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Author Topic:   Overpropped?

Frank O posted 06-16-2007 09:58 PM ET (US)
Some time ago, in this thread:
http://continuouswave.com/ubb/Forum4/HTML/005225.html
Sal made the following comment about the 19-pitch Laser II propeller that came on my 1995 Outrage 21 with 1994 225-H.P. 3.0L Offshore 2-stroke I bought last year:
"Franko, what is the maximum rpms you can twist with that load? If I'm not mistaken, that engine is rated at either 5800 rpms or 6000. I have the feeling that engine isn't twisting over 5100 rpms which means your over propped for how your using that rig. I feel if your not turning at least 5200 rpms, you should drop down to a 17 pitch prop, which would allow the engine to work less while pushing that load. With less pitch, your rig will get on plane easier & plane at a lower rpm."
Because of non-optimal ocean conditions and other factors, it's been quite a while until we could conduct a wide-open-throttle test. However, today we got a chance to do so. With about 600 pounds of divers (3 adult males), maybe another 300 pounds of gear and ~75 gallons of gas in the tank, we opened up the throttle and found it plateau'd at 41 mph and 4600 rpm.
I gather I'm overpropped? As a next step I guess I'll see if I can get ahold of a 17-pitch Revolution 4 prop to try.
Does the above data point bring to mind any other thoughts?

Sal DiMercurio posted 06-16-2007 11:05 PM ET (US)
Franko, when you opened her up [ full throttle ] did you trim the engine back or leave it all the way tucked in.
When testing for the correct pitch, you load the boat as you would be using it most of the time, or a normal load you would be carrying on most trips.
You get the boat on plane, go to WOT, trim the engine back until she starts to vent [ slip ], bring the trim back in until the prop stops venting,....that is the time you check your rpms & speed.
I have the feeling you did "NOT" trim the engine at all.
Is your engine mounted on the transom as low as it will go?
If so, you need to raise the engine "UP" at least 1 set of holes & probably 2 sets.
By raising the engine up a set of holes, you could pick up maybe 150 rpms.
Than try trimming the engine out or back as I described above, & you should pick up another 2 - 300 rpms.
4600 rpms is totally un-acceptable for that engine.
Run the test again & do as I say during the test & than come back here & tell us what the engine is doing.
I figure maybe 5000 rpms,....if so, than you need to drop down 2" of pitch & possibly 4" of pitch [ to a 15 pitch ] to get her up to around 5800 - 5900.
Sal
Tom W Clark posted 06-17-2007 12:19 PM ET (US)
Frank,
Running a 21 foot boat with 600 pounds of passengers, 300 pounds of gear and 400 pounds of fuel is probably not the optimal time to do any top speed, WOT testing. You cannot draw any useful conclusions from such data.
If, on the other hand, you always run your boat like this, then yes, you are overpropped and you will ned a very special propeller to push that load.
At any rat, the Laser II is a poor choice for that boat and motor combination. For ocean conditions you typically experience, you should think about a larger surface area prop like the Mirage Plus or a good four blade like the VenSura (a.k.a. Offshore, Quicksilver Typhoon) or a Revolution 4.
Stiletto, Turbo ad Power Tech all make excellent four blade props as well.
Frank O posted 06-18-2007 11:41 PM ET (US)
Thanks for the advice, that's very helpful.
Sal, your intuitions are correct -- no, I haven't yet done much with trimming the outboard. I tend to keep it down as the boat's bow already looks like it rides pretty high when on plane. For example:
http://www.inkbox.net/whaler/whaler-olympic1.jpg
In part this may be due to how the boat is loaded with equipment, but even unloaded it seems to lean toward being bow-up. I'll try your procedure, though, for trimming until it just stops venting. As for raising the engine up, I don't remember seeing extra sets of holes, but I'll take a look. Any change will probably have to wait until the next time we have the boat out of the water (probably at least six months from now).
Tom, yes, this is how the boat is loaded 90% of the time -- 600-800 pounds of people, about half that of dive equipment, and usually a fairly full 100-gallon tank. As noted I've been thinking about alternative props for a while. I was leaning toward trying a Revolution 4 17-pitch in order to get on plane quicker and get a smoother ride (my priorities being (a) good handling/comfortable ride in moderate seas, and (b) fuel economy. Goosing the speed isn't a priority -- 25 to 30 knots always seems plenty fast for us). How would you expect a VenSura/Offshore/QS Typhoon to compare to a Revolution 4?
Tom W Clark posted 06-19-2007 01:51 AM ET (US)
Frank,
Your boat is not on plane in the photo above, it is in that awkward semi-plane transition which is not a crisp transition with a deep vee hull, especially one that is loaded.
I think the REVOLUTION 4 will serve your needs better than the VenSura/Offshore. Also consider trying a 17" MIRAGE Plus, a very good stern lifting propeller with lots of blade area.
Frank O posted 06-19-2007 10:12 AM ET (US)
Thanks, Tom, this is enlightening. I had always assumed that when bringing the speed gradually up leaving the harbor and the tach suddenly jumps a thousand rpm or more, the bow nudges up in the air and we start going significantly faster that we are "getting on plane." But maybe because of how the boat/engine/prop are set up and the way the boat is loaded we're never getting there. What would you expect to see in the photo to truly be on plane -- would the bow be riding higher?
Tom W Clark posted 06-19-2007 10:15 AM ET (US)
"Getting on plane", yes, but not quite ON plane yet. Once on plane the bow comes back down as the stern comes up and the boat rides more level.
Tohsgib posted 06-19-2007 12:33 PM ET (US)
Flatter the wake, the more level or on plane you are.
simonmeridew posted 06-21-2007 10:04 PM ET (US)
I look at the water about 4 - 5 feet immediately behind the boat: if this is rough and full of churning white water, we're not on plane. Give it a little more gas, pick up a little more speed and look at the same area behind the boat and the white water is gone, replaced with relatively flat non turbulent water, kind of flowing back away from the stern, and I figure I'm on plane.
The advantage to this method is that when you change load position, bow vs stern passengers etc, you aren't just looking at your speed to determine plane or displacement. The next time I'm out I'll try to take some pics of the stern water and post them.
simonmeridew

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Author	Topic: Overpropped?
Frank O	posted 06-16-2007 09:58 PM ET (US) Some time ago, in this thread: http://continuouswave.com/ubb/Forum4/HTML/005225.html Sal made the following comment about the 19-pitch Laser II propeller that came on my 1995 Outrage 21 with 1994 225-H.P. 3.0L Offshore 2-stroke I bought last year: "Franko, what is the maximum rpms you can twist with that load? If I'm not mistaken, that engine is rated at either 5800 rpms or 6000. I have the feeling that engine isn't twisting over 5100 rpms which means your over propped for how your using that rig. I feel if your not turning at least 5200 rpms, you should drop down to a 17 pitch prop, which would allow the engine to work less while pushing that load. With less pitch, your rig will get on plane easier & plane at a lower rpm." Because of non-optimal ocean conditions and other factors, it's been quite a while until we could conduct a wide-open-throttle test. However, today we got a chance to do so. With about 600 pounds of divers (3 adult males), maybe another 300 pounds of gear and ~75 gallons of gas in the tank, we opened up the throttle and found it plateau'd at 41 mph and 4600 rpm. I gather I'm overpropped? As a next step I guess I'll see if I can get ahold of a 17-pitch Revolution 4 prop to try. Does the above data point bring to mind any other thoughts?
Sal DiMercurio	posted 06-16-2007 11:05 PM ET (US) Franko, when you opened her up [ full throttle ] did you trim the engine back or leave it all the way tucked in. When testing for the correct pitch, you load the boat as you would be using it most of the time, or a normal load you would be carrying on most trips. You get the boat on plane, go to WOT, trim the engine back until she starts to vent [ slip ], bring the trim back in until the prop stops venting,....that is the time you check your rpms & speed. I have the feeling you did "NOT" trim the engine at all. Is your engine mounted on the transom as low as it will go? If so, you need to raise the engine "UP" at least 1 set of holes & probably 2 sets. By raising the engine up a set of holes, you could pick up maybe 150 rpms. Than try trimming the engine out or back as I described above, & you should pick up another 2 - 300 rpms. 4600 rpms is totally un-acceptable for that engine. Run the test again & do as I say during the test & than come back here & tell us what the engine is doing. I figure maybe 5000 rpms,....if so, than you need to drop down 2" of pitch & possibly 4" of pitch [ to a 15 pitch ] to get her up to around 5800 - 5900. Sal
Tom W Clark	posted 06-17-2007 12:19 PM ET (US) Frank, Running a 21 foot boat with 600 pounds of passengers, 300 pounds of gear and 400 pounds of fuel is probably not the optimal time to do any top speed, WOT testing. You cannot draw any useful conclusions from such data. If, on the other hand, you always run your boat like this, then yes, you are overpropped and you will ned a very special propeller to push that load. At any rat, the Laser II is a poor choice for that boat and motor combination. For ocean conditions you typically experience, you should think about a larger surface area prop like the Mirage Plus or a good four blade like the VenSura (a.k.a. Offshore, Quicksilver Typhoon) or a Revolution 4. Stiletto, Turbo ad Power Tech all make excellent four blade props as well.
Frank O	posted 06-18-2007 11:41 PM ET (US) Thanks for the advice, that's very helpful. Sal, your intuitions are correct -- no, I haven't yet done much with trimming the outboard. I tend to keep it down as the boat's bow already looks like it rides pretty high when on plane. For example: http://www.inkbox.net/whaler/whaler-olympic1.jpg In part this may be due to how the boat is loaded with equipment, but even unloaded it seems to lean toward being bow-up. I'll try your procedure, though, for trimming until it just stops venting. As for raising the engine up, I don't remember seeing extra sets of holes, but I'll take a look. Any change will probably have to wait until the next time we have the boat out of the water (probably at least six months from now). Tom, yes, this is how the boat is loaded 90% of the time -- 600-800 pounds of people, about half that of dive equipment, and usually a fairly full 100-gallon tank. As noted I've been thinking about alternative props for a while. I was leaning toward trying a Revolution 4 17-pitch in order to get on plane quicker and get a smoother ride (my priorities being (a) good handling/comfortable ride in moderate seas, and (b) fuel economy. Goosing the speed isn't a priority -- 25 to 30 knots always seems plenty fast for us). How would you expect a VenSura/Offshore/QS Typhoon to compare to a Revolution 4?
Tom W Clark	posted 06-19-2007 01:51 AM ET (US) Frank, Your boat is not on plane in the photo above, it is in that awkward semi-plane transition which is not a crisp transition with a deep vee hull, especially one that is loaded. I think the REVOLUTION 4 will serve your needs better than the VenSura/Offshore. Also consider trying a 17" MIRAGE Plus, a very good stern lifting propeller with lots of blade area.
Frank O	posted 06-19-2007 10:12 AM ET (US) Thanks, Tom, this is enlightening. I had always assumed that when bringing the speed gradually up leaving the harbor and the tach suddenly jumps a thousand rpm or more, the bow nudges up in the air and we start going significantly faster that we are "getting on plane." But maybe because of how the boat/engine/prop are set up and the way the boat is loaded we're never getting there. What would you expect to see in the photo to truly be on plane -- would the bow be riding higher?
Tom W Clark	posted 06-19-2007 10:15 AM ET (US) "Getting on plane", yes, but not quite ON plane yet. Once on plane the bow comes back down as the stern comes up and the boat rides more level.
Tohsgib	posted 06-19-2007 12:33 PM ET (US) Flatter the wake, the more level or on plane you are.
simonmeridew	posted 06-21-2007 10:04 PM ET (US) I look at the water about 4 - 5 feet immediately behind the boat: if this is rough and full of churning white water, we're not on plane. Give it a little more gas, pick up a little more speed and look at the same area behind the boat and the white water is gone, replaced with relatively flat non turbulent water, kind of flowing back away from the stern, and I figure I'm on plane. The advantage to this method is that when you change load position, bow vs stern passengers etc, you aren't just looking at your speed to determine plane or displacement. The next time I'm out I'll try to take some pics of the stern water and post them. simonmeridew