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Old 09 November 2009, 17:34   #1
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Sib's Bow Shapes

Hello,

There seems to be a certain issue about sib's bow shape, some sibbers states that point bow like Zodiac old sibs, is better to modern square and round bows, that cuts air better and has more final sib speed, that I know sibs are not tested in wind tunnels as airplanes, buildings, cars, etc. A well correctly inflated standard or deep V keel is what cuts water and has nothing to do with bow shape, anyway if this statement is so, what are your thoughts, ideas, comments regarding this issue.

Happy Sibbing
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Old 10 November 2009, 05:07   #2
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If the bow isn't i nthe water it's going to make s*d all diference to the water based drag, as for the air drag, to put it in perspective a small car will only get significant aero drag above about 40-45 MPH (call it 70-ish KPH, 40 Knots) Not sure about you, but if I was in a SIB at 40 knots I might be more concerned about staying upright than worrying about a bit of drag.

Also you have a big hole behind the toob which will crate the drag, and same again at the transom, and then the drag from the bodies of the helm & crew, so I would guess at the sort of speeds your average SIb does, probably not a lot in it.

I think I read somewhere that it's easier to manufacture a "square" bow , and it does give you a bit more room inside!
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Old 10 November 2009, 06:01   #3
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Form an aesthetic point of view I prefer a pointed bow. Zodiac's Cherokee square-nosed RIB for example is just plug ugly.
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Old 10 November 2009, 06:57   #4
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I prefer the Square nose SIBS. I cant see it impacts speed or performance much at all - as has been said drag/ speed is not a direct relationship - so unless you go really quite fast it will be minimal compared to the drag in the water.

Square - you can run bow up to boats etc with more stability, and get the better storage space. In mine it makes it easier to step on the tube over the bow onto beaches etc .

I 'think' there would be less force on any joins in a square bow - smaller angles to glue/ join ?

When you get to bigger boats ( RIBS) I think the square bow looks worse that on SIBS. But as you can see I have small square nosed RIB & a big pointy RIB - so it cant be that important !

Just my thoughts

Pete
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Old 10 November 2009, 11:20   #5
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Aesthetically, I like the narrow to pointed bows. The squared off bows look clunky to me. I'm sure the storage space is better up front with a squared bow though.

I don't think bow shape would make much difference as far as drag goes. The hull interaction with the water would be the major factor in drag.
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Old 10 November 2009, 17:14   #6
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Quote:
Originally Posted by Blackroady View Post
I prefer the Square nose SIBS. I cant see it impacts speed or performance much at all - as has been said drag/ speed is not a direct relationship - so unless you go really quite fast it will be minimal compared to the drag in the water.

Square - you can run bow up to boats etc with more stability, and get the better storage space. In mine it makes it easier to step on the tube over the bow onto beaches etc .

I 'think' there would be less force on any joins in a square bow - smaller angles to glue/ join ?

When you get to bigger boats ( RIBS) I think the square bow looks worse that on SIBS. But as you can see I have small square nosed RIB & a big pointy RIB - so it cant be that important !

Just my thoughts

Pete
You've made some good points there Pete. If the SIB was to be used as a tender the square bow would be a good bonus too in many ways (getting on/off, more storage room up front etc.) .
I've never seen a RIB with a square bow that looks right though.
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Old 10 November 2009, 17:30   #7
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Having had both .. square SIBs and RIBs and rounded too, the square bow isnt a problem on the rib .. in fact I quite liked it .. stuffing was much harder to do, and when it happened, we slowed up quick and fanned an impressive spray in front of us.. instead of over us.. because of the lift .. on the SIB the square nose is a PITA .. once you start making progress with a couple in the boat.. hit a wave and it just lops over you all .. soaking you.. and particularly if its the tender for your boat.. you gonna be wet for ages

Good thread BTW .. cos I didnt realise just how much this pissed me off till someone asked
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Old 11 November 2009, 06:45   #8
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Originally Posted by Bigmuz7 View Post
Having had both .. square SIBs and RIBs and rounded too, the square bow isnt a problem on the rib .. in fact I quite liked it .. stuffing was much harder to do, and when it happened, we slowed up quick and fanned an impressive spray in front of us.. instead of over us.. because of the lift .. on the SIB the square nose is a PITA .. once you start making progress with a couple in the boat.. hit a wave and it just lops over you all .. soaking you.. and particularly if its the tender for your boat.. you gonna be wet for ages

Good thread BTW .. cos I didnt realise just how much this pissed me off till someone asked
Good point on stuffing - if I 'hit' a big wave in the SIB it can come right over the square bow. Mind you I'm only doing 4knts max ! If it was pointy it may 'split the wave' better ?

I think quite minor points - I prefer the pointy nose on the big rib as its easier to see either side - less of a blind spot , but the SIB & small RIB it gives me more practicality at the slower speed . But the square bow on the small RIB does throw more water forward as
BIgmuz said.

I quite like the look of square bows on SIBs and small RIBS !
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Old 11 November 2009, 08:20   #9
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Does any of you sibbers, have any preference for round as opossed to point and square bows. This last one has a horrible look as does Zodiac's extremely pointed bow. Just a personal taste and color issue.

Happy Sibbing
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