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[GAS]

Hello all,

I've been following the forum for a little while and have decided to build a speedboat from scatch.



So far she measures 800mm x 250mm x 100 deep and I'm a little undecided as to which running gear to put in it?

As it's designed quite shallow would i be better putting the propshaft through a hole in the back (i think it's known as the transom) or out the bottom?

Also with regard to a rudder is it possible to run just one of the below which is offset from the propeller?

http://www.ebay.co.uk/itm/RUDDER-WEDGE-SMALL-model-boat-nitro-78mm-long-electric-/120753992911?pt=UK_ToysGames_RadioControlled_JN&hash=item1c1d7fb4cf

Also, could anyone point me in the direction of a reliable materials, fixtures and fittings online shop in the UK?

Many thanks in advance.

[n33h]

hello gas and welcome

sounds to me like your making a fast electric boat

ref the prop shaft, yes its called the transom, when i made my FE boats, i would measure up from the keel on the transom 5mm then mark horizontal line to get my centre point, drill a hole (same diameter as the brass tube) with the motor and mount in the hull (to get right attitude of the prop shaft, the end of the brass tube needs to flush with the outside of transom) i would then epoxy around the inside of the hull where the brass tube is

have you decided on wether to have the brass tube exiting the transom ??
a strut on the transom ??
a stinger drive on the transom ??

these all play a roll on how the brass tube will exit the transom

here are a few shops to try for parts

ebay
www.cornwallmodelboats.co.uk
www.giantcod.co.uk
www.astec.co.uk
www.prestwichmodelboats.co.uk

or (in america and some great stuff)

www.hobbyking.com
www.offshoreelectrics.com

regards nick

ps

my usual setup in a FE hull was (from the transom) servo for rudder on the right side
reciever on the left side (inside a balloon with all connector wires in place)
motor on the keel line
ESC in front of the motor towards the nose
and batterys on both sides (for balance)

[GAS]

hello gas and welcome

sounds to me like your making a fast electric boat

ref the prop shaft, yes its called the transom, when i made my FE boats, i would measure up from the keel on the transom 5mm then mark horizontal line to get my centre point, drill a hole (same diameter as the brass tube) with the motor and mount in the hull (to get right attitude of the prop shaft, the end of the brass tube needs to flush with the outside of transom) i would then epoxy around the inside of the hull where the brass tube is

have you decided on wether to have the brass tube exiting the transom ??
a strut on the transom ??
a stinger drive on the transom ??

these all play a roll on how the brass tube will exit the transom

here are a few shops to try for parts

ebay
www.cornwallmodelboats.co.uk
www.giantcod.co.uk
www.astec.co.uk
www.prestwichmodelboats.co.uk

or (in america and some great stuff)

www.hobbyking.com
www.offshoreelectrics.com

regards nick

ps

my usual setup in a FE hull was (from the transom) servo for rudder on the right side
reciever on the left side (inside a balloon with all connector wires in place)
motor on the keel line
ESC in front of the motor towards the nose
and batterys on both sides (for balance)

Thanks Nick,

I'm a bit new to all this terminology so have a couple of further questions in response to your reply:

have you decided on wether to have the brass tube exiting the transom ??
a strut on the transom ??
a stinger drive on the transom ??

I'm not sure what any of the above means  

Do you have any pictures you could perhaps post of your / a suitable setup?

Thanks again.

[MikeA]

I made my hull kinda like yours though your craftsmanship looks a little better. ill help ya with some of the terminogly   

When the prop exits the transom/stern its for surface drive propulsion. At some point some clever bloke realised that he could make his power boat go faster by creating less drag if the prop was half sticking out the water. I used a traditional submerged prop with the prop shaft out the bottom for my boat cos it was simpler to set up, but i got my plans for my next boat and im gonna give it a go with surface drive.
 
there a few ways to get surface drive

1 strut :




2 stinger:



another is to just extend the (brass tube) propshaft out the back as close to the bottom and at as close to 90 degrees to the transom as possible:



the rudder goes to the side on most of them and i think it seems to be a favourable choice. its like that so it doesnt interfere with the propwash (propeller thrust in water) keeping speed up and the boat stable in turns.

I reckon i got that down about right im sure these guys will correct my mistakes. out of ten please

[n33h]

you score highly on your descriptions and photos mike

however, an offset rudder and inline rudder make no real difference when turning, a rudder acts like a turn fin when the boat turns, it lifts the back end

i found an inline rudder (the rudder's directly behind the prop) to be a bit better than an offset rudder, it makes no real differnce

[MikeA]

learnt all that from reading on here 

[GAS]

Okay, thanks guys, that all kinda makes sense.

Could you also recommend a motor and esc setup if I was looking for performance? I don't want a rocket ship but a nice balance between performance and run times.

Ideally I'd like to stick with brushed due to cost of brushless systems.

Thanks again.

[MikeA]

I have a brushed graupner speed 600 in my boat. Ill give you some tips from my personal first boat experience.

1, dont use to big props for the size of motor i did and i saw clouds of smoke.
2, dont use mechanical speed controllers. If you lose signal the servos remeber there last command and if thats full tilt then itl be full tilt into a rock! Use electronic speed controllers they shut down when everything goes t!*s up.
3, dont buy cheap batteries from china they are just dangerous.
4, Use 2.4 ghz radio it saves you a monsterous amount of hassle money and heart ache in the long run.

see what you can find on ebay for motors
I looked at graupner motors on here to get a kinda jist of whats what

http://www.cornwallmodelboats.co.uk/acatalog/graupner_motors.html

as for whats best that comes down to experience and im still learning

run times vary but with power boats it isnt that long either way. You need a powerful motor yet you dont wanna go mad and over laiden it with batteries to get  decent run time because itl make your boat heavy and slow it down completely cancelling out the point of having a big motor in the first place. Ive got 2 batteries and when one goes flat i take it out and put the fresh one in.

[GAS]

Right, I've decided to go with a similar setup to below but have a couple of additional questions.



1. The transom is 100mm deep so what sort of length rudder should I be looking to get and what depth below the transom should it ideally sit?

2. Is there any rule of thumb when it comes to length of propshaft? IE. does it really matter where in the boat the motor is positioned along the keel line and how much of the shaft should protrude from the transom and like the picture does the prop really need to be behind the back edge of the rudder?

Thanks again 

[MikeA]

The propnut should be between 10 and 13% of the hull length from the transom. This is jans boat his screen name is pompebled. As far as rudder depth i dont know.  what i do know is that the prop shaft has to be as close to 90deg to the transom as possible so its inline youl have to get the motor down as far as possible too. On my boat i put the motor about 2/5 from the front its about the standard.  in fact how youve done your front bulk head is the same way as me. so put the motor near there. I jst experimented in the test tank shifting all the components about to get the boat to sit right.

[GAS]

theres a post on here somewhere let me find it

Good luck!

[MikeA]

Ive edited that post now. 

[n33h]

i actually found a short rudder (about 50mm long) to be better than a long rudder (about 100mm long) as when turning the blade was about half in the water and did'nt lift the transom as much so i did away with the turn fins

i also find the prop to be about central to the rudder blade is a good position, to long and not enough turning, to short and the same thing, so i suggest something in the 75mm range

in a boat your size, you could use 500/600 (race motor or BB motor) size motor turning upto about 35mm prop (2 blade with 1.6 pitch as a 3 blade increases the diameter of the prop) as this will give a bit more speed with no real effects on power consumption, you could also get away with a 3s lipo with those motors (i have a scratch built vietnam river patrol boat with a 15t ansmann motor with a 3s lipo, at full throttle the hulls almost 3/4 out of the water)

[GAS]

Well here's where I'm up to.

Can't do alot more other than sealing until hardware arrives, some of which is on it's way from Hong Kong!!!

[GAS]

Well a bit of graft and here's where I'm up to.

The superstructure has really just evolved and whilst it's a bit square I think the proportions work quite well and it's pretty light.





I look forward to hearing your thoughts

[gwa84]

looking nice looks very stealth boat 

[MikeA]

dont forget to put strakes on the bottom