Foiler Design

Thanks for that info Doug, very kind of you for sharing it.

 

Mal. One of the reasons I think ventilation could be an issue for a hybrid surface/submerged foil is that there will be a step chang in the amount of lift when a tip breaks the surface. This is different to regular surface piercing foils where lift is a little more continuous. It could be that the effect is small or it could be enough to ventilate the foil. From what I've read of the moths, having a foil tip pierce the surface can lead to ventilation and it is something they try to avoid.
Experimenting will yield the definitive answer.

 

If you are right, then some washout may be required at the tips. In any case, I was planning on using a significant amount of forward rake on the surface piercing elements to reduce the chance of ventilation (that's forward as in forward as you go deeper).

I should mention that my project is to design a set of foils for my old Laser. The current design is a fully surface piercing design, for robust simplicity, but I have been considering the Hybrid system as an alternative.

 

Mal:

Please do not take this the wrong way, but why a Laser? It is a great boat for what it is, but it isn't an optimal place to start a foiler. Even the Opti has very low weight in it's favor.

You are lowering the potential for successful outcome of your project dramatically, even before you get to all the design and tuning challenges. Hull weight, rig power and inherent speed potential of the hull before foiling are all critical elements to even achieve liftoff.

Making a really light, fast hull before you attach the foils will get you a lot closer to foiling than where you are planning to start now. Doug Lord's first attempt at foiling (the aeroSKIFF(tm) ) was prematurely trashed by him due to pre-foiling speed and sail-ability issues in chop. In all of Doug's postmortems about his project he never faults the foils, but always the hull and pre-foiling handling & speed.

If achieving fun frequent foiling with reasonable comfort is your goal, lowering overall weight and optimizing the boat's ability to achieve take off speed would be high on my priorities. Since the hull of a foiler isn't a factor once it takes off, your design brief for the hull can be quite simple. Having now built a couple of lightweight plywood hulls personally, a simple foiler hull like this could be done around 60-65 pounds while easy to build.

If you could cut the hull weight in half from the Laser, your chances of success would go up dramatically. $200 of plywood and $100 of epoxy and paint is worth considering if it makes your project a success.

Just a thought. Best of luck with it and keep us posted.

--
Bill

 

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Completely untrue-just made up BS! I donated the original hull to Calema, a sailing school after evaluating it thoroughly in regard to what my design conception was at that time. The boat had a bow more like a surfboard bow and that caused a higher than desired takeoff speed in short, steep intercoastal chop. I had two choices then-one to change the bow or two to switch everything over to another hull. I chose two and boy was I wrong-it has taken much,much longer to "just switch everything over" than I thought it would.The original boat was not then trashed and is still alive and well.

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Mal, I think the Laser is an excellent idea as long as you keep the power to weight ratio like it should be for how you want to foil. You can compensate for extra weight with more SA or you can be satisfied with taking off later than a Moth does. Saying the Laser is too heavy to foil is not well informed and just not true. It offers advantages more akin to the RS600FF than it does the Moth in that the hull has way more initial stability than a Moth does and there is NO REASON WHATSOEVER that it could not take off as early as a Moth with sufficient power-or not- depending on what you want.
Keep in mind that an RS600FF weighs 2.5 times what a Moth weighs and is very, very similar in performance. But a foiler does not have to have that kind of performance to be a lot of fun-just pay attention to the numbers and do it your way-nice and easy or high performance or somewhere in between.

Good Luck!
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For reference:
Opti with 84lb allup weight 35sq.ft. SA==W/SA= 6.11 lb/sq.ft
130lb crew
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Laser with 155lb allup weight 76 sq.ft SA= W/SA= 4.34 lb/sq.ft
175lb crew----------------------- 86 " " = 3.83 "
-------------------------------- 110 " " = 3.00
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Moth with Veal allup weight 86 sq.ft SA= W/SA = 2.56 lb/sq.ft
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RS600FF same or better than Moth with veal------------
Moth with Gulari-80kg/176lb-------------------------W/SA=2.81 lb./sq.ft.
Moth with 200lb-------------------------------------------3.09 lb/sq.ft
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R Class-two people----------------------------" " =3.14 " "
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My first full size foiler hull-far from trashed-at Calema:
Bill Hansen's "Laser Turbo" rig(legal sail area).....

 

I have a foiling project, too

Dear Doug,

I have this foiling project in mind that some might deem a bit eccentric, but I want to do it anyway. If you look to the photo at the bottom of this post, you will see my hoped-for hull... though it is lookin' kinda rough in the photo.

Doug, you say that, "...You can compensate for extra weight with more SA or you can be satisfied with taking off later than a Moth does." Now, son, that kind of thinking really appeals to me when it comes to this unique project, which I shall outline just a bit in the paragraphs below.

My rough estimates indicate that I should probably be going for a used Hobie 16 rig, retractable foils that are as wide as trailer laws will permit, a couple of those snappy, faux wood textured recycled rotomold plastic park benches on fairly large wings and I'm in there.

Of course, I'm going to adopt those mid-ship wand thingies about which you go on about... dual, if I can get the mechanicals all worked-out. I'm also going for a custom, cast iron rudder gantry that will be bolted to the aft end of the main hull. The local foundry is encouraging me to go for it, so it sounds workable. Besides, they have a website and on there, it says that doing cast iron for just about any self-designed project is right at the top of the art form. That's good enough for me, so I'm passing that info on to you.

The gantry work is just so it all fits together aesthetically, more than anything else, as resale value is important to me and curb appeal is the last chance one gets to make a first impression.

The legs are going to stay on to allow me to take to the hard when the tide rolls out... besides, I like 'em.... probably chrome them, or something. The main hull will be painted blood red as I expect to be clipping a lot of sea life as I dash about and fish blood stains are so hard to get out of ordinary gel coat.

I'd do up a cool illustration of the planned boat, but I'm out of graph paper and my pencils have a bad habit of breaking off at the tip when I press hard enough to go over previous inaccuracies with my circles and arrows.

...and Wayne, I did this post on part of my lunch hour, which I consider personal time, so please don't tell my boss that I'm abusing his interests. ;-)

No offense, Mal. Just workin' on my own project here.

 

Hmmmm. Chris, if any university undergrads see that it may start a whole new challenge cup for the unlikeliest object to foil. I have to admit I'm a little tempted to have a go at it myself although far from my undergraduate days (or shape).

What is your schedule for this? Also please post your foundry's web address, don't keep the good stuff to yourself!

I think a retractable foil might be advisable: I have another concept called the ADF (***-Deployed Foil) which I think might suit.

The foil mounts are already in place I see, but it is hardly traditional to chrome them, is it? It's just a question of rigging a big enough sail, surely. My modified dynarig square rigger concept that should be ideal.

 

Wow. Reading your response just confirms exactly what I said. Cutting off the racks, removing the foils, rig & control systems and stripping the hull IS trashing the boat. It no longer is a foiler. Calling the largest piece of the remaining hull "alive and well" is stretching the truth. And yes, I've seen your pictures of the frankenboat assembled from the remains. It sure isn't your highly promoted aeroSKIFF any more.

Out of interests sake what exactly does "untrue" mean to you?

Doug, you can play with your overly simplistic magic "formula" as much as time allows. Bottom line: adding weight requires added power which requires added righting moment.

I didn't say the Laser couldn't foil, I said it would be one hell of a lot harder to make it do so in comparison to an effort optimized for success by focusing on what elements of the design may affect outcome the most.

None of what I said was untrue.

Cheers,

--
Bill

 

Bill,

I can't disagree with any of your comments, but my goal is not not quite what you suggest. The idea of putting my laser up on foils grew out of the Foiling Opti discussion on Sailing Anarchy, where a comment about putting foils on a Laser sounded like a bit of a challenge. As It happens, I have a Laser, some design knowledge and interest in things of a foily nature. So I have set myself a challenge to put foils on my laser with the following goals:

1) I will use the standard rig.

2) No means of increasing righting moment will be added.

3) The hull must not be modified in any way. The foils must be able to be fitted to a standard laser and must be removable, leaving the Laser in it's original race legal condition.

4) The boat should be able to be launched upright in shallow water and preferably from a standard laser dolly.

5) The non foiling drag should not be so great as to make the boat unsailable in light winds, or to windward, hull bourne, in any conditions.

6) The foil system will be simple, robust and and low cost is also a priority.

This may sound like a bit of a joke, and in some respects, it is. However, my very rough calculations so far suggest that break even point for the foil drag occurrs at boat speed of 4 knots, and the boat should be fully foiling at 8 knots, at which point the overall drag is nearly halved. I think the figures confirm that it won't be possible to get up on foils when sailing to windward, but it should be possible to foil upwind once actually foil bourne.

I don't promise if or when I will ever finish this project, it's not like I don't have anything else to do, but there are a lot of old Lasers sitting in back yards, which I'm sure are just waiting for their foils!

 

Go for it Mal. You've made the rules of your game pretty difficult but then I guess if success eludes, you could relax one or two rules a little until it comes!

 

Nice take, Mal. It'll be fun watching your progress. Just looking at the way you have collected your thoughts, indicates that you're looking to have a good time doing it.

Diddling around in the boat shop with a grin on your face. We should all be so lucky.

 

I don't have time to play this game with you today, Doug. Anyone who disassembles and eliminates the ability of a boat to function as designed is "trashing" the boat. You may not like the terminology, but tough.

Anyone who claims their $18K investment in a design works, uses it once with limited to problematic functionality and then disassembles it is prematurely doing so. Given your unsubstantiated claim it "foiled" for three hours, at $6000 per hour it is one of the shortest lived, least tested and most expensive per ride foilers in the world. Although you go on about how you "evaluated it thoroughly" if any engineer in my employ "gave up" on an 18,000.00 dollar design investment with only three hours on the testing clock they'd be fired. Premature? Yes, in my opinion.

So now that I've cleared up terminology that we use in the real world, when can we expect to see photos of your version 2.0 on the water?

Yes, I reported you to the moderator. Words like "untrue" mean lie to me. Abbreviations like "BS" are not proper for forum etiquette. "Frankenboat" is a colloquial and common forum term for a boat modified beyond it's original purpose. Google "frankenboat" if you aren't certain. Many people "frankenboat" Laser IIs and 29ers for single handling. It isn't derogatory at all.

Every time you call me a liar (i.e. "untrue", "mis-characterized","BS","100% false") I'll report it. In my books your statements are libelous and incendiary. If you are uncertain if your statements are "over the top", try using them in face to face conversations - you will quickly find out what people find problematic in your discussions.

Cheers,

--
Bill

 

Jean-Marc Monnard-JM 42

Mal, here is another small foiler being developed in Switzerland-thought you might be interested in the specs:


13' single handled displacement dinghy JM42, 2001
hull length : 4.00 m / 13.12'
beam max : 2.00 m / 6.5
beam wl : 1.13 m / 3.7'
draft canoebody : 0.09 m / 3.5"
draft max : 0.95 m / 3.1'
displacement in measurement trim : 75 kg / 165lb.
keel and ballast : none
trapezes : none
mainsail area : 11.7 m2 / 125.89
fore sail : none
mast height above wl : 6.39 m / 20.9'
mast construction : rotating wing mast in high modulus carbon by Wilke
hull construction : sandwich glass epoxy pvc-core
built by : jean-marc monnard
architecture : jean-marc monnard, damien cardenoso & seb schmidt
certification : prototype
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And a video under sail: http://www.youtube.com/watch?v=73JgJuRaZK0

 

Surface piercer with wand

Mal, this is a response to a question I asked Tom Speer about the idea of using a wand with a surface piercing foil. As you know SP's are usually controlled in altitude by speed. Since you're considering a hybrid system this may be helpful:
A wand simply measures the distance between the boat and the water. You can have any relationship you want between that measurement and the controls. Other factors besides height can be added to the feedback to the foils. Even when pure height feedback is used, it will depend on the gain between the wand and the lift on the foils (determined by the linkage, size of the flaps, etc.) as to whether the change in area or the feedback from the wand is more powerful.

For example, say the main foil is a V with constant chord. The area is proportional to height, and therefore varies with speed-squared to maintain constant lift if the foil is operated at a constant lift coefficient (approximately constant pitch attitude). The problem is, the span will also shrink with speed-squared. This will make the induced drag from the lift on the foil go up. (On a fully submerged foil, induced drag goes down with the square of speed - that's the principal reason for using foils in the first place.) So you may not want the SP foil to go up as quickly with speed. If instead of a constant lift coefficient, you operate it at progressively lower lift coefficients as the speed increases, meaning the boat is rising but also trimming more bow-down, you can tune it so the foil has essentially constant drag. The parasite drag goes up with speed-squared but on a shrinking area, while the induced drag goes down with speed-squared but on a shrinking span. The two trends can be made to balance each other to get nearly constant drag. The key is in controlling the height to keep from rising up too quickly.

Feedback from a wand would be one way to inhibit the rise. The faster the boat went, the more the SP foil would rise out of the water, but it would meet with increasing resistance to the rise from the feedback. In control terms, there would be increasing steady-state error between the height command (set position of the wand for neutral control) and the flying height. That may be exactly what you need for best performance. If the feedback is very strong, the SP foil will operate with a near-constant flying height and its performance curve will look like that of a fully submerged foil. But the feedback doesn't have to be that strong.

Now consider what happens when the SP foil hits a wave crest. There's an increase in lift due to increased immersion of the SP foil. But the feedback from the wand partially counters the lift increase. The same thing goes in the trough - the wand will deflect the flap down and reduce the loss of lift. The result is a smoother ride with less disturbance from the waves compared to the uncontrolled SP foil. Not as smooth as a fully submerged foil platforming the waves, but quite possibly comparable to a fully submerged foil contouring the waves.

 

Doug,

Thanks for sharing that info. As I mentioned earlier, while I was considering the hybrid system, and I think it does have some merit, I will probably stick to a fully surface piercing system for simplicity. I want to avoid having fragile moving parts like flaps and wands if at all possible. However, my intention is that the surface piercing foil should have adjustable angle of incidence, adjustable on the water, so that it can be tuned to suit the conditions. Put simply, in stronger winds the angle of incidence could be reduced so that, as Tom Speer mentions, a reasonable aspect ratio can be maintained for foil efficiency.