66595Re: Oldshoe Review!
- Aug 1, 2011There is an aspect of broaching that doesn't seem to be commonly addressed. An idealized wave is shown as water particles at the surface in a circular motion, rising and moving forward, then falling and moving backward, with no net motion as the wave passes. A boat loses control and broaches when it is moving at approximately the same speed as the wave, with its bow in the trough and its stern near the crest. In that position, the boat is moving at about the same speed as the water at the crest of the wave, and there is little or no flow over the rudder, resulting in a loss of steering control. This is a momentary condition, and whether the boat actually loses control and broaches or not will depend on its tendency to root and become directionally unstable, and hence the attention paid to the shapes of bows and sterns. A boat with bow steering should maintain control at that point, but would lose directional control at a different point in the cycle, when the bow was near the crest of the wave, but at that point the tendency of the hull to become directionally unstable would be less and bow steering might be safer overall. Apart from that, I would like to see the behavior of a box hull such as Oldshoe, Micro, AS-xx, etc. with a box keel projecting right out to the bow transom. It seems to me that the additional bouyancy would act like a shock-absorber, smoothing out slamming in a chop, and lifting the bow earlier in a surfing-type situation when otherwise the bow would try to dig in. Of course, adding a box keel to one of these hulls would be in effect to create a new boat entirely, with much attention needed to matters of ballasting and stability...
Best regards to all,
--- In email@example.com, BruceHallman <hallman@...> wrote:
> On Sun, Jul 31, 2011 at 6:15 PM, daschultz2000
> <daschultz8275@...> wrote:
> > --- In firstname.lastname@example.org, BruceHallman <hallman@> wrote:
> > >
> > > I believe that broaching is most often caused by a displacement hull
> > > exceeding its hull speed. Perhaps what happened is that the hull
> > > surfed down the face of one wave and gained too much speed?
> > >
> > Yes. That fits with the description of the situation. The writer described the boat heading down the face of the wave, the bow striking the next wave and stopping the boat, except the back of the boat kept coming, broaching the hull.
> > Don
> I am not sure that the bluntness of the transomed bow increases the
> risk broaching due to its bluntness. When I look at designs intended
> for bar crossing or inlet running, they all seem to have in common the
> character of plenty of reserve buoyancy in the bow. This, I deduce,
> is intended to allow the bow to float high upon encountering the
> backside of a wave when surfing.
> (Also, I see in the Inlet Running boats a converse, low reserve
> buoyancy in the stern; which also would help the bow to float high
> when encountering the backside of a wave.)
> In other words, I don't think the goal in avoiding broaches is for the
> bow to cut through the next wave, but rather it is for the bow to rise
> up when it hits the backside of the next wave. I think it is
> misguided to point to "the bow stopping the boat", and if anything a
> transomed bow would have better reserve buoyancy characteristics than
> a knife edge bow.
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