DIYMark

Hi my name is Mark and im new to the boats scene.

Im making a model engine at home and i wanted to put it in a boat and im quite capable of the hull/engine design and construction, however being new to Rc boats im a bit unclear of this main point...

Do non jet drive (propeller) boats have a "reverse" or a form of brakes? or is he only thing with brakes/reverse a jet drive (switch it into reverse via the bucket)?

Do they have those tabs at the back of the boat (forgot proper name - i think they ar called "Trim tabs" ? not sure)?

How is the liquid cooling achived? pump of prop/jet forces in water?

Would prop or jet be better?

ive neever seen an RC boat so i couldnt answer this my self

thanks for your time - sorry for my lame questions but its a steep learning curve and ive neever seen an rc boat in real life before ...

rcBPman04

Well my first question to you is how big is this motor you are making? Is it gas or nitro?

Water pickup for nitro is forced mainly through a water pickup rudder that has a slot drilled into the rudder then drilled down the spine of the rudder forcing the water to the water cooled head.

Tabs are good for most mono hulls or deep vees because it helps to stabilize the hull. Trim tabs are proper wording.

What nitro engines have is a direct drive system that is for .21 motor a 3/16 shaft that goes through a stuffing tube to a strut.
When you shut the carb fully the motor shuts down. So in terms the boat is always running and it can be running some what slow for a mono hull or deep V. Hydros and cats need the air under the hull to keep it up on plane.

For Gas motors its the same thing but with normally 1/4 size and they have square head shaft but some run round.
Along with the gas, many of them have a clutch because of this clutch they have a water pump to cool the motor.

As for prop or jet. Well there are not to many companies out there that make a water jet system because direct drive is so popular and easy to work with. I would suggest using the direct drive. And depending on how large this motor you are working with and whether or not its gas or nitro depends on the cable and strut size and everything else.

DIYMark

Thanks for replying so FAST!!

The engine will be a Nitro of around 8cc's.

Ive decided to go for a Vee hull - more shallow than deep and my most likley way of powering it would be via standard prop (appoased to a impeller/jet).

So model boats dont have a "brake/reverse"??? or is it only the "jet" powered ones that have this feature which is achived by a "reversing bucket" that lowers over the outlet (to redirect the flow)...

And do nitro/gas boats use clutches? are they always spinning their props (even at idle)? im guessing most have a clutch?

Thanks once again

DIYMark

okay ive worked out part of it while reading the forum (funny that)...

Hydros and Cats dont use clutches becuase idling it is useless cuz once stopped they cant "launch" them self, so a clutch is just dead weight... So other hulls (not cat or hydros) can use a clutch - im guessing more so on the gas that nitro ones.

Now, im still unsure of the brake/reverse if any...

rcBPman04

Nitro motors do not run to well with clutches. Let me change that. Nitro boat motors do not run to great with clutches. The initial rpm to torque is not as great as the gas motors so going from a dead stop to fult tilt will not get the boat on plane. With a nitro boat motor you need to understand how that is going to work to the hulls capability to push water.

Your motor you are making is in the terms of a 7.5 cc motor that is equivilent to a .45 .46 motor. So all your running gear like strut and props and rudder will need to be in the standards of 7.5cc Now places that sell that stuff would be http://www.rossisales.com/index.html http://www.bbyracing.com/nitromonohulls.asp and http://www.aeromarinerc.com/ but let me suggest the quality from speedmaster is amazing.

Your shaft could be a 3/16 or 1/4 depending on how you want to set it up.

Have you looked into getting a fiberglas hull pre-made? There are alot of good ones out there.

If i was home and not in college i would take more pics and show you how the set up is from the motor to the collet to the drive shaft to the strut.

Having no "break" for nitro is one of the turn offs for most people entering this hobby. So many turn to electric boats.

Are you machining this motor from stock or are you buying parts and putting it together? Have you ever made a NITRO motor before? I'm just curious and not being rude.

rcBPman04

Exactly as i said in my first post that you can't have a clutch in the riggers and hydro’s and cats because you need that air gap under the hull to keep it going. Now for the rpm to torque ratio for nitro is not good. Your max rpm is say 30,000 at 3 hp. Now the torque is not until 10 12,000 rpms and from there you are running rpms to push the boat. Now with electric boats everything is instantaneous and if you ever watch an electric cat or v, you will see it jump right out of the water from a dead stop.

DIYMark

yes ive had engine experaince with nitros and made a few engines (at home) before, im starting my nitro one now (well actually nitro engine that runs of gas [X(] i had os .46 LA i found at teh tip and made it run of normal gas and 2t oil!!!! so ill try the same with my new motor - if not ill use nitro - like i should!) and the motor is going to be made from bar stock becuase im not really botherd to cast it

ill be making the hull from thin ply and my friend will help me design it (hes the boat man - sailing since we was born - well almost).

I was thinking of nitros and clutches and it did come to me the fact that normal sized nitro boats (.35ish) simply dont have enough torque at low revs so i was a bit unclear.

However, i had a look at gas forum and i seems pretty cool those big boats (and engines) so im not sure if i should just go and find a brushcutter engine (and modify it of course - im the person who cant just leave things if they work - they HAVE to be "better") and use that as a gas boat - but then again my engine will probally be a nitro run of gas lol ill have 2 in 1!! i like the fact of using normal fuel and having a reasonably small model (so i dont want a huge boat/engine just to use normal petrol).

I thought of electric and how easy it would be to have reverse/brake but electric is not for me (i cant stand batteries and charging) so this is why i though of a jet - i can have petrol with a "reverse/brake" but then again the jet housing would be a bit hard to make (im trying to make most if not all this boat).

Also, im guessing that gas boats (like nitro) dont have a reverse/brake - but they do have clutches (most). anyway why use brakes - speed is the key

Seeing as nitros arent suited to clutches it wont really matter i think becuase of the nitro engines nature of high revs (20 - 30k) you can use a lower pitch prop (than normal - ie, gas, electric) and when the boat idles (low rpm) it wont be moving very fast due to teh lower pitch prop.

f16man

The water will slow you down very quickly on a model boat ,so a reverse or brake is not needed at all.

DIYMark

Good point ^^ 9after al it does tae a fair bit of power to move the things!!!)

Thanks for all your help guys, now im headed in the right direction i shal start my ideas ( still not sure to do nitro or gas - i already have a brush cutter motor - VERY HIGH COMPRESION - and my radio gear kinda needs replacing so ill guess ill use teh old gear + old engine to make my first model - then if i enjoy rc boats (its my first experiance) ill embark on a new project with a better motor and rc equiptment)