Virtual Design - part 4

Working the stats.

When designing a new boat, it is standard procedure to study what has been done before in that area. We usually know how other boats performed and it is not difficult to extrapolate from all that data to predict a new design's performance and characteristics.
VPP programs are another tool but only measure speed potential.

Boat design manuals are full of graphs and formulas and professional designers keep archives if not databases of designs and plans.
We have a good collection of boat plans and hundreds of books and magazines.

In this case, we will compare characteristics, ratios and features from boats that fit our description.

We will start with the designs that we listed during the previous step and add a few others.
(Despite their names, all the boats below are around 27-28'. Many of the specifications are in metric.)

Our preferred design was a mix of the RM800 and the Flot 26 designed by S. Langevin.
The Flot 26 is designed for aluminum, 7 panels for the hull instead of our 5 but all other characteristics are very close to our ideal boat.

Flot 26:

Pros:

  • great layout
  • nice proportions
  • clean sail plan
  • rudder on transom

Cons:

  • Aluminum
  • Integral CB, no keel.(We could discuss that in detail but itwould delay our project)
  • Excessive width for towing.

The RM800 appeared on the previous page, when we looked at standing headroom but here is some more information:


Pros:

  • very nice skirt with outboard mount
  • esthetics
  • portholes in side and skirt
  • great interior layout
  • generous main with running backstays
  • ARS on retractable pole

Cons:

  • Twin keels.
  • Excessive width for towing.

The boat is very wide: 11' for 28' long! I suspect that despite good reports in French sailing magazines, she may be difficult to control under certain conditions. French have different standards: very good sailors, they expect boats to behave like a racing car but we want a cruising boat.
We will need less beam but not much less. The advantages of the wide beam are clear: the boat is incredibly spacious, inside and outside.
Another point is that the RM800 is designed for twin keels. We exchanged mail with Marc about reselling the plans but the hull was designed exclusively for the twin keels and they were impossible to make for an amateur. This means expensive castings: out of question.
Some features of the RM800 will be discussed later: there are great ideas in that design.

Before we proceed with other boats, note the similarity in the layouts.
In each case, the designer was able fit a nice, wide double berth in an aft cabin and there is standing headroom in most of the boat.
Those three boats look good too.
The 7/8 sailplans of the RM800 and Flot 26 are attractive. They could be rigged as cutters if the builders prefer.
From first hand experience, reports from reliable friends, magazine tests, gossips etc., we also know that those boats sail well, each in his own way.

To this list, we could add the Multichine 28 from Roberto Barros. That architect is designing in the same style but the Multichine 28 is in reality a 29 footer, 32' LOA and a little bit out of our range.
We looked at the Dudley Dix designs and while they look great, none fitted our description.

Let's include some production boats.
Researching our magazine archives, we found a fascinating comparison article between the RM800 and three well know production boats:

the Etap 26,

 

First 260

Note the angle of the tiller and the wake: with a wider boat like the RM800 you would be in troubles!

Features that I like: the centerboard integrated in the keel.

Hunter 280.

Features that I like: just as in the RM800, nice skirt and portholes, nice interior layout with the typical forward double bunk and U shaped saloon. The Hunter 28 is the largest boat in our group.

Here is the table with their specs in metric and some ratios:

Flot 26
RM800
Etap 26
Hunter 280
First 260
VG27
LOA
8
8
7.85
8.46
7.5
8
Beam
3
3.4
2.78
2.93
2.76
2.95
ratio L/B
0.38
0.43
0.35
0.35
0.37
0.37
draft low
0.3
0.5
0.85
0.75
draft deep
1.75
1.2
1.55
1.22
1.85
1.6
SA/m2
42
40
30
29
35
40
empty kg
1,600
1,800
2,300
2,950
2,300
1,700
loaded kg
2,100
2,400
?
?
?
2,400
ballast kg
400
(950)
850
950
600
650
SA/D
20
16.7
13
9.8
15.2
16.7
ballast/D
19%
(40%)
(28%)
(26%)
26%
27%

The (figures in italic) are thoseabout which I have doubts either because the brochure states displacement = empty boat weight and I had to guess or because they are out of the norms.

The last column shows the specs around which we will design our boat.

There is much to say about the boats listed above and the choices we made but we'll keep that for next week. I wanted to post this to give you something to think about on the week-end!

In the next step, we'll start to sketch our boat.

 

Which one is your preferred boat?

Flot 26

RM800

Etap 26

First 260

Hunter 280

VG27

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