building a prop

[Bill Huson]

pontoon/catamaran design is good . . .

for stability. Of course a single hull 32' long would be faster than twin hulls 16' long, but it would be like riding a tender canoe. I'd do a cat.

Simple Q&D math to determine speed of a displacement hull:

Hull Speed = 1.4 X Square Root of the Waterline Length. A 16' hull = 5.6 Kn and a 25' hull = 7 kn, so you can see the importance of a long, loaded waterline. Unless competition regs limit overall length, consider making the hulls longer. Of course a long hull has more wetted surface = more drag but the Q&D formula accounts for that.

Wetted surface reduction: The cross section shape of the hull below the load waterline should be a semicircle. Hulls should as narrow as possible taking into account the total displacement required for boat and crew weight.

Foam tricks - if you use spray insulation foam for flotation, spray on a thin coat (1/2" - 1") and then *mist* the foam with water. Wait a bit, water mist makes the foam swell more = less weight per cubic foot.

Forget auto fans for a prop. I haven't seen one that would work well in a dense medium like water. Trolling motor props seem like an inexpensive solution - at least worth a test run.

[Skoontz]

As Gomer would say.....

Shazamm!!!!!!!!

[aojesus]

The guy in the picture is Tony. He is very quiet and humble. I put a Pinner, a Dewald and a Hill prop on the desk and let him study them. Our engineering team gave him a rough idea on size and blade shape and the rest is history.

He cut the blades out with the plasma cutter. Each blade was put in a vise and heated and bent with a 6' piece of flat bar that he cut different length grooves in to fit over the blade at different depths where it needed to be bent. The hub is one piece and he turned it on the lathe.

We are very fortunate to have all of the state of the art metal working equipment in our repair shop but what a sight to see someone like Tony pull this off "old school".

The foam pontoons are wrapped in fiberglass mesh and sprayed with concrete stucco.

We should be testing it Friday.

[Racers Edge]

A few other things that could help.

A few years back my bike shop worked with some engineering students at Florida Atlantic University to win the Human Power Submarine National Championships. Some of the key things that we were able to add to their program was a better understanding of how to harness the most amount of power out of the engine (the peddler). The average cyclist will produce the most amount of power when his legs are spinning at a cadence (RPM) of about 90. You can go into any bike shop and get a computer that can measure cadence for about $40. This will give you a heads up on the proper gear ratio to use. The other thing that will help you greatly increase power output(about 20-25%) is going to a clip-less pedal system. With this it uses a shoe with cleat on the bottom of the shoe that will lock to a certain type of pedal. With the current flat pedals that you have will only give you the ability to push down through the pedal stroke. When you go to a clip-less system it will you to recruit power from your hamstrings and hip flexors. This will allow you to get power by peddling full circles opposed to just being able to only push down on the pedals. Basic clip-less pedals cost about $40 and shoes about $60. For this if you are on a budget look on Ebay for some used stuff. The pedals that you should look for are called SPD and the shoes must be SPD compatible.
There were quite a few more details that we improved on while working with them but this should send you in a better direction.
I hope this helps.
John Palmquist

[aojesus]

Thanks

We sure appreciate all the advice and input. This has been a fun project and a great distraction for me.

[25xs]

Russ: Don't let this be YOUR interview after the race!

I hope Russ & the viking clan are on the podium accepting an award after this boat race and not giving an interview like this one!

http://www.youtube.com/watch?v=WcU4t6zRAKg

[aojesus]

That was a good video.
I skipped the race today so I could take Dad to his house in Zephyrhills. Dad and I had a great day but the river racers didn't fare so well.

Here is what was reported to me.....
The raft was loaded with salaried management. They had their fancy blackberry phones strapped to their sides as they started the race.. The raft was a little slow off the line but was quickly moving up through the field as they rounded Monkey Island. As they were overtaking the 2nd place boat something went horribly wrong. All of the welds mysteriously let loose on the starboard side and the pontoon and passengers tipped over backwards into the river along with their blackberries. This caused a sudden imbalance on the port side and they too met the water.

I wonder if the weld failures had anything to do with news we got Friday concerning the future of our plant? I was in Zephyrhills with Dad so my hands are clean!

It was a fun project for everyone involved. Thanks again for all the input on the prop, pontoons, and running gear.

[25xs]

Say no more... <"The raft was loaded with salaried management.">

Say no more... <The raft was loaded with salaried management. >

What a tried and true way to put the kabosh to a perfectly good boat ride...