Apologies in advance if anyone is offended by this post - that is not my intention!
Its just that my scientist brain won't rest once it has seen something that doesn't make sense - and some stuff around scaling and L/B ratio in the post above doesn't make sense to me!
So I did a bit of research, as one does, to try to get a better understanding of the issue.
First some definitions etc:
Definition: L/B = length divided by beam.
Units: Dimensionless.
Usually, the waterline dimensions LWL and BWL are used for monohulls.
What it's used for: Performance
Larger L/B indicates a slimmer hull. This usually implies less wave-making resistance, and thus more efficient high-speed performance, but also suggests reduced load-carrying ability for a given length.
If a boat can plane, smaller L/B often suggests more efficient performance at low planing speeds. The balance generally tilts in favour of high L/B for fast boats.
Typical ranges of L/B are: 2 to 4 - Small to mid-size planing powerboats.
The ratio of length to beam at 3:1 is considered a "classic" proportion, and as an example, the Boston Whaler Outrage 22 is precisely at this mark.
Then some observations:
As I understand it, the L/B ration is usually calculated from the length and breadth at the waterline. However, as we don't have those dimensions for the plans on this site, I have used overall length and breadth, which should do for the purposes of this exercise. All metric dimensions (M).
AB23 (the main subject of this thread) 7.02 (L) x 2.45 (B) so L/B = 2.87
OD18 (mentioned) 5.50 x 2.15 so L/B = 2.55
PG20 (mentioned) 6.20 x 1.85 so L/B = 3.35
MG20 (mentioned) 5.95 x 2.15 so L/B = 2.77
AB23 x 0.9 = 6.32 x 2.21 so L/B = 2.86 (vs 2.87 above) - so scaling down doesn't significantly alter the L/B.
MG20 x 1.1 = 6.7 x 2.45 so L/B = 2.74 (vs 2.77 above). My hull is not quite identical to the MG ie deliberately slightly higher and therefore wider.
Interestingly, I also have a significantly scaled down MG hull, ie MG20 x 0.1, ie a 1/10 scale model = 595 mm x 215 mm so L/B = 2.77 (vs 2.77 above) - no surprise when you think about it.
I can take the dimensions at the waterline on the model: 510 mm x 185 mm so L/B = 2.76
And finally some comments on the posts above:
"The size constraints really limit the greatness of the boat.
6.5m ~ 21' L
2.2m ~ 7' 2" B
This means a boat with a relatively narrow beam. The L/B ratio is a measure that can be overlooked in some sizes, but I prefer not to..mostly for efficiency and ride.
The L/B here is >3"
No, the L/B = 2.96 - right in the "classic proportion" range!
"A 15% scale down I think would be a big risk"
Why?
"scaling down is a crapshoot; high risk idea"
Again, why?
"sometimes the plywoods won't bend"
I would be pretty confident that 1/4" ply would bend as required for this build!
"and the bulkheads are wide"
No, the bulkheads would be scaled down by the same amount and therefore will be in proportion to the rest of the hull!