Here’s a question for all those enterprising designers:
What would you design if the only restriction on a model boat was an overall hull length of 24 inches? And I’m saying that is the ONLY restriction. You can have as many gadgets as you’d like.
Would you go with a monohull or multi? Skiff or needle? How much sail? Canting keels? Twin rudders? Twin masts? Spinnakers?
Lets get those creative juices flowing again…
Graham
Graham,
I’m assuming that the goal of this boat is to sail as fast as possible with that restriction as the only restriction?
One question: Are the main and jib booms allowed to overhang the LOA?
I’d go with as much sail area as I could muster. for convienence, I’d probably choose a M rig. I’d also want a deep light keel. Maybe an M keel with reduced bulb mass. I’d probably try for a skiff hull to see if she would plane.
Another option would be a multi, but nosediving would be a huge problem without foils for active stability.
Will Gorgen
Yeah, thats my kinda challenge! Thing is, there are too many posibilities. You could build a conventional cat or tri that size, but control at speed would be a big problem, but with a few clever tricks to keep the c of e low and back end in the water it no doubt could be made to work. A foiler would be very hard to build as all the control gubbins could too easily make the thing too heavy to fly in all but the best part of a gale.
As to mono’s I have built a canting keel boat not too far off that size that worked well and was pretty damn quick on a reach and upwind, just again hard to control offwind as you have little time to react. I think the problems are solveable but I dont have the time to play with it at the moment. Spinnys and gadgets like that are just going to add more weight than they are worth I feel.
Overall a light, simple boat is a fast boat at this kind of size.
Luff 'em & leave 'em.
I’m picturing an RC version of the Bermuda Fitted Dinghy:
http://www.boats.com/content/default_detail.jsp?contentid=11330
The boat is 14 feet long, carries more sail area than most 40 foot ofshore boats (1500 square feet or more), sails with a crew of 6 and races are held with a very unusual set of rules that allow the crew to be jettisoned to increase boatspeed in lighter winds.
http://www.caribbeanracing.com/artman/publish/article_153.shtml
Rules:
http://www.boats.com/content/default_detail.jsp?contentid=11331
So for an RC boat that was a scale of the fitted dinghy with a hull lenght of 24", the mast would be about 120" tall on the “A” rig and the sail area would be about 2600 square inches.
When I was in Bermuda for Race Week in '95, the top I14 team challenged the RBYC fitted dinghy team to a grudge match. The winds were light (5 to 10) so the RBYC dinghy “Contest III” loaded up their #1 rig. The race was from the RBYC dock to a channel marker about 1 mile away and back. Last boat to touch the dock had to buy drinks for the other crew for the rest of the week.
The race was not even close. The fitted dinhy made it to the channel marker and back to the dock before the I14 was even halfway to the first mark. After tagging the dock to win the race, Contest headed back out to taunt their competitor. They caught up to them before the I14 made it to the marker and proceeded to sail circles around the I14. Everyone had a good laugh about it and everyone was impressed with the speed that a little 14 foot boat can achieve when you give it that much canvas.
Will Gorgen
Edit: I just called a buddy of mine who used to be the skipper for Contest III and I asked him how tall their #1 rig was. He said it was around 45’. So if we were to build a scale of this boat, the mast height would be 77" not 120" as I stated above. The 1500 square feet of sail includes the spinnaker. The jib and main together are closer to 900 square feet. So for our scale this would be about 1550 square inches. Those numbers seem more reasonable. a 10 foot tall mast on a 2 foot long boat seemed a bit too extreme (even more extreme than the boat I remember seeing). He also stated that the bowsprit on the fitted dinghy is about 12 feet long and the main boom hangs over the transom of the boat by about 10 or 12 feet as well…
For the sake of no constricting anything, overhanging rigging (and rudders) would be allowed.
This is just a design idea challenge, I want to see what people would come up with given the relatively short length of 24". To me, having the only rule be LOA = 24" makes it much more difficult to design a boat. If the class were say 48" long, the answer (it would seem to me) would be multihulls because they are proven to be fast and relatively stable at that length.
However, at a mere 24", as both Matt and Will have stated, the length of the boat makes stability an issue. I like the idea of the planing skiff, although the idea of a scaled down hull being unable to plane has been raised a number of times before, although I don’t know whether this is accurate or not.
As for my crazy boat, I think I might go in the direction of a light displacement needle-like hull with sharpie-like lines. With a length-beam ratio of 6 or a little greater, it would seem that the boat could take advantage of the “faster-than-hull-speed” concept of multis but have a wide flat transom to allow planing off the wind. If it were feasible I might put a canting keel on the boat, but I really liked Matt’s idea or simplicity, so perhaps I would just load it up with lots of sail.
Personally, I would stay away from multis for this, as the temptation to load it up with sail would probably get me in trouble. Something like a trifoiler might be possible, assuming it wasn’t too light or heavy, but that would be tricky…
Come on, I know there are more designers out there. What would you draw up if you had a 24" long blank sheet of paper?
Graham
Graham,
A 24" trifoiler might be pretty cool. But it would only be faster than an overcanvased mono in foiling conditions. At 24" you would need to keep things pretty light to get her to foil in light winds but it could be done. Once it was foiling, it would have positive (active) stability so you would be able to carry quite a bit of sail.
If I lived somewhere where you could count on at least 10 mph breeze then that would be a great option. I think I would name it “waterbug” because that’s what it would look like scooting across the water.
The prototype trifoiler used 2 windsurfer style rigs if I recall. Does the production boat have 2 rigs as well or is it a single mast?
Will Gorgen
now this is ironic:
http://www.hobiecat.com/sailing/TriFoiler%20History%20Original/model/history_trifoiler_models.html
A model was built as a prototype for the full size boat and now we are considering using the full size boat as a prototype for a model…
Will Gorgen
I might be inclined to try something like this…
Floats of approximately 10 inches in length and shaped like a modified sailboard. Solid wing with a chord length of about 15 inches in length and about 24 to 36 inches high. Interior lower portion of wing to house electronics for control of angle of attack for wing and rudder(s ?) Deep boards on each float/hull. Might have to stagger floats/hulls within 24 inch overall length - or just use one long float/hull of 24 inches with a long, but shallow keel running length of leeward float/hull. This concept would not requie a specific wind to climb up/stay on foils, nor would it be hindered by weeds except for rudders.
Although using the “pod” concept, the wing would be left sheeted out and only use winch to sheet in to needed angle of attack to get it moving, then play sheets to keep the windward pod on (or very near) the water. A one way course only - not for around the buoys.
Dick,
That sounds pretty cool, but for whatever reason the picture is not showing up on my machine…
About the mini-trifoiler, would the ability to carry massive amount of sail area be enough to get up on the foils even in a light wind? It seems that the foils would stabilize even if not foiling, because if the boat heeled, it would seem that the windward foil would trim down to correct for this. Are foilers never designed to take a negative angle of attack? I thought that was theoretically the major advantage of the design.
Graham
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These babies have been around for over 100 years. You can read all about them by visitingwww.themodelyacht.com. You want overcanvased rocketships? Try a <font color=“red”><font size=“3”>BUG.</font id=“size3”></font id=“red”>[:-witch][:-tophat][:-timebm] Some photos to get you thinking.
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Do it NOW before it`s too late.
First things first, I can now see what you are talking about Dick. That would seem to be a pretty effective one way goer, although i wonder, would there be anyway to make it go both ways? Perhaps take a page out of the Monofoiler concept and have the sail and “crew” pod rotate on a bearing. Mwahahaha…
Hey Will, the balmain bug looks kind of like what you were talking about with the fitted skiff idea, but with a much shorter keel.
Ian, have you ever seen a bug go? They look pretty cool, but I just can’t help but think they’d end up pushing a lot of water around.
Does anybody know how the bugs don’t bury that sprit and jib in every wave?
Graham
Graham,
I agree with your assessment of Dick’s idea. Great for a one way speed record attempt, but not a great all around boat. I asked you early on if this was to be a bouy racing boat or simply a freakish speed machine. Never really got an answer so I assumed buoy boat for all conditions (light wind to heavy wind)…
I gave some thought to the trifoiler over the weekend. It might be a lot of fun to try it.
something that Doug and I have talked about quite a bit is what to do with the foils when not foiling. On his F3, the foils are held at “take off” attitude (they are basically trying to lift up). so they are pretty heavy on the drag when not foiling. I think this could be solved by having an adjustable (2 position) link between the altitude sensing system (wand or skimmer) and the foil attitude. one position would be for when you are flying and would control the angle of attack to keep the hulls an inch or two above the water. The second position would set the neutral lift when the boat was resting on the waterline. That would dramatically reduce the drag in non-foiling conditions. This would allow you to build up more speed and then “command” lift off by switching the arm length. This would also allow the foils to do as you describe and counteract the heeling forces when the boat was not foiling.
By setting a small amount of dihedral to the tri-foiler crossbeam, the leeward ama would be touching the water while the windward ama would be a out of the water by a small amount. so the windward foil would be commanding a small amount of “down” lift and the leeward foil would be commanding a small amount of “up” lift - thus creating righting moment to counteract heeling moment.
I happen to have a spare mast and sail from my fairwind laying around in my basement. If I can find a 24" hull fairly inexpensively, I might try building such a beast.
Of course, I still haveother un-finished projects that need attention before I go off building something new…
As far as the fitted dingy. Those boats have a huge problem with water ingress. Generally they dedicate at least one crew member (sometimes 2) to bailing. There is a technique to bailing those boats. They take a square plastic tub and sort of push the water over the side with thrusting motion. It is a pretty arduous job and you get tired pretty quickly, so they often rotate the position of bailer around to make sure that they do not get too tired. By the time you jettison 2 or 3 exhausted crew members off the transom of the boat, the freeboard increses a bit and you don’t take on as much water…
Will Gorgen
Will,
SOrry about not answering the one way speed machine vs all around boat. For the record I was thinking along the lines of an all around boat.
With regard to the dual settings for the foils: how would you know when you could actually fly vs just counteracting heeling moment? Do you think you would just have to work with the boat or do you think there would be a good way to automate the process?
Graham
Hey Graham,
No problem! I assumed that was what you were looking for. But of course Dick took a different tack.
With regard to assessing “liftoff” speed. I think it would be best left as an exercise in learing how to sail the boat (sort of like deciding when to tack on a windshift or when to wing and wing on a broad reach). You might be able to set the boat up so that when you gain enough speed to fly, the foils work to level out the boat (i.e. the leeward ama lifts out of the water slightly). so when you see the leeward ama begin to lift, you flip the switch to shorten the linkage between the skimmer and the foil flaps (or foil angle of attack setting) and the boat pops up out of the water. On the human powered hydrofoil that I worked on in college, we used a similar process in getting up on the foils. We had a long arm that would control the angle of attack of the main wing (directly under the CG of the boat). You would hold that all the way down while you were initially building up speed such that the main foil would be generating virtually no lift (and therefore very little drag). you would pedal like crazy until the boat gained enough speed for liftoff and then you would pull up suddenly on the handle and the boat would pop out of the water. As soon as the boat cleared the water, the drag would drop substantially so the boat would accelerate quite quickly. While you were accelerating, you would need to keep lowering the handle to keep the boat flying at the same height above the water (generally as low as you could without the hulls touching the water (as the speed of the boat increased, the increasing dynamic pressure required less angle of attack to produce the lift force necessary to hold up the weight of the boat).
So what I am picturing is something similar here where you have a short and a long linkage between the skimmer system and the foil angle of attack or flap system. The short linkage would set the neutral lift when the hull was a few inches above the surface of the water. The long linkage would set the neutral lift when the main hull was sitting on its waterline and the two amas were equal distance above the water (the boat is held level). Then you devise a bellcrack style system that allows you to change the length of the linkage with a servo from short to long. You could even use this system to fine tune the “neutral height” when foiling. That way, you could have the boat fly a little higher when there were bigger waves (so that the hulls would clear the wave tops) and fly lower to the water surface when the waves were smaller. The foils will have lower drag when they fly further below the surface of the water due to the free surface wave generating effect. Here is an extreme example of this from our HPV project: http://lancet.mit.edu/decavitator/images/tsunami.gif . By comparison, notice how small the waves are when the boat is flying low above the water: http://lancet.mit.edu/decavitator/images/flying_fairing.gif .
I noticed in looking at Greg Ketterman’s designs that he actuates the angle of attack of the entire foil rather than having a flap mechanism. This is the same thing we did on the HPV program and I think it makes for a more efficient foil configuration. Plus, it should be easier to make in small size boats… I think this would be my prefferred approach.
I’m headed to the Hobby Shop at luch today to take a look at some helicopter rotor blades that I could chop up and make into “T” foils… I’ll also look to see if I can find a suitable main hull and suitable ama’s. If not, I may try something simple like Dick’s method of shaped foam sections… I’ll let you guys know what I come up with…
Will Gorgen
