Southampton Solent Model Yacht Contest
- Thread starter willp14335
- Start date
JustaBoat
Anarchist
Wow, BJ you must be proud. Will (and all) does all the data points on sail models = accurate data when scaled up? I can see (sort of) how it might work with sail and hull design but seeing the scale between the hull rig and keel makes me wonder. I would guess these would be considered ultralite design and not displacement design? For a better understanding, how would a functional model of RP's carbon cutter help in understanding its possible performance? Am I getting way to detailed and not looking at this at a higher level?
cheers
cheers
willp14335
Member
- Thread starter
- #143
I think because you don't have material restrictions in the same way with a model boat the proprttions differ to take advantage of the fact you can go for deeper draft and larger sail area. This in turn requires a hull shape with different geometry to account for the higher amount of power (hence the hull runs at a higher speed to length ratio than a scaled down big boat with proportionally smaller rig and lower draft). Because of this, models will generally be narrower, more full ended and deeper than a real size vessel. Additionally, I believe form stability also does not scale in the same way as the rest of the boat necessitating more ballast on a deeper fin to allow the sail area to reach full hull speed.
Scaling down Bob's CF cutters would probably work better than most boats because those have an exceptional ballast ratio but I'm pretty sure it's still not 69%.
Scaling down Bob's CF cutters would probably work better than most boats because those have an exceptional ballast ratio but I'm pretty sure it's still not 69%.
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Oregonarchist
Anarchist
great thread.
brilliant work, Will.
I'd be interested in hearing more on your thoughts as to the benefits of an immersed transom.
brilliant work, Will.
I'd be interested in hearing more on your thoughts as to the benefits of an immersed transom.
Designers have used models for a long time, of course. It started getting scientific in the late 1800s, and real precise in the 20th century. Now the computer models are the hot ticket.
I suspect that towed models and tank tests are best at comparing two similar designs, not so good at comparing two very different boats. And the degree of precision required for race boats is very high, maybe better than the model tests can deliver, so the designer can be fooled. See: Brit Chance.
I suspect that towed models and tank tests are best at comparing two similar designs, not so good at comparing two very different boats. And the degree of precision required for race boats is very high, maybe better than the model tests can deliver, so the designer can be fooled. See: Brit Chance.
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Ease the sheet.
ignoring stupid people is easy
- 20,349
- 2,342
Ease the sheet.
ignoring stupid people is easy
- 20,349
- 2,342
Things like wetted surface area get weird when we get to smaller boats too.
I remember reading illingworth and he mentioned the need for smaller boats having to have proportionally greater sail area than larger boats.
Of course, there are more knowledgeable people here that can explain it.
Rantifarian
Rantifarian
You can use dimensional (dimensionless?) analysis as a way to start comparing how dimensions scale. It is a really interesting tool when you start making sense of it, and very useful in real.world investigations.
Should be covered during one of your fluids courses later on
Should be covered during one of your fluids courses later on
willp14335
Member
- Thread starter
- #149
My original thoughts regarding the transom were to design something with the lowest possible drag so I put in a slight overhang. Looking at the boats now though, I think in anything but the lightest air the flatter buttock run aft with a slight immersion could potentially be faster if one was to max out the allowable sail area. I think I'd try it with the transom just touching the water with lots of flare aft to avoid a big corner of the transom dragging when the boat heels rather than the slight overhang I had on this boat. I think it could potentially allow for a slightly better max speed as long as it doesn't effect pointing too badly.
I also think a little more bow knuckle would have been better on this design. She made a smaller bow wave trimming by the stern with the stem out of the water rather than in.
On the note of scaling, I read the owner of Mirabella V has three RC models of the yacht on board. Who wants to bet the keel is deeper proportionally than the real yacht?
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olaf hart
Super Anarchist
A
Amati
Guest
When fooling around with my RC's:
They sail upright only in very light airs. Double ended low prismatic would be a happy condition here?
Otherwise, over on their ear. Higher prismatic here? Immersed stern might start to pay off, but maybe a clean release is good too? Does your class plane? Forced mode?
While round bilges are nice for wetted surface (kind of), square (ish, even) is better for wave making. But as as they tip, wave resistance does goes go up. As much as rounder bilges or a round hull
? As a chined hull tips over, it can get kind of like a v hull, so what kind of flare? (Did Pandora's box have chines? Or was it more round? )
Look at the last skinny low rider Moth designs. Pretty good in light air. I think that's why there are lower wind limitations for racing the foilers? You might check out International Canoe designs too. The Maas hulls kill in medium to heavy air. Not so much in the light. And of course, the open RC classes. Heck, any open class-
(What do you think?{ _} Or not.... { _} Check one please )
Just $.02 from an 'idiot with a computer' (tm!) who who has built some sailing canoes, a few RC's, and enough windsurfers to develop sensitivities to epoxy. :blink: You're on a neat adventure. Remember to check the safety sheets on all the chemicals you're using!
They sail upright only in very light airs. Double ended low prismatic would be a happy condition here?
Otherwise, over on their ear. Higher prismatic here? Immersed stern might start to pay off, but maybe a clean release is good too? Does your class plane? Forced mode?
While round bilges are nice for wetted surface (kind of), square (ish, even) is better for wave making. But as as they tip, wave resistance does goes go up. As much as rounder bilges or a round hull
? As a chined hull tips over, it can get kind of like a v hull, so what kind of flare? (Did Pandora's box have chines? Or was it more round? )Look at the last skinny low rider Moth designs. Pretty good in light air. I think that's why there are lower wind limitations for racing the foilers? You might check out International Canoe designs too. The Maas hulls kill in medium to heavy air. Not so much in the light. And of course, the open RC classes. Heck, any open class-
(What do you think?{ _} Or not....
{ _} Check one please )Just $.02 from an 'idiot with a computer' (tm!) who who has built some sailing canoes, a few RC's, and enough windsurfers to develop sensitivities to epoxy. :blink: You're on a neat adventure. Remember to check the safety sheets on all the chemicals you're using!
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JustaBoat
Anarchist
"I think because you don't have material restrictions in the same way with a model boat the proportions differ to take advantage of the fact you can go for deeper draft and larger sail area. This in turn requires a hull shape with different geometry to account for the higher amount of power (hence the hull runs at a higher speed to length ratio than a scaled down big boat with proportionally smaller rig and lower draft). Because of this, models will generally be narrower, more full ended and deeper than a real size vessel. Additionally, I believe form stability also does not scale in the same way as the rest of the boat necessitating more ballast on a deeper fin to allow the sail area to reach full hull speed.
Scaling down Bob's CF cutters would probably work better than most boats because those have an exceptional ballast ratio but I'm pretty sure it's still not 69%."
---Damn!!, answered in a very clear can concise way. Damn. This is what working with RP can do for your intellect? Sign me up... Maybe there should be a RP institute of naval arch, audio and music. Oh, not to mention the RP Culinary Institute. Did I forget one?
Scaling down Bob's CF cutters would probably work better than most boats because those have an exceptional ballast ratio but I'm pretty sure it's still not 69%."
---Damn!!, answered in a very clear can concise way. Damn. This is what working with RP can do for your intellect? Sign me up... Maybe there should be a RP institute of naval arch, audio and music. Oh, not to mention the RP Culinary Institute. Did I forget one?
willp14335
Member
- Thread starter
- #153
These boats are too heavy to plane but my bigger boat will in the right wind. The next design I hope to build someday is 125 cm so that should plane easily with a light displacement and large sail area.When fooling around with my RC's:
They sail upright only in very light airs. Double ended low prismatic would be a happy condition here?
Otherwise, over on their ear. Higher prismatic here? Immersed stern might start to pay off, but maybe a clean release is good too? Does your class plane? Forced mode?
While round bilges are nice for wetted surface (kind of), square (ish, even) is better for wave making. But as as they tip, wave resistance does goes go up. As much as rounder bilges or a round hull
Look at the last skinny low rider Moth designs. Pretty good in light air. I think that's why there are lower wind limitations for racing the foilers? You might check out International Canoe designs too. The Maas hulls kill in medium to heavy air. Not so much in the light. And of course, the open RC classes. Heck, any open class-
(What do you think?{ _} Or not....
Just $.02 from an 'idiot with a computer' (tm!) who who has built some sailing canoes, a few RC's, and enough windsurfers to develop sensitivities to epoxy. :blink: You're on a neat adventure. Remember to check the safety sheets on all the chemicals you're using!
Bob Perry
Super Anarchist
- 31,943
- 1,338
B/D for the cutters is 43%. Could be 45% if I used a light ship displ.
The BP school of yacht design closed when Will graduated. I have had maybe a dozen requests since Will but he raised the bar and I think I'll just let it end there on a high "C'. ( the musical note, not the grade)
The BP school of yacht design closed when Will graduated. I have had maybe a dozen requests since Will but he raised the bar and I think I'll just let it end there on a high "C'. ( the musical note, not the grade)
Oregonarchist
Anarchist
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Steve Clark
Super Anarchist
I am particularly pleased by the absence of radio control.
I never had the time or patience for it myself, and paddling or rowing around after the model is more than half the fun.
RC can disguise flaws in balance.
Were you able to have articulated rudders or were you limited to fixed skegs?
SHC
I never had the time or patience for it myself, and paddling or rowing around after the model is more than half the fun.
RC can disguise flaws in balance.
Were you able to have articulated rudders or were you limited to fixed skegs?
SHC
Speng
Super Anarchist
One of the kids a couple years behind me (his dad's a famous French multi designer) designed a very close winded boat that auto-tacked on headers (he claims it wasn't on purpose) but of course it went upwind like a bat outta hell.
Yes most certainly. 0.55 is a decent Cp for something like a TP52 which I don't think is as "fast" (Froude number wise) as a model yacht
Kirwan
Super Anarchist
At the model boat basin here, all the guys use a fishing pole to retrieve errant boats. Not sure if it's a hook on the end or just a weight, but it beats rowing or wading.
willp14335
Member
- Thread starter
- #159
I row after mine, but am more partial to RC because you can trim the sails better.
