Bow Thruster

[wesail]

Is there any effect in the boat when you install bow thruster, in term of handling, speed, or performance?

[daddle]

Other than destroying the laminar flow along the hull at the bow instead of somewhere aft and greatly increasing drag...no. Depends if a few moments of ease in docking is worth days and days with the extra drag.

Consider it's a poor design that even has thruhulls ahead of midships.

But it's cruising, so who cares....

[wesail]

i heard some saying, a knot decrease in speed

[motion30]

I think it depends on the type of boat on my 7 kt trawler I noticed no decrease in speed

[Dockhead]

Don't forget that bow thrusters come in different flavors with very different performance effects -- retractable bow thrusters have little effect.

We have a tunnel bow thruster on our boat, which is supposed to cost some performance. I can't tell you how much effect there is on speed because the boat was built with the tunnel in the first place, so nothing to compare it with. In fact, my type of boat was never produced without a bow thruster. She is very fast and no complaint about performance, making 50% to 60% of the wind speed from 10 to 18 knots of wind and capable of sailing several knots beyond hull speed on different points of sail (not just a run) in 20 to 30 knots of wind. There is no way she would gain a whole knot of speed without the tunnel (which means no way the tunnel costs a knot of speed).

The benefit cannot be characterised as "a few minutes of ease in docking". Maybe a more skillful helmsman could maneuver my boat in close quarters and strong cross-winds without a thruster, but I cannot. The thruster transforms the boat's handling in close quarters; I couldn't live without it.

Interesting side question: could the thruster tunnel be closed off for a long -- say, transatlantic -- passage? I wonder if anyone has tried this. Hmmm.

[svBeBe]

We have retractable bow thruster which has 10 hp motor and large prop blades. No drag underway. Love, love, love that thing!! Absolutely the best feature on our boat. Only you know if such a design can be fitted in your boat.

Judy
S/V BeBe
Amel SM2 #387

[bck73]

Hi I fitted an external bow thruster to a bavaria 34 see link below it has made NO difference to my performance or speed it was well worth it. It was very easy to fit just a few hours and you could have it back in the water then just do the wiring. MARINNO * bow thruster * stern thruster * EXTURN the external bow and stern thruster

[daddle]

Originally Posted by Dockhead

Interesting side question: could the thruster tunnel be closed off for a long -- say, transatlantic -- passage? I wonder if anyone has tried this. Hmmm.

Definitely. Foam plugs. Shave to fit flush. Retainer bungee. Try to remember 3 weeks later, as approaching the dock, that you need to take them out....

"Hmmm...thrusters sound funny today"

[Dockhead]

Originally Posted by bck73

Hi I fitted an external bow thruster to a bavaria 34 see link below it has made NO difference to my performance or speed it was well worth it. It was very easy to fit just a few hours and you could have it back in the water then just do the wiring. MARINNO * bow thruster * stern thruster * EXTURN the external bow and stern thruster

Looks like an interesting device; thanks for pointing it out. I thought it was particularly interesting how the device is used for a stern thruster on sailboats -- there isn't otherwise much way to implement a stern thruster on an average sized cruising boat.

If you are connected with the manufacturer or distributer, it would be appropriate for you to state that.

[bck73]

Hi there

No Im not connected with the manufacturer or distributer in anyway just a sailor having fun and wanted to make docking as easy as possible cause I normaly go sailing by myself. The bavaria has a high freeboard and is easly blowed off in wind when coming into a berth.


Rgds
S/V Artemis

[gr8trn]

There is no way the vessel with a tunnel such as mine and Dockhead's from the factory will not disturb, how did you say?, handling, speed, performance.

As far as handling: I use it occasionally to fine tune docking. Just guessing 20% of the time. I don't notice any handling issue when motoring is current...

As far as speed: I reach hull speed often, so who cares if I loose speed, the hull is at theoretical speed, what more is there?

As far as performance: I am not sure what realm of performance to comment on, but I really don't notice the big tunnel in the bow. Mind your thru hulls!

Greg

[CARL]

I wonder where some people get info from, "a knot of speed" "add days to your trip" utter rubbish, if correctly installed performance lost is so min i doubt you will notice it,what you will notice is how much more relaxed you will be in tight situations,be sure to put a more powerfull one than you think is ness,most prod boats that they are fitted too as standard struggle,against the wind when you will most prob need it,A tunnel will prob add strength to the bow, be carefull of through hull,had a freind who had his boat delivered by a crew ,they forgot to retract it after use when they eventually realised ,something had bent a little and they couldnt, for me ,on a old style boat that has a mind of its own in confined spaces especially astern its a great help.

[James S]

Originally Posted by CARL

I wonder where some people get info from, "a knot of speed" "add days to your trip" utter rubbish, if correctly installed performance lost is so min i doubt you will notice it,what you will notice is how much more relaxed you will be in tight situations,be sure to put a more powerfull one than you think is ness,most prod boats that they are fitted too as standard struggle,against the wind when you will most prob need it,A tunnel will prob add strength to the bow, be carefull of through hull,had a freind who had his boat delivered by a crew ,they forgot to retract it after use when they eventually realised ,something had bent a little and they couldnt, for me ,on a old style boat that has a mind of its own in confined spaces especially astern its a great help.

Yeah....I'm with Carl on this one...I often make my hull speed.
I installed a 10in dia one...in order to get the depth below WL and distance from the face of the blades to the skin that I needed (according to the instructions) mine ended up about a quarter of the way back from the bow....not sure if that makes any difference.

[rebel heart]

a tunnel bow thruster provides lateral thrust without affecting headway

- answer from one of my captain study cards

[Pieter Cats]

There is a system with little drag due to very small hull penetration. Called Jet-thruster. Comes with an electrical 12V centrifugal pump, flexibel high-pressure hoses whitch lead to 35 / 45mm openings in hull. Great alternative to the conventional tunnel thrusters. Holland Marine Parts shows details.