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Airboat Talk: Technical Reference Section

Southern Airboat Gallery Archives

10'6" wide bradberry
ok ok let me go my dads ready to take a picture
New Camp in Progress
IMG_1088
S 64 Sky crane
oh so true
leo_081103

leo_081103

Well-known member
Good day to us all guys!

I would like to suggest that we share our own figures in this section for the benefit of everyone. Any contribution I think will be greatly appreciated by our fellow airboaters. I suggest that we start at this sample format:

Hull Size : 15' x 7.5'
Engine/Rating @rpm : GM 454 350hp @ 4800 rpm
Prop Size and Make : 86" x 48" 2 Blade Wood Prop
Prop Set-Up ( for Adjustable props ) : PS 3 Blade 76" @ 12 deg
Drive Ratio : 2:1
Tachometer Reading : 4600 rpm WOT
Attained Speed : 55 mph


Above figures will not only help our fellow boaters but will also help newbies set-up their own rigs. These will also make them do cross references instead of asking for answers except of course when data is not available for their intended set-up.

And for those technically adepth members, please do post comment or reply to our fellow members if their set-up is a bit odd i.e. props that are spun beyond rpm limits, boats that are seem too slow for the power installed, etc.

And btw, please include some comments on your boat on how it performs.

I hope this idea helps a lot!

Thanks.

Happy airboating guys.
 
leo, I think I know where you're going with this but I need to tell you early on that I have already disagreed with one of your earlier permises on another post ...... that it's horsepower and not torque that needs to be considered as regards thrust. That's just not accurate.

You may do well to read some of the hundreds of posts that have already been made by dozens of folks with respect to this issue. Instead of starting a meaningless thread, you may want to try doing a little (available right here) research first.

olf
 
Hi there Olf,

First of all, let me state my intentions why I opened up such a thread. I am new here and yet, perhaps I have read lots of post here more than any new member could have read in the duration of my membership. I have even took part in other forums on other sites regarding airboats, engines and propulsion systems. My intentions was to create a database for fellow boaters who would like to experiment various set-ups. If only a table or list of existing proven combinations exists where they can gather information that their idea/s may work will be a big help to them! If you ever had heard of the term "similitude" then you may have got an idea of my intentions.

I dont expect you to agree on my opinion because we all are entitled to our own opinion. What I have posted in the other thread were "FACTS" and not hunches.

You need consider power to be primary regarding thrust and not torque. Torque, diameter, rpm, etc. are parameters determining thrust! The goal is to blend in those parameters the right amount to convert power to thrust efficiently! Ex. a boat needs, say at least 30 hp to get past the hump speed. I'll give you 25 hp engine, now try to get that boat on plane...GOOD LUCK!!! Anyone who knows simple machine principles can extract even 10,000 ft-lbs from a 25 hp engine. Yes, that is 10,000 ft-lbs ( ten thousand foot-lbs )!!! Now, can you make the boat plane??? I bet that you yourself can even extract 20,000 ft-lbs from a 10 hp engine, can you???

And may I say, is it not that being rude or insulting someone of saying "starting a meaningless thread" is not a good practice of showing a good sense of discipline? I think you should get yourself straightened up before reacting. It's a shame that you may have PM or e-mailed me before you post such a comment. Anyways, it's been insulting but I get to learn something from it!
 
Sorry Glenn, my sincere apologies. I was just so offended by his post and that his words is not a good example especially to new members. Maybe by posting my remarks of the same nature makes me a cold one too. My apologies to everyone. That goes to you too Olf. Sorry. Emotions kicked off.

Anyways, I have no personal agenda against Olf, that was just on his reply.

Hey Olf, I think we need to settle this over cold beer and get to know each other! It's on me!
 
leo_081103":2azjldn9 said:
Hi there Olf,

First of all, let me state my intentions why I opened up such a thread. I am new here and yet, perhaps I have read lots of post here more than any new member could have read in the duration of my membership. I have even took part in other forums on other sites regarding airboats, engines and propulsion systems. My intentions was to create a database for fellow boaters who would like to experiment various set-ups. If only a table or list of existing proven combinations exists where they can gather information that their idea/s may work will be a big help to them! If you ever had heard of the term "similitude" then you may have got an idea of my intentions.

I dont expect you to agree on my opinion because we all are entitled to our own opinion. What I have posted in the other thread were "FACTS" and not hunches.

You need consider power to be primary regarding thrust and not torque. Torque, diameter, rpm, etc. are parameters determining thrust! The goal is to blend in those parameters the right amount to convert power to thrust efficiently! Ex. a boat needs, say at least 30 hp to get past the hump speed. I'll give you 25 hp engine, now try to get that boat on plane...GOOD LUCK!!! Anyone who knows simple machine principles can extract even 10,000 ft-lbs from a 25 hp engine. Yes, that is 10,000 ft-lbs ( ten thousand foot-lbs )!!! Now, can you make the boat plane??? I bet that you yourself can even extract 20,000 ft-lbs from a 10 hp engine, can you???

And may I say, is it not that being rude or insulting someone of saying "starting a meaningless thread" is not a good practice of showing a good sense of discipline? I think you should get yourself straightened up before reacting. It's a shame that you may have PM or e-mailed me before you post such a comment. Anyways, it's been insulting but I get to learn something from it!
Click to expand...

Hey I'll take the engine :lol: I have a 16x6 alum with an 18hp briggs that planes. ( starting out in low water) I never was good at math :cry:
 
The challenge was to make a hull plane whose "HUMP" ( transition speed to enter plane) requires 30 hp to pass through. Anything less than 30 hp would not suffice and even an engine with 30 hp engine would not do either since efficiency is aalways less than 100 percent.
 
Sorry, that was a trick question! You can never make any hull plane if you cannot surpass its hump speed.
 
Well it takes very little HP tp move a hull at "hull speed". Thats 1.3 time the Sq. Root of the waterline length. I'm sure theres a pretty well established formula to move it from hull speed to planing speed.

We all know it takes way more HP to get a hull to plane than it does to remain on a plane.

As for opening a tech ref section, well...... I find it more refreshing to talk with folks than to go grab cold numbers. Numbers only tell a part of the story, the other part is quite subjective and may well me the most valuable part.

Were a fairly close family here and the way to get info is to stick around and partiscipate in the forum with us, not just raid files for data. Soon as we set up a file system with that kind of info in it, someone is going to be held lible for the accuracy of such, because some fool will take it as fact and go tear something up or get hurt with it. In my opinion better to listen to others explain their experiences and try to understand why they get what they get, than to just grab their numbers.

Just think how many gator tail or frog legg dinners have been enjoyed over sharing info on our boats compared to haw many friendships have been gleaned from raiding a file system. I'll take the frawgs anytime.

Scotty
 
I agree with you Whitebear. Not all of the people, members and visitors are that well developed to know what is proper and what is not. I also agree on the fact that talking to people is far better than sorting out figures ( even if they are accurate) and applying them to their boats. Of course, there will always be a good/bad side, advantages and disadvantages in all things. I consider people here to be broad minded and that we are not foolish enough to rely on figures without asking for details... i.e. cost, handling, durability and the likes.

The thing here is to have our fellow members a starting point and get an idea of various set-ups. I'm sure, even I, we dont treat figures as gospel BUT figures and opinions will say that we are in the right track.
 
I THINK IF YOU GOTTA BE ABLE TO DO CHINESE ALGEBRA TO FIGURE OUT WHAT PROP YOU NEED , YOU GOT PROBLEMS BROTHER ...AIRBOATIN AINT THAT HARD GUY'S :D :D :D :D :D

SET YOUR PITCH TO THE RPM YOUR MOTOR PRODUCES AND GO AIRBOATIN GUY'S ....


PIE EQUALS-{}-X ^-++{}-xxx-EQUALS IF YOU TALK LIKE THIS IN THE MARSH YOUR GONNA GET YOUR ASS KICKED!!!!!!.LOL...... :lol:
 
Leo, what do you do in PI? I spent a fair amount of time in PI while in the navy. Fond memmories in Olongapo.

I see you are quick witted. Just remember things don't always come across as you and others intended. Over all, a great bunch of people.

Time will tell on how many people reply to your post. Good luck!!!

San Maguel for my friends, bartender!!!!!!
 
That's what I'm saying D. Buying a prop and setting it to the engine's rpm and having yourself contented would be great...up until you asked yourself, "can I still go better?".

No book, math, engineer/designer can match the real life figures and accumulated experiences and opinions of the ones who had the hours in the boat.

Airboating is not that simple ( not that cheap either). This is why we bang our heads together to get ourselves to it the most practical way we can.
 
Some people desire an understanding that is greater than one coat of paint deep. "Chinese Algebra" doesn't make a boat go, no, it is an enabeler of understanding. Understnad ?

This is the age old delima, that, SOMEONE has to understand it first, then once done, anyone can do it.

There's nothing wrong with raising the bar of understanding among the average users. Everyone benefits from it.

Analytical thought into old age has proven to be a factor in preventing or at least delaying Alzheimers even. A carnium full of mush isn't much of a future, but if ya don't exercise that thing, it could fail ya when ya most need it. By then you won't know the difference, but everyone that you know will.

Scotty
 
Hull Size : 15' x 7.5' 1978 Panther Aluminum with Poly
Engine/Rating @rpm : no real idea... 400 foot pounds at 3000 rpm
I'll add Engine: Stock 500 Cadillac
Prop Size and Make : 74" Whirlwind Stump Puller 2-Blade
Prop Set-Up ( for Adjustable props ) : 18 deg on second mark
Drive Ratio : Direct Drive
Tachometer Reading : 2600 rpm WOT
Attained Speed : NO GPS To Check. See Below I'm not interested in speed!

I can rund dry on hard sand loaded with 4 adults and my 2 year old. Haven't had the guts to try a hill (riverbank) yet. But If I had a run and the hill isn't too long should be no problem.

Edit 8/16 Cruise with 2 adults and 1 kid at 2000 rpm on a nice plane.

If this is what you started this post for then let the info roll. I'd be interested in some combinations.
 
Thanks nebraskaairboater!

Your contribution will surely be a great help to our fellow boaters.

Happy Boating.
 
i think its a good idea, lets see whats out there.

13X 8 Air Ranger
1/4"Poly and sprayer system
Lycoming 0540 SV
260 hp @2750
78" Narrow 3 Blade Sensenich
Max rpms 2800 with pitch set @ 1.25

notes -- has great thrust and good snap. seems longer blade prop has solved porpoising problem. cruise alone at 1800 in deep water at 25 mph. runs dry with 4 adults on flat ground
 
A larger dia prop will push a boat on it's nose. The larger the prop dia the more leverage your prop has to push your nose down. In the same reason a boat that barely rides on it's nose will stop doing so if you go to a shorter prop. That is why car motor boats 14ft or smaller don't run 80 inch and up prop's.
 
i believe you mentioned that before Waterthunder. that was one of the reasons i went with such a long prop. wanted to see if it was true....once again YOU WERE RIGHT!!
 
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