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I am on the fence between a Yahama 60 and the newer F70. It seems like 60 hp should be plenty of power but the dealer is really pushing the newer 70. The price difference is about $600. I will be pulling grandkids on a tube and it will not be unusual to have 4 people in the boat. I have a 2001 50hp Johnson now and it runs great with just one aboard but really struggles with a load only reaching 3500 RPMs when loaded. Any suggestions would be appreciated.
My 1985 SS15 is in great shape always stored indoors. I just finished replacing all of the mahogany and rechroming some parts. I hope to keep it for a good while and my grandkids (12 years old) will be using it soon on their own. I am a bit concerned that the 70 will be to much for them. Thanks

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I would look into having the throttle stop adjusted so they can't get to full power.
There is usually a screw on the motor for that but not sure about the newer models.

Other then that, I would go for the 70hp so when they get older, you could adjust that screw to give them full power if they need it.

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You should get a second prop that is sized for the load. Cheaper than a new motor.

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A new prop would be a lot cheaper. What would that do to my speed? top speed now is 29MPH with just one aboard.

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With a full load, I would guess 24 mph assuming clean or smooth painted bottom, engine at correct height and weight balanced out.

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Thanks for the speed estimate. I have been reading about another Whaler 15 owner who went to the F70 and he seems really happy. It is just a pretty big amount of money to have tied up in a boat I just bought this spring for $5,000. The F70 rigged is going to be $9,250.

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Sailor, I have a 1989 SuperSport 15. I put an F70 on it the first year they came out, in 2010 (it may be newer than the F60, but it's not really new). I love the F70, especially since I finally found the right prop to run on it. I can't compare to the F60, as I have never run one.

I feel your pain regarding putting a motor on that eclipses the cost of the boat - pretty much everyone who repowers has that concern. It does not make sense if you look only at economics, but I can tell you the F70 is a wonderful motor - very reliable, quiet as can be, easy to work on so if you are going to be keeping the boat a long time, it's a good choice. The F60 would have those same characteristics. The price you were quoted seems quite reasonable; the $600 bump over the F60 is pretty minimal in the grand scheme of things, and is less than the typical $100/hp.

Regarding the grandkids running the boat, the 15 is a fast, bouncy, agile boat - a real sports car on the water. They'd easily be able to get into trouble with either the F60 or the F70, or really any motor. If you do go with some type of throttle stop, don't install it until you get to about 50 hours on the motor - Yamaha 4-strokes are best run hard during breakin to seat the rings.

Good luck! Please feel free to ask any additional questions you have.

Tim

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Sailorman - I'm surprised your performace is so poor with your 50 but perhaps its because your motor is old and not producing 50hp anymore. I have a 2005 50hp Nissan and I'm seeing ~34mph with a heavy load (3 young children and 2 adults + fuel and gear) and 38mph with a light load (me + gear). If you get the 60 it will be plenty of power but if it were me I would get the 70 given such a small price differential.

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Rereading your original post: you mention sluggish performance when loaded, and being unable to get more than 3500 RPM. You also mention a maximum speed of 29 MPH when running light. What RPM are you reaching when you hit that 29 MPH? You may be able to improve things significantly by simply changing the prop.

Also, at what height is your motor mounted? That is, what set of holes on the motor are the bolts in? Many motors are mounted too low, which also affects performance.

Tim

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She runs at 5200 when she is running light and things are going well, then sometimes she will start to run a bit rough and not go over 3500. At 5200 she is running 29 MPH. The engine is not mounted as high as some I have seen on this site. The top lip of the mounting bracket sits right on the transom top. It looks like the lower holes in the bracket don't have but one place to go maybe the guy who installed this motor drilled his own holes in the bracket. The upper holes can allow it to be raised a couple of inches but then the lower bolts would need to be redrilled to meet any other holes.
By the way, thanks to you guys who have answered, I appreciate your help and advise.

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Sounds like your motor is mounted using OMC's "blind holes" - see a description in the Rigging folder of the articles section at this site. The blind holes rig the motor "all the way down" which is not optimal. You could improve the performance of your current motor by rigging it 2 or 3 holes up.

5200 RPM is not horrible, but you really should be up around 6000 when running light, so you are overpropped by a couple of inches of pitch at least. That is contributing significantly to your poor performance when loaded.

So if you feel like trying to make it better, as opposed to getting a new motor, you can move your current motor up, and then try a different prop. It will make quite a difference, and cost a lot less than an F60 or 70. On the other hand, it will still be an old-tech 2-stroke, so it's going to be quite noisy, smelly, and thirsty compared to a modern motor.

Tim

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Sailorman, a couple people have mentioned the possibility of making your Yammy 50 run right. Is that something you are open to? Because I think a 50 hp works for what you want right now, and if the engine is clean & you trust it I think it is worth exploring.

A lot of things come into play, like bottom paint, engine height & prop. But I will bet you that doing a proper de-carb on that engine will put a smile on your face. I see this all the time when someone buys a nice clean old boat, the engine runs rough or doesn't perform, etc. Well the very fact that these old boats haven't been used is why the engines don't run right. Engines like to run and every time you randomly run them just means another layer of varnish builds up.

Putting a bottle of magic into the gas tank isn't a proper de-carb, it is a specific procedure to remove the build up. The additive you use needs time to work so you have to allow it to. Initially you will blow a mound of gunk out of the engine, but you aren't done and have to cycle that solvent rich fuel mixture through the engine many times and let it sit.

If you like how the engine runs a new prop is a good investment.

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I do like the idea of this Johnson 50 and I like the way it looks on my boat. Are you suggesting that I should add an additive and decarb the engine. It sounds like there is more to it than that.
How much actual performance benefit is raising the engine two holes? I will need to remove the lower bolts, reglass the holes and redrill holes that will match up with the lower holes on the engine bracket. I can do that if you guys think that it will really makes a difference. A new prop is certainly in the mix. I just don't want to do all these steps and spend another $500 or $600 just to buy a new Yahama F70 anyway.
I know it's my call but I really appreciate your advice as you own these boats too and I value your opinion. Thanks

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Here is wlgarde's project where he drilled the "Green" holes in his 1976 Sport 15'.
http://www.whalercentral.com/userphot...lbum_id=64

You want to drill the lowest holes you can in your transom.
The Red is standard if your 1985 can be drilled using them.
If not see if the Yellow holes will work. If not, then the Green will for sure.
Measure the new holes twice inside and out before drilling.

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I'll also say the F70 is an incredible motor. Super reliable, starts instantly, very quiet, sips fuel - you can run all day hard on 5 gallons or less. But that's a whole lotta motor for a 15 - It would scream. If you don't want that, a throttle reducer is a good suggestion.
I am told by my master yamaha mechanic, that outboard hp used to be measured at the powerhead vs now it is measured at the prop. Thus older hulls are getting more hp at the prop when you are running the max outboard hp rating with a new motor. I am not sure the real difference and end result, but it is an interesting fact. It would be cool if yamaha had a new & light 100hp outboard - Because I would like to see how it would push a 17 hull!

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Sailor, it's obviously your decision, but if you generally like your Johnson 50, making an effort to get it working properly would seem to make sense. It's not a sure thing that you'll be able to get it working, but if you can, you save a ton of money.

You're looking at 3 steps:

1) Fix whatever is wrong with your motor. While a decarb won't hurt anything, it sounds to me that it may be time to rebuild the carbs. This is not a huge deal - many consider it to be a routine maintenance item that you need to do every few years. If you are handy, you can get the factory service manual and tackle it yourself, otherwise it will be several hundred dollars for a mechanic to do it. The parts are about $35 per carb.

2) Lift the motor. I had a Johnson 70 on my 15 before I got the F70. The motor was all the way down when I bought it, and I ended up raising it two holes. It was not a massive difference in top speed, but the Johnson 70 had power to spare - my guess is it would make more difference with your 50. Raising the motor did significantly improve the handling - lightened up the steering quite a bit. You can do this job yourself, if you are so inclined. Also note that if you end up going with the F70, you'll need to do this job anyway as the F70 cannot be mounted with the blind holes.

3) Get a new prop - this may or may not be needed depending on the results of 1 & 2. You have not specified what prop you have on there now, but assuming you don't have one already, a good quality, modern, stainless steel prop will really make the boat come alive. It may take a couple of tries to find the perfect one for your situation, but if you are looking to keep the boat for a long time, it's worth it.

So my recommendation would be to do 1 & 2, and wait and see on #3.

For reference, the switch from powerhead rating to prop rating occurred in 1986, well in advance of the manufacturing date of your motor.

Tim

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I had the carbs rebuilt this spring when I bought the boat. I just dropped her off at a good mechanic's shop to have him check things out more thoroughly he thinks perhaps she needs a new power pack. I'll let you know what I find.
I am going to see what the prop size is so that I can bounce it off you guys who may know if it's wrong.
The new engine vs. old is like fire and ice. It's all I think about.
Caroom, what prop size did you finally settle on on your new F70.
I will make the call when I hear from the mechanic. Thanks again

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sailorman,
Both the Yamaha F60 or F70 will make an old Sport 15 scream. The main difference between the two motors will be the larger one will out hole shot the smaller one, and the smaller one will be a little slower on the top end than the larger one. If you are going to be carrying a load where the hull is at full capacity at all times, you might want to opt for the F70. It will handle the load easier.
The old Johnson might not be the best thing to continue to throw money out. I have the same boat, and after doing many things to my old Johnson 70, I finally sold it. I still have not repowered our Sport 15 yet, but when I do, it will be the Yamaha F70.

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It's certainly a good idea to rebuild the carbs, as you did, when you buy an older motor with an unknown service history. That does not rule out a carb problem now, but it makes it a lot less likely. It will be interesting to see what the mechanic comes up with.

With my F70 it took me 4 tries to find the right prop. I tried the Stiletto Advantage 1 in both 13 and 15-pitch, and the Stiletto Star in 15-pitch. I settled on a 16-pitch PowerTech SCD-3 - with less blade area, it seems to be a much better match for the peaky F70 than the large, grippy Stilettos. Depending on how fast your 15 is, and with what loads you typically run, you may want a 17 or even an 18 pitch in the SCD3. Running alone, I can hit the rev limiter if I trim out enough. I typically can't go that fast in the conditions I am in, so the 16 is perfect - lets me hit close to 40 with only a tiny bit of trim, and acceleration is very strong.

One other prop to mention is the Turbo Quest - they advertise it specifically for the F70 and it looks to have some of the same characteristics of the SCD3, namely low rake and smaller blade area compared to some other props. An advantage of the PowerTech is that as you are experimenting, they'll let you trade for another size prop for a nominal fee.

Tim

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I think I'm going to go with the Yahama 70. There is a promotion on for the next two weeks with a $500 rebate on dealer supplied rigging. The extended warranty doesn't apply to engines under 75hp. Tim, which holes did you mount in on your 70?

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I am two holes up - that is, one hole down from as high as it can go. I have no grip problems or blowout - might try 3 holes up at some point.

The $500 off is a promotion Yamaha runs every year - I opted for doubling the warranty, which was available at the time on the 70. You'll need new controls anyway so the $500 off would make sense.

You'll love the F70! Since I'm spending your money, try the Quest - I'd love to hear how that goes for you.

Are you planning to get a tach, or connect to your GPS display, via Yamaha's Command Link interface? I have that setup and it's really nice.

Tim

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I'm going with the tac. I am trying to keep my boat very basic so going with single digital tac. I don't have a gps. I'm also going to get the fuel water separator but not sure where I will install it so that it is out of sight but accessible. Since I have the blind holes now, they will need to be filled and cleaned up prior to installing new engine.
I am going to put my '01 Johnson 50 on Craig's list and see what it will bring.

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Sounds good. Note that they sell both Command Link tachs and regular digital tachs. The Command Link setup is likely more expensive, but it will let you add a GPS connection in the future if desired. If you care about fine control of trolling speeds, I know the Command Link tach lets you do that, not sure about the other one.

I have a separate fuel-water separator, but only because it came with my boat. I don't know if I'd bother installing it again myself. Despite the great fuel economy, gas just doesn't hang around that long in the portable tanks, and the F70's under-cowling fuel filter is readily accessible and includes an alarm for water. You can see the location my previous owner used for the separator in one of the pics on my personal page. Note that the regs say that you can't use a clear plastic fuel bowl in an enclosed location.

Tim

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I have a 2011 Yamaha F70, first mounted on my 1984 15 CC, then transferred to my 1988 Montauk 17. It is a great motor, but I have had 2 instances where a fuel injector became clogged. The manual recommends adding an external 10 micron filter, which I did. Subsequently I have not had any failures. The one I am using is:

https://www.fisheriessupply.com/racor...025-rac-02

This is really small, has a 10u filter as well as water separating capabilities. I've never had any water in the filter after over 250 hours. I'm also using this same filter on my 1985 Outrage 18 with a Suzuki DF140A.

I've also had great luck with the NMEA2000 link from the motor to a chartplotter/GPS combo unit. There is so much information the motor puts out and the chartplotter makes easy to display. I also have the Yamaha digital tach/combo gauge, but very seldom even look at it.

Dennis

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From Boston Whaler 15 sport/F70 prop discussion with JMartin and Elaelap.

Get a Yamaha Performance Series prop (Stainless) in 13.25x18. It out performs the aluminum and painted stainless Yamaha props. WOT Rpm's is 6300.

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Phil, are you sure you got that pitch right? I used the equivalent Stiletto Advantage 1 in 13.25 x 15 and it topped out around 5700 RPM - within the recommended maximum WOT RPM range, but not where you want it. I wouldn't think you could hit even 5000 RPM with an 18-pitch.

More generally, I found the large, grippy prop was a very poor match for the combination of the 15 and the peaky power curve of the F70. I tried both 15 and 13 pitch Stiletto Advantages, and neither one was satisfactory - even the 13 wouldn't spin to redline without a good deal of trim, and it topped out around 37 MPH. And both the 15 and the 13 were dogs - they really felt like they were holding the motor back. Don't get me wrong, they are great props and worked extremely well on my previous OMC 70 - but my experience with them on the F70 was really bad.

I switched to a Power Tech SCD3 in 13 x 16 and the difference is huge, in every aspect of performance - much more responsive, and better top speed too. My unscientific analysis is that the smaller blades on the SCD3 slip more when accelerating, allowing the F70 to spin up more readily to the higher RPM ranges where the F70 makes its power. I believe the SCD3 is very similar to the Yamaha Painted Stainless.

Note that with the 16-pitch in the SCD3 I am a little bit underpropped. That works great for my needs, but if someone really wants to maximize top speed, trimmed out on flat water, I would recommend the 17 or even an 18-pitch.

Tim

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Just pulled the trigger. Going with the new F70 with 6 year warranty. I haven't spoken with the dealer yet about prop selection. The invoice just calls for aluminum prop right now. I plan to meet with the installer (rigger) about engine height tomorrow.

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Hi Sailorman,

That's awesome. I have an F70 on hold right now at the dealership. Wondering if I should go with the $500 off or extra 3 year warranty.

Simon

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Tim - You are right to question. My information came from a 5 year old thread involving 3 members who I trust.

Your results with the 13.25x 15 is interesting since I have read the recommendation to be one size larger (13.25 x 17) Is it possible we are discussing two different motors.

Does your F70 have a WOT rpm of 5300-6300 and gear ratio of 2.33?

Honestly, trust Tim's information since he has the actual results.

Sailor - For your sake, please review this thread on a recent sales experience. While it is not the same brand/model of motor, read the posts on mounting height and prop recommendations and then what the installer said/did.

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

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Grabbing the thread a bit here, but I'm wondering about going down in power.

We have a 50 horse Yamaha on out S/Sport 15, which I assume is the original motor circa 1989. Whilst there's nothing wrong with it apart from the usual heavy fuel consumption of a 2 stroke (starts easily, runs fine if a little unhappy at low harbour speeds etc), it is a bit old and I have the chance of a Yamaha 25 4 stroke in very nice order and to the right spec. at a good price.

No idea how fast the boat will go as I've never had it to WoT, but it sees 25kts very easily with 1 or 2 aboard. Boat only used for fishing and as a runabout, so speed and power not too important, but I wonder nevertheless whether I'll find it 25 hp adequate. I'm sure it will be happier at low speeds; our harbour has a 4kt speed limit amongst the moorings.

Any thoughts, anyone ?

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It all depends upon what you want but in my opinion 25hp on a Super Sport 15 is way under powered. You would be lucky to see 25mph. Personally I would take a good running used 50 2-stroke any day over a brand new 25.

Also, I would recommend starting a new thread so the thread title matches your question and you will get more responses.

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Many thanks, Wlagarde, that's the sort of reply I was hoping for. The 25 isn't a new motor, by the way, it's 7 years old but hasn't seen much use and that's been in freshwater. But nevertheless the $1500 price difference would buy quite a lot of fuel !

Just been looking at the pics of your boat - lovely ! I've often wondered if our trailer were the original and it seems to be almost identical to yours apart from the rear crossmember. Has yours been altered ? Ours is just box section, the same as the side rails.

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Sailor, that's awesome - you're going to love it! Frankly, I would skip the aluminum prop entirely - an aftermarket stainless prop is probably not much, if any, more than a dealer-supplied aluminum one. Hopefully your dealer will be cool with mounting two holes up - as you may have read in other threads, some of them put up a fight. You're smart to have the discussion ahead of time, so you can just walk away if they won't do what you want.

Phil, those are indeed the correct specs for my F70. I can't speak to others' experience, of course, just pass on my own. I apologize for continuing to gush about it, especially as the Stiletto is a great prop and was a super value (apparently too good since they stopped selling them under that brand name) but the switch to the SCD3 was like night and day - made the F70 feel very similar to my old OMC 70 in terms of responsiveness and accelleration. I guess it just tells us that you can only apply so much science to selecting a prop, and then it becomes trial and error.

Tim

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Thanks for the compliment. The trailer is "original" that is Romps Marine paired the Easy Loader trailer with the boat when it was sold in June of 1976. I restored the trailer as well. The only things that were added are the guide ons and the spare tire holder. Easy Loader still has most of the parts available if you need anything.

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I personally wouldn't do a 25hp on 15'. I found a person who did 26mph with 25hp tiller. Additonal weight and passengers will quickly drop the speeds. You will likely find your self at wot or near wot most of the time. I have been on classic 13' whalers with 25hp and I would want that to be the minimum performance that I would want. On a 15' that is probably 30hp.

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Before buying my 15' I thought about buying a new 130 Sport. In the end I alway like the classic whaler lines and mahogany, but the much better performance swayed me to buying a classic 15'. Infigure even if I have to repower, it is still cheaper than buying a new one. Fortunately haven't had to repower my boat yet with my 26 year old motor is still seemingly going strong but I would have no problem repowering this boat and enjoying it for years to come.

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I'm picking up my 15 tomorrow with the new F70. I'm pretty excited. The dealer mounted it as you guys recommended. He also said that he would work with me on as many props as I wanted to try. Tomorrow I'm going with the aluminum 16" pitch, just to get started. Next I will try the Power tech SCD3 13X16. Top speed isn't important to me, hole shot for skiing and grip for pulling a tube will be more of a priority with my grand kids. Can't wait!!

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The new F-70 is pretty amazing. It is incredibly quiet and smooth. I don't know how much my Johnson 50 2 cycle weighed but with the F70 and 6 gallons of fuel she floated on about the exact same lines. The starboard drain hole was 1/4 in the water, the port drain hole was completely above the water. At idle you can hardly tell that it is running. We did the one hour at under 2,000 rpms then did about 20 minutes up on a comfortable plane at 3300. Can't open her up for a while yet. I am very pleased with the choice. Thanks for all the guidance here on Whaler Central.

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Sailorman- how is the motor running? Have you gone past the break in period so you can do some wot pulls? I'm bringing my boat in for the same engine next week and going with the aluminum prop as a starter as well. The shop recommended a 15 pitch but I know you're running a 16 pitch, so wondering how that's working out for you.

What are the break in procedures anyhow?

Simon

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I just opened her up today for the first time. WOW!!!
The first hour you have to go under 2000 rpms, second hour up on a plane but no full throttle. I just got over the two hour mark and I am really excited. This morning I went out with my 4 grand kids, my wife and I and wide open I got 5800 rpms without messing with the trim we went 33mph. I then dropped everyone off and went out for a quick check I hit 6300 and 40mph by my self with the engine trimmed up a bit. It seemed really FAST. I think that there might be a bit more in it but I was covering so much ground and it was chilly so I came back in. I really love this boat/motor now. The Yahama was my birthday present to me and I have a smile on my face.

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That's an awesome bday present to yourself. Happy belated.

I thought the break in procedure/process will take much longer, so good to know I can probably break it in in one day. I can't wait until my test run. I've never even driven the boat before.

Glad to hear everything worked out great for you!

Simon

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Simon, I don't remember the exact break-in process other than the 1 hour puttering around part, but I do remember that dealer/mechanic I bought it from was adamant that Yamaha four-strokes are better off when run hard during the break-in. I have subsequently seen mention of problems with rings not seating when the motors were babied. So follow the manual, for sure, but once you get past the required slow speed running, let 'er rip!

Tim

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Tim, Simon and Sailorman,
What kind of top speed do you get with the Yamaha F70, and a lightly loaded Sport 15?
Paul

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Paul, I am intentionally a bit underpropped, as I am in the ocean and almost never get a chance to run fast and light. I therefore run out of RPMs before I run out of power and trim - I hit between 41 and 42 MPH at 6400 RPM, with 25% trim. The great thing with my current prop (Power Tech SCD3, size 13 x 16) is that I can hit 40 with little to no trim, which is important when things are bouncy and you're looking to keep the 15 from going into orbit.

Some day I'd like to try a higher pitched prop, just to see what it could do, but in day to day use this one is fine.

Tim

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I'm still learning my new motor. With that said, I can reach 40MPH at 6300 with 50% trim lightly loaded.(My boat has bottom paint) I am pretty sure I will refine those numbers when I get more comfortable going that fast. Just to clarify, I ended up getting a Yahama 13.25 X 15 aluminum prop. Thought I was getting a 16 but turns out I got a 15. I am pretty surprised that at 5800 when you put the throttle down you can really feel additional acceleration from there up ti 6200 - 6300. It looks like I may be able to squeeze out a bit more maybe in speed/RPMs by working with the trim. Top end speed is not really my priority but it is fun when the water is flat.

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Just to clarify, in case someone is wondering, the redline on the F70 is 6300 RPM and the rev limiter starts to kick in at 6450.

Tim

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Tim and Ron,
Those are indeed fast speeds at top end. Ron, I agree with you about top speed not being an important variable in prop selection or motor selection for that matter because a sport 15 can only maintain high top speed when the water is like glass. This, of course, is an exceedingly small percentage of time when these boats are used.
Thanks for responding guys.
Paul

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Do you guys with the F70 need that HP or the RPM to get to that low 40ies speed with those props.
I with my Montauk 150 can get only get to 34-35 at 6000 rpm with my 60HP. So I'm wondering if I get a pith higher than 14 will she go faster?

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EJO -

The 15' Super Sport has a dry weight of ~580 lbs.
The Montauk 150 has a dry weight of ~950 lbs.

The higher speed of the 15' super sport is due to being 370 lbs lighter and 10 more horsepower than the Montauk 150.

The performance report of the Montauk 150 lists the exact performance you are obtaining, 35 mph @ 6000 rpm as shown in their report:
http://www.bostonwhaler.com/boat_grap...4003PM.pdf

In your case increasing pitch will reduce your WOT rpm's and will most likely result in less speed.

If you are unhappy with the WOT performance, your choice is limited to increasing your horsepower.

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E-J, I have seen many reports of 15s with F60s meeting or exceeding the 41-42 MPH that I can hit. And I am sure that if top speed was a priority, I could go faster. So the answer is "no" on whether 70 horses is really needed.

Your boat and situation is completely different. Unfortunately, the mandatory motor tie-in has resulted in you being a bit underpowered.

If you are currently running an aluminum prop you might be able to squeeze out a little more speed by changing to a quality, stainless one, but the improvement would likely be minimal.

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Phil that is what I thought (lots of weight difference) and as tedious said B-4, I too can very seldom run flat out as the water is never that smooth and I'm happy with my top speed I just want a better hole-shot although at 35mph(6000 rpm) my 3-bladed Vengiance (13-5/8 x 14) is hardly slipping.

We'll try some 4-bladed props next spring when the water is thawed. With 200 hrs on the Merc I can never convince the Admiral to change to an F70 although I would like to try that set up on a 150, maybe 10 years from now when it is time to re-power.

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E-J, you never know until you try, but I'd guess a 4-blade prop might well reduce your hole shot - you want a little slip on the bottom end of the power curve to let the motor spin up. As I have said in other threads, I had good luck going to a prop with less blade area and low rake - it greatly improved acceleration and I did not lose anything at the top end.

I am not familiar with the Vengeance prop,so I can't compare it to what I ended up with - Power Tech SCD3. However, I had a great experience contacting Power Tech and getting a recommendation from them. Once I explained my situation in detail, they came up with what seems to be an excellent choice.

Tim

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Tim I agree the Power Tech service is great and they gave me some recommendations including not to change, but from a fluid dynamics/mechanical standpoint based on RPM's, blade area, possible slip, and power. Theory will tell me one thing and only trial will tell.
A 15 foot Glastrom speed boat reacts different than a 15 foot Boston Whaler CC with the same power source. To the prop manufacturer they are both 15 hull of a certain weight with exact same motor resulting in the same prop recommendation.
Like I said before I'll know this coming spring.