Bow Thruster Options

[kurt.reynolds]

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

 

[O C Diver]

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

 

[kurt.reynolds]

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"

 

[O C Diver]

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

 

[O C Diver]

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

 

[steelydon]

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.

Don

 

[sunchaser]

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.

 

[ktdtx]

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.

 

[GFC]

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.

 

[DavidM]

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.

David

 

[ranger58sb]

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

 

[High Wire]

Check out hydraulic for a boat that size.

 

[sunchaser]

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.

 

[Roamer Blue]

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....

RB

 

[Ski in NC]

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.

 

[O C Diver]

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

 

[Conrad]

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.

 

[Codger2]

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.

 

[markpierce]

My 24-volt thruster does it.



Click on it:

 

[Drake]

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.

 

[Irish Rambler]

I bought a 42' boat and was recommended to fit a 75kg Vetus.
I was offered a 95 for the same price and fitted the larger one, the best decision I ever made as the 75 would have been fine on a calm day but would not have been man enough in higher winds.
A hydraulically driven one is far superior because it will run all day as opposed to the electrical with a thermal cut out, which may just cut out in bad conditions..
I highly recommend my mod for single lever control posted on Windmills and Wine thread which you can buy through Hopkins Carter.

 

[Insequent]

I have a 185TT Lewmar 8HP. Their largest 12V unit. I have had no issues with it, but it is too small for my boat, which is around #60,000lb. If there is much wind or current it has to run a lot, but I have yet to timeout. I ought to have gone for a larger diameter tunnel, two blades and 24V.

I installed it before I decided to add active fin stabis, other wise I might have gone hydraulic. And had I known at the time I would be entering a berth in the river going cross current in a narrow fairway, then a stern thruster would have been on the list as well ! I get envious when I see the guy in he Eastbay keeping his bow pointed up-current and moving along the fairway sideways until he is lined up with his berth.

 

[Irish Rambler]

Insequent.
I had the same problem in a marina I was berthed in at the time. I'm not trying to be smart but if you're approaching your berth up river against the current try slowing your engines right down until you're stationary against the current. Now try a little helm so that your bow now is just slightly to the right/left and with a little practice you should be able to 'crab' your vessel sideways across the river.

When your adjacent to, and slightly upstream of your berth with some nifty throttle helm do a smart 90' turn right into your berth.
Practice in the open water until you perfect it, and keep practicing until your really capable.
Have plenty of fenders and try it in an open berth to begin with until you are perfect with the maneouver and only do it facing upstream. It will then become second nature just like riding a bike.
I would recommend half hour practice sessions so you don't lose concentration.

 

[Insequent]

Yes it can be done, and I have. But the existing boats on the finger (I'm 5 in from the river entrance, close to shore) change the current/wind behaviour, and I'm usually solo. I have a 1 yo liveaboard Jeanneau along side me that I really don't want to bump, even with a fender. So I prefer slack tide to get into the berth, put the engines in neutral, and have a little bit of time to secures a couple docklines.

 

[Irish Rambler]

Hi Brian,
Good on you, a lot of people just give up or make a blue.
Glad to hear you have slack tide to help you. I certainly wouldn't want to touch anyone's boat either out of respect for the owner.
All that said once your safely in you can pop the top off a nice cool 'Gold'.

 

[sunchaser]

I installed it before I decided to add active fin stabis, other wise I might have gone hydraulic..

When docking I'd assume you run your engines at low RPM or idle. Most hydraulic systems develop too low a pressure at idle to give the thruster the oomph it needs when docking. Many hydraulic thruster vessels are set up with a hydraulic pump on the genset or get home engine so high pump speeds can be developed when docking.

This is one reason why most Nordhavns up to 60 feet or so use 24V thrusters at each end. The newer electric designs can be variable speed and have few electric cut out issues. My Lewmar has never timed out, in a few cases with steady operation in excess of a minute.

 

[Insequent]

Yes, if just adding pieces I can see the 24V route. But a bunch of independent thrusters (bow, stern and props in forward or reverse) could be a handful. What I would have done is go for an integrated system, like the Twin Disc offering. A joystick system, and a wireless remote would be very nice!

http://www.twindisc.com/marine-products/propulsion-control-systems/ec300js/

 

[Mako]

A hydraulically driven one is far superior because it will run all day as opposed to the electrical with a thermal cut out, which may just cut out in bad conditions.

Do 230/240 volt thrusters have that 2.5 minute duty problem or are they continuous rated like hydraulic?

 

[Transaxial]

I am just in the middle of installing a bow thruster in my 40' Palmer. Based on opinions everywhere, hydraulic is a better way to go in the long run, and once I have the hydraulic system, I can add things like a hydraulic powered windlass and capstain system, prawn trap pullers, davits, 3" bilge pump, etc. As far as choosing a bow thruster, the MaxPower CT HYD 125 had some of the best specs for power at lower pressure and rpm in a 185 mm tube (7.28"). That was the model 317588 with a 11 cc or .671 cu in motor that produces 260 lbs of thrust with 9.25 gpm at 2320 psi. The math shows that to be 12.5 hp at motor 3184 rpm although the prop rpm is closer to 1/2 that I believe. Is it high prop rpm on some of these thrusters that makes them so noisy? I have sized my hydraulic pump to give me max thruster speed at 1100 engine rpm which allows me to throttle back the main to idle and allow the thruster to work at 2/3 speed when I need less than full power. I am running an open center valve with a remote cable to the helm which also allows me to feather the oil to the thruster. Cost wise I am just going to a hydraulics shop to buy a Permco P124 clutch pump - 8.8 gpm @ 1000 rpm. Max speed is 3000 rpm and 3500 psi so specs well over operating conditions. This pump is $500.

I did find a Kobelt thruster, KP 8 which is more of a commercial unit with brass prop and good specs but I could not get info out of the supplier on all the specs to design the pump myself. I still think it is a better unit and bigger 8" tunnel but also $1000 + more cost. Prop speed was 1500 rpm. I like the simplicity and reliability of hydraulic systems, as long as you don't get into fancy electronically controlled valves and controls. Nothing wrong with a good 24 V thruster, I just chose hydraulic.