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Author Topic:   Prop Selection for Dauntless 17

JREvans posted 04-18-2005 09:16 PM ET (US)
We purchased a '95 Dauntless 17 late in the summer of 2004. The original 115 Evinrude had been replaced with a Johnson 130 Ocean Pro. It has a long shaft so they mounted it on a Highjacker that is raised enough to compensate for the extra length. I am a boating rookie and need some input in deciding whether or not I have the correct propeller for our needs. It has a 14 3/4" 21 pitch stainless prop. The engine runs 6000 RPM at WOT and only tops out at or just above 40 mph depending on load. I rarely have more that 2 adults and 2 children on board. The holeshot seems more than adequate but I feel that this boat should top out closer to 50 than 40mph. In addition, the boat seems extremely stern heavy, especially with this particular motor arrangement. I can barely trim it up before it begins porpoising. I have added Doel fins which have helped significantly with handling and planing out quickly. I am considering changing to a 23 or 24 pitch stainless prop. I was hoping someone with similar setup could help me decide whether replacing the current prop would give me the top end I expect without too much trade-off in holeshot. We will occasionally be towing an adult skier or tube rider.

jimh posted 04-19-2005 07:51 AM ET (US)
[Moved from another area. Please use the PERFORMANCE area to ask about specific boat/motor/propeller combinations.]
Teak Oil posted 04-19-2005 05:43 PM ET (US)
Sounds like the engine should be raised higher. Is the jack plate adjustable? Since you are hitting 6000 rpms with four on board I would switch to a 23 inch, possibly a four blade, and raise the jack plate if possible.
I dont know what the weight of your boat is but I would think 45mph should be easy to attain.
You should add a water pressure gauge to make sure you are not sucking air.
JREvans posted 04-19-2005 09:48 PM ET (US)
Thanks Teakoil. My jackplate is raised all the way up. I do think that I need to go to a 23 pitch prop, though. Is there any other clues that I may be sucking air other than by installing a gauge? My boat sans motor is 1350 lbs dry and the motor is 360 lbs.
Teak Oil posted 04-20-2005 08:27 AM ET (US)
You need to find out what you lower unit gear ratio is so you can calculate your prop slip %. If you are getting more than 10% at WOT something is wrong with your setup. Use the formulas in the reference section to calculate this.
Also with the engine down in the run position on the trailer where is the antiventilation plate on the engine in relation to the bottom (keel) of the boat? Is it level, and inch above, an inch below, etc?
Your engine can still be raised, you may have to unbolt it and reinstall on a higher set of bolt holes.
JREvans posted 04-20-2005 08:25 PM ET (US)
The engine is mounted in the highest of the 6 holes you mention. The cavitation plate is slightly above the keel, about 1 inch or less. Where is the reference section you mentioned for me to calculate slippage?
jimh posted 04-20-2005 09:45 PM ET (US)
To help people evaluate their propeller performance, I have provided the PROPELLER CALCULATOR in the Reference Section. See:
http://continuouswave.com/cgi-bin/propcalc.pl
There are dozens of well researched, illustrated, and lengthy articles on many topics in the Boston Whaler Reference Section:
http://continuouswave.com/whaler/reference/
The "forum" or discussion area (this area) is actually the most recent addition to the website, and although extremely popular and dynamic, there are many other resources available here besides this section. I encourage you to explore further. You can always start at the top page:
http://continuouswave.com/
Teak Oil posted 04-21-2005 12:07 AM ET (US)
If you are only an inch above the keel you are definitely too low assuming you have a four or five inch setback plate.
If you already are mounted as high as possible on the plate and the plate is rasied all the way up you are pretty screwed as far as adjustment. You can try some trim tabs, but everything is a band aid until you put an engine on with the proper length shaft
JREvans posted 04-21-2005 07:20 PM ET (US)
I agree with you on being screwed on the adjustment. Do you think that a change in prop pitch would help any on lowering RPMs and increasing top-end mph?
LHG posted 04-21-2005 08:09 PM ET (US)
The Doel fin will be a speed killer, unless your engine is running elevated about 1-1/2". Then you will need a surfacing prop.
Most mid-range engines have 3" vertical adjustment on the engine bracket (5 mounting hole sets) and most brackets can lift at least 4", for a total of 7". You may have to raise the ENGINE on the bracket.
Is that a detuned 2.6 liter V-6 you're running, or a 2.0 liter V-4? I'm not familiar with OMC products. The prop size indicates that it is a V-6 size gearcase. 23" of pitch doesn't sound right on most V-6's unless you can do 55-62 mph.
Turning a 23" pitch prop up to 5500 RPM is good for 55 mph with a 2.0 gear ratio. A 1.87 gear ratio would give 60+ mph. I would say you should be running more like a 17" or 19" pitch prop.
Are you sure the prop is not shot, or giving too much slippage/ventilation? Or maybe it has been improperly re-worked in a prop shop
JREvans posted 04-25-2005 09:00 PM ET (US)
I emailed Boston Whaler for recommendations on a propellor. They sent me a document that says I should INCREASE pitch to get my RPM's down. The document said that I should plan on a rough estimate of 200 less rpm's per inch of pitch increase. That is contrary to some of the posts I am getting on this topic. If I am currently running a 23" pitch, shouldn't I go up in pitch to decrease rev's? If my mechanic is correct my gear ratio is 2.25:1. When I calculated my slip with the calculator it was well over 20%. How do you reduce slip?
davej14 posted 04-25-2005 09:38 PM ET (US)
"Going up in pitch" and "increasing pitch" are one and the same. I.E. going from 23 pitch to 25 pitch should result in approximately 400 rpm's less at WOT.
JREvans posted 05-02-2005 08:17 PM ET (US)
I tried a used OMC stainless 23" pitch prop this weekend and it made a lot of difference in top-end. We were able to cruise at 42 mph at 4900 rpm vs. 32 mph at the same rpm
with the 21". It took a little longer to get on plane which was expected. In addition, I was able to trim up the motor significantly more without it porpoising. The prop dealer is willing to trade out this used OMC for my Viper 21" and he will throw in a spin casting combo to make me feel better. If I don't want to trade for the OMC he will sell it for $200 which seems a little high.

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Author	Topic: Prop Selection for Dauntless 17
JREvans	posted 04-18-2005 09:16 PM ET (US) We purchased a '95 Dauntless 17 late in the summer of 2004. The original 115 Evinrude had been replaced with a Johnson 130 Ocean Pro. It has a long shaft so they mounted it on a Highjacker that is raised enough to compensate for the extra length. I am a boating rookie and need some input in deciding whether or not I have the correct propeller for our needs. It has a 14 3/4" 21 pitch stainless prop. The engine runs 6000 RPM at WOT and only tops out at or just above 40 mph depending on load. I rarely have more that 2 adults and 2 children on board. The holeshot seems more than adequate but I feel that this boat should top out closer to 50 than 40mph. In addition, the boat seems extremely stern heavy, especially with this particular motor arrangement. I can barely trim it up before it begins porpoising. I have added Doel fins which have helped significantly with handling and planing out quickly. I am considering changing to a 23 or 24 pitch stainless prop. I was hoping someone with similar setup could help me decide whether replacing the current prop would give me the top end I expect without too much trade-off in holeshot. We will occasionally be towing an adult skier or tube rider.
jimh	posted 04-19-2005 07:51 AM ET (US) [Moved from another area. Please use the PERFORMANCE area to ask about specific boat/motor/propeller combinations.]
Teak Oil	posted 04-19-2005 05:43 PM ET (US) Sounds like the engine should be raised higher. Is the jack plate adjustable? Since you are hitting 6000 rpms with four on board I would switch to a 23 inch, possibly a four blade, and raise the jack plate if possible. I dont know what the weight of your boat is but I would think 45mph should be easy to attain. You should add a water pressure gauge to make sure you are not sucking air.
JREvans	posted 04-19-2005 09:48 PM ET (US) Thanks Teakoil. My jackplate is raised all the way up. I do think that I need to go to a 23 pitch prop, though. Is there any other clues that I may be sucking air other than by installing a gauge? My boat sans motor is 1350 lbs dry and the motor is 360 lbs.
Teak Oil	posted 04-20-2005 08:27 AM ET (US) You need to find out what you lower unit gear ratio is so you can calculate your prop slip %. If you are getting more than 10% at WOT something is wrong with your setup. Use the formulas in the reference section to calculate this. Also with the engine down in the run position on the trailer where is the antiventilation plate on the engine in relation to the bottom (keel) of the boat? Is it level, and inch above, an inch below, etc? Your engine can still be raised, you may have to unbolt it and reinstall on a higher set of bolt holes.
JREvans	posted 04-20-2005 08:25 PM ET (US) The engine is mounted in the highest of the 6 holes you mention. The cavitation plate is slightly above the keel, about 1 inch or less. Where is the reference section you mentioned for me to calculate slippage?
jimh	posted 04-20-2005 09:45 PM ET (US) To help people evaluate their propeller performance, I have provided the PROPELLER CALCULATOR in the Reference Section. See: http://continuouswave.com/cgi-bin/propcalc.pl There are dozens of well researched, illustrated, and lengthy articles on many topics in the Boston Whaler Reference Section: http://continuouswave.com/whaler/reference/ The "forum" or discussion area (this area) is actually the most recent addition to the website, and although extremely popular and dynamic, there are many other resources available here besides this section. I encourage you to explore further. You can always start at the top page: http://continuouswave.com/
Teak Oil	posted 04-21-2005 12:07 AM ET (US) If you are only an inch above the keel you are definitely too low assuming you have a four or five inch setback plate. If you already are mounted as high as possible on the plate and the plate is rasied all the way up you are pretty screwed as far as adjustment. You can try some trim tabs, but everything is a band aid until you put an engine on with the proper length shaft
JREvans	posted 04-21-2005 07:20 PM ET (US) I agree with you on being screwed on the adjustment. Do you think that a change in prop pitch would help any on lowering RPMs and increasing top-end mph?
LHG	posted 04-21-2005 08:09 PM ET (US) The Doel fin will be a speed killer, unless your engine is running elevated about 1-1/2". Then you will need a surfacing prop. Most mid-range engines have 3" vertical adjustment on the engine bracket (5 mounting hole sets) and most brackets can lift at least 4", for a total of 7". You may have to raise the ENGINE on the bracket. Is that a detuned 2.6 liter V-6 you're running, or a 2.0 liter V-4? I'm not familiar with OMC products. The prop size indicates that it is a V-6 size gearcase. 23" of pitch doesn't sound right on most V-6's unless you can do 55-62 mph. Turning a 23" pitch prop up to 5500 RPM is good for 55 mph with a 2.0 gear ratio. A 1.87 gear ratio would give 60+ mph. I would say you should be running more like a 17" or 19" pitch prop. Are you sure the prop is not shot, or giving too much slippage/ventilation? Or maybe it has been improperly re-worked in a prop shop
JREvans	posted 04-25-2005 09:00 PM ET (US) I emailed Boston Whaler for recommendations on a propellor. They sent me a document that says I should INCREASE pitch to get my RPM's down. The document said that I should plan on a rough estimate of 200 less rpm's per inch of pitch increase. That is contrary to some of the posts I am getting on this topic. If I am currently running a 23" pitch, shouldn't I go up in pitch to decrease rev's? If my mechanic is correct my gear ratio is 2.25:1. When I calculated my slip with the calculator it was well over 20%. How do you reduce slip?
davej14	posted 04-25-2005 09:38 PM ET (US) "Going up in pitch" and "increasing pitch" are one and the same. I.E. going from 23 pitch to 25 pitch should result in approximately 400 rpm's less at WOT.
JREvans	posted 05-02-2005 08:17 PM ET (US) I tried a used OMC stainless 23" pitch prop this weekend and it made a lot of difference in top-end. We were able to cruise at 42 mph at 4900 rpm vs. 32 mph at the same rpm with the 21". It took a little longer to get on plane which was expected. In addition, I was able to trim up the motor significantly more without it porpoising. The prop dealer is willing to trade out this used OMC for my Viper 21" and he will throw in a spin casting combo to make me feel better. If I don't want to trade for the OMC he will sell it for $200 which seems a little high.