Southampton Solent Model Yacht Contest

ProaSailor

dreaming my life away...
6,054
753
Oregon
Nice work Will. I'm curious how your boat would scale to human dimensions? (LOA, Draft, Mast height, Displacement, etc.?)
model boats have proportionately deeper keels and are more stable and powered up. They sail fast for their length (high Froude number) so the hull proportions should be ideally a bit strange (high prismatics etc)
I see. So if volume is proportional to length cubed, then at 62' (27X), Will's boat would displace 39,760 kg? Or 87,660 lbs. (61,362 lbs. ballast and 26,298 lbs. boat/rig/people)? Yeah, that sounds strange.

 
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Panoramix

Super Anarchist
Nice work Will. I'm curious how your boat would scale to human dimensions? (LOA, Draft, Mast height, Displacement, etc.?)
model boats have proportionately deeper keels and are more stable and powered up. They sail fast for their length (high Froude number) so the hull proportions should be ideally a bit strange (high prismatics etc)
I see. So if volume is proportional to length cubed, then at 62' (27X), Will's boat would displace 39,760 kg? Or 87,660 lbs. (61,362 lbs. ballast and 26,298 lbs. boat/rig/people)? Yeah, that sounds strange.
I think that righting moment doesn't scale well with the rest thus "scale boats" need to increase draft to have a realistic behaviour.

 

musicman

Anarchist
735
0
Waterford CT
Nice work Will. I'm curious how your boat would scale to human dimensions? (LOA, Draft, Mast height, Displacement, etc.?)
model boats have proportionately deeper keels and are more stable and powered up. They sail fast for their length (high Froude number) so the hull proportions should be ideally a bit strange (high prismatics etc)
I see. So if volume is proportional to length cubed, then at 62' (27X), Will's boat would displace 39,760 kg? Or 87,660 lbs. (61,362 lbs. ballast and 26,298 lbs. boat/rig/people)? Yeah, that sounds strange.
I think that righting moment doesn't scale well with the rest thus "scale boats" need to increase draft to have a realistic behaviour.
Righting moment ends up being radically out of scale to get RC boats to sail well in a wide range of conditions. For example the 2m AC boats above are pretty close to 1"-1' scale but have 28" of draft with a 21 lb bulb on a 28.5 lb boat.

 

willp14335

Member
408
98
Anacortes WA
Nice work Will. I'm curious how your boat would scale to human dimensions? (LOA, Draft, Mast height, Displacement, etc.?)
model boats have proportionately deeper keels and are more stable and powered up. They sail fast for their length (high Froude number) so the hull proportions should be ideally a bit strange (high prismatics etc)
I see. So if volume is proportional to length cubed, then at 62' (27X), Will's boat would displace 39,760 kg? Or 87,660 lbs. (61,362 lbs. ballast and 26,298 lbs. boat/rig/people)? Yeah, that sounds strange.
That's actually very close. Scaled up displacement in maxsurf is 38.26 tonnes.

 

12 metre

Super Anarchist
3,856
673
English Bay
Nice work Will. I'm curious how your boat would scale to human dimensions? (LOA, Draft, Mast height, Displacement, etc.?)
model boats have proportionately deeper keels and are more stable and powered up. They sail fast for their length (high Froude number) so the hull proportions should be ideally a bit strange (high prismatics etc)
I see. So if volume is proportional to length cubed, then at 62' (27X), Will's boat would displace 39,760 kg? Or 87,660 lbs. (61,362 lbs. ballast and 26,298 lbs. boat/rig/people)? Yeah, that sounds strange.
I think that righting moment doesn't scale well with the rest thus "scale boats" need to increase draft to have a realistic behaviour.
Laws of similitude:

Area varies to L2

Disp varies to L3

HM varies to L3

RM varies to L4

So RM increases twice as fast as heeling moment, so a scaled up boat will always be way more powerful. Which is why bigger boats can have proportionately less beam, or draft, or displacement for the same RM/HM. Or proportionately more SA.

 
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Schmoo

Member
79
0
Ireland
Great thread, brings back fantastic memories of my time there. I was in 1st year in '98-'99 and we designed to the 60cm rule. I'm glad that the bulbs have been standardized, in hindsight, health & safety wasn't high on the list of priorities when we poured ours!

Good to also see that Giles Barkley hasn't aged a day in nearly 20 years!

 

F18 Sailor

Super Anarchist
2,675
253
Annapolis, MD
Very nice Will. Hull structure reminds me of my senior design UAV, we also went laser cut bulkheads with a fiberglass shell fabricated in a female mold. Making the tooling was half the battle.

For wings, your method is very light. May consider Oracover Lite in the future, which is what Dr. Mark Drela of MIT specifies on his built-up balsa gliders. He did a lot of weighing of different materials and that was the lightest, though Doculam from the office supply store is also pretty darn light and cheap and has many uses. Another thought, which may or may not be better, is light XPS foam with a very light (25gsm) glass. You can hotwire cut the foam quickly and cheaply using laser cut templates, plus the foam absorbs less water than balsa, though not a lot less. Thin G10 ribs (laser cut, or CNC routed if available) may be another option, as G10 is pretty much waterproof.

Funny how useful and common off-the-shelf materials intended for other uses are in the real world of engineering. You would be surprised at how many McMaster-Carr and local hardware store parts their are flying...

 
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willp14335

Member
408
98
Anacortes WA
Unfortunately I didn't have much choice of materials when building my sail. The plywood I ordered for the wing and structure did not come in the expected quantity so I had to make an emergency trip to the craft store to get more. They only had bass wood which is fairly heavy and not especially stiff.

I did consider the wood grain for the wing frames but did have to rotate the uppermost frames (considering they probably had the least load) 90 degrees to make them fit. These happened to be first in the water when the rig fell down and as the grain ran across the length of the frame they quickly bowed and some broke when they soaked up the water.

 
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d'ranger

Super Anarchist
29,017
4,184
Will, thanks for answering my stupid question. Of course there is an upwind and then a downwind race.

There are a lot of very bright people posting here so must take in small quantities.

 

zedboy

Member
257
0
Eastern Med
Another thought, which may or may not be better, is light XPS foam with a very light (25gsm) glass. You can hotwire cut the foam quickly and cheaply using laser cut templates, plus the foam absorbs less water than balsa, though not a lot less.
This was our preferred method for model airplane wings back when I was in HS. Hotwire cutting with a jig beats the heck out of cutting a zillion ribs by x-acto. Gee whiz I spent a lot of time doing that. Laser cutting would have totally changed our life.

We built small glider wings out of the school lunch trays, sanded to shape.

 
A

Amati

Guest
Given the reynolds numbers of your wing mast, how important were the cambers (or thicknesses) of its constituent parts?

wondering too about circulation around the jib/main system as far as lift for the jib? Relative to downwash for the main....

 
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