Cox 049 powered race boat

I thought your explanation was both acceptable and succinct Dave.

Potty mouth Bob.

Jim Walker 1/2A Hydro

http://www.americanjuniorclassics.com/movies/Boats.wmv



The Famous Jim Walker starting the Miss Thritway and a run on the pond.

http://www.dumasproducts.com/product_info.php?cPath=39_80&products_id=444



For those wanting to try a 1/2A boat.

The German boat has a flexible drive shaft. Looking a the prop, which has an M4 thread, the flex drive must be 1/8" diameter. It seems that it is not supported much by a brass tube, except maybe where it goes through the hull. Isn't there any risk of wobble? Or is the 1/8" flexible drive thick enough to remain in place. What if you would use a .098 (2,5mm) flex drive?

Yes the reality if used with even a TD engine a 2.5mm flex drive is enough to do the job. You could use wire drive too as an option. I prefer no drag straight drive shaft longer than what dumas sells to minimize the angle of attack.
2mm to 3mm or 1/8th in should hold up.

You can use teflon tube to protect the cable with some brass stock to protect the teflon and reduce vibrations / wobble.

I had seen that vid before.. and marveled at it! There aren't many Cox powered "submerged-drive" boat vids out there. I've had an outrigger in the works for a while.. .. I have a similar Dumas kit to the one shown above. I'm trying to come up with a transom-design that allows for adjusting the height of the drive. I'm leaning toward a vertically-slotted transom.. with a guide-plate for the output shaft-tube, that can be raised/lowered. This is an important aspect for tuning the drive/hull. Flex drive cables are nice.. but if you make your own; you need to note the direction of the "twist" in the cable, so it doesn't "unravel" when loaded.

Just a quick note - as about to leave to the office for the day the hydro is low lying by design and submits itself to more water tension the prop runs on the hub here is the likely on plane water line when not hoping over water ripples. Its light big plus and hops level when it does. Would have been faster if the rudder was reshaped as shown the rooster tail lets you know the prop is airing out a blade.

Interesting information, thanks guys. When reading different building threads of outriggers and other hull-shaped race boats, they are all finished with resin and sometimes also with fibreglass. In case of 049 driven boats, would iron-on covering do the job?

I have used iron covering if you overlap the seams well perhaps use balsarite to make it more sticky would be helpful otherwise the golden rule is a epoxy coat final finish as boats typically use high nitro mixes. If there is anything in the water such as twigs, sticks and the like could compromise the wood.

Don't use iron on covering. It is not tough enough and will easily tear, scratch or abrade away! It will leave you with soggy balsa.

You can get very light glass cloths 18g per Sq M. That and resin with judicious sanding won't add that much weight.

Unless you can seal the balsa very well, iron on covering is not a good choice. Even then - it is not very strong.

As in the previous post - you would me suprised what any sort of float debri can do to a balsa hull!

On a side note I only use aircraft ply for all my boats these days. Back in the day I had some micro balsa boats that held up well with monokote only because they are so light covering to scale and weight was robust. You can use spar urethane with ply construction and only epoxy the inside of the hull but epoxy is king. If you make a balsa boat you should consider glassing the bottom of the hull for RTR boats weighing more than 10oz. There is one other trick with balsa boats applying a thin sheet of plastic to protect / same stuff used for protective covers for documents.

ian1954 wrote:Don't use iron on covering. It is not tough enough and will easily tear, scratch or abrade away! It will leave you with soggy balsa.

You can get very light glass cloths 18g per Sq M. That and resin with judicious sanding won't add that much weight.

Unless you can seal the balsa very well, iron on covering is not a good choice. Even then - it is not very strong.

As in the previous post - you would me suprised what any sort of float debri can do to a balsa hull!

Ian, What constitutes well sealed balsa? Will standard dope applied in enough coats do the job? Thanks, Andy

I would use "sanding sealer". It is dope with fillers and additives. It sands to a nice finish.

I would apply the first few coats thinly so that it can soak a little further into the balsa.

Polyurethane varnish will also work but it can be a little thick.