I am planning to mount a bow thruster on a 41' Sailboat and i wonder if
someone
knows the influence of the tunnel opening at the bow. Namely how much
the created
turbolence will affect the performance of the sailboat.
In the Vetus Web site, as small as possible tunnels (possibly more than
one) are suggested just to keep the resistance under way low;
unfortunately this very statement
makes me worry!
Thank You. Claudio.

On Fri, 22 Oct 2004 17:06:07 GMT, igavioli wrote:
I am planning to mount a bow thruster on a 41' Sailboat and i wonder if
someone
knows the influence of the tunnel opening at the bow. Namely how much
the created
turbolence will affect the performance of the sailboat.
In the Vetus Web site, as small as possible tunnels (possibly more than
one) are suggested just to keep the resistance under way low;
unfortunately this very statement
makes me worry!
====================================

It's difficult if not impossible to quantify the drag but it will
definitely be significant. Racing boats go to great lengths to either
plug up, or put mylar flaps over, through hull fittings that are far
smaller than a bow thruster aperature. The bow thruster aperature is
also in just about the worst possible place as it will disrupt
attached flow over the entire length of the hull. If you are serious
about sailing performance, I would not install a thruster.

Wayne.B wrote:
It's difficult if not impossible to quantify the drag but it will
definitely be significant. Racing boats go to great lengths to either
plug up, or put mylar flaps over, through hull fittings that are far
smaller than a bow thruster aperature. The bow thruster aperature is
also in just about the worst possible place as it will disrupt
attached flow over the entire length of the hull. If you are serious
about sailing performance, I would not install a thruster.

I understand what you write but I happened to encounter quite a few
sailboats with bow thrusters; usually 40" or longer.
I remember all of them very well: entering with nonchalance her narrow
berth while I am struggling with her backing that makes her wander to
all places except the right one!
I wonder if it is possible to put in front of the tunnel openings
something like a flap valve or a venetian blind device. This would
reduce the impact on the flow pattern.

Daniel

On Fri, 29 Oct 2004 08:51:35 GMT, Daniel
wrote:
I remember all of them very well: entering with nonchalance her narrow
berth while I am struggling with her backing that makes her wander to
all places except the right one!

========================================

I've found that the secret to backing a sailboat is to give it a quick
burst of reverse power while still in open water. Get enough speed in
reverse, usually 1 or 2 knots will suffice, that you have water
flowing over the keel and rudder. At that point, take the engine out
of gear and let the boat coast backward under its own momentum. It
should now respond to steering just as if you were moving forward.
Practice, practice, practice...

Wayne B says:

I've found that the secret to backing a sailboat is to give it a quick
burst of reverse power while still in open water. Get enough speed in
reverse, usually 1 or 2 knots will suffice, that you have water
flowing over the keel and rudder. At that point, take the engine out
of gear and let the boat coast backward under its own momentum. It
should now respond to steering just as if
you were moving forward.

I find the best way is to get the "going forward" part just right, so that
reverse is used only to take way off the boat so you can step gently onto the
pierhead with your bow/stern line at the perfect moment. An admiring audience
of curvaceous females who appreciate the art never hurts here.

It doesn't always work like that in practice, however... ;-)

Steve

On 29 Oct 2004 21:31:09 GMT, ospam (Stephen Baker)
wrote:
An admiring audience
of curvaceous females who appreciate the art never hurts here.

It doesn't always work like that in practice, however... ;-)

==============================================

That's true.

Docking Disaster Coefficient (DDC) = N_spectators^3

There IS something very satisfying however about backing a 50 foot, 20
ton sailboat smartly into a slip and stopping the whole thing with a
quick burst of forward power just as you're about to take out the main
pier. It's the element of suspense that really gets them on their
toes.

Stephen Baker wrote:
Wayne B says:


I've found that the secret to backing a sailboat is to give it a quick
burst of reverse power while still in open water. Get enough speed in
reverse, usually 1 or 2 knots will suffice, that you have water
flowing over the keel and rudder. At that point, take the engine out
of gear and let the boat coast backward under its own momentum. It
should now respond to steering just as if
you were moving forward.


I find the best way is to get the "going forward" part just right, so that
reverse is used only to take way off the boat so you can step gently onto the
pierhead with your bow/stern line at the perfect moment. An admiring audience
of curvaceous females who appreciate the art never hurts here.

It doesn't always work like that in practice, however... ;-)

Steve

When docking a boat, head into the dock, a kick ahead on the engine, is
used for:
1. To increase/decrease rudder effectiveness.
2. To increase headway

...... a kick astern is used for:
1. To make use of prop walk in steering
2. To reduce headway

When docking a boat, stern first into the dock, a kick astern on the
engine is used for:
1. To make use of propwalk to increase/decrease rate of turn.
2. To increase sternway

...... a kick ahead is used for:
1. To make use of the rudder to move the stern opposite to the direction
of the propwalk.
2. To decrease sternway.

Notice, I'm saying a "kick" ahead/astern. Any use of the throttle, means
you screwed up the docking, 90% of the time, for one reason or another
(misread wind/current/turning rate/speed).

Are these rules written in stone? HELL NO!!! These are basic rules, to
work WITH, to think about as you maneuver, so you have a basis to judge
how well your maneuver went.
If you are moving astern, fast enough to have steering with your rudder
(even on a sailboat) you are probably moving astern too fast (NOTE, I
said PROBABLY).
The most important line you will PROBABLY use when docking, is a spring
line (either the "fwd after spring" or the "aft forward spring") which
should be run from a point 1/3rd of the way aft of the bow, to a point
midships, or 1/3rd of the way fwd of the stern, to a point midships, but
only if necessary, right AT the bow or stern.

Let the games begin!!

otn

wrote:

I am planning to mount a bow thruster on a 41' Sailboat and i wonder if
someone knows the influence of the tunnel opening at the bow. Namely how
much
the created turbolence will affect the performance of the sailboat.
In the Vetus Web site, as small as possible tunnels (possibly more than
one) are suggested just to keep the resistance under way low;
unfortunately this very statement
makes me worry!
Thank You. Claudio.

igavioli wrote in message ...
I am planning to mount a bow thruster on a 41' Sailboat and i wonder if
someone
knows the influence of the tunnel opening at the bow. Namely how much
the created
turbolence will affect the performance of the sailboat.
In the Vetus Web site, as small as possible tunnels (possibly more than
one) are suggested just to keep the resistance under way low;
unfortunately this very statement
makes me worry!
Thank You. Claudio.

Claudio, normally bow thrusters are mounted on power boats such that
they are out of the water when the boat is on plane. I suspect they
create a lot of drag if they are not out of the water. In your case,
with a sail boat, it would always be in the water. I would talk to a
bow thruster manufacturer (they often have people at the boat shows)
before I installed one, they would know best or they may have models
made for sail boat applications.

John

igavioli wrote:
I am planning to mount a bow thruster on a 41' Sailboat and i wonder if
someone
knows the influence of the tunnel opening at the bow. Namely how much
the created
turbolence will affect the performance of the sailboat.
In the Vetus Web site, as small as possible tunnels (possibly more than
one) are suggested just to keep the resistance under way low;
unfortunately this very statement
makes me worry!
Thank You. Claudio.

My semi-informed opinion is...not much. Water is incompressible, so the
pressure change across the tunnel opening will not be a factor. Here's a
good site on bow thrusters.

http://www.diy-boat.com/Pages/Archiv...e/upgrade.html