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30-03-2005, 09:20 AM
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#1
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On a roll
Country: England
Location: Plymouth
Occupation: Anything in metal
Interests: Bristol Rovers, Cider & Boats
Boat name: Aqua Thunder, Badboy
Boat make: Bernico F2, Phantom 21
Engines: Merc 280efi, Merc 260efi
Cruising area: Worldwide
Join Date: Mar 2004
Location: Plymouth
Posts: 2,249
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Trim Tab positions?
Just been looking on the bennett site and it shows the fitting of the tabs running in line with the V, going across the strakes, yet most of the pictures that I see, the tabs are positioned horizontally. In peoples opinion which is most benificial or does it not really make to much difference?
Cheers
Dan
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All hail to Jail Ale
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30-03-2005, 09:34 AM
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#2
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Registered User
Country: England
Location: South West
Occupation: Development engineer
Interests: Fast boats
Boat name: Xtreme
Boat make: Bernico 21
Engines: Mercury F1, 300 Drag, XR2 "Fingerported"
Cruising area: South West
Join Date: Mar 2004
Location: South West
Posts: 1,043
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Dan I was going to post a similar question very soon as I need to fit a set on Badboy.
Most of the tabs that I have seen have been fitted hozizontaly
but I don't know for sure which way is more efficient.
Some of the bigger Bernico that I have seen have them angled.
Cyco
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30-03-2005, 09:42 AM
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#3
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Registered User
Country: Scotland
Location: Kirkcudbright
Interests: Boats n Lambrettas
Boat make: Boatless
Join Date: Mar 2004
Location: Kirkcudbright
Posts: 978
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Don't know for sure, but I would have thought horizontal, so that when you operate them they push down and not out, minimizing any steering effect .
Although when you operate them together they cancel each other out!!!!!!!! but hey what do I know.
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30-03-2005, 10:04 AM
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#4
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Registered User
Join Date: Mar 2004
Posts: 6,891
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I'm sure everyone will have a different opinion on this one.
Personally, I would mount the tab in line with the hull bottom, it angled as per the deadrise.
When the tab is down you are getting the greatest wetted area on the tab. Mounting the tab horizontally, I would guess, will reduce the efficiency of the tab since the outer edge will effectively be 3 or 4 inches higher (depending on the deadrise) and not effective operation at small deflections of the tab, so you end up using more tab which will be less efficient with a greater angle of attack.
I would also always go for the longest possible tab, a) to reduce the amount of deflection needed to create a given force and b) so that in a neutral or below position it is increasing the effective length of the boat, which I reckon is a good thing in the rough.
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30-03-2005, 10:15 AM
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#5
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Registered User
Join Date: Mar 2004
Posts: 6,891
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And, should it be mounted so the leading edge is in line with the bottom, or raised slightly? I am wondering if having it in line with the bottom means that at slight negative deflection (ie raised) it could actually create bow lift (like the arneson rocker plates). But on the downside, it'll always be 'wet' which could add drag, whereas raising it an inch or so means the tab when fully raised will be completely clear and not adding any drag?
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30-03-2005, 10:18 AM
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#6
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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I'd go with Matt on this. Otherwise you are only using the outside corner of the tab which seems a bit daft have a look at the tabs on offshore only under the classified section, look at the transom pics here you can see they are all pretty much as matt states.
here is the link
http://www.offshoreonly.com/esvon/ca...0caa693985ebdd
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