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Author Topic: Another question......  (Read 1923 times)

Bryan Young

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Another question......
« on: February 03, 2012, 04:37:13 PM »

Just another question.
Why do some vessels...particularly tugs and trawlers have a much deeper draught aft than for'd? That is, why is it thought necessary to have a keel that is nowhere close to being parallel to the waterline. Depth in the water of the prop? Possibly. But that's only a proposition. BY.
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Notes from a simple seaman

Xtian29

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Re: Another question......
« Reply #1 on: February 03, 2012, 04:57:06 PM »

Hello

Depth in the water of the prop is the main reason, there is another the position of the turning point aft as possible (for tug)  but for this one, it still possible to do it with parallel keel/waterline.

Xtian (When I was student as Naval Architect I made my end of year work project on a tug/supply  :D)   
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Bryan Young

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Re: Another question......
« Reply #2 on: February 03, 2012, 06:06:46 PM »

Thanks Xtian...I thought that the depth of the prop was the minor consideration....should have thought about the turning point myself, ....but I didn't. Thanks. BY.
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Notes from a simple seaman

Xtian29

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Re: Another question......
« Reply #3 on: February 03, 2012, 11:01:50 PM »

Not, it's major consideration as air melting with water is very very bad for bollard pull : the main purpose of tug.

 From zero to 10 meters depth the water pressure double !  Then, this zone is the most important for propeller, the deeper side of propeller is working better than the higher one and it's why it's a turning effect on ships when going astern in one time.

Xtian   
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irishcarguy

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Re: Another question......
« Reply #4 on: February 04, 2012, 08:02:25 AM »

If we pay attention, we learn something new every day on this forum, thank you Xtian & Brian, Mick B.
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Mick B.

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Re: Another question......
« Reply #5 on: February 04, 2012, 03:05:06 PM »

Hi Guys

That was very interesting. How can that be applied to modelling a powerful tug?

I've long wondered how you you get the best out of a tug anyway.

Dave
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Xtian29

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Re: Another question......
« Reply #6 on: February 04, 2012, 03:35:19 PM »

Hello

This thing is well applied to model boat, specialy the ones with propeller larger than 6-8 cm. 

If there is air suction with the propeller you will see soon that your bollard pull will decrease.

Then the turning effect is a thing that every modeller, specialy the ones with large one screw tug must know as there is a better side to dock the boat .  You come to the pier at slow speed with a small angle and when you go astern for a short time the aft part of your boat is going transversaly.  If you well know your boat and this turning effect you will do a perfect manoeuvrer   8)  Then if not and if you want to dock on the wrong side of the boat (depending the turning or your propeller right or left) then you will ruin your manoeuvrer  <:(

Xtian
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Netleyned

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Re: Another question......
« Reply #7 on: February 04, 2012, 03:50:28 PM »