Forum: WHALER
  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  1978 Montauk, 115-HP Evinrude

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   1978 Montauk, 115-HP Evinrude
boater12 posted 06-16-2006 01:51 AM ET (US)   Profile for boater12   Send Email to boater12  
I have a 1978 [here the author wrote "'78" but I have changed this and all other year dates to a four-digit prepresentation as is explicitely requested in our style guidelines--jimh.] Montauk with a 1981 Evinrude 115-HP that I just from the original owner who used both on Lake Michigan. It is a freshwater boat and engine, no rust or anything, professionally serviced engine, bottom paint on boat. The engine seems to be running fine, but I just wanted to check what boat speed I should be seeing. With 750-lbs of added people, bags, equipment and other gear, I am reading a top speed of 29.4 knots consistently [29.4 nautical miles per hour is about 33.8-MPH--jimh]. Does this sound like it is about on target for a 115-HP on a Montauk? I thought that I might see something a bit higher with a 115. Any tips on getting the right performance? I haven't had the lower unit oil or anything changed since I think it seems to be running well. Is it worth it to get a tune-up and lower-unit oil change/engine lubrication? Also, I have old fuel lines and was wondering if they may be inhibiting fuel flow?

Also, I am a bit confused as to why my engine speed is topping out at 5,320-RPM. (I have a digital OEM gauge). The highest I've ever seen in three half-day hard sessions is 5,440. I thought that 5500-6000 was a more normal RPM range? Any way to fix this? Is my prop pitch wrong or something? [Give me] suggestions on the proper pitch and on a good propeller for me if I choose to go that route. I'd prefer stainless in that scenario I guess but any suggestions are welcome.

Also, I was wondering if the older motors just didn't have that much grunt in reverse. I can go in reverse and have no problems engaging or anything but there is basically no chance of my moving with anything that begins to resemble the maneuvering thrust of the newer engines. Any thoughts?

Thanks so much in advance. This forum (and the Whalers) is amazing!

Chris Goodrich

pasino posted 06-16-2006 07:51 AM ET (US)     Profile for pasino  Send Email to pasino     
Chris, I have a 1980 Montauk with a brand new 115-HP Yamaha four-stroke, Yamaha steel-teflon prop 19-inch pitch, old bottom paint. Top speed with me (260 lbs) a skinny friend (160 lbs) tank and 350-lbs of gear is 39.7 knots [39.7 nautical miles per hour is the equivalent of 45.6-MPH--jimh] at 5800/5900.
On my very little experience 19-inch pitch with 115-HP is the correct pitch
Tom W Clark posted 06-16-2006 10:11 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris,

My tip for getting the right performance is to remove some of that 750 pounds! It is totally unfair to compare your boat's performance to others if you are loaded down like that. Take you boat out by yourself and do a little testing. I think you will see the performance improve substantially. A top boat speed 34 MPH does sound a bit low for your boat. With a light load I would expect about 45 MPH.

I believe your motor redlines at 5500 RPM but your Owner's Manual will clarify that.

As to reverse, it has nothing to do with the motor and everything to do with the propeller. EXACTLY what propeller do you have on there now?

- Material?
- Diameter?
- Pitch?
- Brand ?
- Number of blades?
- Part number?
- Condition?
- Maximum RPMs with this prop when boat is lightly loaded?
- Mounting height of motor?

Teak Oil posted 06-16-2006 10:27 AM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
A 1981 115 is powerhead rated and not prop rated, so it wont be as fast as a modern 115. Still it should be going faster, around 45-MPH as Tom suggested.

There is nothing wrong with your rpms, that motor redlines at 5500 so anything from 5000-5500 is fine.

I would run an OMC aluminum 13x19 propeller, it is a good performer for aluminum, and cheap. You should be able to get near 5500 rpms trimmed out (you are timming the motor out right?) with that prop.

You do have power trim right? If you dont there is 5mph lost right away

boater12 posted 06-16-2006 10:57 AM ET (US)     Profile for boater12  Send Email to boater12     
Guys,

Thanks for the advice. One question for teak oil: what do you mean by "trimmed out"? I do have power trim and tilt and I assume that "trimmed out" means with the needle in the middle of the gauge - that is, between up and down? Is this correct?

Also, do you think that substantial weight difference would really cause a 10 mph loss in speed?

Tom W Clark posted 06-16-2006 11:02 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris,

No, 10 MPH is a lot to attribute to extra weight, but it may account for several MPH which combined with a motor mounted all the way down on the transom, an incorrect propeller and conservative trim, could make a HUGE difference.

Trimmed out means trimmed almost so far up that the motor starts to ventilate and loose speed. Forget the gauge, look at the motor. If it is not tipped up a LOT then you nee to trim it out some more.

I recommend the motor be mounted one hole up on the transom and that a good stainless steel propeller be used.

boater12 posted 06-16-2006 11:06 AM ET (US)     Profile for boater12  Send Email to boater12     
BTW my prop is an aluminum 13 x 19, so that shouldn't be the problem. Would a service (oiling, et cetera) be worth the money?

I'm going out to test the boat with lighter weights right now but would still love some suggestions!

Thanks!
Chris

Tom W Clark posted 06-16-2006 11:15 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris,

Actually, if you say you have a 19" prop, then that probably *IS* the problem. There is no way you should be able to turn a 19" prop at 5320 RPM and only 29.4 knots. To do so suggests a propeller slip of 30 percent or about three times what we would expect!

Is the propeller mangled? Has it been reworked?

boater12 posted 06-16-2006 11:20 AM ET (US)     Profile for boater12  Send Email to boater12     
Tom,

From what I see the prop isn't mangled and hasn't been reworked. I'm thinking, though, that I may replace it. Any suggestions on a good model for me? Also, I have been trimming out wrong if that is the case - the engine has been down way too low. Thanks for that advice.

Chris

Tom W Clark posted 06-16-2006 11:28 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris,

Before you buy anything, go out by yourself and test the boat again. Trim it out and see what you get for top speed and RPM.

If your current prop is 13" x 19" then it is an aftermarket prop. OMC never made an aluminum prop for your motor that size.

Once you have done some more testing and report back with some good data, I can make a recommendation for you. The OMC/BRP SST props would be very good as are the Stiletto Advantage Is.

bsmotril posted 06-16-2006 12:26 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I have an 84 Montauk and 84 Johnson 100 HP Commercial Motor. With a 14.5 x 21" SST prop I'll just barely hit 45 mph with a light load at 5400 rpm. I'm going to try an SST 19" in the next few days and will post the results. I would think your motor should be able to run a 21" prop if you run light most of the time, a 19" if you run loaded.
BillS
boater12 posted 06-17-2006 12:30 AM ET (US)     Profile for boater12  Send Email to boater12     
OK so the RPM thing seemed to work itself out and trimming out helped a bit. I ran (with 500 pounds people and gear) right around 37-38 mph top speed at 5400ish RPMs with a 13 x 19 aluminum prop. Does this sound like it's about the area I should be in for speed now or am I still underperforming? I trimmed the engine up like Tom said and that helped a bit but I am wondering if perhaps my prop is not the most efficient. If replacing the prop would give me another 5-10 mph I definitely think that it would be worth it but I'm just wondering if maybe I'm performing properly now?

If a prop change sound like a good idea I'd love to get some suggestions. If anyone has any other tips I'd greatly appreciate them. For instance, could the engine be mounted too low on the boat? I really don't know..which hole is it meant to be mounted on?

Thanks!
Chris

Tom W Clark posted 06-18-2006 01:07 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris,

37.5 MPH at 5400 RPM still does not make sense. That's 23 percent propeller slip. WAY too much for a good prop.

I suggest you try a BRP 13-7/8" x 19" #176572 or a Stiletto Advantage I 13-1/4" x 17" #21317

Ideally the motor should be one hole up on the transom, but I suspect it is mounted all the way down utilizing the blind holes. This was typical on Montauks in the 1970s and 1980s.

Teak Oil posted 06-18-2006 09:26 AM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
Tom--OMC makes a 13x19 aluminum propeller. That propeller was on my boat when I bought it. Mounted all the way down on the transom I would get around 42-MPH with two guys in the boat at around 5,300-RPM if memory serves, and that was with a 90-HP motor.

Even mounted all the way down on the transom this boat should be getting in the low forties, period. Raising the motor will help, but there is a problem here that needs to be fixed before you start spending money.

When you trim out the motor, raise it until either the bow starts to slightly "porpoise" up and down, or the prop starts to slightly cavitate, whichever comes first. Then trim down a hair, and this is going to be your optimum trim angle. At this setting, your wake should be as flat as possible. Distributing your weight and passengers toward the rear of the boat will also help top speed and economy slightly.

If you cannot get anymore speed messing with the trim then try another prop or two.

The motor should be raised for optimum performance, but if it is mounted in the blind holes it is not a simple procedure unless you are willing to purchase a jack plate.

jimh posted 06-18-2006 09:44 AM ET (US)     Profile for jimh  Send Email to jimh     
[Converted nautical miles per hour into statute miles per hour. Generally, in small boats, the boat speed is stated in statute miles per hour.]

If you know the engine gear ratio (which may be 2:1), you can use the PROPELLER CALCULATOR to assess the propeller SLIP. A good propeller ought to be able to run with a SLIP of below ten-percent.

See: http://continuouswave.com/cgi-bin/propcalc.pl

If the motor is trimmed out too far you will see the propeller SLIP increase.

Tom W Clark posted 06-18-2006 10:38 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
OMC does';t make anything a anymore. They used to make a 13" x 19" aluminum prop. BRP does not make such a prop though they do make an SST in that size.

At any rate it would NOT appear to be the correct propeller. The slip numbers I have given above were calculated with the propeller calculator. The Gear Ratio of those OMC v-4s is, in fact 2:1.

I agree raising the motor may help but not solve this mystery. That is why I a new prop would be the first thing to try.

I could also well be that the 25 year old motor is simply not as strong as it once was. Indeed i would expect this to be so. Motors wear out and loose compression, etc. They may run smoothly but not generate as much power as they once did.

It could also be the the hull is waterlogged to some extent. Adding a lot of weight will slow a boat down too.

In this case I suspect the combination of a lot of little things may be adversely affecting the performance and limiting the speed of Chris's boat.

Binkie posted 06-18-2006 10:54 AM ET (US)     Profile for Binkie  Send Email to Binkie     
Chris,
You say that the boat is bottom painted. Is it kept in the water full time. If this is the case the bottom might be very dirty and full of growth. This could be the main reason for poor performance, along with running the motor tucked in to far. I hope you wouldn1t buy a boat with out having it hauled and check the bottom, anyway, so this might be a good time to check the condition of the bottom. Leaning over the side, and running your hand under the hull won`t tell you much.

Rich

boater12 posted 06-19-2006 12:27 AM ET (US)     Profile for boater12  Send Email to boater12     
Guys,

Thanks so much for all of your input. I was out again all day today (six hours running pretty hard) and topped out around 38 mph again with a couple people on board. The engine seems to be running fine, if a bit slow for its size.

As to the bottom paint/other suggestions for my problem, I don't think that those are factors. The boat has bottom paint but is trailered and washed/scrubbed after every use. It is in great condition and there is only one nickel-sized repair on the bow. So I doubt that the hull is waterlogged and there is definitely NO growth on the bottom.

Does anyone have one of the props that Tom suggested that they aren't using and might be willing to get rid of a little cheaper than those huge retail prices? This should probably go in the wanted section but I'm hoping..

I also have one more problem that could be a huge factor (I'm starting a separate post on it) that I've had an issue with every time I've gone out.

Thanks so much for your help!
Chris

boater12 posted 06-29-2006 06:07 PM ET (US)     Profile for boater12  Send Email to boater12     
Thanks to everyone for their extensive advice in selecting a prop for my Montauk that would be the right size and pitch. Now I just have to consider whether or not the decent-sized investment would actually be worth the money.
My engine: a 1981 Evinrude 115, turning 5300-5500 RPMs WOT.

My current prop is a 13" x 19 aluminum. The edges are nicked up, though not too badly, and the prop is in decent shape overall - the edges look to be about the only places with damage but I'd guess the prop is original, which would make it a 1981.

The prop I'd upgrade to: a SST Advantage 13 1/4" x 17 (Tom Clark says testing has shown that this is comparable in pitch to the aluminum 19) at a little over $200.

So, my issue is this: I run with about 600 pounds of gear and people almost all the time. The boat's in good shape, bottom painted but not recently, trailer kept, motor freshwater until this year. The highest speeds I've seen are between 37 and 39 mph. My guess is that the problem must be with the prop - using the calculator, this would mean about 20% slippage. Is it worth the $200+ to invest in a new prop? Does anyone have a clue on what my slip percentage would be with that new prop (top speed at 0% slip, which is unrealistic, is almost 50 mph at 5500 RPMs, which I believe is the top of my operating range)?

Just wondering what the consensus is - is this a purchase that is worth the money? Will I just gain 1-2 mph or will I quite possibly gain 5-6 mph?

Thanks in advance!
Chris Goodrich

Teak Oil posted 06-29-2006 07:49 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
You will not gain 6mph by going to a 17" prop, its not possible unless you are turning 6000 rpms, and your motor redlines at 5500. You will gain holeshot and better handling with an SS prop. I would get one, but you can probably find one for less than $150 on eBay.

The important thing is to get between 5200 and 5500 rpms at wide open throttle.

bsmotril posted 06-29-2006 10:20 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Are you sure you want to go with a 17" prop? I have a Sakonnet (old style hull) with a 1986 JohnsonRude 90hp. It turns a 19" SST stainless prop and will do 45mph. I also have a 1984 Montauk and 100HP johnson of the same vintage. It does 41 mph with a stainless OMC SST 19" prop, or 43 with a very worn SST 21". The gearcase on the 100hp is the larger V6 gearcase, so the prop is bigger diameter than on the 90hp. I would think you'd want to go with a 21" unless you are going to run fully loaded, then a 19" should do it. BillS
Tom W Clark posted 06-30-2006 12:50 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
It is not an SST Advantage, it is a Stiletto Advantage I.

SST is a propeller model name trademarked by Outboard Marine Corporation (OMC) c. 1980. The SST line of propellers is still manufactured by the current owner of the assets of OMC, Bombardier Recreational Products (BRP).

A 17" Stiletto Advantage I will perform like an OMC/BRP SST prop in a 19" pitch.

blacksmithdog posted 06-30-2006 07:53 AM ET (US)     Profile for blacksmithdog  Send Email to blacksmithdog     
I used to run a 115 Merc (straight 6) on my 1976 Montauk. It would run in the low 50's. When I first put the motor on the boat, the bottom was painted (with a brush, and it had streaks in it) and it would only run in the low 40's. I had the paint removed and the bottom re-gel coated and gained another 10 mph.
boater12 posted 06-30-2006 11:31 AM ET (US)     Profile for boater12  Send Email to boater12     
Thanks to everyone for their help in diagnosing this problem. I just ordered a new Stiletto Advantage I 13 1/4" x 17 from Tom and will get back to everyone with the results.

Again, thanks!
Chris Goodrich

Post New Topic  Post Reply
Hop to:


Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.