planning a two seater PWC-air boat hybrid

[marthandan]

hi
i am marthandan from India.

i am planning to build a two seater PWC-air boat hybrid with the following basic specs.

hull design:
l - 8 ft
max width - 4 ft
material - aluminium frame with frp body.

powerplant: car engine (800cc, 37bhp@5000 rpm, 59N-m @2500 rpm.)

propellor design - 3 blade of dia - 4 ft.

the engine weighs approx 75kgs includind cooling system, exhaust etc.
so i estimate the fully finished PWC to weigh less than 200 kgs.

i would like to know if the basic specs are compatible.

please do suggest changes necessary.

[Guest625101138]

With 75kg engine, two adult passengers, frame for propeller, prop transmission and the hull it will be more than 200kg. I expect more like 400 to 500kg.

You do not say what speed you are after but it will plane. The prop efficiency will be low but you have ample power.

You will need to keep all the weight low down to keep it stable. The motor should be mounted on the bottom of the hull. Seats should be low. Even then it will be easy to tip with a 4ft beam.

Rick W

[kach22i]

Originally Posted by Rick Willoughby

Even then it will be easy to tip with a 4ft beam.

Good point, plus spinning air propellers have the nasty habit of exploding should they ever touch water, even a little bit at the tip.

[masalai]

google Ramphos it is in production in Italy...

[marthandan]

thank you will....
this is what i have in mind.
my main doubt is that since the rider (and pillion) block some of the swept area of the prop....will there be enough thrust left to propel the pwc to around 35 mph?
if not what other changes?

[Guest625101138]

You may be able to mount the bottom pulley directly off the motor rather than having three extra blocks. You should not have a problem setting the motor further aft.

The issue is not really a problem with getting air to the fan. It is a matter of how much drag the riders offer. A good front AND tail fairing around the riders will reduce their drag and get nice clean air to the prop.

The speed will depend on the weight and diameter of the prop. You should be able to get 30kts with the power you have and 1.2m prop.

A properly shaped fan cowling rather than just a guard would improve the prop efficiency. Look up ducted fan to get an idea. Could be a development to get a bit more speed.

You can get a good idea of efficiency using JavaProp - Google it and run the Applet. I can help you set it up if you want.

First thing though is to do a realistic estimate of the weight. Make a complete list of everything you need and give it a realistic weight. A hull that is slamming across the water at 30kts need some strength.

Rick W

[Submarine Tom]

OR, a streamlined canopy over the entire cockpit and discard the prop

guard...

Tom

[marshmat]

The issue of air props tending to self-destruct on contact with the water is still going to be a problem, I think, no matter how you streamline it. PWCs, by and large, are designed to have the stuffing beaten out of them by overly aggressive riders who aren't thinking things through. They crash, on average, about every eight minutes. A drivetrain that will be seriously damaged by even a minor crash seems out of place on such a boat.

An air prop on such a small craft is also likely to cause substantial torque issues and gyroscopic forces, which will affect handling. It also raises the centre of gravity, and will be noisy.

What market are you targeting with this idea? Is there some particular group of users that you think would benefit from a small PWC/airboat hybrid, that is not well served by more conventional craft of either genre?

[masalai]

Ahem, steering and I imagined initially you would be flying it ? They (Ramphos) use a beamy hull of special stepped design to break free of the water and the wing area is used to stabilise the craft during take-off not designed for turning corners with an air screw.... http://www.ramphos.com/e/home.html

[COLD-EH']

You will probably need to run a wider bottom. if you want to learn about airboat's check out southernairboats.com

[WestVanHan]

Just build a hovercraft.

[COLD-EH']

Hovercrafts are interesting but airboats are simple just like a water propeller boat. Engine mounted high isn't so much of an issue if you can have a wider hull, really surprising! Smaller HP stuff if you have to build your own reduction unit I would consider long belt type setup with engine mounted low but not necessary. Check out the Southernairboat.com mini section. Lots of people doing similar sized stuff and references to ideas like you have. Good source for propellers, reductions, engines or just ideas what a lot of other people have already done. Mine isn't a mini but it's a BLAST! (you can get away with that a lot when you own an airboat!) I like boat's and there isn't one that can do everything you want a boat to do!

Check out my video's, you have to realise that it's a big block chevy hanging up there, my prop is 7' in diameter and while it's only a 180 and not a 360 in these videos.... 360 are fun too!!!

http://www.youtube.com/my_videos

[Guest625101138]

Originally Posted by COLD-EH'

....
Check out my video's, you have to realise that it's a big block chevy hanging up there, my prop is 7' in diameter and while it's only a 180 and not a 360 in these videos.... 360 are fun too!!!

http://www.youtube.com/my_videos

"my_videos" does not show YOUR boat. How about a link to the actual video rather than to my (as in Rick Willoughby's) videos.

Rick W

[COLD-EH']

Sorry? worked when I check before posting? http://www.youtube.com/watch?v=zmIAWEdrgVg

Heres one!

[Guest625101138]

Originally Posted by COLD-EH'

Sorry? worked when I check before posting? http://www.youtube.com/watch?v=zmIAWEdrgVg

Heres one!

It would when YOU watch "my_videos" but not when others go to "my-videos"!

Impressive ride; shows the versatility. Would prefer the music to fade and at least hear a bit of the real music from the chevy and fan.

I wonder how many airboat operators take the potential for hearing impairment as seriously as you do.

Was that a 'gator you ran over? (I guess not in Alberta) Maybe something fury.

Rick W