Wiki Sail by GRF

Originally posted by iGRF So, neither you, nor anyone else has explained why that 'displacement' all you 'boat builders' so carefully consider, isn't published as a technical specification then?

Originally posted by iGRF So, neither you, nor anyone else has explained why that 'displacement' all you 'boat builders' so carefully consider, isn't published as a technical specification then?

Edited by fab100 - 27 Mar 13 at 9:15am

Y'all clearly need a less light hearted thread than this to discuss what actually is going on with your jib and main sail, it is a mistake to assume that air is accellerated through the gap, I think you'll find it's been proven not to, in fact I'd go further and say probably the jib can interact negatively with the lower main for a couple of reasons (my supposition here happy to be corrected). It is in fact 'lee bowing' the lower main (not a good term but essentially means the angle of attack of the oncoming air is altered as you would be getting your nose ahead of an opponent off the start line or in a tactical lee bow situation.) The jib also bends the created part of the apparent wind which is why the angle of attack of a jib is so important and the forestay absolutely must not sag.
So it is important to consider the rig as a whole, not the sum of it's parts.
Offwind obviously different rules apply, there must be books written about all this, read them, this is just a knock about, I've nearly finished my A-Z glossary to help you understand what dinghies are about, but if you want to talk seriously about all this stuff you really need a proper thread, too much deliberate mis understanding going on here and I would have thought joking aside you'd want to know the truth about all this.
That volume displacement thing you're also denying that you need to know, it is key to why some boats are faster than others in different conditions and confusing what modern planing windsurfers require the information for with what long racing board sailors require is also wrong,racing sailboards have had displacement volumes up in the 300 litres. Inland riders would select higher volume boards to race on than sea sailors back in the days of displacement Div 2 hulls, hence my argument about the Laser, if you don't understand and attempt by ridicule to deny any of this makes a difference, it's y'all who are the losers.

So now who's going to tell me the displacement volume of a Laser then?

Edited by iGRF - 27 Mar 13 at 9:22am

Originally posted by iGRF So now who's going to tell me the displacement volume of a Laser then?

Whatever an all up Laser weighs plus the weight of the bod on board. I don't know the 1st, but I'm sure someone on this forum can tell us, given that we hear so often how the top guys go round weighing hulls and spars to get the lightest. The 2nd is rather variable...

Yachts tend to give displacement values when they sell - always have done, but then the crew weight for a big yacht makes very little difference to the displacement, so it becomes a meaningful figure again.

My current design project, a 4m canoe sterned sharpie, currently has a design displacement of 197 kgs to get to the design waterline. This is, I think, too high, so I'll need to tweak either the waterline width or the amount of rocker to bring it to the right sort of value. As I've not done the weight calculations for the materials to build the boat yet, I can only go by what my target all up weight is, currently. Once I have built a sailing model to test the hull shapes, I'll have a better idea of what to tweak.

So, If I'm doing all this with a pencil and paper and cardboard models, what sort of info do you think people with CAD programmes are able to get?

Originally posted by iGRF 2)You're wrong not to want to know stuff like this, it explains lots of things, like why a Supernova is overtaking you in your Laser in light air, when the volume displacement becomes more important than sail size, knowing rather than having your confidence sapped and thinking you're doing something else wrong.

The shape of the wetted area is going to effect how the boat moves through the water as it is the drag from friction that you have to over come. The vessel is completly supported by the water once it is afloat. If your boat has a very narow hull shape then you will sit further down in the water than a wide one but the displacement of both will be the same the effort to move them through the water how ever will not be. This is one of the reasons that a cat is faster then a mono.