B 22 Cat

[Dave Butler]

I am an amateur designer - avid sailor. I just posted some images of my design for a 22 foot trailer-able catamaran with hydrofoil assist and biplane rig.

Just wanted to get some constructive criticism from any knowledgeable designers out there. Images are under Dave Butler.


http://www.boatdesign.net/gallery/

 

[Doug Lord]

Dave, interesting. I have a question about the hulls-they look to be very close together and planing-is that right? If true it may cause a problem with the high low speed drag of the planing hulls. Hydroptere.ch uses planing hulls with a retractable step along with foils. I imagine the retractable step is there to reduce drag in pre planing conditions.
Your foils look similar to the Swiss lake racer, SYZ -how do you control altitude? They use surface piercing foils angled to create lift through speed-speed controls altitude. Your foils look like "J" foils with no vertical lift from the daggerboard section of the foil so they would probably need some sort of altitude control. Now if the foils are designed just for foil assist, they might do better under the hulls where they wouldn't penertate the surface. See the Nacra 20 foil assist cat below. Also, see the picture of Parlier's test cat with stepped planing hulls-non retractable steps.(last)
I "grabbed" one of your pictures and posted it below-if you'd rather I delete it just say the word.

click on the picture for a better view:

 

[Dave Butler]

Hi Doug, Thank you for your comments. Yes, the hulls are at trailering width. The whole purpose of the design is to develop a high performance multihull daysailor with camping style accommodations. (possibly an alternative to the F22) Each hull would have two singles. Or one single with a porta potty. I wanted to create a boat that could be set up very easily. Just unfold the racks, slide the foils in, slide the carbon fiber free standing masts into the sleeves and go!

You make good points about the planing style hulls they may not be useful on this design.

At this point I was only thinking the outboard foils and bi-plane rig would offset the narrow beam as far as stability and ease of setup not necessarily lifting the boat out of the water. Allthough I would not be opposed to coming up with a solution to control altitude to achieve this.

 

[Gary Baigent]

The pivoting foil and mast bases are very clever ... but there will be high loads at base areas. I made a mistake years ago with Misguided Angel having the bases (bi-plane rig, conventionally stayed) cantilevered in front of the main beam ... and one tore off when sailing fast under high loads. And yours are for freestanding rigs - there needs to be a decent bury plus support to handle your foiler/masts contrasting and twisting loads. Will require careful carbon layups and excellent bearings.
Since your cat is really a foiler, you don't need the complications of planing hulls; just make them conventional catamaran bilge shape - and then when not foil borne. will be far less drag than sticky planers, just imo of course.

 

[Corley]

I'm all for variety but cant really see the advantage of a catamaran in this situation maybe if your partner was a chronic snorer it might be useful otherwise a folding trimaran with hull flare offers more useable space in the main hull and you can put foils on it as well.

As Gary notes round bilge is preferable on this type of craft and you want the hulls to be efficient as otherwise you pay a huge penalty in drag and will never be able to reach the speeds required to foil under sail.

 

[Dave Butler]

Thanks for your comments! The primary reason for the design is ease of setup. I live in an area with many lakes and want something that I can set up in minutes. The slide in free standing rigs will not require any mechanism to raise the mast. I would have all the bearings, boom, and sail already in place on the lower section attached to the folding wings. All that would be needed is to slide the upper mast section in the sleeve and raise the halyard. I will try to add some more drawings as to how this would work.

I used to sell Corsair trimarans and 90% of the time most sailors leave the boat in a marina dry storage area with the mast up to save time and effort. I want to be able to leave this boat in my driveway and be able to launch from the ramp in 10 minutes with little effort.

 

[Richard Woods]

Fast assembly is always the holy grail of trailable boats. But I'm not sure your design is going to be quick to assemble. Mentally time out every move - being generous - 4 bolts to fit at 15secs each, 2 masts to step (say 1 minute each), 2 sails to hoist (1 minute each), 2 mainsheets/kicking straps to fit (30secs each). 2 daggerboard/foils to fit (30secs each). That's at least 7 minutes. Plus add for unstrapping two masts/booms and hull, and quite a bit of walking round the boat.

I once was sailing a Laser in 8 minutes from it being on the car roof - I was late for the start of a race. So two similar, but bigger, rigs will presumably take at least twice that.

Will you be able to sail on/off a beach with an onshore wind?

My attempts at the trailable boat daysailer are the Strike trimaran series. I felt the trimaran's deep "sit-in" hull made a better daysailer than the "sit-on" cruising beach cat (assuming no sleeping on board and no trapezes)

And as Corley says, the foils might work at speed, but you have to reach that take off speed first, which might be challenging in light winds - common on most lakes. Foilers have huge drag when not foiling.

Here are a couple of videos of my Strike 18 assembly

We once sailed back to the beach and 13 minutes later we drove away with the boat strapped down.

http://www.youtube.com/watch?v=fi49pEQk3gI

Raising the mast the easy way

http://www.youtube.com/watch?v=1OjzcWl0h6k

You can see more videos on my Woods Designs youtube channel and of course on my website.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

[Dave Butler]

Thank you Mr. Woods for your comments. I have looked at your designs many times and admire your work.

What I was trying to avoid with this design is a stayed rig. I owned and raced a Moore 24 for 20 years and it always took me 1 to 2 hours to launch and get ready for a race. Most of that time was tuning the rig. I also owned and raced a Nacra 5.2 and the idea of raising an unwieldy large aluminum mast is not attractive to me. I have raced on all the Corsair boats (love the boats) but the reality is that it takes 20 to 30 minutes of setup time even for the 24. I now race lasers because I like the simplicity of the boat. I really like the simplicity of no shrouds. I wanted to have a larger boat with the same simplicity but be able to take friends out for an afternoon sail without spending half an hour to put the boat in the water and half an hour to put it on the trailer.

The foils are not large foils. If someone could tell me if there is an advantage to having the foils in the hull and not surface piercing that would be good to know. I don't see them as creating a large amount of drag, anymore than boards in the hull. The Stilleto 27 had one large surface piercing board in the middle of the boat.

Again, thank you so much for your comments!

 

[Richard Woods]

The Stilleto 27 had one large surface piercing board in the middle of the boat.

Again, thank you so much for your comments!

Well they did until a keen racer took out the central board and fitted one in each hull. The boat was much quicker. So when the Stiletto 31 was built it had boards in the hulls

The original Prout Shearwater had a central board but they took it out almost immediately and put them in the hulls instead

Again, as I've said many times, a central board is so easy compared to one in the hulls that if it really worked everyone would do it. But it doesn't, so people don't

Richard Woods

 

[catsketcher]

Gday Dave

I think you will find the masts hard to get up quickly. I too am an ex Laser sailor and sometimes found the mast hard to raise in a breeze. Your masts look about 9 metres long. I am guessing they will weigh about 2-3 kg/m in bare section weight. The 9.3 metre mast on my little cat is 2.5/kg/m and that is stayed so it is lighter than a cantilever mast. In HM carbon you may get down to 2kg/m but still need halyards etc so that weight will go up.

So the all up weight will be at least 20kg and the CG of the mast will be 4.5 metres up. My suggestion to you is to get a 20 litre water container and put it on a stick and see if you can raise this up 4.5 metres and then pop it in a hole like the Laser. I am not weak but I am pretty sure I couldn't. Instead of one mast to raise with a gin pole you need two with gin poles and winches. Then you have to get it down into the hole which may be tricky. Search for the Cat2 fold video of them raising the mast. They had a tricky set up for getting the unstayed masts up.

I think 30 mins is fine for going sailing. When I raced Lasers most sailors spend more time than this getting ready and having a chat. The Laser can be rigged in 5 mins but most sailors potter.

I absolutely agree with your comments on raising the mast. It is the most stressful and worrying part of launching my boat. I have seriously thought of a gunter rig and telescopic rig to reduce rigging loads and time but in the end came back to a standard set up.

One other thing about your foils. They may be less useful in providing stability than you think. Foils work well at speed but stability is often needed at low speeds - coming out of tacks, hit by a big gust under a headland, after a big wave - so your cat will have an interesting stability profile which is dynamic. This is rather like a crew on a trapeze but with a crew you know when they are in or out. You will have to react quickly to times when the foils ventilate or get overloaded and the stability of the boat reduces just at a time when you need extra. This like a crewman coming in off trapeze during a gust.

cheers

Phil