Weight Sensitivity

[5T]

So, I wanted to know if all ski boats are weight sensitive? Is this common? Does it occur in wake boats? I'm asking because of the Sport Nautique 200 V. I rode it in recently and was disappointed in how easily it was affected by people sitting in different seats and the lack of stability I sensed in it. So, I wanted to know if my expectation of having a stable ski boat is unrealistic? Any thoughts?

[AirTool]

So, I wanted to know if all ski boats are weight sensitive? Is this common? Does it occur in wake boats?

Every floating vessel is weight sensitive....some more so than others. In the case of the "ski" boat....a lightweight shallow draft vessel with a hull designed to ride on top of the water to reduce wake, it will be very sensitive. Further, the draft is reduced significantly with speed. The force of the passing water lifts the hull. the pressure is generally consistent across the entire hull. If you add weight in any area, it will clearly not be lifted the same amount. Wake boats less so because they weigh more (especially with ballast). But nevertheless, there is always some equilibrium point for a given weight and center of gravity. If you change the CG, the equilibrium solution changes.

Now take me for example (in two ways) 1: I weight 280 lbs and my ski boat weighs about 2800 lbs. So I'm approximately 10% of the total mass. With just me in the boat and pulling a boarder at 18 mph, my "goofy" son loves the starboard wake due to me and the prop rotation. The other side is rolling foam. When my "regular" daughter is behind, I drive from the spotter seat and cater to her side. I can generally sit just port of center and make perfect wakes on both sides. So, moving 10% of the mass around makes a big difference.

Now the second example. 2: I work in the offshore floating platform engineering and construction business. If someone wanted to make a design change that moved 10% of the mass from one side of the platform to the other, we'd go through a significant "management of change" process for that. That would be considered a big deal...and too far along in the process, it is probably not going to work (depending on the hull form). If the platform has a drilling rig, even moving the rig from one well to another creates another design case to consider. Say a platform is 250 x 250 feet, moving 20% of the payload over 10 feet requires analysis and a change is ballast to stay within the motion limit criteria.

So...floating vessels are weight sensitive.

I still have several videos from INT Texas in a sport V. I (and every rider) was not impressed with the wake and it was very weight sensitive. Only factory ballast so another ton of ballast would have helped. I will try to post the videos...but very busy right now.

[DanielC]

Yes, it is common in ski boat to be weight sensitive. That is why Correct Craft puts a right hand propeller on the ski boats. Propeller torque balances against the drivers weight.
With the wake boats weighing more, and having ballast, that you can load differently from side to side, the weight location is not as critical.

[AirTool]

..... That is why Correct Craft puts a right hand propeller on the ski boats. Propeller torque balances against the drivers weight.

DC - thanks for the correction. It is me minus the prop. Not me "plus" the prop.

[5T]

Great explanation. Thanks for taking the time. So, sounds like this is common for ski boats

Every floating vessel is weight sensitive....some more so than others. In the case of the "ski" boat....a lightweight shallow draft vessel with a hull designed to ride on top of the water to reduce wake, it will be very sensitive. Further, the draft is reduced significantly with speed. The force of the passing water lifts the hull. the pressure is generally consistent across the entire hull. If you add weight in any area, it will clearly not be lifted the same amount. Wake boats less so because they weigh more (especially with ballast). But nevertheless, there is always some equilibrium point for a given weight and center of gravity. If you change the CG, the equilibrium solution changes.

Now take me for example (in two ways) 1: I weight 280 lbs and my ski boat weighs about 2800 lbs. So I'm approximately 10% of the total mass. With just me in the boat and pulling a boarder at 18 mph, my "goofy" son loves the starboard wake due to me and the prop rotation. The other side is rolling foam. When my "regular" daughter is behind, I drive from the spotter seat and cater to her side. I can generally sit just port of center and make perfect wakes on both sides. So, moving 10% of the mass around makes a big difference.

Now the second example. 2: I work in the offshore floating platform engineering and construction business. If someone wanted to make a design change that moved 10% of the mass from one side of the platform to the other, we'd go through a significant "management of change" process for that. That would be considered a big deal...and too far along in the process, it is probably not going to work (depending on the hull form). If the platform has a drilling rig, even moving the rig from one well to another creates another design case to consider. Say a platform is 250 x 250 feet, moving 20% of the payload over 10 feet requires analysis and a change is ballast to stay within the motion limit criteria.

So...floating vessels are weight sensitive.

I still have several videos from INT Texas in a sport V. I (and every rider) was not impressed with the wake and it was very weight sensitive. Only factory ballast so another ton of ballast would have helped. I will try to post the videos...but very busy right now.

[NautiUT]

The sport 200V is a left hand. All Nautique V-drives are left. The DD are right. Just to clarify.

[jc]

All boats are weight sensitive. My bud's 230 fully loaded with stock and extra ballast still needs to be adjusted accordingly. 1 passenger on the wrong side washes out the wake quick like.
Just a part of riding and skiing, there are always compromises.

[5T]

I'm not as much concerned with the weight sensitivity affecting the wake as I am with it affecting how the boat lists or leans. The Sport 200 literally leans to one side and pulls to that same side if you don't have perfect weight distribution. I could deal with a washy wake.