GL: Bow Thruster vs. Stern Thruster?

[Michael Linden]

I am thinking of adding a thruster to our boat. I am hoping the
"List" can provide some good pros and cons of each. Thanks
Mike Linden
Monk 36
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[Gregory Han]

Well you can use the engine and rudder to make the stern move sideways
so I guess the bow thruster would be the best choice if you were only
installing one. It does require cutting into the hull for the tunnel
so it is harder to install.

I really cannot think of any reason to have a stern thruster without
one for the bow.

--
Greg and Susan Han
Allegria Krogen Whaleback #16

[John Ventura]

I'm a strong proponent of a stern thruster, having used one quite successfully
on the loop 2003-2004 (41' single screw trawler). Here's why:

As has been mentioned earlier, every vessel has its pivot point, around which
it turns left or right. On a monohull, that point usually is about one-third
aft of the prow. To visualize, when you turn to starboard, the forward
one-third of your vessel will swing to the right, and the after two-thirds
will swing to the left.

(We used to teach in shiphandling school that the helm station is usually
located at or near the pivot point -- a useful tip in gaining the "feel" for a
vessel while conning her. I have found that tip to be valid on the bridge of
a destroyer as well as at the helm of my trawler.)

Because of the physics related to this pivot point, the stern thruster is
inherently far more efficient than a bow thruster: the lever-arm upon which
the bow thruster works (horizontal distance between the thruster and the pivot
point) is very short -- only a few feet on your Monk. The stern thruster on
the other hand has a very long lever arm -- perhaps 25 or more feet from the
transom to the pp.

This means that the stern thruster acts much more quickly and requires
considerably less power.

There are other considerations:

Some have said you can swing the stern in a single screw vessel by judicious
use of the engine and rudder. While that is certainly true, there are
disadvantages to maneuvering thus in close quarters: among them, there will
always be fore and aft motion which can be undesirable; next, there will be
additional strain and wear on the transmission and linkages; finally it is
inherently inefficient and clumsy compared to use of a thruster.

Stern thrusters are usually mounted on the transom and require no underwater
hull penetrations, which suggest that they may be less expensive to install
and repair.

I bought my vessel for the loop and it had a stern thruster already installed.
I had had no previous experience with such a thruster and was, frankly,
skeptical. I grew to love the thing.

On the Loop there will be scores, if not hundreds of occasions -- other than
docking and undocking -- where you'll appreciate a thruster: Waiting for
drawbridges and locks to open, lining up prior to anchoring, etc. Simply,
you are in tight quarters very frequently, and a thruster -- whether bow or
stern -- will provide you with comfort, safety, peace of mind and flexibility
innumerable times. I wouldn't consider doing the loop in a single screw
without one.

Best Wishes,

John Ventura

----- Original Message -----
From: Michael Linden<mailto:lzfai...@earthlink.net>
To: great...@lists.samurai.com<mailto:great...@lists.samurai.com>
Sent: Sunday, February 11, 2007 7:52 PM
Subject: GL: Bow Thruster vs. Stern Thruster?

I am thinking of adding a thruster to our boat. I am hoping the
"List" can provide some good pros and cons of each. Thanks
Mike Linden
Monk 36
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m/mailman/listinfo/great-loop>

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[Jim Ague]

I had a Vetus 5512 Bowthruster installed on Derreen, a Monk 36, so therefore
I think a bowthruster is a better choice than a stern thruster. The 5512 is
probably a little underpowered for a Monk 36, but price savings and the
intent not to be out when coming in will require a thruster, weighed into
the decision.

Since a Derreen, and probably most Monks, walks to starboard in reverse, you
will soon learn to use that in docking and in doing 180 or 360 manuevers,
counterclockwise only, without using the bowthruster. In fact in practice,
as well as for practice, the thruster was never used, unless extreme
circumstances demanded it.

Now I have seen a situation where a stern thruster makes more sense than one
at the bow. For some reason on the East coast everyone pulls into slips
stern first (we didn't). A stern thruster makes this manuever simpler.

-- Jim Ague

[Dale Lauermann]

Mike,

We bought a Monk 36 last spring (Hull No. 203) that already had a Vetus bow
thruster installed. With the propeller and rudder on the other end, it's
hard to imagine a need for a stern thruster. I agree with some of the other
responses that we should learn to handle our boats in close quarters without
relying on thrusters, but it is handy when you're assigned a tight transient
slip and the approach isn't one that takes advantage of the natural side
thrust of our left handed propellers.

Dale Lauermann
Prime Time

----- Original Message -----
From: "Michael Linden" <lzfai...@earthlink.net>
To: <great...@lists.samurai.com>
Sent: Sunday, February 11, 2007 10:52 PM
Subject: GL: Bow Thruster vs. Stern Thruster?

[Torrens, Kevin]

I have a bow thruster on my 41' single screw trawler and love it. It
provides an added level of comfort and control. But, as others have
stated, it should not be a substitute for being able to handle the boat
with out it. It will fail at the least opportune time (I know).
The pivot point while moving forward is about 1/3 from the bow. The
pivot point in reverse is about 1/4 from the stern. Note the change
depending on the direction of travel.
Since my anxiety is much higher in reverse, I prefer the added lever arm
of the bow thruster. However, you still must be able to point the rear
end at the right spot so rudder and throttle control is still important.
That being said, I would love to have a stern thruster as well but I can
live without it. I suspect either is better than none and you will adapt
to either and take advantage of its best qualities.
A stern thruster will generally set you back fewer BU's due to its
simpler installation.

Kevin
m/v Wisper
DeFever 41

I am thinking of adding a thruster to our boat. I am hoping the
"List" can provide some good pros and cons of each. Thanks
Mike Linden
Monk 36
_______________________________________________