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Author Topic:   Best Hydofoil Stablizer Fin

Smithsm posted 08-18-2008 09:04 AM ET (US)
[Solicits] opinion of the better of two Hydrofoil Stabilizer fins for my twin outboards: Doel-Fin or Bobs Stabilizer Plate
My application is a 1988 Outrage 20 (known to be stern heavy) with twin Evinrude 60 hp, 1994 models - they are three cylinder, loop charged. I currently use 15" aluminum props but plan to check out 17" stainless props.
davej14 posted 08-18-2008 11:24 AM ET (US)
What material is the Bob's plate, wouldn't want aluminum in salt water.
The design looks similar to the stainless turbo-lift fin sold through Grand Isle Marine in FL except the turbo-lift does not require holes in your anti-cavitation plate.
Smithsm posted 08-18-2008 02:44 PM ET (US)
[Bob's Stabilizer Plate] is made out of cast aluminum. It mounts to the bottom of the plate that they claim adds strength
fishgutz posted 08-18-2008 02:52 PM ET (US)
Educate yourself about foils and aspect ratios (I'm an old catamaran sailor) and you'll go with the Doel-fin. That is what I use. Love it. Wouldn't leave home without it.
PS Adding strength isn't an issue. Anti-ventilation plates don't break.
Tohsgib posted 08-18-2008 03:09 PM ET (US)
I always ran the Doel-fin and only use the one bolt per side, no need to drill the one towards the bow as it can't go anywhere.
fishgutz posted 08-18-2008 04:12 PM ET (US)
Dang tohsgib, why didn't I think of that.
Bulldog posted 08-18-2008 05:30 PM ET (US)
Doel-fin! Skip, aluminum in saltwater is never as good as good old plastic, and you can always get Doel-fins on the internet cheap. I really don't think that adding stabilizer fins to the "Hydrofoil" when you already have two engine skegs in the water will help with steering. There are both sides of the debate on Hydrofoils but I think it comes down to underpowered or stern heavy boats just work better with them. I love mine...Jack
Tonym posted 08-18-2008 11:13 PM ET (US)
I have an 18 foot rigid raider with a 130 hp honda and a 9.9 hp honda kicker. It is both stern heavy and underpowered. I purchased a Permatrim hydrofoil and am happy with it. I installed a manual Jack plate-set back bracket (6 ") from Bobs Machine shop which also helped.
It takes a little tweaking but to me it was well worth it.
Tonym
Richard Quinlivan posted 08-19-2008 04:03 PM ET (US)
I tried a Bob's fin with little success and later mounted a stainless turbo-lift fin sold through Grand Isle Marine in FL on my 1995 17 ft Dauntless Dual Console. The turbo lift did a wonferfull job. Killed the porpoising and let me have a useful trim range. I never tried a Doel Fin.
dick
chiro1 posted 08-19-2008 04:34 PM ET (US)
I had [a oscilating rise and fall of the bow] with my 17 foot whaler with E-TEC 90. I didn't want the Doel-fin, so I put transom wedge plates in and it did a great job. More trim, more stern lift. the bow rides about 6-inches lower and no [oscilating rise and fall of the bow]. [Transom wedge plates] are $ 35. I love them
chiro1
sosmerc posted 08-19-2008 11:01 PM ET (US)
I have had very good luck with the Doel-fin. From experimentation I have learned that it is even more effective if you mount it as far back on the cavitation plate as possible.
Smithsm posted 08-20-2008 08:20 AM ET (US)
Chiro
what are transom wedge plates and how do they work ?
Smithsm posted 08-20-2008 08:54 AM ET (US)
fishgutz
can you give us a brief explanation why aspect ratio understanding leads to the doel-fin design ?
I notice the doel-fin is "wider" compared to some other designs that seem to be less wide, but extend further back.
is this difference related to aspect ratio ?
Buckda posted 08-20-2008 09:05 AM ET (US)
Having observed a 20' Outrage with 115 Suzuki and a hydrofoil fin on the motor a few weeks ago for a long trip in the North Channel of Lake Huron, my opinion is that you may want to reconsider and think about trim tabs.
I'd recommend Lenco 12x12 ENS tabs, which you can find online for about $600 shipped. I'd spring the extra $150 for the LED display controls (Which I don't have) that show you the position of the tabs.
I think you will be very happy with that solution in your application, because when you need the extra "oomph" to get the bow down, the tabs will provide it whereas the fin will not. Under normal operation, you will be able to figure out the position you like them to be in normally, and set them and forget 'em.
Something for consideration. THe 1978 v-20 I observed with the fin STILL operated with a very bow-high attitude.
fishgutz posted 08-20-2008 09:27 AM ET (US)
Smithsm,
Aspect ratio is the difference between length and width. That is why the Doelfin is wider side to side. (higher aspect ratio)The ratio of how long it is (to the side) to its length front to back. It's a bit confusing for me to explain with a wing going sideways as opposed to a sail or rudder being measured up and down. The doel fin will produce more lift.
On another note a flat piece of metal is NOT a foil, though they call it one. A foil is shaped like a cross section of a wing (flattened teardrop). Water flowing over a flat piece of metal "delaminates" in the center of the blade.
Here is a good link to foil design and aspect ratio:
http://www.boat-links.com/foilfaq.html
It relates more to sailing. You say, "But sailboats go so slow". Catamarans, proas and sailboards are consistantly pushing over 40 MPH. Check out this badboy:
http://yachtpals.com/fastest-sailboats-2079
Wedges do nothing more than push the nose of the boat down further. The boat will plow and porpoising will stop, but you will be running very inefficiently and slower. A fin will make trimming more precise and you will be able to set your boat right at the perfect angle and go much faster.
The biggest advantage I see with a Doel-fin is the ability to accelerate slowly. No more screaming hole shots to get on plane. You'll save a lot of gas. You can stay on plane at a slower speed and maintain a smoother ride in chop, too.
jimh posted 08-20-2008 09:40 AM ET (US)
Transom wedge plates are just that: they are a wedge shaped device which is inserted between the transom and the engine mounting bracket. They effectively increase the transom angle a few degrees. This allows the motor to tucked in at a greater negative trim angle.
fishgutz posted 08-20-2008 12:21 PM ET (US)
I'll try to explain what happens with a "Flat" foil, basically one made of a flat sheet of metal.
When I raced Hobie Cats, I'd meet new sailors on the water who'd brag about going so fast that their rudders were humming. Sometimes I'd hear the hum as far away as a couple hundred feet. Well, guess what? Yeah they're going pretty fast but that vibration is slowing them down. It's also putting premature wear on all pivot points on and around the rudder creating speed stealing slop and missalignment. The same might be happening with an outboard with a flat fin attached. Only you can't sense it with all the engine vibration and the dampening of the engine mounts. Possibly weakening the metal of the antiventilation plate and even the bushings and o-rings of the lower unit (hypothetically).
A stock Hobie rudder was a flat piece of plastic with a rounded leading edge and a tapered trailing edge. I would get a pair of Hobie Lexan rudders (stronger material) and then with a disc sander start removing material from the sides of the leading edge and the sides of the trailing edge. Eventually getting the NACA shaped foil (check previous post about foils). I'd mark where the thickest section should be and grind away accordingly. Wow. what a difference. Much faster, less tendency to stall (from over steering), no wobble from wear and very quiet (no hum).
If you search further you will find that the NACA shape was researched using sharks. They are probably the most perfect swimming machines. In fact the pectoral fins of a shark would probably make the perfect foil/fin for an outboard motor. The shark propels itself forward with its tail. The force of its tail pushes forward and down on the pecoral fins (yes, down, the sharks tail is mostly above its body)and drives the shark forward faster than its tail would alone. Pretty amazing. Very efficient.
fishgutz posted 08-20-2008 12:27 PM ET (US)
Another good link for NACA foils:
http://en.wikipedia.org/wiki/Foil_(fluid_mechanics)
and:
http://www.vacantisw.com/foildesign.htm
fishgutz posted 08-20-2008 01:24 PM ET (US)
Oh, the reason for all the lengthy posts...the Doel-fin is the closest thing to a real hydrofoil. A Tigershark VG is close to a real foil, too. The Tigershark adds vortex generators and has a swept back design that added about 3 inches to the overall length of my rig. Making it too long for my garage. So I changed to the Doel-fin.

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Author	Topic: Best Hydofoil Stablizer Fin
Smithsm	posted 08-18-2008 09:04 AM ET (US) [Solicits] opinion of the better of two Hydrofoil Stabilizer fins for my twin outboards: Doel-Fin or Bobs Stabilizer Plate My application is a 1988 Outrage 20 (known to be stern heavy) with twin Evinrude 60 hp, 1994 models - they are three cylinder, loop charged. I currently use 15" aluminum props but plan to check out 17" stainless props.
davej14	posted 08-18-2008 11:24 AM ET (US) What material is the Bob's plate, wouldn't want aluminum in salt water. The design looks similar to the stainless turbo-lift fin sold through Grand Isle Marine in FL except the turbo-lift does not require holes in your anti-cavitation plate.
Smithsm	posted 08-18-2008 02:44 PM ET (US) [Bob's Stabilizer Plate] is made out of cast aluminum. It mounts to the bottom of the plate that they claim adds strength
fishgutz	posted 08-18-2008 02:52 PM ET (US) Educate yourself about foils and aspect ratios (I'm an old catamaran sailor) and you'll go with the Doel-fin. That is what I use. Love it. Wouldn't leave home without it. PS Adding strength isn't an issue. Anti-ventilation plates don't break.
Tohsgib	posted 08-18-2008 03:09 PM ET (US) I always ran the Doel-fin and only use the one bolt per side, no need to drill the one towards the bow as it can't go anywhere.
fishgutz	posted 08-18-2008 04:12 PM ET (US) Dang tohsgib, why didn't I think of that.
Bulldog	posted 08-18-2008 05:30 PM ET (US) Doel-fin! Skip, aluminum in saltwater is never as good as good old plastic, and you can always get Doel-fins on the internet cheap. I really don't think that adding stabilizer fins to the "Hydrofoil" when you already have two engine skegs in the water will help with steering. There are both sides of the debate on Hydrofoils but I think it comes down to underpowered or stern heavy boats just work better with them. I love mine...Jack
Tonym	posted 08-18-2008 11:13 PM ET (US) I have an 18 foot rigid raider with a 130 hp honda and a 9.9 hp honda kicker. It is both stern heavy and underpowered. I purchased a Permatrim hydrofoil and am happy with it. I installed a manual Jack plate-set back bracket (6 ") from Bobs Machine shop which also helped. It takes a little tweaking but to me it was well worth it. Tonym
Richard Quinlivan	posted 08-19-2008 04:03 PM ET (US) I tried a Bob's fin with little success and later mounted a stainless turbo-lift fin sold through Grand Isle Marine in FL on my 1995 17 ft Dauntless Dual Console. The turbo lift did a wonferfull job. Killed the porpoising and let me have a useful trim range. I never tried a Doel Fin. dick
chiro1	posted 08-19-2008 04:34 PM ET (US) I had [a oscilating rise and fall of the bow] with my 17 foot whaler with E-TEC 90. I didn't want the Doel-fin, so I put transom wedge plates in and it did a great job. More trim, more stern lift. the bow rides about 6-inches lower and no [oscilating rise and fall of the bow]. [Transom wedge plates] are $ 35. I love them chiro1
sosmerc	posted 08-19-2008 11:01 PM ET (US) I have had very good luck with the Doel-fin. From experimentation I have learned that it is even more effective if you mount it as far back on the cavitation plate as possible.
Smithsm	posted 08-20-2008 08:20 AM ET (US) Chiro what are transom wedge plates and how do they work ?
Smithsm	posted 08-20-2008 08:54 AM ET (US) fishgutz can you give us a brief explanation why aspect ratio understanding leads to the doel-fin design ? I notice the doel-fin is "wider" compared to some other designs that seem to be less wide, but extend further back. is this difference related to aspect ratio ?
Buckda	posted 08-20-2008 09:05 AM ET (US) Having observed a 20' Outrage with 115 Suzuki and a hydrofoil fin on the motor a few weeks ago for a long trip in the North Channel of Lake Huron, my opinion is that you may want to reconsider and think about trim tabs. I'd recommend Lenco 12x12 ENS tabs, which you can find online for about $600 shipped. I'd spring the extra $150 for the LED display controls (Which I don't have) that show you the position of the tabs. I think you will be very happy with that solution in your application, because when you need the extra "oomph" to get the bow down, the tabs will provide it whereas the fin will not. Under normal operation, you will be able to figure out the position you like them to be in normally, and set them and forget 'em. Something for consideration. THe 1978 v-20 I observed with the fin STILL operated with a very bow-high attitude.
fishgutz	posted 08-20-2008 09:27 AM ET (US) Smithsm, Aspect ratio is the difference between length and width. That is why the Doelfin is wider side to side. (higher aspect ratio)The ratio of how long it is (to the side) to its length front to back. It's a bit confusing for me to explain with a wing going sideways as opposed to a sail or rudder being measured up and down. The doel fin will produce more lift. On another note a flat piece of metal is NOT a foil, though they call it one. A foil is shaped like a cross section of a wing (flattened teardrop). Water flowing over a flat piece of metal "delaminates" in the center of the blade. Here is a good link to foil design and aspect ratio: http://www.boat-links.com/foilfaq.html It relates more to sailing. You say, "But sailboats go so slow". Catamarans, proas and sailboards are consistantly pushing over 40 MPH. Check out this badboy: http://yachtpals.com/fastest-sailboats-2079 Wedges do nothing more than push the nose of the boat down further. The boat will plow and porpoising will stop, but you will be running very inefficiently and slower. A fin will make trimming more precise and you will be able to set your boat right at the perfect angle and go much faster. The biggest advantage I see with a Doel-fin is the ability to accelerate slowly. No more screaming hole shots to get on plane. You'll save a lot of gas. You can stay on plane at a slower speed and maintain a smoother ride in chop, too.
jimh	posted 08-20-2008 09:40 AM ET (US) Transom wedge plates are just that: they are a wedge shaped device which is inserted between the transom and the engine mounting bracket. They effectively increase the transom angle a few degrees. This allows the motor to tucked in at a greater negative trim angle.
fishgutz	posted 08-20-2008 12:21 PM ET (US) I'll try to explain what happens with a "Flat" foil, basically one made of a flat sheet of metal. When I raced Hobie Cats, I'd meet new sailors on the water who'd brag about going so fast that their rudders were humming. Sometimes I'd hear the hum as far away as a couple hundred feet. Well, guess what? Yeah they're going pretty fast but that vibration is slowing them down. It's also putting premature wear on all pivot points on and around the rudder creating speed stealing slop and missalignment. The same might be happening with an outboard with a flat fin attached. Only you can't sense it with all the engine vibration and the dampening of the engine mounts. Possibly weakening the metal of the antiventilation plate and even the bushings and o-rings of the lower unit (hypothetically). A stock Hobie rudder was a flat piece of plastic with a rounded leading edge and a tapered trailing edge. I would get a pair of Hobie Lexan rudders (stronger material) and then with a disc sander start removing material from the sides of the leading edge and the sides of the trailing edge. Eventually getting the NACA shaped foil (check previous post about foils). I'd mark where the thickest section should be and grind away accordingly. Wow. what a difference. Much faster, less tendency to stall (from over steering), no wobble from wear and very quiet (no hum). If you search further you will find that the NACA shape was researched using sharks. They are probably the most perfect swimming machines. In fact the pectoral fins of a shark would probably make the perfect foil/fin for an outboard motor. The shark propels itself forward with its tail. The force of its tail pushes forward and down on the pecoral fins (yes, down, the sharks tail is mostly above its body)and drives the shark forward faster than its tail would alone. Pretty amazing. Very efficient.
fishgutz	posted 08-20-2008 12:27 PM ET (US) Another good link for NACA foils: http://en.wikipedia.org/wiki/Foil_(fluid_mechanics) and: http://www.vacantisw.com/foildesign.htm
fishgutz	posted 08-20-2008 01:24 PM ET (US) Oh, the reason for all the lengthy posts...the Doel-fin is the closest thing to a real hydrofoil. A Tigershark VG is close to a real foil, too. The Tigershark adds vortex generators and has a swept back design that added about 3 inches to the overall length of my rig. Making it too long for my garage. So I changed to the Doel-fin.