Cockpit positioning

Alysum

Alysum

Member
Hello,

I have some questions about the ideal place to sit in the cockpit. I read that the lighter the wind, the closer to the mast you should sit to reduce wetted surface.

And my question is; if less wetted surface makes the laser go faster, why not ALWAYS sit at t he front of the cockpit, even in strong winds ? (I've not had the opportunity to test myself in strong winds).

When you do downwind, where should I sit too ?

Cheers,
 
you should always be up at the centerboard unless it is so windy you need to keep the bow from plowing when going downwind or on a reach which means you have to scoot back a bit but otherwise you need to sit forward to keep the stern out of the water especially in light winds, and plus you get the most leverage from hiking when you are farther forward.
 
If you're going upwind in chop if you're sitting at the front of your cockpit you will stuff the bow into a lot of waves. I made this mistake yesterday; finally the last beat of the last race I went 'duhh..why am I so far forward?' I moved back to the center of the cockpit and the bow was able to pop over waves instead of going through them. Also, when sailing offwind in planing conditions you want to move back so the flatter bottom of the boat is in the water and the bow pops up easier.
Basically the lighter the wind the more forward you sit.
 
© Shevy Gunter (drLaser)
Where do I sit in this tiny cockpit?

When I watch newcomers to Lasering or beginners whom I instructed, it is evident that one piece of information that rarely sinks in is where to sit and hike from on a Laser. Especially in light winds. Of course, you never sit "in the cockpit" of a Laser. You generally sit on the deck, near the cockpit, with your feet in the cockpit, under the hiking strap. Here are some specific pointers:

HEADING CONDITIONS SIT AND HIKE FROM
HEEL (H)
Upwind Drifting Sit forward of daggerboard, your bottom right at
centerline. Dangle forward leg to leeward; keep
aft leg in cockpit under hiking strap.
(H)To leeward (to
keep sail full)
[Further information from this post has been removed to remain compliant with US copyright law. Thanks for understanding]

Steve Cockerral (I think) also has some tips about front/back knee down sailing by the lee - advantages/disadvantages of both - but pretty much recommends you don't use any knee-down technique running by the lee when it is blowing hard.
 
If there are waves you'll need to move around to get over the waves, also you get futher out if you sit abit futher back due to the boat beeing wider there =P
 
Josef said:
you get futher out if you sit abit futher back due to the boat beeing wider there =P
Click to expand...

Not entirely true. Yes it may be easier to stay out on the wider part of the boat, but if you are a hiking god, it makes no difference, as your feet are strapped to the centerline of the boat whether in front of the cockpit or in back.
 
Hydrodynamics. In light air, skin friction is the biggest factor. As it gets windier and wavier, and more importantly the flow over the hull moves from laminar to turbulent, you want to move back some. The hull is more effecient in turbulent flow when you're back. In moderate to heavy winds you should be just at the front of the cockpit, not any more foward and only back far enough to keep the bow out. Downwind, be back against the mast in light winds, on the centerboard in medium, and once you start planing you want to be pretty far back- a wide hull is more effecient than a narrow one when planing, so you want to have the back end (wider) of the hull in the water.
 
computeroman2 said:
---snip---Downwind, be back against the mast in light winds, on the centerboard in medium, and once you start planing you want to be pretty far back- a wide hull is more effecient than a narrow one when planing, so you want to have the back end (wider) of the hull in the water.
Click to expand...

A Laser bottom is slightly narrower and flatter in the back then the middle. Once planing, you want to be riding on the narrowest, flattest section of the hull that will allow the hull to stay on plane and reduce wetted surface. That's the reason for moving back.

In nuking conditions there is a second reason for moving back and that is to try and keep the rudder as deep in the water as you can for control
 
upwind in flat water, sit forward, but when there are waves, then whats been said takes into effect

downwind, getting back also keeps the bow from digging into the waves... pitchpulling lasers is no fun. the mast is hard.
 
I finally found the two articles I have on planing. I'll do some paraphrasing and summarising:

When you look at a hull from the water's perspective (head-on) a long, slender hull has a very low aspect ratio while a wide, shorter boat has a high aspect ratio. As we all know, higher aspect ratio=more effecient; thus, fast planing hulls are wide.

There are two main forces acting on a planing hull: angle of attack and dynamic lift. Angle of attack is just that- the hull is at a 4 or 5 degree angle to the water, thus directing it up. Dynamic lift, however, is more subtle but more important. When planing, the water directly in front of the boat that would normally be pushed aside as a wake is trapped there, partly because of the angle of attack pushing it forward and partly dragged by skin friction. This raises the pressure of the water and thus pushes the boat up, lifting the entire hull out of the water. Planing is faster than displacement mode because when you double the speed, you also double the pressure acting to lift the boat and so half the surface area. Thus in displacement mode drag=speed squared but in planing mode drag=speed. If you double the drive force, you can go twice as fast.

Another concept is the stagnation point (the most relevant to this topic). as stated earlier, dynamic force lifts the hull, but not from the back. If, as has been mentioned, the boat planes off its transom, then the dynamic lift that allows planing would cause us to uncontrollably nosedive anytime we start planing because it would lift the transom up. In order for dynamic lift to lift the whole boat evenly, it has to act on the center of the hull, the stagnation point. This point is about where the centerboard is, and moves back by a few inches as you go faster. Parking the transom in the water when planing will only increase the angle of attack, which past a certain point will be a detriment because you are now using some of your speed against you. Thus when planing you want to be somewhere in the middle of the cockpit unless you have to be back farther. Don't ever sit with your backside farther aft then the back of the cockpit.

Lastly, the laser hull is a two-mode hull. In displacement mode it is to be sailed in a very bow-down position with the gunwale a couple of inches off the water. This gets one side of the hull out of the water, halving the aspect ratio. As you transition to planing mode, you move back and flatten the boat to create a higher aspect ratio that is more effecient when planing.
So in fact, moving back when planing doesn't reduce whetted surface area but creates more drag.

-paraphrased from Frank Bethwaite's High Performance Sailing, ch. 20.10 and an unfinished chapter in a yet-to-be-published book by one Chris249 (screenname on SA).
 
a good tip for new sailors, look at the back of the boat. the longer the rooster tail, the better. if there isnt one (bubbles-ish) youre too far back.
 
The Beat
In hiking conditions with a bit of chop, sit just forward of central in the cockpit; with your back foot parallel with the centre screw for the grabrail. This helps because u can easily shift your weight and theres a good balance between transom drag and how far you can get your weight out. In light wind, get as far forwrd as necessary to get the back out of the water, and get a bit of leeward heel. In no wind, as there was for us the other day, I actually tried (this sounds pretty bad) sitting facing backwards on the boom at the gooseneck. It worked quite well and helped the boatspeed along a bit. Then again im only 55 kilos..
 
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