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Author Topic:   Stiletto props
Dick E posted 08-27-2000 10:06 AM ET (US)   Profile for Dick E   Send Email to Dick E  
I have a 17 Montauk with a 90 hp Merc. I am thinking about getting a Stiletto prop. Has anyone been running a Stiletto? What has been your results and pitch?
Clark Roberts posted 08-28-2000 07:32 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Dick, careful! Avoid any "high rake" props as energy will be wasted on trying to lift the bow.. and performance will be gone! Test before you buy...best advice.. I have owned several 17/90Merc combos and have found that the 3 cyl (71 cubic inch,2.3:1 lower unit ratio) will swing a 19-20" pitch standard Quicksilver and the 84 cubic inch (2.3:1)will swing a 20" High Five and hit around 48-50mph...Avoid the Trophy series four blade Quicksilver props... I have a 19" std and a 20" High Five hanging on the garage wall .. too bad bad Gastonia isn't closer to Daytona Beach or you could try them out... If your engine is the old in-line six (higher lower unit ratio 1.87:1 ??) then a 17" pitch would be about right.
Not saying anything wrong with the Stiletto, mind you, just words of caution... and I'm very opinionated, heh, heh....Just prop her so that it will run at 5500 WOT) Happy Whalin' Clark .. Spruce Creek Navy
kingfish posted 08-28-2000 08:36 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Clark/Dick-

I think the experience I am about to describe is a whole 'nother issue (and I'm not even sure what that issue is), but I bought a Stiletto prop for the '89 Merc 100 I had on my last Montauk. I never had the opportunity to dial in accurately the difference(s) in performance, because I found with the Stiletto prop on, when I would shift from neutral to either forward *or* reverse, I would get such a loud and heavy "thunk", that I concluded the extra weight and consequent inertia of the stainless prop was going to do my gearbox in. I took the stainless prop off, put the aluminum prop back on, and all was right with the world again.

Don't know what it all means, but I thought I'd pass it along...

Kingfish

Clark Roberts posted 08-28-2000 05:26 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Kingfish, I use stainless props exclusively and shifting is smoothe and easy... maybe your idle is set too high.. that would "clunk".... also when shifting it's best to do so smartly (quickly without any pause) as this keep the teeth from jumping,, clickity, click... not good.. try setting idle at around 650-700rpm tied to dock and in gear! Happpy Whalin'... Clark.... Spruce Creek Navy
Clark Roberts posted 08-28-2000 05:26 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Kingfish, I use stainless props exclusively and shifting is smoothe and easy... maybe your idle is set too high.. that would "clunk".... also when shifting it's best to do so smartly (quickly without any pause) as this keep the teeth from jumping,, clickity, click... not good.. try setting idle at around 650-700rpm tied to dock and in gear! Happpy Whalin'... Clark.... Spruce Creek Navy
Dick E posted 08-28-2000 10:52 PM ET (US)     Profile for Dick E  Send Email to Dick E     
Clark my Merc a 98 3 cyl. It has a 21" pitch alum stock blade. The RPMS at WOT Trimed is only 5000. It should be close to 5500.
I am thinking of 19" prop
lhg posted 08-29-2000 12:47 AM ET (US)     Profile for lhg    
From what I have read in Mercury prop literature, for mid-range engines (4 1/4" gearcase) they generally do not recommend a high rake, bow lifting prop for a boat that will not do 45mph or better. This is generally why they do not make the Laser or High Five's in less than 20" pitch. It sounds like you are right on the border between an "elephant ear" SS prop (Merc Vengeance) and a high rake prop. The Montauk is pretty light, and that 90 is a strong engine, so the extra lift you'd get from a Merc 20" 3 blade Laser (or QS 2000) might just work. In Overton's catalog for about $325.
lhg posted 08-29-2000 12:51 AM ET (US)     Profile for lhg    
Further to my above note, if you go for a high rake prop such as a Merc Laser, raise your engine one or two bolt holes, as these surface piercing props are not meant to be run fully submerged. I agree with Clark, you should get about 48-50 @5500rpm with such a setup.
JimU posted 08-30-2000 11:36 AM ET (US)     Profile for JimU  Send Email to JimU     
I'm testing a 13 1/4 inch by 15 pitch Stiletto on my 17 foot classic (1971 Model) with a brand new 2001 Yamaha 90. I can't give you any specifics on performance yet as I don't have enough time (about an hour) on the engine to run it at wot long enough to check rpm's and speed. However, it "feels" real good. The boat planes at really low rpms and responds instantly to changes in trim and throttle. We have some real prop pro's here in Louisiana. My "prop man" is a boat builder and custom prop shop who has been in the business for some time. He recommended against more than a 15 pitch Stiletto because its easier on the 90 hp engine. He said he preferred to add some "cup" to the prop if it was not giving the desired performance. We'll see. I'll post the details when I have enough time on the engine to put it through its paces. Jim
Dick E posted 08-30-2000 07:41 PM ET (US)     Profile for Dick E  Send Email to Dick E     
Thanks Guys for all the info.
Barry posted 09-03-2000 10:39 PM ET (US)     Profile for Barry  Send Email to Barry     
Dick E,

Did you make a decision on the Stiletto? Which one were you looking at? I've got a '74 Montauk with a '94 Merc 90 and am currently running just alumiunum props, both 19 and 21 pitch. With the 19 I'm hitting about 5400 at wot and with the 21 I'm getting about 5000. I'm thinking about a stainless steel and have been looking at the Stiletto 13.25 x 19 3-blade (~$275), the Stiletto Bay Pro-I 13.25 x 19 4-blade (~$360), and the Quicksilver 13 x 18 3-blade (~$380).

Anybody else have any comments about sticking with a Mercury prop for my Merc versus something else? Any thoughts on 3 vs 4 blades?

Thanks,
Barry

Dick E posted 09-03-2000 11:13 PM ET (US)     Profile for Dick E  Send Email to Dick E     
Barry have not made the decsion yet? Finances. I was leaning to a 19 inch pitch Stiletto. My rpms are the same as yours.
The 4 blade prop will stick better in rough water and give you smoother acceleration; however you will loose a bit on the top end.
Barry posted 09-04-2000 07:40 PM ET (US)     Profile for Barry  Send Email to Barry     
Because of the finances, I probably will be more concerned about "losing" the $100 dollars more from my wallet for the 4-blade and just stick with the 3 ;-)
Ger posted 09-05-2000 12:32 PM ET (US)     Profile for Ger  Send Email to Ger     
Clark, this whole prop subject gets pretty technical pretty fast!! As someone who thinks his motor might need a different prop setup, are there any source books that could give me a bit of an education? THanks Ger
Clark Roberts posted 09-05-2000 08:20 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Ger, Mercury Marine and OMC have some prop literature with some theory... don't have their web sites... MercuryMarine.com is Merc's site.... dealer most likely has hard copy// etc... Larry Goltz is really up on prop throry and practice... he may offer some sources.... And yes, it gets technical fast! And there is some "witchcraft" involved also.. heh, heh.... Clark
bigz posted 09-06-2000 07:23 AM ET (US)     Profile for bigz    
Hey Clark I think-- heh heh -- the emphasis should be placed on "WitchCraft" and maybe a bit on the "SWAG" approach in prop selection (scientific wild ass guessing) don't yeah know --- Tom

PS then again it could be just having the motor properly tuned --- chuckle!!!!!!!

Clark Roberts posted 09-06-2000 09:50 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Tom makes a good point about the SWAG! I have consulted with T&G Marine (Welaka, Florida) and these guys set up 100mph bass boats etc... they live and breathe props... that's the key to performance... They test each rig and make adjustments... They run small hub Merc props on the Merc V6's and blow the exhaust over the hub... what?? That's right... the old test and retest routine... seems as though there is a max rpm for props, above which strange physics takes place.. this rpm is approx 3000... with a 2:1 lower unit ratio that would be 6000 crank rpm... above that speed the prop tip speed us such that a partial vacuum can form on the prop blade and remove metal and also limit speed... this phenomenon is called "cavitation"... Ventillation occurs when air from surface or hull obstruction gets around prop blaces causing it to "break loose"" Cavitation and Ventillation are commonly used interchangably although completely different things... here I go again... long winded and pointless... heh, heh.... bottom line is that the correct prop type and pitch is oh so important... Later... Clark... aka... the Old Man
bigz posted 09-06-2000 10:22 AM ET (US)     Profile for bigz    
HA HA HA -- oh my I didn't know BASS could move that fast ---- oops oh I see the folks who go to catch BASS have to move that fast --- now that is what I call POINTLESS --- Tom

PS Clark your never to "long winded" for me always learn from you ---

lhg posted 09-06-2000 11:17 PM ET (US)     Profile for lhg    
I am certainly not the expert on props that Clark says I am! But over the years the subject has fascinated me, and I have learned what I can, mostly from reading Mercury's literature & Prop guides, and religiously talking to Mercury engineers at trade shows.
As a student of outboard engines for many years, I can honestly say that I think Mercury rules the prop world, and always has.
They have invented and offered the most complete line of propellers of any company over the years, many a result of their racing and high performance divisions, which have ruled for years. The other companies have simply had to copy and imitate their innovative designs, always playing "catch up". And now, all of their props can be readily installed on any brand of engine. Here's a brief description of what I have learned, money not being the issue here.(but obviously a reality that can override other decisions)

Aluminium props, in conventional elephant ear, but cupped design, are the cheapest, but also the lowest level of performance and efficiency. They are all right for low horsepower engines, such as 25HP or less, or where you boat will not do better than 25mph.
They should always be run at standard transom heights. For any V-6 engine, I believe they are not acceptable.

Standard design SS props are much better (such as the Mercury Vengeance series) and will improve performance and efficiency, and are best for boats that run 25 to 40mph, any size engine. The engine can be elevated about 1/2" with this style without ventilation occuring. (Raising an engine on the transom is generally desireable, reducing lower unit drag and improving speed and effeciency - but the propeller design must be able to accomodate this). I have often seen Whalers where the Dealer has mounted the engine TOO LOW on the transom, resulting in a "V" spray coming off the engine lower unit. This kills performance, and the engine should be raised one bolt hole, so that the engine runs clean through the water, with no spray.
I have run my twin engine 18 Outrage with both Mercury aluminium props, and SS props, of same pitch, and the improvement with the SS is remarkable. You can almost feel the aluminium props go "dead" on you as you pass 35mph.

For a Whaler that will run over 40 or 45, I think a lifting propeller is essential. This gets the whole boat up on the planing surface a little higher, producing a smoother ride and reduced bottom friction, giving more speed for the same fuel used, in spite of the extra effort required for lifting the hull. The Mercury engineers have said this for years, but the proper selection of prop is essential here. There are different types of lifting (high rake performance) props, and not all work the same, and the amount of exhaust venting is also important. And they require different transom heights for the engine installation. The 3 blade Merc Laser is designed for light weight hulls, such as a Whaler can often be, and runs well, provided the engine is lifted 1 1/2". Run these fully submerged, and you have drop down 2" in pitch. Same goes for the 5 blade High Five prop, which is best used for pulling conditions and rough water holding, where top speed is not essential. Clark has said the 4 blade Trophy prop is a dog for a whaler, and I agree, but Mercury says they are their best speed and hole shot prop, but they need to run 2 to 3" high, and are best suited for the hull design on a 70 mph bass boat.

Then, when you switch to the V-6 Offshore category, like Whaler Outrages/Revenge/Conquest, there are other lines of propellers best suited here, especially with counter-rotating twins. Aluminium props here are rarely seen, and not recommended. Merc doesn't even make them counter-rotating in 3 blades for outboards.
The bottom line is the 3 blade SS Vengeance line, also rarely seen. Almost always one uses the higher rake performance blades here, since most of these boats will do at least 40mph. I run Merc Lasers on my 25 Outrage, but now I am hearing & seeing that these are outdated designs for the big V-6's. The Mirage Plus design dominates here, and the Merc engineers tell me it is the best for all around speed, power and holding. They have also come out with a 4 bladed "Offshore" prop, that has great holding in rough water, great total hull lift, but is about 3mph slower than a Mirage. Almost every new Mercury equipped large Whaler that I have seen comes from the factory with a Mirage Plus prop. The latest high performance prop improvement involves the venting holes. Mercury has just introduced adjustable vent plugs, so the amount of accelleration slippage can be controlled for your particular usage. Most of these vented props slip until speed is up to 25mph.

So that's my Prop course 101!

Dick E posted 12-17-2000 10:02 PM ET (US)     Profile for Dick E  Send Email to Dick E     
I have a 1998 17' Boston Whaler Montauk with a 1998 90 hp Merc. It came with a 13x21 Aluminum stock prop. Rpms were only 5000 at WOT. Needed to go to upper end 5500. A guy out in AZ wrecked his boat hitting an submerged dam. Totaled his boat, not his motor sold me the 13x19 Stiletto for $150. Prop was MINT only used it once Put in on, with thrust washer.

Postives: Hole shot super

Handling: It's bites real good.

Top speed went from 38 mph to 44 mph .

Rpms 5400


Negatives: Huge bow lift only trim out about 1/4 of what I use to with the aluminum.

I'm I losing speed potential from the rake of his prop?


Betwen 1000 rpms and 1800 rpms I have significant more vibration when in gear. After 1800 rpms, normal vibration. Checked they gear lube its fine and full . Any thoughts? Thanks,

Dick

Barry posted 12-18-2000 05:23 PM ET (US)     Profile for Barry  Send Email to Barry     
Dick,

I've got almost the same equipment: '74 Montauk, '96 Merc 90, 13x17 Stiletto 3-blade prop. And the same issue: a lot more vibration with low rpms both in forward and reverse.

My boat is put away for the winter so I haven't messed with it lately, but I believe tightening the nut helped. Made me wonder if a thinner thrust washer would work better. I also debated about trying to temporarily plug the "holes" to see if that would make a difference.

Please keep me informed.

Thanks,
Barry

lhg posted 12-18-2000 11:27 PM ET (US)     Profile for lhg    
Dick E - If you're still looking for more speed, you might want to lift the engine another one (3/4") or two (1 1/2") (depending where you are now) bolt holes and go to either a Merc 20" Laser prop or a Stiletto 21". Rpm's should stay about the same due to reduced drag. I'm not familiar with Stilettos, but the vibration could be coming from the slightly vented design. With this style of surface piercing prop, your anti-cavitation plate should not be running more than 1 1/2" above the water coming off the hull.
Hoop posted 01-25-2001 01:45 AM ET (US)     Profile for Hoop  Send Email to Hoop     
Larry, up above you wrote,

"Aluminium props, in conventional elephant ear, but cupped design, are the cheapest, but also the lowest level of performance and efficiency. They are all right for low horsepower engines, such as 25HP or less, or where you boat will not do better than 25mph.
They should always be run at standard transom heights. For any V-6 engine, I believe they are not acceptable."

What is your opinion on my raising my Evinrude 70hp four stroke up one hole so the cavitation plate is 3/4 inch above the botton while I still have my factory 14x17 aluminum prop? Your comment above says, "No," but you didn't explain why. Later I'll get a SS prop of some kind (Mercury Vengeance?). (I'll probably get it in time for our Nor Cal Whaler Rendezvous in May!)
Hoop
San Jose, CA

lhg posted 01-25-2001 12:28 PM ET (US)     Profile for lhg    
Hoop, on Montauks in your HP range, I've got to say Clark Roberts has a lot more hands-on experience in answering your question than I do. I ran mine for 16 years with a Merc in-line 6 115HP with a bronze 2 bladed prop!! (about 55mph top speed).

Anyway, I'll try. I would do as you are planning, and try raising the engine one bolt hole. You really have little to lose. Your aluminium prop MAY even handle this, but you could get increased slippage, especially when lugging into a head sea, or getting up on plane. A good SS, like the Merc Vengeance you mentioned, should handle the elevated height better and give you more speed.

Assuming you boat does between 38-40, you are are just about at the point where raising the engine may help. You could pick up another 100-200 in RPM's and a little speed. Mercury's prop literature seems to indicate 45mph as the point where the engine DEFINITELY should be raised 3/4" or more, and a performance prop used. Don't confuse the word "performance" with "racing". Basically, a good "performance" prop means that it can run "surface piercing", generally up to 1 1/2", giving increased overall hull "lift" to reduce bottom friction and increase speed, and still agressively hang on. If one's boat will go faster than 40mph, they should be looking at these. For 45 and up, definitely.
I'm only familiar with the Merc line of props, but for Whalers these would include the 3 blade Laser & Mirage, 4 blade Offshore & Revolution, and 5 blade High Five. The variable venting design that comes with these is state of the art. They can now be purchased for any brand engine, but you'll have a hard time finding these for less than $400 each.

Hoop posted 01-25-2001 05:59 PM ET (US)     Profile for Hoop  Send Email to Hoop     
Larry, thanks! Right now I'm at about 37 mph at 5600 rpm (with trim way up), the spec for the motor. If raising the motor increase rpm, then I'm probably at a point where I would need to look at reducing pitch. So maybe a SS prop in the 14x16 range would do the trick ... but first, one notch up ... Hoop
lhg posted 01-25-2001 07:11 PM ET (US)     Profile for lhg    
Hoop, you're going the wrong way with the prop. If RPM's are too high once raised, you would want a higher pitch, such as 18 or 19.
Hoop posted 01-26-2001 12:49 AM ET (US)     Profile for Hoop  Send Email to Hoop     
Oooops ... Thanks!
Hoop posted 01-26-2001 11:42 PM ET (US)     Profile for Hoop  Send Email to Hoop     
My dealer suggested an OMC Viper 13 7/8 by 17 SS prop to replace my aluminum 14 x 17. And he agreed that raising the motor 3/4 inch could help. He has one in stock which he offered to let me try. (Chapter 11 is probably not an issue for a prop!) I double checked my speed ... which is averages 36 mph at 5600 rpm (after running in both directions and averaging the speed). Hoop

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