If two tandem keels work, then that is the way I would go. Possibly 2x500mm speer ogive with about 600mm between,
personally ,
I prefer to be able to allow it to dry out as I plant to cruise some areas with large tides.
--- In harryproa@yahoogrou
>
> <<How far apart do they need to be to avoid interference?
>
> That's a good question.
>
> Tandem keels, an option on Etap and Bavaria monohulls, have been very
> well received -- reports are that they develop significant lift. I've
> not seen one in person, but from photos, it appears that each keel might
> be 750 mm, with the same space in between.
>
>
> http://www.yachtwor
>
> http://www.yachtwor
>
> If one were to build a tandem keel for a proa, real dimensions
> wouldn't be too difficult to find. The section would obviously have to
> be symmetric.
>
> The big question for me would be how this would interact with a
> thruster or sail drive. I have no idea how that would affect the spacing.
>
> Perhaps it would still be angled slightly to windward in order to
> minimize interference.
>
> A question for anyone skilled in fluid mechanics: would two
> higher-aspect keels or mini foils be better than a single lower-aspect
> keel? I'm told the twins would generate more lift, but don't know if
> that's true or not.
>
> Also, how deep? My guess is that 300-450 mm would be enough to help
> handling without being too obtrusive.
>
> - Mike
>
> / /
> robert wrote:
> >
> >
> >
> > Possibly the time has not come for electric drive on these boats but
> > as batteries get lighter and more efficient and liquid fuels get more
> > expensive the time should not be too far off.
> > Good point about twin keels not bringing CLR as far forward. How far
> > apart do they need to be to avoid interference?
> > --- In harryproa@yahoogrou
> > <mailto:harryproa%
> > <ahakkara@> wrote:
> > >
> > > I have also thought about this kind of arrangement for the
> > auxiliary. The idea I like most is twin keel with saildrive unit
> > between the keels or even faired in to one of the keels. Twin keels
> > should move the CoE less forward and they would give great protection
> > for the drive unit. Retractable thruster would of course be nice but
> > also complex and expensive. Steerable electric saildrive would provide
> > great manouverability in all conditions, especially if combined with
> > electric outboard close to ww hull. Would the complexitiy, weight and
> > price of electric be worth it... well let the boat buyer decide.
> > Inboard and saildrive would be enough for most situations.
> > >
> > > Arto
> > >
> > >
> > >
> > > From: Mike Crawford <jmichael@>
> > > Subject: Re: [harryproa] Re: sailing BD with leeboard
> > > To: harryproa@yahoogrou
> > > Date: Monday, November 2, 2009, 5:38 PM
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > One thing I have debated for a while is going with a
> > propulsion-rated retractable thruster in the lee hull for the boat's
> > motor.
> > >
> > > On one hand, I realize that this carries a $10,000+ penalty when
> > compared to outboards, as well as some weight (once you figure in a
> > genset and any propulsion batteries).
> > >
> > > On the other, it would have a number of benefits:
> > >
> > > - Convenient collapsing without having to worry about 000 cables,
> > outboards, or other apparatus. Everything could be in one hull, with
> > just house power going to the windward hull.
> > >
> > > - A highly cavitation-resistan t drive system that's unlikely to
> > get beaten up or swamped by waves or chop.
> > >
> > > - The ability to drive forward or reverse without issues.
> > >
> > > - The option of charging batteries, either propulsion or house,
> > while under sail.
> > >
> > > - The option of using diesel, or fuel cells in the future, instead
> > of gasoline.
> > >
> > >
> > > But retractable thrusters are expensive, and they likely won't
> > take very well to grounding or running into logs.
> > >
> > > A mini keel could be a nice way of making sure there's something
> > sturdy to take impacts that would wipe the thruster out. There could
> > be either two mini-keels in tandem, each with its own foil shape, with
> > the thruster in the middle, or the keel could be one piece with the
> > thruster angling out to windward.
> > >
> > > There would be less need for a keel if the boat had a deeper draft
> > and the thruster could poke out above the hull bottom on the side, but
> > that's not likely to happen with a proa that has any reasonable
> > performance.
> > >
> > > - Mike
> > >
> > >
> > >
> > >
> > > rpvdb@ymail. com wrote:
> > >
> > >
> > > Hi,
> > >
> > > We sailed BD again with the repaired leeboard.
> > > I fixed it to the lw hull with a Dyna One line through the hull side
> > to the mast frame. There were a lower and upper guard to keep it in
> > position, at least that was the intention. It appeared very hard to
> > obtain enuogh tension on the line to keep the board thightly next to
> > the hull. A bolt would be better.
> > > Results of the sail pretty much confirm the earlier ones.
> > > I asked somebody new to the boat to come along for the test.
> > > When we where less concentrated on sailing the boat (too busy
> > talking)the board would come off the lower guard and after that it was
> > hard to bear away and the boat luffed into the wind a couple of times.
> > > Next day I sailed with the board of the foundation owning the boat and
> > > After a while the line connecting the leeboard to the hull broke.
> > > Now they could see with their own eyes the difference between having
> > the leeboard and not having it. The boat would luff into the wind when
> > steering higher that a close reach.
> > > For simplicity they prefer a keel as I expected.
> > > The extra hassle of uphauls and downhauls and keeping an eye on the
> > leeboard is more that they care for.
> > > So I will try to get a keel under the boat before winter really
> > kicks in.
> > > Regards,
> > > Rudolf
> > >
> >
> >
>
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