Weight of airboat please.

Airboats with smaller powerplants.
Alpal
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Weight of airboat please.

Postby Alpal » Mon Jun 20, 2016 1:48 am

I think my Aluminium 11ft 6" by 6ft 3" deckover with it's 4cyl. Subaru car engine is too heavy at 880 lbs. Was wondering what other Minnies about this size weigh..Our boat cruises ok but if I try to go too fast the nose digs in a bit. It is like the water friction gets too great and the high up thrust pushes the nose down. I have tried adjusting the engine angle. I am thinking some slick stuff would help but can't find any down here. Any clues on weights of boats and, or home made slick coatings would be nice.... Allan

jeepinocala1111
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Re: Weight of airboat please.

Postby jeepinocala1111 » Mon Jun 20, 2016 6:38 am

Alpal wrote:I think my Aluminium 11ft 6" by 6ft 3" deckover with it's 4cyl. Subaru car engine is too heavy at 880 lbs. Was wondering what other Minnies about this size weigh..Our boat cruises ok but if I try to go too fast the nose digs in a bit. It is like the water friction gets too great and the high up thrust pushes the nose down. I have tried adjusting the engine angle. I am thinking some slick stuff would help but can't find any down here. Any clues on weights of boats and, or home made slick coatings would be nice.... Allan


Level your engine to the bottom of the boat.

papajack
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Re: Weight of airboat please.

Postby papajack » Mon Jun 20, 2016 7:10 am

G'day mate. Should have hooked mine up to the r.v. when you were here and taken it home with you!!!

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CactusJack
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Re: Weight of airboat please.

Postby CactusJack » Mon Jun 20, 2016 7:57 am

jeepinocala1111 wrote:
Level your engine to the bottom of the boat.


Or tilt the engine down at the front or up at the back? There are a few other things I would look at... hook in the hull, how far forward the gas tank is situated, the weight and position of the driver or any passengers or gear like cooler, if it has a rake that is heavy (and things tied to it) etc.... and a cav plate might help. It could be a simple case of the weight and balance being a little too far forward?

When you get it on the plane, where does the spray start coming out of each side? Nearer the front? Nearer the back? As you go faster and it wants to dig the nose in, where the spray comes out of the side move closer to the front? I would say when planning, any spray should be coming out between the drivers seat and the motor meaning the front of the hull isn't even in the water to create drag?

Got any pics?
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
Airboat experience so far, limited to having bolted a gyrocopter to a flat bottom punt.... but THAT.... is about to change, bigtime :-)

Alpal
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Re: Weight of airboat please.

Postby Alpal » Tue Jun 21, 2016 5:59 am

Hi guys. Kate is trying to attach a pic of 'Didgeredo" showing it running ok. Problem is when I try to go faster, the nose sinks to horizontal , especially when the front seat is occupied. I think the drag of the hull in the water is the problem. Allan...PS. G,day to you and Cindy, Jack and you too, Cactus and thanks for your advice Jeepo.

2012_1221 010.jpg
Airboat in action

papajack
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Re: Weight of airboat please.

Postby papajack » Tue Jun 21, 2016 6:30 am

Allan, if you remember, my hull is 12 x 6 on the bottom. However it only weighs 512 lbs with a full tank of gas. I think yours is a little heavy for the displacement. You might also check the bottom edge of your transom. If it is bent downward it my be pushing the back up and the nose over. Have Kate check inside the hull for manhole covers as they add weight quickly. Cheers, Jack

Alpal
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Re: Weight of airboat please.

Postby Alpal » Wed Jun 22, 2016 6:08 pm

Manhole Cover! Heh heh heh. I am not in France now, Jack....

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CactusJack
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Re: Weight of airboat please.

Postby CactusJack » Thu Jun 23, 2016 4:37 am

Hi Al, is that the ' swamp people' boat you dropped in on me with? Does it nose down more when the front seat is occupied?

Because the Subaru motor is so light, having someone sit in the front seat will easily make the weight ' balance point' move very far forward... the bigger boats with heavy engines are less affected by weight towards the front.

If you look for hooks in the hull (where the skin goes concave between stringers) ... if you find any, fit some jacks to push the bottom straight and it will stop the hull sucking onto the water, like holding the back of a t spoon under a running tap.... the t spoon gets sucked into the water flow. The skin of the hull needs to be straight.

If it is straight enough, try moving anything you can that is heavy rearward as far as you can. That pic looks like it is running fine, but I can see that anyone sitting in the front seat will make the front of the hull want to sit on the water, creating the drag you speak of.

Try putting a spacer under your rearmost engine mounts so the line of the crankshaft is higher at the back, so when you power on the back of the boat gets pushed into the water... if the crank/thrustline is level, or high at the front, as you power on, it tends to lift the back and push the nose down, especially if there is weight in the front seat as well...
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
Airboat experience so far, limited to having bolted a gyrocopter to a flat bottom punt.... but THAT.... is about to change, bigtime :-)

Alpal
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Re: Weight of airboat please.

Postby Alpal » Thu Jun 23, 2016 9:45 pm

Yes Cactus. Our boat ,"Didgeridoo" is the one you saw at Landsborough. We plan a trip down to South Australia later this year so I want to get her going really well for that big trip. About 2500 miles probably. Like an Airboat Roadtrip with our little Toyota Coaster Motorhome towing "Didge" and checking out all the wet spots on the way....The mighty Murray River especially...I wish our Coaster was 4wd. Steep boat ramps are a bit tricky. Anyway, I will be looking for hooks in the hull as soon as the weather warms up. It is freezing up here at the moment. So thanks for all that good advice and I will report on results when I have them...PS.. You being a Gyro bloke, what do you reckon the Subaru engine, box and prop would weigh.. Allan

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CactusJack
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Re: Weight of airboat please.

Postby CactusJack » Fri Jun 24, 2016 1:32 am

I would say the EA81 and rotax box would be about 100kg or 220# or there abouts. Because the light weight motor at the back, any weight you put up the front will have a greater effect on the center of gravity/balance point. It is like, if you have a fat bugger sitting on a see saw (the motor), you need alot of weight on the other end (front passenger seat) to have any effect on him... if the person on the back is not heavy, even a small weight in the front seat will cause the boat to ride on the front of the hull and effectively become like a barge, rather than a planning boat.

So, you need to get any weight you can to the back of the boat (battery, gas tank, cooler, radiator, storage etc) and make sure the drivers seat and front seat is back as far as possible. Do you find it is much better with no weight in the front seat? Does skinny water help it or not really that much?
Attachments
airboat 280714s.jpg
airboat ea81.jpg
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
Airboat experience so far, limited to having bolted a gyrocopter to a flat bottom punt.... but THAT.... is about to change, bigtime :-)

Swampbuggy
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Re: Weight of airboat please.

Postby Swampbuggy » Fri Jun 24, 2016 6:23 am

gatorglide.com Sound to me weight and motor a just ment

Alpal
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Re: Weight of airboat please.

Postby Alpal » Fri Jun 24, 2016 6:38 pm

Yes Cactus, having no passenger on the front helps of course but the pass. seat is not too far forward. You ask about how it goes on skinny water??? What skinny water..I would love to find some but don't plan to go 1500 miles north to croc country and get eaten so we have to play around on rivers and lakes down here... I get green with envy when I remember all the swamps in Fl. and the shallow sandy bottom Platte River up in Nebraska. Those Quad-Copter video's from the States are unreal.. Keeps me "Airboat excited." Thanks for your advice....Allan


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