OMC- ALUM. to STILLETO???

[Boilermaker]

Hi, I have raised the engine hight on my 18ft,1971 modified vee hull and now my 1978 Johnson 115hp is turning 5500rpm. I am running a used (slightly abused) 14x17 OMC aluminum prop and would like to step up to a Stilleto. Will a 13.25x19 S.S. Stilleto give me abt the same rpm as the 14x17??? <br />Smaller diameter & higher pitch. Also will the vented prop help with the holeshot(its pretty good with the 14x17)??? ANY PROP RECOMENDATIONS???<br />THANKS in advance for your time!!!

 

[LubeDude]

Re: OMC- ALUM. to STILLETO???

I would say you are going to be close, Are you getting a good deal on this stelleto? Why are you dropping diamiter?<br /><br />LubeDude

 

[rickdb1boat]

Re: OMC- ALUM. to STILLETO???

Stainless steel props will raise your RPM's about 200 with the same pitch. Dropping down in diameter will not give you too much more. The one you are talking about should be real close though. 200 More RPM's would be good for your motor anyway.

 

[wtrojan]

Re: OMC- ALUM. to STILLETO???

I don’t know if I get it right, I understand that Boilermaker is going form 14x17 alu to 13.25x19 SS. Two inches more in pitch mean about 400rpm less. It is SS, less flex, so probably some 150-200rpm more than aluminum, is that ok? So, if the diameter has no influence (according to Rick), that would be like 200-250rpm less in total. I’m also about to adjust the prop, so I’d like to know if this is correct.

 

[Boilermaker]

Re: OMC- ALUM. to STILLETO???

This engine originally had an OMC 13x19 alum. (old style)prop, and had a good hole shot, and good topend>>we didn't have a tach on the engine then. After taking the boat "out of mothballs" we found the old prop was no good>>>hub spun under load.<br />The new omc alum prop that the dealer sold me was a 14x19>>killed the hole shot. I put a new style (loaner)14x17 on, and things improved alot. I guess these engines are down on torque compaired to todays engines. When I do a search for props on this site>>>most are 13.25 to 13.75 diameter in this pitch range. As far as Stainless, I figure the thinner blades (leading edge profile) is most responsible for the increase in rpm over alum. <br />I know in aircraft, that a reduction in diameter has as much effect on rpm as the pitch>>>less surface area=less loading>>>I can only assume its the same with boats, right???

 

[Boilermaker]

Re: OMC- ALUM. to STILLETO???

One other thing. Will the "VENTED HUB" help much in holeshot??? Or is it more marketing hype??? Are these props good in rougher seas???I would hate to get a prop on there and find out that it doesn't hold a hook-up in a snotty inlet crossing. <br />I am not locked into the Stilleto (it was recommended to me here). I am opened to suggetions from people that are VERY satisfied with there props.<br /><br />THANKS AGAIN!!!

 

[backdraft]

Re: OMC- ALUM. to STILLETO???

Boilermaker, the 19 in stainless will cut your rpm considerably. The reduction in diameter is not that great but the reduced surface area does have an effect in overall thrust especially in the " slop". The stainless prop does not bent or flex to any degree so it is more efficient. Therefore a reduction in pitch over your aluminum prop is called for . Venting the prop allows exhaust to push out the sides of the prop allowing a more rapid acceleration the the rpm due to a lack of solid water. A17 ss is a good starting point.A15 ss with double cup maybe best. nevjb

 

[Dhadley]

Re: OMC- ALUM. to STILLETO???

The Stiletto will bite much better than what you have. It will also require "dialing in". Any new prop may, but going from an aluminum to a SS certianly will. <br /><br />The larger the diameter you run -- generally speaking -- the higher your X dimension can be. A SS prop will still flex but way way less than an aluminum. The Stiletto is an excellent choice. To compare the Stiletto to the OMC brand props -- the OMC SSTII is better than the aluminum. The Raker is better than the SSTII. The Stiletto is compareable, maybe slightly better than, the original Rakers and better than todays Raker. <br /><br />You will see that the Stiletto not only has slightly more cup angle but it extends further around the blade than most other props. This is lift. <br /><br />The vent holes work well improving the holeshot. Overall I think youll love the prop. If you have trouble finding a 19" Stiletto, let me know.<br /><br />Good luck!

 

[StillFishin']

Re: OMC- ALUM. to STILLETO???

I have a rig similar to yours(82 18ft sylvan walk thru 82 115 OMC) with lots of stuff as to make the rig heavey. Last summer I put on a 3 blade 15P Stilletto and it was superior to my SST's that I have in both 17P and 15P.<br /><br />Just thought I'd throw this out that you may want to consider trying a 15P also.

 

[rickdb1boat]

Re: OMC- ALUM. to STILLETO???

Just re-read my post and Let me correct myself after my brief brain freeze! Going to the 19" SS WILL LOWER the RPM's over the 17" by around 400 RPMs, but will be more efficient, as mentioned. Stick with the same pitch for proper operation. The slightly smaller diameter will also increase RPM's slightly, but not really significantly. The vent holes will definitly help with hole shot, too. Sorry for the backward reply before. Just to clarify! Sorry.

 

[vissertrades]

Re: OMC- ALUM. to STILLETO???

In recent prop testing I actually saw INCREASED rpm when going from aluminum to stainless!<br /><br />OMC alum 11-3/4x17 -> OMC SST 11-3/4x17 -> 300 rpm<br />OMC alum 11-1/2x19 -> OMC SST 11-1/4x19 -> 300 rpm<br /><br />The only thing I could figure was I noticed the exhaust port was larger on the SST props. Can I get a Stiletto 11-1/4x19? What would this do rpm-wise from the SST?<br /><br />Boat: 15' SmokerCraft Johnson 50 VRO

 

[Boilermaker]

Re: OMC- ALUM. to STILLETO???

DHADLEY, do you think I should go with the 19 pitch Stilleto??? or stick with the 17" and gain somemore RPM???

 

[Boilermaker]

Re: OMC- ALUM. to STILLETO???

??? BUMP ???

 

[walleyehed]

Re: OMC- ALUM. to STILLETO???

Boilermaker, Dhadley, Check out my post on "Homemade setback". this is what allowed me to go from a 13.75X15", to a 13.5X18" RAKER (old style), and gained about 200 RPM over the 15" pitch with the original set-up.<br /> I also have to add that ventilation holes are by no means, a "marketing scheme". I've drilled solid props and found it doesn't take a very big hole to make a whale of a difference in hole-shot.

 

[Boilermaker]

Re: OMC- ALUM. to STILLETO???

Thanks Kenny, but I couldn't find the post with the sites search feature??? could you please post the link???I would be interested in the "homemade setback" also. <br />Thanks<br />Jim

 

[walleyehed]

Re: OMC- ALUM. to STILLETO???

It's on "Boat questions" (not engine topics) under "Homemade set-back installation-pics".

 

[Solittle]

Re: OMC- ALUM. to STILLETO???

Jim - If you were happy with the original prop why not get it rehubbed?

 

[Boilermaker]

Re: OMC- ALUM. to STILLETO???

Original prop was OK>>>but we didn't have the technology in the 1970's of todays props>>>I'm sure with the right prop, performance will be improved. The old prop was just an OMC aluminum that came with the engine. My dad also gave me an old SST that has a slight bit of leading edge damage. If anything, I would get this rehubbed and reworked. Its an original SST with the teflon coating.<br />I just think with todays cupping,metelurgy, technology and computer/cad engineering>>> I will find a better product for myself.