I have been google searching like mad for any places that sell belt reductions, but I can't seem to find any. Does anyone have a good site or brand that makes belt reduction drives?

Go to SDP/SI

http://www.sdp-si.com/index.asp

Have a look at their Timing Pulleys, and Timing belts.
https://sdp-si.com/eStore/

Use their automatic TIMING BELT DRIVE SELECTION page to size your
pinion and drive pully, and size your belt..
http://www.sdp-si.com/Cd/default.htm
If the "teeth in mesh" number is red, there is not enough contact between the belt and pulley.


[8D]

here is good source for ready made belt drives:
[link]http://www.mikessubworks.com/page1.html[/link]

Thanks for all the help, I never noticed you live in oregon, you in portland?

Yup, Beaverton actually.
I go to Westmoreland Park, and Tualatin Commons to run RC boats.
And hang out with the static shipmodelers on the Steamship Portland once a month.
http://groups.msn.com/NauticalSociet...s/welcome.msnw

[8D]

For competitions, I go to Bellevue Washington, twice a year and sail with the
Northwest RC Shipmodelers.
http://www.shipmodelers.com/

What are some guidlines for prop size, hull size, motor size, and reduction (If needed). For instance anything over 2" prop with a 380 or smaller motor needs at least 2:1 or something along those lines.

It is my impression, that you want to turn the propellers at 9000rpm or less.
Typical rc car motors run around 18000 rpm and up, Hence the gear reduction on most motors.

Pat Matthews(patmat) says, " The propeller should be equal to the size of the motor can..."


Seems that if you can meet those requirements you should do alright.
If you make the propeller much bigger, then three or even five to one gear ration is not unheard of.

Nope, CGBob says that about the can. I have different theories- I look to the tables at www.raboesch.com for typical max speeds for scale props (just a function of prop diameter), and try to achieve that limit (which will usually be too fast anyway for a scale displacement hull). That may require direct drive with an appropriate motor, or a reduction drive with a smaller motor (gear or belt reduction).

On my new tug, the motor is significantly smaller than the prop in direct drive, but the match is quite happy.


Pat M

My main goal for power of the model, is to just have enough torque to drive the boat in heavy currents. I don't need lots of speed, just the ability to overpower the elements. With those requirements what would the best prop for my situation? 3,4, or higher blade?

I used to run my warships on the Willamette river decked out with Christmas lights.
The water is typically high and the current quick at that time of year. The two boats
did alright with twin three blade propellers. The DD had 1.5" propellers and ran on
two Dumas 4.8volt motors and a 6volt gel cell battery. The Cruiser ran on 2" three
blade propellers and Pittman motors. I don't think either set up (both direct drive) ran
over 10,000 rpm.

It was always fun to run upstream, slow the motors till the ship was stationary on the water, then
flick the rudder and let the current sweep the bow around and race down stream.

I don't think you need to run five bladed props. Three or four should run fine.
You are trying to get a hold of a Thompson trawler right?
Is that single propeller or twins?

Yeah, I have had horrible luck getting a TT. The first one I got completely ripped off still haven't got my money back. And this one I just bought from a guy in Ny, and I was tracking it's progress and it says my package is delayed due to a trail derailment. So I am wondering if it was the train my boat was on, or if it's progress is just slowed due to the rails being down. Hopefully it will arrive in one peice, or at least the peices it is supposed to be in. The Hull is setup for single screw, for a 36" hull what size prop should I go with? I am trying to work out everything for the drive system right now. I am looking at doing a 12V system, with a speed 700 12V motor, 2: 6 volt 7 AH sealed lead acid batteries only 12.15 each [X(] and a proboat 12V esc. I am just trying to figure out prop size and blade number, what prop shaft I'll need, any adapters to connect it to the motor, something to mount to the motor. and if I'll need to use a reduction based on motor and prop size, the speed 700 has a free load RPM of 11.1K so DD might be possible. Thanks again for all the help, maybe we could meet up sometime and drive our boats together, I don't know how you feel about salt water and your ships but I know where some rough "seas" are around here, lots of fun.

I need to build one of those Midwest Life boats for salt water and rough seas...

The old Trojan Power plant has a couple freshwater ponds...

Just have to watch out for fisherman and their lines here and there...

[8D]

I dunno, I might be afraid of my hull melting away in the water

With a 4 or 5 blade prop, you will get more thrust but less speed right?

For the most part, in scale models, it is a matter of whether what propeller the real boat used.

I used to use three bladed propellers on one of my destroyers.
For the heck of it, I changed them to four bladed propellers.
What I found, was that I had to put less pitch on the four blade propellers
to make the boat run "scale speed" or the same speed as the three blade propellers.

So, hmmm, the four blade propellers could provide more speed at the same rpm.
Therefore more thrust.

I could also conclude that the four blade was more efficient than the three blade propeller
in this case, but it could have been a crappy three blade prop.
Also in this case, since the top speed of the boat was regulated, the lower pitch of the
four blade propeller made starting and stopping the boat take more time. The boat
could not start or stop as quickly with a lower pitch propeller.

My impression of the number of blades on military ships, is that more blades makes for
a quieter propeller. I am also learning, through David Merriman, that there is a maximum
blade area/propeller diameter that should be maintained.

Not sure if that even helps you, just my observations on the subject.
[&:]

I can remember one fishing boat was running a 6 or 7 blade sub prop...From what I have gound online (which is extremely limited) it seems that a 4 blade will provide better thrust and initial take off, but will be slower then a 3 blade. So it would seem that a 5 or 6 blade would only be an extension of that principle. So I think I'll first try a 4 or 5 blade prop, I came pretty close to getting a drive system setup tonight. But I am going to need the boat here for some measurements for placement of the motor, and overall length of the prop shaft. I am going with a 75MM prop, with the before mentioned motor, battery and esc setup. Along with a 2:1 belt reduction, I am guessing this setup with be a bit over torqued and under worked as far as the motor goes. Hopefully I'll be able to attain good thrust from this setup, without having to order diffrent pulleys for the reduction setup.

LOL CCW_tester

CCW_tester,
Rats! Can't find my ruler. So, with the limits of my not so knowledgeable knowledge of metrics kept in mind, I think that 75mm might be sort of large.
One way of looking at it is by how much water a particular prop will move in one revolution. If the pitch of the prop is about the same for each, the less number of blades the prop has the less water it will move at the same rpm as a larger two bladed prop. If you increase the number of blades and they have the same pitch as that two bladed one, it's gonna move more water per revolution. A two bladed prop will move as much water as a four bladed prop if it spins faster (all else being equal, prop diameter and pitch). That's fine till you reach the point where the prop starts to cavitate, or the motor hasn't got any more 'speed' to it, or it over heats, then you have a drastic loss of speed. So, you might think of the number of blades per prop as a substitute for motor speed, sort of. The more area a prop has the more torgue/power it takes to spin the thing, more resistance or a bigger load on the motor. Low torque, high speed motors don't do as well with props with a lot of blades. The same sort of thingy applies to the prop's diameter too, to some extent.

***This is a generalization so don't expect it to be very 'accurate'/scientific/true! It does give you a vague idea of what's happening, sort of. ***

All this can be figured out mathematically. Uh, don't look at me, I'm too lazy and don't know how anyway. How would I do it? I'd use the prop that came with the boat, and then go from there (hope one comes with the boat!). Lot'a help, huh?
- 'Doc

(A little 'too much' prop is probably 'better' than 'not enough'. There are limits to that too! Don't ask! I don't know that either.)

I went with a 70MM 4 blade, which hopefully will work out good. The 12volt 700 sized motor with 1/2 reduction should have enough torque to spin the prop with out too much struggle. I'll let you guys know how it goes.

Jonjoe "LOL CCW_tester " What is so funny? Not sure I'm on the same page.

How would you guys recommend to attach a motor plate to the fiberglass hull?

I clean the bottom of the boat, and rough it up with some course sand paper.
I take a block of wood, or plywood, and drill some holes that match the mounting
holes for the motor mount. The holes are oversized, and a blind nut is placed into
the holes on the bottom side.

I put a little vaseline into the blind nuts, and then epoxy a block to the bottom of the boat.

Something like this...

What should I use to bond wood to fiberglass?

There are special epoxy's formulated for bonding to fiberglass. If your LHS doesnt stock it, try the local DIY store

Never thought about that before.
I have always just brushed the first coat onto the wood, and then pressed the fiberglass into the resin.

For polyester resin, there is a "Bond" coat, which cures tacky and flexible.
If you use finishing resin all the way through, the fiberglass can end up a bit brittle.

Ive currently got a pair of Graupner 30mm 3-blades on my Lutzow hull, 1/144. Shes terribly slow at max speed, so, all things being equal, does it make sense to use a pair of graupner 30-35mm (1.5" approx) 2-bladed "racing" props?

Im torn on ways to get as much thrust out of my direct drive 550 motors as I can. Im pretty sure the problem is blade pitch, the props dont LOOK very mean at all.

For comparison my brothers Konig with twin 35mm 3-blade brass props at 45degrees produce an enormous amount of thrust ! It can almost plane up.


I want to keep myself limited to the graupner 4mm threaded zone. Any experience would be appreciated