BOWTHRUSTERS: NOISE AND DRAG - the cons?

ianj99

ianj99

Well-Known Member
Joined
11 Nov 2009
Messages
2,097
Location
UK
Visit site
I am having a Sidepower SE80 bow thruster fitted in the next couple of months but ask those who have had a thruster fitted, whether there are any significant downsides.

Such as noise and drag (apart from the noise when in use). I'm hoping the benefits to manoeuvrability of a long keeled 10tonne steel ketch will be worth it.

Ian
 
Bump, seeing as nobody else responded!

Tbh I don't really know, except that having two huge holes under the waterline is definitely one for the 'cons' list :)
 
Mavanier said:
Bump, seeing as nobody else responded!

Tbh I don't really know, except that having two huge holes under the waterline is definitely one for the 'cons' list :)
Click to expand...

I suppose unless you've had one retro fitted you won't be aware of the before vs after change in noise or drag.
Ian
 
I had one on Pegasus. I will never be without one again.

You will wonder how come you lived with the particularities of a long keeler for so long without a BT.

Enjoy!! Noise only happens when you use it... and with a long keeler... you won't notice the speed diff.
 
Agree with Monique totally. There was a big, and at times very heated discussion (now that's unusuall [/irony]) on here a while ago re bowthrusters in general. The purists say that you should be able to do without one if you're a 'good' sailor, but when you're in a tight marina space with a cross wind and tide running against you they are just fabulous. The 'good' sailors used to say that an engine was unnatural and that you should be able to sail onto any mooring etc. etc. and whilst they are of course correct in one sense at the end of the day it's your boat and you know best how she handles.

Look at the bowthruster as another piece of safety equipment, like the engine. If you don't need it then great but if you do, well.....

As far as noise and performance go I have noticed no difference at all, but mine was installed professionally and faired well etc.

Good luck

Chas
 
Aside from the noise when you operate the thruster, there will be some flow noise as the water passes over the tunnel, but I doubt you'll hear it over the flow noise caused by the bow wave. To minimise the drag the tunnel should have a lip moulded on the forward side and a scallop taken out of the trailing side. The lip trips the flow and causes an eddy, the scallop helps the flow reattach to the hull.
77268d1356453697-new-way-fitting-bow-thruster-thruster-insert-.jpg
 
chasroberts said:
Agree with Monique totally. There was a big, and at times very heated discussion (now that's unusuall [/irony]) on here a while ago re bowthrusters in general. The purists say that you should be able to do without one if you're a 'good' sailor, but when you're in a tight marina space with a cross wind and tide running against you they are just fabulous. The 'good' sailors used to say that an engine was unnatural and that you should be able to sail onto any mooring etc. etc. and whilst they are of course correct in one sense at the end of the day it's your boat and you know best how she handles.

Look at the bowthruster as another piece of safety equipment, like the engine. If you don't need it then great but if you do, well.....

As far as noise and performance go I have noticed no difference at all, but mine was installed professionally and faired well etc.

Good luck

Chas
Click to expand...

Thanks for the replies which were what I hoped for.
The hull being steel, means the fairing in will have to be external using Watertite but it should be possible to achieve a profile shown in the Sidepower installation guide - basically a deflector on the leading edge, without too much protrusion of the steel tunnel. (I'm thinking about 1cm on the leading edge and a few mm - weld thickness on the trailing half.)
Ian
 
I'm afraid I have nothing to offer re noise and drag, but we have a long-keel steel ketch too and I can't imagine the benefits of having it might be outweighed by the cons. At 17tonnes+ and 13m. I was absolutely crapping myself regarding manoeuvring in close quarters, but - honestly - the bow-thruster makes it easy and I thank the gods for the invention.
 
I think thrusters are brilliant with one con -when you really, really need it such as when the wind is howling then it won't be up to the task as it won't move you against a really strong breeze, but otherwise ....
 
ianj99 said:
I am having a Sidepower SE80 bow thruster fitted in the next couple of months but ask those who have had a thruster fitted, whether there are any significant downsides.

Such as noise and drag (apart from the noise when in use). I'm hoping the benefits to manoeuvrability of a long keeled 10tonne steel ketch will be worth it.

Ian
Click to expand...

Hi Ian

Without boring you about flow dynamics I trust you know there is a right and wrong way to fit a bow thruster to reduce drag.

The out lip to the thruster tunnel should have a raised edge as shown below, with the raised edge the water flow will deflect away from the tunnel itself and reduce drag.

If the outer lip is flat water flow will go into your tunnel and increase drag.

Mike

Flat edge will 'increase' drag
View attachment 41826
Raised leading edge will 'reduce' drag
View attachment 41827
 
Caer Urfa said:
Hi Ian

Without boring you about flow dynamics I trust you know there is a right and wrong way to fit a bow thruster to reduce drag.

The out lip to the thruster tunnel should have a raised edge as shown below, with the raised edge the water flow will deflect away from the tunnel itself and reduce drag.

If the outer lip is flat water flow will go into your tunnel and increase drag.

Mike

Flat edge will 'increase' drag
View attachment 41826
Raised leading edge will 'reduce' drag
View attachment 41827
Click to expand...

Yes Mike, thanks. The Sidepower blurb has diagrams for the uninitiated so hope to end up with something like your photo.
Ian
 
sailorman said:
You forgot to say that one forgets how to handle one`s boat prior to that strong wind
Click to expand...


Not really. I plan to use the BT sparingly but with 10-12tonnes, quite pronounced prop walk astern and a long keel, I won't feel guilty about using it even in calm conditions. The old girl does not like to be rushed and does not stop quickly or neatly if you try so the BT will get used in a marina.
Ian
 
Scotty_Tradewind said:
When retro fitting, try and fit the tunnel deeper below the waterline rather than shallower.

Mine is a fraction deeper than some I've seen and thrusts well without a lot of surface water disturbance.
Click to expand...

Thanks. The restriction is being able to get in to weld the tunnel on its underside but it should be possible to get the top about a foot below the waterline. (Its the yard's job to fit it, I'm just doing the fairing, epoxying and wiring - my welding skills are negligible)
Ian
 
Scotty_Tradewind said:
When retro fitting, try and fit the tunnel deeper below the waterline rather than shallower.

Mine is a fraction deeper than some I've seen and thrusts well without a lot of surface water disturbance.
Click to expand...

I would also agree with this recommendation. Mine is a tad shallow due to hull curve restrictions. Place it as deep as you can get it. You will ask yourself upon first use why you did so long without it. Esp if you moor Med style, stern to..
 
You must log in or register to reply here.

Share this page

Top