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I have a 1989 15 Supersport equipped with a Yamaha F70. I've run it with and without a 5" setback jackplate, which is currently not installed as I'm looking to get it anodized. For prop I run, and am generally happy with, a Stiletto Advantage 1 in 13.25 x 15 size.

My one performance challenge is porpoising - it's not terrible, just a bit annoying sometimes - where I boat, it's rarely calm enough to be able to do a top speed run anyway. I was wondering if a bit less bow lift (that is, going to a more stern-lifting prop design) would be worth a try. I say that not even knowing whether my Advantage 1 is considered a bow-lifting or a stern-lifting prop, or somewhere in the middle. I would be willing to give up a little top end in favor of being able to keep speed up more in bouncy conditions.

Thoughts about whether that makes sense, and what props to try, would be appreciated - it's the time of year to annoy the chancellor of the exchequer with expensive boat purchases. Thanks.

Tim

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For only $149 , You might consider a new Mercury Spitfire 4 blade aluminum for less bow lift. It should be easy to re-sell if you don't like it. It's supposed to be a pretty good propeller.

http://www.mercurymarine.com/propelle.../spitfire/

Porpoising is usually caused by excess trim. Raising an engine can help too. The Stiletto prop could be giving you more bow lift than the boat needs with a relatively heavy engine on it.

Detwiler makes a really nice anodized jackplate.

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Tim,

I like Finn's recommendation with the pre finished plate if your boating activity requires one. I have a Bob's on my 17 wahoo, and after one or two uses in the water the surface went bad to the point where it looked old and dull. On my 15 BW, I had the Atlas Jacker sanded, polished, and annodised. The annodising process on my jack plate was $750 (I could have been penalized because I used a high volume shop and clogged a tank for hours, but they had a QA process to ensure a min finish thickness of 50 microns), polishing and prep was $300 and was easier, because we started with a brand new plate. Marine annodising requires at least twice the tank time of standard annodising. I used the "brite-dip" electropolishing process prior to annodic coating. If you are not looking for a chrome look, It would probably be more cost effective to prep and paint it. Have you ever tried the motor without the jack plate? The tendency to porpoise will be reduced. Both of my skiffs with jack plates had a propensity to porpoise with both types of props. I'm sure Tom Clark knows a prop solution for you.

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I found the power tech! to be the best stern lifting prop for me.

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Thanks guys, I'm OK on the jack plate. I really like the design of mine, and I have a local shop that can do a black teflon anodize at a reasonable price. I'm not even sure I'm going to bother - the dull gray natural aluminum takes on in salt water doesn't really bother me. Now that I know the right height, I may eventually build a fixed plate out of 316 stainless. But that's a ways off.

James, your jackplate is gorgeous, like the rest of your boat, but tad pricey for me at this point. I too am hoping Tom chimes in on the prop thing.


Tim

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Which Power Tech prop huckleberry?

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Yes, which PowerTech propeller model? PowerTech makes no less than 23 different models of propellers that would fit a Yamaha F70.

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For more stern lift, the Yamaha Painted Stainless Steel model is good because it uses a semi-cleaver blade design and reltivley low rake on the blades.

If you are running a 13-1/4" x 15" Stiletto Advantage now, you would want to try the 13" x 17" Painted Stainless Steel model, part # 688-45930-02-98.

PowerTech makes an imitation of the Yamaha Painted Stainless Steel model, it is their SCD3 model.

Generally speaking, larger diameter, more blade area and less rake all contribute to stern lift, which is why the Stiletto Star (aka Yamaha Pontoon Performance Series) is so good at stern lift.

A propeller with four blades will add a great deal of blade area, even if the diameter is smaller, and thus often provides good stern lift.

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A propeller with four blades will add a great deal of blade area, even if the diameter is smaller, and thus often provides good stern lift.


Somebody has been studying! :)

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Thanks Tom and all!

The Yamaha is really pricey - over $400 at the cheapest place I could find - a bit more than the budget will stand at this point.

The PowerTech is a bit more reasonable, around $325.

What would you think of going to a Stiletto Star II in 14.00 x 13? This could be had for $250, and if I have the math right, increasing the diameter from 13.25 to 14 is an 11.64% increase in area, while going from a 15-pitch to a 13 is a decrease of 13.33%, so should be about a wash in terms of WOT RPM. Of course, that assumes the designed blade area on the Advantage and the Star are the same - it's not just about circle area.

Tim

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Yes, the Star would provide a lot of stern lift. You would not use the 13" but the 15". The Star has much more blade area but the calculated propeller slip is comparable to the Advantage as far as I have seen.

It is a big piece of stainless steel so you may want to use a Flo-Torq III hub kit with it.

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I'm sorry Tim, I assumed the Power Tech! props were all the same model, just in different pitch. I guess I didn't give that much thought and need to do a little more research before making a reply. I guess thats how we all learn. Anyway, I returned the prop to Skip's, my local prop guy so I don't know the model was but the pitch was 13x17. A lot of stern lift but it still had my rpms up around and above 6k. Long story short, thats how I ended up with the turbo 13.125x17, which I like, but with the hydrafoil, I don't know which one is doing the stern lifting, the prop or the hydrafoil.

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Well, I got the Star 14x15 and initial results are positive - seems like a very good ocean prop for the 15/F70. Compared to the Advantage, it feels like it holds plane better at lower speeds, and in general has a less abrupt transition from on to off plane. I guess you'd expect that with the larger blade area.

It has not been calm enough for a true speed run yet, but with just me and 9 gallons of gas I saw 38.5 MPH at 5400 RPM at 25 percent trim, with minimal porpoising, and a fair chunk of throttle left, so I don't think I've given up a lot of top end.

Shift clunk is OK, not noticeably different than the Advantage. Mileage is pretty much the same too - between 9.5 and 10.5 MPG in the cruise range.

Tim

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Just to wrap up this thread, and in the hope this information helps someone, I will link to the post below describing my experience in switching to a Power Tech SCD3, which seems to be a great match for the high-revving F70. The Stilettos are great props and a good value (too good apparently, since they stopped making them) but the SCD3 seems to be a much better match with the power curve of an F70, at least on my 15. In other words, huckleberry made the right call 2 years ago, it just took me some time to catch on...

http://www.whalercentral.com/forum/vi...ost_136303

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Looks like it was Tom who actually pointed you to the specific model of PowerTech prop (i.e. the SCD3).

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Tim -

Where do you have your battery located? I can't tell from your personal page pictures. I suspect you already have it mounted under the rear thwart seat or in the rear storage compartment. However, if it's mounted in the stern you could try moving it under the rear thwart seat. That is what I did when I added my jack plate to help offset the rearward shift in weight. Beautiful boat by the way and I'm sure you are loving the new yamaha 70!

Bill

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Thanks Bill - my battery is indeed in the stern. I have thought about relocating it but it would be a lot of work, and with my new prop it's all working well now. Thanks for your thoughts!

Tim