Boat tuning

dont slow down · 06-23-2009, 09:10 AM

Ok so I bought the pro boat formula fast and now I'm wondering how to dial it in. It has two trim tabs, two turn fins and the prop angle is adjustable. I'm wondering what each if those will make the boat do if I adjust them.

NitroVal · 06-23-2009, 10:16 AM

Use the trim tabs if your boat is "porpoising" at high speeds. Porpoising is when the boat is riding on the very tip of the keel and rocks back and forth, causing an unstable condition. Lowering the trim tabs will help steady the boat at higher speeds. Prop angle will adjust how high the nose of the boat rides in the water. Too low of an angle and it will never get on a plane and will be slow. Too high and it will porpoise and cavitate all the time. The turn fin angle you really dont need to mess with unless your racing.

dont slow down · 06-24-2009, 02:05 PM

So lowering the trim tabs will steady it at high speed? will it cause any drag and slow the boat down? Do I just bend it down? How precise is it and can I measure it? Where is a good source for props, I can't seem to find anyone that has any instock. RC Car Action did a review on the nitro version and changed to a Octura x435 prop and said it did wonders but I can't find anyone that has it in stock.

MrUnlimited · 06-24-2009, 11:22 PM

Quote:

Originally Posted by dont slow down

So lowering the trim tabs will steady it at high speed? will it cause any drag and slow the boat down? Do I just bend it down? How precise is it and can I measure it? Where is a good source for props, I can't seem to find anyone that has any instock. RC Car Action did a review on the nitro version and changed to a Octura x435 prop and said it did wonders but I can't find anyone that has it in stock.

If you trimtabs cannot adjusted, leave it that way. IF you bent them, the chance is that they are not equal after bending resulting in a bouncing mono. IF you want adjusteble trimtabs you have to remove the old ones and replace them with adjustable ones. Here are the ones you need: http://cgi.ebay.com/CNC-Trim-Tabs-tu...lenotsupported
If you don't want to replace them, move some weight towards the bow to make it more stable at high speeds.

dont slow down · 06-25-2009, 06:33 PM

No I haven't bent mine or anything but those other ones definatly look more precise. Any clues on where to look for props?

NitroVal · 06-25-2009, 09:20 PM

http://www3.towerhobbies.com/cgi-bin...=BGFVNR&P=0&S=
I've ran Aquacraft's Grim Racer props before and they are pretty nice. I think you have to get Octura props directly from Octura..

MrUnlimited · 06-26-2009, 01:56 AM

If you get Octura props: they are NOT balanced and sharpened. Shapen and balance them before you use them! If you cannot balance them or not know how to do that, ask at the local boat club somebody or your LHS to do that.

dont slow down · 06-26-2009, 09:42 AM

I did notice that most of the octura props were unfinished. There isnt a boat club in the area that I know of. Is there another brand of prop that comes ready to go? Also how do I know what size prop I have now? Such as pitch and whatnot. That is another thing I would like to learn, what pitch does and also the pros and cons of larger or smaller props. Anything on props would be helpful really. Thanks for the help so far.

MrUnlimited · 06-26-2009, 10:01 AM

This is what you need: https://secure.rcstore.com/pcd/eServ...N1YlRlcm09MA==
It discribes also about props, setups etc.

chunk t · 06-29-2009, 11:11 AM

DSD,

Regarding the attributes of a prop (pitch, cup and diameter) Generally you will choose a pitch/diameter combination that will allow the motor/engine hit peak RPMs. My answers may seem a bit dis-jointed; but there is so-o-o-o much going on with the prop that it would take more typing to explain than I care do. So hopefully these statements help a little.

Pitch- is the "gearing" for the boat. The greater the pitch the farther the prop will move forward in one revolution. (too much pitch can cause cavitation and in general be hard on the motor/engine). more pitch = more theoretical speed

Cup-refers to a curl of the outer edge reletive to the hub. Cup controls how much water on the blade is allowed to come off the outer edge vs. following the pitch from tongue to TE (this affects the shape of the thrust cone). more cup = less slippage

Diameter-is generally the size of the blade. Bigger blade = more water pushed (more load on the motor/engine).

an example would be that I like to run a prop with more pitch and a reduced diameter (X640 reduced from 40mm dia to 36mm). I've reduced the diameter and taken out a bit of cup to reduce the load on the engine so I can keep the RPMs above 30K. But the greater pitch allows me to hold a high top speed.

It takes A LOT of time on the water to find what is right for your set-up. You & I could have the same hulls, but a different motor/engine or running hardware kit and this can dramaticly change your prop choice from my prop choice.

texazbadboy · 06-29-2009, 11:41 AM

So Chunk T what your saying i can step down in prop size and go up on pitch right?If i'm running a two blade whats the benefits of going to a three blade?

MBenjamin · 06-29-2009, 12:28 PM

Quote:

Originally Posted by texazbadboy

So Chunk T what your saying i can step down in prop size and go up on pitch right?If i'm running a two blade whats the benefits of going to a three blade?

A three blade prop generally has more lift at the transom than a two blade. but it all really depends on the prop design. One of the worlds best prop cutters is Andy Brown @ CMDracing.com call em up and tell em your set up. he'll pick a prop sharpen, balance it and cup it if necessary. If you notice your rooster tail with the stock prop it shoots up about 3-4 feet. that is a sign of a high lifting prop. when you have too much lift it becomes a waste of power. When a prop is cupped it reduces the lift and transmits that lifting power to forward propulsion resulting in higher top speed. check out this video. this is my sport 40 hydro running with a 1455 cut, balanced and cupped by CMDi. look at the rooster tail. it runs flat. This boat ran in race trim at 60mph. when it comes down to it the choice of a 2 or 3 blade prop depends on your center of gravity and handling characteristics.

youtube.com/watch?v=7X4d8TfR23I

MrUnlimited · 06-29-2009, 02:19 PM

Andy is one of the best boatracers in the world and holds many records. I have some props from him for my 1/8scale.

chunk t · 06-30-2009, 05:47 AM

Quote:

Originally Posted by texazbadboy

So Chunk T what your saying i can step down in prop size and go up on pitch right?If i'm running a two blade whats the benefits of going to a three blade?

Basicly yes, but... you want to run the greatest practical pitch w/o putting too much load on the motor/engine. Load is controled by diameter and cup. A small change in cup can have a big effect on load and offer little to no gain if done incorrectly. A change in diameter has a softer effect on load, but you need to be mindfull how much you reduce the blade dia, because you are lessening the effective area of the drive surface. On a stock prop the outer third of the blade (tongue to tip) provides 80% of the thrust, so you have to be careful not to remove too much material on a diameter change. My rule of thumb is ... if the diameter needs to be reduce by 10% or more from it's original size to unload the prop, then the pitch is too great for that boat, and you need to pitch down a size.

I honestly don't know the story behind 2-blade vs 3-blade. Though in my experience I've had better performance w/ 3-bladers on courses w/ tight turns or in exceptionally rough water.

Hi-lift vs low-lift prop choices are usually dictated by hull design. Riggers for example touch the water on the front sponsons and the prop. So a rigger need a high lifting prop to lift & carry the transome above the water. a hydro may or may not need a high lift prop depending on how the hull is designed. Tunnels and monos do not need nor do they like high lifting props (hurts their cornering).

Andy is a good guy for props, there's another fella, Mark Sealund who's really good with props as well.

MrUnlimited · 06-30-2009, 12:23 PM

Chunk is right, check out www.intlwaters.com for more tips. You can also try www.rumrunnerracing.com which is dedicated to fast electrics. Besides Andy there is also Propshop who delivers very good props and you can try ETTI who has now smaller cnc machined props for fast electrics: http://shop.ebay.nl/items/__etti-pro...86Q2ec0Q2em283