Trim Tab Drag
11-02-2005, 06:40 PM
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Re: Trim Tab Drag
OK, I am going to go through the the real answer to your question as I see it. You will have to fit this to YOUR particular hull/use/water conditions. You (I assume) have already installed your tabs on the transom at the recommended 1/2 to 3/4 inch above hull line. Now, determine from research or photos of your boat running just what the ideal angle of attack your hull runs at WOT in calm water and attains top speed. That would be that angle between the hull keel line and the horizontal water surface. Take that angle, (which would be extending that horizontal water line) and extend out from end of hull off keel line. Set your full up tab aft tip position just a bit (maybe 1/4" depending on tab length) above that line. Your tabs will never cause any unnecessary drag and will be close to the surface and react quickly when you need them. --- Jer
11-04-2005, 08:49 AM
#13
Re: Trim Tab Drag
Don't forget that there is a significant amount of wave rise, depending on the trim angle of the boat, and the speed. I've generally seen K-planes mounted at 1" above the running surface, and they are capable of retracting about 10 degrees up (asssuming a 13 degree transom angle). Mounting them above the transom ensures that the water flow will not remain attached and be drawn up the tab. You must retract the tab quite a bit more than parallel with the hull to actually get it out of the water.
For instance, I know that my K-380 planes are parallel to the bottom of the boat at a indicated reading of about 4.5. At lower speeds, they will still produce lift as low as 3, and at top speed, I have to leave the port tab at about 4 to just drag the tip and overcome the propeller torque. I can really tell on my boat whether I have the tabs dragging or not. I have a SSMIII running a full cleaver, and the combination of the tabs being pulled up free of the water occurs right about where the prop finally hooks up at about 60 mph, and it takes off with little increase in power or engine RPM.
If anyone is interested in trying out a new set of Carbon Fiber tabs, I am developing a set based on my research. I have the molds made already, and am just about to lay up the first set. They are going to be a little more expensive than most, but will be incredibly strong and stiff. My design condition is a 20 degree deflection at 95 mph, which generates around 12,000 lb of lift per tab (this is the relief point on the hydraulic pumps). I still have a factor of safety of nearly 4 on the tab structure and around 3 on the pistons, according to both conventional analysis methods, as well as a Finite Element Analysys.
They will be supplied with a really cool piston made of solid 316 stainless with a 3/4" piston rod (compare to 1/2" for competitors...) I have the first two pistons done now, and they look really cool. The tabs will be 25" in length, which puts them squarely between K-280 and K-380. They will be the ultimate in looks and corrosion resistance!
My boat only runs 75 mph, so I have been looking for someone with a faster, heavier setup who would be willing to mount them and test them in exchange for a free set! The only catches are that they won't work with the same bolt pattern as existing tabs, and you'd have to report back your findings after testing.
For instance, I know that my K-380 planes are parallel to the bottom of the boat at a indicated reading of about 4.5. At lower speeds, they will still produce lift as low as 3, and at top speed, I have to leave the port tab at about 4 to just drag the tip and overcome the propeller torque. I can really tell on my boat whether I have the tabs dragging or not. I have a SSMIII running a full cleaver, and the combination of the tabs being pulled up free of the water occurs right about where the prop finally hooks up at about 60 mph, and it takes off with little increase in power or engine RPM.
If anyone is interested in trying out a new set of Carbon Fiber tabs, I am developing a set based on my research. I have the molds made already, and am just about to lay up the first set. They are going to be a little more expensive than most, but will be incredibly strong and stiff. My design condition is a 20 degree deflection at 95 mph, which generates around 12,000 lb of lift per tab (this is the relief point on the hydraulic pumps). I still have a factor of safety of nearly 4 on the tab structure and around 3 on the pistons, according to both conventional analysis methods, as well as a Finite Element Analysys.
They will be supplied with a really cool piston made of solid 316 stainless with a 3/4" piston rod (compare to 1/2" for competitors...) I have the first two pistons done now, and they look really cool. The tabs will be 25" in length, which puts them squarely between K-280 and K-380. They will be the ultimate in looks and corrosion resistance!
My boat only runs 75 mph, so I have been looking for someone with a faster, heavier setup who would be willing to mount them and test them in exchange for a free set! The only catches are that they won't work with the same bolt pattern as existing tabs, and you'd have to report back your findings after testing.
11-04-2005, 11:03 AM
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Re: Trim Tab Drag
Originally Posted by tcelano
Don't forget that there is a significant amount of wave rise, depending on the trim angle of the boat, and the speed. I've generally seen K-planes mounted at 1" above the running surface, and they are capable of retracting about 10 degrees up (asssuming a 13 degree transom angle). Mounting them above the transom ensures that the water flow will not remain attached and be drawn up the tab. You must retract the tab quite a bit more than parallel with the hull to actually get it out of the water.
For instance, I know that my K-380 planes are parallel to the bottom of the boat at a indicated reading of about 4.5. At lower speeds, they will still produce lift as low as 3, and at top speed, I have to leave the port tab at about 4 to just drag the tip and overcome the propeller torque. I can really tell on my boat whether I have the tabs dragging or not. I have a SSMIII running a full cleaver, and the combination of the tabs being pulled up free of the water occurs right about where the prop finally hooks up at about 60 mph, and it takes off with little increase in power or engine RPM.
If anyone is interested in trying out a new set of Carbon Fiber tabs, I am developing a set based on my research. I have the molds made already, and am just about to lay up the first set. They are going to be a little more expensive than most, but will be incredibly strong and stiff. My design condition is a 20 degree deflection at 95 mph, which generates around 12,000 lb of lift per tab (this is the relief point on the hydraulic pumps). I still have a factor of safety of nearly 4 on the tab structure and around 3 on the pistons, according to both conventional analysis methods, as well as a Finite Element Analysys.
They will be supplied with a really cool piston made of solid 316 stainless with a 3/4" piston rod (compare to 1/2" for competitors...) I have the first two pistons done now, and they look really cool. The tabs will be 25" in length, which puts them squarely between K-280 and K-380. They will be the ultimate in looks and corrosion resistance!
My boat only runs 75 mph, so I have been looking for someone with a faster, heavier setup who would be willing to mount them and test them in exchange for a free set! The only catches are that they won't work with the same bolt pattern as existing tabs, and you'd have to report back your findings after testing.
For instance, I know that my K-380 planes are parallel to the bottom of the boat at a indicated reading of about 4.5. At lower speeds, they will still produce lift as low as 3, and at top speed, I have to leave the port tab at about 4 to just drag the tip and overcome the propeller torque. I can really tell on my boat whether I have the tabs dragging or not. I have a SSMIII running a full cleaver, and the combination of the tabs being pulled up free of the water occurs right about where the prop finally hooks up at about 60 mph, and it takes off with little increase in power or engine RPM.
If anyone is interested in trying out a new set of Carbon Fiber tabs, I am developing a set based on my research. I have the molds made already, and am just about to lay up the first set. They are going to be a little more expensive than most, but will be incredibly strong and stiff. My design condition is a 20 degree deflection at 95 mph, which generates around 12,000 lb of lift per tab (this is the relief point on the hydraulic pumps). I still have a factor of safety of nearly 4 on the tab structure and around 3 on the pistons, according to both conventional analysis methods, as well as a Finite Element Analysys.
They will be supplied with a really cool piston made of solid 316 stainless with a 3/4" piston rod (compare to 1/2" for competitors...) I have the first two pistons done now, and they look really cool. The tabs will be 25" in length, which puts them squarely between K-280 and K-380. They will be the ultimate in looks and corrosion resistance!
My boat only runs 75 mph, so I have been looking for someone with a faster, heavier setup who would be willing to mount them and test them in exchange for a free set! The only catches are that they won't work with the same bolt pattern as existing tabs, and you'd have to report back your findings after testing.
11-04-2005, 11:07 AM
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Re: Trim Tab Drag
Icelano,
Re: "You must retract the tab quite a bit more than parallel with the hull to actually get it out of the water." how much more in degrees at ~70mph? I am installing 16" length tabs.
Re: "You must retract the tab quite a bit more than parallel with the hull to actually get it out of the water." how much more in degrees at ~70mph? I am installing 16" length tabs.
11-04-2005, 10:43 PM
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Re: Trim Tab Drag
My question would be, has anyone had tabs mounted flush or near flush and tested true/performance/drag by pulling them off or way up to be sure they were out of the way, and seen a good result?
Mine'sobviously not a performance hull, thus I need every advantage I can get.
My tabs are factory installed at near flush and retract just enough that I have to look doe the running surface to tell if they are not flush.
I've though about (ok, bobl suggested) a way to test them would be to remove/unhook the ram from one side and tie them up. I have a feeling they are dragging quite a bit.
Mine'sobviously not a performance hull, thus I need every advantage I can get.
My tabs are factory installed at near flush and retract just enough that I have to look doe the running surface to tell if they are not flush.I've though about (ok, bobl suggested
) a way to test them would be to remove/unhook the ram from one side and tie them up. I have a feeling they are dragging quite a bit.
