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Old 05-04-2007, 06:15   #1
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Bow Thruster

I kicking around adding a bow thruster when I get stateside. Anyone have any recommendation as to brand and sizing? 40' monohull.
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Old 05-04-2007, 07:02   #2
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Some Bow Thruster Manufacturers:

Arcturus Marine Systems
ARCTURUS MARINE Ride Control Thrusters Integrate Hydraulics

Hydra-Power Systems Inc.
Hydra-Power Systems, Inc.

Van Dusen & Meyer, Inc. (NAIAD Marine Systems)
Yacht Stabilizers Boat Stabilizers Ship Stabilizer Fin and Roll Stabilizers Naiad Marine Systems

W.H. Den Ouden (USA) Inc (Vetus)
Welcome to Vetus.com!

Western Marine (Wesmar)
Western Marine Company
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Old 05-04-2007, 07:20   #3
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How hard is it to add one? Would this have to be done by a yard? I guess I had just always thought that if my boat didn't have one... it didn't have one? This is interesting!

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Old 05-04-2007, 08:44   #4
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Definitly a yard project. Boat on the hard and cut thru the hull (both sides) and glass in and fair the tube. Then the wiring etc., which I can do myself.
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Old 05-04-2007, 08:46   #5
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I see Lewmar has them now. Any feedback in theirs?
What I'd really like to find is someone who has used a specific brand and their feedback. Yes, I still believe in Santa.
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Old 05-04-2007, 12:19   #6
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Vetus also has bow thrusters. I have one of their catalogs.

Welcome to Vetus.com!

Check them out also. They do have their products here in the US also.
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Old 14-05-2007, 18:32   #7
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Lewmar thrusters

The Lewmar TT thrusters have proven themselves to be the quietest and most durable of the bunch in the electric class. Longest run times, lowest draw and easiest maintenance, which is nearly none. Equal thrust in both directions and some important safety features built in. There are a lot of details to a successful install for maximum benefit from the investment so do your homework and select an experienced installer. It will save a lot fo headaches down the road and save you some green on the install.
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Old 14-05-2007, 18:44   #8
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Quote:
There are a lot of details to a successful install for maximum benefit from the investment so do your homework and select an experienced installer.
The elctrical work being just as import as cutting a hole in both sides of the bow below the water and structurally making it sound. There a are great many bad things that can come of a poor job.
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Old 14-05-2007, 21:59   #9
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So, anybody have hard data on how much some big nasty turbulence making holes in the bow slow you down. I guess it's much more of a concern to sailboaters than motorboaters. Also, I've heard people wonder about loss of buoyancy. I suppose a boat designed with a bow thruster will have compensated for that, and I would guess big heavy broad bowed cruisers will be far less affected than fine IOR style bows.

You still have to learn how to drive your boat, with or without a thruster. I transit the locks in Puget Sound a lot. I've watched a fair number of boats that even with thrusters provided a show. A couple of the most memorable: A couple of matching powerboats with bow and stern thrusters took several minutes to get square on the wall. I had to push a sailboat to the wall that had a bow thruster, the woman on the bow was telling the lock attendant how it was all his fault. When they left the skipper was yelling at the attendant to pull in his stern as his bow kept heading for the wall, when his stern got about 4-5 feet forward of me I could see his rudder, I yelled at him to center his helm. (Last part not a thruster problem.)

John (Who has never provided a show in the locks, yeah right.)
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Old 14-05-2007, 23:17   #10
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My local yard rats say IMTRA/SidePower is the best. They make their own motors (Sleipner AG makes them and they are part of the same conglomorate). Everyone else's thrusters are either re-brands or copies (for electrical types that is).

ST-75 is a decent size for a 40 footer. Needs a 7.25 ID tunnel.
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Old 15-05-2007, 05:31   #11
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My local yard rats say IMTRA/SidePower is the best. They make their own motors (Sleipner AG makes them and they are part of the same conglomorate). Everyone else's thrusters are either re-brands or copies (for electrical types that is).
Yeah, I concur: Have used the IMTRA/SidePower thrusters on more than a few occasions and found them to be good and reliable. Also good support from the factory.
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Old 15-05-2007, 06:21   #12
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I thought I remembered seeing something like this. Probably horribly expensive, but solves the drag issue.

Max Power

Picture of it extended.

Max Power

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Old 15-05-2007, 06:43   #13
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Originally Posted by cal40john
I thought I remembered seeing something like this. Probably horribly expensive, but solves the drag issue.

Max Power

Picture of it extended.

Max Power

John
Yeah, I saw one of those up close at last years IBEX. Great idea. That thing is better suited for more performance oriented boats that have a shallow U shaped bow. Thrusters need to have a minimum depth below the water to operate efficiently (otherwise they start to suck air). Usually about 6 or 7 inches at least. Compared to deep 'V' bow cruising boats, some shallow 'U' bow performance boats just dont have the depth. That is where the Max Power would be useful.

But it is also at the expense of more room inside.
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Old 15-05-2007, 06:45   #14
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Performance losses are usually not noticeable as long as the install was done properly. A spoiler should be added to any thruster to deflect the laminar water flow over the hole rather than letting it swirl into the rear side of the thruster hole. That will cause some drag in sailboats. Powerboats need them too as it keeps the rushing water from pounding through waves out of the exposed tunnel and provides a quieter dryer ride. Bouyancy is really not much of an issue since you are not carrying a captured load. It does detract a little but its a very little and not noticaeable as a performance hinderance. The only hard data I have ever come across was from a German firm that did some hydro analyisis on the option of using a spoiler ahead of the tunnel or a depression at the rear of the tunnel. Their conclusion was that the spoiler was better. The dish actually caused more drag, which was counter-intuitive to me but it had to do with a vacuum created by the dish whereas the spoiler throws the flow clear of the tunnel.

Fine entry boats usually are not well suited to a traditional bow thruster as they do not have the forefoot depth to get the tunnel low enough and far forward enough and limit the size of the thruster to one that would be inappropriate. The rule of thumb is a tunnel diameter below the waterline, 6" as a minimum and 4" up from the keel. Usually they need to be 24 V as well which will provice more thrust. In Lewmar's case we see about 20% more thrust with a 24 v system. A result of the motors not bogging down. The retractable is certainlty the way to go for these boatsa and anyone concerned about the n-th degree of performance. They are as mentioned very expensive and more commonly hyrdraulic. The modfications to the boat make up a large part of the expense. to my knowledge Max Power is the only one making an electric retracting thruster for smaller vessels. Lewmars are intended for larger cruiser/racers.
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Old 15-05-2007, 06:53   #15
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Originally Posted by cal40john
So, anybody have hard data on how much some big nasty turbulence making holes in the bow slow you down. I guess it's much more of a concern to sailboaters than motorboaters. Also, I've heard people wonder about loss of buoyancy. I suppose a boat designed with a bow thruster will have compensated for that, and I would guess big heavy broad bowed cruisers will be far less affected than fine IOR style bows.
Not really data, but it depends on how "fast" the sides of the hull "diverges" as you move aft. Try to imagine...

a place near the bow, under the waterline where you might put the thruster. Imagine cutting the holes and slipping in the tunnel. Now chop the sides off of the tunnel so it is flush with the hull. Now look aft straight on from the bow at the waterline. Depending on how much "flat spot" you see from the "inside back" of the tunnel determines how much turbulence you may get. Again, on "U" shaped bows where sides are almost sheer, this is not a big deal, but fat and wide "V" shaped cruisers tend to have more of a flat spot. Often installers will "sculpt" the surface fore and aft of the tunnel to help water flow more smoothly around the tunnel.

Coincidentally, I am starting the finishing glass work on the tunnel I installed on my 42.
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