- Hi Bruce,

> As capacity goes up with volume, not length, I suspect that the Big

...snip...

> Tortoise has even more than 25% greater capacity.

Increasing length increases volume, even if breadth and depth are not changed.

If the boat is scaled up in only one dimension, length being a good example, the increase in volume, and thus displacement, is proportional only to the change in that dimension. Big Tortoise is 23% longer than Tortoise on the same beam, but I'm not sure about depth. Assuming that depth is the same as the original, it's tempting to say that Big Tortoise would displace 23% more.

However, that would imply pure lengthwise scaling, which would increase the rake of the bow transom and flatten the rocker of the bottom. I suspect that the rake of the transom was not increased on Big Tortoise, and so she's going to have a slightly fuller forward bottom volume than if she were simply scaled from the original. Thus, I said "around 25% more" as an estimate of the actual increase in capacity. Obviously if the depth was increased too, the increase in capacity will be greater still.

Jon - Displacement of Tortoise is given on plans as 300 lb at wl just below transoms. At the equivalent point on Brick, the displacement is given as 875 lb. See page 88 of Build The New Instant Boats for Tortoise and page 7 of Boats with an Open Mind for Brick.

another point that may be worth mentioning is that the instant boats series are designed such that lofting is not necessary.

V/R

Chris

adventures_in_astrophotography wrote:Hi Bruce,

As capacity goes up with volume, not length, I suspect that the Big Tortoise has even more than 25% greater capacity.

...snip... Increasing length increases volume, even if breadth and depth are not changed. If the boat is scaled up in only one dimension, length being a good example, the increase in volume, and thus displacement, is proportional only to the change in that dimension. Big Tortoise is 23% longer than Tortoise on the same beam, but I'm not sure about depth. Assuming that depth is the same as the original, it's tempting to say that Big Tortoise would displace 23% more. However, that would imply pure lengthwise scaling, which would increase the rake of the bow transom and flatten the rocker of the bottom. I suspect that the rake of the transom was not increased on Big Tortoise, and so she's going to have a slightly fuller forward bottom volume than if she were simply scaled from the original. Thus, I said "around 25% more" as an estimate of the actual increase in capacity. Obviously if the depth was increased too, the increase in capacity will be greater still. Jon