What speed does air compression start to work on a cat hull

[franklins]

I am going to billed a cat hull next and I am wondering about a few things. One is if it is a 24 foot cat with a 7 foot beam would a single 250 or 300 have enough power to get the speed you need to get the air compression to start working.
The second thing I am wondering about is twinn 150s better then one 300 on a boat. I am trying to figure out the best way to go for cost whys and to get the most HP out of your money.
Thanks
Dean

[olmo40]

IMO ,Id limit a single engine to a 21ft Cat .Im just talking generally here .
The air entrapment you are talking about is dependent on several factors weight/ weight deitribution ,engines and setback etc etc ,generally in the 80MPH + range you start to get the feeling the hull is benefiting from air entrapment .Also turning engines in or out can effect this .

Tell us what you are looking to achieve and im sure some smarter people than me will chime in

[donmac]

are you thinking offshore or inland hull.

[97 TWISTER]

I have a 22' Rapid Craft Tunnel (790lb hull bare) I bought as a single engine boat,it ran mid 90's with a single 2.5 260. I rerigged it with twin 260's and it ran 115-120. I think a single 300 may be faster than twin 150's due to the wieght your adding with the second motor and all of its rigging. If I had my choice I would do twin 280's, plenty of power plus a good charging system. As far as packing air most of the tunnels I have owned start packing air about 75-80 but don't have enough lift unit mid 90's. IMO save your money up and rig it once with plenty of HP and you will have the boat you want. You may want to post in rigging and set up for some more input.
Good Luck Jerry

[fastcat300]

Tunnels and a true cat are two different hulls,depending on the width of the tunnel and how much it compresses some cats will cruise at less than 50 mph.What hull do you want to rig?

[200VEGAS]

i am going to billed a cat hull next of your own design, or buy and rig. Like a LIBERATOR....[if your buying]

[WILDMAN]

I've noticed in every cat I've driven, that they start to lift at 55-60 mph. A single 300 will be quite a bit faster than two 150's.

[franklins]

I have been working with David Lemke on a design .So far I have gone 24 feet long 7 feet wide at the beam. The two side hulls are going to be v hulls with large pads at the back. The hull will be 36 inches a the deepest point witch has worked great on my last two hull for the great lakes and St.Clair river.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
This is what I have learned so far with my boat building.<o:p></o:p>
My wood hulls are very light and float in very little water.<o:p></o:p>
The longer and narrower I have gone has given me a much smother ride.<o:p></o:p>
I have gone from 18 degree to 22 then 24 degree and each time smother ride.<o:p></o:p>
With a 250 Vmax Yamaha I am getting 62 mph in my 23 foot 7 foot wide 24 degree v hull.<o:p></o:p>
Now my questions are if I get that speed on my last boat turning a 23 pitch prop would I do better speed on a cat hull similar size?<o:p></o:p>
Would the tunnel with air traveling through it lift my boat so that I could put more HP pushing me forward rather than trying to hold me up and push me forward?<o:p></o:p>
Is this how a cat works or am I thinking wrong?<o:p></o:p>
You can see I really don't know what I am doing with a cat but watching you guys drive them they look amazing. They look like they fly across larger holes and are much more stable on rough water. I was watching them this year racing on <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:place w:st="on"><st1:PlaceName w:st="on">St.Clair</st1:PlaceName> <st1:PlaceType w:st="on">River</st1:PlaceType></st1:place> as we fished our bass tournament and they were flying across 4 foot holes like they weren't even there.<o:p></o:p>
Any way any help would be great.<o:p></o:p>
I don't even no if I am understanding how they work but they look like allot of fun to me.<o:p></o:p>
Thanks<o:p></o:p>
Dean<o:p></o:p>

[franklins]

Sorry about my last postsing. When I posted the weard thing in the spelling poped up.
Dean:confused:

[200VEGAS]

Ha, i can barely write. There is a article on the home page of this site but i think ive tried to get into it and couldnt. It sounds like you have like a glacier bay style boat. I didnt think something like that would go 60. I thoght they were like semi displacement or so, almost. IM ACTUALLY FROM UP THERE ON ANCHOR BAY MAINLY, BUT WORKED ON THE NAUTICAL MILE BACK IN THE 70S. IVE SEEN THOSE 4' HOLWEDS OF WICH YOU SPEEK. WE WENT OVER ONE IN A 15' CHECKMATE AT ABOUT 50 ONCE. THAT WAS EXCITING, I NEVER FORGET IT MY FIRST NEAR "OH ****!!!!!!"

[us1]

The lift all depends on the design and dimensions of the tunnel vs. the weight on the boat. Do you have the tunnel boat design software. Its great.
http://www.aeromarineresearch.com/

[ripstop]

I can definately feel the effects of the air on my Cougar 22mtr anywhere from 50 mph onward. Just turn it into the wind and watch your speed climb!

[franklins]

Thanks guys for the info it sounds like a single will be the way to go and I think I should get enough speed to give me lift with the tunnel. I don't think I will have much trouble getting up to 60 mph unless a cat hull drives hard through the water. How much back set do you guys have on your boats to hang the motor on or do you hange directly on the hull it's self? I guess hanging on the hull though would be hard to move motor up and down on different water condtions.

[Jimboat]

Have a read thru the article "what makes a tunnel boat work" (http://www.screamandfly.com/home/hull_tech/tunnel_hull_tech_1/tunnel_tech_1.htm) on this site. It may help clarify the relationships of aerodynamic Lift/Drag and other forces working on a tunnel boat.

Or see the full book on "Secrets of Tunnel Boat Design" (http://www.aeromarineresearch.com/stbd2.html).