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Old 27-12-2014, 06:31   #16
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Re: Outboard Planing Fins

Yes it is funny but unfortunately the damn things do work!
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Old 27-12-2014, 06:32   #17
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Re: Outboard Planing Fins

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Originally Posted by rourkeh View Post
If these fins on the lower unit actually worked don't you think the outboard manufacturers would have incorporated them into their lower units to make them perform better? Funny that not a single company produces an outboard with a finned lower unit!!!!
Outboards are manufactured to go on a very wide variety of boats with widely differing characteristics. Planing fins only work for certain applications (mainly, short, light dinghies, where the engine is mismatched with the boat design). Outside this narrow application, planing fins actually harm performance and maneuverability.

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Old 27-12-2014, 13:41   #18
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Re: Outboard Planing Fins

The fins are a patch, a fix that is not necessary for a properly set up boat, usually they work on a boat that has a CG that is too far aft, they work by lifting the rear end up to lower the nose.
Yes, I do realize that with a tiller steered RIB and one person on board it's not possible to get the CG far enough forward and the fin is the best solution, but if you could get the motor trim and depth set right and the CG correct, you would go faster and burn les fuel without a fin than with.
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Old 27-12-2014, 14:29   #19
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Re: Outboard Planing Fins

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Originally Posted by colemj View Post
Outboards are manufactured to go on a very wide variety of boats with widely differing characteristics. Planing fins only work for certain applications (mainly, short, light dinghies, where the engine is mismatched with the boat design). Outside this narrow application, planing fins actually harm performance and maneuverability.

Mark

Hmm... on a 22 foot boat with a 200hp outboard, the SE hydrofoil was a substantial improvement. Only a little quicker to plane, but more noticeable was the huge increase in response to trim adjustments, and the ability to stay on the plane at much lower speeds.

It certainly didn't hurt performance or manoeuverability.
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Old 27-12-2014, 14:49   #20
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Re: Outboard Planing Fins

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but if you could get the motor trim and depth set right and the CG correct, you would go faster and burn les fuel without a fin than with.
Yes, and if a frog had wings he wouldn't bump his ass when he jumped!

In many RIB/inflatable applications, it simply is not possible to make the adjustments you suggest, hence the foils are a big improvement.

I'm looking for a foil as we speak, for since we had new tubes put on our old RIB the balance is different enough to make getting onto a plane difficult at times. And yes, I've got the engine tilt at max and the movable weight forward...

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Old 27-12-2014, 14:51   #21
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Outboard Planing Fins

Jim, I'm not saying they aren't the cats meow for a RIB, or possibly other applications, trying to explain why they don't come on outboards from the factory. They have been around for what, maybe 40 yrs?
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Old 27-12-2014, 15:01   #22
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Re: Outboard Planing Fins

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Originally Posted by 44'cruisingcat View Post
Hmm... on a 22 foot boat with a 200hp outboard, the SE hydrofoil was a substantial improvement. Only a little quicker to plane, but more noticeable was the huge increase in response to trim adjustments, and the ability to stay on the plane at much lower speeds.

It certainly didn't hurt performance or manoeuverability.
The point I was addressing is why outboards are not manufactured with planing fins already on them.

Yes, as I mentioned, there are engine/boat combinations where they work well - you point out an example, and most dinghy setups are also examples. However, there are just as many situations where they don't work and actually decrease top speed and maneuverability.

Thus, it doesn't make sense to design outboards with integral planing fins. The after-market takes care of it nicely, and I don't think there is any business reason for the outboard manufacturers to want to be involved with them.

Not to mention that they would then have to be liable for them. Right now, they can plausibly deny warranty issues if the fins are used.

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Old 28-12-2014, 12:58   #23
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Re: Outboard Planing Fins

Wow this thread has taken some twists, bottom line hydrofoils work. Just not the answer for all applications
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Old 28-12-2014, 14:03   #24
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Re: Outboard Planing Fins

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I have a 1977 .evinrude 9.9 on a Caribe C-9. The stern REALLY squats when trying to get on plane and with only about 320 in crew weight it struggles to get fully flat when planning. With around 200 lb of crew weight it is quite fast.
There is something wrong with your motor, probably poor compression given it's age. My 1998 2 stroke 8hp Yammie moves my 10' RIB with 350 lbs. like a scalded cat.

I'd do a compression test. If it's low, sell it and buy something newer. The cost of a rebuild would be more than the value of the motor. If the compression is OK then buy a carb rebuild kit for @ $25. Will take you 30 minutes to put in new jets and gaskets. New wires/plugs would not hurt either I bet.
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