Originally Posted by JAndersB
the question of ballast ratio, AVS and stiffness is a complicated one and need careful calculations of among other things center of gravity. I do not intend to go into that. I have also traditionally been an advocate of high ballast ratios.
These new boats are bult on form stability as you know, as is a trimaran or a catamaran. They do not score high on ballast ratios either. ....
The stiffness is not a difficult issue . You have only to have a stability curve and to know the boat sail area.
I think there is some confusion here regarding high ballast ratios. The reason some modern boats need less ballast ratio is because today the drafts are a bit bigger but mainly because today most performance boats have all the ballast in a bulb on a keel while some years back the ballast was distributed by all the keel, sometimes with a small bulb and that can make a big difference in righting moment.
The Ballast/Displacement is only comparable in what regards similar keels with similar weigh distribution and similar drafts.
What matters is the stability curve. If I remember correctly the one from the Azuree cruiser has an AVS around 110º and the one from the Opium 39 an AVS around 125º. That is a huge difference not only on the AVS but on the force that the boat is making to right itself up from a knock down position and also on the inverted stability.
Some types of new cruising boats have in common with multihulls the fact that they take most of its initial stability (needed to sail) from form stability but contrary to multi-hulls they take the ballast needed to recover from a knock-down or needed to recover from an inverted stability in a short period of time or at least they should have. All the racing boats that served as model to this new generation of boats have that safety potential. The ballast is there not only to increase the stiffness of the boat but mainly for the reserve stability (at high angles of heel).
If you want a boat without or with a bad a reserve stability you should have a multi-hull. At least you would not be tricked into thinking a boat has a safety potential he does not have. Being knocked out on a sailboat, specially for guys that like to push their boats and have a lot of sail out is a fairly common occurrence. It had happened to me already and I bet it had happened to a lot of sailors that like to go fast. It is not a big deal in a boat with a good reserve stability. In a boat with a poor reserve stability it can be a huge problem.
I remember than on the last Transat with Figaros a guy was knock down for a looong time (1 hour?). The Figaro 2 has a good reserve stability (AVS 125/130º) but the boat was caught by a wave and partially flooded and that have diminished its reserve stability. That sailor had a lot of work taking out the water of the boat (not an easy task with a lying boat) till it managed to get enough stability to bring it up again. What would have happened if that boat had a poor reserve stability?
The Elan 350, the Pogo and the RM are boats that rely on form stability for most of the stability needed to sail but that have the ballast and the draft needed for having a good reserve stability and a good AVS. I believe the Azuree fast cruiser has it too, but not the Azuree cruiser. I would not take offshore a boat that would have difficulty from recovering from a knock-down, or at least I would be very careful to sail that boat and that would take all the fun away.
Originally Posted by JAndersB
Shure, a knock down might be more fatal but as have been discussed in other threads, we spend 99% of our time in not knock down conditions so...
So basically, how much is the ballast ratio really worth for these kind of boats or should we look at other aspects, if we are takling about performance, not flipping around? I am not sure but I think we have to reason slightly different than for more normal single rudder narrower shaped performance cruisers.
I remember that on some test with the Elan the guys from the magazine were amazed because they have tested the boat with lot's and wind and no "wipe-outs". They were not caring because they knew that a knock-down would not have been a problem. Who wants a sportive cruising boat where a wipe-out can be a problem? It makes no sense. It is dangerous.
The ballast/draft should be the necessary to provide a decent AVS and a good reserve stability, no matter what. Otherwise what is the advantage of a monohull over a multihull? if you don't want to have a ballast capable of generate a good reserve stability why bother? Get a multihull
Originally Posted by JAndersB
I am also a little bit pussled that Opium can be so much lighter than all other similar boats with similar interiors. Opium is built very similar to my old Dehler if I compare hull cut outs, even if the Dehler is built without vacuum and basically Opium hull is built as Azuree (balsa instead of pvc sandwich). Pogo is understandable if you look inside but I have a hard time understanding why an Azuree should be 1800 kg (200more in the keel) heavier, you get a lot of interior material for 1800 kg.
The interior of the Opium is much lighter than the one from the Azuree and probably of much better quality. Infusion makes a lot of difference in the weight, there are lot's of different qualities in the infusion process.
I don't think the Wauquiez use a balsa core they say: "balsa and PVC foam sandwich with a vinylester core" and they use In the laminate multiaxial fiber glass (equivalent to multiple layers of unidirectional material). The quality of the vinylester resins or fiberglass can be very different and the same with the workmanship quality.
I know that they make the boat with that weight because they have made a big fuss about that when they have weighted the first boat (and got the correct weight). Quality and control is as important as the process to warranty high standards of quality and in that regard Wauquiez has a long tradition while Azuree has yet to prove itself as a high quality brand.