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Old 14-11-2006, 14:39   #76
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I don't know if they plasma spray copper, you'd have to ask. Copper is also electroplated as part of the base coats for chrome or nickel plating though, so any conventional plating shop might be able to build a couple of coats of copper up for you.

Interesting idea.
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Old 14-11-2006, 18:14   #77
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I will start a new thread on this copper coating idea. This is the wrong place to discuss it. Ill bet there is a good reason it has never been done.
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Old 14-11-2006, 19:37   #78
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Ummm, if you don;t have enough left to sand and polish, don;t play around with repitchign. It would be best to get a new prop. The thickness of the prop is very important. A prop is a rotary wing. The "wing" is part of the shape of the blade. If you look closely at each blade, you will see a subtle curve in each so as the front face of the blade "lifts" the blade through the water. It is actually a misconception that the blade pushes(to a point). It actually lifts and draws itself forward. If the blade was flat, it would easily cavitate. There must be enough metal to have the correct shape in the cnetre area of the blade. But there must also be enough metal to have the correct leading edge profile and trailing edge profile. If those edges are incorrect, cavitation is also caused, but this type of cavitation results in the eventaul destruction of the blade due to erosion.
So you would be best to buy a new or at least Second hand blade in good condition and one closer to your pitch requirements.
I am also very surprised at the diameter. That is a very large swing for such a small boat. Now the diameter is probably not going to affect your power so much, seeing as the prop speed is so low. But I wonder if you have enough gap clearance between the blade tip and the hull????
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Old 14-11-2006, 21:16   #79
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Its already been repitched. That was my spare prop. That was done at the root of the blades. There is enough NOW, but not enough to take much away.

There is plenty of clearance. Enough for even a 26" wheel. But I think 18" is plenty...#8-)

The 18" is fairly normal for this boat and engine combination.

The 19x18 is definately over proped though. The 18x14 should be ok but I am going to try to get the 19x18 repitched to 19x13 and use the 18x14 (the one that is thin) as a spare for emergency use.

And if I find that coper over bronze it OK I will plate on 10 mils or so giving me an additional 20 mils of metal in the 18x14 spare.
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Old 15-11-2006, 01:08   #80
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I am really not sure about the copper over the bronze. Not saying no, but I ahve never seen it done and would be a little suspect. It is very different having copper mixed in an alloy to make bronze, than having two compleatly disimilar metals. Even in Bronze, if a stray current occurs, the Zinc is leached straight out and the copper is left creating a very soft pinkish spoting all over the blade. I have also seen two different types of Bronze react to one another. A shaft key completely disolved away allowing the prop to start spinning ont he shaft.
I just have this feeling that if it could be done, copper coating would have been done by know. But hey, I stand to be corrected. It's just my opinion.

As for the cleaning of the prop, you don't grind much away. You are just going to take the growth off and clean the very surface. Don't go cutting into the Bronze. Use a sanding disc on a grinder with about a 120grit, which brings the surface up very smooth. don't apply to much pressure. Bronze maybe soft, but it very easy to control the sanding on. After you have sanded it, use a polishing buff with some Autosolve or Brasso or best is the proper metal cutting compounds that come in stick form. It will shine it up, but not take away any bronze to be concerned with at all. The smoother you get it, the better it is at reamining clean and most importantly the more efficient it is in the water.
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Old 15-11-2006, 09:14   #81
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Engine overheating?

Hi,
Just saw this thread on prop size. I have a 31ft waterline, 45lod, boat weighs gross at 44k, tranny is 2:91 and prop is 18X14 Michigan 3 blade; drinks just under 1 gal/hr at 3000 rpm and 7.5 - 8.0 kts gps. Any more is waste of fuel/engine. Engine is 4-108, boat is 1977 model.
For your info.
Alan @ middle east somewhere

ps: I (the yard) also coated the New prop with 6 coats of the metal primer and then 4 coats of trinidad bottom paint. Others said to use multiple coats of epoxy first on the prop and then the bottom paint. At least this was what I was told, since I was over here when it happened...
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Old 15-11-2006, 09:54   #82
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Thats a good datapoint. My boat is a Gulfstar 36 at 18,000 lbs.

I just got back from the prop shop and they say the 19x18 that I just took off the boat isnt worth repitching so it will become a coffe table ornament. They are selling me a 18x13 refurbished for $275 so that is what I will put on the boat and the recently repitched 18x14 will go in the engine room for a spare.

I checked out the Propspeed stuff and found that West Marine has it for $200 for the smallest can, 200 ml. It sounds good, BUT I just bought a prop for a little bit over that!


I am going to try some of these ideas on anti fouling the prop using my "ornament" prop hanging in the canal with different substances on each of the three blades to get a comparison. Of course that wont test the durability of the coating under power.
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Old 21-11-2006, 20:39   #83
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The overheating problem is solved!!!
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Old 21-11-2006, 22:07   #84
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Old 21-11-2006, 22:57   #85
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Cool.
OK, for interest, how does it perform now. It is often found that the boat can become much more responsive and in some cases actually gain speed. Have you noticed any difference.?
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Old 22-11-2006, 09:30   #86
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OK, my last post was just a tease to get everyone listening...#8-)

As this forum started I described my overheating problems and we discussed the possibilities and I made some changes. The discussion continued and we ended up concerned about the propeller after I reported that it was probably 18x18 since that is what the spare was. Turned out it was 19x18...even worse. Now will THAT cure the overheating?

You were quite right, it did. Thats the way a discussion forum is supposed to work, discuss, try, and solve.

The details:
Perkins 4-108 engine with no load 600 to 4000 RPM
We are going for 3600 RPM (90%) under load.

The 19x18 prop gave 2200 RPM max
At 2000 RPM it gave 5.0 Knots and tengine temp of 200F

The 18x13 prop gives 3600 RPM max (right on the button of 90%)
At 2000 RPM it gives 5.0 knots and 170F engine temp
At 2500 RPM it gives 6.0 knots and 170F engine temp (thermostat temperature)
At 2600 RPM it gives 6.2 knots and 170F engine temp

I am predicting it will hit hull speed (6.8 Knots) at 3000 RPM and 170F but I have not yet tried it.

In any case, I believe that I have the cleanest and most efficient cooling system on the planet right now because I went over it with a fine toothed comb before discovering it was NOT the cooling system that was causing the problem...#8-)

As to improved performance, I find that getting alongside at my berth which requires a bit of backing and filling is much easier and more predictable when backing. Yesterday I laid it up to the wharf single handed and then jumped ashore to tie her, no assistance needed. Usually someone jumps ashore to keep me off the concrete but this time I laid it against the fenders without a problem.

Thanks to everyone on this Forum for all the suggestions. Its fixed!!!
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Old 22-11-2006, 11:16   #87
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Yeeeeehaaaa!

We'll send the bill then.;-)
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Old 27-11-2006, 20:35   #88
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Thought so.

Glad you sorted it out.
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