In the good old days the only way to come alongside a pontoon successfully was to plan your approach carefully, and use a lot of careful steering and throttling back and forth. Only then could you be sure of a smooth and impact free arrival.
Whilst this works just fine for vessels under 40’, and indeed any skipper worth his salt should be able to make such a manoeuvre more or less with his eyes closed, for larger vessels it can be a more nerve racking experience, especially if you’re not out on the water as often as you’d like.
Bow and stern thrusters were developed with exactly this scenario in mind, and whilst some would debate how necessary they are, there’s no denying they can be a powerful feature to assist with otherwise tricky maneuvers. After all if something is available that genuinely makes life easier, then why not take advantage of it? I’ll bet that even the most experienced of mariners won’t opt out of using thrusters if they’re available, and neither should you!
What Are Bow Thrusters?
If you haven’t seen a boat with bow and stern thrusters before, they’re basically mounted in the hull, at either end, perpendicular to the main propellers to enable full side to side thrust, greatly reducing the skill needed to come alongside a pontoon, jetty or other vessel.
Thrusters can either be electrically or hydraulically powered, and there are advantages and disadvantages to both which I’ll cover below.
When Are Bow Thrusters Needed?
As a concept bow and stern thrusters are met with a bit of derision from many in the boating community who view using them as ‘cheating’ and not becoming of proper mariners. Their argument is further compounded by the fact that people without basic boat handling skills have been known to rely on them, sometimes with destructive consequences!
However, assuming you have said basic boat handling skills, there’s no reason not to exploit the use of thrusters. If you want to take the stress out of docking, and more importantly make it a quicker and more efficient process, thrusters are a major bonus.
Docking in tight spaces where there’s a real risk of colliding with other (let’s face it, expensive) vessels is ideal thruster territory. In particular, if you’ve got limited space for turning your boat, a thruster will effectively allow you to ‘turn on a dime’, and ‘slot’ into narrow gaps that would otherwise require a lot of skillful throttle and steering work to get into using conventional maneuvers.
The larger the vessel you’re commanding the more evident the benefit will be because no forward motion is required to move sideways. Sailing vessels with long keels that require a large turning circle can be especially problematic in crowded marinas, so thrusters are always a welcome addition for these.
Bow and Stern Thrusters
Depending on how much additional control you want over your vessel you may choose to fit thrusters at both the bow and stern of your boat, or simply at the bow. Clearly with a single thruster you won’t have the ability to move in a completely sideways motion as the boat will still ‘pivot’ about the stern, so for maximum flexibility both thrusters are needed.
What Sort of Boats Are Bow Thrusters Suitable For?
Any boat of a medium size or larger can conceivably be fitted with a thruster. Larger boats are likely to be easier to fit thrusters to because they have more internal room to play with, and less chance that the real estate required by the thrusters is taken up by something else such as a water tank, but at the same time there’s nothing to say 30’ keelboat can’t be fitted with a thruster as long as it doesn’t adversely affect the performance of the craft.
Whilst newer boats are increasingly either fitted with thrusters as standard, it’s also becoming more and more common for older boats to be retrofitted with thrusters, so don’t think it’s not an option to you just because you own a 40 year old classic.
What Types of Bow Thruster Are There?
If you like the idea of retrofitting a pair of thrusters to your boat but you’ve got reservations about taking an enormous hole saw to your pride and joy, fear not for this isn’t strictly necessary. Several types of thruster exist, including those fitted external to the hull.
Externally Mounted Thrusters
Externally mounted thrusters such as the ‘Yacht Thruster’ offered by The Yacht Group, have the great advantage of being easy to install, and not requiring any significant butchering of the hull to fit.
The downside of externally mounted thrusters is that they look like an afterthought, as well of course that they add drag, and can reduce your boat’s performance and cruising speed by half a knot or more quite easily.
Through Hull Mounted Thrusters
By far the most popular type of thrusters are what I would describe as ‘through-hull’ thrusters. As the name suggests these are mounted in the hull of the boat, typically within a GRP ‘tunnel’ that is glassed into the hull, with the thruster motor/electronics or hydraulic connections inside the boat.
This type of thruster creates slightly less drag than an externally mounted thruster, but is obviously more time consuming and challenging to fit.
Retracting Thrusters
The slickest of the bunch, retracting thrusters use an actuator to deploy the thruster from the underside of the hull when required, remaining hidden at all other times.
Not only does this type of thruster look the business, it is also the best choice from a hydro dynamic perspective too – there are no permanently protruding parts, holes in the hull, and a curved plate that matches the hull form can be fitted to the bottom of the thruster housing such that the retracted thruster sits seamlessly within the hull form.
You’ll find that retractable thrusters are in general larger and more powerful than the other types and are the thruster of choice with boats over 70 foot.
Should I fit Hydraulic or Electric Bow and Stern Thrusters?
Besides the basic form and location of your thruster the other major consideration is what method of power you choose. I don’t know of any combustion engine driven thruster systems (but that’s not to say they don’t exist), but commercially you’ll find there are two options available: electrical or hydraulic power.
Hydraulic systems are idea for larger vessels that already have a hydraulic system to power other items that can be ‘tapped into’ because there are fewer components to install, and the cost is reduced. This is probably the best option for not adding much additional weight to he vessel either, given that the hydraulic power pack is the heaviest part of the system.
Hydraulic thrusters are also quieter, and can be run for longer without depleting battery energy reserves, or overheating.
Electrical thrusters are typically available in 12 volt and 24 volt systems. 24 volts is the option to go for if you can (ie if your boat is already running off a 24 volt system) because smaller cable can be used to wire in the thruster, and there is less resistance, meaning less chance of the thruster motors overheating.
Despite these advantages 12 volt systems remain more popular on smaller retrofitted vessels for the simple fact that these boats are more typically fitted with a 12 volt system. Fitting a 24 volt thruster system to a boat that is otherwise running 12 volts requires a separate dedicated 24 volt system. Again this adds complication, and weight.
What is Involved in Retrofitting a Bow Thruster
Aside from any changes to your boat’s primary electrical or hydraulic infrastructure, installing the thrusters themselves isn’t too demanding, provided you select thrusters that will physically fit your vessel, although some specialist expertise is necessary, particular when it comes to glassing in the tube.
Before you do anything (or pay anyone to do anything) you first need to decide where you will locate the thrusters. In an ideal world they would be located a the very extremes of the hull to maximise the turning moment afforded by having them.
In reality there are practical reasons why you can’t get too close to the tip of the bow in particular, chief of which being that a certain amount of width is needed to accomodate the thruster tunnel. Now, although this can be trimmed to fit the width of your hull, it’s a good idea to have a tube of a decent length to achieve a more powerful through flow jet of water. Typically you’ll find most vessels have their thrusters inset between 4 and 8 foot (120cm – 240cm) from the bow and transom. As far as height goes you’ll want your thrusters to be a minimum of 5” (12cm) from the vessel waterline.
As I touched on above, I wouldn’t attempt to do any laminating work yourself if you’re not experienced with it, particularly when fitting a high value critical component such as a thruster. The difficulty is compounded by the fact that thrusters perform better when a ‘leading edge’ is added the thruster tunnel where it meets the outside of the hull. Achieving a fair result when doing this is a skilled task. There are of course many experienced boatyards who can help with this critical step.
Yacht thrusters are perhaps a different story given that they can be fitted without the need for any laminating work, so you can attempt the job yourself if you feel confident to do so.
Be prepared for extensive rework of your boat’s interior, particularly on a smaller vessel. You’ll need to be able to route cabling and move anything from the space that will ultimately be occupied by the motor. Make sure you’ve got a plan in place for where things will be moved to before you start hacking the hull apart!
How Powerful Does My Thruster Need to Be?
The usual method for determining suitable bow and stern thrusters involves calculating the required torque to turn the boat whilst counteracting typical side wind. Thrusters are not typically designed to counteract gale force winds (Beaufort 8 or above), however they should still be able to provide at least a degree of assistance in higher winds.
I won’t go into detail with regard to the actual calculations involved, the important figures for typical size vessels are as follows:
| Vessel Length Range in Feet | Thruster Force Required (pounds force [lbf]) | Thruster Force Required (kg force [kgf]) |
| 18-28 | 55 | 23 |
| 21-32 | 77 | 35 |
| 28-41 | 121 | 55 |
| 29-42 | 132 | 60 |
| 34-49 | 165 | 75 |
| 39-55 | 210 | 95 |
| 45-66 | 275 | 125 |
| 54-72 | 352 | 160 |
| 63-85 | 485 | 220 |
| 65-87 | 507 | 230 |
| 72-92 | 628 | 284 |
| 72-95 | 665 | 302 |
| 88-112 | 905 | 410 |
| 108-141 | 1215 | 551 |
How Much Does a Thruster Installation Cost?
Installing a thruster is a fairly costly undertaking. Using Vetus’ hugely popular range of thrusters as an example, you’re talking a minimum of $1500 dollars for the smallest unit, while larger thrusters can be many thousands of dollars.
Just as significant as the cost of buying a thruster is the installation cost, whether in your time, or your money in exchange for someone else’s. Once you factor in the time required for measuring and marking out, cutting, laminating, electrical work and any rework to the boat interior layout, you’re easily looking at a good week’s worth of labour time.
To that end a $4000 to $5000 installation cost is a reasonable estimate, possibly more depending on the level of complication involved with the interior work.
How are Bow Thrusters Operated?
Thruster kits typically come supplied with a joystick(s) for controlling thrusters from the helm. These are generally pretty simple and intuitive, especially when you’ve got other people on board to put eyes on areas you can’t get to.
The other far more flexible option is to use a wireless remote control that enables you to be up on deck operating the thrusters and keeping an eye on your progress in person. As you might imagine, this method of control really comes into its own when you’re sailing or yachting solo when you haven’t got a crew to rely on, but you do have the full breadth of technology to assist you.
Does Fitting a Bow Thruster Add Value to a Boat?
Just as alloy wheels or a built in satnav are ‘nice to haves’ that people will gladly pay a premium for on a car, the same is true of bow and stern thrusters on a boat.
Should the day arrive when you decide to sell your current boat you should certainly factor in the cost of getting the thruster installed and reflect that in your sale price, and you should certainly sing its praises in your advert.
Bear in mind however that whilst some people fully appreciate the value of having a thruster on a smaller vessel, some will see it as an unnecessary feature that they won’t want to pay for given that smaller boats might be perceived as more deliberately simple. The bigger the boat the more welcome it will be as a feature to the market in general.
