> Subject: Re: Balancing the helm when reefing - Mast attitude
>
> Here's how I understand these things.
> 1. A sailboat has a tendency to pivot around it's mast (and keel).
Not to pick nits with a post i generally agree with, but more precisely a
boat pivots around the center of lateral resistance. On a potter or most
other fin-keel sloops, it happens to be at just about where the mast and
keel is, but thats happenstance.
> Therefore, if the foresail area is larger (and/or its thrust greater) than
> the mainsail, the boat will have a tendency to want to pivot in the
> direction of the foresail's thrust which is (except directly
> downwind) away
> from the wind ("to the lee")
Actually, directly downwind is precisely where the thrust is exactly away
from the wind, since its 100% drag at that point! on other points of sail
(particularly as you get to sailing more on the wind) you're trying for a
maximized lift component to the thrust (perpendicular to the relative wind)
and minimize the drag. I agree with your result though.
>, generating "lee helm." With a
> reefed main and
> a full lapper, this is likely to occur assuming that both sails are shaped
> for their maximum thrust or drive.
...or drag :) ... any helm is usually most noticeable when the sails are
sheeted too tight generating more drag than useful lift.
> If the mainsail is relatively
> overpowered with regard to the foresail, the opposite will happen, and the
> boat will want to pivot into the wind ("to the weather"),
> producing "weather
> helm." Having to hold the tiller in any position other than
> exactly in the
> center in order to maintain course is inefficient in that it
> increases drag.
This isn't necessarily true, particularly when traveling to windward. a
couple degrees of positive angle of attack on both the rudder and keel help
lift the vessel to windward. Its also an important safety factor as a boat
with nobody at the helm will typically round up and luff. But its a fine
line. With lee helm the lift of the rudder is opposite the lift of the keel.
Another major cause of weather helm (particularly on the wind) is the fact
that both the jib and the main have a forward component to their thrust
vectors. But since both sails are necessarily leeward of the centerline of
the boat, theres nothing but drag through the water on the windward half of
the boat, so the boat is twisted to windward. Think of a twin-engine
aircraft with only one engine running - in the absence of corrections by the
pilot, the craft with rotate towards the dead engine.
> Thus no "helm" at all is ideal although I prefer a little weather helm so
> that I can head up as a default maneuver if I need to.
> BTW, this is why a
> boat to leeward has right of way (so it can head up and stop for
> safety and
> not be sailed into a disaster or an unwanted gybe by a boat to
> its windward
> that wont give way).
I've never heard that one, but it makes sense. The explanation I've always
been told: Its long been a concept in rules of the road that a more
maneuverable boat gives way to one with lesser maneuverability. A leeward
sailboat is often in the situation where its wind is shadowed by the
windward boat. The windward boat is more likely to be in clear(er) air and
has more options available to it, so it is the one that must give way.
> 2. To de-power the main, it is always helpful to flatten it.
> Thus, pulling
> on the downhaul or Cunningham, on the outhaul, or tightening the backstay
> will all de-power the mainsail allowing a more upright sailing
> attitude and
> producing less weather helm (or more lee helm). Easing the
> mainsheet or the
> traveler will add twist to the sail (as the boom rises - assuming the
> Cunningham is also eased), spilling wind and further de-powering it.
> This has made sense to me and seems to pan out in sail trimming. I also
> agree that in a P-15 anyway (very very hard to tighten the backstay or do
> much of anything with the Cunningham!), any kind of a chop can really make
> your life miserable if you are trying to come about into the chop. That
> high prow catches wind and water making any kind of low speed tack
> impossible at times.
I find it helpful in chop to bear off and trade some degrees of pointing for
more speed over the water, and use the momentum thus gained to carry you
through the tacks.
This archive was generated by hypermail 2b29 : Sun Apr 30 2000 - 03:27:09 PDT