A Common Problem with the Latest State of the Art Boats

[havliii]

Bill, I have the utmost respect for what you have done. Never would I count the design and building of the Supercat and ARC line of boats a failed endeavor. I will re-phrase my question at a later date, I have enjoyed and will always enjoy our chats on this board.

[havliii]

Bill, here's a question, relating to MY BOAT and very specific. I bought a Supercat 20 and cut the cross beams to create a boat with a 9 foot beam. This is similar to the ARC 21 which has an 8' 6" beam. For the greatest percentage of the time I sail, these are the conditions, 14-18 mph winds, mostly choppy seas, 33 foot mast.

NOW the question: Is the boat faster or slower than a stock SC20? I say faster. Give me your opinions and the math behind why this might be better or worse.

[Bill Roberts]

Hi havliii,
I appreciate your technical respect for the SC and ARC products. But, that is not where the rubber hits the road. The factory building the boats must make a profit is what counts. A business can struggle along for a while based on stock holders and savings from other business efforts etc but there comes a time when the business must pay all the bills and make a profit.
This is the defination of "business success". SuperCat and ARC have never been there. The sailing public has never bought boats at a fast enough rate to support even a small business, a few well trained employees. The business has had four or five different owners. Much money has been spent on advertising in the past. No one has ever made a profit on SC and ARC products. They are the best designed and built catamarans in every way but no one will buy them. You can't make a profit if you build one and then have to coast for a month or two or three before you get the next order. You have to build one boat right after another and sell them to keep the cash flow working.

[Bill Roberts]

Boat width question: Havliii, you have reduced the max width of your boat from 12 ft to 9 ft. That is a 25% reduction in boat overall width and also max righting moment. Sailing to windward, max sail thrust is directly related to max righting moment as long as there is sufficient wind strength to demand max righting moment, two sailors traapped. In a 14 mph breeze and 9 ft wide boat you will need double trap because in a 14 mph breeze there are puffs to 17 to 18 mph. This will be the wind speed where your 9 ft wide boat will reach best vmg to windward. At 18 mph windspeed with puffs to 21 or 22 mph your 9 ft wide boat will be very much overpowered and the vmg to windward will be less than in the 14 mph wind,
Wind pressure, force per unit area, varies as the square of the wind speed. So at 14 mph wind speed, the pressure is relative to 14**2 or 196. At 18 mph wind speed, the pressure is relative to 18**2 or 324. the force on the sail is 1.65 times
greater in the 18 mph wind than in the 14 mph wind. The torque trying to turn the boat over is up by 65% in a 18 mph wind as compared to a 14 mph wind. You have a boat that is down by 25% in max righting moment relative to a 12 ft wide boat. AS you can see your boat is going to become righting moment limited significantly sooner, in less wind, than a 12 ft wide boat. This is the time, the wind strength, where your boat will be slower than a 12 ft nwide boat. In 14 mph wind and less, there should be no difference in boat speed between a 9 ft wide SC 20 and a 12 ft wide SC20.

[fjviola]

Havliii
If I had a full time beach where my ARC21 could sit with her stick up ready to launch, and/or if I had the brass ones to drive her down the highway on a not-so-legal oversize trailer, then I would expand her beam to a permanent 10 ft. While not a full increase of 25% in righting moment (8.5 ft to 12 ft), I am convinced the addition of 18 inches would definitely enhance the ARC21 windward speed and performance (as Bill's math concludes) in winds over 14 knots. And she is already an incredible beach cat to pilot!

Bill
At the risk of being publicly keel-hauled, what I would like to entertain is "wing seats" for my 8.6 ft beam ARC21!
I had a Hobie 21SC and loved trapping from the wings. Was like piloting an aircraft carrier And, they were wonderful to lean back against in light air, or for relaxing on in end of the day runs.

So, may I ask for your pro's and con's of incorporating wing seats into the operation of my ARC21?

Thanks
Franklin Viola
ARC21.01

[Bill Roberts]

Franklin,
Wing seats are OK as long as you support the outer edge of the seat woth the trap wires. This way the sailors weight travels
the same path and goes directly to the pressure in the sail, same as if you were trap out without wings. Also the wing structure can be built out of lighter weight tubing with trap wire support. Now, a wing built out of lightweight Al tubing, 6061T-6 alloy, will weigh about 25 pounds each. So, you are adding around 50 pounds to the weight of the boat, That 50 pounds is there all the time. One cubic of water will support 60 pounds. If your boat weighs 50 pounds more than it did before adding wings, now every time it moves ahead one boat length the hulls must push aside almost another cubic ft of water. That is 12ins by 12ins by12ins more water must be displaced or pushed out of the way for the boat to move ahead one boat length. Adding weight doesn't come for free.

[havliii]

Bill, thanks for the great review of righting moment. How does wetted surface factor in? What I have noticed is that I fly the hull sooner than any of my peers, my wetted area drops immediately and the boat takes off. The sooner the better, the 20 with the greater beam will stay down and push more water.

Edit: One calculation that I am very interested in is; when does lift off occur? given the known weights of the crew on the wire and the approximate weight of the windward hull and tramp, at what wind speed is the pressure great enough to lift the hull? the surface tension of the water must be a factor, maybe negligible? but once you break that tension the pressure to keep lifting becomes very minimal, i.e. it is easier to lift the hull higher once out of the water.

[Bill Roberts]

One hull carrying all the weight is less drag than two hulls sharing the weight. How soon the hull flies depends
on where you and the crew sit.

[havliii]

I get your drift, if we trap to leeward we can pull the windward hull up. Not very comfortable but doable.

[Bill Roberts]

It's why rowing shells are configured like they are. They could be multihull configurations, but one long skinney hull seems to row the best. Ya know, a semicircle has the lowest perimeter length to enclosed area ratio of any geometrical hull bottom shape. Then a hull shape made out of a lot of connected semi circles would have the smallest wetted area to displacement volume ratio of any geometrical shape except for half a sphere. If all our catamaran hull shapes were sphere halves, they would have minimum wetted area for the weight they have to support but they wouldn't be very stable in the fore and aft direction.

That trapeze belt is about the same amount of discomfort on the leeward side as it is on the lwindward side. People don't complain much about using it on the windward side; sometimes you get wetter on the leeward side. I think they call it "tea bagging".

[havliii]

Good Morning Bill,

Since righting moment = weight x moment arm, I typicaly just add weight to the narrower beam boat and arrive at the same righting moment of the wider beam boat. In bigger air I just call up another "bag of hammers' (boat groupie) and have them ride along (3 up). The overpowered issue is gone and the good times are shared by the three of us. I have increased my moving ballast options and find trimming the boat three up is way easy. There is another really BIG plus to going three up in the bigger air, I have more hands and more available 'moving ballast' to right the boat in a capsize event. The downside I suppose is that I have added weight versus width which has no 'weight penalty.' My power to weight ratio is lesser than the wide boat but I can still trailer mine home quite handily.

I have both the 19 and the 20, why not just stick with the 19 would be a good question? We sail in a lot of nasty (really nasty) chop in the Chesapeake Bay and the 20 goes through this stuff with ease. I like the fatter bow and volume of the 20 versus the 19. The extra foot makes a big difference in the pitch characteristics.

Sidebar: I was also able to rid myself of the barber haulers that the stock wide boat needs for the jib. I absolutely hated those things. As did anyone who ever crewed for me. I sailed a stock SC20 before I ever bought one, there were many issues that were either unpleasent or required a 'just deal with it attitude.' Only a hardcore will put up with 'pain the butt type issues', not your everyday sailor. The SC20 is a GREAT boat but it wasn't brought to the market in a configuation that would attract mass buyers.

That's just my 2 cents, looking through the lens of time and my own bias.

[Bill Roberts]

I like your comment about sailing with three persons. Six hands can do more than four. There is no reason the ARC 22 could not be a three person racing boat. It is another direction beach cat racing can grow in. The monohull classes do it. What are we waiting on? Cats have added the spinnaker and two persons can handle the up and down better than one. A three person racing boat with chute is a natural. Maybe this makes the need for the trapeze less necessary. It also brings forward two and or three person boat ownership. Many possible money deals here and it lowers the boat ownrship cost per person.

On the ARC27 and 30: There is nothing wrong with a four person racing boat. Maybe drop the traps and divide the cost.
How about a two couple boat? Adding a person to each of the ARC boats opens many doors that haven't been considered before. Sailing faster boats is much more challanging and much more fun than racing slow boats. These two boats sail like an AC boat. They go downwind with the headsail and main strapped in tight. The telltales tell you that the wind blowing across the boat is well in front of abeam, a reach. You look back and watch the white caps following you. How can this be? You jibe in much less than 90 degrees. On top of this you are going much faster than the true wind is blowing. The boat is flying a hull going downwind. What's going on? Which way is up? This is the whole new world of sailboat racing that most sailors don't know about. ARC boats will take you into this world for $100K. Any other boat built anywhere else in the world that will sail like an ARC boat will cost $500k to a mil. Come on, let's go racing.

[Bill Roberts]

The ARC22 with three persons: The max design righting moment for the boat has not changed. The design load was two 175 pound men times safety factor in traps on a 12 ft wide boat. On a 12ft beam each of these persons can generate 1,5 times the righting moment they could on an 8 ft wide boat . Therefore two persons trap on a 12 ft wide boat are equal to three persons trap on an 8 ft wide boat from a structural point of view. If you want to sail an ARC22 with three persons, eliminate the traps. Otherwise you will exceed the max design righting moment. Righting moment sets the max loads in a catamaran
sailboat system. Max righting moment sets max loads. At zero righting moment, the loads in the system are zero.

My position for three persons on the ARC 22 was to satisfy the situation where a group of sailors wanted to buy and race 22s but they did not like the trapeze. They like the speed and performance of the 22 and the AC like sailing characteristics especially downwind but they did not like the trap sailing to windward. They are old men like me.

The same logic goes for the 27 and 30. Add a fourth person and do not trapeze anyone. Observe the boat's original design criteria. Nothing has changed. Race with four persons, 8 hands, and nobody on the wire. If this opens the door for some people who want to race a 27 or 30 but for some reason don't like the idea of the trap. For goodness sake, "open the door for them, let them race four up and no trapeze". SOME DAY THERE WILL BE FLEETS OF THREE AND FOUR PERSON RACING CATAMARANS. I mean real racing catamarans. Not two hulled sail boats with overnight accomodations that double the weight and cost of the boat and slow it down but real "racing catamarans".

[havliii]

Dead on, 5 man crews, no trapeeze, wing racks, no foils, the Marstrom 32 league already exists in Europe. The racing is close quarters, fast and lots of lead changes, still a tough sell to an American audience.

[gahamby]

Bill,
Let me preface this post by stating that I love my '84 SC15. Your hull design is brilliant and timeless. I can't imagine owning another brand of cat.
"Why don't they sell?" In automotive terms, Aquarius is Lotus, Hobie is Toyota. Hobie stole the march on mass marketing back in the '70s and have held their ground ever since.Try to find an Aquarius dealer beyond the factory. Please direct me to the Aquarius display at this fall's Annapolis Sailboat Show.The market for high performance beach cats is small.
Try to find a sailing resort that has something other than Bravos, Waves, or Getaways. No resort owner in his right mind in going to push the next tourist, with an umbrella drink in hand, off the beach on a high performance cat. I was obliged to do that back in the late '70s at Bayside Watersports in Nags Head NC with H16s. The results were broken boats and dissatisfied customers.
There's no Aquarius racing fleet that I know of. I know some of the members here race. Nacra, Hobie, A cats, and the F18s seem to have the fleets.
How many members on this site are sailing 30 year old SCs that we rescued from the weeds as opposed to new ARC owners. I'm 60, with two boys in still in college, hoping to retire soon, a lower back that knows when it's been on the tramp all day, and a lovely wife that looks askance at the price of a new ARC or any other boat for that matter. I'm afraid my demographic is not your market. Guys like me will keep your old girls flying the best we can and dream of making the pilgrimage to Wyoming, MN to pick up that new Arc. I don't know how many of us will make it.

Thanks for the best damn cat on the water,
Sincerely, Geoff Hamby