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Old 04-04-2017, 09:52 AM   #1
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Bow Thruster Options

Considering installing a bow thruster in my 42' Grand Banks Motoryacht. I have done some research on line and gotten a few quotes for turn key installation.

Any advice on brands, sizing or general bow thruster experience would be appreciated.

I had a bow thruster in my Mainship 390 and also in my Camano 31, my only complaint was that the Camano thruster seemed to be inadequate in a stiff breeze on the beam.

Thanks in advance,
Kurt
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Old 04-04-2017, 10:26 AM   #2
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Why don't you tell us what they're quoting in terms of tunnel size, HP, and voltage.

Not aware of anybody ever saying, " I wish I had a small weaker bow thruster ".

Ted
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Old 04-04-2017, 10:34 AM   #3
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Why don't you tell us what they're quoting in terms of tunnel size, HP, and voltage.

Not aware of anybody ever saying, " I wish I had a small weaker bow thruster ".

Ted
All three quotes I got referenced a Vetus Thruster BOW95. One quote wanted to do 12v, one wanted to do 24v. The GB 42 is 40,000 lbs. I looked up the thrust on the BOW 95 and found:

Type: Single Prop, Blades: 6, Thrust: 210 lbs @ 12 VDC (8 HP)
Operating Power: 12 or 24 Volts DC, Draw: 610 Amps @ 12 Volts DC
Boat Length: 39' - 55', Tunnel Diameter: 7-9/32"
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Old 04-04-2017, 11:05 AM   #4
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My boat is similar to yours at 45' and around 45,000 lbs. I have a dual prop Side Power SE100 24 volt in the 7" tunnel. Mine is fine and so far I haven't been in a situation where there wasn't enough thrust. That said, they make 1 size larger in the 7" tunnel, SE120, and if I were doing the original installation, would likely have gone with it.

You should be fine with a 7" tunnel. I would probably go for a bigger motor and dual props, but that's just me. Absolutely go 24 volt and mount the batteries (sealed) in the bow thruster area. My original motor was 12 volt with a 30' 4/0 cable run. Still had low voltage issues because of the high amp draw. A 24 volt system draws half the amps and with the batteries close by, yields a very low voltage drop (lower the voltage, slower the speed).

Ted
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Old 04-04-2017, 11:08 AM   #5
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Forgot to mention, there should be almost no labor cost difference with the different models, but the labor will be most of the cost of adding a bow thruster.

Ted
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Old 04-04-2017, 11:11 AM   #6
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Quote:
Originally Posted by O C Diver View Post
Why don't you tell us what they're quoting in terms of tunnel size, HP, and voltage.

Not aware of anybody ever saying, " I wish I had a small weaker bow thruster ".

Ted
Well said! I have a stern and bow. The bow is a Wesmar 7HP and the stern is a Lewmar 185TT 4.0. The bow is functional for winds up to about 15 mph and current of 1kt. The stern is less functional, I believe, due to the depth of the keel. (4.5' draft) Also, it is mounted center stern and is only about 8-10" below the surface. Originally it would cavitate but I fabricated a pair of hoods to aim the thrust down slightly and keep air from entering the tube. It has stopped cavitating and works better.

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Old 04-04-2017, 11:27 AM   #7
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A great treatise on installing a bow thruster on a GB can be found on TF member twisted tree's blog site.

Mine was done right by a very good yard. Be sure the yard you use is experienced and knows their stuff. A good (most are) thruster can be rendered second class by a poor overall system design and inferior install.
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Old 04-04-2017, 11:49 AM   #8
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See if you can hear the one you are considering actually work in the water.

My bow thruster is irritatingly loud compared to some I have heard which are very quiet.
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Old 04-04-2017, 12:35 PM   #9
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Ken, that's an interesting comment you made about your noisy thruster.


I can hear mine but it's not annoying and, for the few seconds of its use, I don't mind the sound at all. Mine is a SidePower in a 10" tube with, IIRC, ~325 pounds of thrust. My boat weighs ~65,000 pounds with fuel and water at half, and that thruster really moves the bow around.
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Old 04-04-2017, 01:37 PM   #10
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I would think hard about going with a 24V system. Such a system will require an expensive charging system: either a voltage converter or a relay combiner like this one: Trollbridge2400 Information. Unless your boat is 24V but the great majority aren't.

You can use a 12V bow thruster with a Group 31 AGM mounted near the bow to minimize the big 4/0 cable run and therefore the voltage drop. Set it up for charging with smaller cable and a combiner like this: How to add a remote battery bank on a boat.

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Old 04-04-2017, 01:50 PM   #11
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From reading... 12V is OK, 24V is better, more V could be even better, 110V isn't unheard of, hydraulic is best. Batteries are best if very closely located in DC installations. Dual Odyssey PC-2150s (G31s) for major cranking amps but limited off-gassing in in underberth installations, either 12V or 24V.

Very much a generalization, I expect, and the actual solution would likely be very boat specific.


Yes, a 24V thruster in a 12V boat would need some charging solution. A separate 24V charger could be "cheap" enough. Maybe dock with the genset running to power that could be a work-around to 24V alternator or converter or whatever?

Somebody (Vetus?) just announced a new smaller rim-drive thruster, but I can't remember what voltage that was. Might be intended for larger boats...

-Chris
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Old 04-04-2017, 02:14 PM   #12
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Check out hydraulic for a boat that size.
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Old 04-04-2017, 02:16 PM   #13
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I thought hard about 12 V vs 24V, maybe for about 2 minutes. My Lewmar 12HP thruster is 24 V with 2 AGMs powering it. I'd guess a motor around 8 HP may have a different 12V vs 24V decision tree. Cost out the options and look at motor and wiring sizes. The answer will become clear.
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Old 04-04-2017, 02:25 PM   #14
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The old "series-parallel" 12/24 volt switches are still out there, from long ago truck starting applications. Google " Delco Remy 1119845 " and surf for explanations/diagrams and sources. Obsolete from Delco, others had it for $100....

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Old 04-04-2017, 04:28 PM   #15
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It is not a big deal to run 24v thruster on a 12v boat. Just put the batts up there near the thruster and set it up with a 120v to 24v charger. Batts won't charge unless on shore or gennie power, but unless dogging the crap out of the thruster, the batts will store enough energy for normal use.

I purposely sized my thruster a little on the smaller size. There are wind and current conditions that will overwhelm it. But those conditions would have also overwhelmed one that was two sizes up. I just try to avoid those situations.
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Old 04-04-2017, 04:33 PM   #16
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Simple solution is a 24 volt smart charger. Mine cost $160; has a 6 amp charge rate; and will run off a modified sine wave inverter, generator, or shore power. Before you tell me a 6 amp battery charger is too small, running a 24 volt 200 amp thruster for 1 minute draws less than 4 amps out of the battery. So an hour or 2 will have it back to float charge. My inverter is always on when I'm running.

Ted
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Old 04-04-2017, 05:11 PM   #17
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We have 24V Wesmar 13HP bow & stern thrusters on our 35,000 lb NT42. Love them; more than enough power to dock or undock in any conditions we would care to operate in. I think we're probably overpowered for most situations we'd ever encounter, but the extra power means less run time and less chance of timing out, which has never happened.

Everyone we talked to said to go 24V and dual prop.

When making the decision, we were down to Wesmar or Sidepower; both seemed to be about equal, but the Sidepower control lever panel was too large for the available space at the helm station.
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Old 04-04-2017, 06:18 PM   #18
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My boat is similar to yours at 45' and around 45,000 lbs. I have a dual prop Side Power SE100 24 volt in the 7" tunnel. Mine is fine and so far I haven't been in a situation where there wasn't enough thrust.
I'm about the same weight and a 7"-24v-10hp thruster. No problems.
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Old 04-04-2017, 07:20 PM   #19
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My 24-volt thruster does it.



Click on it:

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Old 04-04-2017, 10:17 PM   #20
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Quote:
Originally Posted by kurt.reynolds View Post
Considering installing a bow thruster in my 42' Grand Banks Motoryacht. I have done some research on line and gotten a few quotes for turn key installation.

Any advice on brands, sizing or general bow thruster experience would be appreciated.

I had a bow thruster in my Mainship 390 and also in my Camano 31, my only complaint was that the Camano thruster seemed to be inadequate in a stiff breeze on the beam.

Thanks in advance,
Kurt
I recommend that you be very careful with choosing a vendor to do the installation. I made the mistake of listening to what they told me and what they promised, but didn't check with past customers. Then, when I had an issue, the "guaranteed great service" turned into "sorry, no one is home".

Due diligence is the key.
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