Would this work?

Rcsailing.net General Discussion
21

<font face=“Arial”>Hi Marcus,

I have enjoyed your posts and have some comments on the design. I hope this is the type of critical thoughts you are looking for.

You make a bold statement, ?I didn’t like the drag that is caused by the steps at low speed in the hulls of the hydraplaneur, so I thought of a way to get rid of them.?

As I see it, you?ve traded the ?drag caused by steps at low speed? for transom drag. You will need submerged transoms on the amas unless you are planning to have the angle of attack adjustable while in motion. If the sponsons are fixed then you will have transom drag which will be greater than on the hydrapaneur.

It would be good for minimum resistance to get up to displacement speed and then increase the angle of attack to create lift and reduce the wetted surface. In the powered outriggers, the angle of attack of the sponsons is critical to performance. That will most likely still be true in your design.

I am curious of the dynamic lift from the keels. When the craft heels such the leeward foil is horizontal (about 45 degrees), it will still produce lift as the angle of attack will be large since the ama is quite offset from the centerhull. Also the leeway would increase lowering the heeling moment. These two might combine to make the hull more likely to remain on its feet. OR since the lift from the foil will be to windward of the ama it might contribute to the heeling moment if the cg moves far enough to leeward at the boat heels. I think that the choice of angles is important for the keels to get the former situation rather than the later.

One more thing to consider is the shift in the center of lateral resistance aft as the boat transitions from displacement to planning mode. How is this accounted for in the skiff designs that seem to sail even with no boat in the water?

I hope this provides you some food for thought.

Regards,

Luke

PS what software did you use to the draw the pic, looks like a nurbs surface.</font id=“Arial”>

22

Hi Luke,

Thank you for your feedback.

I actually thought of the amas to be adjustable in angle of attack, so that I loose most of the transom drag while under hull speed. When speed is high enough the amas would increase their angle of attack to start lifting. To have this function to be adjusted automatically, might be quiet a challenge thou. and maybe its not even necessary…

I believe - but maybe I am wrong here, that Transom drag is less of a problem than the submerged drag of the stepped hulls (if you got a nice spoiler shaped end like most modern boats with submerged transom do).

The foils should be adjustable in AoA so that the windward foil pulls down and to windward and the leeward foil pulls up and to leeward. I guess I have to test that to see how it works. Either the boat will slip sideways and loose power when heeled too much or it will point away and have even more sail area exposed.

This concept has to answer many questions on the water. Too many factors that I can’t predict. But it looks like fun to buildt, so I will go on with it.

I am currently working on the concept of a Zero net righting moment rigg for this boat (like on sailrocket) to support the concept of the dynamic stablity further - Thanks to Will for this idea and Dougs input on this.
I am thinking about a mast that is mounted in two points: one hinge that is at about half the mast height and is supported by two carbon rodds running to the middle of the amas. The other point is a ball bearing mounted sledge that is running on a rail across the beams.
That way the mast foot can slide from side to side and the CoG of the mast is fixed. With this configuration it should be possible to lean the mast to windward to reduce heeling force.
By making the rail an arc it should be possible to have a fixed sheeting line. The angle of attack of the sail would be adjusted by sliding the mast from the side to the middle (leaning sideways to leaning backward).
Hope I did make myself clear.[:-propeller]

Its in an early conceptual stage, but maybe it’ll work…

The software is Lightwave. I am not using Nurbs, only subdivision surfaces. They work great for organic shapes.

Marcus

23

Hi Marcus,

I haven’t had much time to think about what you posted but I thought you might find this website usefull for your tilting rig idea.

http://www.wingo.com/chriswhite/tiltrig.html

Cheers,

Luke

24

Luke,

That’s a configuraion very close to what I thought of. I believe thou, that the performance might be better if the rail is an arc, so that the mast leans backward when centered for broad reaching. This might reduce nose diving.

When sailing to windward, the mast would be tilted but not leaning backward that much to reduce heeling moment.

I haven’t had time to sketch it out yet, but i think it could work.

HJ,

I am really courious to see the pictures you wrote about. Do you have the email address of the guy who buildt the ship? Maybe he’ll keep me from wasting my time…[:-indifferent]

Marcus

25

Hi Marcus

I’m not sure I understand your curved track idea that well. Is it understood that the sail will be vertical and tilted aft when reaching and tilted to windward but more upright in profile when on a beat? If that is the case, then I begin to understand.

Also, are the foils retractible, then you could have a zero heeling moment craft like Sail rocket, but I think the extra foil on your design will upset the balance.

It would be nice from a wetted surface point of view to fly one of the hulls, but the heeling angle of the craft is naturally coupled with the angle of attack of the foils. This is an area of the design that will require a lot of study.

Luke

26

That’s exactly how I pictured it, Luke. By using a curved rail, the mastfoot moves forward on the reach and tilts the mast backward.

With this configuration it should be possible to have the mainsail sheet fixed and use it just for fine tuning, since the rotation of the wing/sail would happen through the position of the mastfoot. (The sheeting point on the boom would basically follow along the rail with pretty much the same radius)

You would need the windward foil for resistance against the rigg forces. I think that it might be better to leave the leeward foil in the water for supporting the righting moment, just like on Patient Lady 6. But I guess that is hard to judge in theory and maybe not that much easier to judge on the water…

Regarding flying a hull: When using a Zero heeling force rigg, I wonder if it makes that much of a difference if you either fly a hull or have the whole ship plane on its three sterns. Always assuming the whole thing works good enough to have it plane, of course…[:D]

I think I’ll try and build a test setup over Christmas and see how that works.

I am still courious to see the pictures Beachbum was refering to. I sure there is a lot to learn from…

Marcus

27

Hi Luke,

I know you got what I mean. Just for the fun, I did a little rendering:

http://www.digitallightfactory.com/Private/Concept.mov

Quicktime 424kb

The yellow cross is the pivot the mastfoot rotates around. I didn’t have time yet to calculate the angles and arm lengthes needed to get a decent tilt in each position.

Mmmmh, I actually don’t even know which tilt might be best for each position. Any input appreciated.

thank you,

Marcus

28

I haven’t been around here for a while, so excuse me if I ask questions answered before.

Thats a cool looking beastie, but why the long bows? It seems to me what your working on is a cross between a windsurfer and sailrocket that can sail on both tacks. But surely when the rig is moved back and sheeted in the c of e is moving a long way behind the angled daggerboards on the amas and therefore loading up the rudder, which will have to be pretty huge (therfore with lots of wetted surface) to stop the boat spinning into the wind.

Could the amas be a bit further back so that whe the rig is at max cant(?) and sheeted in the c of e of the rig lines up with the CLR of the windward board (somhow youve got to lose the leward one really, and have the boards assymetric), with the rudder just being a tiny trim tab to keep the thing on track? Or even ditch the rudder and just slide the rig back and forth on the end of the track to keep the balence…

Sorry If this is all useless garble, if i had a scanner handy I would post some sketches.

29

Matthew,

No garble at all. You are right, its somewhere betwen a surfer, sailrocket and maybe a bowerboat hull concept.
The whole concept is far from fine tuned. So its absolutely possible, that its far from being balanced right now.
The reason why I think the daggerboards have to be far forward is that the force vector of the sail points roughly in direction of the amas bows. If you take a look at the ORMA Tris, you’ll see, that they all have the daggerboards on the amas further forward than the center daggerboard to compensate for that when sailing on their amas only.
I am pretty sure that the daggerboards are too far forward right now, but the boat is really wide and so I wouldn’t move them too far back. I have to make some decent sketches with the force vector at different sail angles in them to see where the lateral center of the wetted surface has too be.
I doubt thou that I’ll be able to come up with a precise result that would work right away, since its hard to guess how the ship will behave when planing. I guess it’ll need a lot of testing.

Marcus

30

Hi Marcus,

Interesting little video there. Do those take long to make?

I have been very busy at work so sorry for not responding for a while. I was just looking at the motion of the mast and sail. I wonder what you will use to tension the two forestays or if they will be rigid. Using the vang would mess up your sail trim and using a backstay, it would need to be automatically adjustable. I don’t think you could manually adjust to the correct tension eash time you want to sail on a new tack.

Thats my thoughts for now. Any new progress in your camp.

Luke

31

Luke,

Doing animations like this (usually of a higher complexity) is my profession, so I should be reasonably fast… at least I hope I am. doing a design like this takes one to two hours. But its only designing by the look of it. No math or VPP involved.
When it looks about right, I print it and do some finetuning of the lateral plan and the sail plan to get it balanced. Works pretty good so far. No idea however if the results are any good speedwise.

The forestays are rigid carbon rods. The mastfoot, the feet of the two forward rods and the joint up in the mast need to be stable hinches with ball bearings since they take all the load. The only lines on this boat would be the main sheeting line and the lines to move the mastfoot.

Haven’t proceeded any further because of work. I am currently thinking about how to build everything: the rail, the sledge, all the hinches and so on.
The little devil and the little angel on my shoulders are having fights wether I should buy myself a small CNC Mill for easy construction of all the moulds. The two have not decided yet… [:D]

32

I hope you do some buckling calcs on your ridid mast supports. At one sail angle, only one support will transfer all the sail force to the hull and it is very thin for its length. Maybe make them wing shaped and add a cross beam halfway up connecting the two.

I think making the forward amas adjustable will be the biggest challenge. With such long forward hull, the transom will need to be quite deep to have an inclined lifting surface. I think that will present a lot of drag that will hinder the concept breaking free and reaching planing speed. If you could build speed and then pop the amas down into an inclined position, it might just lift off and scoot.

cheers

luke

33

I thought of using 12mm Carbon rods of about 1,3 meters length. As far as I know, this is pretty much the diameter they are using for unstayed M-head masts. I think i could even go a bit thinner, but I might be wrong.

regarding the amas:
That’s exactly how I planned it: keep the amas flat on the water until the boat is fast enough to incline them and take of - just like on a plane. [:D]
I believe thou, that in practice you would just use this feature when there’s little wind and transom drag becomes a major problem. If there’s enough wind, it might not make that much of a difference… and you might have too little time to take care of it.

Marcus

34

I’ve used 10mm carbon tube for un-stayed masts of that length before, you wont get it to bend that much.
Now this CNC Mill, are you thinking of getting one big enough to do 1m long hulls?

Luff 'em & leave 'em.

35

yep. That’s my experience too. a 10mm is hard to bend. 12mm is nearly impossible to bend.

Matt,
You can find the mill I am thinking of here:
http://www.team-haase.de/content/typen_cut2000_1.html

Its in German, but I guess you can figure out the Specs quite easily.
Lengthwise its no problem, but there is one reason why you cannot mill a 1m hull in one piece: Small mills like these have just 3 axis movement, but are not able to tilt the mill head. That way the dimensions of the mill head (don’t know the technical term) limits how deep you can digg in vertically. In fact its limited to about 20mm vertical, then the head will hit the piece.

You can make the two halfs of a slim F48 Tri hull, but you would have to mill a one metre hull in several layers.

Damn expensive for a hobby thou. My wife would/will kill me.

Marcus

36

ja !!!das ist aber teuer! [;)]

Wis

_/ if it isn’t broken, don’t fix it! _

http://wismerhell.esmartdesign.com/index.htm

37

Very ‘teuer’. Even if you want to build the thing by yourself. Maybe you save a buck or two, but you end up roughly at the same amount.
I thought of different strategies to sell it to my wife: “OK, honey, here’s the deal: we all pass on our vacation for the next two years, and I get the mill in return.”[:D][:D]

38

I thought to myself man, that is very cheap for a CNC mill. But I managed to find a picture here

http://www.desktopcnc.com/haase_cut_2000.htm

And then the “cheap” price makes more sense. Its just a rotary tool, three stepper motors with screw drives and the software to run them. We had one of those at school that was built as a thesis but it had accuracy issues because the vertical arm was not stiff enough. It was built with a router and it’s software could only cut waterlines. so you still had to back and sand out the cutter marks. Even so it sure beat just about any other method of getting a foam plug.

Would you be able to use the cut2000 for aluminum or only foam?

I didn’t realize the carbon spars were so strong. Are those kite spars or something special for masts(expensive)?

cheers

39

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lucashurt

Even so it sure beat just about any other method of getting a foam plug.
<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

Always trying to save money … for myself and for you !

Bandsaw (or cut out) the top and side profile of your hull from foam following hull top and side profiles. Draw directly on the foam and use a coarse bladed hand saw if necessary. Stay wide of the lines.

Then take the station templates and make very thin metal or aluminum FEMALE templates.

Press the templates into the sides of the hull at each station location. This will press a line/groove into the foam.

Using 80 grit or real coarse sandpaper and a wood block for support - or even an electric planer if you have access… simply remove the foam between the stations until you reach the end of the groove that was pressed into the foam.

Bingo - you have just shaped your hull side to match the FEMALE template. Fair in between all the template grooves, finish sand and glass. You are done. - OR - make a female mold off the foam plug if you want to make more than one hull.

In a sense, you are doing by hand what the CNC is doing by motor, but at a fraction of the price.

Often we get so immersed into the use of a male station template, we forget about the “other” (female) template that is produced when cut out.

To shape foam quickly and accurately, go to Jean Margails web site (WATER RESIST) and he has a photo sequence that shows this process. I have received written permission from him to do a process manual, but in English… just haven’t had time.

If you make full size templates for a one meter, and press down from an up-turned keel, the process works the same. It provides grooves that match the template, and you simply sand down until the grooves disappear!

Now you can still make the F-48 trimaran, AND go on vacation. Your wife will be so proud!
[:-bonc01]
Cheers [:D]

<u><font color=“brown”>EDIT/ADDED:</u> here is the link to the photo area of Jean’s site: </font id=“brown”> http://water.resist.free.fr/Anglais/Construire.htm

<font color=“brown”>and two photos… first shows the FEMALE templates after being pressed into the side of the foam hull half. They are located per drawing template stations. Second photo - have to look closely - shows where templates were removed leaving the grooves. Now one just sands and fairs the hull half down until the grooves disappear.

[Jean used thin 3mm plywood for templates - I prefer to use aluminum which can be sharpened and used almost like a knife.]</font id=“brown”>

Download Attachment: [ build10.jpg](http://www.rcsailing.net/forum1/data/dick lemke/20041118165117_build10.jpg)
15.67KB

Download Attachment: [ build11.jpg](http://www.rcsailing.net/forum1/data/dick lemke/20041118165128_build11.jpg)
16.02KB

40

Luke,

you are right, that its sort of a CNC Mill ‘light’.
Its stable enough on the horizontal and vertical axis thou. Since the software is able to interpolate over all three axis, you are able to mill 3D shapes not just crossections. At a little extra price you can add a better rotary tool and mill Aluminum too.
Obviously its no industrial mill, but since work is keeping me from building, I am thinking that this might be a good compromise to advance at least a little bit with my design.
Design it - hit the button in the morning- and when you come back from work in the evening its already waiting for you.
A little sanding, a little glassing, and you got the perfect shape without any dents.
(Its obviously a perfect tool for building hinches or moulds for fins etc.)

Maybe I am wrong about this. Anyone ever build a plug with actual 3D milling?

Anyway, even if it works great or not at all, this forum will never no. Cause my wife will have killed me already before I can even post here.

Marcus