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Another U-joint bites the dust

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I was out on Elbow Valley lake for a 2 hour training spin, and test of the new steering rig, U-joint and a crazy idea I had for the prop.


I sanded down the hull again and was able to sand off some of the weave texture. I also spread a thin coat of micro on the port side of the bow and sanded it smooth. I don't want to do any more because: A. I hate sanding - can't stand it, and B. I'm afraid of making the surface finish worse due to my total lack of ability in that area, and refer to A; my very poor attitude toward surface finishing.


If the reason for the missing 12% speed is due to the surface finish of the hull, then wouldn't you think that I might measure just a tiny bit more speed today after a some sanding and a slightly smoother bow? I didn't see any speed improvements at all. It's possible that I need a glass-like finish all over the hull and I will pursue this regardless. I'm just not going to be the one to do it, I'll probably job that out to a body shop or something. I'm just not convinced that is the reason for my speed issues.

I do not think that the hull is deforming. I reached down today while she was in the water and I was still able to press the sides of the hull in with my hand - meaning they weren't already depressed due to the water pressure. Also a more careful visual inspection resulted in no deformation that I could see.


The other purpose of today's ride was to test out my steering handle. It is a bit awkward to hold onto the steering cables, so I rigged up an aluminum stick and it worked really well. There is enough tension on the hinge for the handle to keep the rudder exactly where I leave it, so steering is MUCH easier now. I can let go and the boat tracks perfectly straight.


This might sound silly, but I had a dream the other night that I solved the speed issues by adding my second prop to the existing prop at the end of the shaft. I tried that today just for the hell of it and it surprisingly had very little effect. I had BOTH props on forming an "x". My speed with both props at 100 watts was 9.2 km / hr compared to 9.3 km / hr with one prop (about the same) , but my cadence was 71 rpm compared to 78 rpm. There was no spinner on the trailing end of the double prop configuration which could have been worth the missing 1 km / hr (but that could easily be error - it was a bit windy and the lake wasn't as calm as the first Elbow test).


The bad news is that after only 2 hours my new U-joint donated to me by Curtis Universal broke! This is strange because it is rated for maximum static torque inch-lbs of 100. Both Manny and Rick think this should be strong enough.


Strangely, I didn't measure any significant difference in speed from the new narrow profile u-joint compared to the old draggy u-joint with the fat flanges.



This boat is very fast - don't get me wrong regarding my constant bitching about the speed. To provide some perspective, the winning human powered boat at last years Hydrobowl finished the two km time trial with an average speed of 9.36 km / hr. Power output for an average person for 20 minutes might be around 200 watts or so which would equate to an average speed of about 11.5 km / hr in my boat. To average the hydrobowl winning speed of 9.36 km / hr in my boat would take only about 100 watts. At 100 watts of output power, you might be able to do the whole 2 km time trial with one leg.

BUT, let me put that into further perspective for you: On May 18th Lewis Laughlin won the Epic Kayak Molokai World Championships - a 32 mile surf-ski kayak race across the Molokai channel between the islands of Molokai and Oahu. He averaged a whopping 14 km / hr for 3 hours, 40 minutes. The stretch of water between Molokai and Oahu isn't exactly mirror flat either.

I have some work to do!

A delivery guy just backed his van into my boat which was strapped to the roof-top carrier on the Suburban! He cracked the carbon near the stern, bent my rudder and forced the kayak cradle off of the roof rack. Idiot. And he wasn't even going to tell me about it. As I was signing for the delivery I noticed the boat was sitting DIAGONAL on the suburban. I looked at him and he fessed up to backing into it.

Oh - and one more thing (almost forgot!) - exciting news: My friend Roz Savage has departed for her Pacific ocean row from SanFransisco to Hawaii. I'll be following closely:

http://www.rozsavage.com/blog/

(I designed Roz's new logo for her)

gk



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8 Responses to “Another U-joint bites the dust”

  1. # Anonymous Dr. Leslie Brown

    Regarding the surface finish- Yes I believe it would make a big difference, especially considering you've admitted that you're not proud of it. I.e its probably pretty darn rough.

    I would have thought most of the resistance of this boat would be water-resistance not air-resitance, so it is quite significant.

    I've dug up an old article I wrote about sanding & polishing. While some of it isn't relevant, most of it still is. There are not many ways to get the best mirror/glass finishes from a raw finish. Have a look here:

    http://www.cr-x.org/cbr250/forum/topic.asp?TOPIC_ID=21701

    Not that it does take time. You just can't do this job well in a hurry... I think you'd be best to get it to a finish of about 1000 and then use a wax compound or something like that...

    2c  

  2. # Blogger fhe

    Why not do away with the U joint altogether? Does the angle of the prop matter a lot? i.e. does it need to be vertical?

    Reduced complexity is a good thing. Also, the fact that it breaks despite being rated strong enough shows that something is not quite right there. This could easily be a source of wasted energy.  

  3. # Blogger Kitlani

    You most likely already know but any angle at all from the shaft to the prop would multply the load on the u-joint significantly.  

  4. # Anonymous Jason

    I'm thinking a flex shaft might be the answer, no?  

  5. # Blogger neil

    I'm not an engineer or world record holder at anything, so disregard this post if my suggestion isn't practical.

    Why not add a second sprocket (gear) to the drive system? I know that pedaling against water is far harder than pedaling on asphalt, but doesn't the law still hold true that objects in motion tend to stay in motion? Once you've reached cruising speed (at which point the boat's momentum contributes to the spinning of the prop), wouldn't you gain extra speed by changing to a higher gear and increasing the prop speed? I only suggest this because I assume the boat is easier to pedal against moving water than right at the start. Considering your engineering talent, you could design a second sprocket/derailleur that would be reliable.  

  6. # Anonymous Koen

    Just like fhe says: why not give it a try without the u-joint. I think it might help.

    I also think dr. leslie brown could be correct too. The surface will be of much more importance in the water.  

  7. # Blogger biff

    I am not sure what the volume of your hull is, but putting some expanding foam in there shouldn't add much weight, I would guess 300grams per compartment. Expanding foam should be much less dense than the foam you used as a mold. If you want to decrease the density more, put ping pong balls (available at dollar stores), or packing peanuts (extremely low density) in there first, then inject in the foam.

    I would use a cardboard box lined with cling wrap to test and see how much it weights, try different injection techniques and test to see if it is possible to just coat the sides with foam.

    As far as drag, if you say the surface is rough, than I bet it needs lots of work. Consider this: if your boat is draging 1kg of water (I don't know what your surface area is but I think 1L is a reasonable estimate as to the amount of liquid that is being accelerated up to the speed of your boat by the hull) up to 10kph in 1 second, that is 2.7m/sec. Thats a power of 3.6W (P = change in energy (dE)/ change in time(t), dE = 1/2m*v^2 = 2.7*2.7 /2 t = 1s a=2.7m/s/s)

    I guess since you will have Ricks prop soon that will help figure out if the problem is the prop. Otherwise to test if the problem is the hull, you will have to either, spend the time and make it perfect and see if that helps, or drag it at fixed speeds (without the prop on and with you in it) and see what the force required to pull it at those speeds is.  

  8. # Blogger biff

    I just read the Dr.'s article about polishing.

    If I were you, I would use a product called Duratec. Its a polyester primer that can be sprayed on as thin / thick as needed and sanded / buffed perfectly. We used it on the Solar Car plugs and it works great. When polished it looks like marble. it Sands and buffs quickly all the way out to 3200 to give a mirror finish. The black would look good on your boat.

    http://www.duratec1.com/dp04.html

    http://www.ippnet.com/EN/main/products/FIBREGLASS/4491/1051.html

    Its pretty expensive ($50 per gallon, if I remember correctly) but I think one gallon should do you. Maybe the guys at IPP can suggest something else. If done right I think you could spray / sand and buff the hole hull out in about 8 hours of work. a couple hours you could do the front third. Make sure you clean your spray gun well with acetone after each mix (its a 2 part, and once it starts to gel inside the sprayer you stuck) after every second mix, I suggest taking the gun apart for the cleaning. I think if you just start working on the front of the boat, you would only need one mix. I might be able to help you out if you want. Give me a call or send me an e-mail (just search the internet for ryan biffard my phone number / contact info is all easy to find)  

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