Skiff Design Thread

[TimClark]

This is for Zerogara, me, and some other people to toss around ideas for a skiff.

Zero-I would think that you would get a little more speed if you beefed up the Upwind SA and kept the downwind SA...But I think it would be good to add a second trap. For 20 knots of wind, the downwind SA would create 448.24 pounds of sail wind load. I think you would be able to keep the boat flatter if there was a second trap for the skipper.

Tim

[TimClark]

ttt...Zero we gotta get this started

[zerogara]

So is this going to be some design exercise that we can all participate in?
Should we vote on the basics to start with?

Length 14-18ft
1-2-3 person adult skiff
Monohull with fixed or adjustable wings (weight equalizer)
Foiler / no foils
Daggerboard/swingboard
Wind range
choppy open water or closed flat water
Straight line performance or maneuverability?

In my opinion if you want to push the limits of technology and not rehash old technology the boat should be designed with foils. It will require LESS of everything because of the efficiency of the foils and probably less expensive overall.
From a marketing perspective the thing should have retractable foils ,buoyancy pods and other touches that make it easy to sail w/o impacting negatively on incredible high performance.

[zerogara]

I will admit that to this point I know nothing about foils other than the basic principles that make it work. At some point during my undergraduate career I switched briefly to aeronautical engineering because I thought I had a good grasp on thermodynamics. I disliked it and went back to more solid things. Maybe it was the fighter aircraft crowd that I was surrounded by that turned me off. And as you can see from my avatar "I don't want a pickle, I jus' wanna ride mah motorcICKLE" as Guthrie once said.

Nevertheless, I am a quick learner and willing to try it really soon.
From a sailors perspective I think I've had too much fun sailing more conventional boats to substitute the fun with something so different. I thought I'd love jetskis and after a couple of hours I found them boring.

Fun, as a description of the total experience, should greatly be incorporated into any design. Extreme performance and technological advancements should be secondary. It shouldn't take hours of team work to rig up a little sailboat for a few hours of ride, it shouldn't take protected facilities to do so, one should be able to do on the beach from a trolley!

Just out of curiocity, I imagine your test sails have been in the Orlando lake with very light wind. How long did it take you after practice to rig everything up from the time you parked your trailer till the time you were on the boat and left the shore?

Z, it takes about twenty minutes to rig my boat singlehanded. Less than to rig a Hobie 16. The foils stay in place with the boat and it is launched with off a trailer or it's own dolly on any beach. Lowering the main foil and rudderfoil are done from the cockpit. The boat has been sailed so far in 10-12 max in the intercoastal with a 20 mile run-so the waves were fairly big for that lite wind.
It's a complete misconception that you have to spend ANY longer getting ready to sail a well sorted foiler than you do any other boat. Moths ,mainly because they stared out as conversions from standard Moths, require the foils to be inserted from the bottom in waist deep water. NOT NECESSARY on a boat designed from scratch as a foiler. And if a wand is used for altitude control then you sail very much like you do a normal boat.
A foiler "skiff" can be designed to be easy to sail and set up and will have more speed for less money than any other way you might go....

[zerogara]

OK, let's make it a foiler then.
Single hander or double hander?
I'd like to see something that is designed for 2 average sailing adults but also capable of been fully utilized by a hefty single hander as well.
Would that translate to a single upwind sail with one asymmetric?

There are lots of other considerations. You need to consider hull design: my hull has a low flat "windsurfer" like shape because I thought that shape provided the additional dynamic lift that might be required when re-entering from a jump the #2 priority on my boat after foiling in the first place.
Today I'm not sure that even for jumping that that shape is necessary. For a foiler to be really good in the marketplace it needs to take off as early as possible(in the lightest wind). My hull shape is not ideal for that since it has excess wetted surface. Unless you use a method to literally shift the foils for early takeoff and shift them again as you go faster(easy to rig) you'll probably want a hull that is very easily driven and double ended. The reason for this is if you DON"T incorporate a method to shift the foils you have to shift the boat. You've seen the pix of Moths with a real bow high attitude: that gives the foils the angle of attack necessary to take off in lighter air.
If you want to jump AND take off early you'll just have to test the boat and see if it has charateristics that will allow it to re-enter safely-and add "anti diving foils" if necessary.
In designing the boat you'll have to keep in mind that to be an effective foiler the boat MUST foil upwind in additon to taking off in light air. So a high power low drag rig is essential. I'm convinced that technology would allow an unstayed carbon rig with square top main and camber inducers. Both the Moth and Hoot (I think) use stayed rigs with camber inducers.The square top and a correctly designed mast allow the sail to unload as necessary and probably not have to be reefed.
In my opinion one of the most important numbers you can look at in boats under 20' is "wing Loading": pounds of all up sailing weight per sq.ft. of sail area.(weight divided by SA) It's better than any other ratio at predicting when a boat will foil and IF it should foil upwind.Moths that foil upwind do so within an approximate range of 2.4 to 2.58 pounds per sq.ft. SA.Lower is better . Below 2.4 is excellent but hard to achieve. Then you have foil loading,SA/foil area ratio(sq.ft.SA per sq.ft. foil area done on just the main foil), main hull beam to length ratio ,SA/wetted surface for the 0-takeoff range etc.
For righting moment I've become convinced that for a single or doublehander a sliding bench seat may be the right answer for a foiler.
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One other major consideration: max crew weight. I think that a singlehander ought to have the max competitive crew weight set at 220 or 250 FOR MARKETING purposes. That means the boat could be designed to have a wide crew weight range from say 140 to 220 using the sliding bench seats for weight equalization if desired. There are too many boats on the market than can only be competitively sailed by flyweights so if you go for as wide a performance crew range as possible you'll have a larger market(no pun intended).It's not an easy task: the 140 pounder has to be able to develop enough RM and carry extra weight on the boat to make up for the designed crew weight at 220/250. But if you work it out it would be good for business.Same thing to a lesser degree on a doublehander:design for a high maximum crew weight to increase the usable range of the boat.

[zerogara]

http://team.abnamro.com/web/show/id=111901

This link came from an other thread. It is impressive to see it move rather than look at pictures.

[TimClark]

Yeah the videos of the boats are awesome. I think that is the best one I have seen yet. I defenitely would consider hydrofoils. I think if it was to be a foiler, I would have a single trap and the boat be doubled handed. I would think that it would be tough to balance the boat if you are on a foil with both people out. I think we should go for simplicity and speed on this one. What do you guys think? Below is a list of specs which I think would be good

LOA-14 ft
Beam-3 ft
Draft-.4 ft
Asymmetrical spinnaker
Removable wings that will be fixed by sliding into adapters then getting locked in place
Single Trap
Main and jib

Tim

Tim, you might want to read what I wrote regarding beam; my 16 footer has a hull about 3'
wide. Do you think it's wise to put a guy on a trapeze on a foiler? How would you handle maximum sailing weight so that the most people possible can sail and be COMPETITIVE in any resulting class?

[Baronvonrort]

Here is a 18 ft skiff on foils.

[TimClark]

Doug, with a foil concept that I was thinking of, foiling would be stabler and would not require as much shifting of weight. Sorry for missing your post on the beam, I'll check it out.

Tim

Well, Tim, what is your concept? Note that the 18 above uses surface piercing(I think) foils mounted out on the wings. Whether surface piercing or not three foils are not as effective as the bi-foil arrangement either for stability or speed but they were the first foil system on Moths to win a race.

[TimClark]

I was thinking that it could be like a surface piercing foil, but circular and it would be mounted on the bottom of the hull, and you could adjust trim by increasing and decreasing the size of the circle through the tiller extension. It seems really weird and out there but I think it would provide excellent lift and there would be more stability as it could be made to a bigger size. I'm off to bed for now but I'll talk to you guys tomorrow.

Tim