I don't see that rocker in the lw hull really helps. It will still require similar extra buoyancy in the bow to counteract the sailing loads. (it would also give more vertical load vectors form the sail, but this is pretty marginal) A rockered ww hull would make it worse.
A higher prismatic coefficient giving greater extra bow buoyancy for less side area should make it better.I am working on 8.5-9 prismatic coefficient, depending on the payload
Your work with a single leeboard is dominating my ideas at the moment with the rudders at 9m apart just out from the hull, though I am wondering about two leeboards. This is starting to look a bit excessive.
--- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@...> wrote:
>
> Hi,
>
> The steering problems on BD to me seem related to the bow being pushed down so it becomes the deepest part of the boat.
> It took me some time to realise that this seems to be happening and that it relates to experiences on other boats. For a non-proa a solution may be to trim the stern down. For a HP that would mean pumping water ballast. Another solution for a proa might be to design rocker in the lw hull.
> A rockerless lw hull of a HP in my opinion needs its rudder as far aft as possible. The small ones like Harriette are easily trimmed by shifting weight, which is a instictive reaction when sailing a small boat at speed.
>
> regards,
> Rudolf
>
>
>
> ----- Original Message -----
> From: Gardner Pomper
> To: harryproa@yahoogroups.com.au
> Sent: Tuesday, June 22, 2010 2:58 PM
> Subject: Re: [harryproa] Re: Rudder lift?
>
>
>
>
> Hi,
>
> The leeway is not my primary concern. I am worried about steering. I have heard several mentions about Blind Date and also about Sidecar, that they lose steering control, can't shunt, or head uncontrollably up into the wind before their rudders were enlarged, moved, etc.
>
> I don't see the advantage of a shallow draft boat if I need to have my rudders down 5' in order to steer. I have been trying to find out if this is just a problem when the boats are overpowered, or strong winds or something, but no one has admitted to that, so I am worried that I won't be able to sail in less than 4-5 feet of water. I will be able to drag my boat up near the beach, but the last mile will have to be done under power.
>
> - Gardner
>
>
> On Tue, Jun 22, 2010 at 8:05 AM, robert <cateran1949@...> wrote:
>
>
> In shallow water, there is a some leeway resistance due to the water having a hard time getting out of the way. The shallower the water, the greater the effect for the same depth of boat.
>
>
>
> --- In harryproa@yahoogroups.com.au, Mike Crawford <jmichael@> wrote:
> >
> > Gardner,
> >
> > Your Mainecat/5200 idea is safe with me. I'm building a plywood dory
> > this summer and will be doing the same thing. Even if it doesn't work,
> > the theory is comforting./ /
> >
> > So now you're basically tripling your submerged foil area for a 1.5'
> > depth: two rudders at normal width, and two mini keels that I'm assuming
> > would each be twice as wide as a rudder. You won't have ideal steerage
> > and leeway prevention, but my guess is that this is a moot point.
> > Either you have two rudders, or you have rudders plus dagger boards or
> > mini keels. Anything you do beyond the rudders will likely help.
> >
> > I'd try keeping the keels as close to each other, though. This
> > wouldn't be idea for beaching, but as Rob pointed out, tires are
> > probably better than keels anyway -- that way there's no risk of gravel
> > sanding off your bottom paint, or of bouncing in the surf taking your
> > keels off. In keeping the keels close together, almost like Rudolph's
> > tandem keel, the keels shouldn't impact steering that much, and could
> > even conceivably help. Two keels far apart, on the other hand, might
> > make it harder to shunt, particularly when you don't have as much rudder
> > in the water as you'd like.
> >
> > At least you'll have the option of two counter-rotating rudders.
> > That's definitely going to help steering in minimal depths when compared
> > to a cat.
> >
> > - Mike
> > / /
> >
> > On 6/21/2010 1:53 PM, Gardner Pomper wrote:
> > >
> > > Hi,
> > >
> > > Yes, your description of when to use mini-keels is what I had in mind.
> > > I would rather not build them, but I am unclear as to what the minimum
> > > rudder area needed when sailing in light winds. Here is the scenario I
> > > have in mind:
> > >
> > > In the chesapeake, or the bahamas, there are many spots that are 2-3
> > > feet deep that I would like to glide along in relatively light winds.
> > > The waters are sheltered, and therefore flat, and the wind is likely
> > > to be less than 10 knots. When doing this, I would like to have a
> > > draft of 2' or less. I can't have my rudders extended to 4 or 5' depth
> > > to get the requisite 2% of sail area, so I thought that fixed
> > > minikeels, maybe 1' deep, would give the boat a 1.5' draft. That, plus
> > > the rudders raised to 18" draft would give me more foil area than the
> > > rudders alone. I would not be looking to sail at > 5 knots under these
> > > conditions, because i really don't want to hit anything.
> > >
> > > In that scenario, with a boat about the size of a harry, or a
> > > harrigami, would I be able to steer with just the rudders (total
> > > submerged area of 3 sq ft, vs 400 sq ft of sail)? Would I be better
> > > off with an additional 3 sq ft of mini-keels?
> > >
> > > My Maine Cat 30 had the mini-keels attached with 5200, for precisely
> > > the reason you mentioned.. in a severe collision, the keels were
> > > supposed to break off without ripping open the bottom of the hull. I
> > > have no idea if that would have worked or not, but it gave me peace of
> > > mind to believe it, so please don't contradict the idea <grin>.
> > >
> > > - Gardner
> > >
> > > On Mon,
> > >
> > >
> >
>