What Class Boat Is This???

Technical discussion of ARC products
J Drew
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Re: What Class Boat Is This???

Post by J Drew »

Bill,
Does the shape of an air foil work the same on the shape of a hull?
Does water density cause it to flow differently than air around a foil.
Should the widest part of a hull be closer to 40% aft of the bow?
Or am I incorrect
John
Bill Roberts
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Re: What Class Boat Is This???

Post by Bill Roberts »

John,
Water flows around a hull like air would flow around a hull at low speeds. The reason for nonsymmetrical hulls, airfoil shaped footprint, is to enable them to generate a side force equal and opposite to the side force from the sail and MAKE LESS DRAG THAN A SYMMETRICAL SHAPE doing the same job. If you take the side force generation out of the picture, the nonsymetrical hull shape makes more drag than a symmetrical shape just moving straight ahead, no side force.
Using the hull to generate side force like a H16 hull results in a very low aspect ratio lifting body shape, roughly 1 ft deep and 16 ft long for an aspect ratio of 1/16. A daggerboard could be 3 ft deep and 1 ft wide for an aspect ratio of 3. Hull slip angle or hull angle of attack
and hull induced drag, drag due to making lift, are inversely proportional to aspect ratio. Therefore the nonsymmetrical hull shape is going to make much more induced drag than a CB boat and operate at a much greater slip angle.
Examples: The Space Shuttle and the Concord have very low aspect ratio wings. What are their angles of attack during landing? A glider has very high aspect ratio wings and what is a glider's angle of attack during landing?

Bill
T Peterson
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Re: What Class Boat Is This???

Post by T Peterson »

Popularity is partly being good enough, not necessarily the best. The rest is timing.

They were surfers. They caught the right wave at the right time.
havliii
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Re: What Class Boat Is This???

Post by havliii »

Popularity contests aside, I know the H16 is not a great boat, now I am partly educated as to the 'why?' In one design racing people will race anything that floats, 'Rubbermaid' tubs will suffice, the speed and characteristics of the boat aren't that relevant.
SC15Av8or
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Re: What Class Boat Is This???

Post by SC15Av8or »

Being an aviator I would have said.... If this were a wing or the cut away view of a venture vacuum tub the left side of the sketch was the bow. As a wing creates lift from wind flowing over the upper camber of the wing, Bernoulli's principle. In fact if you look at the sketch it is exactly a venture or what we called a vacuum tub to create suction so as to spin back up gyros by air flowing through it. In the picture left to right. Between this and the Newton's theory of lift on the flat side a wing rises. The cat is squeezed forward.

If the bow is where you said it was, something is really wrong with this boat design.

What is it ??????

This said if the bows were at the skinny end the camber is too far aft laminar flow over the hull would separate and cause heavy cavitation/drag before the rudder. The "lift" would be way to far aft of your center of effort. Lots of weather helm ??
Lifes 2 short for cheap GROG
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Bill Roberts
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Re: What Class Boat Is This???

Post by Bill Roberts »

Hey Grogman,
Do you think an airplane wing will fly backwards? Laminar flow, turbulant flow doesn't make a hoot when the wing shape is totally screwed up, a non aerodynamic shape like an airplane wing trying to fly backwards. H14 and 16 hulls generate lift like a flat plate and make more drag than a flat plate.
Next time you get ready to take off, head the airplane down the runway backwards, put the engines in thrust reverse and "let her rip".
See if it will take off flying backwards.
havliii
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Re: What Class Boat Is This???

Post by havliii »

Bill, if I understand this, I could take a Hobie 16 and sail it with the hulls reversed, (stern forward) and it would sail better? if so let's build one! for no other reason than to 'really mess' with the hobie guys at a one design regatta. I can see it now! transoms forward, rudders on the pointy end, going faster and out pointing a stock H16 that would be an all time best 'UP YOURS!'
SC15Av8or
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Re: What Class Boat Is This???

Post by SC15Av8or »

Bill Roberts wrote:Hey Grogman,
Do you think an airplane wing will fly backwards? Laminar flow, turbulant flow doesn't make a hoot when the wing shape is totally screwed up, a non aerodynamic shape like an airplane wing trying to fly backwards. H14 and 16 hulls generate lift like a flat plate and make more drag than a flat plate.
Next time you get ready to take off, head the airplane down the runway backwards, put the engines in thrust reverse and "let her rip".
See if it will take off flying backwards.
I know for a fact they wont fly backward. When I tail slip my SR71 I get no where fast and have to exit the slip into a hammer head and round it out into a split S. I pull a few G's doing so and black out for a few 1000 feet but I usually start the maneuver above 37000 feet. How ever put enough thrust behind anything and it will fly. Just ask the bumble bee and Dragon fly. They do not have upper cambers on their wings. In fact the profile of a dragon fly's wing looks a lot like the speed data off my GPS from a day of sailing with Havliii. :wink:

So my answer to your question is that the bows were to the left side of the picture and the thin pointy side to the right are the sterns.

Your other question as to what would happen if this were reverse and the bows were the thin pointy part is what I attempted to answer.

As far as what "CLASS" a boat this is, which is the title to your post......um this is a guess MULTIHULL??? But this is a TYPE not a CLASS of boat right?? There have been 46 different Olympic Classes of boats since the summer games of 1896. Is this what you were referring to and in that case it could be multihull Olympic class which was from 1976-2008 Olympics
Lifes 2 short for cheap GROG
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Bill Roberts
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Re: What Class Boat Is This???

Post by Bill Roberts »

OK Grogman,
The hull footprints shown on the drawing are of a H16 beach cat standing still with the weight of two people average size males on board. The pointy ends are the bows of a H16 and the fuller end; the more rounded and wider end is the aft end of the hull. For sailing on 'design point' think of the boat sailing on one hull and the other hull in the air. In the drawing you could, for example, erase the upper hull. Now you should see an airplane wing flying backwards, pointy end forward, clearly.
The class is the H16 class of beachcat.
SC15Av8or
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Re: What Class Boat Is This???

Post by SC15Av8or »

Bill I see that. But why the heck would you build it that way when all you talk about is shared lift. Any pilot knows a wing will not produce lift flown backwards. Why then are you boat folks thinking this would make lift?? I give up what was the point behind all this ???
Lifes 2 short for cheap GROG
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Bill Roberts
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Re: What Class Boat Is This???

Post by Bill Roberts »

Hi Grogman,
The point of the hull load water line drawing for H14s and 16s was to show everyone the design folly of the most popular catamaran, beach cat, in the world. The hull shape is not the only design folly in these H products.
It was this total lack of good design work and good engineering work that led Steve Edmonds and I to think that we could design a much better boat in every way. Now I wish Steve and I had come out with the SC17 first and gone head on vs H16s and P16s. Instead we went head on vs the Tornado and the early SC20s were awarded a PN lower than the Tornado, proof that it was faster. So what, it was a good design, but it was the wrong boat at the time and the wrong price.
Bill
fjviola
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Re: What Class Boat Is This???

Post by fjviola »

Bill

We just had the Hobie Nationals here in Galveston. One of our cat buddies with a H-Tiger got 'roped in' to rounding up volunteers for week-long week-day event. Sadly there was very little 'show' by the manufacturer as well as the local dealer, which begged the question: "WTF?" :roll:
One would think there would have been 'demo' H-cats for spectators to ride and learn about. Maybe even a manufacturer rigged H-16 to raffle. Anything and everything to promote the 'life-style' of catamaran sailing!

Then again, the 'event' was during the week while adults (prospective buyers) were at work and their kids (future cat sailors) were at school, so the potential for growth was 'limited' :shock:

Hindsight .. yes, SC17 should have been the 1st to roll off the chocks. But that ship has already sailed.

So, as a follow-up to your original thread ('what class boat is that'), what can be done by the manufacturers (ARC et al) to build a new/healthy catamaran community/lifestyle .. short of installing 'devices' (iPad et al) on the trap wires to hold the interest of 'new' sailors after the first hull-flight is crossed off their bucket-list? :lol:

Thanks
franklin VIOLA
ARC21
Bill Roberts
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Re: What Class Boat Is This???

Post by Bill Roberts »

Promote SC lifestyle?
Have a class newsletter and have a Western Hemisphere Championship Regatta every few years.

Technical point: Why do H14s and H16s run so much rake?????
Ans: The rudder is a much better side force generating body than the hull, wing flying backwards.
Therefore, lean the rig back as far as possible and make the rudder carry some of the sail side force.
The rudder is a much better side force generating body shape, lower drag, than the H14 and H16 very low aspect ratio hull shape. Raking the rig back will unload the hull and load up the rudder and the total underwater boat drag will be reduced.
The negative to this is that the overloaded rudders are very prone to stall especially coming out of a tack. Stalled rudders will put the boat back in irons and a 30 second tack turns into a 2 to 3 munute tack. There is nothing slower than being in irons except being turned over.
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