Shortened LM18

[Matt Gent]

BBC no longer posts line drawings in the study plans, but from the 3D images the lm18 appears to me near constant section running surface in the aft third or more.

I bet the boat would run fine just re-lofting the transom 18” forward (no scaling) on the same panels and bulkheads and adjusting the deck layout to suit. Will make a bigger and more stable boat than scaling down for the same build cost. May not pole quite as well.

These shallow V skiffs aren’t rocket science. Other designers offer the similar designs in varying lengths. It’s (understandably) much easier to just make a 10% up/down rule than to answer redesign questions from each potential customer, or to re-draw all the flat panel shapes.

[TomW1]

Jeff,
I love your boat and the sizing of it

How did you go about scaling it up?

Thanks! It's a great little boat: carries the two of us with ease but is small enough to paddle like a SUP when called for. I should have moved my B frame forward so my client-wife has more foot room, or else made my consertical instead of swept, which would have reduced my footroom very slightly but increased hers quite a bit(though this would move weight rear-ward, so maybe not)

The scaling is pretty simple: go through each measurement on the plans, add 10%, cross off the old measurement and write in the new one. To easily calc the 10%, I created a spreadsheet that let me enter the inches, 1/2 inches, 1/4 inches and 1/8 inches and it would output the new measurement in inches, 1/2, 1/4, 1/8 etc.
thSo if I input 20 3/8, I'd get 27 3/4 output.

It's a bit slow, but effective.

Don't scale the transom height!

He has to scale the trasom height to meet the the height of the sides then cut down an area where the motor goes to meet the shaft length of his motor, 15 or 20".

Tom

[TomW1]

Duplicate

[NaplesEuroTech728]

Jeff,
I love your boat and the sizing of it

How did you go about scaling it up?

Thanks! It's a great little boat: carries the two of us with ease but is small enough to paddle like a SUP when called for. I should have moved my B frame forward so my client-wife has more foot room, or else made my console vertical instead of swept, which would have reduced my footroom very slightly but increased hers quite a bit(though this would move weight rear-ward, so maybe not)

The scaling is pretty simple: go through each measurement on the plans, add 10%, cross off the old measurement and write in the new one. To easily calc the 10%, I created a spreadsheet that let me enter the inches, 1/2 inches, 1/4 inches and 1/8 inches and it would output the new measurement in inches, 1/2, 1/4, 1/8 etc.

So if I input 20 3/8, I'd get 27 3/4 output.

It's a bit slow, but effective.

Don't scale the transom height!

That sounds easy enough but is that truly 10% scale? If my math is correct 20 3/8" scaled up 10% should land around 22 7/16"

[jonnymac]

I’m sure that was a made up example, without exact math.

Jeff,
I love your boat and the sizing of it

How did you go about scaling it up?

Thanks! It's a great little boat: carries the two of us with ease but is small enough to paddle like a SUP when called for. I should have moved my B frame forward so my client-wife has more foot room, or else made my console vertical instead of swept, which would have reduced my footroom very slightly but increased hers quite a bit(though this would move weight rear-ward, so maybe not)

The scaling is pretty simple: go through each measurement on the plans, add 10%, cross off the old measurement and write in the new one. To easily calc the 10%, I created a spreadsheet that let me enter the inches, 1/2 inches, 1/4 inches and 1/8 inches and it would output the new measurement in inches, 1/2, 1/4, 1/8 etc.

So if I input 20 3/8, I'd get 27 3/4 output.

It's a bit slow, but effective.

Don't scale the transom height!

That sounds easy enough but is that truly 10% scale? If my math is correct 20 3/8" scaled up 10% should land around 22 7/16"

[VT_Jeff]

That sounds easy enough but is that truly 10% scale? If my math is correct 20 3/8" scaled up 10% should land around 22 7/16"

Good catch, 22 7/16(22.4125), which is actually what my spreadsheet says, maybe a misfire between the read and the write!

[pee wee]

. . . and there's a good example of why the metric system is better for scaling boat plans! Get the metric plans (some plans come with both systems of measurement), it's much easier to work with. 2.7 meters x 1.1 is easier to figure (less likely to make an error) than feet, twelfths of a foot (inches) and eights, quarters or halves of an inch. Buy a metric tape measure and you'll be set.

[jonnymac]

. . . and there's a good example of why the metric system is better for scaling boat plans! Get the metric plans (some plans come with both systems of measurement), it's much easier to work with. 2.7 meters x 1.1 is easier to figure (less likely to make an error) than feet, twelfths of a foot (inches) and eights, quarters or halves of an inch. Buy a metric tape measure and you'll be set.

I agree, but some people can’t make the shift. Even with metric I would still use a spread sheet to calculate the dimensions. I would put every dimension in a column, formula that applied the change in a second. Its faster than by hand and less error prone.

[VT_Jeff]

. . . and there's a good example of why the metric system is better for scaling boat plans! Get the metric plans (some plans come with both systems of measurement), it's much easier to work with. 2.7 meters x 1.1 is easier to figure (less likely to make an error) than feet, twelfths of a foot (inches) and eights, quarters or halves of an inch. Buy a metric tape measure and you'll be set.

I agree, but some people can’t make the shift. Even with metric I would still use a spread sheet to calculate the dimensions. I would put every dimension in a column, formula that applied the change in a second. Its faster than by hand and less error prone.

Agreed. Working in metric has clear advantages when scaling, but for me, I was not going to make that shift to a metric tape measure etc. Which is why I did the pre-work to calculate/scale every measurement on the plans and then build in inches and feet. A day or so of work with the plans and a spreadsheet was a lot easier than months of adjusting to metric.

[VT_Jeff]

The hardest part of the scaling for me, btw, was not actually the changes of dimensions, but the re-nesting, and I'm sure I didn't get it exactly right. Someone with good cad skills would probably have no problem but it was a bit of a brain-twister for me.