If only every day was like this

Calm, clear, and cool.

Not much more I can ask for.

Ready to enjoy

Well, the past few weeks have involved building and then working a few bugs out of the new gearbox.  It is a 6.5 ratio using two stages (chain then bevel gear) of the design shown earlier.

It is installed on the boat and I have had a few outings.  I have been trying to tweak the chainline and a few other things to decrease what seemed to be more noise than I was expecting.  I haven't done a full sprint, but it has held up to brisk cruising.

The new prop from Rick is also on and this was  designed for the new gear ratio.  Rick has a mold for steel core, carbon fiber blades, and he is able to adjust the pitch somewhat to accommodate various boats by changing the root angle in the folding blade hub design.  For me cruising has been about 5.5-6 mph at about 72-78 rpm, and I find this to be quite comfortable.  Tiring but sustainable for an outing.

Everything is back together and I have also built a new dolly for walking to the lake.  The boat is balanced with maybe 10lbs to hold at the stern.  I need to watch for potholes, but so far it is going without incident.  I have met a lot of people who are really interested in hearing what it is all about.

I would say I am still quite pleased with the result.  I would also say that now that I have indulged my fascination with steerable props, I would be very happy to go towards a simpler drive design.  I am thinking of tackling an ultra light weight version next, whenever that might be.  Two boats is never enough.

Nice and shiny

Well, the sanding is done and the varnishing is underway!  It is always a really satisfying process to start with the dull sanded finish and instantly see the final result.  I have two coats on and will apply a third later in the week.  Overall, I am happy so far.  It isn't perfect, but I'm getting better.  I only wish it wasn't at the very end when I am more impatient to get it back on the water.

I have ordered the final parts for the new gearbox, and I'll get hopefully make progress on this soon.  The weather has been perfect for boating, but I guess having nice weather for varnishing isn't a bad thing either.

Sanding at last

When I first had the new boat assembled last fall, I knew my warm days were numbered, so rather than miss another week doing the sanding and varnishing, I decided I would wait and do that in the spring.  Well, warm weather is here at last.  I have put the garage back into workshop mode, and I have even taken the catamaran out for a cruise since the new boat was disassembled again.

I have been able to use my fancy new sander.  I also decided to try and hook up our indoor vacuum cleaner as a dust collector, since the shop vac has an oversized hose.  It worked remarkably well, and I'm sure as long as I change the bag when I'm done, it won't be any worse off.

The finish quality should be another incremental improvement over previous boats.  At least I would say the sanding results are an improvement.  I will be varnishing when I return from a trip next week.  Someday I will hopefully get professional quality results, it is a good challenge.  Maybe someday I will even get a spray gun.  Until then my brushing and rolling will only get me so far.

I have also spent some additional time on the drivetrain.  My previous posts showed a few images of a new all bevel gear design.  I would still expect this to be an improvement, but I have moved towards yet another iteration.  This one is a hybrid chain and bevel gear system, but it is still housed in a similar sized box.  The crank arms attach to a first shaft with large ANSI 35 sprocket.  An intermediate shaft has both a small sprocket and a large bevel gear.  This has the advantage of a higher gear ratio, I should hit 1:6.5 with this design.  It also uses a 1:2 bevel gear set which is significantly cheaper than a 1:4 set (enough that the cost of the sprockets is still cheaper overall).  Lastly, this means that the torque on the bevel gears will already be reduced by the chain gear ratio, so this will improve gear life.  With the lower torque, I will likely test a slightly smaller diameter shaft tube (5/8"), and I am eager to test a prop with carbon fiber blades made by Rick Willoughby that has been sized for this approximate gear ratio.

My budget will hopefully be stretched further by doing a greater amount of machining myself.  I have found a local "makers" organization with a shared workshop and inexpensive dues.  This should allow me to do most of the milling myself.  I have found a space with power for my welder, so if I brush up with a little practice, I can do this as well.

Seasons changing

Everything is back up and running, and I've notched a few more successful outings.  I had my first windy trial this week.  It's a small lake so waves were not bad, but it was maybe 25 mph gusts.  After getting so used a catamaran, I admit it was a little unnerving at first to feel the wind rock the boat.  By the end of the day, I was much more comfortable.  It will still take some getting used to, especially when I do hit some bigger swells.

All things considered, I would have to say the project has been quite a success.  There are a few bugs to work on, but I've had fun on the times I've been on the water.  Hopefully I don't make anything worse when I take it apart to sand and varnish in the spring.  I'll work on some of the bugs before I put it back together.

The first priority will be the gearbox.  It is currently fine for cruising, but not for anything needing more power.  I suppose I am glad I opted for less expensive straight bevel gears rather than spiral gears.  If the box isn't stiff enough, the more expensive gears would have met a similar fate: worn, rounded teeth.  I have some thoughts on reinforcing the housing with cross pieces and also cover plates with a lip on the edges to help prevent pedaling forces from flexing the housing.  If there is an improvement, maybe then I will upgrade to spiral gears.

Next up is the prop.  There is a yet unexplained difference in speed at a given blade pitch compared to calculations, so I have had to modify the blades to make things work well enough.  I suspect my first attempt will simply be to remake the blades and attempt a more accurate foil shape when grinding.

I might also go ahead and replace the full shaft, I'm not sure.  It isn't that expensive, so it might be nice to try one that wasn't accidentally bent before assembly.  I'm still undecided about the drive leg.  There are several options to increase the strength of the chain loop.  The current setup can handle more than the gearbox, and I think it would be fine for distance race speed, just not short full sprints.  I might also try a leg fairing that slides over the drive leg tube rather than move with it.  The steerable prop is nice and it works well, but I think it limits my options on making the chain loop stronger.  I doubt I will decide until spring.

On the boat side, I don't think there is much I would change.  During the design I wasn't sure how far I would place the gearbox from the seat to fit my height.  My other boat has a profiled recumbent seat and this one has a sharp angle, so comparing the two was difficult.  Now that it is set up, I can see I could have shortened this about 3 inches and decreased the windage of the gearbox support.  There might be a few other changes to reduce windage, but it all amounts to fine tuning.  I have modified the stabilizer mount: reattaching the two halves and I also added a cross pin between the vertical pivots to reduce flexing.  It has made a big difference, so for now I will leave this alone.  I really like the vertical adjustment and the ease of setup when launching.  I imagine starting over I could shave off some weight, but it would again be minor changes.  As I mentioned before, in a new boat I would probably make the stabilizers out of foam sheet and also reconsider the weight of cloth in some areas.  It might all amount to about 5 lbs.

Last but not least, repurposing the trailer for the cat works OK, but I will eventually make or buy a better setup.  Ideally something small I could stow on the boat, so I wouldn't even need to walk back up the shore when launching.

In the mean time, the garage needs to be turned back into a garage.  I don't think I would get much support for my hobbies if it meant scraping frost off the car windows.  I've already put the cat up in the rafters and cleaned up my tools and mess.  Hopefully I can get out on the water again before the cold water deters me, but there is a chance this is it.  At least the outing this week was a nice sunny (but windy) day with fall colors.

Hopefully some of the people reading have a nice warm shop or are just getting ready for summer!  If you have a project, it would be great to see it.  Turns out this blog stuff is pretty easy...

Maiden voyage!

I had my first trials yesterday and today.  Generally, they were successful.  I had a few bugs to work out with the steering cords and chain tension, but I was on the water doing nice laps after a few false starts.  A priority will be grinding the prop to add the lift from a proper profile.  Also, I may adjust the pitch as I was spinning out on the pedals before getting to max effort.  A future priority will be sealing off a greater portion of the stern hull.  You will see the stern sits low due to water that enters a fairly large drive leg stern partition through the drive leg opening.  This will be an easy modification once I take the time to work on it.  It's been a long day, so I apologize for a lack of a storyline on the trials.  This will have to be a photo post for now.

The rest of the drivetrain

I can say now that the scope of my summer project has been changed slightly.  The boat is ready to hit the water (it already has actually, but I'm behind on posts), but it is not finished.  I have yet to do any final sanding on the hull; and no varnish yet, either.  I will do a few more things to prepare for the Hydrobowl this coming weekend, but I will focus on the prop and steering.  Varnish will probably wait until spring.  Right now I want to enjoy it for a few weeks before the weather turns.  And winters are long here...

The final area of the boat I have not focused on in posts is the rear end of the drive.  It is a variation of the flex shaft design Rick has refined lately.  I like a lot of advantages of the "standard" flex shaft, but I have had an idea in my head for a few years, and I really wanted to see if it would work.  Now that it is mostly done, it is easier to explain.  I am using a flexible shaft, for the full length of the boat, but it does not extend below the hull as in Rick's system.  I am running the shaft under the seat and along the deck line to the stern where it joins with a separate drive leg.  The drive leg uses a 1/4" pitch chain common on twisted chain drives, but the chain does not need to twist since the gearbox has already changed the pedal motion 90 degrees.

After a lot of searching I was able to find inexpensive stainless 9 tooth sprockets for this chain.  The max shaft size was 1/4" but I wanted to drill them out for 3/8" shafts.  This meant there wasn't enough material left in the hub for a cross pin, so I found a local bicycle fabricator who silver soldered the sprocket on, and it looked pretty secure.

I realize now that my photo collection is incomplete for the drive, but I can add photos later if there are any requests.  The shafts are mounted in stainless bearing and I leave it all open to water.  This is the same approach I used on my first boat, it is 7 years old now on the original parts with no corrosion on the stainless.  Good enough for me.  The chain runs through a 1 1/4" OD aluminum tube.  This is the smallest possible size drive leg I could figure out how to make.  The round tube is welded to a 1 1/4 rectangular tube which houses the prop shaft and bearing.

The drive leg tube has a foil fairing based on precise plywood pieces cut from the CNC batch.  I sandwiched foam and wood to maintain and accurate shape.  I precut a (slightly undersized) hole in the wood pieces, and once this was all together, I cut it into front and back halves along this hole centerline.  I then wrapped sandpaper around scrap tubing and sanded away the foam from the inside.  This allowed me to glue the fairing to the drive leg and essentially not add any width to the tube except for a layer of glass cloth.

 One of the key reasons this general design appealed to me is that the prop is steerable.  The drive leg tube nests inside a square tubing with flange bushings.  The drive leg tube has a slot for the upper drive shaft, and the clearance in the slot allows for about 20 degrees of rotation each direction.  It can be increased slightly if needed.  The square tubing is bolted to the inside of the hull.

 One of the primary concerns with drive legs is weed catching and collisions.  Generally, these are not issues where I will be boating for the near future, but I added a small strut to help deflect weeds and ramp over obstacles if I hit something.  I will eventually file this strut to a nice profile.  The twist isn't ideal because it will add slight drag, but it is the fastest approach for now.  The bottom of the strut is bolted with a shoulder bolt to the drive leg bottom so the leg can pivot about the strut.

There are plenty of downsides to this design relative to using only a flex shaft under water, and I was aware of them and willing to try it anyway.  I accept it is not an ideal solution for most home brew boats.  But there are a few advantages, and I will focus on these.  Because the shaft only has a small amount of curve, I can use 3/4" diameter (.058" wall) tubing the full distance, and maintain the best possible torsional stiffness with a minimum of weight.  I calculate the shaft at about 44 Nm/rad stiffness, significantly higher than cases where a thinner shaft is used underwater to accommodate the increased bending.  There is no need for a rudder of any kind, and the strut fairing can be more effective since it is not surface piercing.  This is in addition to the steering from prop thrust.

Beaching is more of a gray area.  The strut is currently fixed so it will hit when beaching.  The lake I am on is deep, so this is not a concern for me.  The downside is that the strut is fixed, the upside is that the shaft is protected so beaching will not bend the shaft, which can happen when not using spring steel.  In fact, the second reason this design was appealing was that I intended to make the drive leg beach-able.  My idea was to detach the stern portion of the hull and add a transom.  Then I could use the deck panel or a portion of it to flex up with the shaft.  It would essentially be a long hinge flexing/pivoting with the shaft.  Since the shaft does not flex a large degree in steady state use, it could accommodate more flex with beaching.

In the end I decided this would take more time, and I would prefer to proof the general concept and reliability before I cut into the boat.  If I decide not to continue with this drive leg it is currently easy to undo.  If it works out for a year or two, I can still use it as a test bed for a steerable and beach-able flex shaft drive leg.

The complete drivetrain is very low friction.  I can easily rotate the shaft with my fingers and maintain motion for about a prop rotation; however, I managed to bend the shaft slightly during my experimenting and it has a slight pulsing as it rotates due to this bend, so it always stops at the high resistance point when I try to spin it.  It is not something I can feel with my legs.  I replaced my original bushings with ball bearings since they are protected from water.  I would consider it relatively light weight as well.  The drive leg adds weight but there is no rudder and the shaft has only 12 inches of steel.  In the end, the full assembly with full shaft, shaft bearings, drive leg and rudder control is just under 4 lbs.