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View Full Version : Wide blade or Skinny blade



Randy Jr
03-16-2008, 05:49 AM
I'm jus curious whats the diffrence in all these props with the skinny or narrow blades then i also see these super wide props on some airboats whats the reason for that and how dose it affect proformance ect... all i can guess is its for people that just have and excess of HP.. and need more blade to soak it up... but im just a rookie so go ahead and explain this to me airboat builders

Snapper
03-16-2008, 09:42 PM
randy I'm new also but I think the wider the prop is because it actual has more surface area it can actually push more air and therefore usually generate more thrust at a lower rpm , at least I think thats right , if it aint it sure sounds good don't it ... but you may want to check with dave or chuck to be certain , cause I may be steering you wrong ... I'm pretty sure wider is usually better , hey randy my lil boy saw your pictures and wants to build his own now , he built a little styrofoam hull and hot glued a bunch of cut up coat hangers together to make a cage and took a battery operated electric motor and mounted a lil prop on it and made some cardboard rudders and plays with it in the bath tub , it's awesome to see his little mind at work , hes already starting to lay out the wood in the garage for his project mini too , If I can get my wife to post some pictures I will , of his little toy he made ...

Papee
03-16-2008, 10:13 PM
Wider blades are better, the wider the blade the more air you push but it also takes more horse power to push a wider blade. I'm sure as we go on with the mini class you will see some experimenting with wider blades. As of yet I don't think that anyone makes a wide blade in a length that can be used on a mini. Maybe at some point these guys will be build the higher horse power and experiment with it. I'm not sure the demand for a wide blade mini prop would make it worth someone making one available. Never say never though.

Randy Jr
03-17-2008, 08:44 AM
i think arrow prop makes some pretty wide once that aren't to long.. well i say they are pretty wide compaired to the composite props we have papee

Spyda-Ryda
06-02-2008, 12:52 AM
I posted my vote as wider is better! This is based on my experience with warp Drive props VS. Power Shift props on our tour boats. I find that the wider props push harder and aren't as loud as the narrower blades. The only props that I have ever run on our Rotax minis are warp drive props. I'm curious to see Chuck's opinion on this subject, as I'm sure that of all of us here, he has the most experience in experimenting with different props for minis.

yamahaulerG1
01-17-2010, 10:49 AM
lets bring this thread back to life to get some answers maybe. I was also wondering the difference a wide blade makes on a mini. I have a 12' boat with a chevy 350dd i know its not a mini but maybe it will help someone out its still an airboat. when i bought the boat it came with a 72"-36 stick prop turned 3100rpms and wouldnt move on the ground but got on plane the easiest and took less rpms to stay on plane , next i found a 68'-3blade ivo prop it wouldnt get on a plane @ 2800 also tried 2blades it was worse,then a 70'-40 stick prop turning 2900rpm it would run dry till you let off the throttle then i had to get off and push to get it to "brake free" at 2900rpm ,i just put on a 70'-30 paddle prop and drove up the lake okeechobee dike twice in a row not sure how tall it is but i dont have to worry bout finding a bigger hill and it will now brake free from the grass with me on it at 2000rpms but it takes more rpms to keep it on plane. I dont know the affect these props had on top speed because i cant top out my boat, it needs a trim tab.Now since minis dont try to run dry much its hard enough to get mine on a plane. WHAT PROP IS BETTER FOR GETTING THE BOAT TO PLANE OUT WIDE OR SKINNY, 2 OR 3 BLADES

Papee
01-17-2010, 01:06 PM
Now that is a question with many answers. The prop that will better for getting you on plane may not be the prop you need to get the overall performance you want. It's a pretty general question so I'll just say that a prop that you can spin up the fastest(with enough thrust generated) will get you out of the water faster. This could be a narrow or wide prop depending on your setup and the pitch of either prop.

I've used a short narrow prop with maximum pitch to get out of the water fast but there is no top end and you have to run your motor harder. Each situation is different so without and exact situation it's pretty hard to make a blanket statement for that question.

yamahaulerG1
01-17-2010, 07:27 PM
yeah i guess it would be hard to say every boat is a lil different.

brlcla
01-17-2010, 07:45 PM
wider is better.... on a mini i would choose a whirlwind mini prop over a warp drive... Also be on the lookout for a three blade mini prop from whirlwind... heard rumors that it may be coming... I will have one on my boat as soon as they are available.

chuckitt
01-17-2010, 09:13 PM
This question also has to do with the reduction ratio you are running and the rpm the motor you have will turn and still have power. Most motors will turn more rpm after the torque has topped out. It want help any to turn your engine 1000 more rpm's after your torque has peeked. Maybe 300 more is ok. A good rule is, low rpm motors should use a high ratio reduction ( 1.65, 1.69 to 1 ) Higher rpm motors can use a lower ratio reduction ( 2.0, 2.3, to 1 ) ect.
A good example of this is the 084 motor. This motor turns 1800 rpm constantly when running a generator. It will turn 3600 with ease and last awhile. It want last long turning over 4000. The first drives we got for the 084 was a 1.89 to 1. At 3600 rpm, we only got a prop speed of 1904 rpm which don't work good for max rpm's with most 3 blade ultralite props. We put a 6038 wood prop on it and it jumps on top of the water but the top speed suffers. Now when we change the ratio to a 1.65 to 1, we will get more prop speed and it will still get on plane good but will have a better top speed. We got the best performance from the Briggs motors with the max rpm at 3800 to 3900 no matter how we had them moded. We could take some pitch out of the prop and turn the motor 4400 but the performance fell off. We were running the 1.69 to 1 ratio. We have determined that high rpm would just cause the motor to wear out faster with no benefit. A 5000 rpm motor that builds torque up to 4500 rpm could use a lower ratio reduction like a 2.0 to 1 and work good.
I guess what i'am trying to say is the reduction ratio matched up to the torque of the engine may be more important than the prop you sellect.
Thanks, Chuck

brlcla
01-17-2010, 09:48 PM
I agree with you Chuck that the Briggs motors make best torque at 3600-4200 but that torque also does not drop off that much past those RPMS... Say I am making 61 ft.lbs at 3600 and 53 ft.lbs at 4400RPM. Taken from the online torque curves...

Prop Speed around 2200RPM +/-

3600PRM with 1.65:1 at 101 ft.lbs at the prop

4400 RPM with 2:1 at 106ft.lbs at the prop.

These modded Briggs depending on which one you have about a 5HP +/- increase between 3600 to 4400 rpm.... So to me I gain prop torque and I gain a few ponies... But i do loose some engine life running at higher RPMs but its all worth it in the end.

Once again it all depends on the motor but this was my reasoning behind going with a 2:1 instead of a 1.65:1. I wanted to run the slightly higher RPMs. With a 2:1 I actually gain the amount of torque at the prop which may allow me to run a degree or more in the blade... dont have a comparison because i have never run a the higher reduction to test my theory. So it is just a theory.

Now just to wait for a Whirlwind 3 Blade and do a little more testing.... 2 Blades are good for now but I can always use more...

That being said I do not stay at 4600 very long unless I am running a long distance and then I stay in the throttle... Just riding around ill use all 4600 to jump up but i easily back down to below 3600 and cruise at around 27-30 mph.

Now with a full load of two people and all our gear use all 4600 for a little longer but once I am up I am down in the 3900-4100 rpm range and easily cruise at 25-27mph....

yamahaulerG1
01-17-2010, 10:10 PM
thats some good info since i am running a 2:1 honda it is set up for the high rpms a new cam is coming tuesday they say it has lots of torq up to 6000 rpms but wth so many cam grinds to chose from hopfully i got a good one so the power curve dont drop out to soon. how good does the wide mini ww prop push?does it push more weight with less top end.compared to the three blade ultra prop the same length if it was on the same boat?