Human Powered Boat 2001 - Sidewinder HPB
Sidewinder 2001

The performance of last years iteration of the Sidewinder HPB was less than spectacular, even though I made major changes to it, so for this year, MORE major changes! 

This past fall, in a fit of cabin fever, I narrowed one of the hulls by 4 inches with a hand saw. It's pretty ugly right now, but vast amounts of filing should improve that. The hulls were previously a foot wide, and 12 feet long, and had boat loads of flotation (ha!). They'll ride lower in the water, but be faster. Also I got a Bolly carbon fiber 15x25 "Man Powered Prop" to replace the assortment of model airplane props I had been using. It still looks more like a model airplane prop than a boat prop, but should be much more efficient. The Australian manufactured Bolly boat prop is available in the US through Aero Products for $43.

I finally took a look at the hull I hacked up this past fall, and got out the big rasp file. I spent about an hour rounding and shaping it, and it looks pretty darn good. With only 2/3 the width, and a more rounded profile, it should slip through the water much easier. It just needs a little cleanup and it will be ready to cover with fiberglass and epoxy. I guess it's safe to terrorize the second hull now, using the same template I used on the first.

George Tatum did some cold water prop testing this past weekend, to determine if the Bolly HPB prop would be more efficient than his hand made WaveBike "SeaGull" props. His testing showed that at the 3:1 gearing ratio that the WaveBike uses, which give a prop speed of about 300 RPM, the WaveBike props were more efficient. As my drivetrain is either 4:1 or  5:1 depending on the chainring, I'm hoping the higher prop speed will allow the Bolly prop to operate closer to it's optimal RPM.

What better to do on a cold January Saturday, than go out to my dark, cold garage, modify the other hull to match the one I previously hacked, and take pictures of it?
The rule of thumb is that 1 square foot of air will float about 60 lbs. I figure I'm safe trimming off a couple inches here and there...

Here's the hull before I began modifying it. 12" wide, 8" deep, and 12 feet long. Only the leading and trailing 4 feet of the hull were shaped, and the center section was pretty blocky.

hpb2001-hull1.jpg (14680 bytes)

hpb2001-hull2.jpg (7571 bytes) To create the arc of the new profile, I strung a rope from the middle of my yard, into the garage (about 30 feet), and tied a pen to the end of it. I then used it to draw a 6 foot arc on a old piece of paneling, and used that as a template to draw the same arc on the old hull (4 times). This made a fairly consistent radius along the entire length of the hull.
I then got out my trust hand saw and started cutting along the marked lines. 2" were taken off each side, and actually more width was removed closer to the ends, as the tapering of the hulls is more gradual now.

The hand saw actually works pretty well to cut through the combination of pink foam and fiberglass. Here's the aftermath:

hpb2001-hull3.jpg (15261 bytes)

hpb2001-hull4.jpg (34655 bytes)

After peeling the remaining fiberglass off of the bottom of the hull, I got out the big file and roughed in the shape, generating large piles of pink foam in the process.

hpb2001-hull5.jpg (32808 bytes)

Now both hulls are 8" wide at the maximum width, and tapered much nicer. I'm waiting until the weather gets warm enough to epoxy outside to finish the hulls.

A couple weekends ago I got motivated, and finished shaping the foam hulls. It took a little longer than I thought though, as I discovered that I had cut one hull to 8" overall width, and the other to 9". I guess that's what happens when you cut up one hull and then wait 6 months to do the other... After fixing that minor aberration, I used a 24" x 3" piece of coarse sandpaper glued to a 2 foot long two by four to even out all of the oddities and keep the curves and transitions in the hull shape smooth.  A final sanding with fine sandpaper on a rubber sanding block prepared them for covering with fiberglass. 

Last weekend I covered the hulls in 2 layers of 8oz fiberglass cloth. The first hull went nicely, but I had some problems with the second. I ran out of epoxy after the first coat and had to run out to the store to get more. By the time I got back the epoxy on the hull was "tacky", making it very hard to position the second layer of fiberglass and smooth out the wrinkles. The second layer of epoxy went on well, but by that time in the day the sun was shining brightly though the latticework of the deck that I was working on, and it was getting hot out. This caused a couple problems, the first of which was the plastic cup of epoxy I was holding went endothermic, causing a steaming mass of wasted epoxy in a melted cup, and It also caused some ugly bubbles between layers in the epoxied fiberglass. Lessons learned: Make sure you have enough materials before you start and don't expose uncured epoxy to the sun!

Things looked better the next day after I judiciously applied the belt sander to both hulls and removed most of the irregularities. I then covered the hulls in a thin layer of epoxy based aircraft body filler to fill in the low spots and fiberglass weave. The hulls will need to be sanded once more, then they can be painted. The pictures below and to the right are of the hulls after applying the filler. The front of the hull is to the right.

This past weekend I found time to finish sanding the hulls. I used the coarse sandpaper glued to the long two by four to hand sand the hulls. This made sure the high spots were sanded down and the low spots were left filled with the Aero filler. The rest of the boat was then taken down from the garage attic and bolted onto the hulls. I added a couple of chain guides to make sure that the chain doesn't pop off half way through a race as it had last year. I also used the rear prop shaft mounting assembly from the '98 version of the Sidewinder, which was basically just a "V" made of 1x1/8" aluminum strap, to replace the '00 version, which didn't work out so well. OK, looks good! 

Between rain storms, I took the boat down to the river and tested it out. Hey, it works well too! The newly reconstructed pontoons seem pretty fast, and still have plenty of floatation. The use of the old prop shaft support made the boat regain it's ability to turn well. The Bolly prop works nicely, and the RPMs seem about right with the 4 to 1 ratio drivetrain. With the old hulls, when I would sprint the front end would lift out of the water, and the back end would sink down. I think that some efficiency was lost by this happening. Fortunately the new hulls do not do this. In fact, they seem to squat down into the water a bit when I am sprinting. I notice this because the drivetrain that normally has a couple inches of clearance tends to drag in the water when I am sprinting, which sprays water all over, and slows me down. I'll need to make some spacers to jack up the superstructure a couple inches to prevent that. Besides that it looks like it is ready to race at this year's Hydrobowl!

The 2001 Hydrobowl went well, and I came in 2nd place overall behind Jake Free, who was riding his new 25 foot Proa HPB. My drive train is now pretty bulletproof, and worked great throughout the races. While even in the 2K race, I wasn't too far behind Jake, I was working my butt off, and he wasn't. Since my hulls should have been much faster this year, and my sprint times didn't improve too much, I can only conclude that the Bolly prop is not very efficient. Bill Murphy used a Bolly prop on his HPB for a while as well, and has since switched back to the APC 16x16. I think this corroborates with what George Tatum of Wavebike fame noticed, which is that the Bolly prop just isn't very efficient as an HPB racing prop.

SideWinder 2001

Here are some pictures of the drive train. It works pretty well, but my neck gets tired of looking sideways while racing to make sure I don't run over a buoy, or another racer. Also that little u-joint gets beaten up pretty badly. The next boat will probably use a compact twisted chain drive system. This is a little harder to engineer, but is still very efficient, and allows you to look where you are going without a visit to the Chiropractor...

After this last Hydrobowl, I realize that there there really is something to that long hull thing. While short 12 foot hulls like mine are good for general use, they are not long enough to really go fast. This of course, means another complete redesign. As that probably won't happen this year, I'm going to try some different props to see if I can find one that is better suited to this boat. 

More Later...



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