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
Deconstructing a Bad Race
Last Sunday was the first race of the Frostbite series. It lived up to its name. It was cold. It was wet. It was too windy. The only thing missing was high waves.
I showed up about an hour early, to clean up the boat a bit. With all the work I’d done this summer, I never really had the time to put things away. So I gathered up tools, and moved things around that were sitting on the galley counter. I knew it might be a bit rough and I wanted to minimize the mess in the cabin.
It started to rain pretty heavily before Paul and Grant arrived. But it was short lived. The sky didn’t clear up, but it wasn’t quite as black. So I had hope that the race would go well.
Paul and Grant are usually good about arriving a bit early. So when they hadn’t shown up by about 15 minutes before we planned on leaving, I thought they might have decided against coming, having seen the weather. But they arrived. We all put on our foul weather gear and headed out to the starting line.
I hadn’t finished tightening the bolts on the engine mounts. So I had Paul take the wheel while I went below and took care of that. I also wanted to take a look to make sure the engine looked good and that the stuffing box was performing well. A big OK on both fronts, so I headed back up.
I tend to be very cautious still. 3 years has not made me feel like any sort of expert yet. So when the weather gets rough, I’d rather not put out the full sails. I feel more in control that way.
But as we started out, the wind wasn’t too bad, although we could see the next band of rain headed our way. So we put the mainsail up all the way, and headed towards the starting line. The wind had picked up a bit by the time we reached our buoy, and we’d had our first band of rain hit us. I only have one jib, but it’s a roller furler. So we tied off the roller furler in such a way that only 1/2 the jib was released. We winched it in and got ready to start the race.
We were in a good position. I was psyched. We were, however, the least experienced one out there. And, as I already mentioned, I do tend to be a bit overly cautious. So we hung back a bit. I don’t mind being a couple minutes late over the start; I’m not going to come in first, so why risk ramming someone else going over the starting line.
Time was called. The race was to be around another buoy and back. We played follow the leader, to get a better idea where to make our turns.
First leg went smoothly and we were moving well. I wasn’t sure how well we’d be able to follow the leaders; we were a bit downriver from them and it would depend on how the current took us whether we’d get too close to the refinery’s docks. But no, we weren’t too close and we turned at the point that the others did.
Second leg, I could see a few white caps ahead, so I knew the wind was going to pick up. And it did. But it was very isolated and we came out of it fine. We put the jib out more to give us a bit more power and and made the next tack.
Third turn. Again the winds were picking up. This time a bit stronger. On top of that, I saw one of the other boats rounding out, so I knew they were having a few problems with the wind, too. Not only that, but a second boat was heeling over enough to wash windows.
I got a bit nervous. We’re out there for fun, not to make it dangerous. And I didn’t want to get in over my head. So I asked Paul to reef the main in. He went to do so. He was having trouble doing so, so Grant went to help him. At that point, I realized I should have steered into the wind to make it easier for him. But I couldn’t do it then; it would have been too dangerous. I was afraid that I’d lose one or both of them over the side.
We had a big gust at that point, and it pulled the boat over quite far, although briefly. At that point, I called Grant back to the cockpit to pull in the jib and I started the motor. There was too much wind; I didn’t feel comfortable and I wanted to head back.
We brought the jib in. Paul had to help Grant because the wind was quite strong at that point. I then turned the boat more into the wind and Paul brought down the main.
We tied everything down and headed back to the docks. We called the committee boat to let them know we were out of the race. As we headed back in, the wind died down again. In fact, it looked like the other boats were having a heck of a time making it around the buoy and back to the finish/start.
So what should I have done? I’ve been thinking about this for a week.
I still think I should have brought the main down, if only briefly, if I felt that I couldn’t control the boat in the given winds. But I should have turned into the wind before I sent Paul up there.
I should have insisted we all wear life preservers. If there was even a hint of a chance of someone ending up overboard, especially as the water is getting colder, I should have been prepared.
I should have looked head to see if this, like the other two rain bands that hit us, was going to come and go as well. We might have been able to in the race if I’d paused long enough, or let the sails down long enough, to let it pass, then continued as before. As I said, we weren’t going to win. But that way, we would have at least finished.
Well, there’s always next week!
[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!
[Top]Aligning an Engine
OK so. I thought the simpler coupler would make it much easier to tell if my engine was aligned to the shaft. After all, the coupler wouldn’t fit together right if the engine wasn’t aligned correctly.
But it doesn’t seem to have worked out that way. The first time we took the boat out, it ran like a dream. I heard a slight knocking from the engine compartment, but that didn’t seem to be too bad. When we got back to the marina, however, and put the boat in reverse to back it into the slip, we didn’t move: the prop had slipped out of the coupler!
The engine sits on a bracket, with bolts and spacers to attach from engine to bracket. There are three different slots on the bracket to fit onto two different screw holes on the engine. You select the slots and holes that will fit your engine. Mine was an ‘in between’ issue: too low for one location, too high for another. We selected the ‘too low’ one and raised the bracket on the rail to adjust. By doing so, we put it almost to the top of the bolt on the rail.
There are two bolts on the bolt that attaches to the rail: one under the bracket, one above it. The idea is to adjust the lower bracket upward, then tighten it down with the top one. Moving the attachment to the ‘too high’ one, I had to remove the underneath bolt. I put in washers instead to try to bring it to the correct level.
Try again. Get it all attached and take it out again. Same problem. But this time I actually lost it while we were out in the water. Terrible knocking started. When we got back, we found the prop shaft had slipped out again.
I called Scott at Electric Yacht again. He said that they’d started sending another bracket along to stabilize the engine, once it had been adjusted correctly. I received the bracket after getting the boat down to Portsmouth. So I installed it before heading back up to Yorktown. It shook less, but the knocking was still there. So I made use of the outboard instead to get the boat home.
And I’ve given up. I’m turning to the professionals at the marina to get it aligned. Hopefully, they can fix what I couldn’t.
Follow up: Seems the problem wasn’t the engine. And I need stop blaming everything on it. I had a bent shaft. Once that was replaced, all the knocking stopped.
Once that was fixed, all I had to do was loosen the bolts holding it from rotating and run the engine at low speeds. I then rocked it, checked it for motion, then rocked it a bit more. When I was satisfied that it was seated properly, I tightened everything down.
Oh, by the way, I figured out the prop shaft problem myself. The marina, in this case, wasn’t much help.
[Top]Hard Times
Every relationship has them. And right now, the boat and I are having ours.
We put the lifelines back on yesterday. Realized afterwards that one set was put on backwards. Problem with that? The connection at the bow is meant to stay connected. The one at the stern is made to be removed, to make it easier to get on and off. Now, that isn’t possible.
The other set of lifelines was twisted.
In both cases, it can be fixed. It’s just one more thing on the long list of things still to be done.
There’s the rest of the non-skid that needs to be applied but hasn’t arrived yet.
There’s the stripes on the hull that need to be put on.
There’s the layer of bottom paint to put on.
And there’s the engine.
My plan with the engine was to ask the marina to remove the plug that was put in when they pulled the prop off, put in the battery box for the new 400 lbs of batteries, and mount the engine. The estimate I got back? $4900, give or take. And that estimate included a fabricated platform for the engine that I kept telling them I didn’t need.
Since the piggy bank doesn’t have that kind of money around, I’ll be doing it myself. Well, I’ll be doing it with the help of friends. I made a desperate call to Dave A., who said he’d be happy to help. If there’s anyone who knows anything about engines, it’s him.
But it brings up the other frustrating part. I’m leaving town next Wednesday for a week and it doesn’t look, at this rate, like everything will be done before I leave.
<sigh!>
This has been one hell of a spring. I thought I’d allowed myself plenty of time to get all the projects done. And what has made it most difficult is the long hours at the job that lets me keep this expensive hobby also does not allow me to work on the boat very easily during the week. The weekends have given me so much rain that it’s made it difficult to get the painting done.
And, on top of all of that, I now have wasp nests in the boat. I’ve counted three so far: two in the vberth and one aft, near the cockpit locker. I don’t like wasps. I’ve picked up some spray that I hope will work fast enough that I won’t get stung when I use it on them.
Enough venting.
Now this is a post that won’t get alot of hits.
[Top]