Sunday, September 11, 2011

Hydrobowl outing

I've been reading about Hydrobowls for years and was hoping I would finish in time to make it to the event about 6 hours from Minneapolis.  It is a multi-discipline race with overall winners based on points over 5 races.  It is intended to be a measure of overall performance, and I would say it does a reasonably good job at it.  The races are a 100m flying start sprint, a slalom, a 100m drag race from standstill, a 2k criterium, and a static thrust test.  I wish that there was a race where a fast boat could go fast over a distance without the need for agility, but I suppose this is because I found that my boat was slowest cornering boat of the group!

 It is an informal competition, but several of the racers have been going for years, or decades, and have tailored boats to the event and refined over the years.  My boat held it's own, but the drive definitely suffered some wear and tear.  Before the start I had adjusted the angle of the prop blades to increase the pitch - the distance you are supposed to go each rotation.  I ended up with a better feel on the sprint, but the long distance events had me wishing for a faster cadence.  I suspect I will go back to somewhere in the middle.  The final points totals are pending, but I was somewhere in the middle.

The course is a 100m set of buoys, with two parallel rows.  The rows are about 20 meters apart.  The slalom weaves between the 5 or so intermediate buoys along the 100m, but you have to span the 20 meters each time.  The 2k criterium is 8 1/2 laps around the buoys.  This basically means you need a boat that can corner with a 10m turning radius to have any success on these 2 of the 5 events.  I would say my boat is more like 20-25m radius.  This means the slalom needed some reverse thrust with a paddle to make the turns, and the criterium for me was a lot longer than for everyone else because my oval was about twice as wide as the buoys.  My boat turns just fine for cruising a lake, but the 20 degree limit on the rudder rotation means it can't compete on agility.

The drive showed some signs of trouble.  I had anticipated both, but there is no good way to know for sure until you just try it.  The gearbox skipped teeth in the gears while sprinting.  This could be both due to the large size of the housing and the ability of it to flex, but I suspect it is also a result of the bearing bores coming back a little oversize from the shop.  The shop ran the reamer at a high RPM and this caused vibrations and a hole that was a little too big.  I tried to close it a little by peening edges with a punch to close the opening a little.  But it is still not a great fit and allows the output shaft too much play.

Also, I have been using the 25 pitch chain for years without issue on my cat, even after sprints, but this older drive is geared a little higher and also uses 12 tooth sprockets on the prop shaft rather than 9 tooth for the new boat.  It doesn't seem like a huge difference, but it means the chain has about 25% more tension during the same pedal force.  Given the demands when sprinting, this pushed the boundaries a little too much and the chain started to stretch and get too loose and could get jammed up.  Before I could adjust it properly I limped through the slalom and drag race.  I wasn't too surprised; I had debated sticking to 12 tooth for a while.  I would say the drive would manage just fine for years under normal use, just not all out sprints.

Hard to say where I will head from here in terms of design.  The Hydrobowl's future is uncertain since the organizer moved away from the area.  It is a fun challenge to tackle an all around boat for these events, but it is hard to say if the events will happen again soon (unless I host one in Minneapolis!).  Otherwise I could throw on a new chain and cruise the lake quite content with the way thing are.

This is with the caveat of fixing the stabilizer mounts.  As I mentioned, I was concerned about the stiffness after splitting the bracket into two halves.  This was a well grounded fear.  I've found that the vertical supports behind the seat will rotate slightly and also flex the bracket such that the long supports angle 5-10 degrees (estimating) towards the stern.  This means the stabilizer drags at an angle and plows the water, causing more drag and more flexing.  During the drag race I crossed a wake and this set off this feedback loop until I almost went for a swim.  I will definitely modify this.  I am very happy with the vertical adjustment part, but I will join the halves into one.  I will also remove the pivoting pieces from the bracket and use a short horizontal double ended nesting tube on the same bracket that connects to both long arms.  This will eliminate the flexing.  In order to achieve my goal of self contained stabilizers for walking to the lake, I think I will add separate short nesting tubes pointing towards the stern and I can remove the arms from the "in use" tubes and click them onto the "transport" tubes.  My timeline for this is uncertain.  Fall approaches and it is time to build up a good store of outdoor memories to last through the winter.  Fortunately the overall boat is quite sound.  I can work on the small stuff like mounting arms and gear boxes in my basement over winter.  I'm not sure I will, but at least I could.  Come spring, I will get the boat sanded and varnished and actually "finished".  Hopefully I will post some more nice cruising photos this month, and then I'll have to wait and see.

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