JT,
-Have been thinking a bit more on the subject. The long thin foils on
the rudders are probably not so suitable for redirecting prop thrust
but might be OK for a narrow nozzle directed flow. This is one of the
advantage of the flexible direction of the outboard, though a similar
effect could be obtained with an arrangement on the nozzle as on jet
drives. A possible problem with a bow thruster is that there is so
little draught that the 190mm hole would probably interfere with the
water line unless so far forward that it is still in the bow wave-
that would certainly upset Mark and Rob. DO you really need so much
thrust out at the bow- you have a pretty long lever arm? Is it
possible to have a retractable electric thruster with a directional
nozzle? My experience with trying to get bows to behave themselves
with a strong crosswind once the boat has lost way suggests that we
need either a small to moderate thrust near the bow or something with
a bit of grunt at the crossbeam.
One of the things we found with a nozzle is we had to change our
berthing technique as we didn't have the paddle wheel effect to shove
the stern around.
I certainly understand your trying to get the berthing controls
within the ken of the general boating public but I feel that if the
system can be made relatively simple and unambiguous they will learn
without too much trouble. In some ways being completely different
makes it easier to shift.
Robert
-- In harryproa@..., "jjtctaylor" <jtaylor412@c...>
wrote:
>
> Robert,
>
> Thanks for the input. I am optimistic about the fore aft rudder
> opportunity, but only testing will yet determine response. That
> 50-70 ft LW hull is a long piece of boat and control in a
> crosswind may be difficult. Most marinas I am familiar seem to
> be relatively small channels, favoring sport power boats and
> mono's of moderate proportions. They will probably gasp in
> disbelief if I showed up with a 26ft beam 60 ft long cat.
>
> I don't particularly like the crosswise thruster but seems most
> economical to install and compact, thus getting it farther forward
> as you recommend. I am not sure which drags more a parallel
> thruster or crosswise. Likely a 210lb thruster would be only a 7.5
> inch (190mm) opening based upon my calc of wind force
> against the hull sillouette. It would only be used for docking or
> tight marina handling.
>
> I will be chartering the boat a little, mostly to build the
experience
> base of likely HP buyers and was trying to keep the dock
> handling fairly simple and straightforward. Have to turn the
> upwind wheel opposite direction to move the forward rudder to
> turn the boat sharply. Of course turn them the same direction to
> crab. Prefer not to excite the helmsman with new tools in their
> early stages of experience.
>
> The aft (main) motor will be directed at the aft rudder so that
> should kick a turn off to a good start. That should be comfortable
> maneuvering for a newbie.
>
> I'll have to "thimk" some more on your forward parallel thruster
> idea. I had not thought of that option.
>
> I personally kinda like having all that propulsion stuff on the LW
> hull as it focuses those purposes in one place and all the
> support hardware can be colocated.
>
> I do know Rob will prefer a clean sleek hull when under sail, I
> would be damned as the basphemer to poke a crosswise hole
> in his nice clean hull. Eh ? Still plan an outboard"ish" electric
> drive for main power but it will retract (swing sideways & up)
>
> Regards,
>
> JT
> --- In harryproa@..., "Robert"
> <cateran1949@y...> wrote:
> >
> > Good to hear from you. I've had a little bit of experience with
> bow
> > thrusters on fishing boats. They are bow thrusters and really
> need to
> > be at the bows to work properly.The best one was one a 20m
> purse
> > seiner with the bow thruster in a pod attached to the front of
the
> > bow. There is always the problem of drag having a hole at right
> > angles to the boat Unless you have a small thruster running ll
> to
> > the hull feeding onto the forward rudder- is this what you had in
> > mind. My own feelings are that the paired rudder system with a
> single
> > outboard drive would give enough manoeverability for just
> about any
> > circumstances. This would be my preference but a paired set
> of fixed
> > screws that fed onto the rudders would also work. How about
> an out
> > board for the main propulsion and a small thruster to use
> while
> > docking .
> > Robert
> >
> >
> > -- In harryproa@..., "jjtctaylor"
> <jtaylor412@c...>
> > wrote:
> > >
> > > Been so long nearly forgot my password !
> > >
> > > With the progress so far with Johnnie's boat, the visionarry in
> > > latest stage of development, the aux drive has left me with
> some
> > > questions and possibilities for input from our distinguished
> > > forum. Albeit a quiet forum.
> > >
> > > Outboards is the current plan, a pair of 15 horse honda's
> which
> > > is a highly reliable 4-stroke. Certainly the most economical
> > > choice and most likely to succesfully get it in the water.
> > >
> > > The question I have,... is there better choices ? Lot's of
> history
> > > with swamped outboards and propulsion woes with prop out
> > > water in sloppy seas. I find the outboard closest to the WW
> hull
> > > most at risk since it is not really close to the hull itself
but
> > > suspended part way across the beam due the WW hull
> > > expansion. Yes OB's are a workable solution in moderate
> seas,
> > > and perhaps a little awkward with initial manuevers in close
> > > marineas cause the motor is not evenly spaced across the
> > > beam, but functional. Rob's & Mark's plan includes 24 hours
> of
> > > fuel aboard.
> > >
> > > As food for thought to kick off the discussion I suggest a
> single
> > > electric drive near the LW hull either as outboard or
> extendable
> > > from inside the LW hull. Must be kept close to the hull,
> > > upstream of the rudder to insure better helm control and the
> prop
> > > stays in the water. At the other end would be a bow thruster
> > > likely just aft of the leading rudder. An electric drive is
> > sufficient
> > > to replace both outboards (an equivalent 20-25 HP diesel)
> and
> > > slow speed maneuvering can be deftly handled by the bow
> > > thruster.
> > >
> > > Anybody ever had a bow thruster ? Some issues remain
> such
> > > as the thruster tube nacell, will it cause excessive drag in a
> > > bi-directional shunting kind of mode ? There are retractable
> > > options but much more costsly than an electric thruster and 2
> > > batteries. (est 210-220 Lb force required)
> > >
> > > Taking input, preferences, previous experience, or technical
> > > saavy !
> > >
> > > Regards,
> > >
> > > JT