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Bow Thrusters


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Nice to see Crew back to what it does best, giving good technical advice rather than a complete slagging off,

Oh I get it, deflecting so we don't notice you fitting a thruster to one of those SeaFleas of yours. Cunning plan but you're busted buddy :lol: :lol:

Bugger....... :D :D :D

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Some good points on the battery setup and location.

 

I recently had my boat rewired, and the cost of the cable from my house bank to the anchor winch made my eyes bleed. It was something like $1,500 as it was about 20m of mighty big marine cable. My 440Ah house battery bank only cost $1,000, therefore a few new batteries close to the thruster might be cheaper than running cable from your current setup.

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. . . In reality, you do not actually want to have to much shove. It is better to be slow and controlled as long as you have enough power to easily overcome side wind of a reasonable stiff breeze of upto say 20kts.

 

I disagree wheels.

 

I would of thought the time a bow thruster is worth it's weight would be when the wind is OVER 20 knots. So the MORE thrust the better

 

(am about to be thread hijacked for that comment :lol: )

 

Further the WEIGHT factor of tunnel, bow thruster motor and TWO props, and now batteries but with admittly "shorter" but still thick battery cables forward, would be a lot more than the weight of:

 

2 x skin fittings

2 x gate valves (still wanting the flush closing ones though)

4 x hose clamps (2 on each hose as below waterline YNZ SRs)

2 x bits of hose as per the WATERJET option

 

Further for another set of skin fittings & gate valves, you would have a stern thruster as well.

 

Remember the 40ft yacht :?: Weight forward should be avoided, so I'm still favouring the Waterjet option as worth more investgation.

The water inlet, hydraulic pump and thick cables can all be fitted beside / under the engine.

 

Perhaps even using the larger water inlet for the engine cooling supply (and galley sink?) as well, just replace the existing water inlet skin fitting & gate valve with a larger one.

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You are quite right Paul. But there are a couple of points in regards to sizing. One is that a yacht usually has less Hull area to be caught by wind than a Launch. And the second point and most influential, is the fulcrum point. A bow thruster in a Yacht(sailboat) is way further forward of the pivoting point of the Hull than a Launch. The further forward you can get a thruster, the better the effort in turning the Hull.

The next point is that a thruster has a lag time. It takes time to start the water flowing in the tunnel and when you take your finger off the button, it takes time to stop the water flowing. If you have too big a tunnel, you have a big mass of water to stop and that can keep the boat moving sideways when you don't really want it too, if you have too big a unit.

It is only my personal opinion, but my view is, as long as you have real good control in winds upto say 20kts, then you will still have control in winds much higher. Most Marinas are well sheltered. But if you are in a Marina with poor shelter or 20kts and higher are very common, then sure, specing a bigger unit will be the better. You will also note that the manufacturer has a fairly wide "fudge factor" to play with on each model. For instance, the one I suggested above, will suit a hull from 35 to 48ft. Thats a big boat length range. But they suggest it is perfect for a 40fter and the extreme ends of that are down to what the boat is size wise. It may be prudent to step up or step down depending in the situation.

The supplier should be able to give you the correct advice on what unit is best suited.

I had a client that decided he could save a heap of money by importing a Sidepower unit himself for his Launch. He chose a size two sizes up from what he really needed.

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Wheels: I hope Santa brings you reading glasses!!

 

Original comment was:

 

We have a 40 ft Cruising Yacht based at Pine Harbour Marina.

 

 

You should be penalised a bottle of rum by Squid for hijacking this excellent tread by introducing "Launches" :twisted: :twisted:

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On the other hand Wheels, valid comments about the thrust delay factor. Same applies to engine throttles but most of us do knot use full throttle astern or ahead when docking . . . . except perhaps KM's steel attacking the refueling jetty . . . .

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You should be penalised a bottle of rum by Squid for hijacking

Wooow, don't hang me just yet. Sidepowers Website gives info for Launches. Don't ask me why not Yachts. They need to be brought into the real world. So my comments were in regards to using their specs and relating that to a yacht.

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except perhaps KM's steel attacking the refueling jetty . . . .

I can't use full throttle, the motor is too big for the boat so if I go for a black smoker all I do is make a milkshake.

 

Yes watch thruster lag, it's a common trap for new players.

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Many thanks folks for the excellent feedback and comments. This is exactly the sort of help that I was hoping for from all you Interweb experts.

My thoughts are tending towards a dedicated battery next to the unit as being the most elegant solution.

Both the Vetus and Sidepower sizing charts come up with units of 95kg thrust. This may be a tad on the generous side but better too big than too small, as the Actress said to the Bishop.

Re the current draw, the Sidepower SE80/185T (thanks, Wheels) is about 7.5hp = 5595 Watts. Using the old W=V*A, this comes out at 466 amps at 12V, not including losses. The Vetus unit recommends a 500A fuse so we are in the right ballpark.

The waterjet option sounds intesting but I think that to be effective would need quite large diameter piping and/or very high pressures. The 95kg thrust bow thruster has a tube diameter of 185mm and with 7.5 hp will be shifting a huge mass of water. I would envisage this would only be in bursts of 5 or 10 seconds at a time.

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. . . Sidepowers Website gives info for Launches. Don't ask me why not Yachts. . .

 

Perhaps the greater windage of launches and the general lack of skilled crew and the 'turn key / chequebook " ability of most (but knot all) launch owner/drivers means that the marketing demographics for bow thrusters concentrates on launches, (especially in USA boating mags), not yachts, IMHO.

 

Launch drivers have a car licence already.

What can be so difficult :?:

The launch starts just like the car and the steering wheel is the same. :think:

 

 

Most people on yachts have more skills and experiences :thumbup: before they ever get on the tiller to bring a yacht into a berth.

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Florence: Ask for a demo of boats with different bow thrusters, especially on a windy day and with an under and by contrast an over powered setup.

 

It could be a wonderful learning experience.

 

If we had a bit of warning, I, and I am sure other posters here, would be interested in joining you for the occasion.

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The waterjet option sounds intesting but I think that to be effective would need quite large diameter piping and/or very high pressures.

 

From the Wilbro PDF file:

All WillDo electrical Jet Thrusters consist of an electric motor

(12 Volt D.C.), which drives an impeller. The impeller sucks in the seawater

and presses it, through flexible high-pressure hoses (2 or 4 - Single

or Combi execution), to the nozzles in the bow and/or the stern, which

have an inside diameter of no more than 45 mm.

 

The nozzle openings in the boat are not bigger than

45 mm in diameter, this contrary to ø 250 – 300 mm

in the case of a conventional bow thruster. In other words:

the installation is much easier, there is hardly any risk of

flotsam or a plastic bag entering the openings and there is

almost no resistance when sailing or motoring.

 

So skin fittings are not very large at all, very suitable for a 40ft IMHO.

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Yes, that is why I very much like the idea of the water jet. I haven't been able to play with one yet and never installed one. So I can not comment on how well they work. I don't think they are cheap, but I am sure the installation cost being far faster, easier must mean it would be cheaper and make up the difference. The Hose most likely would be the expensive part, as you would be getting into specialised high pressure hoses I imagine. It all comes with the cost of the unit anyway. It also pusts the pump in the engine area which helps with weight and also closer to the Engine start batteries, so no expensive wiring and charging.

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I agree and So Wheels all we need is a boat with the water jet option

to have a play with :thumbup:

 

Have a happy, safe and wonderful cruising Chrismas in the Sounds.

Cheers :clap: :clap: :clap: :clap:

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Well in reality, it is just a high presure centrifugal pump, probably multistage. They can be bought cheap in both Bronze or SST. Some are even composite plastic these days. Or it could be a Gear pump with a pressure relief. That would maintain a constant pressure ready to blow, instead of the lagg time for water to get going in a centrifugal. Then some hoses with solinoid valves on each skin fitting. A simple joystick switch for control and Bobs the auntie of the boy next door. I have had this in the back of my mind for a long time. Hook pump to Main engine with mag clutch of it will spin happily with noload when all Valves are closed. Or I fit a coupling to my Diesel Genset motor and fit the pump to that.

Even just a little effort from a jet could be a big help at times.

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