Barnacles!!
Argh!! The bane of my existence.
So, when I first bought the boat, I found that the previous owner had painted the prop with the same stuff used on the bottom. And it worked pretty good. The boat had hard paint on it and the hard paint was keeping the prop cleaned as well.
The first couple of years I had the boat, I used the same paint, and I did the same thing with the prop. But I am not a hard core racer, and I don’t play one on TV even. So the marina owner suggested that I might want to switch to ablative paint. That way, I could just slap it on and go, rather than going through all the prep process. So I did. He also suggested using PropSpeed to prevent barnacle growth on the prop. I did that as well.
PropSpeed is a pain in the patootie. It’s a two part application, and part two has to be applied immediately after applying part one. So it takes two people to do it.
So what happens when I pull the boat out in the fall? Well, the prop is full of barnacles. So much for PropSpeed. And at $250 (at the time – price is up another $50 now), that was a very expensive experiment. Mind you, I still have enough around for a second application. And there are still alot of people I’ve met who swear by it. So maybe I just didn’t get it on correctly.
But I moved onto the next suggestion: Barnacle Barrier. It’s much easier to apply. You just spray it on. But I pulled the boat and, again, the prop was filled with barnacles. Mind you, they were easier to scrape off from the prop. But the prop was still covered in Zinc, the main ingredient in the spray, and covered with barnacles as well.
Again, there are plenty of people who swear by the stuff. But with this, I can’t see how I could have applied it wrong.
Lately, members of the CAL mailing list have been touting the use of Lanocote for preventing barnacle growth. The literature says that it only works for 6 montsh. But I could be happy with that. It can also be applied underwater. So, if it isn’t working as long or well as expected, whoever is diving the boat can apply some more.
I’ve applied this to the prop and to the knotmeter paddlewheel. The latter may not be a good test, since it’s plastic, not metal. But it can be used as my canary in the mine: if the knotmeter isn’t working, it means the paddlewheel is covered in barnacles. So we’ll see how well it works.
It does apply pretty easily. The directions say to heat the metal to apply easily. I heated the substance, which melted under a blowdryer pretty well. I could then paint it onto the prop. Since I really couldn’t heat the paddlewheel easily, this allowed me to apply the Lanocote to the paddlewheel fairly easily as well.
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I’ll try to update here to let everyone know how well it works.
[Top]Engine Efficiency
I checked the engine out the other day, when I had the luxury of a winter sail. It was making some awful racket. It was rattling quite a bit. So yesterday, I pulled the panels off to take a closer look. It seems the bolts holding the engine in place had worked their way loose. So I tightened them up again and took the boat out for a spin (hey, someone has to take her out! 🙂 ). Much better! Looks like I need to put some Locktite on the engine support bolts as I did with the coupler to the shaft.
While out there, I took some measurements on the efficiency of the engine. It’s something the electric boats mailing list recommends; it’s a good way to determine how far you can go on your setup. The wind was blowing, and the tide was coming in pretty strong, so I’ll need to do this again come summer when everything is calm. But this was a good ‘first run’:
Amps vs Knots
Not exactly a straight line, and it probably never will be, since I’m not running in a bathtub where I can control all the environmental factors. But interesting nonetheless. However, part of the ‘hiccoughs’ are because I would run downstream, then upstream to see how the values changed.
20120202 – Amps vs RPMs
This is actually more interesting, because it will help me determine how far I can go on a charge. I’m guessing the formula would be:
Battery amp-hours/amps * knots/hour = knots to travel
That’s amp-hours, as in the amount of energy stored in the battery, not amps minus hours.
Using this calculation, it appears I can go about 16.5 NM on a single charge, if I stay under 2.5 knots. If I up it to 5 knots, I can only go about 2.5 NM.
As I said, I’ll recalculate this in the summer when things are a bit calmer. But it’s interesting nonetheless!
[Top]Prop Pitch and Cavitation
After all this time, I’m still having prop problems. When the engine reaches about 800 RPM, I can hear cavitation. How do I know that’s what it is? Well, one of my regular crew is a Navy boy and he said that’s what the sound was. Not only that, when we revved it up more, there what a strong vibration to the boat – more than I’d expect to be normal.
So I asked Scott at Electric Yacht what he suggested. He said to try decreasing the pitch on the prop.
Pitch is the distance a propeller will advance with one turn. So, a 10″ pitch means that the propeller will move forward 10″ with one revolution.[1]
The prop is a 13″ 2-blade Max Prop. If you check the specs on the thing, you can see that it’s fully adjustable: pitch and direction of movement. I had based the pitch I set it at to what it was before I took the old inboard off. Or so I think. I didn’t know that I could look inside and find the settings. So I measured the angle and found a formula online to calculate what the pitch was. The pitch was 12″. So we decreased it to 10.
What’s so bad about cavitation? What is it? Well Wikipedia defines it as
… the formation and then immediate implosion of cavities in a liquid – i.e. small liquid-free zones (“bubbles”) – that are the consequence of forces acting upon the liquid[2]
The problem is, those bubbles can cause pitting on the prop. Enough of this and you have a non-functional prop.
After decreasing the pitch to 10″, the vibration at high RPMs seemed to go away. But the cavitation sound was still present. So I turned to the wisdom of the CAL boat and electric boat forums. The comments attached are the responses I received.
What now? Well, we’ll try decreasing the pitch to 8″ and see what happens.
[1] http://www.propellerpages.com/?c=articles&f=2006-03-08_what_is_propeller_pitch
[2]http://en.wikipedia.org/wiki/Cavitation
[Top]Doing it Wrong
In our family, the story of the farmer and the mule is near and dear to our hearts:
A farmer is heading out of town. While he’s gone, his neighbor is going to take care of his mule.
“He’s a good mule, ” says the owner. “Treat him well, say kind words, and he’ll not give you a lick of trouble. He works hard, that’s a fact.”
So the owner leaves and the neighbor decides to make use of the mule. So he hooks him up to a plow and tries to get him to move. The animal won’t budge. So the neighbor tries speaking kind words to him.
No good. The mule won’t move.
He tries bribing the animal with apples, with carrots, with hay. It doesn’t help. The mule won’t budge.
The next week, the owner returns. His neighbor relates his frustration.
“I tried everything, just like you said. Kind words, treats. Nothing worked. That damn mule wouldn’t budge!”
“Hmmm,” said the farmer. Then he picks up a 2×4 and smacks the mule on the side of the head. The mule looks up, startled, and slowly starts to move.
“First,” said the farmer, “you have to get his attention.”
So, in our family, we talk about 2×4 mentalities.
This brings me to my ‘engine’ problems. Because the engine was the new piece on the boat, I blamed all the problems I was having on it. Everything wobbled. It had to be the engine. The boat wouldn’t move. It had to be the engine. In each case, that 2×4 came and smacked me hard on the side of the head to make me see it wasn’t the engine; it was other problems instead.
The serious vibration problem was a bent shaft. It had been suggested to me that I have the shaft checked before I put it back on the boat. I tried rolling the thing on a flat surface. It rolled just fine. I didn’t think it was an issue. But, after exhausting all other possibilities, when I took the boat out of the water again, I disassembled everything and took the shaft into a machine shop to have it checked. It was bent – at the conical section that attaches to the prop. So roll it all I want, I wasn’t going to see the issue.
Hooray! So we put everything back together, and checked it before putting it back in the water. I was told that might not find all the problems, because most of that vibration came when trying to move the boat through the water. But I figured it would point out any serious issues as I had been seeing.
Everything looked fine, so we launched again.
And the boat wouldn’t move. I mean, if it wasn’t a calm day, I would never have made it back to my slip!
Again, I blamed it on the engine. I wasn’t getting nearly the RPMs I should have. So I figured I’d connected something up wrong on the engine to make it less efficient.
Bless his heart! Scott McMillan said I was certainly getting enough amps out; I should be getting some speed. So he mailed me a new controller.
In the meantime, Irene happened. And, since we were expecting 100 MPH gusts in the area, I had the boat pulled out of the water. Luckily, those never materialized. In fact, Williamsburg and Richmond, more inland than we are, got the brunt of the storm in this area.
But I digress.
While we had the boat out of the water, I wanted to check to make sure I’d put that Max Prop together correctly. The damn thing has a hundred pieces and, having had inexperienced help to put it together, I figured we should recheck it.
While we were pulling it apart, someone else in the boat yard came by:
“Not moving the boat, huh?”
Yes, I answered, can’t move at all.
“I had the same problem. I put the prop together wrong, and couldn’t move at all.”
He offered to help us put it back together right. So we got out the installation instructions that I pulled off the web, and, very carefully, put the thing back together.
What had happened was that the blades were spinning flat. There was not corkscrew effect. So the thing wasn’t pushing the boat through the water at all. It’s also why the thing sounded like a blender in the water, rather than making the sound I was used to hearing.
As it happens, the guy who helped us out started explaining about the wobbling he was now experiencing. I strongly suggested he check out whether his propeller shaft was straight or not. 🙂
We put the boat back in the water again. This time, it ran like a dream. It did everything I expected it to. It is the end of the summer, but I finally have a boat that is a pleasure to use again. But, as a friend pointed out, I missed the hot miserable summer and I have a boat just in time to enjoy some beautiful fall weather!
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