Active tunnel wing for cat

[Ralf]

I agree with randy.
I put such a tap on a 138 mystic which was extremly light, 7.8kg running 100-110mph.
The tab had no effect on the bow. It simply liftet the whole boat out of the water, running on the props only at 70amps per motor.
Nice but lot of risk.

I think it helps heavy boats lacking on lift. Helping to surpress blow overs not very much help.

[bonewar]

Bonewar has returned...

hi guys,
i thought i'd better come back and finish this M12 Cat.
This is where im at with it...192086107_1805127792993652_474868245117797552_n.jpg191330304_1436884930008580_6029607181139569850_n.jpg191517671_1165872393930189_2917570307827014486_n.jpg191571094_329370991910692_239319655111433984_n.jpg5586.jpg

[Fluid]

Glad you?re back with an update - but that last pic is over 10 years old….

F9D6B150-E526-4B44-B0D5-355507D5A178.jpg







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[bonewar]

Fluid, I took all the pictures of the Boats this morning mate.
They have been sitting in there wall mounts this whole time.
Just waiting on me to pick up interest in them again.
I love just looking at them.
They look Fast?.

[bonewar]

Hay I just noticed the date on the pic, I don?t no how that got in there.
Bit rusty on adding the attachments to my posts..
Good spotting mate.🤘💀

[hughb]

They look bloody fast Bonewar! Love to see some Aussie offshore cats, and they look like scale replicas too!

[bonewar]

cheers buddy.

[rufus2000]

I like the cat in the middle (the one with the simrad logo), where can I get one of those?

[Old School]

Just giving this some thought, why do cats have such large foredecks? Sailing catarmarans achieve some phenomenal speeds and utilise a trampoline forward of the mast to I presume prevent pressure building up under the deck. Some earlier models with solid foredecks even had blowout panels to relieve pressure. Could a power cat have a shorter foredeck to prevent excessive pressure build up prior a blowover or perhaps replace the foredeck with a spoiler to maintain a down force on the nose?

[NativePaul]

For speed in a straight line I believe. For a given amount of lift a long narrow tunnel has less frontal area and thus less aero drag.

I have built several cats with much shorter tunnels and longer pickleforks than is usual, as well as moving the centre of lift back closer to the centre of gravity, it also allows a wider tunnel for the same amount of lift, which was good for me as I wanted to prioritise handling as I was racing on a more or less square course at the time.

[Fluid]

Just giving this some thought, why do cats have such large foredecks? Sailing catarmarans achieve some phenomenal speeds and utilise a trampoline forward of the mast to I presume prevent pressure building up under the deck. Some earlier models with solid foredecks even had blowout panels to relieve pressure. Could a power cat have a shorter foredeck to prevent excessive pressure build up prior a blowover or perhaps replace the foredeck with a spoiler to maintain a down force on the nose?

Catamarans are air compression hulls, like hydros using air rather than just water to lift the hulls out of the water, reducing drag and increasing speed. Sailing cats don?t weight nearly as much as a powered hull of similar size, and when running with the wind there is less air passing between the hulls to be compressed anyway. It?s no surprise they lack large decks as they woukd provide little if any advantage.

Full-scale cats need long decks to trap enough air to counteract their weight, but model cats may not need as much particularly if they are very fast or lightweight. Like Paul I?ve built cats with shorter decks to move the center of pressure back to reduce drag while also reducing the risk of blowovers. One of these held the top cat SAW record for years. The downside is that the resulting hulls are just not as aesthetically pleasing as are scale models.




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[larryrose11]

I worked with a fellow in the past that was having lift issues with his cat. We came up with the idea of using a Diffuser like in race cars. It worked!! He got past the blow overs and was able to run his struts back down to zero degrees (previously a few degrees negative)
Difuser_3.jpgDifuser_4.jpgDifuser_5.jpg

[Steven Vaccaro]

I worked with a fellow in the past that was having lift issues with his cat. We came up with the idea of using a Diffuser like in race cars. It worked!! He got past the blow overs and was able to run his struts back down to zero degrees (previously a few degrees negative)
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Thats wild, how did you come upon that particular design?

[Fluid]

I can’t say what inspired him, but similar tunnel extensions have been used on a few OPC models for many years. I used adjustable trim tabs on several of my record-setting SAW cats which performed the same function. The faired tub is pretty cool.

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[fweasel]

Thats wild, how did you come upon that particular design?

That's Mike W's bulgarian cat. It's a triple digit, super stable runner and has a lot of body work done to it. He sectioned the entire hull and made it lower profile, in addition to the diffuser design Larry Rose came up with.