Jeanneau Sunfast 36 - Directional instability

[tane]

when (over?) loading any modern sailboat course stability inevitably has to suffer: the hulls having very much more volume in the back than front, with the (over?) loading the CG will move backwards & thereby aggravate any yawing. Putting more load in the front will not help either, as this will move CLR forward (the comparatively fine bow is immersed further), again aggravating yawing.
Before doing any serious grafting under water, that will require extensive remedial surgery if unseccessful I would try something exterior:
transom mounted casettes with dagger foils, either fixed("stern-daggerboards") or as twin additional rudders. Can be deployed or retracted while sailing & easily taken off from their pintles

 

[akela]

I have not sailed on a SF36, but I owned a 32 for many years, it was a delighful little boat but somewhat unstable, you could not let the helm alone for even a moment. These were racing boats in their time, we should remember this. Briand is a very good designer and knows how to draw fast boats. Some friends who sailed the 36 say that the helm was very stiff in heavy winds. Originally the boat was designed and built with a tiller, perhaps the problem with your boat is in the excessive (or insufficient) gearing of the wheel. In any case, I would not try to modify a 30-year good old boat. If this boat doesn't suit you, perhaps the best option is to trade her for another one.

 

[gonzo]

Boats designed to maneuver fast in a race are not going to track like a full keel heavy boat that has a hard time tacking.

 

[akela]

And remember, sooner or later you will want to sell this boat. Extensive modifications can dramatically affect resale price.

 

[CarlosK2]

Madeira --- Canarias
August 2024
Oceanis 45

European award-winning sailing yacht of the year 2012

Time and again we are faced with the reality: a bewildering industry summed up well by its apex, Bayesian, and an army of servile sycophants, palace scribes, and servile magazine editors.

And all wrapped up in tons and tons of silence, silence, silence.

The yacht is equipped with not one but two powerful and very expensive autopilots, and yet the owner, after spending a fortune on the yacht, is forced to spend 14 hours at the helm, and when he is exhausted and calls for help, the crew are very seasick and he has to spend two more hours, a total of 16 hours chained to the helm

But, brothers, let us keep silence, silence, silence

By the way: in the last four years, about 8 sailors have died from the impact of the boom or the mainsheet

But all is well because that is what our Lord, the creator who designed this world, wanted

Our attitude must be obedience and silence, silence, silence

 

[CarlosK2]

L_CG: 369 cm
L_CB: 360
L_CF: 350

It really isn't that complicated to do things right with a little love and respect for the sea

LCG > LCB > LCF

or if you prefer

LCG = LCB = LCF

 

[CarlosK2]

It is not so complicated to study a little and learn from those who preceded us on this path

T. Harrison Butler in Memoriam

 

[CarlosK2]

A simple summer cruise in the Atlantic, in August, Force 6 - Force 7

The far-sighted owner installed a second autopilot even more powerful and even more expensive than the one he already had

And he finds himself chained to the helm for 16 hours

This is how it is, summer after summer

We don't even talk about Force 10 anymore. We live in a frightful decadence; but now let's distract the public and the clientele with planing sailboats on flat terrain hoisting gigantic gennakers with Force 5

 

[CarlosK2]

You spend a fortune to enjoy the enormous privilege of being your brother-in-law's driver, the brother-in-law who is seasick on the sailboat, of course.

This joke has gone too far. Users remain silent, like someone who suffers from hemorrhoids who doesn't go around talking about his condition.

---

Ports and more ports full of sailboats that do not go out to sea.

You buy the sailboat with great enthusiasm, but later you realise that you have become the driver who takes people around.

And on top of that, you realise that (seen from the aeronautical industry) many sailboats are designed by real troglodytes or, what is worse, by people who think they know and have not studied carefully and lovingly the dynamic problem of the relatively slow sailboat.

 

[CarlosK2]

A sailboat so fast and so big that no one would even think of coming with you

Yes, Exactly

But, man, between an insufferable Dinosaur and a heroic boat I think there should be a reasonable middle ground