Radio controlled sailboats

Excellent advice for all. For design issues in modern fin and bulb boats, this is a good place to start:

http://www.rcsailing.net/forum1/showthread.php?6472-Nzl-20

If your taste runs to full keel boats, the issues are discussed here:

http://www.rcsailing.net/forum1/showthread.php?6472-Nzl-20

Cheers,

Earl

 

The challenge you have is getting a scale hull to float on her lines unless the displacement is scaled also.

65 cm is small for a RC boat that has good control and sailing ability.

 

If you put the drawing available I can pass it to the freeship and make an analysis, but in principle, as Doug said, the problem is the displacement. A RG 65 has a displacement of 1 kg in average, a real boat with 6.5 m would have 1000 kg to be able to offset a decrease in scale.

 

Hello Dia de Playa

Hi,
Iam an amateur designer and I build scale models to see my designs sailing on the water.

My first attempt (without experience in rc modelling) was a 1:10 build of a 8m sharpie, 80cm model. The model is sailing well now, but i had to add a lead bulb at the tip of the centerboard. With it i just just managed it to stay inside the 1,6kg scale displacement.

See my posts here: http://www.boatdesign.net/forums/boat-design/30-plywood-sharpie-30029-32.html


I am doing the same with my newest design, a 6.6m Modern Racing Sharpie,

http://www.boatdesign.net/forums/sailboats/seaworthy-bigger-i-550-suggestions-39226.html .

I think you can build your model in a 1:6.5 scale and get a nice sailing boat.

Assuming that a mini transat has a fully loaded displacement of 1050kg your model would be 1 m long and 3.8kg heavy. If you build the boat as light as possible and make the keel heavy i see no reason not to do it.

I don' understand the reason why you stick to the model racing classes as one meter or the rg 65? Do you expect you can race against these boats? If so ... sorry, there is no chance of winning.

Have fun with your scale model!

Michel

 

I only have this draw:

 

Why do you think that a scow have no chance to win? Under strong winds I hope this design would be competitive. I was doing some simulations and I concluded that with 35º heeling or more the scow is very efficient upwind, and downwing was the design purpose.

 

Based on the calcs below and the weight estimated from the following website, this boat would scale down to one meter perfectly. Whether or not it would fit the IOM rules or not I couldn't say.Much of the advantage of Raisons boat was his power to carry sail as compared to other Mini's: if you scale this down to a rule that limits all boats to the same SA it is not likely to work well... Thanks for the drawing of Raisons boat.
Based on the new info (below) that Fred found, the scaled down displacement of Raisons boat would be too light for an IOM.

http://www.minitransat650.com/html/ratios.html

1074kg=2362.8lb(This displacement was an estimate-Fred found Raisons actual displacement see post 26=700kg=1540lb)
21.32' cubed=9690

3.38'(one meter) cubed=38.61

38.61/9690=.00398 ; .00398 X 2362.8= 9.4lb(.00398 X 1540lb= 6.12lb)

 

Another very popular model of a scaled down boat is the EC-12. It is claimed to be a direct descendant of a 12 meter model built by Charlie Morgan, His model was tank tested at Stevens (or somewhere). His Americas Cup challenger was based on the model. The AC boat did not make the cut. The model did lie around for years until some bright guy decided to make it into an RC boat. In the process some of the scale components were violated but the hull remains as originally designed by Morgan. The EC-12 has become an international class with a large subscription and a very well administered class association.

 

Hi Dias de Playa,

You cannot win in a regatta against a IOM. Its not the fact that you will build a scow, its the fact that you want to build to scale. The IOM as well as the RG65 are designed as model racing boats and your scow is designed as a 6.5m transat racer.

The IOM Designs are designed to face the higher resistance from the water (that cannot be scaled). One model designer told me that models are sailing thruw oil, compared to real boats. So they benefit from their very slim hulls and their very deep, very heavy ballast to counteract the very tall rigs.

Even the planing skiff designs in the IOM are are very slim and are not really competitive.

So, you have two options:
If you want to sail IOM regattas you have to build a IOM design to be competitive. One of the Planing Skiff types could be a lot of fun in a strong wind.

If you want to build a scale model, you will have a lot of fun with the real appearence of the boat. Perhaps it will plane.

I forgot to say that the model of my current project is built in a scale of 1:4,5, to give more realistic stability and sailing behavior. A friend is building my Sharpie Cat Ketch Design with a 1:5,5 scale. The 1:10 models is sailing very good now, but I had to make two modifications (more and deeper ballast) to make it sail realistic. The boat is designed for harmonic and balanced cruising behavior, thats why the 1:10 scale model is working good. My more radical CF 6.6 would'nt sail that well in 1:10.

Michel

 

I have heard this several times, but a yacht designer told me this is a myth, that the models are tested at scale in a totally realistic. He said the only thing that changes is the speed, if you see a video of an R / C in slow motion looks like a real yacht, and that's what designers do, videotaped evidence in tanks and then the play at a slower speed to see how it will move the actual design.

 

DiasDePlaya

By here:


http://seasailsurf.com/seasailsurf/actu/5868-david-raison-va-degainer-son.html?lang=fr

- Longueur coque : 6,50 m
- Largeur : 2,99 m
- Tirant d’eau : 2,00 m
- Surface voilure près 51,0 m2
- Surface voilure portant : 127,0 m2
- Déplacement de jauge : 700 kg

I do not know the rules of this class, but if the total weight of the boat is 700 kg, if you reduce by 1/10 scale, which is what you want, the displacement of the model is 0.7 kg, which is good for one RG 65, the problem is that you have to really excel in the construction, but if you stay with 0.8 kg or 0.9 kg, will have no problem, only that the freeboard will be somewhat diminished.
For me, it can reduce to 65 cm, but I have no idea of ​​the performance.
One thing I'm pretty sure, I think the rudder will cause problems since the RG 65 can only have one rudder, it will have to be very long.

 

Researching more I definitely have to build the boat in one meter, 65 centimeters would be too light to float in the water line design and is almost impossible to achieve.

Whether it will be competitive against the IOM designs there are people telling me that is impossible and others tell me it might work. Since I love to think outside the box if you prefer to dream that will work.

Regarding the density of water, a person who handles very well in Reynolds numbers and hydrodynamic told me that the theory that a miniature hull is equivalent to a real-hull sailing on oil has no basis in physics.

 

There are lots of scale, one meter designs of proven performance.

They race them here every Tuesday night!

Happy sailing.

 

==================
See the link in post 22.....

 

The physical aspect of models and real boats is that the Reynolds numbers of both are different.
Make a test on a scale model does not really represent the actual vessel, as tests have different Reynolds number. The model Reynolds number (which represents the conditions of flow of the water) is much smaller than the actual Reynolds number of the real boat.

William Froude solved this problem for quite some time. He divided the total resistance in two components: the friction and and the other, he called residual.
The model test tank, even today, are made using the Froude model.

In this model, the residual resistance of the model can be applied for real boat directly observing the scale model, being the problem of the Reynolds number powered only the frictional resistance, and so this can not be passed to the real boat using actual scale model.
But empirically known, calculating the frictional resistance, both model and actual boat as it solves the problem.

The Froude process is to obtain the total resistance of the model, in a test with the same Froude numbers. We removed the resistance of friction of the model (calculated) and obtain the residual resistance of the model.
This value is passed on to the real boat using as few real scale model.
We calculate the frictional resistance of the real boat, and we add the two getting the total resistance.

In practice, for models, the Reynolds number helps us to calculate the frictional resistance and choose the rudder and keel foils.

The problem in using the design you have is to know the correct displacement.

700 kg is acceptable to RG 65 if you make a careful construction of carbon fiber and very optimized weight and use a light bulb. If 1000 kg , is much better and is within the average weight of RG 65.
For IOM is only see the calculations made by Doug.
I will pass the project to the Freeship and make a correct assessment of displacement, but it will take a few days, for lack of time, but I will this weekend.