Would any of the "scientific" sailors help me with a question?
In "light air" with the "crew trapping out off the lee hull" and the "skipper under the boom" to lighten the windward hull; create less drag on the lee hull, than the crew sitting on it? I got this idea that maybe because with the crew trapped, the compression of the lee hull is not as great as sitting on it.

Any ideas from the engineers?
Dave [color:"blue"] [/color]

When concerned with getting the weather hull out of the water, trapping would be the way to go. Trapping would acheive a greater moment arm. But as soon as the weather hull comes up, the leeward hull goes further in creating MORE wetted surface on the lee hull. In light air the crew is typically laying on the leeward hull, creating a very small wind silhouette. When trapped, the wind sees the full length of your crews body, thus creating more resistance to forward motion -- very bad in light air. Seems petty, but if you are trying eek every bit of speed out, that might matter.


To more accurately address your post, the compression will be equal whether trapped or sitting. All the weight of your crew must be reacted by the boat somehow. Sitting on the hull, 100% is going straight into the leeward hull. If you trap out to leeward, some is going to the hull through your feet, some is going up the wire, which puts the mast in compression, which is reacted at the mast base and puts the forward cross bar in bending, which reacts at the hulls as a compressive force. If your weather hull is out of the water by now, it's all being reacted by the leeward hull. Thus 100% is still going to the leeward hull in roughly the exact same spot (since the crew should be quite far forward).


Not to mention, the slightest puff and you are the dude that teabags his crew and capsizes in 3 knts...

Hope that helps.

Thanks Shannon;

You have supplied some valuable information. My wife and I have always been able to move quite well in light air. Yes, she is stretched out (low) up forward of the beam on the lee hull. I get up under the boom at the mast. I have not clearly understood why some sailors feel they have to carry the windward hull "at all costs". I can see, now, that in the light air the greatest return is in how little you can present yourself to the wind.

Thanks! Will add it to the learning curve.
Dave

Here`s my non-scientific view on the subject :
Where I sail we sometimes have to race in less than ideal catamaran conditions - All sailors are on the same boats (Dart 18), some sail double-handed, some single handed in which case they remove the jib and are fairly similar in speed.
The single guys tend to trapeze off the leeward side in light breeze on the downwind leg, and can sail dead downwind at the same speed as the double-handed guys, but the double-handers can`t do this with the same effect - the jib gets blanketed by the main & you are effectively sailing 2up with only a mainsail working on the downwind legs.
What this translates into is that the solo sailors cream the light wind races, while the 2up guys have to wait for 10knots of wind before we can win races. Very frustrating. I`m not sure what makes it work, but I know that it does ! Nobody tries it upwind (yet), probably due to the teabag effect explained in the last post ! Having said that I have seen a few capsizes in 3 knots.
Very entertaining, since most of the solo guys aren`t heavy enough to right the boat.
I have no idea what makes the solo boats run faster than they reach, other than lower wetted surface area. I do know that it looks silly. We probably shouldn`t go racing in these conditions anyway !

Cheers
Steve

Due to the inverse/square law, the FASTER you go, the more (sq) the resistence, therefore, more of an impact at higher speeds.

It's about wetted surface area....that's all. You are always displacing water weight equal to the weight of the crew and the boat combined minus any lift supplied by the sails (the spinnaker is the only sail that really provides any lift).

Suppose you are sailing the boat flat with both hulls equally 6" in the water... you have the thinnest part of both hulls displacing the water. If you move your weight to leeward and use more of one hull to displace the same amount of water, it runs deeper and more into the thicker/wider part of the hull. This means that the hull displaces more water with less penetration into the water than both hulls combined (because it's thicker in the water now). There's less gel coat exposed to the water because the hull profile is wider the higher you go. Less surface area in the water is less drag.

Putting your crew on the leeward trap will increase mast compression and sail tuning slightly as a result. However, the big picture is the lateral center of gravity of the crew weight and the boat weight. The more weight to the leeward side, the more weight the leeward hull carries (and displaces water) and the less the windward hull deals with. We all know that putting your crew on the leeward trap (especially lake sailing) is like sitting in a tree with your kahunnas exposed above a pinatta party!