What are the drawbacks of bow thrusters?

[taxwizz]

I have a Nonsuch, which has it's mast at the bow rather than midships like a sloop. As a result any crosswind blows the bow downwind when docking. A couple of years ago I installed a bow thruster and I LOVE IT. It makes docking, even in a crosswind, relatively easy. I cannot imagine not having it. It is a CRASHSAVER.

[Jammer]

Thanks for the replies.

Notably, there seem to be no replies from anyone who has a bow thruster and wishes they could get rid of it and recover the storage space under the v-berth.

[buzzstar]

If wishes were horses I'd have had bow thrusters. I did not, but I did not have a horse either. Sailed a few times on boats similar to mine that had them, and envied the captain each time. Fourteen year old kids eat too much to carry around, they are unreliable, and the maintenance is horrendous even if you call them, "son."

[Auspicious]

Originally Posted by Jammer

Well, aside from cost, maintenance, and the loss of potential bragging rights from being able to dock without one.

From my perspective as a naval architect and an active delivery skipper:

The drag contribution of an open tunnel is very real and significant. It slows you down. There is a reason commercial and military ships put doors over thruster tunnels. The numbers are astounding - I remember big impacts in hydro and fluid dynamics. Commercial carriers don't put doors on because they are cool.

At the recreational level the thrust is just not enough to help when conditions get sporty. If you don't practice in benign conditions you won't be able to move the boat where you want it when conditions are more stressing.

Not only do they chew up a lot of storage space but they often are dirty, leaving carbon dust throughout the space where they are mounted so you can't pack things in around them. Remember the ventilation requirement as well. Start adding battery capacity and wiring and the dollars go up along with the space impact.

In my opinion for the cost of a thruster you would be better served taking lessons from a credible instructor on your boat.

Thruster control is just one more thing to pay attention to while docking. What will you be distracted from that will bite you?

[boom23]

I've owned many boats, powerboats and sailboats, catamarans and monohulls, twin engine and single engine ones. I single hand a lot.

Personally, I like thrusters. I will not consider a monohull over 45ft without a bow thruster. I do not rely on it but it I have it ready just in case. On a 60+ foot monohull, I would want a stern thruster also. A twin engine boat is more controllable with engines alone.

The Amel bow thruster is inside the hull covered and drops down when in use. Most Amel's have one and it works. Does it, or any other bow thruster, break down? Eventually, everything breaks down on a boat... Faster, if it's not maintained properly.

[Auspicious]

Originally Posted by boom23

The Amel bow thruster is inside the hull covered and drops down when in use. Most Amel's have one and it works. Does it, or any other bow thruster, break down? Eventually, everything breaks down on a boat... Faster, if it's not maintained properly.

Retractable thrusters like that on the Amel (nice boats by the way) are as close as you are likely to see to the doors you'll find on ships. You add the failure modes of limit switches (BTDT), seal leakage (BTDT), and limits on boat speed. For the latter, the thruster and it's mechanism are subject to damage if they are left deployed above a fairly low boat speed, often about 3 kts. Think about the implications of that in marinas with fairly high tidal currents.

[Mr O]

There are few drawbacks to thrusters and little to go wrong. However, on my 39’ monohull cruiser there were batteries of unknown age and condition when I bought her. Everything worked fine for a while until one Day while using the thruster the voltage dropped and spiked enough to kill my remote plotter. Once new batteries were installed, no problem.
Consider installing a separate 24v battery bank close as possible to thruster as opposed to a 12v thruster with long cables to batteries way aft. Totally eliminates voltage spikes in house bank and will have very little line drop. You will also need a echo charger that’s 12 to 24v. It will add weight to the bow and take up space.
Other than that, I find that the thruster is very useful in tight spots and cross winds/current. It has kept my bow away from boats next to my slip more than once!

[taxwizz]

I have a 12v thruster and the dedicated battery is in a bow compartment. Three foot cable run from battery to thruster. The long run is from the control to the thruster solenoid, and for the charging cable.
Low power, no problems. I use a cheap car battery as it only runs for a few seconds.

[danielamartindm]

I don't think the argument that bow thrusters result in over-reliance, and the loss of skills we'd be practicing in their absence, makes sense. One could say the same thing about autopilots.

[Flextron]

Long power cables running through the boat. Have a dedicated battery close to the unit. Any hole cut in a boat is a potential issue.

[Scotty Kiwi]

68ft Herreschoff second yacht, single handed or with drunk/incompetent crew/clients, I had a tunnel and bowthruster professionally installed.



I'm sure it saved all sorts of potential scraps and damage, and enabled berthing in positions that would have otherwise been too risky given my then boat handling experience. For example in strong cross winds in a marina finger too narrow to do a 180 spin, we could maintain a speed astern fast enough to not be blown off, and angle into a "berth" closest to the wharf, too difficult even for smaller boats. It meant we could tie up in marinas where the manager had initially said they can't take us.

With skill, we could jump the whole boat directly sideways to port 2 meters (prop cavitation in reverse and port thruster).

This meant cruising with confidence in a greater range of conditions and in busy periods. Invaluable on a larger boat.

When we installed it I redid the entire house house battery system to 8 x 6v deep cycles at 24v, with benefits to living conditions generally. Had 20 meters of two 1in cables going to and from the batteries to the thruster.

Downside of both = more long term maintenance, but this way paid for by the savings in paint scraps and chips that occur even in regular docking situations.

I did wish I'd had an option of foot (toe) controls at the base of the pedestal. Spinning the wheel, using the throttle forward and reverse, and using the bowthruster required three hands (and a fourth for a line).

As I gained experience in a wide range of conditions, (say 5 to 10 years) I used it increasingly less.

[IslandHopper]

If fitting a tunnel thruster and fairing it correctly the drag is negligible, hence why the vast majority of commercial applications don't have doors. If suited to the vessel and correctly fitted I don't see any drawbacks

[boom23]

Originally Posted by Auspicious

You add the failure modes of limit switches (BTDT), seal leakage (BTDT), and limits on boat speed. For the latter, the thruster and it's mechanism are subject to damage if they are left deployed above a fairly low boat speed, often about 3 kts. Think about the implications of that in marinas with fairly high tidal currents.

I have not heard or read any serious problems about the Amel bow thrusters. If anything, they spend most of their time out of the water and are designed to be accessible. In addition, I have not read anything about the 3 kts limitation you mention. It is not in the Amel manuals I have. But, I will ask the factory next chance I get.

Again, anything can break... I like thrusters and I will spec them on all my future boats.

[DumnMad]

Originally Posted by boom23

I've owned many boats, powerboats and sailboats, catamarans and monohulls, twin engine and single engine ones. I single hand a lot.

Personally, I like thrusters. I will not consider a monohull over 45ft without a bow thruster. I do not rely on it but it I have it ready just in case.

What is the minimum 12v x amps you would want with a 45ft mono ?

[Auspicious]

Originally Posted by IslandHopper

If fitting a tunnel thruster and fairing it correctly the drag is negligible, hence why the vast majority of commercial applications don't have doors. If suited to the vessel and correctly fitted I don't see any drawbacks

Simply not true. The drag is far from negligible. Any decent hydrodynamics course will show that, and the accounting department of a shipping company can show you the fuel costs.

Originally Posted by boom23

I have not heard or read any serious problems about the Amel bow thrusters. If anything, they spend most of their time out of the water and are designed to be accessible. In addition, I have not read anything about the 3 kts limitation you mention. It is not in the Amel manuals I have. But, I will ask the factory next chance I get.

Again, anything can break... I like thrusters and I will spec them on all my future boats.

My experience has been with the microswitches at top and bottom. Leakage is when the switches shut off retraction before the thruster is up against the seals. Talk to Bill Rouse. End of the world? No. Frustrating and time-consuming? Yes. The speed limit is in the boat manual. By the way, Amel produces the best boat manuals I have ever seen.