First Water Test

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johnp
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First Water Test

Post by johnp » Tue Jul 03, 2012 2:16 pm

Well, it worked. i think i need more pitch on the prop. she seems to be using alot of steam and turning as high as 1000rpm. when i turn her down to 350ish the steam seems to maintain. the LWL is 213 1/4" she is 18' 3" LOL with a 5 1/2' beam. Plywood and epoxy, Ray Hasbrouck #10 2hp, 20sqft VFT, Wood burning. had her as fast as 4.5knts. but using alot of steam. Really had to put the wood to her. Maybe i need to switch to coal or better wood? or more pitch and slow down the engine. she was design for 400rpm. Possibly 14"x20". i can only go as large as 15" Diameter. Please any thoughts and suggestions are welcome. i'm new to the hobby and can use all the info i can get.

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DetroiTug
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Re: First Wate Test

Post by DetroiTug » Tue Jul 03, 2012 2:42 pm

Beautiful boat, you did a really nice job on it. The 2 hp engine scoots it right along.

Careful on changing to another prop, a few inches on diameter or pitch can make considerable difference, it looks as though it's pretty close right now.

I went from a 20X20 to a 19 X 25 with bad results. The engine seemed to be struggling too hard, it looked like it was going to rip itself out of the bed rails. Went back to the 20X20.

I would only increase pitch about one or two inches if any at all. One thing to keep in mind, when the engine is slowed down and we attempt to yield the same horsepower, the frictional loads go up on all the wear surfaces. Like driving a car in high gear all the time.

-Ron
johnp
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Re: First Wate Test

Post by johnp » Tue Jul 03, 2012 3:24 pm

Thanks Ron, now she has a 13.5 dia x 16.5 pitch, I can openly he valve and get 1000 plus rpm. At wide open I can't maintain steam pressure. So was thinking about a 14" x 20"?
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Lopez Mike
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Re: First Wate Test

Post by Lopez Mike » Tue Jul 03, 2012 3:57 pm

Boats are more sensitive to pitch changes than you might think. On my sailboat, with one of those stinky engines, I have a prop than I can change the pitch in about one inch increments. I find that going one inch shorter makes the boat feel like the prop has fallen off and going one inch longer makes the engine lug and not come close to reaching normal rpm.

It's worth trying to find a prop that you can borrow for a test before buying.
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Re: First Wate Test

Post by Mike Rometer » Tue Jul 03, 2012 4:43 pm

Well done that man! Nice job!

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DetroiTug
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Re: First Wate Test

Post by DetroiTug » Tue Jul 03, 2012 5:00 pm

What Mike said, or Ebay for cheap props ($50). Also props can be repitched.

Here is my theory on your setup: The high RPMS you are running are creating probably double the calculated 2 horsepower, but you're outrunning the boiler. Going to a bigger bite (cutting the RPM by half at the same throttle pressure) is probably going to result in half the torque (speed) delivered to the prop and less performance. I'm a bit of a "newb" myself, but this is how I would be addressing your set up.

The power comes from the boiler, and with a 20 sq/ft VFT in an 18 ft rather heavy beamy hull, there is a definite limit on how much speed you can get. About 5 knots is going to be it I would say. Drop the RPM in small increments until the boiler can keep up and that is the sweetspot.

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Re: First Wate Test

Post by johnp » Tue Jul 03, 2012 5:13 pm

So, just by throttling down? No changes? I thought this was a light narrow boat, plywood and epoxy.

The prop has been repitched to 16.5, can it be repitched again?
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DetroiTug
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Re: First Wate Test

Post by DetroiTug » Tue Jul 03, 2012 6:40 pm

Same throttle setting, going steeper on the prop is going to lower the engine RPM.

I think a prop can have it's pitch increased only a certain amount, like 20%. It's due to the angle of the blade root cast in to the hub of the prop. Of course, on our slow turning plants in comparison to I/C engines, probably not so critical.

-Ron
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Re: First Wate Test

Post by fredrosse » Tue Jul 03, 2012 11:01 pm

I happen to have a 14 RH 17 Michigan DYNA-JET Prop that was on my electric boat, 1-1/4 shaft, standard marine taper. It is a good 3 blade bronze prop, with a few minor dings & scrapes. I will lend it to you for tryout, if you want it then you can buy it from me, or return via the mail. Being close to what you may need, a 17 inch pitch, it would be a good canidate for re-pitching if needed.
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fredrosse
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Re: First Wate Test

Post by fredrosse » Tue Jul 03, 2012 11:04 pm

Very nice job you have done there! I don't know where you are from, will you, or a friend, be at Waterford NY next weekend??
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