Robert,
Both you and Tarjan make a good argument for reverse bows with
buoyancy down low in terms of handling and safety.
Melvin makes a good point, though, about the shape being
boat-specific and requiring some research and development. Tarjan also
mentions that it might make for a wetter ride.
So, not being skilled in naval architecture of fluid mechanics
myself, I'm not really equipped to move the state of the art forward.
At the moment the design is a great idea that I can't wait for someone
else to try.
Thanks for keeping the idea alive and under discussion.
- Mike
Robert wrote:
Hi Mike,
Welcome the discussion.
--- In harryproa@yahoogroups.com.au , Mike Crawford <jmichael@...> wrote:
>
>
> It's definitely great to see the performance of Rare Bird, as pointed
> out, with no whitecaps to be seen. Especially since it's substantially
> heavier than Blind Date. With the planned larger rig, that will be some
> boat to behold.
>
> Some of the old discussions were annoying at best. I'm glad to see
> that the real world has proven the design -- no need to argue any more
> about the ww hull forcing the whole boat to round up.
>
> I think the new beam-mounted rudders are close to the center of the
> boat. Without the hull-mounted bracket, they should also be less draggy
There is the problem that the rudders have less resistance to rounding up being closer to the center and thus would need to be slightly larger, thus creating more drag and greater spray.
> and create less spray. Being closer to the cockpit, though, it will be
> interesting to see what happens to the spray they do create. At least
> it's always to leeward!
>
> ---
>
> Robert: speaking of spray, how does this relate to your
> reverse-sheer-volume-down- low design?
>
> You asked me for specific objections a while back, but I got busy and
> forgot to respond. There were a few thoughts I had:
>
> - Spray. I think your planned design may be more suited to racing,
> where no one minds getting wet, than to cruising or multi-purpose use,
> where it's nice to have the option of being as dry as possible. It
> seems as if it would be easier to deflect spray with topsides that were
> angled down towards the water, at least slightly, and a deck and stem
> that aren't going to throw water or spray up. That said, I'm no expert
> in how your intended design would work in terms of spray, so I could be
> mistaken.
Spray is certainly a consideration. I would expect the quantity of water displaced to be less but would tend to flow further back over the bow but with a lower velocity. This is contrasting with water squirting out of the way with vertical or forward rake. I have worked in spray rails that start just back from the bow and end up as part of a 400mm flare that helps give greater bury to the crossbeams and allow attachment of rudders. The rails would theoretically transfer some of the energy of the spray into lift. I was working on the rails to be rising slightly to the bow at an angle.
>
> - Ease of construction. Rob's U-shaped bent panel seems to be about
> as easy as it can get for a quick build. Switching to a compound shape
> could add a lot of build time. Unless you're just talking about the
> sculpted bows made of foam, which perhaps was your intention in the
> first place.
The compound area is only in the bows and anything difficult in foam.
check out how much spray there is from Oracle bows.
http://1.bp.blogspot. com/_hD8FFMGlAMo /Smp-VoKWxzI/ AAAAAAAABcc/ PyccmkL03cU/ s1600-h/sideshot _s.jpg
Having the boat sail flatter with less pitchpoling would reduce spray.
Some articles about the reduction in pitchpoling
http://www.aeroyacht-supercats. com/Innovation_ Center/Melvin_ article.htm
http://www.synfo.com/news/ allnews.asp? news=&id= 14025
>
> - Reserve buoyancy. I like having a bow that keeps on providing more
> buoyancy the further it gets depressed. That said, this may be just
> because I grew up with bows like this, and am therefore used to it. You
> make a good argument for a bow that sheds water from the top down when
> the going gets rough.
I have probably beaten this drum a bit too much, but any buoyancy after the stern starts to rise is going to increase the chance of pitchpole as it increases resistance , thus increasing the pitchpoling torque. Low down buoyancy keeps the boat sailing flat.
>
> As you can see, none of these are definitive stances. But I thought
> I'd pose the issues anyway for discussion.
>
> Any thoughts?
>
> - Mike
>
>
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