The Bayfield 29 is hardly a racing boat
. Therefore there is no need to be able to flatten the main to squeeze out the last tenth of a knot
of speed or the last half degree of weatherliness. Therefore there is no need for a vang qua
sail trimming device.
HOWEVER, in an accidental gybe, the boom end can rise up a heck of a long way, what with the sheet taken to the transom. Therefore a "vang" can be fitted as a "preventer" to alleviate the worst effects of an accidental gybe in that it prevents the boom end from rising and then crashing down again.
Looking at pictures and at boats, the device looks the same from a distance whether it has one employment
or the other.
Unless your boom is flexible enuff to bend under the tension of the vang no flattening of the sail will happen as a result of hauling on the vang. My boom is not that flexible, so I'm quite content not to have vang.
The proper procedure for "wearing ship" ("jibing" to Americans) in a Bayfield 29 is to do as MySaintedMother taught me: Induce a slow turn, and keeping pace with the turn haul the sheet taut. As you get the wind on the stern, the sheet will be fully taut and will, by itself, prevent the boom rising into a "Chinese gybe". As the wind comes on the other side, you let the sheet run and trim to the new point of sail.
My own technique in a tiller-steered boat like the B29 is to stand up facing aft, stick the tiller twixt my legs to hold it at the appropriate degree of helm
, use both hands to haul the sheet in hand over hand, timing the haul to the rate of turn. When the boom is nearly midships, I duck under it. Once I'm through the wind, I plop down on the new weather-side seat and resume normal steering
and sail trimming. The whole rigmarole from wind on one quarter to wind on the other quarter takes maybe 10 seconds.
So it's all very quick, and it's just a matter of practice to develop the technique. So in a B29: No — you do not NEED a vang, but don't let that stop you if you want one :-)
Wear your little ship in good health