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Author Topic:   Repowering MT 170; Prop Recommendations?
smgrogue posted 02-10-2003 12:11 AM ET (US)   Profile for smgrogue   Send Email to smgrogue  
Following up on an old thread, I am re-rigging my Montauk 170 with Johnson 140 4s. The Merc 90 2s goes on my other boat unless someone here want's to buy it from me. Anyhow, I really need help selecting a prop to try out for field testing. Using the Clark Roberts formula and based on a total weight 2800 lbs (hull; 450 lbs for passengers; 100 lbs misc. gear; 26 ga. fuel; 2 grp 31 agm batteries; minn kota motor; cmc jackplate and motor), predicted speed is 45 mph. This might be conservative based on Tabasco's reports with the 90 to 115 migration (hull factor of 200 is too low for the MT 170 hull form?). The Reference Section's prop calculator suggests I need a 20 pitch prop (diameter is 14" for this motor). This is based on 5900 rpm (midpoint of oper. range); 2.4:1 gear ratio; 5% assumed? slip; and 45 mph top speed.

Any suggestions as to what size and type (rake, cup, stainless?) and brand of prop I should consider would be greatly appreciated. I am willing to give up some speed at WOT (which should be in abundant supply anyway) in favor of better hole shot for skiing/towing. With the hydraulic jackplate, the motor can be lowered when skiing, but I assume that certain water piercing props may not be intended for this purpose. Thanks

jimh posted 02-10-2003 12:47 AM ET (US)     Profile for jimh  Send Email to jimh     
At first I thought you were confusing the nomenclature of the old and new Montauks. I didn't think anyone would be repowering a new boat so fast!

Next, I was quite impressed with your presentation of the material. Clearly you understand the process of assessing boat speed and propeller choices.

Finally, I would mention that it might be possible to deduce an appropriate hull factor from the table of data in the Reference article which compares predicted vs actual speeds. Those numbers do seem to suggest that the hull factor is higher than 200, particularly as the horsepower increases.

smgrogue posted 02-13-2003 12:06 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Since my first post I have done quite a bit more review of old posts and articles on this site regarding prop selection. I think Clark Roberts has it right in saying there is a bit of witchcraft involved in prop selection. I now find I also need to consider the number of blades (three, four or five) for my application. Clark has high praise for Merc's High-Five (aids hole shot; did not experience others' reported loss at top end), while Larry is a proponent of four bladed Merc Laser IIs. For all I know, neither of these is a good choice for my Suzi/Jonny 140 4s, as Bigshot seems to suggest that when using non-OEM props you can experience more slip for some reason. That would suggest that I should stick to Johnson or Suzuki props. I bought my motor from Ed's. But my local OMC dealer--a good and honest guy who is rigging the boat--is just not a 4s proponent; said I wont be happy with the hole shot for skiing purposes and that I should have bought a 135 FICHT (given that a 135 OPT would be too heavy). From everything I've learned so far, the High-Five is supposed to provide the most help in that regard, and lets face it, I can afford to loose some top end since I'm pretty sure I've underestimated top speed at 45 mph WOT. Am I headed in the right direction here?
rsess1 posted 02-13-2003 12:54 PM ET (US)     Profile for rsess1  Send Email to rsess1     
I have a high five on a 175hp Merc EFI on a ski ray ski boat. It is unbelievable for hole shot. It could pull up anything. It takes off smooth as silk and top end is great. About 50mph. I would recommend trying one. Try e-bay. As to non-oem props, this is an oem prop for Merc, but not for Johnson. I think this prop will be fine for you. Good luck.
Bigshot posted 02-13-2003 01:30 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Hole shot should be pretty good no matter what you run. I think a 20" 4 blade might do the trick but in a 3 blade you will need a 22-24" in my opinion. My bud runs twin 115 Zukis on his SeaCraft and is running 23" alum at about 6k. I would call the local Zuki dealer and ask what they recommend on your weight hull, etc. If a 70hp Zuki would turn a 17" alum on that hull, I think I see at least a 21" Stainless but probably a 23 or so.
tabasco posted 02-22-2003 09:37 AM ET (US)     Profile for tabasco  Send Email to tabasco     
I will be interested in your results after you have repowered. I also considered the 140 HP when repowering, however I didn't want to go though all the problems of redoing the controls. The change to the 115HP EFI was simple. It was just the reconnecting the cables
smgrogue posted 02-22-2003 04:35 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Tabasco--If it wasn't for all that I learned from what you and others have shared on this forum, I probably wouldn't own a MT 170 right now. So I will be more than happy to report back on my findings once I have everything all put back together. It is turning out to be quite a little project, and more than once so far I've wondered whether I made a mistake in not just following your path. Hopefully it will be worth the effort. I sure have learned a lot in the process, though. The rigging process should finally start in earnest next week; I just pulled the 90 this week and now I need to decide whether I want to keep it for another repowering project this fall or sell it now (the direction I'm currently leaning).

Thanks to Bigshot and others for the prop advice; hopefully I'm finally going to have need for one soon!

boxers posted 02-25-2003 09:15 PM ET (US)     Profile for boxers  Send Email to boxers     
smgrogue Excellent idea! I came SO close to doing nearly the exact same thing last November. MT-170 with a Suzuki F140, I was a little gun shy about the MT-170 as I wanted the boat to be selfbailing. Ended up finding a really nice OR-20 and repowered with a Yamaha F225. Four strokes are really quiet until mid range rpms you basically just hear the water. We have a Honda BF 40 on our 13 GSL too. You have made a great decision-just wait to you fire it up for the first time. You won't know the motors running at idle. Go for it & good luck!!
tabasco posted 03-10-2003 02:38 PM ET (US)     Profile for tabasco  Send Email to tabasco     
Smgrogue_ Give us an update as to how the repowering is going. Waiting to hear about your final results.


smgrogue posted 03-10-2003 04:47 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Tabasco--The good news is, I think this is the week that the boat will finally get (mostly) rigged. The bad news is that we are leaving town for a couple of weeks starting next week, so I won't be able to give a water test reports for a while. Hopefully my first report will be something along the lines of, "No, the boat did not sink, despite all that extra stuff I put on her."

My approach in re-rigging the boat has been to wait untill all the parts and pieces were in hand before starting the process, and I am now waiting on only two items that should be ready in the next couple of days. The big hold-up (literally) of late has been the electric trolling system, the selection of which has been quite an odyssey. I've been through all the bow mount vs. transom mount and 24 vs 12 volt decision trees...all have their positives and negatives. After a great deal of research, discussion and analysis, I finally decided that the system that was best for me was the Lenco Trollin Tabs. This is a 24 volt system, though, and as you well know, the challenge of stuffing three batteries into that console is no easy task (especially since there isn't backing everywhere), but I eventually found a way.

I will keep you posted as to my progress. Thanks for your inquiry. Regards, Stephen

tabasco posted 03-11-2003 07:23 AM ET (US)     Profile for tabasco  Send Email to tabasco     
Look forward to your update.
tabasco posted 03-21-2003 07:15 AM ET (US)     Profile for tabasco  Send Email to tabasco     


tabasco posted 03-31-2003 10:41 AM ET (US)     Profile for tabasco  Send Email to tabasco     
are you back yet? we are awaiting the results
tabasco posted 05-06-2003 12:12 AM ET (US)     Profile for tabasco  Send Email to tabasco     
Were still waiting for the test run speeds. The new motor should be installed by how about some GPS numbers
smgrogue posted 05-07-2003 04:04 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Tabasco, here's the scoop: Yes, the boat has been in the water, but I still have not been able to get enough hrs. on the motor (schedule constraints on my part) to be able to run over 4000 rpm. I have not taken a gps out with me on any of my runs during this initial break-in period, but I will the next time I splash the boat. All I have been able to do so far, per mfr's break-in procedures, is peg the motor to WOT in order to get up on plane, and then immediately backing off the throttle to the specified rpm's. I can tell you that the motor makes very nice sounds. Naturally, it purrs like a kitty at idle, but when you get on it the sound is reminiscent of an inboard/outboard runabout setup. Of course, this is to be expected given that it's a four-stroke, but it is still odd to turn around and see an outboard hanging on the transom. The motor seems to have tons of mid-range power, and nice throttle response from about 3k on up.

One cautionary note about my early findings--I elected to initially purchase a three blade 14 x 21 aluminum propeller (which will become my spare). This is so that I could gather some real world data with which to help choose the correct pitch of 4 blade ss prop. Unfortunately, I couldn't work out an exchange program for a Trophy Plus prop, which I from all the advice I have gotten so far is apparently the best overall 4-blade choice for my setup.

The hydraulic jackplate works like a charm, and I can see already is going to be extremely handy. But I have to say, between the jackplate, the trim tabs and the trim on the motor, its going to take me some time to get the hang of all the adjustment potential and their varied applications.

I can, of course, confirm that the boat floats with all the "extra stuff" on the transom. As to static trim I have not had a chance to take any dockside pics yet, but the stern sits high enough so that the splash well drains are above the waterline unless I lean out over the splash well to take a peak at the motors or stand on one of the stern seat/steps, at which point my 250 lbs helps introduce a couple inches of water into enter the splash well.

The only problem with my set-up so far has been with the Lenco Troll Tabs, which should be remedied shortly. First, one of the motorguide motors is defective; it turns at a slower speed than the other, so the boat does not track straight. Second, one of the tab actuator pistons is defective (does not free-wheel when fully retracted and instead goes "thud"...not good for longevity sake). The Lenco folks have been very good about responding to these problems. The trolling system is really slick, though. I managed to run the fuel level in my Pate down below the level of the pick-up tube (dumb), so I ran out of fuel about 100 yards short of the boat ramp. Even with the malfunctioning troll tabs, though, I was able to trailer the boat and be on my merry way. Woulda never happened with a bow mounted system, which I thought long and hard about.

The boat's in sick bay right now, awaiting the troll tab change-out. I hope to get back out on the water this weekend if I can squeez it in between Mother's Day observances and youth soccer matches. I will report in due course. Regards, Stephen

lhg posted 05-07-2003 08:04 PM ET (US)     Profile for lhg    
I just caught up on this one, and like Clark, I would definitely recommend a High Five Mercury prop for your 4-stroke. You will need the hole shot improvement and hull lift this prop offers. Any aluminum prop for your rig should only be an emergency spare, and will kill performance with that much HP on a light boat. I do not like the 4 bladed Trophy Plus for anything but a Bass or Flats boat, and with a two stroke, as they need a lot of torque to get moving. If your engine was a two stroke or DFI, I would recommend the 3 bladed Laser II because of high HP to weight, but not for a four stroke where acceleration counts.

The other nice feature of these Mercury performance props on a 4-stroke is the variable venting system. You can open them up for more initial prop slippage, giving even better acceleration. Expect to pay $400 for one of these, bought right, but well worth it. They are very smooth performers and hang on exceptionally well in rough water or elevated transom heights. Because of the 5 blades, you will give up about 1 or 2 mph top end however.

Sal DiMercurio posted 05-07-2003 09:44 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
IHG, I have to dissagree on both the 4 blade & 5 blade.
The boat is only a 17' monauck with a ton of hp.
A 3 blade s/s Stiletto 13.25 x 23 will break his neck out of the hole, & should push that boat to close to 55 mph, plus lift the whole hull at the same time.
Only $249. at aftermarket, compared to about $550 [ retail ] for the 4 & 5 blade Merc props.
The 4 & 5 blade props are intended for the bass boat boys who fish in 18" of water & need to get up right now.
That Stiletto will put his small boat on plane in twice the length of the boat.
I'v tested 3, 4, & 5 blade props, their way, way, way over rated.
When I put the 200 on my 20' outrage, the top whaler dealer in N. Calif insisted I needed a 4 blade, I told him he dosen't even know how to mount an engine other then all the way down on the transom, & he knows less about props.
Saw him 6 months later & he slapped me on the back & asked if I broke 50 mph, when I told him 60, he said yeh, sure,......3 months later I blew off one of his boats that he rigged [ 20 outrage ] with a 200 or 225 with a 4 blade by at least 10 mph .
I'v never seen a 3 blade that couldn't do at least a little better then a 4 or 5 blade through out the whole rpm range, with the exception of holding the boat on plane just a couple mph slower.
Leave the 4 & 5 blades for the guys who run on pads & need to get out of the hole fast for fear of hitting something in the skinny water.
smgrogue posted 05-07-2003 11:50 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Larry--Funny you should mention that; I took a run at a new 13 x 22 (4.25" hub) High-Five that was on ebay recently, but it didn't reach reserve and I see has now been relisted. I don't know if 22 is the right pitch, but I thought given that this is one inch less diameter than the available Suzuki props it might spin up faster and not be too much prop for the motor. I was willing to take a chance on it if it were an outstanding buy, thinking I could resell it if it wasn't right. Do you think this prop would have worked out?

Sal--I always enjoy reading your posts, but I must admit, your advice creates somewhat of a quandry for me. I have heretofore formed the clear impression from researching this site that four and five blade props, and particularly the Merc High-Five, aid significantly in the hole shot of four-stroke motors (though sometimes at the cost of some top end performance). I am not all that concerned about top end performance, because I know this boat is going to be fast enough for my needs regardless of which high performance stainless prop I put on the motor. So my bias has been toward choosing a prop that favors hole shot over absolute speed. Are you suggesting that a three blade stainless prop would offer a superior hole shot vs the High-Five?

Sal DiMercurio posted 05-08-2003 12:26 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
No i'm not saying a 3 blade is better out of the hole then a 4 or 5, but keep in mind a 3 blade will put about a force 6 on g force out of the hole, do you really think a force 7 is better.
I guarranty you a 3 blade on that engine will put you flat against the back of your seat & throw everything that isn't tied down at the bow, either straight to the stern or out of the boat.
Do you need to be shot out of the hole from a 12 guage 3 inch magnum or from a 10 guage magnum?....thats the difference .
With all that hp on that little boat, your only going to need to put the throttle at only 3,500 rpms & your gonna be on plane in less then 3 seconds, do you think getting on plane in 2 seconds at 3,500 rpms is what you need ?
If so, get a 4 or 5 blade & put the hammer down to 6,000 out of the hole,......whats the advantage ?
I guarranty you couldn't tell the difference between a 3 blade & a 5 blade if you put the hammer down to wot out of the hole, all you will say is, thats to much power to give the boat & punish myself all at one time.
So you buy what you want at $249 or $550
jhill posted 05-09-2003 12:47 PM ET (US)     Profile for jhill  Send Email to jhill     
What about insurance on the montauk with that large of an engine. The plate says 100hp???
jimh posted 05-09-2003 12:58 PM ET (US)     Profile for jimh  Send Email to jimh     
There has been extensive and repeated discussion of the situation of boats powered in excess of the rating plate. The short answer is to buy insurance coverage that acknowledges the higher horsepower. Also check the laws of your local state or municipality. It is not against federal boating law to power a boat in excess of the ratings.
lhg posted 05-09-2003 02:57 PM ET (US)     Profile for lhg    
Without knowing how powerful the Suzuki 140 really is, compared to their 115, I would say that boat has got to do at least 50. If so, and with such a low gear ratio, you are going to need a 22" or 24" pitch prop.

I only mentioned the High Five, which I think is well worth the $125 (Sal - you're exaggerating on the price!) extra because of it's all-engine brand adaptability for re-sale, and adjustable venting, because 4-strokes can be slower our of the hole. The High Five is particularly recommended for I/O 4-stroke stern drive in waterski use. Mercury recommends the prop be run 1 1/2" elevated, but when run fully submerged recommends dropping down in pitch 2". Whether 22 or 24" pitch would work is a tough call, and can probably only be done with testing. I think I'd go with the 22 first, however.

I must repeat, however, I have absolutely NO experience with power output and torque Suzuki 4-stroke engines! With the HP ratings these days, that engine could be putting out anywhere from 126 to 154 HP. I'd bet on the lower side, since it is stretched from the 90/115 block. A friend just learned that his 1992 Yamaha 200 is really only putting out 170 HP, if the mechanic can be believed, but who is a racing guy!

Before buying any performance prop, which you really should do, I would fully test it out with the low cost aluminum you already have.
Run it as high as possible without getting slip to determine where you are with RPM's. If the 21 will barely turn up the full RPM's, you would want a 20" prop, since these performance props have a lot more bite than an aluminum. If the 21 will slightly overrev it, a 22 may be appropriate. If a 21 will badly overrev it, with lots of throttle left, you may be able to use the 24.

Bigshot posted 05-09-2003 04:39 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I have never seen any gain with a 4 blade.....EXCEPt when running a Hydraulic jack which you have. The rednecks all swear you need 4 blades when lifted high or else you'll lose the bite. I would try the 4 blade stilleto for $299 maybe. remember that engine has the V6 gearcase I believe. I also read in boating where they state that the 115 Zuki is the only 4 stroke they have driven that performs like a 2 stroke from design and I bet the 140 is even sweeter. The nice thing about 4 strokes is their power curve. Although holeshot suffers compared to a 2 stroke, when you have 5 people in it the holeshot will be almost identical as with 2 people. With a 2 stroke that is never the case. Whichever prop you chose i think ventilation holes are a must to get the rpms up initially. Ironically I have tried 6 props on my Suzuki and still not satisfied. I have 3 OMC stainless 13 3/8 x 17" and each ones gives me a dfferent redline....puzzling.
Sal DiMercurio posted 05-09-2003 06:40 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Ihg, I just called our Merc dealer & asked him for a price on a 13-1/4 x 23 s/s Merc high 5.... 5 blade.............$615 plus 8.50 %tx.
He said it's not an option for a 4 stroke suzuki 140 hp , it would have to be re-hubbed for another $75 to $100......thats over $700.
smgrogue posted 05-10-2003 01:50 AM ET (US)     Profile for smgrogue  Send Email to smgrogue     
I had a chance to put the boat in the water today to test the trolling system repairs. Since I was finally over the 3 hr. mark, I was able to run at WOT. Unfortunately I was doing my testing on a small lake that is only about a quarter mile across; each run I made I would have to back off before I ran out of lake and I was still gradually building rpms while adjusting the trim angle. I could only get her up to 5800 rpms (calm, cool, no wind) while running all the way up on the jackplate (cav plate is 2.5 inches above sole plate of the hull at the transom). I doubt that I am currenly underpropped, and may be a bit overpropped. Max rpm for the motor is 6200, although the tac tops out at 6k. Clearly, more testing is required.

The boat is certainly no flyweight. I checked it today, and it weighs a bit over 2000 lbs not accounting for any fuel load--thats pretty much just for the boat, motor, trolling system, 3 batteries and the pate tank.

For the record, the cost of the correct Merc hub kit for my motor is $48, and either the High-Five or the Trophy Plus can be had from for $430 delivered to my door. No try and buy though, but that service is not offered by the local dealer either.

Regardless of which stainless prop I ultimately buy, I'm taking Larry's advice and thoroughly testing the existing alum prop. That way the sages on this board can more effectively guide me toward the correct pitch in stainless.

By the way, I was wondering if rpms at WOT will increase over time as the motor gets broken in? I know that auto engines often don't develop peak rated hp until they are broken in, but I do not know if rpms in a marine 4s are similarly affected.

Sorry Tabasco, couldn't find my GPS when I needed it today (since found...I promise numbers next time out). Generally, I can say that the boat feels swift and powerful. Thanks again for all the input. Stephen

smgrogue posted 05-10-2003 02:08 AM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Sal--I just read your post again, and I think I can account for the discrepency between my figures and what your dealer told you. Recently I talked to my local Mercury dealer and also a guy with the Merc high performance prop division in WI. None of their 2002/2003 Merc application guides listed options for the Suzuki DF140 or my motor, which is rebaged a Johnson 140 4s. The Merc prop expert put me in touch with a fellow in the engineering department who was extremely helpful. He did indeed remember doing the engineering on the hub conversion kit for that motor, was able to look up the file on it and gave me the part number. (On a humorous note, he also asked me to call him back to let him know if it actually fit right!)

I checked the part number with my dealer and there are exactly 10 such hub kits in the country, all sitting in the main warehouse back in WI. Perhaps your local dealer gave you a figure based on some alternate option that is used when purpose built hub kits are not available from Merc? Regards, Stephen

smgrogue posted 05-12-2003 11:09 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
I now have additional performance data on my setup runing the 14X21 Suzi alum prop. Passengers: my 45 lb dog and myself (250 lbs). Fuel Load: about 12 ga. Conditions: light wind; light chop; 68 degrees. Jackplate: all the way up (2.5 inches above bottom of boat). Results per handheld gps:
Speed at idle in gear (750 rpm)--3.2 mph
2000 rpm--7.4 mph (motor trimmed all way in)
3000 rpm--22 mph (motor trimmed all way in)
4000 rpm--31.5 mph (motor trimmed all way in)
5000 rpm--39 mph (motor trimmed all way in and engine at WOT)
6000+ rpm--46 mph (WOT and motor trimmed at or very near max, gauge pegged a bit past 6k rpm)
When gradually backing off throttle, boat seems to fall off plane around 2300-2500 rpm (annoying).

Mfr. spec. for "operating range" is 5600 - 6200 rpm.

As the data suggest, the boat does 5000 rpm at WOT and trimmed all the way in, and then gains 1000+ rpm as the motor is trimmed out. I did't expect rpms would climb quite so much as I trimmed out; there may have been some room left to go but I do not have my water pressure guage hooked up yet and lighting conditions were making it difficult to keep an eye on the telltale.

I suspect that I may still benefit by raising the motor one more hole, at which point I would be 5.5 inches set back and 3.0 inches up. Hopefully would gain a few more rpms without blowout.

It seems the 14X21 is within acceptable limits or even verging on too much prop for the boat if I were going to run alum all the time (it should be fine for my backup). I really wonder if the alum prop looses a LOT of bite on this motor.

Assuming I need to drop down in pitch when going to stainless, the question of the day is how many pitches and does it depend on the number of blades I would be running? Keep in mind that I may gain some rpms by going up a hole, and I will probably test this before my purchase decision.

Props for my 4.25" gearcase motor that I am still interested in: From Merc -- High-Five (but smallest is 12.75x20; too much prop?); Laser II (maybe the 14x19 would do the trick?); Trophy Plus (perhaps a poor match as Larry points out, but it does come in lower pitches--even down to 17"). From Stiletto -- Obviously I need to learn more about their 3 & 4 blade props based on the recs from Sal and Bigshot.

As always, your questions, comments and recommendations are appreciated. Thanks, Stephen

Sal DiMercurio posted 05-13-2003 01:07 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Stephen, it sounds like your pretty close right now, the only thing I see not needed is the 14" diameter for a Montauk.
You could drop down in Diameter to a 12-1/2 or 13 dia., should give you another 100 or so rpms.
Your going to have to try a s/s first before you buy because you might loose more rpms because the s/s bites better.
I don't feel that high five 12.75 x 20 is going to be to much prop, your dropping down 1-1/2 inches in dia & an inch in pitch, should put you close to 6,200.
I would certainly try a Stiletto 13.25x21 at $259.00, should get you close to 6000 - 6100 which would be close enough.
By the way, that is a good report you gave, but put a water preasure guage on that boat before you suck air & really have a problem.
Aftermarket has the Stiletto at that price, but you can test a Michigan Raptor, then buy the Stiletto as the props are darn near identical, but the Raptor is more expensive.
Overtons will allow you to exchange if it's not right, but their about $20.00 more then Aftermarket.
tabasco posted 05-15-2003 07:57 AM ET (US)     Profile for tabasco  Send Email to tabasco     
Thanks for sharing the info with the members. My feeling is if I am getting 50.3MPH with my merc 115 four stroke you should see 55-57MPH with a SS prop once the motor is broken in.

Please continue to keep us informed

bluerunner posted 05-15-2003 03:08 PM ET (US)     Profile for bluerunner  Send Email to bluerunner     
Hello gentlemen, I am a first time poster to this forum and I would like to say that the content and discussion is excellent. I have been a frequent visitor over many months but I never felt as though I could contribute anything that your members didn’t already know. However, having done some research on theoretical speed calculations using different props, I prepared the following chart that illustrates the theoretical top speed with no prop slip, and the speed with a 10% slip on the Suzuki 140. Please note that the calculations are my own using formulas from some of the “Prop Calculators” available at several websites. Although I believe the calculations to be correct, I make no such warranty. I hope this is helpful. Gear ratio used is 2.38.

Reading the chart from left to right the numbers are:

Pitch, RPM, Top Speed @ 10% slip, Theoretical Top Speed No slip.

19, 6000, 40.8, 45.4
20, 6000, 43.0, 47.7
21, 6000, 45.1, 50.1
22, 6000, 47.3, 52.5
23, 6000, 49.4, 54.9
24, 6000, 51.6, 57.3

19, 6100, 41.5, 46.1
20, 6100, 43.7, 48.5
21, 6100, 45.9, 51.0
22, 6100, 48.1, 53.4
23, 6100, 50.2, 55.8
24, 6100, 52.4, 58.3

19, 6200, 42.2, 46.9
20, 6200, 44.4, 49.3
21, 6200, 46.6, 51.8
22, 6200, 48.8, 54.3
23, 6200, 51.1, 56.7
24, 6200, 53.3, 59.2

dogfish2 posted 05-15-2003 11:58 PM ET (US)     Profile for dogfish2  Send Email to dogfish2     
I"ve been following this thread and everyone seems to have good ideas based on their experience. Your boat with all that h.p. whould literally "FLY," as the others suggested, in the 50-55 mph range. I just put a 115 4s on my 2000 Montauk, which isn't as fast a hull as the 170 Montauk, and after experimenting with four different size and types of props, settled on a 13.25"x18" Vengance (5500 rps/ 46.5 mph)and a 13/25"x 17" Ballistic (5800 rmps/ 45 mph). I had expectations of 50 mph, but have accepted reality. Just thought I would give you a little comparison with Tabasco and mine. I, too, think the s/s props will enable you reach a higher speed. Thanks for the test reports. Good luck.
tabasco posted 05-16-2003 02:11 AM ET (US)     Profile for tabasco  Send Email to tabasco     
First how many hours do you have on the new motor? When mine came out of the box after a few hours of breakin it also would do around 45mph but after about 15 hours of use and learning the correct adjustment to the motor trim the speed climbed up to over 50MPH as per the GPS.

Keep the faith you will make 50 yet ........if not in the water will do it in birthdays ;-)

tabasco posted 05-16-2003 02:19 AM ET (US)     Profile for tabasco  Send Email to tabasco     
PS: Im running the stock SS Vengence that came from Whaler on my 90 HP four stroke
smgrogue posted 05-16-2003 09:32 AM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Thanks to everyone for all the feedback.

Bluerunner--I don't know what hull factor you used in developing your calculations (I'm assuming you used the Propeller Calculator in the Reference Section), but one of your calcs happens to correctly describe to boat's current performance. With the current 21" alum prop and at an estimated 6100 rpms, the boat goes about 46. Could just be a happy coincidence, but the formula seems accurate for now (though I agree with tabasco that the boat should get faster even with the alum prop as it breaks in).

One interesting note. I called Stiletto Propellers and they unfortunately do not make propellers for Suzuki motors. Not to be deterred in my quest for SS prop, I finally found someone locally that can loan me a 12.75x22 High-Five to try out. This is definately too high a pitch versus the 12.75x20 High-Five I suspect is the right match for my needs, but it should give me a good relative reference as to what the 20" pitch would do on my boat. What's the general rule of thumb with a SS prop--that you gain roughly 200 rpms for every 1" decrease in pitch? So, hopefully the 12.75x22 would develop between 5600 and 5800 rpms.

I now have the Merc hub kit for my motor, so I'll be able to try various Merc props as the opportunity arises, and hope to try a Merc 3 blade stainless at some point as well. I will, of course, post my results. Thanks, Stephen

lhg posted 05-16-2003 12:09 PM ET (US)     Profile for lhg    
I just noticed that Bass Pro catalog sells the Mercury Flo-Torque II hubs, for all brands of engines, including Suzuki 140's, for $40. They are readily available. Sounds like some of the Dealers referenced in this thread are a bit overpriced or un-informed!

Incidentally, when you buy a Mercury performance prop, say for $400, that includes the hub of your choice. All Mercury props seem to boxed at the factory with the Mercury hub (in a separate little box), but the selling Dealer can pull that out and put in any hub kit needed, at no extra charge.

Bigshot posted 05-16-2003 12:56 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Get a water pressure guage and jack that thing up. my 70 is 4 inches up and handles fine. With a 140, that thing should do well over 50.....something aint setup right or prop is screwy.
dogfish2 posted 05-16-2003 10:46 PM ET (US)     Profile for dogfish2  Send Email to dogfish2     
PATIENCE is the operative word here. We are like kids with new toys. But everyone is correct is advising to break in the motor before making too many changes.
Tabasco: I have 11 hours on the 115 Merc 4s. Will be able to put on a few more this weekend. Something is going to have hit 50, age or mph, preferably the later.
Another question for you guys is the difference between a Ballistic prop and a Stiletto prop. Differences in performance??
bluerunner posted 05-17-2003 12:39 PM ET (US)     Profile for bluerunner  Send Email to bluerunner     

I did not use a hull factor in developing my calculations. Instead, I used a slippage factor of 10%. From everything that I have read, 5% to 12% slippage at speed is probably pretty close to real life for boats in the size and weight range that are being discussing here.

I used an excel spreadsheet to produce the above speed chart because I wanted to see multiple Prop Calculations on a single page. I was not aware of the Propeller Calculator in the reference section of this site until you mentioned it. It is one of the best that I have seen and one of the very few that allows you to enter zero slippage to determine the maximum attainable speed for a given Gear Ratio, Prop Pitch, RPM and Slip combination. The mathematical formula I used is the same.

According to the Prop Calculator on this forum and others, a 22-pitch prop on an engine with a 2.38 gear ratio would reach 50 mph @ 6000 RPM only if the slip factor was down to 4.8%. Certainly possible, but probably not typical. A pitch of 23 would reach 50 mph @ 6000 RPM with an 8.94% slip factor. Probably much more attainable.

smgrogue posted 05-17-2003 03:39 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Bluerunner--Given how your data was presented, it was a silly question for me to ask in the first place, now that I think of it. The "Hull Factor" is a key variable in utilized in the predicted speed formula set forth in the Propeller Basics--Part II article contained in the reference section. I understand now that you were using a different algorithm (similar to the one used in the propeller calculator) to solve for speed. The way I had been using the propeller calculator was to use Clark Roberts' formula first to try to estimate speed and then input it as an assumed variable (along with rpm, gear ratio, and slip) in order to solve for pitch. Regards, Stephen
bluerunner posted 05-17-2003 05:14 PM ET (US)     Profile for bluerunner  Send Email to bluerunner     

Not silly at all smgrogue. I think if you work with just the components of the Prop Calculator you can develop some pretty good data. I think that the people who developed the Prop Calculators deserve our thanks.

bluerunner posted 05-18-2003 09:10 AM ET (US)     Profile for bluerunner  Send Email to bluerunner     

If you would like to see some published in-water tests for the Suzuki 140, go to the Suzuki website: There are a small number of boat tests that may be useful to you. Note that there is a discrepancy in the Aquasport Osprey test. The prop is listed as 3 x 14 x 22, but the part number is for a 3 x 14 x 20. The top speed suggests it may actually have been a 20.

bluerunner posted 05-18-2003 09:18 AM ET (US)     Profile for bluerunner  Send Email to bluerunner     
Corrected web address. Hope this one works.
tabasco posted 05-22-2003 07:21 AM ET (US)     Profile for tabasco  Send Email to tabasco     
After checking the Suzuki site mentioned above none of the boats tested were able to break the 44-45 MPH range. Am I missing something? Maybe the manufacture is just not running the right prop. It doesn't make sense to me. There one boat tested that weighs just a little more than the Montauk 170 and has the same design and yet it only achieves 44MPH.

So why am I achieving 50.3 MPH with a 115HP EFI Mercury on the same boat (according to GPS)?

bluerunner posted 05-22-2003 02:21 PM ET (US)     Profile for bluerunner  Send Email to bluerunner     

The Mercury 115 EFI has a gear ratio of 2.07. The Suzuki 140 has a gear ratio of 2.38. If these engines were on identical boats with identical props, say a 20-pitch, and both were running at 6000 RPM with an identical slip factor of 10%, the boat with the Suzuki would be running at 43.0 mph while the boat with the Merc would be running at 49.4 mph. Assuming all the same variables, the Suzuki would have to run a 23-pitch prop to reach 49.4. See the Prop Calculator in the reference section to verify this data. Be sure to use two decimal places.

If you are running a 19-pitch prop at 6000 rpm and getting 50.3 mph your calculated slippage is 3.55%. Not typical, but certainly possible. If you are running a 20-pitch prop at 6000 rpm, your calculated slippage is 8.37%. At 6100 rpm, the slip factors would be 5.13% and 9.88% respectively. Again, see the Prop Calculator in the reference section to verify this data.

The chart below illustrates the theoretical top speed with no prop slip (this is not achievable in the real world because there is always some slippage) and the top speed with a 10% slip for the Mercury EFI 115. Slip factors below 10% are somewhere in between.

Reading the chart from left to right the numbers are:

Pitch, RPM, Top Speed @ 10% slip, Theoretical Top Speed No slip.

18, 6000, 44.5, 49.4
19, 6000, 46.9, 52.2
20, 6000, 49.4, 54.9
21, 6000, 51.9, 57.6

18, 6100, 45.2, 50.2
19, 6100, 47.7, 53.0
20, 6100, 50.2, 55.8
21, 6100, 52.7, 58.6

tabasco posted 05-27-2003 10:55 PM ET (US)     Profile for tabasco  Send Email to tabasco     
Bluerunner- didn't realize that the Suzuki had a 2.38 gear ratio and that makes the difference.
tabasco posted 06-03-2003 07:45 PM ET (US)     Profile for tabasco  Send Email to tabasco     
So what's the latest on your testing? Waiting to see some new numbers.
smgrogue posted 06-03-2003 11:19 PM ET (US)     Profile for smgrogue  Send Email to smgrogue     
Tabasco--I was going to hold off on updates until I had some real numbers to report, but I'll give a brief update.

I was able to locate a 13x22 High-Five for testing. I was concerned that this might be too much prop for the motor and my limited testing confirmed this. I didn't bother with test data; couldn't get her up anywhere near 6k. Based on this experience I procured a 12.75x20 High-Five. I've only had it on my "pond" so far and have not had a chance to run it on a large body of water (soon, hopefully), but I was able to make a couple of observations right off the bat. I am sure the motor will top 6k with this prop; if anything I may be a touch underpropped with this one--I'll need more lake to know for sure.

One thing is for sure, this prop is very hot off the line compared to the 14x21 alum or the 13x22 H-F. The boat really jumps out of the water.

I know that motors tend to get faster as they get broken in. Does this mean that if the motor currently turns say 6k at WOT, that it will eventually turn more rpms as the motor breaks in, or will it simply develop more hp at the same 6k rpms and therefore go faster?

That's all I have for now. I hope to be able to post some data soon. Regards, Stephen

tabasco posted 06-10-2003 08:19 AM ET (US)     Profile for tabasco  Send Email to tabasco     
In my opinion it won't reach higher RPM's once it's broken in however, it will take less time to reach those higher RPM's
lhg posted 06-10-2003 05:50 PM ET (US)     Profile for lhg    
Stephen - Reading through all of this is interesting, and I'm happy to see that the Mercury High-Five series of props run well on the Suzuki. They are one wicked looking prop.

With this extensive testing and reporting by many, it appears a few observations can be made. First being, unfortunately, Suzuki may be utilizing the 10% allowable "over rating" of HP on the engine, and it really only is about 125 HP. After all, they are stretching the rating off the 90/115 block. My guess is that the Honda 130 4-stroke is also over rated. Performance wise, the Evinrude Ficht 135 or Mercury Optimax 135 V-6's will probably out-run them easily, but the Mercury I know is more like a 140-145.

Getting back to the Suzuki 140, and looking at my Mercury prop charts for the similar gear ratios, it appears a 20" High-Five can deliver up to 45MPH and the 22" pitch 49 MPH.

An interesting fact about High Fives is that their RPM ability is related to engine mounting height. They need to be at 1 1/2" to perform properly, when compared to pitches of elephant ear props. If they are run submerged, as with a conventional alum or SS, pitch has to be dropped 2" and same speed will still be attained. So in your case, if the 20" HF seems a little light, drop it down a little to control high end RPM. Conversely, if the 22 seems a bit much, raise it up a little, and open up the vents to "large", and see how it does.

While I'm on the subject, I looked at the prop charts for Ray's rig, with the 2.07 gearcase Merc/Yamaha 115 4-stroke. They are showing a Mercury 18" Vengeance Prop at 45mph top speed capability. The 18" of pitch does not appear capable of pushing the boat to 50.
Ray, is your GPS working OK? If the boat does indeed do 50, a 20" 3-bladed Mercury Laser II, lifted 1 1/2" would seem to be called for. The bow lift from the prop alone should add about 2 mph to top end.

With both of these boats, it seems the true HP is somewhere in the range of 110-125. I think BW published figures of 43 MPH with the 2 stroke Mercury 90, an engine which I think really puts out about 105HP. Once again, all of this makes sense performance wise.

Finally, while we're on the subject of overpowering a new 170 Montauk, here are some more performance figures from the Mercury Prop catalog, using the total load weights of the 170 w/engine etc:

Mercury 135 Optimax: 21"pitch and 52 MPH.
Mercury 150 EFI/Optimax: 23" pitch and 63 MPH.
Mercury 175 EFI/Optimax: 25" pitch and 67 MPH!!! (Sal - this one's for you).

tabasco posted 06-11-2003 09:03 AM ET (US)     Profile for tabasco  Send Email to tabasco     
I have crossed tested my Garmin 2006 GPS with my laptop computer GPS ......same results. Maybe I just lucked out and got a blue printed 115HP motor ;-) My personal belief is that top speed can vary 5 MPH just by triming the motor. I recently installed a trim meter so that it will be easier to find the motors sweet spot.

If it every stops raining on weekends here in the east I will get to try out the new meter.

lhg posted 06-11-2003 05:25 PM ET (US)     Profile for lhg    
I have heard that for really accurate speed calculations, DGPS should be used.

If that 115 Merc does push the boat to a true 50, that's one strong engine. The 170 is about the same weight as an Outrage 18, and most say it takes 150 HP to move it 50 MPH.

tabasco posted 06-23-2003 01:29 PM ET (US)     Profile for tabasco  Send Email to tabasco     


Sal DiMercurio posted 06-23-2003 04:24 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Ihg, 67 mph in a Montauk is flat out cookin, whew!
tabasco posted 07-01-2003 08:39 AM ET (US)     Profile for tabasco  Send Email to tabasco     
Smgrogue- It's now July must have some new results for us!
tabasco posted 07-13-2003 07:47 AM ET (US)     Profile for tabasco  Send Email to tabasco     
Smgrogue- Still waiting to hear your resullts!!!!
tabasco posted 07-14-2003 03:26 PM ET (US)     Profile for tabasco  Send Email to tabasco     
I guess the results are not good or you whould have posted them
tabasco posted 07-14-2003 03:27 PM ET (US)     Profile for tabasco  Send Email to tabasco     
sorry for the typo" would have posted them"
tabasco posted 08-25-2003 07:54 AM ET (US)     Profile for tabasco  Send Email to tabasco     
So Stephen......... we haven't heard a word from you since June 3rd. Hope you are OK. How about an update to us forum members on how the repower worked out. I'm sure by now you have selected the correct size and are running a SS prop. HOW ABOUT SOME NUMBERS !!!


InHerNet posted 09-08-2003 08:13 AM ET (US)     Profile for InHerNet  Send Email to InHerNet     
I would like to know the numbers also.

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