Real Time Thrust Tests with Complete Boats
- Thread starter Roxy7430
- Start date
F vs I as tested. How do they compare when riding? If unknown thats ok. They are close on the thrust/weight ratio ( with the gpu having the advantage) but they have a big diff in Hp. In the scheme of thing I would think the only thing that matters (for dry running)are two numbers thrust/ weight ratio and bottom friction coefficient, granted engine angle and weight placement will come into play.
Btw thank y'all for the testing I have been watching this thread like a hawk.
Btw thank y'all for the testing I have been watching this thread like a hawk.
muffled500hp
Well-known member
Interesting that the 3 blade R propeller with pitch setting 2.5 on test boat "A" produced more thrust that the 4 blade R with pitch setting 3 on test boat "D" with the same ratio.
saltwatershooter
Member
Prop RPM difference?
Blackcoffee
Well-known member
Maybe they should pitch the 4 blade R at 2.5 get some more rpms to equal numbers out and see what happens. Cruise speed was almost the same.
Waterthunder
Well-known member
Keith the numbers are believable. One is where a R blade performs well and the other is just below where the R shines. Plus with the 2.68 the window gets bigger. I have the 2.38 motor here and were about to put a 2.68 on it and turn it 400 or 500 RPM's more and trust me the numbers will do nothing but go up. The two best ways to make thrust with a small block is more gear ratio and more engine RPM's.
hmgm123
Well-known member
Waterthunder said:
Seems to me that tip speed is coming into play being relative to thrust being produce. But I also think the lower gear ratio and bigger or more pitch in the prop gives the snap to break a boat loose on the dry ground. I be willing to bet if gradually give the motor gas it would take more thrust for a boat to break loose than if you were to do it quickly and use the snap to break it loose with less thrust.
CarMotorBarge
Well-known member
muffled500hp said:
I definitely believe this. A 4 blade 82 inch R spinning at 5400 engine RPMs with a 2.68 gear box will create the same static thrust has an 82 inch 3 blade R spinning at 5800 engine RPMs with a 2.68. Dave informed me about this when I was inquiring about buying a motor from him. The RnD work that he had done on his thrust tester showed this. You can't beat a 4 blade R for static thrust when properly set up. The 3 blade provides more snap and a higher top speed. The 4 blade will provide more static thrust and a better cruise.
So what type and thickness of metal is the Ford boat made from? Poobought why is your boat the heaviest? Do you have lots of poo inside of it? :lol: I am trying to understand what is causing the difference in weight between these 2 boats. Thanks.
HuntingBigun
Well-known member
CarMotorBarge said:
The devil is in the details the same engine that can spin a 4 blade R at 5400 will blow by the 5800 rpm on the way to 4.5 pitch. I know because my thunder boat with Dave's 550 and 2.68 spun the 3 blade r on 4.5 at 6000 rpm = no push on the ground went to 4 blade R at 2.5 turn 5800= run dry no problem. Sure if I could have put 82 that would have help but no room. Lost 10 mph also on that boat.
The point I trying to make it takes X hsp to turn Z blades with Y gearbox, so if is not a matter of just saying heck I twist another 500 rpm out of my motor. That is why I went with 2.52 belt if I ran 2.6 been way past 3, heck I am almost at 3 now turning 5200 WOT. Brad put more pitch in Thunder brought the rpm down to 5000 cruises better rpm not as snappy but 4.00 gal it was Worth it to him.
Now my first GTO with 2.55 man well that makes another story
But heck the only testing I have done is on 3 different LS powered boats with 3 different hulls and engine combo's Carry on I like reading all this stuff and I want my turn on that thrust tester bet ya I can beat that ford or BBC. I anit scared
LS Rules just have to know the sweet spot CarMotorBarge
Well-known member
Bigun,
In your first paragraph, I think you said that a 4 blade produced more static thrust at 200 RPMs less than the 3 blade and the 4 blade lost 10 MPH. If so then I think we are saying the same thing. Also what was your reason for not going with a longer prop on your new boat? Thanks.
In your first paragraph, I think you said that a 4 blade produced more static thrust at 200 RPMs less than the 3 blade and the 4 blade lost 10 MPH. If so then I think we are saying the same thing. Also what was your reason for not going with a longer prop on your new boat? Thanks.
Good info...Just curious if anyone would have a rough idea on the weight comparison (bare hull) of test boat C the scorpion sled vs a fiberglass hartline hull....I know the hartlines are a heavy hull, but have no idea how they would compare in weight to a sled of the same length....This info is outstanding and I am sure it will help a lot of folks on future builds...It sure has me thinking, and rethinking.....Once again, thanks for all the good info I applaud all of you for your efforts...
HuntingBigun
Well-known member
CarMotorBarge said:
Well I did not get stuck anymore so must be more thrust :lol: :lol:
The GTO only had room for 80 prop, we did not think Dave's mod's to my motor would push us past 4.0 or I would not went up from 2.5 to 2.68. 4 blades cost more :toothy7: It was Dave's fault for tweaking the engine with new intake and cam when I built the 2nd GTO. Plus that was a stock bore and stroke LS. I ran it at 6000 to get the extra HSP (dyno 600 at 6000) but Brad stuck more pitch in save fuel, I have to run it top end and see if the speed picked up.
Keith tried to tell me if I went to 2.68 that may run out of prop on Dixie Thunder. :dontknow:
the DB we are runnning 82 and fighting enough torque roll with that when the supercharger kicks in 800 ft lb torque at 3800 rpm 8) Plus this time I let the boat builder pick the ratio, Bobby tried 3 differant belt ratios and he said if ran the best all around with the 2.5, I figured he knows more than me
So how long prop do you think I have to run if I am turning 4 82R almost at 3 if I went to a 3bld. answer is too long at least that was what Sensich & Bobby said.
That is my main point there all lots of reason we may run a certain prop so gear ratio is matched to the prop & engine combo. I am not a 2.68 for everything fan. But heck I no expert
So when do I get to play on the tester 8) 8) 8)
CarMotorBarge said:
At the time of testing the Ford powered boat had nothing in it. And mean that literally. It only had five gallons of gas in it and one battery,mine was full of all my junk and two batteries. My rigging is one of the biggest difference. It is built heavy to help support the air ride suspension. The hulls are the same thickness, the differance is just in the details.
Hey Begun, I'm sure you will blow more thrust than that ole junk yard Ford but be careful when calling him out. You may get your feelings hurt in a 400ft race. Sometimes money cant out run knowledge. And he is a racer from the old days. He knows how to make them run.
CarMotorBarge
Well-known member
Thanks poobought. The boats looked very similar. I was just trying to understand why the weights were so different.
Thanks Bigun. I was trying to understand why you didn't try an 84 inch 4 blade R pitched at close to 2 on your new boat and turn the engine at 5400. I would expect more static thrust because of the additional prop length, but also more torque roll. Sounds like you were worried about torque roll.
So I have been thinking about all of this prop testing that is being done by the North Florida guys. This prop testing is very useful for static thrust. The problem is that this testing only shows how well your boat will do when breaking loose on the hill or moving at slow speeds. It doesn't show dynamic thrust while at a cruise or hauling butt.
Look at Anvil's boat. He has his prop over pitched so that he gets better fuel mileage. He is getting better fuel mileage because of lower engine RPMs, but I suspect that he is also getting better fule mileage because he has more dynamic thrust.
The Sensenich R blade is supposed to be the most efficient set on 2. However I think this is only true when the boat is not moving. As the MPHs that a boat is traveling at increases, an R blade set on 2 will become more inefficient. That is why the over pitching helps. It makes the prop more efficient at higher boat speeds. However you give up static thrust.
This is the entire idea behind the variable pitch prop that David Wine was talking about several months ago. When you are stuck, you can set the pitch at 2 and get the most efficiency. When you are traveling at 30 MPH, you can over pitch the prop and maintain the same efficiency.
So I am bringing this up to see if there are any ideas about how to test dynamic thrust. Without this data, you cannot get a complete picture of how well a prop combo performs. This goes for performance, fuel mileage, and sound.
Look at Biguns boat. Should he use a 4 blade 82 inch R pitched at 3? This gives him the flexibility to adjust static and dynamic thrust depending on where he sets the pitch. However what happens if he uses a 4 blade 84 inch R with a 2.68 gearbox? He could set the engine WOT at 5400 and make more static thrust then the 82 inch R. He could also pitch the 84 inch R and bring down the engine RPMs to get better fuel mileage and increase dynamic thrust. Will this provide better fuel mileage and more dynamic thrust than his current setup (82 pitched at 3)? I don't know, but it would be nice to get this type of data.
Please do not think that I am saying that the current thrust testing is being poorly done. I personally think that it is being well done and has caused lots of useful conversation about something very important to the airboat industry and how it is perceived by the general public. :salute: I am just trying to help out from over 200 miles away.
Thanks Bigun. I was trying to understand why you didn't try an 84 inch 4 blade R pitched at close to 2 on your new boat and turn the engine at 5400. I would expect more static thrust because of the additional prop length, but also more torque roll. Sounds like you were worried about torque roll.
So I have been thinking about all of this prop testing that is being done by the North Florida guys. This prop testing is very useful for static thrust. The problem is that this testing only shows how well your boat will do when breaking loose on the hill or moving at slow speeds. It doesn't show dynamic thrust while at a cruise or hauling butt.
Look at Anvil's boat. He has his prop over pitched so that he gets better fuel mileage. He is getting better fuel mileage because of lower engine RPMs, but I suspect that he is also getting better fule mileage because he has more dynamic thrust.
The Sensenich R blade is supposed to be the most efficient set on 2. However I think this is only true when the boat is not moving. As the MPHs that a boat is traveling at increases, an R blade set on 2 will become more inefficient. That is why the over pitching helps. It makes the prop more efficient at higher boat speeds. However you give up static thrust.
This is the entire idea behind the variable pitch prop that David Wine was talking about several months ago. When you are stuck, you can set the pitch at 2 and get the most efficiency. When you are traveling at 30 MPH, you can over pitch the prop and maintain the same efficiency.
So I am bringing this up to see if there are any ideas about how to test dynamic thrust. Without this data, you cannot get a complete picture of how well a prop combo performs. This goes for performance, fuel mileage, and sound.
Look at Biguns boat. Should he use a 4 blade 82 inch R pitched at 3? This gives him the flexibility to adjust static and dynamic thrust depending on where he sets the pitch. However what happens if he uses a 4 blade 84 inch R with a 2.68 gearbox? He could set the engine WOT at 5400 and make more static thrust then the 82 inch R. He could also pitch the 84 inch R and bring down the engine RPMs to get better fuel mileage and increase dynamic thrust. Will this provide better fuel mileage and more dynamic thrust than his current setup (82 pitched at 3)? I don't know, but it would be nice to get this type of data.
Please do not think that I am saying that the current thrust testing is being poorly done. I personally think that it is being well done and has caused lots of useful conversation about something very important to the airboat industry and how it is perceived by the general public. :salute: I am just trying to help out from over 200 miles away.
HuntingBigun
Well-known member
poobought said:
Heck I want to race on the trailer
I have seen that boat run, I do not want no of that plus I bet ya I weigh 3000 lbs, that is why I need all the hsp
HuntingBigun
Well-known member
poobought said:
NO idea really but with all the stuff I haul for all those women who knows :lol: :lol: :lol: