controlliner

Has anyone bought a Dumas Big Swamp Buggy lately? Are the kits now laser cut or are they still the ungodly Die Crunched?

Got RPM

Don't know, but the one I built 30 years ago was "die cut", meaning smashed by a dull butter knife. Not sure why they would change, where they mention how the current kits are cut there is NO mention of laser cutting. Over the years I have built four Dumas boats, while they can look good they were heavy and the cutting was mediocre. How they justify $150 for a kit is amazing.....


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1QwkSport2.5r

I'm surprised anyone wants to still build the BSB anymore. The one I had ran and handled like crap as built from the kit except with lighter building materials. It ran better with the bottom converted to a flat bottom (1/8" Lexan covering the keel/rake), but it still didn't hold a candle to my Kamikaze flat bottom boat I scratch built. The Selph Inflicted tapered flat bottom .40 series boat is a nice running boat... I built one of those too (from scratch) - it handles great on water, but not as good on grass. No longer available as a kit, but the plans are available from some folks. Chris Selph is out of the RC airboat hobby now and his airboat forum is no longer running unfortunately.

controlliner

I agree it performed like crap, I especially hated the fact that the "no trip chines" did not prevent a tip over. But...As you stated, I want to build another one with no tunnel hull. Mabe it would slide better on the turns. I plan to put an Enya 60 III on it. I would really like to build a Cajun Gator too, but sourcing nice hobby grade plywood is a drag.

1QwkSport2.5r

The Cajun Gator boat is a drag - a friend of mine built one brushless/LiPo powered and couldn't get it balanced to run right. It would hopelessly spin out. If I were looking to build a flat bottom boat intended for water only, I would scale up the SI tapered flatty.

sublunacy

i like building mine if your up for the challeng - its maybe NOT for novices / i dont know. i built a .46 rv4 by great planes first. the hard part with the bsb is waterproofing the tunnels and using 150 dollars worth of epoxy... it is under appreciated because this is dumass best airboat and it is better with 4 stroke motors turning 3 blade props. however dumas should have made something for the speed demons looking for nonscale type performance.

passing 30mph out of the box needs a totaly different hull......or a smart builder. you could get flat bottomed dumas airboats that are nearly the same size as the bsb. its just a boat... pick one and face reality head on.

Got RPM

Two-month-old thread, but I'll bite. I built one about 25 years ago, sealed it with 3/4 ounce cloth and thinned epoxy - not that expensive to do, not difficult and never leaks. I mounted a Fox .45 and a 10x6 prop, timed it at about 37 mph through the club's timing traps. When on plane the tunnel hulls will run faster and turn better than flatties.

I did change the motor mount to a monopod with zero angle with twin rudders. The CG position was also critical, mine ran best at 25%. The boat did not turn well until it got OB step, the it hauled...for the time. Prop choice was critical, a 11x7 just didn't cut it. It has to match the engine's power band.

Dumas kits are crude compared to many other makers, which is sad because many of their designs are very good. Wood quality is mediocre, and the die cutting is......terrible. But with patience they can be built into decent models.


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sublunacy

cg at 25 percent sounds good. i here that if you make the engine level and move the prop forward an inch it will be a more neutral steering and slide in the corners more and less overpowered by the tunnel hull. an inch forward brings the prop to 50 percent of the flat bottom before the hull curves up towards the front.

reports are the hull can handle a 10cc gas or nitro engine if i have it right/ like a .91 maybe. that sounds like 10cc to me. the extra weight keeps it planted on the water for i believe / kick ass acceleration and respectable top speed

Got RPM

A tunnel does slide in a corner like a flatty does, it is designed to hook up tight around the buoys. There is very little weight difference between similar 7.5 and 11 cc engines, for example just 11 grams difference for OS engines. The advantage of the greater displacement is the ability to spin a larger diameter/higher pitch prop - but that means the larger engine has to be mounted higher. I think that either engine is a good choice for the careful builder, but the 11cc OS engine is $50 more than the 7.5.

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J330

My Feedback: (3)

As far as the cut, I'm sure they turned over the butter knife by now? I'd bet money it's still got rough edges and requires lots of filler and sanding. It's not like it's a big seller deserving upgrades in manufacturing. What masochistic experience building these boats were/are. Never liked the tunnel quirky feel, digging in and turning faster than I wanted it to, fearing a flip and water soaked engine. I never ever saw a tunnel ever slide, not on a Dumas.

I bought one here on RCU years ago and that was the only one that worked like no other. He filled the tunnel and made it flat bottom for a much more pleasurable feel, like the real thing. If you're set on doing this, I highly recommend that mod, and as always, keep your fishing rod handy.

sublunacy

hey genius. a flat bottom dumas bsb is called a dumas windy.

J330

My Feedback: (3)

The Dumas I had took a .60, twin rudders. Not a puny .10 - .15 sized airboat for swimming pools. For more information, http://www3.towerhobbies.com/cgi-bin...P=ML#technotes \

The .19 Swamp Buggy that I started in RC back in 1977 with (2 channel radios were all I could afford as a teenager), also had a flat bottom. Removing the strakes on the hull really made it slide. It was more fun than the BSB, especially with a .32-.40 on it. Kept it until 2005 when I ditched my fins for wings.

Edit:
Pictures added of the .60 that was converted over to a better hull. I also covered the "bird bath" on the top deck as it serves no purpose but to catch more water, if you use a .60 that is. Height changes aren't needed with a 10X8 prop. As I recall raising the height of the rudders did a better job. I used a Webra Speed .60, today you'll just have to settle for O.S.

sublunacy

maybe if you tried moving the prop forward 1 inch for water you could debate a boat designed to walk on land. im entitled to my critisism same as you seem to throw around. i like the hull limitations.

J330

My Feedback: (3)

Here is a modified BSB on youtube with the tunnel filled and note the slide in turns that's perhaps a preferred behavior of the boat for many. https://www.youtube.com/watch?v=l12QLxWGrdU

Also note all the things immediately wrong with "moving the prop forward an inch" with the mod mounting, servo compartment, and not to mention the negative impact it would have on the rudder's effectiveness.

The flat bottom mod makes the boat much drier a ride for the prop too if you compare videos of the same model without the improved hull. He also enclosed the "bird bath" compartment as was the case with the big swamp buggy I had. No point in leaving anything open on these in the event of a flip which eventually will happen with speed and waves.

sublunacy

i apoligize/ if you need help with engines or whatever let me know. i have been the authority at many forums for 5 years running while i polish my diploma in the field. the best? no but whos going work for free? i cant find better on any continent. this avid bmx rider can tell you the bar is set very low.

motorhead540

Been reading up on these as much as possible I am getting ready to be putting one together . hope to be using a 12 X 6 3 blade on a e-flite BL-50 on 6S3000-4000 packs i'll try to get some pictures of it soon

Got RPM

Success with electric power depends on the motor size and Kv. What is the Kv of the BL-50 you intend to use? If it is the 525 version, eCalc predicts about 9 pounds of static thrust and 60 amp draw. Pitch speed is a bit low at 60 mph, figure abut 40-50% efficiency at best. Going to an 8” pitch raises thrust to over 11 pounds with a pitch speed of almost 80 mph and a 65 amp draw.


BTW, I noticed a typo in my previous post. I meant to say the boat does NOT slide in turns. Sorry it took so long to correct!


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motorhead540

I do not understand how it can be at 60 amp draw still . The stock setup in the Carbon Z Cub where this motor came from was a 15 x 5.5 prop and it only had a 60 amp esc from stock
why is it that battery 6S3000 and motor being same and dropping 3 inch in diameter I would still have so much draw . I have never played with e calc just tried and did not find a place for just getting motor and prop numbers and do not find the e flite BL 50 on their list ... I do believe it is a 525 kv . Just hoping to build a cool project from my extra left over aircraft parts ...

Got RPM

An airboat isn’t an airplane. Planes go fast enough for the motor to unload in the air, reducing amp draw. Airboats don’t go fast enough to have as much reduction in current draw.

Remember that eCalc is just modeling software, not an actual motor and prop. I find it quite close most of the time, but not always. Still, it is far better than just guessing. I use it to get close in prop and motor sizing, then actually test in the boat to find the best prop.


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Prohack01

I picked one up last year that needed some work, I replaced the undersized 2 stroke with an fs70, alil over powered, 60 fs is probably about right but still fun on grass and snow. I'd like to see some close ups of the flat bottom mod, as I would prefer this for water. I am not sure I understand the easiest way to convert this model to flat bottom, esp with the comment above 1/8 lexan, I have 1/4 lexan but not sure how to do it, can I just epoxy it in the Tunnel? I was thinking about addin gtrim tabs to help with the hop it gets at high speed.

SWAMP_RAT

If you look at my gallery you can check out my SWAMP RAT airboat. These are superior to the Dumas boat and handle better on the water, grass. I built these boats myself. They are built for the .61 and .72 IRVINE engines as well as the OS .65 series.

1QwkSport2.5r

Will they handle Dub Jett engines with full tuned pipes? I like to go fast.

SWAMP_RAT

The motor mount will handle the .65 and the .72. When i make them i leave them undrilled so they can be cut and drilled by the end user. I also can make the width of the mount custom to accommodate the engine required.

1QwkSport2.5r

Eh.. I’ll pass.