DRAGONFIRE81M

yeah i know . i used them in my rock crawler as well . i would but there just anof room for one in the 17" mite go with that on the 25" hull or maybe even twin 29mm drives [sm=wink_smile.gif]

DRAGONFIRE81M

sorry it tock me so long couldnt find the card reader . heres some pics of the new boat be kind its my first balsa hull build oh yeah sorry about the messy table .

grael

Looks good dragonfire.

Just some possibilities...

First, if you want it to grip a bit better when turning, and lift higher out of the water, then you need strakes.

If you want some resiliance to centre of gravity problems, and to be able to have your weight a little forward from normal, then you could modify for stepped hull.

The easy way to do it. is to run a 1/8 balsa skin from 1/3 forward of the transom, and cut out in the middle to make the first set of strakes.
Run the balsa grain sideways, and it will follow the bends really nicely.
Do again from 2/3 forward of the stern, and let cure.

Not saying your boat isn't nice, it looks really good. Just my suggestions to really improve the handling, without much extra work.

Haven't been running my jetboat much lately, still haven't found a good way to waterproof my servo, and have it still work fast.
Been learning how to fly gliders off a local slope, surprisingly, they have the speed record out of all the RC models. I think ice yachts go pretty fast too, but youtube dynamic soaring, and you'll see what I mean.

Wind's hopeless at the moment, so I'll make some more progress on the new mould for my latest boat. Really keen to try it in kevlar/carbon, and with a heli motor: http://www.hobbyking.com/hobbyking/s...i_Motor_4400kv

The motor weighs 75 grams with connectors soldered, thinking of pairing it with a 2650mAHr 3S I have, but ought to go crazy fast just on a 2200mAHr 20C 2S or, a 1000mAHr 40C 2S One of these would work: http://www.hobbyking.com/hobbyking/s...idProduct=9607

My normal boat weight empty, deck and hull in epoxy/glass is about 420 grams, but it looks like I can do a hull and deck in under 150 grams in the epoxy / kevlar/carbon blend. I should be able to get more than double the power to weight ratio.

DRAGONFIRE81M

thanks grael . i plained on some strakes just havent got to the bottom yet been working on the top trying to smooth things out . thanks for the tips play around with them . i plain on two more hull in diffrent sizes the smalles being a 12" made from foam then epoxyed not sure on drive yet im eather going to do a micro prop or jet drive still up in the air . the other is going to be a 25" and i plain on running two 29mm drives in it .

grael

Just to give you an idea of what I mean, take a look at this. I have deep steps, but shallow works too. forward of the front step actually needs a set of strakes too, I added them in later.
Otherwise, it sprays a bit too much water sideways at the bow.
You could do the same thing with balsa skins.

grael

I tried vacuume moulding some deck parts out of thin polycarbonate today, vacuume cleaner, custom box, and mould with holes drilled in the depressions. I need to get it a bit hotter, and put screw stops sticking out to stop the deck original buckling under vacuume, but it is a pretty simple, and easy process. I used a pain stripping heat gun to warm up the sheet, double sided foam tape to lock the sheet in place, with a second open frame to help hold the edges of the sheet down.

Definitely a recomended process for decks !

BIG22BIRD

My Feedback: (1)

thats awesome. dont be sorry, just have fun!!!

madphil

First run of traxxas jet boat today , after a bit of trimming and moving weight forward it runs nice and fast , very scale like on 1/2 throttle ( if you snap the throttle open you get mad wheelies )

damfurst

Nice pics Phil, but we need vids. Love to see this thing run.

sundogz

What Damfurst said! Video's! Looks right nice. Got pics of the inside and bottom of the hull? Here's some thing that happened to my Powerjet: the large (6x19x6) bearing at the motor end of the jet drive seized up, taking out the esc and overheating the 6xl motor (had tubing cooling then). Turned out, it had rusted and didn't appear to have any grease in it. This is a sealed bearing! Anyways, I replaced it with a hybrid ceramic bearing. The small bearing at the impeller end was useable, but not real smooth, so I replaced it with one I had on hand (for a CX2 Heli).

madphil

pics of inside its running on 8s with kontronik power jazz ESC , geared down with a impeller speed of 22,000rpm

phil

grael

Hi Phil,
Itook a really close look before I realised that your cabin area is all in the back half of the hull, and your C.O.G. about halfway along the cabin. Probably standard setup for a standard speedboat, but I just wanted to say, don't write-off using stepped hulls for jet boats. I designed up my own one, and it works really well. One of the nice things about it, is that you can move the weight forward a bit, and it will still perform, but you loose the wheelies, and get better handling going into strong winds. People who say stepped hulls won't work with jets simply haven't tried, and are failing to consider that the aeration of the hull is in specific zones, the jet intake will still work fine priming in a wet zone.

Graham.

madphil

Hi Graham , Stepped hull are the way to go now i race Mono 2 and Mono 3 classes with 2 and 3 step hulls they are needed for speed and run time but they still loose out on cornering , overall you will get a faster lap with a step hull . in Mono 1,2 and 3 racing we use the stepped hull to get it out of the water for max speed ( as you can see with my lindenau mono3 ) ,

with a jet as long as you can keep the intake in the water it should work .

I have my C of G slightly to the rear on the jet boat to give a nice scale look its good to drive round between race classes

phil.

grael

I made my stepped hull to corner well also
In action:
http://www.youtube.com/watch?v=rEj1ainByTs

I managed to get a good composite epoxy/glass/dynel/silicon rubber mould done yesterday, which is the one with light blue colour inside.(non stick)
Planning to do a single layer(with strategic overlaps) carbon/kevlar woven skin inside this, and I'm hoping for an empty hull weight of less than 150 grams.

New motor (to be tested) is only 80 grams, air cooled, and high KV. If it all works as planned, I'll get double the previous power to weight ratio. It's going to be fast!!!

grael

I bought a full sheet of 1mm thich PETG today, it's similiar to what's used to make clear soft drink bottles, only it ther****rms slightly easier.

I was also given some samples of other thicknesses, and a slab of 2mm thick polycarbonate.
I'm planning to vacuum mould the polycarbonate to make intake halves.

Possibly... there may be an all clear stepped T-Rap boat coming It's certainly an easier, and faster process than fibreglassing, although you can't get really sharp corners.

We have our full sized jet boat nationals in a couple of weeks... I'm keen to be there

The hull is about 145 grams so far, with deck and cockpit+hatch bubbles fitted.

DRAGONFIRE81M

looking good grael . i have every thing to build a vac former just havent put things together yet . but i plained on makeing my own intakes for the 29mm drive .

grael

Dragonfire,
The PETG is working pretty well, here's a link:
http://www.plasticsmachining.com/mag...9802/petg.html
I'm using cheap double sided foam tape for once only seals, and a paint stripping heat gun to bring it up to temperature.
Using a normal vacuum cleaner. A long stretch into a tight corner can pop the PETG if it's still hot.

DRAGONFIRE81M

i had gotton some plains off line . it uses an electric grill turned upside down on rails and a window frame to hold the plastic sheet . of course a shop vac anf wooden box with a cookie sheet that the frame sets on . ill find the build page and post it soon .

sundogz

Yes, I've read about using a heat lamp, but an electric skillet sounds interesting. The element from the bottom of my electric meat smoker looks like it's made to order for the task! Grael, can you post a pic of the bottom (intake) of the stepped boat in the videos? I looked back thru the thread but couldn't find one.

DRAGONFIRE81M

found it heres the link http://www.halloweenfear.com/vacuumformintro.html

grael

sure.. see these:
Hopefully, three pictures:
1) all my current "tyranorapidus" boats, also my vacuum mould.
The hull centre left looks patchy mostly because the PVA release agent is peeling.. like sunburnt skin!

2&3) my beaten up, scuffed up undersurface of the hull, showing the intake.
I don't like much about my intake at the moment, it's too narrow inside, and it's a pain to re-contour.
Still mulling over whether I'll vacuum mould an intake, or do another model and take a silicon mould of it. I have water clear 2-part polyurethane that sets like a rock, for if I want a clear intake.

p.s. I have run this boat a LOT !

sundogz

It's beyond me how a recessed jet intake can work at all, much less perform like yours does. Maybe that's why it leaves a frothy trail behind (air with water). But that could be water quality. And with the stepped strakes at such an angle it looks like it would be 'plowing' the water. But if it is, it doesn't show it. Thx, Sdg.

pakachiku_11

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DRAGONFIRE81M

i take it you havent looked at a singel thing on this thread or what catagore its in . just to feel you in your in the speed electric boat forum and this in the threaad on water jet drives for boats .

grael

I was a long time thunking it up sundogz

Easier to see when you have one in your hand, to imagine how the strakes are interacting with the water surface.
Designed for forward lift, outside turn lift, inside turn grip, and to entrap air in multiple zones.
Less wind affected due to C.O.G. further forward, front of boat designed to ride on first step.

Thanks for the compliment on it's performance

p.s. I think the frothy trail behind it is a combination of the salt water, and the entrapped air from the steps in the hull.