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500 cad stuck onthe hill with carbon prop

spooledup50

Well-known member
i just built a 500 cadi with a 1.74 gear box and sensinich super wide blade carbon 2 blade prop set at just passed notch 3 when i check it with my digital protractor at the tip of each blade i am getting 22 degrees of pitch don at sensinich said to turn the prop 2100 rpms witch is 3700 at the motor my engine revs fast to this point and i can actualy put more pitch 24 degrees to bog the engine down to 3600 but at setting one two ore three i seem to have the same amount of push or not enough push to run dry ground with out getting hung up i have seen this prop 2 blades on 16 foot boats with 6 passangers run great and actually run right were i get stuck if they are spinning it 2100 rpm and set at level 3 like me were is all my push going my boat is a 13 foot diamond back hull built in 1995 it cant weigh more has brand new polymer i just cant figure it out unless the angle at witch my thrust is pushing it well its at 2 degress down ward weel this boat is killing me any one got any sugesstions shore wish it ran like my dd 350 !
 
do you mean 2 degrees down on the backside of the engine? If so you might be driving your nose down trying to plow dirt. I was told when setting up my boat (which is direct drive) to have the engine level with the stringers. I have a 15' aluminum 1978 panther with a dd 500 caddy and 2-blade whirlwind stump puller and it will run my grandma's cow pasture all day dry. You are running a bunch more prop than me and a smaller boat... I'd think you would have no problem running dry unless it is the terrane that is sticking you but you said other (larger boats) have no problem.
 
I have seen this problem a few times. When you sit on the ground and give it gas does the boat rock onto the nose before moving?
 
yea it twist up pretty good it almost lift theleft corner but if you snap the throttle back and forth the transom rocks side to side but it runs the pasture fine bit if i go threw some bull rush or thick thatch im stuck
 
Sounds like it is pushin the nose down into the ground. Mr Combee who built a few airbaots in his time always told me if it won't porpise in the water it wont run the hill. I know there are exceptions but generally speaking i have found this to be true. Once again it comes back to no one boat being good at everything unless you want to throw a bunch of money at it to tweak every problem.

As for the boat in this thread I would try raising the rear of the engine up which should lift the nose up because props always try to run vertical. If it is already raised up then how far from the back is it to the prop, might be too far forward. If thats ok how much junk you got in the front hold area, where is your gas tank lofcated? where are you sitting yourself and passengers, is it in front of the roll in the bottom of the boat. There are a multitude of things it could be.

And as for other boats running the same spot you were stuck in well the spot may look the same on any given day but I bet it is different everytime between morning and afternoon even on the same day so just get after it and try things one at a time, let me say that again try things one at a time, till you find a cure.
 
If it rocks when you first start to move you have some major bottom issues, no doubt about that. Do you have any jacks? if so how many and where. When you let of the gas does it rock back or stay where it is. If it rocks back you can fix it by changing the bottom. If it doesn't you got a tough long row to hoe.
 
I think you would do better with the motor up about 1.25 in the rear from level. I was thinking of changing my rubber motor mount bushings to the poly ones.. the rubber ones seem to breakdown after a few years. I have always been for a little higher in the rear.
 
Call diamond back and ask them if this is one they built to run on the nose. I missed the diamondback part at first. they are famous for nose plowing, GTO also from what I have seen, it must be a safety in handling thing.

Alumitech always starts out with them level. I ahve found level is good, I may porpise a little but I can run the hill a lot.

13' is kinda short for a caddi with a gear box because you have moved your motor quite a ways forward. Basketcase went through this same thing on a 14' diamondback. I would call them first because they usually will gladly help especially if all they need to do is talk to you. I belive they are listed in the airboatdirectory.com in the upper right hand corner of this page.
 
My boat ia a 14.5ft GTO and if the boat is level the rear of the motor is just a bit lower. It runs the hill O.k for a big boat, Im going to change the rubber bushings for the poly this weekend and raise it just a little in the rear so the motor is level or just a little higher in the rear. i do notice a little nose push. im a ferm beliver in having the rear just a bit higher. I also like to keep as much weight as i can to the rear. I was thinking about building a jack in front of my fuel tank too. I have a good strong 500 DD and still want to try a 6 blade warpdrive.. I know everyone says not a warpdrive on a caddy but i havent talk with anyone who has tried it.
Has anyone out there tried a warpdrive or seen one on a DD Caddy
 
yes water thunder it rides on the nose im going to try a buddys hull tomarrow i tried a three blade k seriers to day my new two blade super wide and a power shift two blade stump puller and i maxed all three pops out at there max rpm with the max pitch recomended by there manufacture and still had plunty of throtle left with out turning the pitch to the point were they no longer push but i saw no improvement it has to be in the hull or the rigging it ran better as a dd with a bone stock 425 cadi then with my 510 ci torque monster with a gear box{1.74} and back then i could only spin my two blade q series 3000 rpm on pitch seting 1, 1/2 and it would scoot up date coming soon but all suggestions welcome oh and the boat does not porpse what is the best thing to do to make it porpise if that will help it run the hill
 
if you are getting max prop rpm and still have throttle to spare then you don't have enough pitch in the prop. You should use the prop pitch to control your engine rpm. I would start by leveling your engine and work either way from there. If you have bottom jacks in your boat if it hops then pull the bottom up... if it plows then push the bottom down. Engine angle should only be a fine tune adjustment. Remember Thunders famous quote.... "use your gear box as a torque multiplier not an rpm enabler." I run a Whirlwind Stump Puller on my boat (DD) but it seems to push the same at 2600 WOT as it did at 3000 WOT and it is a bunch quieter. There is no perfect plug in and go setting for a prop it takes trial and error to get it were it performes best for you and factory MAX rpm isn't always the best.

A qestion... my boat plowed and I jacked the bottom down to bring the nose up. In the forums opinion would it run dry better if I changed the angle of the engine and took some jack out? If it most likely won't improve the dry running I will leave it where it is as it runs great in the water and OK on level ground the way it is. Also what is everyone using for rear engine mount bushings? I have big rubber donuts now but probably need to make a change as they are looking cracked and flat.
 
Props are complicated ... max rpm is one issue, max thrust is another, max sound is another .. the diameter of the prop, the number of blades, are just as important as the pitch and yeild different responses. If you pitch your prop past a certain point you will slow your engine down but you will lose thrust because you are not screwing the air you are chopping it. Don at sensenitch told me that I am not getting the most out of my prop because I am past the last marks. he said I need to add a blade and come back on the pitch until I am in the middle ground of the marks +/-.

There are as many opinions on this as there are airboats. The manufacturers even disagree on some issues even amongst the one who work at the same place. So I guess the best advice is never quit trying and changing if you are not happy until you get happy then I say quit because it costs a lot to experiment with props. One run one one day will not give you the whole story on a prop setup.
 
one of the reasons I say max rpm isn't best is because my prop is rated for 3000 max which I origionally set it at. It ran good but when I pushed it hard it sucked my eardrums out. I contacted Whirlwind and asked if these blades had a "sweet spot" and Patti said "the seem to work pretty good at 2700." So I added pitch till I maxed at 2700 and it pushed the same but was easier on my ears. I then added a couple of more degrees to try to get my crusing rpm down and it maxes at 2600 rpm. I can cruise at 2000 rpm and still run dry like I did at 3000 rpm. Like you said though if thrust falls off when he sets pitch to turn prop at max at wot then he doesn't have enough prop. So his engine is stronger than he estimated when he built it which is awsome.
 
How big is the super wide series prop that you have? Also you need to raise the back of your motor up to make it porpoise. It needs to porpoise a little not alot.
 
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