Can you resize a design without complications?

[Stumble]

If possible means it could be built, then yes it is possible.

But let's take the 6' headroom the 30' boat has... When we scale everything up you now have a boat with 11' instead. As you mentioned it would be insanely heavy, and twice the width it should be, all sorts of problems are created by trying to do this.


On the other hand a good designer can take a 30 footer, and keep the same look, and similar concepts and design a larger boat using the smaller as a prototype. As I understand it, the maximum change is around 10%. More than this either way and you really need to redesign the boat.

[tunnels]

Originally Posted by MartinV

I was wondering; if you were to have plans for say an 36" boat, can you just half all the measurements and build an 18" boat without complications, or would the entire design have to be altered? I am talking mainly about hull shape off course.
(in extreme: think about RC model boats)

Simply dont even think about it !!
It is possible to respace frames to change the size aa small amount but the more you do it the bigger the inherant probelms become .
Saw a 28foot Yacht that was scaled to a 36feet and was a absolute pig of a thing ! Only one out of the mould was ever made and then the moulds were scrapped . Same with power boats . For each foot added the inherant problems the boat may have can grow by 20% or more !!

[themanshed]

Another option is give the boat to the US Government and you would have the values of the boat reduced to 50% in no time.

[tunnels]

Originally Posted by themanshed

Another option is give the boat to the US Government and you would have the values of the boat reduced to 50% in no time.

Or you can get married and the divorced and end up with a boat big enough to Hold in one hand Maybe but you wil have lost the bath tub as well so !!

[outside the box]

Originally Posted by MartinV

I was wondering; if you were to have plans for say an 36" boat, can you just half all the measurements and build an 18" boat without complications, or would the entire design have to be altered? I am talking mainly about hull shape off course.
(in extreme: think about RC model boats)

JFWIW..
Here is a simple formula we used when checking things for ½ scaling our prototypes of 30 and 40 foot catamarans as we wanted the prototypes to be usable as Picnic boats ready for market upon completion, instead of a lost cause as prototyping is too expensive to throw away in my mind. The scaling worked well.
To scale displacement take the scale ratio. For example you want to reduce a 10 foot boat to 0ne foot. That is a 10 to one ratio. Raise the scale ratio to the third power. 10 x 10 x10 =1000 divide the displacement of the full sized boat by the scale ratio cubed...in this case you divide 1000 by 1000 and the quotient is one. Lets take a different case in which the one thousand number does not occur twice. That is kind of confusing, so think of a ...16 foot rowing or sailing skiff. It might displace 360 pounds when occupied by one person. Let us build a model that is scaled to one and one half inches to the foot. That would be one eighth scale. so.....8 x 8x 8 = 512....divide....360/512 = 0.703 pounds. That is all the model could weigh in order to simulate the 16 footer. If you built the model to 3 inch to the foot scale then that would be a quarter scale or 4 to 1 model 4^3 = 64 .....360/64 = 5.625 pounds. The same rule applies when using the metric system of measurement.

[PAR]

Originally Posted by PAR

If a 36' boat is scaled down 50% to an18' boat, the laws of mechanical similitude will apply, meaning it will be a vessel with 16 times less stability of the original (which is why smaller boats are proportionately wider then bigger ones), she will have 8 times less mass and her surface area will be decreased by a factor of 4. In short she will be unstable given this scaling proposal. If you look closely (okay you don't have to look very close really) RC models usually have an absurdly large set of appendages under a model sailing yacht. This is because of the stability loses mentioned. The same rules apply for powerboats as well.

This said you can make an 18' version of the 36' boat, but it will incorporate "styling clues" not precisely reduced physical dimensions. In other words it'll carry more beam then the full size version, but the sheer line will be shaped similar to the full size, to bring along the styling clues. There are other factors to consider as well, so your best bet is to find an18' boat and work with it so it looks like the 36' yacht.

Originally Posted by boatn00b

I wonder what'd happen if you tried to scale a 30-something ft stepped (racer) hull up to about 55. And tried to put a couple of full size cabins and a flybridge on it. Obviously, planing area would go up with square of scale, and the weight would increase in 3rd power...and it'd weigh even more than that of course...Still, possible or not?

The laws of mechanical similitude apply in both directions (scaling up or down) folks. So, if you want to make a 22' boat a 24' boat, it probably will not kill you, but stray very far from little steps and you'll be "talking to Davie".

[ancient kayaker]

Scaling a boat down by a significant amount runs into 2 things that do not scale: the human body and the wind.

In the first case, the smaller boat ends up with too much heeling force because that scales to a cube law compared to the stability which - as noted above - scales to the 4th power.

In the second case, you can cut down on the number of crew but they'll object to the removal of body parts to fit them into a narrower cockpit.

However, for a certain range of boat size the disproportionate increase in heeling force is compensated by the proportionately greater weight of the crew and its ability to act as mobile ballast.

[viking north]

In the true meaning of the word "scale" yes objects can be scaled up or down but in doing so it would be common sense to use the engineering appropiate for the size of the new scale. One wouldn't use 2x4 framing for a dolls house, nor should one use the 3/8 by 3/4 in. steamed bent ribs of a 16ft. runabout for a 35ft. cabin cruiser. I realize these are extremes but even minor adjustments in scale could easily surpass the specs. on the dimensions of the materials used and the operating characteristics of the new machine. The stretch DC8 being a prime example.

A yacht is not defined by the vessel but by the care and love of her owner--

[PAR]

Again the law of mechanical similitude applies in both directions. Sam Langley sure proved this out in his attempts to scale up his flying rubber band powered models to full size. They folded up as soon as the structures where loaded. So as Bataan mentions, the scantlings too need the appropriate application of engineering.

[Easy Rider]

I think it should be obvious what scaling will work and what won't. If you scale a typical tandem canoe 100% up or down you'll have a useless boat. If you scaled a 42' Uniflite down 100% it would be ridiculous scale the cabin and deck. But to scale the hull only and make a center council open sport fishing boat w OB power should make a good boat w much of the qualities of it's 42' parent. And if you scaled up an 18' canoe 100%, cut about 10' off the stern and installed a transom you'd have a big "Laker" freight canoe. If I was to scale up my 10' Whitehall style row boat to 30' like my Willard and incorporate the "innards", cabin and deck of the Willard I'd have a very useable boat I think but it obviously would'nt handle like the Willard. Would be considerably wider and have the characteristics of a wider boat. It would have Greater stability and a quicker motion. The WLL would be longer and the displacement less (unless it had 2 tons of ballast like the Willard) so it would be faster and go all speeds w less power. All in all i think it would be a good boat .....just a different boat than the Willard.