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Pitch adjustment question and Stump puller Question

AlaskaTours

AlaskaTours

Well-known member
Hi all,

Instead of two seperate posts I'll combine the two.
First question is I'm trying to get more push out of my boat with 5 people in it on the river I have to skip over sand bars to get it up on step . I'm running a 350 small block, gear reduction (belt) 3 blade 76 inch WhirlWind not sure what type blade I do not see it listed on the web site It is set at 16. What are my options ? I was told I should run the 2 blade 76 Stump puller and my problems should be solved , What do you guys think ? Airboaters are far and few up here so I can not get any good info beacause not as many of us up here as there are down there.

2nd question is pitch could I adjust my pitch on the prop I have now to give me more push ? If so How does pitch work ? Red Neck terms please....... :D , I'm not a very ebujacated man... :shock:
I did learn a trick from a fellow airboater up here that I'll share with you ,You might allready know this trick . But go to you local Home Depot buy a carpenters level Sit it on top of your blade get a reading than put it on the end of the blade at the tip on the angle of the blade and you will have your pitch do the same to all your blades keeping the top number on the blade the same all the way around .That way they will be exact no guessing and it's quick. I keep one in the boat

Here is a few photos

prop2.jpg


prop.jpg



 
I'll try to get things going and I'm sure other folks will fill in more details.

Push: It looks like you have a decent setup. Id say keep your prop, and diss the belt drive, or at least get the set of 2.3 pullys for it. Best for you would be the 2.68 gear drive according to a LOT of testing that has been done by folks on this forum. Maybe go to a low end cam for the engine as well. Thunder knows exactly what numbers to ask for for lift and overlap. It seems the current trend is to go to the 3 or even 4 blade props instead of 2 baldes. Maybe make sure you have the right amount of carburation on the engine as well. There are some CFM threads here for that.

Pitch: What you describe is not pitch it is angle of attack of the blade. Pitch is the number of inches the blade will travel forward in one rotation if there were no slip in the air. Angle of attack (AOA) is the number of degrees of tilt you have in each blade of the prop.

For airboating purposes AOA works just fine and most folks call it pitch regardless. You are making a relative measurment between each blade to make sure they are all the same. You can increaase or decrease the AOA by the same amnount on each blade this way. The way you describe is just fine to keep track of the relative measurment. Relative measurments work fine because we arent in a lab where were comparing this boat to that boat etc, were working on one boat and comparing it to itself as we make changes.

The actual question of will adding pitch give you more push is a good one. The answer is "maybe". You can try to add pitch and see if it drops your RPM then try and see if it actually pushes better or not. It needs experimentation. There will be a point where the engine cant make the power to swing the prop and you will lose performance. Watch your RPM, you want to keep the max RPM somewhere around the RPM your prop is designed for its max push. This could take an email to the manufacturer to ask what is the design RPM for your prop. If you have unused power in your engine and the prop can absorb it yes it will puch better by adding pitch. If your all tapped out in the HP department then you need to go back and address the first question before you can add much or any pitch. In the same line if your prop is already at max efficient pitch and you still have unused HP in the engine your prop is all tapped out. This is where you have to decide to stay where it is or go to a bigger prop.

There are some good threads here about matching prop RPM and engine RPM curves using a reduction drive. The idea is to get the engine running at max torque or HP at a reducted RPM where the prop is at its best.

Hope this don't dound like double talk, Theres enough folks here that can contribute that someone can say it so it clicks for ya man. Were all jus a bunch of rednecks with a common passion and were all here to help if we can.

The Dalli Llama said to share your knowledge, it's a path to immortality.

Scotty
 
First thing i would do is call whirlwind and ask them. You can find them in the airboatdirectory.com showm in the upper right hand corne rof this sites screen.

If you keep the prop you gotta keep the beltdrive because a gear box spins to the right and a belt spins tot he left, they don't interchange.

Finding the exact right angles to set everything at is a result of trail and error on each application. You can get close but trail and error gets it exact. You are close maybe with the 16, I assume you are reading that on the hub marks. Whirlwind has the best marks going of anyone making props. The measurements your taking are tip measurements and are not where the actual pitch is calculated at on the blades. However if you tell them where you are measuring they will be able to convert it. It is a lot easier to just read the marks on the hub that the mold seam lines up with and tell tehm that number.

As for the push part ... well agin trail and error. I like setting based on static thrust but that is just me. I ask my rig to give its all everytime I run it it seems. So static thrust numbers work for me just fine. If you don't have a thrust guage of some sort well then pick you a spot and always do your comparisons there. Always use the same load and water conditions if possible and only make one change to one item for each test run. That way you know what it changed and how much.

BUT CALL WHIRL WIND they are smart and friendly folks.
 
the drive on your rig looks like a ch2 what ratio is it i dont belive you mentioned, if its anything below 2 to 1 you are limited to pitch. your boat looks pretty heavy the cage wire looks like it would hold a griz bear also what kind of hull do you have?
 
I don't want to change the subject. Last year I decided to measure the push of my props. My method was to use a dynamometer 0-1000# (dynamometer a scale that has a pointer to mark the Maxim #)

I use my truck as a anchor and had the boat in the water, to remove all resistance in order to have consistent reading. Granted it's not a perfect setup. Each time I changed angle I could track the # of push/ rpm. :D

Please continue with AlaskaTours question.
 
Some very good info. The thing we have found that help us was to wright every thing down as we test -- It sure saves on the double guessing and rechecking 6 mounts from now. The hub marks are close but I have found that using a carpenter square off the transom lip then measuring to the trailing edge tip of each blade gives me a much closer setting. And by changing that measurement by 1/8" will change the max RPM of our 600hp engine by 250 RPM. We too have found that at a certain point we would gain speed but loose bottom end..(dry ground) And the same goes for the opposite way. It is well worth the time to take one day and do the testing and logging of the info to find your boats sweet spot for what you want it to do.
 
Great point, Ron. Every combination has it's own sweet spot ..... no two are ever the same.
Tune your rig for where it's happy and you're there.

olf
 
Thanks all,

Sorry I did not respond earlier but my buddy spotted a large grizzly and we took off after him for a few days.

But anyway this is why I asked here.The knowledge here is overwhelming
I'll give it a try this spring

Plumbcrazy ,

Thats not my boat its a fellows in Fairbanks, I Think thats where he puts the tourist when he does bear viewing tours.......... :D
 
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