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TOPIC: Drive fin, reverse testing

Drive fin, reverse testing 08 Jul 2012 01:48 #1

  • kjs
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When we got our boat 2 years ago it came with a Sting Ray fin installed and we used it this way. Steering was a bit rough as in 1996 they didn't install power steering but it was just a bit to much for the admiral but I could handle it. She never came up on plane as well as I had expected and trimming and keeping her on plane at lower speeds was always a bit tricky.
At the beginning of this season I had the boat at my mechanic to exchange the original 1996 oil filter and spark plugs and change the impeller (was the original 1996 too as we found out! Never trust a seller who says all services performed!). While he did all I asked him to do he also removed the Sting Ray fin. His argument was: "I believe the boat runs better without and if you find out it doesn't it's just 4 bolts to put it back on. If you bring it again I will remove it again". He's good but stubborn!

Well, yesterday we went out with 5 people on board and very close to the weight limit. Without the fin she behaves just as you want it! At 2800RPM she makes it on plane (slow) and at full throttle she just jumps up. Even with a skier in tow she comes on plane immediately and stays up even at 2700RPM. WOT is 4700RPM and with a tube behind she still reaches 4600RPM.
Steering is easy even for the admiral now and she behaves exactly as I had hoped for! The Sting Ray fin will find its way on ebay. Don't buy it!!
Forgot the GPS so I don't know the speed at WOT nor 2800RPM and the speedo is meaningless as I had proven before. Used as a thermometer it would be equally useful and accurate.

Bottom line: think twice before you ruin a good design with an after-market part!

Now I have to install larger fenders and 15" wheels on the trailer as the admiral approved going to larger bodies of water and I don't want to do this on stroller wheels. For the 10mi to the lake it's fine but no way I will go the 50mi and more....

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Jürgen
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Drive fin, reverse testing 08 Jul 2012 04:30 #2

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I just put a planning fin on my dinghy and uaed it for the first time on the4 of july. I think the boat runs slower but it does run smother and planes faster

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1989 Avanti 3450 Sunbridge twin 454's

1979 Bayliner Conquest 3150 hull#23

1979 Bayliner Conquest 3150 hardtop hull#24
Twin chevy 350's

Drive fin, reverse testing 08 Jul 2012 14:52 #3

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I'm sure that it depends on the hull shape and behavior of the boat whether a fin improves or degrades the performance. A dinghy isn't a well designed planing hull and lifting the rear may improve the handling/planing.
With the 1996 175 hull it looks like Bayliner did a very good design job and it doesn't need the help of lifting fin to get it right, With the fin installed I always had to trim out a bit to get her go right and she had some problems to stay on plane at lower speed. Now I just trim down all the way and she just does everything on her own. Never played less with trim than yesterday: down once and leave it there. Only when it got choppy from a lot of boats I trimmed the bow up a tad as she handles the waves better that way.

Don't know whether they changed the hull for new models. Didn't look that way when I looked at 2012 models last week.

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Jürgen
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Drive fin, reverse testing 08 Jul 2012 23:57 #4

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I don't know the Stingray fin but I do know the Se300 as I oput on on my outdrive.

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Best thing I have done, The boat holds on plane much better, gets out of the water onto Plane faster all without loosing top end speed.The only think it hasn't fixed is low speed wandering which I think Smart Tabs will do.Once I have the Tabs I may remove but until then I can't do without it.

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Tony.
Christchurch, New Zealand.
"Thirsty Merc"
2006 185BR Capri
190hp V6
Alpha 1 Gen 2
SX Smart Tabs 60Lb
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