new boat launch-propeller question
-
- Just Starting Out
- Posts: 19
- Joined: Thu Nov 03, 2022 3:22 pm
- Boat Name: assassin-Wes Farmer
new boat launch-propeller question
Launched my boat yesterday. It is assassin by Wes Farmer with a Hasbrouck #1 engine. My prop is a 12 x 12. 300rpm gives me 3 mph at 60-100 psi. 400 rpm gives me 4mph at 60-100 psi. 500rpm gives me no increase in speed. At 400 rpm I have to keep turning my steam nozzle (1/16 dia) off and on to keep the psi from going over 100psi. Most steamboats would have more pitch than I have. Am I being held back by my prop? My boiler is on the small size (9sq ft heating surface) , all copper, but seems adequate if I feed it good wood. If I need a prop can anyone recommend a source?
- RNoe
- Full Steam Ahead
- Posts: 250
- Joined: Sun May 26, 2019 5:29 pm
- Boat Name: Cluaran
- Location: Northern Oregon, USA
Re: new boat launch-propeller question
Nice work on your Assassin! Congrats on getting it onto the water.
My instant thought is that your prop has insufficient pitch.
It is difficult to "over prop" a steam engine, and I think a higher pitch will get you improved performance.
Sources? Not sure for the smaller props. Making your own prop a is possibility and there are people on this discussion board that could assist you.
(Just not me...}
And assuming your hull is fully a displacement hull at 16 feet long, top water speed (in knots) will be approximately 1.34 times the square root of the water line length.
That calculates to about 5.3 knots max.
Go for a higher pitch prop, and please let us know the results.
RussN
My instant thought is that your prop has insufficient pitch.
It is difficult to "over prop" a steam engine, and I think a higher pitch will get you improved performance.
Sources? Not sure for the smaller props. Making your own prop a is possibility and there are people on this discussion board that could assist you.
(Just not me...}
And assuming your hull is fully a displacement hull at 16 feet long, top water speed (in knots) will be approximately 1.34 times the square root of the water line length.
That calculates to about 5.3 knots max.
Go for a higher pitch prop, and please let us know the results.
RussN
- Kelly Anderson
- Full Steam Ahead
- Posts: 173
- Joined: Fri Feb 11, 2011 1:28 am
- Boat Name: Vividus
- Location: Strasburg, PA
- Contact:
Re: new boat launch-propeller question
A rule of thumb for steam launch propellers is to make the pitch 1.5 times the diameter, or 18" in your case. That may not be exactly right for your boat, but it is almost certain to be satisfactory.
Do you have a pressure gauge on your engine's steam chest? That can be very helpful in determining how much the propeller is loading your engine. My first propeller on my first boat was a 16" x 16", and I was shooting for a top engine speed of 500 rpm. On the first trail, the engine was nearing 500 rpm with a steam chest pressure of roughly 40 psi ( the boiler pressure was 150 psi). By the time I got the engine loaded down to 500 rpm while working at near maximum boiler pressure, the propeller had grown to 17" x 27", 1.59 to 1 pitch to diameter ratio.
If you are obsessed and good at math, buy a copy of Propeller Handbook by Dave Gerr. It is very readable and the formulas are understandable to the common man. Note that finding the best propeller can be a matter of trial and error for even the largest ships. IIRC, even the Queen Mary needed a couple of propeller swaps until they found the optimum combination.
Do you have a pressure gauge on your engine's steam chest? That can be very helpful in determining how much the propeller is loading your engine. My first propeller on my first boat was a 16" x 16", and I was shooting for a top engine speed of 500 rpm. On the first trail, the engine was nearing 500 rpm with a steam chest pressure of roughly 40 psi ( the boiler pressure was 150 psi). By the time I got the engine loaded down to 500 rpm while working at near maximum boiler pressure, the propeller had grown to 17" x 27", 1.59 to 1 pitch to diameter ratio.
If you are obsessed and good at math, buy a copy of Propeller Handbook by Dave Gerr. It is very readable and the formulas are understandable to the common man. Note that finding the best propeller can be a matter of trial and error for even the largest ships. IIRC, even the Queen Mary needed a couple of propeller swaps until they found the optimum combination.
It was not easy to convince Allnutt. All his shop training had given him a profound prejudice against inexact work, experimental work, hit-or-miss work.
- barts
- Full Steam Ahead
- Posts: 1070
- Joined: Wed Nov 18, 2009 6:08 am
- Boat Name: Otter, Rainbow
- Location: Lopez Island, WA and sometimes Menlo Park, CA
- Contact:
Re: new boat launch-propeller question
"Propeller Handbook" is indeed well worth examining; the math is pretty empirical. In general, for displacement boats you want to run the largest practical propeller diameter. One thing to note; the most efficient props in abstract are typically near 1:1 pitch/diameter ratio, but most small steamboats cannot swing a large enough propeller so the designers choose the diameter that fits and has adequate tip clearance and increase the pitch instead to load the engine down to a practical and comfortable rpm.
A larger diameter propeller will provide more bollard pull (stalled thrust) and will be affected less by increased resistance due to wave or wind actions.
- Bart
A larger diameter propeller will provide more bollard pull (stalled thrust) and will be affected less by increased resistance due to wave or wind actions.
- Bart
-------
Bart Smaalders http://smaalders.net/barts Lopez Island, WA
Bart Smaalders http://smaalders.net/barts Lopez Island, WA
-
- Just Starting Out
- Posts: 19
- Joined: Thu Nov 03, 2022 3:22 pm
- Boat Name: assassin-Wes Farmer
Re: new boat launch-propeller question
Is there any problem with using a left hand prop? They seem to be more available on E-bay
- Kelly Anderson
- Full Steam Ahead
- Posts: 173
- Joined: Fri Feb 11, 2011 1:28 am
- Boat Name: Vividus
- Location: Strasburg, PA
- Contact:
Re: new boat launch-propeller question
That depends on the engine. Many designs have a definite forward direction built in, and that should be respected. For example, some crossheads are designed with only half the bearing area when turning counterclockwise (when viewed from astern) as they do when turning clockwise.
Likewise, valve gear can have a definite forward direction built in. For example on Stephenson valve gear, where the the reversing links connect to one end of the link, then the valve gear should be set up with that end of the link as forward gear. The reason for that is that the link block slip is much less on that end compared to the other end, meaning that the valve events will be more accurate. Since the engine will spend 99% of its life going forward, it pays off to pay attention to that detail. If your engine has equal crosshead bearing area in either direction, and valve gear that works equally well in either direction, then you are free to run rhe engine in either direction that is convenient.
Likewise, valve gear can have a definite forward direction built in. For example on Stephenson valve gear, where the the reversing links connect to one end of the link, then the valve gear should be set up with that end of the link as forward gear. The reason for that is that the link block slip is much less on that end compared to the other end, meaning that the valve events will be more accurate. Since the engine will spend 99% of its life going forward, it pays off to pay attention to that detail. If your engine has equal crosshead bearing area in either direction, and valve gear that works equally well in either direction, then you are free to run rhe engine in either direction that is convenient.
It was not easy to convince Allnutt. All his shop training had given him a profound prejudice against inexact work, experimental work, hit-or-miss work.
- Kelly Anderson
- Full Steam Ahead
- Posts: 173
- Joined: Fri Feb 11, 2011 1:28 am
- Boat Name: Vividus
- Location: Strasburg, PA
- Contact:
Re: new boat launch-propeller question
In an edit to my post above, after rereading your first post saying that you have a Hasbrook #1 engine, and finding this video of it in operation, I'll modify my statement to say that the tunnel crosshead will allow the engine to run equally well in either direction. If it was mine, I would reset the eccentrics to have the forward motion end of the link timed to drive the engine in the opposite direction.
It was not easy to convince Allnutt. All his shop training had given him a profound prejudice against inexact work, experimental work, hit-or-miss work.
-
- Just Starting Out
- Posts: 19
- Joined: Thu Nov 03, 2022 3:22 pm
- Boat Name: assassin-Wes Farmer
Re: new boat launch-propeller question
There is a 14 week wait to have a new prop made so I will search e-bay for one. I the meantime I will explore the possibility of making one . In the 1961Nov-Dec issue of Steamboats and Modern Steam launches there is an article where he mentions about the possibility of making one out of fiberglass. In the 1962 September-October issue there is an article by Wes Farmer on how to layout a prop. Might be a fun project.
- RNoe
- Full Steam Ahead
- Posts: 250
- Joined: Sun May 26, 2019 5:29 pm
- Boat Name: Cluaran
- Location: Northern Oregon, USA
Re: new boat launch-propeller question
Here is a YouTube video of Steam Launch "Reciproca."
https://www.youtube.com/watch?v=BDv_J1RXTB4
Note the home made 2-blade prop and how it propels that 20 ft. long(?) launch at 6+ knots with just 2 horse power.
The prop is easily visible at the beginning of this video.
I have not found a description of how it was laid out and fabricated, and would like to learn that.
But it illustrates what is possible.
RussN
https://www.youtube.com/watch?v=BDv_J1RXTB4
Note the home made 2-blade prop and how it propels that 20 ft. long(?) launch at 6+ knots with just 2 horse power.
The prop is easily visible at the beginning of this video.
I have not found a description of how it was laid out and fabricated, and would like to learn that.
But it illustrates what is possible.
RussN
-
- Just Starting Out
- Posts: 19
- Joined: Thu Nov 03, 2022 3:22 pm
- Boat Name: assassin-Wes Farmer
Re: new boat launch-propeller question
A two blade prop would be alot easier to make than a 3 blade but I do not know if that would work for my boat. I would think I would need a larger diameter than 12".