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Old 17 November 2012, 08:37   #1
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Power vrs Rigidity

Just a boating experience that wanted to share with Ribnet inflatable lovers...

Scenario : Lima’s South American Spear Fishing Game Contest
Field location : 12 Km ride from mainland
Water conditions : flat crystal no wind, slight foggy morning
Outiside temp : 20C, water temp 16C
Participants : 15 Zodiac F470 sibs, 01 Sear Rider 420 rib

Main Engines :
Yam 2 Strokes 30, 40, Etec 30, 40 HP, 90 Octane Unleaded E8
Tohatsu 2 strokes 18 HP, 97 Octane Unleaded E8

Engine & crew distribution :
F470 : 30 HP crew of 3 & fishing gear
F470 : 40 HP crew of 4 & fishing gear
SR420 : 18 HP single driver, empty deck & cold beer cooler.

All participants had dived for 2 previos days the contest field to spot the best place and fish, so the dilema was who got there first and secure & dived the best spot as you could not have any other fishing competitor closer to 60 meters. Who won ? Zodiac 470 with Etec 40 ? Wrong. Sea Rider 420, Tohatsu 18

How could that be : Having already reached the engine transom sweet height spot years ago, placed an extra " shim for water flow to pass in between upper and lower AC plate to have minimum tail drag as the race was a perfect straight flat course. All boaters went full wot from second one, as power HP rules, the 470-40 HP sibs lead the lead followed by 30 & 18 horses, after completion of just 1/3 course pointer boaters were already losing track and final speed along the way due to tech matters.

To my complete astonishment and fully excitement ended first followed by 50 meters difference by a 470 with Etec 40 who was riding on top my near flat perfect wake. Sorry folks, no French Champagne for the winner, jus t my plain boating satisfaction and racers total disbelief...

Tech explanation : All 470 had been inflated in the morningr and were not air topped once rsting in water after some minutes for air preesure to stabilize, so all 15 had under inflated main tubes, lower speed tubes, air floor & keel, fishing gear was badly deck distributed and above all, all 470 with engine transom water splash issues and excessive rear wake due to underinflation issues. At 1/2 race though my Tohatsu 2006 engine was going to explode or loosen cylinder head bolts while hearing sweet 5.6 K rpm’ delivering 41.5 Km/H at top 3.5 psi well inflated tubes and perfectly ballanced & trimmed rib.

Conclusions : This story confirms that it’s not a power matter, it’s lack of rigidity matter, if in pursuit of achieving best top speed and cruising perfection it’s a must have :

1-Air top inflated sib as factory recommended
2-Well deck ballanced sib
3-Engine properly trimmed
4-Correct engine height on transom

Happy Boating
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Old 17 November 2012, 13:11   #2
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good info and just shows how much more efficient a rib is than a sib .
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Old 17 November 2012, 13:51   #3
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Quote:
Originally Posted by Locozodiac View Post
Conclusions : This story confirms that its not a power matter, its lack of rigidity matter,
Any woman could have told you than!
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Old 19 November 2012, 00:40   #4
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Interesting. It would have been great if one of the F470s had the proper inflation pressure to compare against the under inflated F470s. With the substantial load in the F470 with the ETEC (4 crew and a 240 lb outboard) proper air pressure in the F470 becomes that much more critical.
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Old 19 November 2012, 15:02   #5
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This example shows that even for local navy men and most civilian inflatable lovers with very few exceptions the use of a pressure gauge monitoring for air topping once sib is resting on water is totally irrelevant, even going medium loaded with a 40 HP engine racing against a 18 HP rib...

Happy Boating
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Old 20 November 2012, 01:30   #6
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Apples to oranges comparison

I have no doubt that a RIB of a given length and weight will be more energy dfficient than a SIB of the same length and weight. Nonetheless you are comparing a smaller RIB with a minimal load to a larger SIB carrying 3-4 x the load.

Great pictures, by the way!
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Old 20 November 2012, 17:56   #7
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Definitely a rib performance compared to a sib of same size is more hull efficient. Just thought that a larger sib medium loaded with a 40 HP would beat a lightly loaded less size rib with 18 HP. As it's more than twice the HP, but underinflation issues proved the contrary.

Practice has taught that best is to let sib rest on water for some minutes to give time for air pressure to settle down and then top to at least 3.0 psi all chambers for nice sib/engine performance.

Happy Boating
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Old 21 November 2012, 02:28   #8
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Practice has taught that best is to let sib rest on water for some minutes to give time for air pressure to settle down and then top to at least 3.0 psi all chambers for nice sib/engine performance.

Happy Boating
Indeed. The immersion in water will have a big impact on tube pressure - especially if it is a hot day.
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