Total Chaos used boat purchase info wanted

Aircraft powered airboat discussion.
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Planeguy
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Re: Total Chaos used boat purchase info wanted

Post by Planeguy » Sun May 08, 2016 8:37 pm

The cheapest way I know of to check the tach is to find someone who is semi serious about having their RC airplanes and/or helicopters set up correctly and borrow their tach or just go to your local hobby store and buy one similar to this:
http://www.amazon.com/KASOTEK-Professio ... tachometer

I had a cable driven tach I thought was reading fast based on performance but once we got it checked out it was actually reading slow. The performance drop was from something else.

stonny9
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Re: Total Chaos used boat purchase info wanted

Post by stonny9 » Sun Feb 11, 2018 10:18 am

Long update and some local help requested. 4 like new 4 ring pistons slightly higher compression(can't remember style and owner is riding now) and 4 rechromed stock bore cylinders all from Don Davis. Don took out a degree in prop and now turning 2300 rpm. Don said tack is off alternator and alternator might have been changed and reading wrong. Also said he should swap to a holly carb and he has a warp drive that would be better.
Carb was tuned up a while back but after cylinders when cold it idles and stalls. Will idle warm. If I remember correctly he was told he should go to a 72 jet in a Holley 500 2 Barrel?

Tight on money after all the work but any opinions welcome.

Prop is 66" Water walker cypress. We cruise from camp to camp. Higher speed would be cool as we ride with CM reduction and o540 boats. But they won't leave us behind.

Boat has always had a hop on water at higher cruise speeds. Put 2 washers on rear motor no change. I went out by myself(140lbs) once 3 months ago before washers installed and boat was hopping so bad it was undriveable until I put cooler and 5 gal can on front rake and was ok at best. Has rear and center jacks with poly. We just dont know what to do.

Anyone know about electronic tach on alternator. Would like to at least confirm it is reading right before we do anything further.

We are mechanical(owner installed cylinders/pistons) but just don't know the finer details of what to do.

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Slidin Gator
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Re: Total Chaos used boat purchase info wanted

Post by Slidin Gator » Sun Feb 11, 2018 8:46 pm

Stoney9,

With an electronic alternator tach, is is very likely that your tach is off. The difference between a motor running right and an issue is 100-200 RPM at the prop.

You are describing a 700-300 RPM issue (pre-post Don Davis). Since Don changed the prop pitch, you can't use the previous performance as a guide, only the present. So now you have to determine if the motor is running right or if it still needs some work/tuning.

The thing with an electronic tach off the alternator is that the alternator does not run at the same speed as the engine due to the ratio between drive and driven pulleys. Plus, as a belt wears in (and you tighten the belt), the ratio changes. So an electronic Alternator tach is more of a guide vs. an absolute measurement.

You should listen to Planeguy, he is recommending that you use a strobe or nose cone type tach to directly measure the prop RPM. I use a device that requires a piece of reflective tape on the fly wheel (for outboards) or prop. It give a direct measurement of prop or flywheel RPM (1 reflection per revolution). The nose cone devices use a direct mechanical engagement to a prop nose cone, but don't work well for airboat prop systems. Once you confirm your actual RPM everyone will be better able to advise.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

Striker543
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Re: Total Chaos used boat purchase info wanted

Post by Striker543 » Mon Feb 12, 2018 7:41 am

No offense to Don, but he would tell you to run a warp drive on an 18ft gearbox boat. They’re tough, but very old technology in my opinion. Once you figure out your rpms, I would go to a 70” prop rather than a warp drive. Depending on what you have, you may be able to do that just by switching the hub.

sanshandaobojue
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Re: Total Chaos used boat purchase info wanted

Post by sanshandaobojue » Mon Feb 12, 2018 9:23 pm

Slidin Gator wrote:Stoney9,

With an electronic alternator tach, is is very likely that your tach is off. The difference between a motor running right and an issue is 100-200 RPM at the prop.

You are describing a 700-300 RPM issue (pre-post Don Davis). Since Don changed the prop pitch, you can't use the previous performance as a guide, only the present. So now you have to determine if the motor is running right or if it still needs some work/tuning.

The thing with an electronic tach off the alternator is that the alternator does not run at the same speed as the engine due to the ratio between drive and driven pulleys. Plus, as a belt wears in (and you tighten the belt), the ratio changes. So an electronic Alternator tach is more of a guide vs. an absolute measurement.

You should listen to Planeguy, he is recommending that you use a strobe or nose cone type tach to directly measure the prop RPM. I use a device that requires a piece of reflective tape on the fly wheel (for outboards) or prop. It give a direct measurement of prop or flywheel RPM (1 reflection per revolution). The nose cone devices use a direct mechanical engagement to a prop nose cone, but don't work well for airboat prop systems. Once you confirm your actual RPM everyone will be better able to advise.
Hi, as mention the ratio changes when you tighten the belt, this will only happen the old "V" type belt, because it runs by friction. Now most airboats use synchronous belt, so the rate is fixed, never change when you tighten the belt.

I have the equipment to measure the propeller or flywheel 's speed directly. I am using it to measure the actural speed of propeller, so I know the thrust at difference speed. There are 2 type of portable digital tachmeter: 1 is laser, no need touch the object, measure the rotation rate in rpm; other one is touchable, which deliver with many wheels, touch object and measure the linear velocit and rotation rate.
see pic below, I purchase it from Taobao.
rs.jpg
rs1.jpg
Last edited by sanshandaobojue on Mon Feb 12, 2018 10:04 pm, edited 1 time in total.

sanshandaobojue
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Re: Total Chaos used boat purchase info wanted

Post by sanshandaobojue » Mon Feb 12, 2018 9:25 pm

My digital is in the workshop, so I post some pic of others to show how to use them.
1.Laser type.
rs2.jpg
rs3.jpg

sanshandaobojue
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Re: Total Chaos used boat purchase info wanted

Post by sanshandaobojue » Mon Feb 12, 2018 9:27 pm

2. Touch type
rs41.jpg
rs5.jpg
rs4.jpg

sanshandaobojue
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Re: Total Chaos used boat purchase info wanted

Post by sanshandaobojue » Mon Feb 12, 2018 9:56 pm

All the above is portable tachmeter, suitable for installation or mantaince the airboat, I also purshased tachmeter with hours, and deliver with magnetoelastic transducer, easy installed nearby the flywheel. It's same as the ABS transducer of vehicle wheels.
Usually the fly wheel speed means engine speed, but difference with propeller's speed due to the gear reduction or belt reduction. on it's back there is a button, which you can manually input the rate of readings and meased speed, usually the rate is the number of teech of fly wheel multiply by reduction rate.
Forexample, the flywheel of engine have 100 teech, and the belt reduction rate is 2:1, so manually input the rate 50:1 to the tachmeter, it will shown 3000rpm when engine runs at 6000rpm.



tm3.jpg
tm2.jpg
tm1.jpg

stonny9
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Re: Total Chaos used boat purchase info wanted

Post by stonny9 » Tue Feb 13, 2018 11:27 am

San. Thanks for the info. I think you are too smart for most of us. I dont have much use for a laser or strobe reader. Just something to put in a toolbox but maybe I could use it on my small equipment to see if I am getting the most rpm/power.

I would like a quality one and would spend maybe $50. I know nothing about the brands so I found a cheap one on ebay. It looks the same as several others just a different color and seller.

I dont know of an RC hobbyist to borrow one. I am gonna go check a RC Hobby Shop when I pass by one then decide what to get. Will get a pistol grip one as it seems like a safer idea around a prop. This isn't my boat I am just doing the leg work and will make a small purchase for a tool myself.

Also the boat has a matching set of Faria White gauges and I found an old post for a local speedometer shop lspeedo.com

https://www.amazon.com/NKTECH-Tachomete ... 3Z1QS1MFJ7

SWAMPHUNTER45
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Re: Total Chaos used boat purchase info wanted

Post by SWAMPHUNTER45 » Tue Feb 13, 2018 11:40 am

Dang our Asian buddy if pretty smart!

Cool idea San ! very good

stonny9
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Re: Total Chaos used boat purchase info wanted

Post by stonny9 » Sat Jul 28, 2018 9:06 pm

Update after $6k spent at don davis and maybe 6 hrs of run time motor is now blown. Puking oil and had to be towed back to ramp. Before it was hard starting when hot.

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