Hull Shape

Rcsailing.net General Discussion
1

Would someone be so nice as to give a short(or long)lecture on hull shape. Things like the effect of-
-more or less rocker
-rocker forward or aft
-more or less draft forward or aft
-narrow vs. wide transom
-narrow vs. wide beam
-anything else that you can think of

I know that this is a rather large request but I would really appreciate it.
Thanks
Don

2

Don, I suggest that you get:“Princibles of Yacht Design by Lars Larsson and Rolf Eliasson” which will give you the tools you’ll need to accurately compare hull designs.Another excellent explanation of the factors considered in sailboat design is:“Yacht Design Explained” by Steve Killing You can go to boatdesign.net and they have a wealth of information on available design software including free downloadable software.
The dimensions area’s etc. that are to follow could be used as an excellent benchmark set of design parameters for a one meter monohull; they are taken directly from one of Graham Bantocks latest designs ,the F100CBTF.So here goes:
1)-LOA-one meter
2)-LWL-38.19"
3)Beam: 6.25"
4)-Displacement: 6.6lb( canoe body only)
5)-Prismatic Coeficient(The ratio between the volume of displacement and a solid having a constant section the shape of the largest section multiplied by the waterline length-smaller numbers mean finer ends;larger numbers mean fuller ends;boats have optimum prismatics based on their speed potential-normal range for an all round boat .53-.57)=.545
6)-Max depth of rocker: 1.9375"
7)Wetted Surface(level-can be expected to increase 1.2% heeled at 25 degrees)=200.58 sq. in.
8)- Waterplane area(also slight increase when heeled) 154.72 sq.in.
9)-Block coeficient( ratio of displacement(above) to a block having the lwl,beam at waterline and rocker depth described above)= .397
10)-Longitudinal Center of Buoyancy=52.6% aft of bow/waterline intersection.
11)- Beam at the transom 1.5" above the waterline compared to beam at the widest section at the same height: 56.5%

These measurements can be very valuable if you use them as a comparison to other one meter designs you might do.
The design goal here was to produce the fastest one meter hull possible with no restrictions and loads of power. The hull design is basically a semicircular design ,very narrow.
On boats like the IOM rocker is limited and other factors such as a minimum displacement come into play. This boat was designed to sail at around 15 degrees angle of heel whereas on boats not using movable ballast the designed angle could be as high as 30-35 degrees at the top end of any particular rig(A,B,C,etc).This boat would sail well at those angles. Some boats have a class rule specified maximum ballast/displacement ratio like the IOM ;others are wide open like the Marblehead. In the non restricted classes a maximum ballast/ displacement ratio is important-some have reached 80% or more.
I was privledged to be able to put a group of guys together that allowed me to engage Graham to do this design and sharing these specs is a small way of helping others who haven’t been able to be involved in such a project. I’ve done many designs myself of full size and rc boats ,mono’s and multi’s(more multi’s) and I think it is one of the neatest things you can learn and do–Good luck-and I’ll try to answer any questions that come up.

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

3

doug is the new graham boat a IOM or a us i meter. i have plans from graham (rythmnn) and the rocker is only 1.5 inch. the boat does not sail well in heavy winds but it is a rocker in light airs?
and don
i agree with doug
I started with the book by killing. it is a bit long winded, if you dont understand what he meens but after you design a boat . go back and reread it. it will then make alot of sense
good luck