sails of top-end laminates, and extremely good foils. If a design doesn't have such things it struggles to foil and is held back by aero drag and other factors when foiling.