Hi all,

Does anyone know of a nice buildplan for a first timer? Ive never built with wood before, but we all gotta start sometime, right? I kinda fancy one of those tunnel hull outboard motor boats, but they look a little hard to make, with all the curving. Also, I preffer it to be not to big, somewhere around the 20" region would do nicely.

Ive already found a buildplan nammed HydroMite, but it looks a little iffy, the motor is sticking out the top and such (on the buildplan).

Cheers,
Sven

I saw about three things wrong with that boat
1) Balsa framing
2) Not built on a jig, could be twisted
3) The way he installed the flotation

For a high performance boat, balsa isn't a good choise of materials. It acts like a sponge around water, absorbing water almost as fast as it gets into the boat. It's also not strong enough to take the pounding a boat takes at high speed, so leave the balsa for the airplane builders. I would recommend aircraft grade plywood, using 1/16th for the sponson insides, the bottom and the sponson bottoms, For all the rest of the framing and skin, 1/32nd ply, while the sponson transoms and stern transom should be 1/8th ply for strength. I would also use 1/8 spruce square stock for glue blocks to reenforce all the 90 degree joints

A boat of this type needs to be built on a jig to prevent having a twisted hull. The builder may have a twist in the hull and not even know it, causing some of his problems.

The third thing was the flotation. He had all the foam in the back half of the boat, This tends to put extra weight on the rear, ultimately making the boat more prone to blow overs, as demonstrated in the pics. On a boat of this type, you want the boat to have less than 10% of the weight at the back of the boat when balanced on the sponson transoms. You have the weight of the rudder assembly, the strut, prop and driveline, as well as the back half of the hull to begin with. By adding all that foam, the boat is stern heavy. He will need to rebalance the boat to fix his blow over problem, if he can fix it at all.

Having said what I didn't like, I will say what I do like. I like the design. It's simple, easy to build, and with the sponson bottoms angled up at 6 degrees from the sponson transoms to the bow, looks like it could be a fun little boat. If you like the design, get a set of plans. By following them and using the proper materials, it could be a fun project

Hi Hydrojunkie,

Thanks for replying.

First you mention the balsa framing, Id like to mention that its only a 16" boat. Do those things really take such a savage bashing? Ive seen em skip around and fork down in the water quite nasty though. Balsa is very spungy (in all aspects). Although the boat is sealed watertight, theres always a time where some water finds its way inside. Cant you just spray some blank laque or wax it a little on the inside to shield it from water? Or can it actually penetrate the layer of paint on the outside and creep though the plywood?

Second you mentionned its not built on a jig. Im not exactly sure what you mean by a jig, but I think he did use one though:


Third is the foam thing. I would have done it like that, too. I figured the thing will keep afloat on its sponsons anyway, so to keep it level so the electronics are more or less safe, id put some floatability on the backend. Is foam really that heavy? The guy in the buildlog could get there by lumping all its batteries infront of the motor I think, but that might cause some overheating. Just a note, he already put the motor further back then planned, might be for that reason you mentionned.

It seems this thing has some construction aswell as weight problems, so it might not be the best choice? Changing wood thickness will render the buildplan a little off whack, because its all made to fit into eachother at the given thickness.

Perhaps you know of a buildplan thats perfect from the start? "Boatbuilding for dummies" you might say. Ive never built anything out of wood before, so I preffer not to have tomuch fuzz to think about. Remember those paint by the number kits? Im looking for something like that for boatbuilding. Simply cut out parts and put it together like a big jigsaw puzzle.

If youre interested, heres the buildplan: Hydro Mite (TIF format)

Cheers,
Sven

If you have the plan, build it. It doesn't take much to resize the wood. If the ply is thinner than the balsa specified, add a little more length to the piece glued to it to compensate. For example, if the plan calls for 5mm balsa, you can use 3mm ply and add 2 mm to any piece that is glued to it at 90 degrees. With this design, the only places this will matter looks to be the bottom, between the sponsons, the transom and bow blocks.

Balsa will absorb water and flex, so even a coat of paint will not keep it dry. As it gets compressed and springs back, the paint or varnish will crack, leaving places for the water to get in to the wood. It's just the nature of balsa[]

I think its easier said then done. A friend of mine is gonna build one, and hes gonna send me his jig, so I can build it too. We both think it would be fun to do a little racing.

Also what im wondering, Why does that guy have a zillion AA cells in there? Cant you just punt in a couple Sub-C cells?

If your going to build a hydromite there are a few things you should do.
1) Scale the plans up to at least 21". The boat was originally designed for a 480 size motor and 7 scr1700's. A larger hydromite can handle an 05 on 6 or 7 2400's or even 6 3300's. I've seen a 29" version that was really fast on 24 cells.

2) Balsa is fine. Just seal it with thined epoxy or Polycrylic. Done it many times , never had a problem. Make sure you seal the underside of the sheeting and hard to reach places before glueing the sheeeeting down.
If your still worried about the balsa not being strong enough go down one size on the balsa thickness and laminat a 1/64" piece of ply to it. If it makes you feel any better , one of the fastest " Electric, not gas or nitro" 1/8th scales in the country is built from balsa and sheeted with lite ply.

3) As stated earlier. Definatly use a jig to keep everything square and straight.

Go for it
Happy building and have fun.

You say scale it up for a bigger battery, but woulnd that make it much slower?

Ive found a video of it, but im wondering if its a 480 motor at all, its just so insane fast for that.
Have a look: *HYDROMIYTE - MPG - 2.9mb*

You would think scaling it up would make it slower but in reality just the oposite.
One thing to consider on a Hydro is that your going to get more lift from the hull. The main reason for scaling it up is that at 16 1/2 inches it can't handle the weight of the heavier cells. Plus a modified 05 motor is going to produce more power than a 480. A Brushless would be a real riot.

Trying to put todays batt's and power into that hull as it's designed doesn't work as well as a slightely larger version would.

Ive seen , read and heard of people trying to the same thing only to be dissapointed. The gentleman who designed that boat says the same thing every time " The boat isn't big enough for modern cells and power"

Good Day Mate.
But most important "Have Fun"

You might be right, bigger = stronger, and its less vulnerable to ripples in the water.

So wich size would you reccomend, and can you put down the full names of the equipment I should use? Like wich type of motor, wich screw (Octavus, right?), wich rudder, all that stuff.

Im gonna make a nice page about it with step by step build logs, so other people can step in more easily. So its kinda like reading instructions from a lego booklet, but then a little more advanced. Just an idea.

Thanks for helping me out, I cant wait to start on it.

I would look at Fuller's Fast Electrics for hardware and either Octura, Prather or PropShop for the props(PropShop if you want it prebalanced and sharpened)

Prebalanced and sharpened.. and priced like gold? Eh, nobody said it would be cheap.

Prop Shop is expensive, but for many, it's the only way to get a "good" prop

50 bucks for a prop..... No offence, but I think thats utterly mental...
Ill stick with something less perfect and save the 25 bucks for something usefull.

Hydrojunkie is right. Fullers or Fine design both have top of the line hardware. Propshop has great props , if stickershock is a problem , pick up a Octura. OffshoreElectrics has an excellent article on sharpening a prop. It's realy not that difficult.

As far as size? 21" , 22" would get you in the ball park.

Which prop to buy depends on the motor you plan on running. Which motor depends on how much you want to spend.
What kind of motors do you currently have? What kind of Batt charger do you have?

Ive got some big mabuchi's laying around, But I think theire a little on the large. Theire rated as battery drill motors. I dont have much interesting motors left, just a speed400 from my airplane hobby. Id say I want to spend around 30 or 40 bucks on a motor. No brushless anytime soon anyway, that would cost a fortune because it eats cells and needs a honking ESC to run it. Ive got a 75amp cont. esc that runs up to 12v, that id like to use on this.

Just dont forget, It doesnt have to go lethal speeds right away. Im only a beginner. If it turns out I get hooked, I can always dub it up with some big cash, right?

And 22" would do perty well. Ive already got a 21" conversion boat, so I know what size I can expect.

As for charger, it maxes out at 5amp 14cells for NiCD/NiMH, 5amp 5 cells for lipo, 5amp 12v for Pb lead acid.

How big are the mubachis? Is your speed control water proof or water resistant?

I do believe it can take a few splashes, but a complete soaking will probably kill it. It does look like its easily sealed up though. I could probably make it watertight, if I can use siliconkit to squirt around the heatsink. The rest of the casing is pertymuch watertight.

The motors are heavysize electric drill motors (They really are, they actually came out of a drill). I was gonna use them for a battlebot, but ive got a few spares. I think this is the one: *Click*

A 22" Hydromite , Trinity 15turn and an Octura x432(balanced and sharpened) should be a fun and fairly fast package on 7 cells.
As far as making your speedcontrol a little more water resistant use shrinkwrap. Leave about 3/8th's of an inch hanging past the ends and fill with silocone or epoxy. The best alternative would be a speed control from RCHydros available at OffshoreElectrics.com.
To play it safe don't let the silicone or epoxy touch the board.

I cant find the trinity 15 anywhere. Can you please show me a shop that has it all? Include the URL, last few times you guys left me fishing google for half an hour to find the shop you where talking about.

I have an Airplane prop balancer, so I hope I could use that on the oct prop.

I dont think it would like being shrinkwrapped, because of the heatsink?