Do i need a Hydrofoil Stabilizers

nitromike · 04-26-10, 12:14 AM

My last boat had a Hydrofoil Stabilizer on it and was wondering what they actually do.
My new boat is a 2004 nitro 640lx and it has a 75hp Mercury and it seems to be kind of hard to turn when i am going fast. i do not have a trim guage on it and was wondering if it was because i was not getting it trimed right or if i needed one of the Stabilizers. or both.

Thanks for any info

nofearengineer · 04-26-10, 07:41 AM

Mike...the hydrofoil won't help with your high-speed problem. When you reach your planing speed, the hydrofoil should actually be out of the water. What is does it help you get on plane faster. When the motor is trimmed down, the fin helps to lift the stern.

Your "hard to steer" comment is the torque of your prop making your outboard (and boat) prefer to steer in one direction. The water at the top of your prop has more air in it, and thus has less resistance to the prop's motion than the water at the bottom of the prop. Since the top is moving to one direction, and the bottom the other, and the forces are not equal, the prop wants to go left or right, depending on which way your prop spins, clockwise or counter-clockwise.

This can be largely corrected for by trimming back down slightly, lowering the motor's transom height, installing a torque tab on the lower unit of the motor, or some combination of the three. If I have left anything out, I am sure 1FastLaser will pop in and set us all straight.

zooker · 04-26-10, 08:55 AM

04 nitros should have teleflex hydroilic steering.see if it is pinched or under lubed,there is a grease fitting. they should turn under power as easily as your car or there abouts..trim up till the moter sounds differant.-sound like it opens up-i actually hear my yammer-who exhaust ports clear the water..

zooker

nitromike · 04-26-10, 12:45 PM

Thanks guys

Abbeysdad · 04-26-10, 09:45 PM

My 90 HP Mercury outboard has an adjustable fin on the top rear of the lower unit to compensate for prop torque - maybe you have one that needs adjusting?
As the others have pointed out, I notice that when trimmed down, my steering pulls - as soon as you get up on plane, trim up. As zook says, keep trimming up until it cavitates (sounds really bad as the prop starts catching air) then trim back down slightly so it sounds good again - that'll be the sweet spot.
Frankly, I used to trim down and accelerate, then trim back up once she was up on plane. However, after "playing" I discovered she pops up on plane just fine with the trim up at the sweet spot - so I often just leave it there (for what it's worth).

CABINDOC · 05-02-10, 10:32 PM

Hi guys,

New to this site, but not boatin. Have a 93 Hydra Sports 170fs which is a 17' fish and ski. The problem I'm having is porposing. When trimmed into the sweet spot, or just before, she starts. It has a Erude 90 and I installed a hydra-foil to help get on plane and to elliminate the porposing. Any idea's?

nofearengineer · 05-03-10, 12:15 AM

Cabin....if the boat is porpoising, it obviously is not the sweet spot. Do not believe any claims of a hydrofoil helping with porpoising. When you are up on plane, the hydrofoil isn't even in the water. A hydrofoil is pretty much a one-trick pony...it gets you up on plane slightly faster.

lilmule · 05-03-10, 01:01 AM

Actually in real rough water they do a tad more stabilizing the boat,inbetween huge breakers,the boat actually being held up somewhat and less drop after each one,creating a slightly better ride.
But their first and best use is predescribed by no fear,as in assisting getting on plane easier,but also allows slower planing speeds than without,once up,any action that forces the tail down also gets the hydrofoil actually working again creating resistance,and keeping the bow somewhat higher as a result.Otherwise out of the water,at speed.

CABINDOC · 05-03-10, 08:42 AM

You are both right and no, it is not the sweet spot, your right there as well. I cant get it to the sweet spot. Could it be the motor is too small for the size? I have 2 props, a 3 blade and a 4 blade, no diff. I had the 3 blade on last night and @WOT 4800, I am @ about 36 mph. this w/ 2 adults and 2 childs. If I go up 1 pitch to improve speed, I'll have trouble getting on plane.

CABINDOC · 05-03-10, 08:44 AM

Oh, and it was late when I posted last night. My motor is a Johnson and it has very low hours and looks almost new.

04-26-10, 12:14 AM	#1
nitromike BassFishin.Com Member Join Date: Apr 2010 Location: ElDorado, Kansas Posts: 22	Do i need a Hydrofoil Stabilizers My last boat had a Hydrofoil Stabilizer on it and was wondering what they actually do. My new boat is a 2004 nitro 640lx and it has a 75hp Mercury and it seems to be kind of hard to turn when i am going fast. i do not have a trim guage on it and was wondering if it was because i was not getting it trimed right or if i needed one of the Stabilizers. or both. Thanks for any info

04-26-10, 07:41 AM	#2
nofearengineer BassFishin.Com Premier Elite Join Date: Mar 2009 Location: Southwest IN Posts: 5,630	Mike...the hydrofoil won't help with your high-speed problem. When you reach your planing speed, the hydrofoil should actually be out of the water. What is does it help you get on plane faster. When the motor is trimmed down, the fin helps to lift the stern. Your "hard to steer" comment is the torque of your prop making your outboard (and boat) prefer to steer in one direction. The water at the top of your prop has more air in it, and thus has less resistance to the prop's motion than the water at the bottom of the prop. Since the top is moving to one direction, and the bottom the other, and the forces are not equal, the prop wants to go left or right, depending on which way your prop spins, clockwise or counter-clockwise. This can be largely corrected for by trimming back down slightly, lowering the motor's transom height, installing a torque tab on the lower unit of the motor, or some combination of the three. If I have left anything out, I am sure 1FastLaser will pop in and set us all straight. __________________ Many men go fishing all of their lives without knowing it is not fish they are after.

04-26-10, 08:55 AM	#3
zooker BassFishin.Com Premier Elite Join Date: Jan 2004 Location: denton nc Posts: 13,441	04 nitros should have teleflex hydroilic steering.see if it is pinched or under lubed,there is a grease fitting. they should turn under power as easily as your car or there abouts..trim up till the moter sounds differant.-sound like it opens up-i actually hear my yammer-who exhaust ports clear the water.. zooker __________________ the godfather.. aml in remission since 7-20-09

04-26-10, 09:45 PM	#5
Abbeysdad BassFishin.Com Super Veteran Join Date: Jul 2008 Location: Central NY - Finger Lakes Posts: 1,307	My 90 HP Mercury outboard has an adjustable fin on the top rear of the lower unit to compensate for prop torque - maybe you have one that needs adjusting? As the others have pointed out, I notice that when trimmed down, my steering pulls - as soon as you get up on plane, trim up. As zook says, keep trimming up until it cavitates (sounds really bad as the prop starts catching air) then trim back down slightly so it sounds good again - that'll be the sweet spot. Frankly, I used to trim down and accelerate, then trim back up once she was up on plane. However, after "playing" I discovered she pops up on plane just fine with the trim up at the sweet spot - so I often just leave it there (for what it's worth). __________________ Fish now, work later Last edited by Abbeysdad; 04-26-10 at 09:54 PM.

05-03-10, 12:15 AM	#7
nofearengineer BassFishin.Com Premier Elite Join Date: Mar 2009 Location: Southwest IN Posts: 5,630	Cabin....if the boat is porpoising, it obviously is not the sweet spot. Do not believe any claims of a hydrofoil helping with porpoising. When you are up on plane, the hydrofoil isn't even in the water. A hydrofoil is pretty much a one-trick pony...it gets you up on plane slightly faster. __________________ Many men go fishing all of their lives without knowing it is not fish they are after.

04-26-10, 12:45 PM	#4
nitromike BassFishin.Com Member Join Date: Apr 2010 Location: ElDorado, Kansas Posts: 22	Thanks guys

05-02-10, 10:32 PM	#6
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Hi guys, New to this site, but not boatin. Have a 93 Hydra Sports 170fs which is a 17' fish and ski. The problem I'm having is porposing. When trimmed into the sweet spot, or just before, she starts. It has a Erude 90 and I installed a hydra-foil to help get on plane and to elliminate the porposing. Any idea's?

05-03-10, 01:01 AM	#8
lilmule BassFishin.Com Super Veteran Join Date: Feb 2010 Location: Buchanan,Tn Posts: 2,685	Actually in real rough water they do a tad more stabilizing the boat,inbetween huge breakers,the boat actually being held up somewhat and less drop after each one,creating a slightly better ride. But their first and best use is predescribed by no fear,as in assisting getting on plane easier,but also allows slower planing speeds than without,once up,any action that forces the tail down also gets the hydrofoil actually working again creating resistance,and keeping the bow somewhat higher as a result.Otherwise out of the water,at speed.

05-03-10, 08:42 AM	#9
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	You are both right and no, it is not the sweet spot, your right there as well. I cant get it to the sweet spot. Could it be the motor is too small for the size? I have 2 props, a 3 blade and a 4 blade, no diff. I had the 3 blade on last night and @WOT 4800, I am @ about 36 mph. this w/ 2 adults and 2 childs. If I go up 1 pitch to improve speed, I'll have trouble getting on plane.

05-03-10, 08:44 AM	#10
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Oh, and it was late when I posted last night. My motor is a Johnson and it has very low hours and looks almost new.

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