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I currently have an omc 13 x 19 aluminum prop on a 1992 70hp Johnson for my 1991 Super Sport 15. I am currently seeing 40-41 mph top end at 5600 rpm. I do have a stingray III jr hydrofoil which allows me to trim up more and still get bite. Does anyone have advice for a stainless propeller? I was looking at a stiletto advantage and was told if I went with this prop I would need to go to a 13.25 x 17. I was told that the reason for going from a 19 pitch in the aluminum to a 17 pitch with this stiletto was because it had a progressive pitch. I do not want to lose top speed by going with this prop. Does anyone know if I will. Also does anyone think that the siletto 13.25 x 19 would be too much pitch for my engine. Other things to keep in mind are that I have a 12 gallon tank, 2 batteries and an oil reservoir in the back of my boat and usually 200-400 lbs body weight. Any advice is very appreciated. Thank you.

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Erich, I have a 1989 SuperSport 15 and had the same motor. I tried several props and ended up with a Turbo 13.25 x 17 - same as the Stiletto Advantage except for the sticker on it. The 13.25 x 17 is a perfect fit for that motor and hull combination.

You did not mention how your motor was mounted - many from that era were slammed right down on the transom. With the Stiletto, you'll be able to mount your motor two holes up (that is, one hole from the highest the motor could be raised) and that will improve your performance, handling, and mileage. Also, get rid of the hydrofoil, unless you really, really need to plane at the lowest possible speed. If your motor is mounted all the way down, I guarantee that hydrofoil is costing you several MPH with your current prop.

You do NOT want a 13.25 x 19 in a modern, cupped prop. Don't even try one unless you know your overheat alarm and S.L.O.W. circuit are working - ask me how I know! A 13x19 SST, which is an older, uncupped stainless prop, would work OK.

I also PM'ed you.


Tim

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I recommend you try the Stiletto 13-1/4" x 17" propeller with the motor raised a hole or two.

Loose the hydrofoil; it will just cause problems.

For the record, all OMC SST propellers are cupped, but early ones were only very modestly cupped. Tim is otherwise correct on all points.

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Tim and Tom,
Thank you for the quick response! I decided to order the Turbo 1 13.25 x 17 today and will be able to pick it up on Monday. My motor is currently mounted in the lowest setting (top hole). This puts my cavitation plate almost directly in line with the bottom of the boat. I guess from what you are telling me I will need to raise it two more holes with the new prop. Will doing so really make that much performance improvement? I hate to disturb the bolts that have been nicely set to the boat for the past 18 years if it isn't necessary. However, Tim, you have already done this and if you say the performance gain is that dramatic I guess I have no choice. I will also take off the hydrofoil since the 1/4" increase in diameter will no long give enough clearance with it on. Is raising the motor difficult to do with just two people and no lift or hoist? Any tips? Thanks, Erich

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Easy to do by yourself. Use your trailer jack to rest the skeg on a block of wood. Remove the 2 fixed bolts and loosen the other 2, and then use the jack to raise or lower the motor. Seal and tighten the bolts and you are done. Takes about 30 minutes.

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Thanks Mike. I'll use the jack.

Here are my findings on the aluminum OMC 13 x 19 propeller without the hydrofoil. Propeller was in fair shape with more than minor dings. Engine mounted in lowest setting, 3 gallons of gas, 2 batteries, myself (190 lbs) and a bow mount trolling motor.

Slowest Plane speed
15-16 @ 2800 rpm

6 mph @ 1500 rpm
7 mph @ 2200 rpm
18-19 mph @ 3000 rpm
22-23 mph @ 3500 rpm
28 mph @ 4000 rpm
32 mph @ 4500 rpm
36 mph @ 5000 rpm
40-41 mph @ 5450 rpm

Can't say I miss the hydrofoil much over and above the fact that it is more difficult to maintain a plane at lower speeds.

40-41 mph @ 5450 rpm

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For speed I have a regular aluminum mercury 13X19 prop. Does about 47mph. I also have a stainless 13x17 for pulling tubres. Remember, keep it within yours wot rpm's. It's not all about speed.

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Eric, Tom Clark knows what he is talking about. I listened to him and raised my motor up and gained about 2mph.

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No go on raising my engine. The way my engine is mounted is by using the very top hole of four mounting holes for the top two bolts. The bottom two bolts, however, utilize a tapped hole for only this height configuration. The only way I will be able to use the slotted mount holes for the bottom two bolts would be by raising the engine the complete 1 1/2" to the maximum height setting for the the top bolts. This would put one of the top mounting hole well above the transom and you would be able to see right through it. I do not believe this would look right. My engine as it sets now puts the bottom of the cavitation plate directly in line with the lowest point of the bottom of the boat or a little less than 1/2" below the transom. Is it that much of a performance gain to raise my engine 1 1/2" and having one of the top mount holes exposed above the transom? Shall it be functionality over looks or looks over functionality. If I am reconvinced that this will be that effective I am definitely going to use a friends Bobcat to hoist the engine. I just can't take a chance with the floor jack and having the engine free without proper support.

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So what? There is nothing wrong with that. That is why there are multiple mounting holes on all outboards.

Your motor in mounted with the blind holes for the lower bolts, that is understood, but the remedy has been discussed a hundred times already.

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Erich -

On the left sidebar, under Articles: Engine Rigging, is a great article illustrating mounting options for motors using the old bolt holes and/or blind lag holes.

Link to Article

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Thank you guys for your insight. It looks like I have a few options.
A: raise engine and drill new holes for the lower mounting bolts
B: raise engine and use lag bolts for the lower mounting bolts
C: install a jackplate
D: leave it be and do nothing

I just picked up my Turbo prop from Precision Propeller where they manufacture Turbo/Stiletto/Yamaha propellers here in Indianapolis. Boy what a cool operation they have going up there! I will report the performance data asap. I am really interested to compare it to tedious' data with his new F70. We have the same hull and prop except with different engines.

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After taking my new Turbo 1 13.25 x 17 out for a spin today I was surprised to find how similar the performance curves were in comparison to the original fairly dinged up omc aluminum 13 x 19 propeller.  Here is my data:

6 mph @ 1500 rpm
7 mph @ 2000 rpm
15 mph @ 2750 rpm 
16 mph @ 2800 rpm (slowest plane)
18 mph @ 3000 rpm
20 mph @ 3150 rpm
23 mph @ 3400 rpm
26 mph @ 3750 rpm 
28 mph @ 4000 rpm
32 mph @ 4450 rpm
33 mph @ 4500 rpm
40 mph @ 5450 rpm (top end W.O.T.)

The first thing I noticed was that when putting the motor in gear the prop seemed to kick or jolt a little. My idle is set at 975 rpm and I wonder if this needs to be adjusted. I was very impressed at how the prop performed. It feels like the prop may have improved the time it takes to accelerate and get the boat up on plane.  I am extremely impressed with how the boat and motor handled at top end. I was able to trim the motor way up (3x+) and still maintain speed or thrust. The motor was able to trim past what the gauge would read and the rpms did not go any further than 5700. With the old aluminum prop the engine would shoot to 6000+ and loose thrust at a fraction of the new trim capabilities are. I noticed that at top end the steering became very stiff or tight rather.  I was able to steer the boat better however it was more difficult.  I was somewhat surprised that I did not gain any top end even though I was told I probably would not.  This goes to show just how little I know I guess. It appeared that I actually lost 1 mph and I am hoping this is due to the extra 4 gallons of gas that were in the tank.  There was not a wrinkle on the water at this small reservoir and the water was more clear than it usually is. 

I am in limbo as whether or not to install a jack plate or just raise the motor up directly mounted to the transom.  If I were to keep the motor directly on the transom I would be limited to a maximum of one and a half inches of lift and would have no choice than to drill two new lower thru-bolt holes.  With the jack plate I would have the ability to see higher mounting capabilities and with the increase in setback my prop would see "cleaner" water to chew. With a jack plate I would no longer need to drill into the hull of which I really am opposed to doing. I am looking at the CMC ML-65 manual model with a 5 1/2" setback which would add about 35 lbs. to the all ready somewhat well loaded stern. Is anyone partial to any particular jack plate manufacturer and how much setback would be recommended? I was also considering the Detwiler 4" setback or the TH Marine 6" setback models.  Any advice will be much appreciated.  Thank you. 

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Erich, I don't have a jackplate, so I can't advise on that, other than to say designwise, I like the Hydrodynamics HDEZ-50: http://www.hydrodynamics-usa.com/e-zliftjackplate.html

I had my 70 mounted two holes up, exactly 1.5 inches higher than yours is - perfect with that new prop. In your situation, I would move up two holes and redrill.

Tim

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Thanks for the advice Tim. Since most oc the time I am running in shallow lakes and rivers here in Indiana feel like it is a good idea to be able to raise higher than the factory limitations. Of all the manufactures I had researched I some how missed Hydrodynamics. They do have a very nice design and probably the most bang for your buck compared to CMC, TH Marine, Bob's, Vance, Rite-Hite, Detwiler, etc. I like how they offer custom color selection as I probably would have chosen red. I also like how they offer custom solutions and seem to have customer service that would be above the rest. I However got a really good deal on the CMC on eBay. I am somewhat debating whether I need to use transom washer plates or not. I think maybe I should. In preparation to installing the jackplate, I do not think my steering cable will be long enough. If this is the case it will be a good excuse to upgrade to the Teleflx Safe-T II since it is NFB and my current steering is not.

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I installed a Bob's 4-1 Convertible Jackplate, 5" setback and I like it a lot. I was in the position as you with the motor install in the lowest position with the blind holes (I notice most 15's I see FS are mount this way, it's unfortunate so many dealer improperly installed the motors this way.) I have 15' SS and 1989 60hp Evinrude with 70hp carbs (same weight as your 70.) One nice thing about the jackplate is you can fine tune the height, the Stiletto lifts the hull quite a bit. By raising the motor 1/4" higher, it made my hull from wild chine walk (almost corkscrew motion) to a light chine walk.

I gain ~3 mph from raising my Jackplate from the lowest position on the jack plate to the height I eventually ended up at. I would guess you would gain about 3 mph by raising up your motor with the Stiletto.

I am currently using a 13 1/4" X 19P Stiletto and I am hitting 46mph @ 6100, I am curious if I will gain some more mph with the cold fall weather. I think I could really use a 20P Stiletto :) I had about 2mph higher top speed this spring when doing testing with 60hp carbs (colder weather).

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Thank you dgoodhue for the reply. My first question is about the 19p stiletto you are running. I wanted to use the 19p but when I was switching from the aluminum 13 x 19 I had to the Turbo 13.25 x 17 the guy from Turbo prop as well as Tom W Clark insisted a 19 pitch Turbo or Stiletto would be TOO MUCH. This makes me question if I could get away with the 19 pitch. You also said that you upgraded carbs on your motor and from how I understood you had lost mph. If you can post some pictures of your boat. I would like to see your jack plate. Did you run into any problems with steering cable length when you installed the jack plate? Also, did you use a transom washer plate? Thanks.
Erich

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Sorry I was unclear, I tried to summarize a lot of info. I was running 44mph in my with a SST 13 x 19P in May. With a 12 3/4 x 21P SST and 13 1/4 x 19P Stiletto, I was running 42 mph in JUly and Ausgust.



I will post some picture for you this weekend, I was going to downlaod them last night but my wife had brought the Camera to PC USB cable with her on her business trip.

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I didn't have any problems with the steering cable length.

http://s202.photobucket.com/albums/aa...Jackplate/

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Thank you Dave for the pictures and being so thorough. Wow, with your jack plate your cavitation plate is considerably higher than where mine is currently. I do like the Bob's 4 in 1 and I've heard a lot of people are very happy with it. Are you running yours without the wedge? My only reasons for not choosing it is I did not feel comfortable with the two piece design and I did not want to have a black jack plate as my motor and hull are both light colored. Some may say "so what" but the appearance would bother me. I do like how the Bob's 4 in 1 weighs only 19 lbs and the CMC I have purchased is I think 32 lbs. Do you think that I should go with the Turbo 13.25 x 19? I wonder why so many seemingly skilled and knowledgeable people frowned upon the idea? If you guys are reading this please reenforce your opinions. You are reaching 6100 WOT with the Stiletto 13.25 x 19 and I am seeing 5450 WOT with the Turbo 13.25 x 17. I wonder if my WOT will increase once I install the jack plate.

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The camera angle doesn't quite show it (boat is on a hill), but if you put a straight edge on the bottom of the hull the tope of prop is right about that height. When I bought it I was a little concern whether or not the teleflex cable would reach, and like the option of having 2.5" setback.

You will get additional speed at WOT by raising the motor. I would put the Jackplate on with your current prop and fine tune the engine height. You can decide from that point whether or not you need a larger prop. I am probably going to buy a 17P Stiletto for my boat for watersports and heavy loads, I would guess I had 17P Stiletto on my boat I would be right about 6000rpm with out trimming the motor out.

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How much does the jack plate weigh? I would love to put one on mine. Is it electric or manually adjusted?

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I have a mechanical Jack Plate, it's about 20#'s

http://www.bobsmachine.com/Products/jackplate_convertible.cfm