Foiling Sailboats, Foiling Beach Cats

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Bill Roberts
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Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Foiling Sailboats, Foiling Beach Cats

Post by Bill Roberts »

Foiling sailboats and foiling beach cats are the latest point of interest. Why is ARC not into foiling beacg cats???

Answer # 1. Cost of the Boat. Sizing the foils and their design etc is the easy part.
For example lets say we want to lift a 300 pound boat with 300 pounds of people on it, 600 pounds total. Lift = lift coefficient X foil area X water density X vel**2 / 2 X gravity(32.2). Let's say we want this boat to become foil born at 15 mph or 22ft/sec. Therefore the lift, 600 = Lift coefficient X foil area X 64 X 22**2 / 2 X 32.2 = 1.24 ft**2 for a lift coefficient of 1.0 and 1.0 is reasonable. Now that wasn't too bad was it? Now we are foiling at 22 ft/sec and the drag is greatly reduced and in a few seconds we are going 50% faster or 33 ft/sec. At 33 ft/sec the lift will increase with vel**2 so now the foil lift is 1350 pounds and the foils/boat climb right out of the surface of the water and the lift goes to zero and the boat suddenly stops, crashes, with a big splash. So, now we see that once a boat is foiling, the lift, therefore the foils, "must be controlled" to keep the lift constant at 600 pounds. Now we see the difficult part of foiling design. It is CONTROL of the lift. This can be done by varying the foil area or the lift coefficient or the angle of attack of the foil.
To build the best, lighest weight and fastest, 20 ft foiling catamaran you are talking about an all carbon boat built with prepreg cloth and Nomex honeycomb core cured in an autoclave. You are talking about a 100K boat at least. Now, how many do you want???

Answer # 2. Where are you going to sail this boat???
For the last Americas Cup several locations were considered.
How about Newport, RI? Several Americas Cup races have been held there. ans: Not enough consistent and dependable wind.
Well, how about Anapolis ? Not enough consistent wind.
How about Charlston? They put on the Olympics there. Wasn't that good enough? Not enough consistent wind.
Well how about Miami and Biscayne Bay? They get good winds there when the fronts come through in the winter. The strong winds, 15 to 20 knots, last for two or three days. The AC needs two weeks of dependable wind.
Well, how about Tampa Bay? Same as Miami in the winter.
Well, let's go on around the coast to New Orleans. Not enough wind.
How about somewhere in the Baha? No big cities and technical support and wind questionable.
Well, Los Angeles? Need more wind.
Monterey Calif? Need more wind.
Newport Beach? Need more wind.
Well, how about Atlanta Ga? That is a big town and they have lakes. No wind!
How about Salt Lake City or Denver Col? Wind/weather problems.
Guess what, here we are back to San Francisco Bay. There is a big city with technical support
and the necessary wind conditions. Even here the races were not sailed for a couple of days because the weather was not up to requirements and one race was not counted because it ran over the time limit.

Summary: If ARC built a foiling beach catamaran, who is going to buy one at 100K+ dollars
and where are you going to sail it on a regular weekend basis with wind /weather to go foiling?
havliii
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Joined: March 27th, 2011, 8:12 pm
Boat Make/Model: SuperCat 19, Modded SC20
Location: Fredericksburg Virginia

Re: Foiling Sailboats, Foiling Beach Cats

Post by havliii »

Bill, Great to see you posting again! What projects are you cooking up these days? Foiling is not my cup of tea no matter how refined or simple it gets, just to much 'hassle' for a trailer sailor like me. What am I gonna do when I run aground with all 4 foils down at speed? (Running aground is pretty much a guarantee in the Chesapeake Bay!!)

Somebody is reviving (or attempting to revive) the Stiletto. They plan to offer a foiling option. I'll attempt to cut and paste their P.R. here, not pumping for them I could care less, just for general interest.



Check out the final hull shape -- FAST, TRAILERABLE, BEACHABLE, AFFORDABLE catamaran, the Stiletto-X!
unnamed.png

Stiletto X-Series
FAST, TRAILERABLE, BEACHABLE, AFFORDABLE
A new Stiletto Catamaran has been discussed and whispered about for decades, and now Stiletto has married the old with the new to launch the Stiletto X-Series. Preserving what we love about Stiletto Classic, building on four decades of savvy Stiletto owners’ insight, and tying in cutting edge new tech, the bar is set anew for the next forty years.

After several weeks of collaboration, Schichkler Tagliapietra and the Stiletto-X product development team have finalized the Stiletto X-Series Catamaran!


Waterline maintains a sleek 12:1 beam to length ratio translating into fast sailing
A splash rail introduces hull stiffness, interior room, and reduces spray
Reverse wave piercing bows lengthen the waterline to 30 feet for stable sailing
Cabin width accommodates standard twin bunks on each side
Cabin height accommodates 6’2” headroom under the canopy
Canopy design is now watertight when closed, easy to operate, and more durable
Canopy is repositioned pushing crew weight forward and allowing the helmsman to get weight outboard
Trampoline size is increased in width and length
Additions for ocean racing rules including optional toe rail and lifelines
Below deck escape hatch offering nice lighting into the interior
Option available for rear entry hatch into a private head/shower

Sail Stiletto around the world at sailstiletto charter locations.

Stiletto Manufacturing
107 Water Street
855-410-7245
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Mac M
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Boat Make/Model: SC17
Location: Lugoff, SC

Re: Foiling Sailboats, Foiling Beach Cats

Post by Mac M »

I'll probably get blasted for posting this but......

I've been racing A cats some this winter amd the boats are getting much better at foiling. They are getting in the air at around 7-8 mph winds. They are only foiling downwind right now, but I've seen a video of a new design doing it upwind. Not sure how well since it's a short clip. The new foiling A's are selling for about $20k for the eXploders and a few thousand more for the DNA's. The performance of the foiling A's has grown by leaps and bounds over the last year or more and looks to keep improving. They have a rule that only allows the boards to be inserted from the top so that is making the designers work hard at the foil packages. They say if they could insert the boards from the bottom the foils could be made to work better, but that would be a hassle to launch amd retrieve I imagine. As of right now with the top loading boards, I haven't noticed a big difference in them launching and retrieving.

I'm not interested in foiling myself right now and the foilers aren't guaranteed a win by any means. If the winds are up there is no contest, light winds they aren't as fast downwind. As Bill stated, many conditions don't suit them, but they are still pretty darn fast even when in displacement mode. I personally am enjoying watching the development immensely. My boat with curved boards and L rudders is just fine for now.
havliii
Professional
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Joined: March 27th, 2011, 8:12 pm
Boat Make/Model: SuperCat 19, Modded SC20
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Re: Foiling Sailboats, Foiling Beach Cats

Post by havliii »

Mac M wrote:I'll probably get blasted for posting this but......
Your observations and opinion are perfectly legit. Foiling is here to stay. There are many ways to sail, at the bleeding edge of technology, or on a square rigger, it's a very personal choice. When the day comes (and it will) that a used foiler can be dragged out of the weeds for 3K, I will be interested. :-)
Bill Roberts
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Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Foiling Sailboats, Foiling Beach Cats

Post by Bill Roberts »

Hi Mac,
There is no magic to determine the "begin foiling speed". If we go back to our example that was to begin foiling at 15 mph and now we want to reduce that to 7.5 mph or 11 ft/sec, we simply plug
11**2 in place of the original 22**2 velocity and we get a foil area of 4.96 sq ft. Now our 600 pound boat and people can begin foiling at 7.5 mph instead of 15 mph. As you can see the foils are four times as big in area as the 15 mph begin foiling system. Now the version of the boat with the 4.96 sq ft will have a slightly lower top speed because the foils are larger and make more drag at top speed than the smaller foils.
As to A Cat price. I was a race official at the Islamorada Worlds a few years ago. At that race I was told that a new boat in Islamorada ready to race would cost 29K dollars. Now that is boat price at the factory plus packing and duty and freight and shipping insurance, etc. Now you add FOILS to that number and I'm sure you are close to 50K dollars with trailer and padded covers and US owner insurance, an extra sail and battens and some spare parts, tiller extension etc. It all adds up; it will surprise you. Also you might have purchased a larger SUV to tow the boat and trailer with. The larger car might cost 10k dollars more that the smaller one you could have purchased without the boat considerations.
Bill Roberts
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Posts: 515
Joined: November 17th, 2003, 9:13 pm
Location: Stuart, Florida

Re: Foiling Sailboats, Foiling Beach Cats

Post by Bill Roberts »

Havlii,
The Stiletto factory has had several injections of large sums of money to make it go, grow and make money. So far all efforts have failed. Here goes another one. I wish them well.
The reveres slop bow, stem, is an A Cat thing. The A cat can do this because it is a one person boat that is 18 ft long and only 7.5 ft wide with 150 sq ft of sail. The waterline is long, much forward stability because of this length , and having only one person on the boat, the righting moment and therefore the forward sail thrust is small for an 18 ft long boat. The natural tendency for this boat to pitchpole is less than on other beach cats with more sailors on board like two people. Take the F18 class. Here you have an eighteen ft long boat with two sailors on the wire and the boat is 8.5 ft wide. The forward thrust is more than twice that of an A Cat. The tendency to Pitchpole is more than twice that of an A Cat. Therefore an F18 cannot/should not have a cut down front end like an A Cat. Neither should any other boat that is highly powered, high sail area to length ratio and high righting moment to length ratio. The "length" term should be length squared because as length is added to the hull so is forward hull volume. The pitchpole resistence or restoring moment is a function of hull length squared. So, an imaginary F18 beach cat, two persons, with twice the forward thrust of an A Cat should be the square root of two times as long as an A Cat to have the same pitchpole tendency. This brings us to a 21.6 ft long beachcat two persom boat 7.5 ft wide with 150 sq ft of sail. Now we can cut the front down on this hull like an A Cat.
Now let's look at some boat design history.
PLAYSTATION was originally was 100 ft long. During the first few sea trials the boat could only reach 25 knots top speed and it was on the verge of pitchpole. It was a scary ride and scared everybodys' goat. This performance data provided valuable information and PLAYSTATION boat went back to the drawing boards.
What came out was a 125 ft long boat with a fore deck that shot upwards like a modern ski jump aircraft carrier. Back to sea trials. Now the boat acheived 35 knots bumping 40 knots and everyone was cool. The boat was stable and very much under control, no pitchpole problems.
So, now we see that the cut down foredecks and reverse slope stems have nothing to do with boat speed except as they affect pitchpole. They change boat dynamics and they do limit top speed but they do not make a boat faster.
havliii
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Joined: March 27th, 2011, 8:12 pm
Boat Make/Model: SuperCat 19, Modded SC20
Location: Fredericksburg Virginia

Re: Foiling Sailboats, Foiling Beach Cats

Post by havliii »

Thanks for adding some clarity to the reverse bow 'trendiness.' I have only been up close to one Stiletto, but it looked massively underpowered compared to my Supercat 20. My boat has 33 feet of stick and the Stiletto looked like it might have had 38? It looked like a smallish sail plan for a boat that large. I could be entirely wrong, don't know, the owner wasn't around to ask.

I did not read up on the sail area for the new Stiletto X, it's not a boat I would own. It looks like they plan a foiling option so I thought it might be relevant to this thread. Pitching poling this boat off the foils will put a real damper on the 'family fun' that they advertise. Just the mere thought of pitching it (with toddlers on board) makes my stomach churn.

It is their money to spend. If it is a 'turd' they are bringing to market, we will know soon enough. This boat is on a hot rush, the mold halves are almost done. (and by golly! they are using the Supercat vertical seaming methodology) A video can be seen on their website of the hull plug being milled on a 5 axis machine.

If we scaled a Supercat 20 to 'crawl into' hull dimensions how long and wide would it have to be?
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