WEIGHT DISTRIBUTION

[mark couty]

On a 1/8 scale hydro, do you want weight on the skid fin side of the boat or the opposite side. And what is the reason for it. Thanks.

 

[jwo]

You want the boat to be even. Equal weight on either side.

 

[Hydro Junkie]

I have to agree, even left to right or slightly more on the left if the left sponson tends to lift.

 

[glenng]

I have to agree, even left to right or slightly more on the left if the left sponson tends to lift.

I agree, I have two Scales- one a Modified Dumas PaynPak The other a glass MTO- the weight on the Pak is even- The MTO is biased to the right- and both lift the left sponson at the end of the straights- has not been an issue - as soon as you give it right rudder the fin sucks the boat back down . I'm more concerned with front to rear weight bias as I do not want the boat to blow off but want it to launch and get on plane easily.

 

[Hydro Junkie]

I have to agree, even left to right or slightly more on the left if the left sponson tends to lift.

I agree, I have two Scales- one a Modified Dumas PaynPak The other a glass MTO- the weight on the Pak is even- The MTO is biased to the right- and both lift the left sponson at the end of the straights- has not been an issue - as soon as you give it right rudder the fin sucks the boat back down . I'm more concerned with front to rear weight bias as I do not want the boat to blow off but want it to launch and get on plane easily.

This is also very true, but at the same time, the boat needs to be balanced so that air under the boat supports the boat as much as the sponsons and prop do. Too much weight up front will kill a boats speed quicker than the wrong prop

 

[Dasboatman]

Hey Mark,

Lots of factor to play with. Engine torque, prop walk, hull design and overall weight will determine what the boat will want. I've always believed it much easier to add weight as necessary - rather than try to reduce weight after the 'beasty' is finished. Give yourself some adjustability. A few ounces of stick on weght startegicly placed will give you immediate feebback after the hull is launched and up to speed.

Only boat I've built in 40 years of playing with these things, that I didn't play with weight in different areas was my Clasic Thunderboat (CT). I considered that calculated Luck rather than Skill. Could have very easily been a weight hangers nightmare. With a Scale boat - I like to run them all white first, figure out what needs to be added, bore a hole and implant in the hull. Nothing looks worse than a completed Scale boat with weight holes visible through a brand new paint job. I have had a new hull design not work out despite a lot of work doing some significant hull changes. The first MHR 8255 we built, turned out to be a Real DOG !!! Nothing Jack tried semed to make it even a moderate hull. Running it through a band saw numerous times helped it emensely. Jack's next, and my next received some serious 're-thought'. Jack's Speedy, and my Oberto were significantly different from the Gus #1 hull. Of those 4 hulls, only two are still around. Gus' Executone, and a heavily modified Randy' Miss Houston. Each boat since has been a revision of the previous Jack' or Bob's hulls.

I'd start with the CG of you Dumas Atlas maybe an inch aft of the sponson rear touch. Those hulls tend to be tail heavy when built. Some of the previous builders/ owners of Dumas hulls can give you a rough idea of how to balance it out. Start 'light' - - a 20# Scale boat ain't pretty to watch run. CHEERS !!! Bob

 

[Mark Anderson]

Mark

Go to a race and watch what boats do when they blow off. They always lift the left side first and roll to the right as they go over. This also happens in the corner usually just after entering the turn as the side of the boat is exposed to the on coming air as the boat slides. Yes they all slide. When I add weight to the front of a scale or sport boat it all goes in the left side.

Mark

 

[glenng]

Mark

Go to a race and watch what boats do when they blow off. They always lift the left side first and roll to the right as they go over. This also happens in the corner usually just after entering the turn as the side of the boat is exposed to the on coming air as the boat slides. Yes they all slide. When I add weight to the front of a scale or sport boat it all goes in the left side.

Mark

Sounds like good advice Mr. Anderson, Just thought about a few things I forgot to mention- The sponsons on my Dumas Pak were cut down almost 3/4" . The turn fin is a full 1" longer than the one that Dumas provided with the kit and I like to keep the front-rear balance point 1/2"- 3/4" aft of sponson transoms. If you use the mahogany that Dumas supplies with the kit- make some carbon fibre doublers for all the areas where hardware is attached.

P.S. 10 Oz. of stick on lead weights is now a MUST HAVE in the tool kit.

 

[mark couty]

I am the one weirdo in my area wanting to run a scale hydro. There are NO scale boats here.

 

[glenng]

I am the one weirdo in my area wanting to run a scale hydro. There are NO scale boats here.

I feel your PAIN Mark, I am the one weirdo in N. UT that has Scale/ Sport 60 boats. I did not run any last year but for me they are a HOOT- and yea they slide in the turns and they look like the full size boats- I don't think I'll get to finish this season here It UT -not worried about points or winning- think I'll get out the the boats that are the most fun.

 

[Bill Gibson]

There is NOTHIN COOLER than runnin a model race boat that looks like a REAL RACEBOAT! Although im sure a big twin would be a rush too!

 

[Grimracer]

My 82U55 has 13oz in the left sponson.. My sport 40 has 7oz.

The drag from the fin and the torque from the drive system really play heck on the balance of a scale or sport hydro.

Mark Anderson is one of the best. He is dead nuts on.

Grim

 

[glenng]

My 82U55 has 13oz in the left sponson.. My sport 40 has 7oz.

The drag from the fin and the torque from the drive system really play heck on the balance of a scale or sport hydro.

Mark Anderson is one of the best. He is dead nuts on.

Grim

A lot more than I would have thought. If I took my boats down to sea level I might have serious problems if they are already lifting the left sponson here @ 4200 Ft.

 

[mark couty]

Where do you place your weights, in the tip at the sponson, at the rear,where ? Are the weights enclosed and permanent or are they accessable and detachable ? How do you guys do this ? Also I am right outside of New Orleans which you know is below sea level. Thanks.

 

[Grimracer]

Mark.. I test with stick on weight and then when i know what I need, poor in a slurry of lead shot and west systems in the front tip of the sponson.

Grim

 

[Kez]

I have been trying to find lead shots or fishing sinkers but they are not made of lead anymore. The fishing sinkers are now cast from some kind of a white metal and the shots are steel. Anyone know of a source please post here.

Thanks.

 

[Mike Rappold]

I have been trying to find lead shots or fishing sinkers but they are not made of lead anymore. The fishing sinkers are now cast from some kind of a white metal and the shots are steel. Anyone know of a source please post here.

Thanks.

Might try looking for a gun and ammunition store. Some sell loose shot gun pellets with different size diameters. They come in 5 lb or so bags.

Mike

 

[mark couty]

Mark.. I test with stick on weight and then when i know what I need, poor in a slurry of lead shot and west systems in the front tip of the sponson.

Grim

How do you do this if the deck is already on ?

 

[Dasboatman]

"How do you do this if the deck is already on ?

"

Hey Mark,

Come on Mark - it ain't rocket science.

You bore or cut (Dremel cut off wheels work great) a hole in the bottom or inside plate of the sponson and pour it in. I generally get my hulls completely finished, less paint, install all the hardware and add weight( tire balancing weights work well) to balance to CG before paint. I hope you made a weight box in the forward sponson area to contain the added weight. The sound of a loose chunk of weight loose and sliding back and forth in any hull is not good. My sponsons are WOF. I moved the radio box on my Oberto a couple years ago. Here is a pic of how I accessed to remove weight after moving the radio box forward, and outboard the engine.

Note to self: Be careful when using an electric hand drill with 1/2" drill bit to hog out lead - it grabs and will go through the top of sponson quickly. CHEERS !!! Bob

 

[mark couty]

Yeah, I sorta figured that was the only way to do it. I just have a hard time cutting up a boat that is just put together. ( YUCK ). I don't have the deck on yet so building a weight box wont be much of a problem.