How does that work? I got 2.44kph come out for the speed potential of my boat, thats barely a slow walking pace!
Luff 'em & leave 'em.
Can you give me the data you installed in the program?
Once I have them I can see what is wrong.
Hugo
Hugo, because I have webtv I can’t access your program; could you tell me what data you need and I’ll post it here if you would run the F3, F48-X3 and F48-D4Z. I have good data on the F3 so it would be interesting to see what you come up with.
The comparative numbers I’ve found so far are limited since they don’t consider righting moment and I’ve been trying to figure out a way to include righting moment of normal rc multihulls.
Ideally, I’d like to include the RM of a foiler which is a special case in terms of my boats(and all Bradfield and Ketterman foilers) which generate righting moment using the foils and therefore have virtually unlimited RM…
Just tell me what you need; I would appreiate the help…
Doug Lord
–High Technology Sailing/Racing
Hi,
I need the data from the top row.
It starts with “total weight” next “total wide of the boat” next “out rigger wide” etc. etc…
Hugo
1.4 48 7 91 91 4 4 2 85 10 100
there you go!
I think its the twin masts screwing it up, no input for number of masts!
Luff 'em & leave 'em.
Is the total wide only 48 cm?
This is extreme small!!
For this length of boat it must be at least 65cm.
A fast boat will be approximately. 85cm to 90 cm.
Hugo
Is the weight only 1.4KG?
This is with mast, electronics, battery etc??
Hugo
Well, this one breaks that rule! Not many cats have a center of effort as low as this one, with the twin rigs, it has no need to be wide.
Luff 'em & leave 'em.
Its all carbon, uses 4 cell nicad pack, its as light as I could make it!
Luff 'em & leave 'em.
This starts making sense.
I was also wondering how the sail was installed.
The program is not made for this type of boat.
Can you send me some photos?
Hugo
Explain this one to me. I just put some figures into your program and the results were very interesting.
When the boats weight was 5.0kg the speed potential was 13.46
When the boats weight was changed to 2.5 kg and nothing else was changed the speed potential was 8.56.
Tell me how a lighter boat is slower than a heavier one?
If this is so right(as suggested) I might go out and build a really heavy boat as the speed potential can only go up.
With this test I think you need to try again.
Peter
yup…put a higher main sail; and the speed goes down! more weight—>faster!
I am no multi pro at all; wondering!
Wis
if it isn’t broken, don’t fix it!
Hi
A higher main sail gives more torque on the boat and the boat will turn over more easy.
If you reduce the height of the sail on the boat it becomes more stable and can cope with more wind which will give more speed.
On a mono hull you have the same principle.
If there is a stronger wind, and you reduce the amount of sail the boat will go faster.
If there is a little wind the torque on the boat will drop.
If you get more sail on the boat the torque and trust will rise and the boat is faster.
I once had a steal boat.
Whit standard sail we never where able to go over the wave speed of the boat (hull speed 13 km/h).
In a storm with 1/3 of the sail area we where able to go over the wave speed (15.5 up to 17 km/h).
Conclusion:
To achieved the max. speed out of you boot, you need less sail, low on the boat and as much wind as possible.
To get the max. speed out of you boat with little wind you install as much sail as possible.
Regards,
Hugo
Seems to me that somewhere, a mathematical relationship of the size of a triangle drawn between the mast, and 1/2 the beam would need to be included. Actually it would be a 3D calculation, as there is also the distance from the mast to the bow of the main hull as well.
The higher the mast goes, the more stability is lost. If a narrow beam, the boat will tip to it’s side. If a short distance to the bow, the more loss of stability to a pitchpole. For true accuracy, a diagonal triangle from mast to bow of floats would also be usedful as on any broad reach, the force vectors would be in that direction.
Download Attachment: [ stability.jpg](http://www.rcsailing.net/forum1/data/dick lemke/2004422152122_stability.jpg)
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Forgetting wind, waves and apparant wind direction, a tall mast (high aspect ratio) while faster would also be easier to tip over in any of the above 3 directions. Thus my suggestions to purposely keep sail area and mast height limited and short while learning to sail.
For a fast boat you need to look at old ships.
They had long boom to keep the sail low on the boat.
The fastest multi-hulls have a low mast, are wide en minimal weight.
For mono-hulls the wide is replaced by depth.
A German friend of mine had a classic light weight steal boat with a deep keel.
When in the '80 new sail boats build for racing was tested he always came on the water with his boat and was most of the time much vaster.
Modern boats are usually build for a rating not for absolute top speed.
Hugo
The problem with anything(formula/program) I’ve seen so far is that it can’t cope with the fact that Bradfield(F3 ,X3 and described under foiler I and II) and Ketterman foilers develop their own righting moment and thus have virtually unlimited stability at the cost of very, very little weight. No formula I have yet seen can cope with this.
Now for structural reasons the Ketterman foiler uses twin rigs while the full size Bradfield foilers Rave and Skat use single moderate aspect ratio rigs.
The downside to these boats is that they are limited in speed only by structural limitations not by lack of stability; if you sail too fast you break the boat-not capsize/pitchpole! On model foilers that is the only limitation(outside of certain types of waves) but on full size boats they can sometimes ventilate though that is very rare; doesn’t happen on models.
Doug Lord
–High Technology Sailing/Racing
With the caveat that …
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The wind is strong enough to keep them flying!
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The race course is free of weeds!
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None of the above boats have ever managed to compete against a “normal” multihull in closed course, around the buoy racing, where tactics, and tacks comprise a percentage of the effort needed to win.
When a foiler can be demonstrated to be superior in all of the above instances, then it would be something to consider.
In the meantime, with no sales, limited number being home-built, no race results, the concept certainly has not been proven in the real r/c world. Perhaps if we saw 6 of these entered in actual races, and they consistently end up in the winners circle, most of us might get excited.
There are classes where these can be shown and demonstrated - some day they might? I reserve my acceptance until they do - and are.
Hi alle,
If you look at my program you can see 2 figures torque and stability there is you problem.
The torque is based on a fixed wind speed.
It is possible that your lighter boat has turned over all ready at the mentioned speed and by adding more weight you get moor stability and therefore more speed.
I?ll come with an next version where you can ad the wind speed in the program and I?ll tell you if the boat will turn over.
Hugo