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Propeller selection/WOT question for Dauntless 15
joz	#1  Posted on 06/08/15 - 5:48 AM
Member Posts: 19 Comments: 0 Joined: 05/27/15	I took my new whaler out for the third time since I've owned it this morning. Beautiful calm morning, 6 gallons of fresh gas yada yada. I wanted to see how it would perform with just me and get some numbers. Here's what happened: At WOT, I was running about 30-31 MPH, at 6000 RPM. With a slight trim, I hit 32, but RPM jumped to 6200. It's a 1995 50 horsepower Johnson, and the manual says WOT is between 5500-6000. First question: Is 6200 going to hurt this engine? Second Question: The prop on the engine is a 13 3/4 x 15 prop. The manual suggests a 13 1/4 by 17. Anyone have this boat with a prop they love? Should I not run at 6200? Thanks for any help!
dauntless-n-miami	#2  Posted on 06/08/15 - 7:48 AM
Member Personal Page Project Albums Posts: 315 Comments: 0 Joined: 11/05/08	Hello Joz, 6200 rpm is a bit excessive and will certainly hurt your outboard!!! How were you confirming your mph, GPS or speedo? The 5200-5500 rpm sounds correct, what make and year is your outboard? Is it a 2-stroke or 4? I have run a 13-1/4" x 17P (round-ear) Solas and am currently running a 13" x 17P (semi-cleaver) Power tech, both in stainless. Unfortunately I have a bit more horse power hanging on the back so spinning these diameters is fairly easy for any good reference/comparison to your set-up. I will tell you that I have experienced a noticable difference between my 2 prop types. The round-ear responded slower to get on plane and kept the bow high while the semi-cleaver brings the stern up quickly on plane and maintains the bow level with minimal outboard trim. Round-ear props are known to be "bow-lifting" while semi-cleaver are "stern-lifting". Your current prop diameter (13-3/4") seems large for your 50hp outboard, what diameter is your gear case? If I recall correctly my gear case size is 3-1/4" diameter which places it in a medium size with a gear ratio of 2.33:1. This gear case diameter will allow me to turn from 13" up to a 13-1/2" prop safely and perhaps even up to a 13-3/4" diameter prop which would be excessive. Knowing this type of information is helpful in determining suitable propellers. Even the 13-1/4" diameter you mentioned (factory suggestion) I consider to be on the high-side for a prop diameter for your 50 h.p.. A different topic for you to review, your outboard's height on the transom. Check and measure the height or distance of your (lower unit's) cavitation plate in reference to your keel (at the transoms lower leading edge). A practical height for the cavitation plate should be better than 3/4 inch above the keel. Outboard height is a great factor in a boats performance and in material type for a prop selection. Aluminum props are light to turn and are designed to run primarily submerged (to much positive trim will damage them) while stainless being a bit heavier to turn can run much closer to the surface or (surface piercing) when outboard is trimmed out for performance. You did not mention your props material type and brand. Other than yourself, typically how many occupants will enjoy boating with you on the Dauntless 15? The Dauntless 15's max H.P. rating is either 70 or 75 H.P., at 50 H.P. your at the mid to low end so depending on your intended use (cruising, fishing, water ski towing) you may need more than one prop to keep the outboard happy with the loads. Hopefully more W/C members will chime in with their thoughts and expertise on the subject, continue your research and review the motor height topic. Best, Angel M. 1996 Dauntless 15, Sportsman Pkg. - 2007 Yamaha 90 HP 2-Stroke
Phil T	#3  Posted on 06/08/15 - 10:08 AM
Administrator Personal Page Personal Album Project Albums Posts: 7043 Comments: 6 Joined: 03/26/05	6200 exceeds the WOT range of 6000. You are over -reving the motor. Do not do this. The optimum rpm is 5800 but WOT results in the range is the target. Without knowing the engine mounting height, gear/fuel/passenger load, I suggest you are under propped. You need more pitch (angle of the blades) Prop designs and sizes are not universal. The part number should be stamped on the back/inside of the hub. That will get you make/model and size. Roughly speaking you need a 17p in the same brand and model.
dauntless-n-miami	#4  Posted on 06/08/15 - 12:31 PM
Member Personal Page Project Albums Posts: 315 Comments: 0 Joined: 11/05/08	Sorry Joz, missed you had given make and year of outboard initially. Also I miss wrote your factory suggested w.o.t. rpm range (5500-6000) being correct not the (5200-5500) I listed...my bad. Joz if you have any prop shops in your area stop in and discuss your current set-up with r.p.m.'s, ask if they have a "lend-lease" type option where you can test suitable props. Phil T's 5800 w.o.t. rpm suggestion is a good call, no reason to run your motor all out at 6000 rpm. Angel M. Edited by dauntless-n-miami on 06/08/15 - 12:47 PM 1996 Dauntless 15, Sportsman Pkg. - 2007 Yamaha 90 HP 2-Stroke
gary0319	#5  Posted on 06/08/15 - 1:49 PM
Member Personal Page Posts: 218 Comments: 0 Joined: 08/25/12	Hmmmm.........I'm suspicious. I'm by no means an outboard expert, but running that large a diameter a prop on a 50 hp motor and still turning over 6,000 rpm's on a Dauntless seems kind of high. Are you sure your tachometer is giving you an honest read? Others may set me straight, though. I have a 60 Merc 2 stroke and am running a 12" x 11 pitch stainless and manage about 33mph at 5400 on calm seas. I like the low pitch because it gets me out of the hole like a jack rabbit and allows me to plane at 14mph, even in a chop. 1998 Dauntless 15 - 1998 Mercury 60
joz	#6  Posted on 06/09/15 - 6:15 AM
Member Posts: 19 Comments: 0 Joined: 05/27/15	Thanks for all the input. I have a local marina looking to see if he has a test prop or two I can try out. Very helpful. The engine I have has the large gear case, which is why the diameter is so big. Obviously it has no trouble spinning the 13 3/4 prop. I'm hoping to get my hands on a 13 1/4 x 17 which is the recommendation in the manual. I'll report back. A gentleman on another site recommended a stainless steel stiletto prop, but they're significantly more expensive, and I run in a rocky river often. I'd rather ding up an aluminum prop than a fancy steel one. None of my boats ever had stainless, and they all ran acceptably. I hope to get from 30-31 mph up to 32-35, which is what others suggest they can get this boat up to.
dauntless-n-miami	#7  Posted on 06/09/15 - 6:26 AM
Member Personal Page Project Albums Posts: 315 Comments: 0 Joined: 11/05/08	Sounds good Joz. Definitely Aluminum after you mentioned river adventures with rocks in the same sentence. I came across a post in iboats.com (2003 post) of a boat owner with similar prop concerns. He too had a 15 foot boat (not a whaler) with your same 1995 Johnson 50hp and 6000 plus rpm issue. After testing various relevant prop diameters and pitches he final solved his issues with an O.M.C. make 11-3/4" dia. x 17P. His W.O.T. and with minimal positive trim was 5900 rpm's. Curious which of these is your outboard Joz??? Manufacturer: Johnson Horsepower: 50 HP Years: 1994 - 1998 Model: 3-Cyl., Pleasure Outboard Specs: Thru Hub Exhaust & 13 Tooth Spline Large Gearcase Max RPM: 4500-5500 RPM Manufacturer: Johnson Horsepower: 50 HP Years: 1975 - 2005 Model: 2-Cyl. Outboard Specs: Thru Hub Exhaust & 13 Tooth Spline Small Gearcase Max RPM: 4500-5500 RPM These posted rpm's for both types of 50hp are conflicting with your manuals info...thought this info might be helpful. Its from the iboats.com site for prop selections. Off topic...sounds like you have your trailer issue solved...great. All the best, Angel M. Edited by dauntless-n-miami on 06/09/15 - 7:35 AM 1996 Dauntless 15, Sportsman Pkg. - 2007 Yamaha 90 HP 2-Stroke
Phil T	#8  Posted on 06/09/15 - 9:01 AM
Administrator Personal Page Personal Album Project Albums Posts: 7043 Comments: 6 Joined: 03/26/05	Joz - I visited your thread "over there" and as I expected, you have gotten the advice of a prop guru and should run out and just do exactly as advised. There is an old tale about aluminum is better than stainless and you have fallen for it. Even in rocky conditions you want an stainless prop since it is stronger than the aluminum and will take a hit with less damage. Aluminum will also no perform as well.
joz	#9  Posted on 06/09/15 - 9:18 AM
Member Posts: 19 Comments: 0 Joined: 05/27/15	Angel, the first engine is mine- 3 cylinder, large gear case. Those RPM numbers do conflict with the manual, as it says WOT is 5000-6000, with 50 HP @5500. I actually think I'd run over RPM's with an 11 3/4 as the gentleman on the thread you found indicated. I base that only at how easy the motor seems to spin the 13 3/4. Phil, I'm so tempted to buy the Stiletto from "the Guru" but it's so expensive and I have no way of knowing FOR SURE that it's what I need. The problem is not being able to get your money back once you buy a prop. This is so confusing! Wish I could take a bunch of them out on the water with me!
joz	#10  Posted on 06/09/15 - 9:24 AM
Member Posts: 19 Comments: 0 Joined: 05/27/15	Phil, by the way, I live along the Merrimack River in Haverhill, MA. That is where I do most of my boating. I saw that you've been out there on your web album. If you hear of any Whaler events out there again, let me know!
joz	#11  Posted on 06/26/15 - 3:54 PM
Member Posts: 19 Comments: 0 Joined: 05/27/15	UPDATE- Thanks to all who contributed to this thread. I ended up going with the recommended prop in the manual, 13 1/4 x 17, and had the boat out today. I went from running WOT at 6200 RPM and 31 MPH, to 5600 WOT and 35.2 MPH on my GPS! It is just an aluminum prop, and I bought the BRP prop at an Evinrude dealer. The hole shot is still fantastic, but top end has been nicely improved. Enjoy the summer!