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Made a deal on a F70 last Saturday. Dropping the boat off next week for the installation. I think I found a knowledgable dealer who has repowered quite a few Whalers. Tells me starting out at 2 holes up is no problem. We did not include a prop in the deal so I need something to get started with. I have read many threads but mostly on older Whalers with different hulls than my Dauntless which is pretty much a vee hull compared to my prior classic sport. My Dauntless also has Smart Tabs which work great and is the reason I am starting at 2 holes up and not the highest engine mounting height. Hoping someone here can give prop advice.

Thanks
Jim

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Prop selection is tied to the engine, it's WOT limit and the lower unit gear ratio. Following that you take into consideration the hull, average load of people/fuel/gear etc.

This thread has the information. Don't get thrown by the different model whaler.

http://www.whalercentral.com/forum/vi...rowstart=0

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Thanks Phil,
I really respect your input, but the thread has different members giving great performance figures mounting their engines both 2 and 3 holes up and has prop recommendations of the Stiletto Advantage, (which I am leaning towards) of 13 1/4 x 13, 14, and 15 pitches. I was hoping to narrow it down a bit.

Thanks Again
Jim G.

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Like Phil said it depends on your running conditions/weight.. If the 15 pitch doesn't let your OB come up to max RPM at WOT then you need less pitch, If the 13 pitch makes your OB run over max RPM at WOT you need a bigger pitch.
Hard to figure out with our current weather here in the Mid-West.
Good luck and hopefully your dealer lets you try each different pitch to determine your best set-up.

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I have found giving one prop as a suggestion is not always welcomed.

If you want "the" prop, lets discuss in detail how your boat will be loaded and how it is run.

Describe what performance characteristics you are looking for, i.e. high speed, quick hole shot with heavy load, general overall performance.

Describe the load in the boat 70% of the time. How many people? Typical fuel load. How much gear (tools, safety equipment etc). How much stuff do you bring onboard? ice chests, fishing gear etc.

Is the boat going to be used on Great Lakes? Small lakes or rivers?

When it comes time to test the prop, I would take off the tabs for testing purposes. Only once you have the motor and prop dialed in would I install the tabs.

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Skipper E-J,
Thanks for the input. I understand the, "pitch" concept. However, my Dealer does not have a selection of props for me to try out. I was going to use Discount Dan to pick up a Stiletto Advantage 1. He will let you return a undamaged prop and exchange for another for a $49.00 fee. That is why I was trying to get close enough with a base line recommended prop to either only have to exchange once if the pitch is really off or have my prop guy re pitch it for me. He can repitch up or down a max of 2 inches which he has done for me in the past on other boats.

Thanks
Jim G.

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Phil,
The boat is used mostly on Lake Michigan loaded with me, (270 lbs), the wife, (160 lbs), wifes purse, (50lbs),good for nothing dog, (30 lbs), 12 gallons fuel, and not much else other than saftey equipment. I am looking for best all around performance as rarely does the boat go over 20-25 mph due to water conditions. While it is mostly a, "harbor toy", we do take cruises up to 15 miles to surrounding ports so mileage should be decent, however anything will be an improvement over my 1995 Evinrude 70 H.P 2 stroke that the Yamaha is replacing.

Thanks
Jim G.

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Jim -

Just so you know where this comes from. The goal is to prop the engine so that with the typical load, the engine's rpm's will get to or within 200 rpm's of the top of the WOT range. It is not that you are going to go that fast. This means the engine is performing right in whatever rpm's you choose.

Since the Turbo model is NOT offered in 14 inch, I would not get it tweeked. I would go with the Yamaha Performance prop.

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Jim, although the Stiletto Advantage is a great prop, I can tell you from direct, personal experience that it is a VERY poor match for the F70. I ran an Advantage for several years on my Supersport 15 and put up with lackluster acceleration and general blah performance, primarily due to procrastination. I finally got off my duff and switched to a Power Tech SCD3 last summer and the difference is astonishing - much better acceleration and improved top speed too, and no loss of mileage.

I am not sure what pitch would be best, but if you go to the Power Tech website. find their contact info, and explain your situation, they will make a recommendation. They returned my request in less than 24 hours, in the middle of the busy summer season.

Power Tech also will replace your prop with a different pitch for a nominal fee. After getting a recommendation from Power Tech, I did buy mine through Dan's Discount Props - they do not show the SCD3 on their website, but can order any of the Power Tech line.

I am sure that the above sounds like I'm just promoting Power Tech, but I am not. I'm convinced that any prop with a lot of blade area is a bad idea for the F70, and possibly other 4-strokes that make their power at high RPMs. With the additional power needed to drive a V-hull, I would think the Advantage would be even worse on your Dauntless than it was on my classic 15.

If you want to stay with props made by PPI, the manufacturer of the now-defunct Stiletto line, you might want to try the Turbo Quest - they advertise it specifically as being good for the F70, and it seems to have the same characteristics as the SCD3 - lower blade area, low rake. The Quest is available on Amazon - isn't everything?

By the way, great choice! The F70 is an awesome motor, especially with the right prop! Good luck!

Tim

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Hello jgortva,

I currently use this prop make and model mentioned by tedious but on a late model Yamaha 90 2-stroke. Prop size is 13 inch diameter x 17 Pitch, I have seen a very noticeable improvement from this prop as compared to a Solas early model Saturn (round-ear-type) prop that I used previously. The Solas measured 13-1/4 inch diameter x 17 Pitch.

From my signature you will gather that I too have a Dauntless 15, 1996 vintage.

This particular Power Tech prop (SCD3) if I recall was recommended for the Yamaha 90 2-stroke according to the Power Tech website, you should verify application for an F70 if considering.

Thought to share...
Angel M.

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I have a 1999 Alert 17 with a Yamaha F70 on it and Tom Clark recommended a 13.25 x 14 Yamaha Performance Series 3 blade Stainless Steel prop with the motor mounted 3 holes up and IMO this is the perfect set up for my boat. I'm not sure about the Dauntless,maybe others can help, but it is perfect for the 17 foot Montauk/Alert hull.You will love your new motor, the fuel economy is unbelievable!

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Thanks to all for the advise. The boat is in the shop and even though I wont be able to get it on the water for a while, I still cannot wait to get it back. Phil, I respect your recomendation highly for the Yamaha Performance Series, however after doing some online shopping that is not a cheap investment compared to an aftermarket SS prop after plunking dow 8 grand for the motor, controls, labor, guages, etc. I really dont want to be cheap, but is there any aftermarket SS prop you would feel confident recommending for my setup as the, "one" prop?

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You can start with the Yamaha painted stainless steel or their aluminum prop.

If you choose one of these, the size will be different.

If you do decide on the aluminum, I would get the dealer to throw it in for nothin. You are spending 8k for chripes sakes. If he balks, he's an idiot.

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I believe the Power Tech SCD3 is a copy of the Yamaha Painted Stainless, but it is a lot cheaper. That is certainly "the one prop" that worked well on my F70. But if you are asking if anyone can guarantee you that a prop you buy will be optimal, the answer is no - it takes some experimentation.


Tim

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I would try a Yamaha mar-gyt3b-v4-14. ( 13.25x14) This is what I have on my F70 on a 1998 Montauk. I have had 4 people on the boat, full cooler and gas tank. Pops right up. It is not a speed prop but getting around 7.8 mpg at 21 mph.

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Sorry for the delayed response. Finally got to break in my F70 and found some smooth enough water to get some performance numbers. Ultimately I went with Tedious choice of the Power Tech SCD3 13 X 16 prop with my decision to have the engine mounted 2 holes up. The cavitation plate looks to be roughly 1 inch or so above the bottom of the boat. The engine performs great for my all around use as I rarely am able to get it above 20-25 MPH or over 3000 RPM due to water conditions and in those conditions it cuts thru the chop easily. However, the full out performance is lacking. With 2 persons, safety equipment, and 96 pounds of fuel for a total of 551 pounds on the boat, WOT topped out at 30 MPH at 5000 RPM's. The range Yamaha states as optimum is 5300-6300 RPM, which to me is a pretty wide range. I would like to stay with the Power Tech brand of props as Dan's Discount Propeller very generously gave me a trade in period where I can pitch up or down for very little cost. My question would be, should I be looking maybe at a different blade diameter as well as pitching the prop down? I have seen the SCD3 in 13.25 diameter as well as the 13 I have. Also any other theories would be appreciated.

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Jim, diameter isn't really a variable - you get a prop which is the proper diameter for the motor, and that's it. I would be inclined to drop down in pitch, possibly all the way to a 13, and see how that works for you. With your usage model where you can't go that fast much of the time anyway, that will give you a nice low gear for power, and it should get you up in the RPM range where that motor will sing.

For reference, the trade-in for a different pitch policy is standard for Power-Tech - one of the things I like about them.

Tim

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We buy props by Pitch.
The engineers take care of the diameter.

Here are some basics:
http://www.whalercentral.com/articles...cle_id=108

If you change brands or models of props, then you would need to start over or follow others with the same prop/motor combination.

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Joe,
I appreciate your input and I understand about staying with the same manufacturers blade design. I just added the blurb about staying with Power Tech so I wouldn't have to fend off any advice for other manufacturers props for this very reason.

Tedious,
I thought diameter was also governed by the size prop that would fit on the gear case. I guess then my next question would be why prop manufacturers including Yamaha make multiple diameters from 13, 13.25, and 13.50 for my F70.
Will the lower pitch improve top end? It seems like the higher pitch would have a higher top end but a longer planning time while the lower pitch would have a shorter planning time but a slower top end speed?

Jim G.

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The SCD3 is only available in 13 inch diameter for your motor..
Again, we only have a choice of pitch with any given brand of prop.
http://www.ptpropeller.com/content-pr...amaha.html

You have a 16 pitch SCD3 prop.
Less pitch will give you more RPM's at WOT and usually slower top end speed but a faster hole shot.

More pitch will give you less RPM's at WOT and usually slower out of the hole but faster top end.

It sounds like you need less pitch, like an SCD3 15 pitch prop (maybe even a 14 pitch) which will increase your RPM's at WOT. As it is right now, you are at 5000 RPM and you should be 5300 to 6000 RPM's.

I would try the 14 pitch during your trials and trying different SCD3 props.

See the diameter of all the SCD3 props which is 13 inches.
Below is the SCD3 R14 pitch prop for Yamaha motors..

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Jim, it is counterintuitive, but yes, a lower pitch is likely to improve your top end. If you were still going to max out at 5000 RPM, a lower pitch prop would indeed result in a lower top speed. But the lower pitch will let your motor spin up higher, and the net is likely to be more speed.

The F70 is rated 70 horsepower at 5800 RPM. At the 5000 RPM you are currently hitting, I'm guessing the motor is producing between 50 and 55 horsepower (just a guess) so you are leaving a lot on the table. The rule of thumb is 1 inch pitch = 200 RPM, but like all rules of thumb, sometimes it works, sometimes it doesn't. You have a lot of RPM to play with, all the way to 6300, and in your situation it would be best to put your WOT RPM right up there - it will improve your performance in the rougher water when you can't go that fast anyway.

Some math:

5000 RPM, 16 pitch, 30 MPH
5000 RPM, 13 pitch, 24.3 MPH
6300 RPM, 13 pitch, 30.7 MPH

Of course, this assumes things are linear, which they aren't, but it gives you some idea why the 13-pitch won't necessarily slow you down.

Tough call between the 14 and the 13 - I guess, having thought about it a bit more, you might want to try the 14 first. With the usage model you describe, I would certainly keep trying props until you at least hit that 5800 RPM where your motor makes 70 horses.

Another possibility is that the SCD3 is just the wrong prop for your boat - I hope not, but it's not an exact science.

Tim

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Tedious,
Thanks again for much good information. My last question would be about trim. I might of forgot to mention it up front, but the 5000 RPM was at between 3/4 down and 1/2 trim on the trim gauge. I didn't notice a significant rpm increase while trimming the motor up as on past boats I have owned if memory serves me right. How high do you trim to get max rpm's while not porpoising or robbing the motor of the ability to pump water? On older 2 strokes I have owned I have really never went too much higher than I did on my test run with the Yamaha.

Jim G.

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Hello jgortva, let me add one additional design aspect regarding your prop search.

There are some performance differences between a "round ear" prop and a "semi-cleaver" design as are a few of the Yamaha (painted black) stainless props. I transitioned to the latter when replacing my Solas to Powertech and immediately notice that my "getting on plane" time was cut in half and with less rpm.

Semi-cleaver props as is my Powertech in some discussion circles are considered "stern-lifting" props while the round ear assist in "bow-lifting". I have experienced each condition with my props and for my 15 Dauntless I prefer to get the stern up quickly when getting on plane instead of looking at sky when the bow points up.

I always tuck my drive completely in when getting on plane and this did not help with my Solas prop. It took time and rpm to get up on plane, great top end (wot), but useless when cruising or entering "no-wake" areas as the Solas didn't like slower to idle speeds. Maybe a smaller pitch may have been better.

The Dauntless 15 is very sensitive to outboard trim input, porpoising will be the immediate effect if excessive. You will need to test trim positions and each will be dependent on the prop selection. Avoid cavitation and starving the water pump with trim input. Stainless Steel props are better suited for running near the surface (jack plates, drive trim, etc.). Outboard height on transom also has significant input on the performance and trim effects.

Hope this helps a bit and good luck with your prop search...
Angel

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Jim, if you were not gaining more RPM when trimming out during your test run, then there's no additional speed gain to be had there. With the 16-pitch on my 15, I am a little underpropped (meaning too low a pitch) but I like it that way as it gives me the power to get good speed even when trimmed down in rough conditions. I don't know if you've spent time on a classic 15 but keeping it on the water can be a challenge! If I was looking for a full-on speed prop, I'd probably want to go up an inch or two, but the conditions when I could use it would be pretty rare.

Will Dan's let you swap more than once?

Tim

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Jgortva, which prop did you finally end up with? Can you post performance numbers? How does the f-70 Yamaha perform on your Dauntless 15 with a full capacity load?

I love the performance of my Mercury 75elpto but not the smell and fuel consumption.

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What is your performance with the 70/