Bow thrusters

[mad_boater]

I had a bow thruster fitted in the winter it is a Sidepower 80, since using the boat this year I have not been able to get more than 24 knts top speed.Last year she would pull 28knts and seems to be using more fuel.This is the only thing that has been done to it apart from having the hull professionally blasted and antifould since last year.I now have a clean hull ect after a preasure wash so that can't be the problem.I just hope it hasn't been fitted too low thus not clearing the water when at high speeds.Unfortunatly having no dinghy I can't check this out.Any one had the same problem?

 

[Ripster]

I know very little about exactly where they should be fitted except that the postion is important for both BT performance and hull performance. Also, I understand that the shape of the tunnel profile as it meets the hull has be right too. To know if it is causing drag when you are planing, perhaps someone could go out with you and run along side with a video cam and zoom in to see what is going on. That and comparing notes and measurements with other 360 owners who have got a BT fitted.

Have you spoken to the fitter?

 

[mad_boater]

I know very little about exactly where they should be fitted except that the postion is important for both BT performance and hull performance. Also, I understand that the shape of the tunnel profile as it meets the hull has be right too. To know if it is causing drag when you are planing, perhaps someone could go out with you and run along side with a video cam and zoom in to see what is going on. That and comparing notes and measurements with other 360 owners who have got a BT fitted.

Have you spoken to the fitter?

I think that could answer my questions.That will be my next step.
Thanks

 

[pappaecho]

I had a bow thruster fitted over the winter. The guy who installed it faired the exits into a teardrop formations to prevent, counter currents entering into the pipe, and causing currents which slow the boat down.
Have you got teardrops on yours?
My fitter was very careful that the top of the pipe was about 4 inches below the waterline when the boat was at rest... we actually measured its twin ( in the water at the time) to ensure that we had got it right

 

[Deleted User YDKXO]

Who fitted the thruster? Was it a recognised bowthruster specialist (eg Osmotech?)? AFAIK, the top of the thruster tunnel should be at least 1/2 the tunnel dia below the waterline and preferably 3/4 to 1 x dia below the waterline for optimum performance. The edges of the tunnel should be radiused and the hull faired so as not to allow the back face of the tunnel to present and obstruction to water flow.
I must say though that even if whoever has fitted your thruster has ignored all this, I'd be surprised if this could result in a 4kt difference to your speed but I'm happy to be corrected if somebody knows better. Have you got any pics?

 

[MapisM]

I'd be surprised if this could result in a 4kt difference to your speed

Seconded.
It doesn't take a genius to understand that a transversal hole in a hull is not going to improve speed or fuel burn at any speed, but they should have made a real mess in the installation, to make the boat loose 4 kts at WOT for the B/T alone.

 

[mad_boater]

Who fitted the thruster? Was it a recognised bowthruster specialist (eg Osmotech?)? AFAIK, the top of the thruster tunnel should be at least 1/2 the tunnel dia below the waterline and preferably 3/4 to 1 x dia below the waterline for optimum performance. The edges of the tunnel should be radiused and the hull faired so as not to allow the back face of the tunnel to present and obstruction to water flow.
I must say though that even if whoever has fitted your thruster has ignored all this, I'd be surprised if this could result in a 4kt difference to your speed but I'm happy to be corrected if somebody knows better. Have you got any pics?

I have no pics of it going as I have no one to take them.I will have to buy a dinghy.
I just can't understand why we are not achieving last years top speed.This is the only thing I have had done apart from having the bottom blasted and antifouled.Very strange.

 

[Ripster]

I have no pics of it going as I have no one to take them.I will have to buy a dinghy.
I just can't understand why we are not achieving last years top speed.This is the only thing I have had done apart from having the bottom blasted and antifouled.Very strange.

Just have a quick look at the main props (if you have not already done so) to make sure nothing else is dragging you back. Otherwise, let the investigations begin...! Keep us informed.

 

[Deleted User YDKXO]

I have no pics of it going as I have no one to take them.I will have to buy a dinghy.
I just can't understand why we are not achieving last years top speed.This is the only thing I have had done apart from having the bottom blasted and antifouled.Very strange.

When you say you are not achieving last year's top speed, what exactly does that mean? Are you down on max engine rpm as well as speed or are you just down on speed but the engines are reaching their normal max rpm? If the former you might suspect another cause like a fuel issue or turbo issue or damaged prop (although you'd likely feel a vibration if it were that). If the latter, then it might just be the b/t tunnel but I'd be v surprised.
IMHO, it would be a good idea to take a qualified mechanic out on a seatrial to check over the engines just to eliminate any mechanical problems before you start modifying the b/t tunnel

 

[MapisM]

Are you down on max engine rpm as well as speed or are you just down on speed but the engines are reaching their normal max rpm? ... If the latter, then it might just be the b/t tunnel but I'd be v surprised.

I'd rather be shocked than surprised. If the additional drag of the tunnel is high enough to steal 4kts (which I agree it's very unlikely), also the engines would be down on RPM.
Your assumption implies that the tunnel, rather than additional drag, creates additional turbulence in the water flowing under the hull, enough to negatively affect the props slip.
Not impossible, but almost.

 

[Deleted User YDKXO]

I'd rather be shocked than surprised. If the additional drag of the tunnel is high enough to steal 4kts (which I agree it's very unlikely), also the engines would be down on RPM.
Your assumption implies that the tunnel, rather than additional drag, creates additional turbulence in the water flowing under the hull, enough to negatively affect the props slip.
Not impossible, but almost.

Yes I agree that extra drag of any kind is likely to cause a reduction in engine rpm too but I'm clutching at straws for the OP here. I still think that the reduction in speed is far more likely to be a fuel or engine related problem, perhaps caused during the winter engine service or simply dirty fuel being drawn into the filters?

 

[MapisM]

Yep, possibly. I also would look elsewhere first, anyway.
As you say, based on the OP inputs, we're just clutching at straws.
It would be interesting to have his answer to your previous question.
And if he has electronically controlled engines, also the load numbers at WOT.

 

[mad_boater]

Yep, possibly. I also would look elsewhere first, anyway.
As you say, based on the OP inputs, we're just clutching at straws.
It would be interesting to have his answer to your previous question.
And if he has electronically controlled engines, also the load numbers at WOT.

The dirty fuel or partialy blocked filters had crossed my mind,allthough the engines Volvo kamd42 have been totally rebuilt at a cost of £20,000 by the previous owner they are circa 1996 so not exactly state of the art.They max at 3800 ish rpm which may be slightly down from last year but I can't be sure.A filter change might be the answer its worth a try before pursueing anything else.

 

[Cheekybrat]

I had a bow thruster fitted in the winter it is a Sidepower 80, since using the boat this year I have not been able to get more than 24 knts top speed.Last year she would pull 28knts and seems to be using more fuel.This is the only thing that has been done to it apart from having the hull professionally blasted and antifould since last year.I now have a clean hull ect after a preasure wash so that can't be the problem.I just hope it hasn't been fitted too low thus not clearing the water when at high speeds.Unfortunatly having no dinghy I can't check this out.Any one had the same problem?

Just a quick thought before going too deep into it. How do you measure your speed? if its a through the water "paddle" or similar it could just be that acting up with antifoul paint on it. Don't always look for the worst thing

Nick Heath

 

[aquatom]

Have any extra batterys been fitted and if so where. A lot of extra weight in the bow could cause an issue but it would have to be a lot of weight.

 

[mad_boater]

Have any extra batterys been fitted and if so where. A lot of extra weight in the bow could cause an issue but it would have to be a lot of weight.

There is no extra weight up front I purposely had the bt conected to the main batteries, not specificully for weight but so I would have plenty of rechargable power.Incidently I measure the the speed both with gps and paddle wheele that has been taken out and cleaned,also the speed is checked both ways (turning round) these things should iliminate any false readings.