| Subject: |
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Re: Bowthruster |
| Name: |
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Guillermo Gefaell |
| Date Posted: |
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Jan 31, 05 - 7:29 AM |
| Email: |
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bmccommodore@banjer37.net |
| Website: |
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http://www.banjer37.net |
| Message: |
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Dear Frank:
Considering a lateral area of around 20 sqm for Banjers, and asuming a mean density of 1.2 kg/m3 for air and a Cs =1, the wind force for a 7 knots wind is already 300 kgf. Asuming the bowthurster turns the boat remaining fixed the stern, we can say it should cope with half of that, so 150 kgf.
Doing the same calculations and suppositions, we'd need around 300 kgf to cope with a mere 10 knots wind and 700 for 20 knots. Much higher than the available thrust for yatchs recommended bowthrusters.
So it seems these expensive pieces of equipment are really only good to manoeuvre in absence of wind when you have short hands aboard.
Maybe you should choose the 160 kgf one, just to have the posibility of coping with some wind, let's say around 5 knots. On the other hand, take in account that, when entering a narrow berth in a Marina, you'll be usually surrounded by other boats, and wind forces will be considerably dampened.
As I do not have a bowthruster aboard MARIE, I ask for the opinion of other fellow members on my theoretical statements.
Regards. G. |
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