Foiler Design

Hello Olav,
I sailed my Scow foiler on monday in light winds 5-8kts with interesting experiences.

The inverted Y foil gets up, but is rather unstable laterally. I canted it 30 degrees to leeward and it is much more stable but requires more wind to get up. One big effect is that the centre is then to leeward and you get quite a big lee helm. This becomes particularly apparent when the sensor clears the water and the boat dives to leeward. (The Y foil broke and now I need to fix it!)

Conclusion 1: A simple Tee foil on the centreboard will give the best all round results and is the simplest construction and operation. The area of the Tee should be about 1500 sq cm for a Moth for all round performance. Wider and higher aspect ratio is best. It would even be good to have some dihedral on the foil to assist with stability.

The normal position of the centreboard and rig etc seems to work fine. If you move the board aft, then the rig will also have to go aft too. I think the mast at 1.2m from the bow would be a maximum. I am using a very high aspect rig with a 6m carbon mast. While it feels powerful, it also puts a big forward moment on the canard in gusts.

Conclusion 2: I therefore think a standard Moth rig in the standard position and configuration is a good solution. To lower the centre of effort would be beneficial.

Of course a longer lever arm to the Canard is better as it allows a smaller canard and lighter loads, but we are limited by the 3.3m length of the boat. I do not see any problem to increase the size of the canard (currently 45x10cm) if required, as there is little drag on this.

One final comment, is that my testing is based on practical results gained through progressive trials. You are currently up to date with the status. Unfortunately it takes more time to build new foils than write emails or make hypotheses about how it should perform and sometimes the results are not quite what you expect, so don't be surprised if I change some details as we go along.

Please keep us up to date on your construction and results of your trials.

all the best, Ian

 

Hello Ian,

thanks a lot for your quick answer!

As it will unfortunatly take some time until I can have any experience to share with you (I have to build both the boat and the foils first and stand the northern hemisphere winter - it's already pretty cold and dark here in Kiel) all I can do at the moment is think about it... which is REALLY important in my opinion - on my current boat I got some things wrong due to lack of experience and thinking about the effects on boat handling that some features cause (photo on the Student Design Gallery).

If I did understand correctly you can also rotate your centreboard (and the canard as on Miller's sailboard) around the longitudinal axis. I aim to have no moving parts at all. The reasons are clear (esp. to those who know what sailing a narrow skiff Moth is like): Production gets simpler, it can be build lighter, and - most important to me - it will be easier to operate on the water (if it's a system where one has to adjust things manually).

Before discovering this thread I had the idea (which was also mentioned here) to build a V-shaped canard that can handle heeling angles of maybe +/- 15 degrees without immersing the tips to even avoid a canting canard.

It's really interesting you come to the conclusion a T-foil would be the better allround solution. I think you're right (esp. with regards to transverse stability) unless the foil comes close to the surface and gets likely to ventilate. Or is this not common with the Miller system (as it may happen from time to time on the Ilett foils?)? How effective are ventilation fences in your opinion? I don't think a Moth will operate at heeling angles large enough to have the wing tips come out of the water as Miller fears so this would not justify the inverted Y, too.

Another question at the moment: Would tell me your scow's weight so I can estimate if we're talking about similar loads on the foils (my body weight of maybe +85kgs sometimes makes me worry about this...)?

Thanks so far and all the best,

Olav

 

Olav,
Yes I can pivot my main foil around the longitudinal axis, but not the canard.

I agree that simple is best, I am experimenting with as many options as possible to find out what works and what does not! I have only ever had two moving parts on my bifoiler arrangement and hope in the end to have none at all, as you also propose.

Fine adjustment is always necessary so I have built in as much adjustment as possible in the beginning only.

I agree that you are heading the right way. I have spoken with Asetvo who is planning the same approach with the forward canard.

Miller necessarily runs close to the surface to reduce rolling moment on the board. He must keep in balance in all axes at all times, it is an amazing feat!

On a Moth you can go much deeper, without any problem, so I recommend you do this.

My Scow is not that light, about 30Kg all up and I am embarrasingly 80 Kg also, so I figure you will have a good chance with similar sized foils.

Winter is always good for building and dreaming... keep at it!

 

Having read some of the messages on this thread I thought I would mention my web page at:
http://www.btinternet.com/~sail/boatbuild02.htm

This describes a bi-foiler which probably predates the Moth and other bi-foilers. This boat has shown promise when it is sailing on the foils but has poor maneuverability when not foil borne and that is the main reason I have hardly sailed it in the last few years, it is just too much of a liability when there are other boats around, either to run into or to laugh at you when you get stuck in irons.

The bi-foil configuration I chose has a lightly loaded front foil, or canard if you like, which acts as a surface sensor to control the incidence of the aft Tee foil which carries most of the weight and also acts as the rudder, hence the foil system has just the one moving part. The boat is intended to sail heeled to windward so that the lift from the Tee foil acts partly to windward.

I am pretty sure the poor low speed maneuverability is due to the aft part of the hull sinking too low in the water when not foil borne, hence the rudder (ie main foil) has to fight against the lateral resistance of the deeply immersed box section stern. I have thought of several ways to improve this, although all of them would require making a new boat. Firstly the hull beam is too narrow, if it were a bit wider the stern would not sink so deep. Secondly, perhaps the crew could move forward when not foil born. This would require the sitting out racks to be extended further forward, that is not impossible but how do you actually move your body weight fore and aft when you are in a sitting position and are holding a tiller in one hand and a mainsheet in the other - I find that virtually impossible but I guess you Moth people can do it somehow! The third option might be bow steering, the lightly loaded front end would be much easier to push sideways than the heavy stern. Bow steering would be mechanically a bit more complicated and if it means some cumbersome mechanism attached to the bow I think it might spoil the appearance, unfortunately I find it hard to forget the idea that a sailing boat should look a little bit pretty! The boat could also do with wider sitting out racks, not just to get more leverage but for comfort, sometimes I have had to drop down off the foils only because I have cramp from the dreadful seating position. There was a reason for this, the boat was originally intended to be used with a trapeze and I thought the width of the racks would be quite enough in that case, also I wanted the racks to fit (more or less) within the legal limit for a car roof rack. I soon found that using the trapeze was well beyond my skill and I think the Moth boats have shown that the extra righting moment of a trapeze is not really needed.
John

 

A quick update on what is going on in Moths, a scene I am keeping an eye on.

1) Rohan Veal won the Australian nationals over the new year.

2) The Aus Moth Association voted against the motion to ban hydrofoils.

3) Some interesting calcs of Rohan's speed around the course show that he is up with I14s, 49ers etc in speed. See the Aus moth message board.

4) The UK magazine Yachts & Yachting (probably UK only) Early Jan edition and the RORC magazine Seahorse (Feb edition) have both run articles on Rohans achievements and the developments by the Ilets & Bret Burvil. Seahorse is available in some marine stores in the US. See their website.

Exciting times!

 

Foilers

I agree-very exciting times!

 

Moth design

You have all been very quiet recently so I think it is time to spill the beans on what I am doing and thinking and ask for your 'peer review'.

The International Moth Europeans are to be held in Portland Harbour UK, in July, only 2 hrs from me and this seems like an opportunity too good to miss. Already three UK Olympic Trials level sailors have ordered foil sets (and / or boats) from Fastacraft in Australia, the same as Rohan Veal.

The hull of my design is in build in thin plywood (as befits an experimental vehicle!). I think that the Rich Miller/Ian Ward configuration with a surface tracking bow foil has the great merrit of simplicity and deserves a thorough trial so that is what I am going for.
This is how it is looking so far (This is all design data, hardware is still in raw material form).
The main foil is positioned at 75% length (where the bow is 0%) at around 2 ft 'static' depth. The reason for the position is that, on an 11 ft boat it seems sensible to have the foils as far apart as possible for pitch stability and to make a 'bigger' foiling configuration. The foil has a 110 mm chord and aspect ratio of 10. It is mounted on 2 foil legs (a Pi foil, not a T) to releive the huge torques that could occur on a single legged foil of this length and this means the hull is wider and flatter than the 'normal' 300mm beam. (Moth rules imply that all appendages have to enter the water inside of the unloaded waterline beam). The foil legs act as twin centrboards.
The foil section is Tom Speer's H102 and consruction is solid carbon (with some glass and a small wood core thrown in at the neutral axis to save on expensive material).

The bow foil is as near the bow as practical and is also the rudder. It is cruciform so that the rudder works when the foil is at the suface . The foil is at a (static) depth of 1ft. Any offers on a flat or concave bottomed foil section that has a sharpish leading edge for wave slicing, low immersed drag and good immersed lift characteristics? The reason this does the steering is that the centreboards are getting near the stern and even with a gantry, the leverage seems rather unfavourable for a normal stern rudder. It also cuts down on the immersed foil count.

The rig has to be moved back to balance the centreboard position and I have it planted around 50% with the boom overhanging the stern. Like Rohan's rig it looks more winsurfer that dinghy, with lots of rake and bend. Is there any reason this aft position will not work?

So the whole thing has the distinct whiff of iceyacht and windsurfer about it, with its long nose and aft mounted rig.

As for the wings and shroud base, I am still debating and sketching the best (lightest, robust, economical) solution but it will probably be carbon tubes unless I run out of budget and have to use up the plywood.

I have always dreamed up names for my boats as I go through the design processes. This one is currently called 'In for a penny....' (as in 'in for a penny, in for a pound') on the basis that I am redesigning so much of the current Moth 'baseline' that there is not much more to change! An alternative is 'The whole hog'! In other words the whole venture is rather high in development risk; but it promisses to be a lot of fun.

Comments?... Suggestions?... Warnings?...Questions?

Tom Edom

 

Good ideas

Tom, you are well on track with some good ideas and I think it is well worth a try.
The only downside I can see is that you will be compromising light wind displacement sailing performance, which is still a major issue for Moth sailing, as it is not just about foiling, but competing across all wind ranges.

You may also find it hard to tack with the rig so far aft, however the bow rudder could help with this, it is an interesting experiment...best of luck and keep us informed how it goes.

Ian

 

You might consider a reversible bow foil in a dagger trunk, such that you could swap ends to make it a pure rudder. That would save you some wetted surface in light winds. Probably have to go swimming to make the switch, but I can't imagine a Moth sailor afraid to go into the drink!;-)

For upwind performance, I'd ensure the main foil is at least as deep as you'd make a conventional board. The area can be split into your two struts. Since height is controlled by the bow foil, the main foil can be as deep as possible.

Besides the planing surface forward, you might consider a fully submerged foil controlled by a smaller forward surface in a Shutt-strut configuration. This was developed by Sid Shutt and proven in a number of human-powered hydrofoils. Sid's hydrofoil trimaran used a forward planing float, much you are proposing, that could be swung up in front of the boat for beaching. But the Shutt Strutt could have less wetted area and greater span for better efficiency.

 

Two routes to speed:


(photo by Andrea Francoloini)

 

Sounds really interesting indeed, Tom!

Some comments:

As I'm also about to build a new Moth with the Miller foils torque is one thing I worried about, too. As it doesn't seem to be a problem on Rohan's foils (which - if you have a close look at the joint between the daggerboard and the lifting foil - share just a very little area) I will do it with a single dagger and lots of layers of uni carbon running from the daggerboard's top to the tips of the foils (i.e. they'll be a major part of the foil's laminate). Size of foil is 100*1500mm in a simple rectangular planform featuring a NACA 2412 profile. At the moment I'm thinking about two little struts with a low drag profile running from the middle of the dagger to maybe 400-500mm from the centreline on the foil to support the whole thing. Did you think about such an option, too? If yes, with what results?

As I need light wind performance, too, my boat will not be so far beyond from what is nowaday's standard in Moths (that's why I will use a standard aft rudder on an outrigger) although I also moved mast and daggercase further aft (mast step is now @ 1200 from the bow or 35.8%, front edge of daggerboard @ 2160mm or 64.4%).

I totally agree that the distance between daggerboard and rudder is critical. On my current boat the board is located at 2200mm from the stem with a transom-mounted rudder in the first configuration. It was awful on a reach in a breeze as the boat was far too nervous and it would always end up in a capsize to windward when inevitably losing control... A rudder outrigger (450mm) I fitted prior to the Worlds in France last year fixed the problem and it is now always controllable. So as a conclusion I think you're on the right way with your canard rudder, otherwise you would need an enormous gantry! Two questions though: Do you rotate the whole cruciform foil (i.e. with the canard hydrofoil, too or just the area below the transverse foil)? Do you have a front tiller or do you use cables or struts to connect a "standard" tiller with your rudder?

I'll start building next month and will put a homepage on the net to keep you up to date!

All the best, Olav

 

Olavs boat

Wardi, are the breathtakingly excellent sketches done by Olav representative of your boat as well? How will you guys ovecome the extra strut drag ascopmared to John Illets design and won't the strut impair manouverability off the foils?

 

Replies & Qs

Guys,
Thanks for your encouraging replies. Here are some answers and further questions in order of your postings.

Wardi
It is true that I have not majored on sub foiling performance but in keepng the foil count down and the aspect ratios high I was not too worried. My 600mm beam hull has a low Cp with lots of rocker (spring) and I am hoping that will help. Is there a particular design feature that concerns you on this?
I am having lots of ideas/worries about the bow rudder and am wordering whether a stern rudder might be needed as well. It is difficult to fly in the face of several millenia of aft steering! I know that a few have tried bow steering and had difficulty tacking, which is why it is considered good for proas, that don't want to tack! We will have to 'suck it and see'.

Tom Speer
Great picture. Imagine the disparity in $/Knot!
About upwind performance and main foil depth, I was hoping to match the existing C/B area with my twin strut/boards with a good aspect ratio and get away with a shallower assembly. It seems to me that having a fixed depth of a metre is a bit unfriendly for launching, beaching and running in to things so I have gone for as shallow as I can. This may prove a problem in waves but most moth sailing is done in protected waters. Does this argument stack up or have I missed the point.
The Shutt strut sounds interesting and it may be tried in Mk2 if Mk1 fails. For the moment I am going for KISS and a minimised parts count.

Olav
Excellent views of your design! It looks good. Interesting that you also wanted to move the foil & rig back. With your narrow hull you have little choice but to use one strut and any additional bracing will be parasitic but I would go for strength and put them in. I like a boat that is not going to break down.
About my bow rudder/ foil at the moment it is all moving, not separate parts but it still needs some thought. Today I thought up a twin blade system that fits over the bow and looks a bit like the font forks of a motorbike. So is has become an H rather than a +. Ideas are changing so much, the challenge is to declare a build standard!
Steering would be through lines to a yoke on the rudder I think but that detail is a long way from being defined.

Thanks for your interest everyone and please keep the thoughts flowing.

Cheers

Tom E

 

Tom,

first of all thanks for your answer and it's nice you like my pics!

In my opinion you should be careful with too much rocker! Especially if you are mainly interested in foiling rather than "conventional" sailing in light airs I'd prefer low rocker to help the boat accelerate and jump up on the foils. If you have a look at the current top designs (Hungry Tiger, Prowler) you'll notice how straight they are. However your wider hull will of course plane up earlier... My new hull design has its deepest point around midships with the stern raised 40mm and the bow 20mm but it must compensate its narrowness (Bwl 360mm).

Last night I thought again about ride stability. I now think another benefit of the Miller system is that one has a fixed axis where the whole boat pivots around (the canard). So the distance between the canard and the main foil does not have to be that big (as Wardy once said) in contrast to the Fastacraft foils where the axis may be located somewhere in between the daggerboard and the rudder due to the fact they both have adjustable flaps and so are both able to change the longitudinal trim of the boat. The question is, am I right?

All the best, Olav

 

Tom's ideas are similar to my ideas
My proposal to build foiler ( but probably not in time for this year )
Simple cheap ply hard chine hull, ~ 350mm beam with pintail
The pintail works well at low and high speed.
T or Y foil on daggerboard moved further aft than normal. ( maybe canting in wedge box)
No aft rudder.
miller bow foil / rudder, but with the rudder mounted forward of the stem on outrigger. There would be a rudder blade below the horiz foil. The rudder pivot can then be a rod so that the foil is retractable, and also the blade can be trailing the pivot. The rudder can be lifted so that the horizontal foil is above the waterline, but still a normal rudder below. This is needed due to the high drag of the horiz foil at low speeds.
The steering can be by (crossed ) strings... I used this on my 1994 axeman 3 foiler, with short normal rudder, linked to canard rudder/surface piercing v foil, to keep the steering action of aft tiller the same.
I think that the drag of the surface piercing foils is significant, so it's best to keep the number of surface piercing foils to 2.
The IACC boats have very long thin foils with many tons in the bulb, so i guess that moth foils could be built to take the twist OK with enough 45 degree carbon.