Concept and Design

The dream

This project is born from our passion for classic boats (and a lot of naive ambition and dreaming). The boat is inspired by Brittany’s traditional sailing work boats, more precisely the tuna fishing dundees. It is to be built of steel but have the charm and details of a traditionally built wood boat.
 
The limit

The boat had to be as big as a crew of two could handle, which set the limit to a sail area of about 1700 sq ft, therefore a displacement between 50 000 and 60 000 lbs was the target. The size would be just a touch smaller than average the 1850/90’s size tuna fishing boat.Lower are a scanned images of the type of boat the Pepe Berrou will be.
Dundee

Design

Art or science? Boat design is both. A mix of intuitive and calculated choices always within standards (ABYC, Loyds). We started from our common knowledge, desires and mostly our aptitude to learn. We researched everything from industry standards to skills. Books, web, regulations, pictures, museums, trips, people….we don’t discriminate any source of information.

The objective has the looks of the past but we would be fools not to use the tools and technology today has to offer.

The lines were drawn with the marine design software package PROSURF using NURB surfaces. The hull modeling software is used to generate a hull surface of the desired shape, to fair it, provide lines, hydrostatics, curvature information and 2d expansion of the 3d surface. It is then possible to export all the geometric information as text files, so xyz coordinates, offset tables; or as different cad files like Dxf or Iges. PROSURF allows us to analyze the hulls curvature and provides tools to fair the shape in nice curves. We aimed for a shape that would compromise between roundness and relative ease to build of steel plate. Before obtaining the wanted hull shape, a few scaled models were quickly built to be stared at and discussed in the evening for hours on end…….Every proposed hull also came with its stability data (compiled with Prosurf and spreadsheets). The boat has to look good but it would be a bonus if it was safe and sailable (ok, it’s not a bonus but an important prerequisite).

Once we agreed on a hull, drawings were exported to a generic CAD package for detailing and solid modeling. Drawing it once is like building it once. The construction grunt work is not all fun, having detailed plans drawn in the comfort of the office minimizes the time spent sweating and swearing.

Boatscreen

Final drawings on RHINO

The ribs and some other parts were numerically controlled cut (NC cut) from the drawings on a large plasma cutting table at Brannon Steel in Brampton. The ribs were fully detailed, I had the notches for the longitudinal and the limber holes cut in the shape. This was a huge labor savings as all the parts are perfectly cut and the ribs went together within 1/32 of an inch. The files I sent to get parts CNC cut were 2d dxf files, projections of the parts profile. I use Dxf as most cad software can import and read those files. I divided my ribs in pieces that would be easiest nested, there would have been way to much waste if I kept each rib ring intact. That meant welding later the parts together to reform the rings but was the best way to make it economical. The NC cutting shops should have a nesting software to organize all the parts as efficiently as possible on the plate so the positioning of the parts on the file sent to them doesn’t matter. I only had to make sure that all the parts were small enough for the max size plate the shop could cut.

I didn’t get the plating of the boat NC cut. I didn’t think the gain was worth the risk of a plate not quite fitting the frame. A very slight misalignment of a frame, which otherwise would not be a problem , could cause the plate to be that 1/8 of an inch off. We template all our plates and cut them out of regular plating and it worked great with very reasonable waste. I used the plate expansion from probasic to plan the plate size I would need and how much material to buy but didn’t use it for cutting.

Murielle did all the design and CAD work for this project.

 

Updating

Reading over this page I realized that there has been changes over the years and it would make sens to add a note on the software I currently use.

The original solid modeling were done using CADKEY which was the cad package I used and learnt in school. I have since moved on to other software. The change occured with microsofts desire to change everything, when vista appeared my old CADKEY became obsolete and unusable. I transferred all my models into Rhino which I actually really enjoy using now. It did take quite a bit of cursing but that’s to be expected with a change after using the same tool for 10 years . Prosurf still does the job but there again I have tried to move on to learning more and quite like freeship (delftship).

Rhino has really become my main tool but for non boat related CAD and for certain parts or when I need some technical drawings from my model I find I’m better to use parametric software. The most affordable fully functional parametric CAD software we have found on the market is Alibre.I ‘m hoping to get back to this page and add some more recent screen shots, the boat model in Rhino looks quite neat and the interior concept has materialized in CAD