MONTAUK 17: Propeller Comparison--17 and 19-inch Pitch

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Author Topic:   MONTAUK 17: Propeller Comparison--17 and 19-inch Pitch

boatdryver posted 06-12-2006 11:09 PM ET (US)
Here is some performance data that may be of interest to people considering a prop change. The nearly identical performance of two props 2-inches different in pitch and the same diameter can only be explained by different materials and blade design
Boat: '79 Montauk with clean bottom. Motor: Honda BF 90 mounted with AV plate 1.5 inches above bottom (3rd hole). One adult, 12 gal fuel. motor trimmed way up till it got a little squirrelly. Both runs within a half hour. Flat water. 5 kt wind, no canvas up.
Old prop: aluminum 13X19 either Honda or Merc, in new condition with minimal cupping:
WOT rpm 5800
average speed by GPS (up and down current and 5 kt wind): 34.7 kt=39.9 mph
Stilletto 13x17 SS
WOT rpm 5800
average speed by gps: 35.0 kt=40.3 mph
Subjectively the hole shot with the Stilletto is faster and mid range acceleration is better. Idle speed seems slower, better for trolling, and minimum planing speed seems to require more rpm. (I had little experience with the old prop on this recently purchased boat/motor package.)
No fuel flow meter.
I hope to do some speed runs at different rpms next
JimL
jimh posted 06-13-2006 12:42 AM ET (US)
It looks like you have that Montauk running quite nicely with the Honda BF90 outboard.
There is quite a bit of data that shows that the marked pitch of a propeller is something of an arbitrary value, and among several manufacturers it is common to see differences in the assignment of pitch. What one manufacturer calls a "17-inch" propeller may, as you have demonstrated, produce performance very similar to a "19-inch" propeller from another manufacturer.
If you stay within a particular brand and also in a particular model or style of propeller in that brand, then propellers of different pitch ought to produce different results.
RobertRibley posted 06-13-2006 10:22 AM ET (US)
Thanks for info I am waiting for a Stiletto 15 to test on my 82 will report soon Robert
pasino posted 06-14-2006 10:59 AM ET (US)
I had the same experience when I put a new yamaha 115 on mi 1980 montauk.
The motor came with a 21" aluminium prop and performed 38.7 knots at WOT 5800. Then i put a 19" teflon covered steel yamaha prop that performed 39.7 knots at 5900.
Am I wrong supposing that was because the steel propeller was much more efficent?
davej14 posted 06-15-2006 11:06 AM ET (US)
Shouldn't a 115 on a Montauk do at least 45 mph? Less than 40 mph at WOT doesn't seem right to me. Maybe the motor is mounted too low??
Tom W Clark posted 06-15-2006 11:09 AM ET (US)
39.7 knots is 45.6 MPH.
davej14 posted 06-15-2006 11:42 AM ET (US)
That makes more sense, I didn't notice the "knots" vs. "mph" on the post.

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Author	Topic: MONTAUK 17: Propeller Comparison--17 and 19-inch Pitch
boatdryver	posted 06-12-2006 11:09 PM ET (US) Here is some performance data that may be of interest to people considering a prop change. The nearly identical performance of two props 2-inches different in pitch and the same diameter can only be explained by different materials and blade design Boat: '79 Montauk with clean bottom. Motor: Honda BF 90 mounted with AV plate 1.5 inches above bottom (3rd hole). One adult, 12 gal fuel. motor trimmed way up till it got a little squirrelly. Both runs within a half hour. Flat water. 5 kt wind, no canvas up. Old prop: aluminum 13X19 either Honda or Merc, in new condition with minimal cupping: WOT rpm 5800 average speed by GPS (up and down current and 5 kt wind): 34.7 kt=39.9 mph Stilletto 13x17 SS WOT rpm 5800 average speed by gps: 35.0 kt=40.3 mph Subjectively the hole shot with the Stilletto is faster and mid range acceleration is better. Idle speed seems slower, better for trolling, and minimum planing speed seems to require more rpm. (I had little experience with the old prop on this recently purchased boat/motor package.) No fuel flow meter. I hope to do some speed runs at different rpms next JimL
jimh	posted 06-13-2006 12:42 AM ET (US) It looks like you have that Montauk running quite nicely with the Honda BF90 outboard. There is quite a bit of data that shows that the marked pitch of a propeller is something of an arbitrary value, and among several manufacturers it is common to see differences in the assignment of pitch. What one manufacturer calls a "17-inch" propeller may, as you have demonstrated, produce performance very similar to a "19-inch" propeller from another manufacturer. If you stay within a particular brand and also in a particular model or style of propeller in that brand, then propellers of different pitch ought to produce different results.
RobertRibley	posted 06-13-2006 10:22 AM ET (US) Thanks for info I am waiting for a Stiletto 15 to test on my 82 will report soon Robert
pasino	posted 06-14-2006 10:59 AM ET (US) I had the same experience when I put a new yamaha 115 on mi 1980 montauk. The motor came with a 21" aluminium prop and performed 38.7 knots at WOT 5800. Then i put a 19" teflon covered steel yamaha prop that performed 39.7 knots at 5900. Am I wrong supposing that was because the steel propeller was much more efficent?
davej14	posted 06-15-2006 11:06 AM ET (US) Shouldn't a 115 on a Montauk do at least 45 mph? Less than 40 mph at WOT doesn't seem right to me. Maybe the motor is mounted too low??
Tom W Clark	posted 06-15-2006 11:09 AM ET (US) 39.7 knots is 45.6 MPH.
davej14	posted 06-15-2006 11:42 AM ET (US) That makes more sense, I didn't notice the "knots" vs. "mph" on the post.