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Got questions need answers... Please help!!

Smuggler

Smuggler

Well-known member
I have been looking to buy another boat. This time I want to go with a gear reduction unit but I have a few questions..

1. I was curious as to why so many gear boats for sale have a ratio of more than 2 to 1? Some boats I see have 2.38 and I think I even seen some with a 2.73 to 1. Why is this? Even with a 2.38 to 1 you would have to turn the motor 7140 RPM to get the prop to turn the max of 3000. Isn't that to many RPMs for most motors unless you have major money invested in the motor?

2. Why not run a 1.73 to 1? Than you could get 3000 at the prop and only turn the motor 5190. That way you could save a bunch on building a race motor to handle 7000+ RPMs. Isn't the rule of thumb, 5000 rpm is what most motors will turn with ease, produce a good amount of HP and still be dependable?

3. To be honest I have already made my mind up and I am going with a Stinger box BUT my question here is... Are the gears interchangeable? Meaning if I bought a used boat with a 2+ to 1 gear ratio can I pull those gears and install 1.73 to 1 using all the same parts including the case, just change the gears?

Can someone out there answer these questions?

Thanks Chris
 
I think most box companies will exchange the old box plus some cash for a new box with different ratio i think most people tend to trade up to a higher ratio rather then lower

Boxes on car motor boats especially allow them to run up to a full RPM range without over spinning the prop it also adds muscle to the amount of prop your able to turn thus you can swing a bigger wider prop and not need to turn it as fast at the same time get better results.
 
The props the guys run on the higher ratio gear boxes don't turn up to 300 rpm. the use longer props with more blades (usually) and much wider blades. the gear box multiplies the engines torque and allows them to crank in more pitch in the propeller, with mor pitch and more torque they can run the props slower and still get the thrust they need. when these guys are cruising their props are turning way slower and that makes them quieter. Thats the short answer, these guys can elaborate a little more on the subject.
 
MOST GEAR BOX COMBOS ! HAVE A WIDER PROP THAT MAX,S AT ABOUT 2200 TO 2400 RPMS !WE ONLY TURN SOME ABOUT 1600 TO 1900 FOR LESS SOUND ! GET MORE PITCH LESS MOTOR RPMS ! ITS ALL ABOUT WHAT PROP YOU USE !ITS HARD TO EXPLAIN ALL THE SET UPS ! WE USE THE GEARBOX FOR TORQUE NOT RPMS ! AS THE WALLET ALLOWS! I AM SURE YOU GET SOME MORE ON THIS AS THE DAY GOES BY !
 
Your thinking is all wrong on the ratios!! Water thunder spent allot of time trying to explain it to allot of people. A reduction unit is NOT an rpm enabler,rather it`s a torque multiplier.So,instead of havinga prop that has a max out point of 3000 rpm,they have desighned props that turn much much slower and produce a helluva lot more thrust,and there able to do this because your torque is multiplied by the gear box ratio thus enableing you to turn a prop that looks like a redwood tree :lol: With the carbon adjustable props,you can just add more pitch to bring your rpm down to your likeing,more pitch = more thrust. For example,I have a 2.37-1 box on my boat,I only turn my motor 4500 rpm wfo,and it will go any where i want.The bigger blades are desighned to turn slower. Hope this explains it for you
 
Okay now I get it... Thanks for every ones help!! I just thought that the final goal was to turn the prop 3000 no matter what. I didn't know these adjustable pitched & or extra wide props were designed to turn less RPMs. Now that makes sense!! I now see what I was missing.. So let me ask you this...

1. what is the designed RPMs for those type props? Or is every non-wood prop different? Better yet is there a website/s that have these prop specs listed?

2. When you guys buy/build a boat do you work it like a math problem or just wing it? Like do you say we have "x" amount of weight (boat, gear, fuel, passengers ect) and per pound we create "x"amount of drag, times the amount of surface contact (boat bottom to dry ground) = the amount of force we need to push this on dry ground. Then we take the force we need and find a prop that will produce that much force and at what RPM and what HP/torque then build the motor to produce it?

Thanks again for the help.. I just want to make sure what I buy fits my needs.
Thanks Chris
 
every prop will have a different sweat spot on every boat. No prop or box combo is right for all boats. Give us some specs on your hull,where you want to ride and what you want out of your boat as far as performance and You`ll get lots of advise
 
Gatorgetter":1wun59yt said:
Okay now I get it... Thanks for every ones help!! I just thought that the final goal was to turn the prop 3000 no matter what.

I was told that by a lot of old timers when I first started my airboat. common misconception it seems.


2. When you guys buy/build a boat do you work it like a math problem or just wing it? Like do you say we have "x" amount of weight (boat, gear, fuel, passengers ect) and per pound we create "x"amount of drag, times the amount of surface contact (boat bottom to dry ground) = the amount of force we need to push this on dry ground. Then we take the force we need and find a prop that will produce that much force and at what RPM and what HP/torque then build the motor to produce it?

I see very few people using a scientific approach I'd guess because there is too many variables. Even on outboards experience can get you close but sometimes even when you think you got it nailed you need to drop a pitch or two. Nice thing about airboat props is experience can or even the prop company can help you decide what length prop you need for your specific boat and what kind of riding you do. pitch can be adjusted without buying a new prop on composite props and even some wood ones.. Even with that you see guys trying new props , trading props, or borrowing props because even with all those years of experience and know how it may not do exactly what you want.
Click to expand...

I'll give you an example on my prop. I wanted more push then top end so when I got my new boat together I dropped pitch and added length (wood prop) so I went form a 66" long by 36 degree pitch to a 68 long to a 34 degree pitch. Anybody selling props should be able to get you pretty close to what length you need and blade style by looking at your setup.
 
I would like a 14-15 boat that will run up and down the hill all day long.. I really don't care how fast it is on the water. Of course I would like it to plane out, run in deep water but the main focus is I just want to be able to put a couple of hefty guys including myself on it and be able to go anywhere we want without getting stuck. I am a licensed to collect alligator hatch-lings this year and i need a boat to get me to them and back out with ease. I had a IO520 on my last 15' hull and it just didn't have as much a$$ as I have and it was supposed to be 300HP.. It would get stuck if I let it. This time I want the same size hull with MORE POWER!!! I want to go were no man has gone before.. BUT be able to get out!! I just was looking for someway to be able to tell if the boat I was looking at would do just that. I didn't want to depend on the owner to say it will go where ever you want but then find out it is no better than what I had.. I figured they had to be some mathematical solution that would tell you what a particular boat would do.

Thanks for every ones input!!!
 
Well if you want a 15'boat you better get a car motor cause that's to big a boat to run the hill all day with an aircraft.But Jpatter wrote there are adjustable pitch wood props,but I have never seen one.
 
first off you need to get a different power plant,dont get me wrong i like aircraft i ran one for years,but to push a hull that size and weight you need a car motor.To push a boat that size a small block gear boat would work if it was built right but i would recomend a big block with gear box combo.i have a small block 330hp belt combo on a 14 ft hull and i can get stuck,but i have freinds with 502 stinger combos that will go anywhere and climb antyhing!!!!!For the weight of your rig and all the fat guys gas ect you need a lot of torque!!!383 and stinger 502 and stinger 572 and stinger and you will climb mt everest.Talk to waterthunder on this site i hear he builds the best out there for high torgue asms!!!!!!!!
 
Thanks for every ones input! Now this gives me a WHOLE lot more to think about... but since we are on the subject I have another one.. Is it true that the belt drives loose 18% compared to the 4% of a gear box? Someone told me those numbers and I was curious if they were correct.
Thanks
 
Tony480":2415i4xf said:
.But Jpatter wrote there are adjustable pitch wood props,but I have never seen one.
Click to expand...

I have seen a couple with a hub like a composite and the wood blades that fit into the hub. I think I remember a warp drive knock off out of wood on ebay that did the same thing. I don't think any of the big name manufacturers make them.. Could be a reason for that :wink:
 
The loss numbers arnt correct,infact it would be imposible for anyone to tell you how much a reduction unit will loose. Ambient temp and a whole lot of other factors change way to much to say you loose X amount, The weather aint the same every day so it`s different every day,hell even some times hourly with all the rain,box temp,gear oil weight and so on and so on
 
Don't remember the exact numbers, but a belt drive is not the most efficient
means of power transfer. The most efficient would be direct drive of course
then, gear to gear, then the belt drive ( which varies quite a lot with different
configurations) and then a hydraulic drive is even less efficient.
Keep in mind there are many other reasons to use these means of power transfer
besides efficiency like cost, alignment, and convenience just to name a few.
Some of us oldtimers may remember running trac hoes with cable and clutch drive.
They were a more efficient transfer of power from the engine to the hoe but what a
pain in the but to run. same reason a truck with an automatic tranny burns more
gas than a stick. let's not forget belt drive motor cycles, quieter and smoother
than a chain, but not as efficient ( a drive chain falls between a belt, and gear drive.)
I wont vouch for the numbers, but there are exact numbers that come from
laboratory testing where the different types of drives are compared under controlled
conditions. they talked about this stuff back in millwright school, but I forgot
most of it.
 
I have boat that was built for going for gator eggs. Diamond back built the boat and the motor is a fresh rebuilt supercharge 0540 with the gear reduction. Rest assured that boat will go anywhere any time. If your interested I will sell just PM me.
 
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