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New to Raingutter... need pics!

Posted: Mon Aug 07, 2006 10:13 pm
by Teeeman
Anybody got pics of Catamaran designs?

I've read enough to know we are building the cat...

I have a laminar flow formula tucked away somewhere at home, would be awesome to scale it to our 2 pontoons and then try (with a Dremel) to match the profile. This is a declassified Navy high-speed torpedo design :)

I got a gazilion questions:

Should the boat track level with a steady air stream, or try to picth up at all?

Side bumping... plan for it or try to avoid it?

Pontoons = Balsa (BSA kits)... what to use for deck?

What kind of glue?

Sail design: We want max force, minimal drag and the force center (center of pressure?) as low as possible to the deck... anybody got suggestions?
Would something akin to a parachute (soft, collapsable) work? Can you (like a parachute) vent the "expended" air with vents in a way to further reduce drag?

Sail design: What material works best? We are trying to minimize boat weight.

Pontoon design: Does a pointy nose really buy any less hydro-drag? I am worried about having the nose (if tapering to a point) try to dip in the water... is this overcome by weight placement and sail placement?

Where to put the sail?

Are alternative materials to balsa allowed?

Any other thoughts? We are 200% new to this and our old Nemesis purposefully requested an "open" class to allow pre-built regattas to what was supposed to be a "build day of race" event.

Now that the white glove is on the ground, we need to respond (as we have in PWD and Cubmobile with success).


Re: New to Raingutter... need pics!

Posted: Tue Aug 08, 2006 12:40 am
by gpraceman
A good place to start is

Re: New to Raingutter... need pics!

Posted: Tue Aug 08, 2006 3:23 pm
by Teeeman

Just what I wanted, the "skip to the good part" version :)

I really didn't want to have to buy 12 kits and build them all and sail them in the bedroom at 4a.m. (sorry, having a Down and Derby flashback....)...


Just found out I get to help create our rules :)

I will use the on-line rules and maybe add a few things to keep it simple and see what the communal vote is with our leaders.

any ideas on straws for blowing?

Water depth, timing or judging the event?

All help appreciated!


Re: New to Raingutter... need pics!

Posted: Wed Aug 09, 2006 4:53 pm
by Da Graphite Kid

I've only seen one Cat at a RR race in person but unfortunately my cameraman was more interested in something else besides taking pictures and we didn't end up with one of this boat. Don't know if you would want to copy it as it did not do so well due to trying to nose over when raced. It was adult built (Leader) out of only one RR Kit plus I think two popsicle sticks. I think he had the sail/mast too far forwards.

Torpedo design? I think that you will find on the Lastufka site that you want to build a planing type hull and not a displacement type hull - you want it to get up on plane and run across the top of the water and not through it.

I think that the bow pitching up is preferred having worked around Bass boats for 20+ years. They are basically speed boats with trolling motors (though I've never caught a fish while running 70+ mph...) and are shaped to get 'up on plane' as quickly as possible.

If you can get the boat to plane out I don't think that side bumping is a concern. At least it wasn't on the boat I raced some 3 - 4 years back (I could generate more wind back than! :mrgreen: ).

We use 5 minute epoxy but only needed to attach the mast, rudder and keel. I think the guy that built the Cat used white glue or possible a wood glue but it was sealed with paint and so did not come apart.

Sail Design - we are restricted to the RR Kit as our non-Cubs race under the same rules as the Cub Scouts do. However, I would think that you want the sail as low as possible so as not to make the boat any more top heavy than it has to be. This may factor into your material and shape choices as well. We had a Cub Scout show up this year that had put glitter everywhere including the sail. After two runs, we got him to switch his sail out for a plain plastic one from a new kit. Before all it would do is keel over; with the undecorated sail he actually did quite well as it would remain upright.

Pointy nose? The stock RR Kit hull is pointy but I don't think that this is the best design. If it were flat and angled as to pitch the bow upwards the boat should get on plane that much faster and with less effort. Once up on plane the boat will be guided by the direction of wind blowing it, the keel/rudder and the sides of the raingutter - so who needs a pointy nose or a pointy centerline on the bottom of the hull?

We try and put as much weight rearwards as possible, so the mast gets moved back to about an inch - inch and a half from the rear. Wait a minute: that weight placement deal sounds somehow familiar...

Replacement for balsa - We are stuck with the kit but I think you would only find something like plastic would be as light and as strong as balsa. Hmmm, thermoformed RR boat hulls...

Straws - Our Pack supplies the straws for our races. This was done because some were showing up with larger diameter straws than others which may be an advantage or not. I will warn you about the straws with the bend in them: the ones we found cracked at the bend joint after minimal usage. I'm sure the boys had flexed them quite a bit before and after their races and this only added to the number of straw failures. We use straight straws now because of this.

Water depth? We fill our PVC Pipe "raingutters" to the brim!

No timing - all heats are judged by someone on each side of the finish line. The first boat to touch the end is the winner. We used flags this year to help indicate which boat won. This kept the record keeper from having to hear the finish line judges over the laughter and cheers. Since we have one Blue and one Gold (okay, its really yellow...) raingutter/PVC pipe; each finish line judge had one blue and one yellow flag. It would have worked perfectly too it that big oaf of a judge we had would have raised the correct flag (name withheld because he is typing this message :mrgreen: ). Both finish line judges raised the color flag corresponding to the lane that won. If both did not agree; we first made sure that I raised the correct color flag :lol: , and if they still did not agree the boys re-ran that heat.

Da Graphite Kid

Re: New to Raingutter... need pics!

Posted: Fri Aug 11, 2006 10:17 am
by Dad of 3
Teeeman you need adjust your frame of mind for RR. Its true the catamaran design gives you a huge benefit but everything else pales when you consider blowing techniques. If you are using a fan then it doesn't matter but most have the boys blowing their boats. Work with your son to breathe from the diaphragm to get a big breathe that he can sustain. In the heat of the competition the natural tendency is to take quick short breathes and blow too hard. When you blow too hard as the boat starts the nose dips below the surface which really slows you down. Blow gently at first and as the boat increases speed you can blow harder. With a lot of cheering and other noise distraction it takes discipline to concentrate on proper blowing techniques. A poorly designed boat can usually beat a well designed boat if the boy with the poorly design boat knows how to blow his boat properly. With regards to boat design let your common sense guide you. Rear weight to offset the leverage from the sail. We just use popsicle sticks for the catamaran deck, remember not to make it wider than the gutter. Yes lighter is better just make sure it isn't top heavy (not usually a problem with the catamaran). Good Luck and have fun.

Re: New to Raingutter... need pics!

Posted: Fri Aug 11, 2006 10:59 am
by jasncab
Wow this is awesome! And something I can do with my daugter here locally.

I raced these as a young boy in boy scouts. I remember how much fun it was and cutting my hand on the gutter. It was fun, interesting, clean and I suppose the kids have fun too ;)

Just picked up a PWD kit, I think I will start looking at some RR designs and gutters.

We dont have gutters on our houses here, and I havent even seen them for sale at the home depot... An odd delima. where to buy a rain gutter in AZ.

Re: New to Raingutter... need pics!

Posted: Sat Aug 12, 2006 7:16 am
by clemsontigerfanatic

I went with these plans . They worked great . We had a great time.
I'd recommend a Hot melt glue gun.

Any straw will work with these. The race does not near as long as the regular boats

Just have to make sure you don't make the boat too wide for the gutter.

Re: New to Raingutter... need pics!

Posted: Sun Sep 10, 2006 11:58 am
by Teeeman
Quick question:

The cats have very wide-hull pontoons... and very little space down the middle...

would the design evolution simply not be a flat-bottom hydroplaner?

The cats almost appear to be simply to small hydroplane styles tied together...



Re: New to Raingutter... need pics!

Posted: Tue Sep 12, 2006 10:07 am
by BigSilver
Great cat picks and movies!
As for the laminar flow pontoons you are likely referring to the extended laminar flow hydro shapes developed by Bruce Carmichael at NASA. The laminar flow shapes may not help much but they would look cool! You will need to use the transform equation from 2d to 3d if you use the profiles from "The theory of wing sections" book to get a true laminar flow body shape for the pontoons. As for improvements to the cat design, I am wondering if a covered forward deck could help a bit in popping the front of the boat out of the water and up on plane if the air entering the sail is allowed to “inflate” or pressurize the forward area between the hulls under a covered deck? AKA air cushion vehicle???? Try a search for the Caspian sea monster on line….

Re: New to Raingutter... need pics!

Posted: Wed Sep 13, 2006 2:12 pm
by BigSilver
More fun with lifting body ships..... 8)

Re: New to Raingutter... need pics!

Posted: Thu Nov 08, 2007 1:17 am
by pcar993
how wide can you make a catamaran?

And i was thinking of cutting a styrofoam cup in half and using it for the sail. Any thoughts? good, bad, experience....