Aerodynamic Q: Which Sponson Has Less Lift

[Meniscus]

I'm trying to determine which sponson design has less lift at around 64-65mph.

A or B???

Sponson-Lift.gif

[RaceMechaniX]

my guess is B

[T.S.Davis]

My uneducated penies worth.

Neither of those is actually making lift. Lift is the result of negative pressure on the top side.

Those two will pack air. Each a little different. The pressure pushing up on the sponson on the lower one will be further forward giving that force more leverage if the trailing edge of the boats are the same distance.

Wild behind guess though.

[fatboyelectric]

My answere is B as well

[m4a1usr]

Sponson AOA has far less effect then tunnel AOA. If you look at the fastest hydros they have more sponson AOA then slower hydros. Its all due to ride surface. The need is for less contact with the water. Its that simple. But its the trapped air under the hull where the pressure builds that you want to minimize or disturb to keep the hull planted. Between your 2 choices I wouldnt judge on sponson AOA alone to determine which is faster.

But that wasnt your question. You asked which has less lift. I would have to say B as well.

John

[sundog]

Definitely B. The longer arched surface on the bottom will tend to pull it downwards more than the shorter straight surface.

[U1Racing]

sponson angle of attack is what determines lift of a sponson, shape really doesn't have much to do with it at all.

[Meniscus]

Thank you all for comments. I am modifying a hull to allow for more speed and stability. AOA will remain the same, but I'm looking at different elements to help reduce lift/increase ground effect without adding additional drag, all for the purpose of increased speed and less chance for blow-over.

I'm specifically looking at adding material to the front of the sponson to create this effect. I just wanted to get some confirmation before I go through the painstaking task of making this modification.

In a perfect world, I would just reduce the angle on the deck, but that isn't feasible, so I'm looking at other elements. It seems that I've hit max speed for this hydro hull, even with a skip/plow setup to the point where it has come down to diminishing returns. I'm sure that I can pull in another mph or 2 in the prop, but the hull won't take it without adding considerable amount of weight, say up to 3-4 oz. additional to handle the 3 mph more.

Where's a wind tunnel when you need it? I guess at some point I'm going to have to spring for some drinking straws for the poor man's version in the shop!

[Boaterguy]

I'm assuming the shape of B would act as a slight air dam, therefore less lift

[U1Racing]

if you want to change AOA, you could make up some tape on ride-pads, to try and if it worked then you could make a pair and solid mount them, fill it then paint it and no one would know that you have a set of ride-pads on your boat!!

[Meniscus]

Thanks, but I'm not looking at changing the AOA. Instead, I'm trying to determine if I can change the shape of the sponson to reduce lift.

[Boaterguy]

what hull type is this going on?

[Meniscus]

Hydro, not rigger, but did want the info for a few other models to include a rigger.

[Boaterguy]

well, a hydro would have more lift from the tunnel, and a rigger doesn't usually have enough lift to be a problem, usually sponsons are more concentrated on riding on the water, more AoA will lift the boat out of the water and have less contact - less friction

[Meniscus]

I wasn't planning on going through the details, but this hydro currently blows over at 62-63mph. I've tuned in as much as I can to keep her planted without simply plowing. I'm looking for a few more mile an hour, but can't get there without making mods to the hull. Consequently, this is one of the areas where I'm looking to set her down.