Air dam lose speed?

[kfxguy]

I haven't used an air dam but once long ago on a boat I wasn't chasing speed on a cheetah. Was just trying to keep it on the water so I don't know if it slowed it or not. My question is does an air dam on a cat slow it down to any measurable degree? I prefer not to lose any if possible.

[Darin Jordan]

I haven't used an air dam but once long ago on a boat I wasn't chasing speed on a cheetah. Was just trying to keep it on the water so I don't know if it slowed it or not. My question is does an air dam on a cat slow it down to any measurable degree? I prefer not to lose any if possible.

Properly done, overall it should be faster.

Remember, also, that what you are trying to do is kill lift... On something like a Hydro or Cat, especially, that's not just done underneath.

[kfxguy]

Thanks Darin. One more question, wiper blade? Velcro? Lexan? And how tall? Thx

[dmitry100]

pencil

[Darin Jordan]

Thanks Darin. One more question, wiper blade? Velcro? Lexan? And how tall? Thx

On my PT Stealth and on my old N2 sized Mystic, I used a piece of 1/4" Styrene angle. I've seen people use pencils, etc., or even fuel tubing in a pinch.

Just has to be something to break the airflow over the surface.

I watched several SAW CATs in LA blowing off the water run after run, even with airdams in the tunnel. I suggested they put them on the deck, towards the front, and after that they were making clean passes.

On Sport Hydros I've placed them across the tops of the sponson decks, etc...

[kfxguy]

On my PT Stealth and on my old N2 sized Mystic, I used a piece of 1/4" Styrene angle. I've seen people use pencils, etc., or even fuel tubing in a pinch.

Just has to be something to break the airflow over the surface.

I watched several SAW CATs in LA blowing off the water run after run, even with airdams in the tunnel. I suggested they put them on the deck, towards the front, and after that they were making clean passes.

On Sport Hydros I've placed them across the tops of the sponson decks, etc...

Thanks and good info!

[Fluid]

Darin is right, dams kill lift by creating drag (just like spoilers on cars). The bigger the air dam the greater the drag, and square-edged dams are more efficient than rounded ones. Most of the time a boat which needs an air dam has more than enough power to go faster, it just can't because it won't stay on the water.


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[dmitry100]

Darin, what do you mean by put them on the deck? You mean sort of like a spoiler in the front instead of blocking the tunnel?

[kfxguy]

Darin is right, dams kill lift by creating drag (just like spoilers on cars). The bigger the air dam the greater the drag, and square-edged dams are more efficient than rounded ones. Most of the time a boat which needs an air dam has more than enough power to go faster, it just can't because it won't stay on the water.


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Thanks Jay. I'm trying to find that balance right now. What I'm doing is having to give negative on the prop (which I think is less efficient) to keep the nose down which in turn causes more drag when it's running on the front steps too. I have two boats right now running exactly the same speed (98mph) and they both have the same strut position and almost the same props (one boat is 37" the other is 32" so the 37" has a larger version on the prop the 32" has). If I get them to run a tad drier then they start flipping.

[T.S.Davis]

I've seen Doug Jr. do this with a strip of tape. He folds it to make tee shape with the flanges stuck to the hull. Not a permanent solution but in a pinch on windy race day sometimes that little disruption is enough to finish.

[Darin Jordan]

Darin, what do you mean by put them on the deck? You mean sort of like a spoiler in the front instead of blocking the tunnel?

The deck is like the top of a wing... the top is actually where the "lift" is created. Slow the air down over that long, curved surface, and you'll kill lift. Think about which side of an airplane's wing the speedbrakes are located on... OR the roof-flaps on a NASCAR Super Speedway car...

Cat_Airdams.jpg

[modvp55]

An air dam under the nose that reduces air flow will also cause a loss of pressure at the rear of the tunnel thus allowing the transom to squat which can in certain conditions make a boat more prone to blow over. A properly placed dam on the deck will help keep the nose down while also adding transom lift.

[Beaux]

so would this work on my f1 sponson to sponson in front of the nose?

[SD Eracer]

My Genesis had issues flipping, mainly because we run in ocean water that has a mixture of strong current and wind. I had to drop the strut to the point it was slowing down the boat to prevent flipping. Even with the batteries far up in front in the sponsons and the ESC all the way to the front, I still had this issue.

However, once I stuck an airdam on the boat, I was able to put my strut up to even neutral, and actually picked up about 5-7 mph while no longer flipping.

So whatever speed I lost because of the airdam, I gained back in stability and better trim which resulted and even higher top speed (low 70s).

Here is picture of my airdam, its just a Kintec carbon fiber airdam for UL-1 ($10), which I cut down to fit my Genesis. I used 3M double sided outdoor tape to install it, has been there for over a year in salt water, hasn't come loose.

Airdam 1.jpgAirdam 2.jpg

[kfxguy]

Awesome!