Will K-Planes make you faster
01-19-2010 | 07:25 PM
#2
I hate the winter!!
Joined: Jul 2001
Posts: 2,707
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From: long island, new york
They are just for control. However , if you were to compare 2 identical boats running in rough water, the boat with a good set of tabs, will outrun the boat without them. Unless the driver of the boat without the tabs, doesnt care about seeing tomorrow alive. 
01-19-2010 | 10:59 PM
#3
RIPSTA Racing Team
Joined: Nov 2008
Posts: 2,093
Likes: 1
From: Philadelphia, PA
I agree with Vinny, however control is not just to be defined as steering and handling. Being able to control the attitude of the hull cutting through the water and raising the stern of the boat out of the water, leaving your throttles at a constant rpms you can effectively increase the speed of the boat by properly adjusting the tabs. If tabs where not available then you would not have that ability therefore I feel that tabs can increase your speed available. Back to Vinny's point though, the guy without them in rougher water will be slowing down while having to work the throttles where the tabbed boat can continue cruising at a higher speed. Beter to have them and not need them than to need them and not have them. Just my 2cts worth.
01-20-2010 | 12:27 AM
#4
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Joined: Oct 2004
Posts: 616
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From: Portland, OR
Your boat should be balanced so you are completely off the tabs at full throttle. That means they are really just dead weight at WOT. Some boats have known instabilities that require one or both tabs to be dragged slightly to prevent chinewalking, etc. (Not naming names.)
However, at mid range throttle settings, that same boat that was balanced to run flat out will have its CG postion way too far aft for efficient running, and the tabs are required to bring the nose down to an acceptable trim angle, and provide some stern lift. In this speed range, the boat is actually more efficient using the tabs, as the extra resistance generated by the tabs in the course of producing their lift is less than the induced drag created by the entire hull operating at the higher trim angle (yes, I have all the mathematics and towing tank tests to prove this.)
None of this addresses the previously discussed benefits to rough water handling, and the ability to get on plane at slower speeds, lower trim angles, and less power.
However, at mid range throttle settings, that same boat that was balanced to run flat out will have its CG postion way too far aft for efficient running, and the tabs are required to bring the nose down to an acceptable trim angle, and provide some stern lift. In this speed range, the boat is actually more efficient using the tabs, as the extra resistance generated by the tabs in the course of producing their lift is less than the induced drag created by the entire hull operating at the higher trim angle (yes, I have all the mathematics and towing tank tests to prove this.)
None of this addresses the previously discussed benefits to rough water handling, and the ability to get on plane at slower speeds, lower trim angles, and less power.
01-20-2010 | 11:47 AM
#5
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Joined: Nov 2007
Posts: 432
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From: The River
Thank you, this is what I was looking for guys. I was recently discussing this with a very good diesel mechanic, and his thoughts were if you had trim tabs level with the boat at wot you have a longer boat and will be faster due to displacement speed or aka hull speed. I didn't know if trim tabs provided enough contact with the water to actually count as hull length.
01-20-2010 | 03:29 PM
#6
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Your buddy the diesel mechanic is confusing planning hulls with displacement hulls. They are quit different in how they move.
Only sailors and trawler captains need to know this stuff and it is kind of tedious for go fast guys, but here goes.
If you look at the side view of a displacement hull as it moves along, you will see a bow wave and stern wave with a trough between the the two. The longer the boat, the longer this wave. The theoretical hull speed is limited by the speed of this wave as it advances through the water. The longer the wave, the faster it can travel.
Planning hulls, where trim tabs are common, climb up on top of all this and have no such limit.
This may be more than you cared to know, but here is what Wikipedia says about hull speed:
Hull speed, sometimes referred to as displacement speed, is a rule of thumb used to provide an approximate maximum efficient speed for a hull. It is only ever an approximation and only applies where the hull is a fairly traditional displacement design. It is usually described as a speed corresponding to a speed-length ratio of between 1.34 and 1.51 depending on which of the limited sources one refers to.
In English units, this may be expressed as:
v \approx 1.34 \times \sqrt{LWL}
where:
"LWL" is the length of the waterline in feet, and
"v" is the speed of the vessel in knots
AJ
Only sailors and trawler captains need to know this stuff and it is kind of tedious for go fast guys, but here goes.
If you look at the side view of a displacement hull as it moves along, you will see a bow wave and stern wave with a trough between the the two. The longer the boat, the longer this wave. The theoretical hull speed is limited by the speed of this wave as it advances through the water. The longer the wave, the faster it can travel.
Planning hulls, where trim tabs are common, climb up on top of all this and have no such limit.
This may be more than you cared to know, but here is what Wikipedia says about hull speed:
Hull speed, sometimes referred to as displacement speed, is a rule of thumb used to provide an approximate maximum efficient speed for a hull. It is only ever an approximation and only applies where the hull is a fairly traditional displacement design. It is usually described as a speed corresponding to a speed-length ratio of between 1.34 and 1.51 depending on which of the limited sources one refers to.
In English units, this may be expressed as:
v \approx 1.34 \times \sqrt{LWL}
where:
"LWL" is the length of the waterline in feet, and
"v" is the speed of the vessel in knots
AJ
01-20-2010 | 04:27 PM
#7
Thread Starter
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Joined: Nov 2007
Posts: 432
Likes: 9
From: The River
Your buddy the diesel mechanic is confusing planning hulls with displacement hulls. They are quit different in how they move.
Only sailors and trawler captains need to know this stuff and it is kind of tedious for go fast guys, but here goes.
If you look at the side view of a displacement hull as it moves along, you will see a bow wave and stern wave with a trough between the the two. The longer the boat, the longer this wave. The theoretical hull speed is limited by the speed of this wave as it advances through the water. The longer the wave, the faster it can travel.
Planning hulls, where trim tabs are common, climb up on top of all this and have no such limit.
This may be more than you cared to know, but here is what Wikipedia says about hull speed:
Hull speed, sometimes referred to as displacement speed, is a rule of thumb used to provide an approximate maximum efficient speed for a hull. It is only ever an approximation and only applies where the hull is a fairly traditional displacement design. It is usually described as a speed corresponding to a speed-length ratio of between 1.34 and 1.51 depending on which of the limited sources one refers to.
In English units, this may be expressed as:
v \approx 1.34 \times \sqrt{LWL}
where:
"LWL" is the length of the waterline in feet, and
"v" is the speed of the vessel in knots
AJ
Only sailors and trawler captains need to know this stuff and it is kind of tedious for go fast guys, but here goes.
If you look at the side view of a displacement hull as it moves along, you will see a bow wave and stern wave with a trough between the the two. The longer the boat, the longer this wave. The theoretical hull speed is limited by the speed of this wave as it advances through the water. The longer the wave, the faster it can travel.
Planning hulls, where trim tabs are common, climb up on top of all this and have no such limit.
This may be more than you cared to know, but here is what Wikipedia says about hull speed:
Hull speed, sometimes referred to as displacement speed, is a rule of thumb used to provide an approximate maximum efficient speed for a hull. It is only ever an approximation and only applies where the hull is a fairly traditional displacement design. It is usually described as a speed corresponding to a speed-length ratio of between 1.34 and 1.51 depending on which of the limited sources one refers to.
In English units, this may be expressed as:
v \approx 1.34 \times \sqrt{LWL}
where:
"LWL" is the length of the waterline in feet, and
"v" is the speed of the vessel in knots
AJ
Thank again
01-21-2010 | 07:22 AM
#8
Charter Member #232
Joined: Oct 2000
Posts: 18,417
Likes: 6
From: Carlisle, MA USA
Tabs can actually slow you down. We put went from 280's to the long surgboards on the race boat and it actually slowed the boat down almost 5 mph even with them in the full up position.
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