Model Test 2

[fede]

Hi, this is my second thread on the same topic.
I've finally built a 1:6 (1200 mm) scale model of a racing rib,put on a 7.5 cc outoard,weights centered on the CG (6.5 kg) and tested it.
Results are very satisfatory,the hull is very stable both long. and transv. and it gets on plane very fast with no big hump,also compared to other similar scale models.
Now my question is:
I'm not intereseted about resistence but more about stability,how does scale model trial relate to full size behaviour?
Can I expect the full size RIB to behave same/similar way?
For those who care I have a 2.8 Mb video of the scale model I can e mail.

[Raggi_Thor]

Stability will increase when you scale up to full size.
The full size boat will have 6x6x6=216 times the displacement of the model, it will be 6 times as wide, so it will have 1296 times rightening moment :-)

[fede]

Hi Raggi Thor, thanks for your reply.
Yes, I used the cubic relation for weights the 1:1 scale will weight (hopefully) 1400 kg.
The thing is all other forces (heeling,trimming moments etc) will be scaled too...

[Raggi_Thor]

It's almost allways safe to scale up, the stability scales like L^4 while heeling moment scales more like L^3.

[fede]

Thanks again,you have been very helpful.

[netjaws]

I think the question is: are stability characteristics scalable?

Any takers?






Joshua N Straume

[Raggi_Thor]

Yes it is.

[RANCHI OTTO]

no, it isn't because the waves and wind characteristics are not scalable

I mean...only static stability and not dynamic stability