SWE 335 Stradivari "Spinal Tap"

Underwaterbody Mariner

Tweaking the width.

Checking displacement at different widths.

SWE 335 Stradivari "Spinal Tap"

Marinerized Stradivari.

Here’s my own project that I have been fiddling with for the past 2 years. It’s the by now 11 year sold

prototype for the Stradivari that I designed in 1995.

Through the years she has been performing well in the hands of a number of owners.

A couple of years ago I got the opportunity to bring her home but the edge was not there anymore.

First of all the level of optimising has steadily become higher and higher so the structural reinforcements had

become outdated and most probably she also had gone soft after many hours of sailing so I decided it was

time for a second coming.

  The original prototype at a Frostbite regatta.

Studying the design development in the bigger sisters, especially the Twelve’s one cannot neglect

the Mariner fiasco.

In short B Chance Jr. had in the tank work prior to the design of a Twelve for the 1976 Cup found that by increasing the bustle and introducing an underwater transom there was a an evident increase in speed

potential at least in the tank testing.  

Unfortunately it did not turn out as predicted. The boat was slow and though there was a lot more to it

than just the design error it still was evident that the problems inherent in scaling was completely misgauged.

For a curious designer/builder the natural question arising from this experience is then “at what rate of scaling

does the findings from the tank testing become invalid”.

Would the Mariner concept work for a 2,4mR, there’s only one way to find out – full scale testing.

First I tried an increased bustle in the style of ¼ tonners like Mazanita by Ron Holland that looked like having dimples when seen from behind.

This did not work out very well so I decided to rethink the Mariner concept and move the underwater transom back to the L1 station as opposed to Mariners that was positioned at the waterline position. This had the effect

not only to decrease the relative size of the transom it also increased the length of the underwater body and the volume of the hull.

One alternation had been done earlier and that was a shift to a slightly larger keel than the original,

increasing the displacement some 7 L.

The increased volume of around 15L with the bigger keel and the added volume building the transomed end

of the underwater body also added significantly to the RM.

I then decided that as I ripped the deck off in order to rebuild the internal structure I would use this extra

“space” given by the increased volume to make the boat more narrow and “slippery”.

In august 2007 I finally made it to Långedrag and got her out for the first time.

These first trials against my friends in our fleet leaves no doubt in my mind, the boat has been improved


The boat I cut into two years ago was a poor performer upwind never being able to point as well as the competition.

So far I have sailed her in conditions varying between 6 and 14 knots. As it seems now I have no problem

with the pointing and the pace is there upwind as well as downwind.

Don’t ask me how the different alternations are working or which one doesn’t. What can be said for sure

is that the underwater transom does not create the kind of turbulence and drag so obvious on Mariner.

I still have not had the opportunity to sail her on a heavy downwind leg.

More reports from further trials will come.

Now I have sailed her in all sorts of conditions and the results are promising though there are some problems left to solve. Upwind the boat sails very well but the added volume aft seems to lift the stern out of the water as speed increases which means the boat goes bow down and becomes more wet upwinf and has become much more prone to dive on heavy downwind legs.

Moving the helm aft would probably solve this and would be very interesting to try but that takes a new decklayout.

The only situation that the boat is slow is downwind in light winds.

I am convinced that these shortcomings can be overcome and that the concept would be worth developing further.

As I was asked to deliver a new design to a UK builder I decided to use the boat as plug so I have now rebuilt the hull to a more conventional shape aft and it has now ended its sailing life. Maybe I will take up the thread again with a new hull later.

The first boat out of the mould has been sailed a couple of times and looks like this:

The original prototype.

Internal structure including tabernacle.