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  MONTAUK: Change to 90-HP from 100-HP

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Author Topic:   MONTAUK: Change to 90-HP from 100-HP
Lame Duck posted 07-18-2010 01:41 PM ET (US)   Profile for Lame Duck   Send Email to Lame Duck  
Hi group. What change in performance I can expect with my [1989] Montauk if my faithful but aged Mercury 100-HP blows up and I have to re-power with a 90? I have a [1989] [MONTAUK] with a Mercury 100, both of which I bought new. Although I’ve never had the top speed checked, I can honestly say I’ve never been beat by any boat powered by a similar-size engine, unless it was a performance hull. I’ve run along side other Montauk boats, and it has been a dead heat. Not only does [the MONTAUK with 100-HP] have plenty of top speed, but it has gobs of low end torque for pulling skiers out of the water as well--very important since I sometimes [water ski] barefoot or used to. How do the new 90-HP outboard motors perform compared to the old 100-HP I’m presently using? I sure hate the idea of giving up performance when I have to re-power. [An unidentified outboard motor with] 90-HP is 80-lbs heavier to boot--don’t need that hanging on my transom!

Thanks,

Al Phillips

contender posted 07-18-2010 02:28 PM ET (US)     Profile for contender  Send Email to contender     
I heard one time you had to be going 32 mph to [water ski] barefoot, but do not know if it is true or not. I guess you are going from a two-cycle 100-HP to a four-cycle 90-HP [whose weight is] 80-lbs [greater]. Do you have your [mind] set on a four-cycle motor? Since the difference is more than 15-years you will probably need new controls and everything else. Since you are going to have to change everything I would look at the Evinrude. Think you would save on the gas and the weight, and the bolt holes in the transom will still be the same, Take care.
jimh posted 07-18-2010 05:44 PM ET (US)     Profile for jimh  Send Email to jimh     
Boat speed is proportional to horsepower and inversely proportional to weight. If you decrease the horsepower and increase the weight, both changes will tend to reduce speed.

If your current motor is a six-cylinder motor, you should also consider that changing to a three-cylinder or four-cylinder motor may also affect performance, that is, reduce speed or power.

Since your inquiry is simply hypothetical, it makes no sense to talk about any engines available presently. When you reach the point of buying a new engine there will likely be different models available then compared to now. We can help you pick a good engine when the time to re-power arrives.

jharrell posted 07-18-2010 07:04 PM ET (US)     Profile for jharrell    
There is one 100hp motor currently in production the Suzuki DF100. This is actually the old DF90 re-tuned to 100hp. However it is very heavy at 416 lbs. It is a strong motor at 1950cc a very large displacement and the largest new motor you can repower with and stay in the 100hp limit.

I myself would not sacrifice the weight just to get the extra 10hp, the new DF90 from Suzuki is only 340lbs and has various improvements to get much better gas mileage.(8-9mpg vs around 6mpg on the DF100 at cruise).

If you don't mind exceeding the HP limit I believe some here have put a 115 ETEC on a 17 Montauk classic with good results( and top speeds above 45mph). At 375 lbs it is still lighter then the DF100 with more HP although mpg would probably be around 5 at cruise.

From what I can gather here and from boat tests a modern 90 should get between 39-45 mph depending on how its proped and which engine. For instance the 3 cyclinder Etec at 1296cc seems to top out at 39-40mph on a 17, where a 4 cyclinder 1502cc 90 Suzuki should get 42-43mph.

This is not hard data though, I have seen now good definitive test of the Etec 90 or Suzuki 90 on a classic Montauk 17, Some here say they can get closer to 45mph with the Etec 90 perhaps with jack-plates and more aggressive props, but most reports seems to be around 40mph.

It would be nice to have boats test similar to these done with classic Montauk instead:

http://www.suzukimarine.com/boat_builders/boat_tests/proline_boats/ prolite_flats_18/df90/

http://www.evinrude.com/Content/Pdf/neutral/performanceReports/PE670.pdf

I personally want very good mileage and less weight when I re-power my Montauk so I am leaning toward the Suzuki DF90 or Etec 90 currently.


L H G posted 07-19-2010 02:07 AM ET (US)     Profile for L H G    
The leftover Mercury two-cycle 90-HP motors are just as powerful as your 2+2 100-HP Mercury. Get one while you still can, as they are now in short supply. Bass Pro Shops have some. The only other 90-HP on the market with as much power is the Mercury 90-HP FOURSTROKE [or Veradito] EFI, the engine Whaler is currently installing on the 170 MONTAUK. But it weighs in at 399-lbs.
jimh posted 07-19-2010 09:03 AM ET (US)     Profile for jimh  Send Email to jimh     
Since we are not talking about actually re-powering now, I don't see the point of recommending any motors currently in production. When the re-power actually happens, there will probably be different motors available than are available now.

If you reduce power to 90-HP from 100-HP, this is power ratio of 0.9. We know that speed is proportional to power according to the 0.5 exponent, so we would expect speed to decline by 0.948. Because you have never actually measured the speed of your boat, I wonder if you could even detect the change. For example, if your boat currently can go 45-MPH with 100-HP, with 90-HP we would expect it to go 42.7-MPH. Could a person detect the difference in speed from their recollection when the difference is only 2-MPH at 43 to 45-MPH? I doubt that most people could detect such a small difference, based solely on their recollection of how fast the boat used to go compared to how fast the boat can go now.

It is harder to estimate the effect of adding weight because we do not know how much weight you are carrying around in the boat at this time. If the boat is loaded down with people and gear, an extra 80-lbs may not make a noticeable difference. Again, since you have never measured the speed of your boat, it would be hard to say if from your perception of speed and comparison with recalled perception of speed you could be expected to reasonably detect the influence of 80-lbs on the boat's top speed.

In any case, the speed differences are going to be marginal. For someone who has never measured the speed of your boat, I do not understand the great concern about a marginal change in speed if the power is reduced to 90-HP from 100-HP. Most boaters never operate their motor at full-throttle for more than a moment or two. If absolute maximum speed at full throttle is important, I have to ask: why have you never measured the speed of the current boat?

Lame Duck posted 07-20-2010 10:24 PM ET (US)     Profile for Lame Duck  Send Email to Lame Duck     
Thanks, Group for all your helpful insights. From the general tone of your excellent responses it would appear that you do a lot of fishing. Oddly, our family decided on the Montauk for its versatility and have used it mostly for skiing. We used it for just about everything you can imagine- except fishing While I do have ambitions of landing a big one some day, my real dream is to get back into barefooting. When I was shopping for boats back in ’89 the BW dealer demo’ed the Montauk with a 90. It would have been fine for fishing, but definitely would not be able to cut the mustard for the type of skiing I was into. The hole shot just wasn’t there because the engine didn’t have enough low end torque. It didn’t have the torque because the motor didn’t have enough cubic inches. As I’m sure you know, when it comes to pulling skiers out of the water it’s not about horse power but torque and not about total weight so much as it as about distributed weight. Anyway, I got the boat with the 100, which had 105 CID / 1721 CC, and the performance difference was significant. The biggest difference was the hole shot but the top end was noticeably faster too. As to why I never had the speed checked- I never had an easy and accurate way to do it. When I first got the boat hand held GPS receivers hadn’t been invented yet-at least I don’t remember any- and after they had I lost interest in nailing down a top speed. After all it’s just a number. It’s what you can do with it that counts- like barefooting.

I suppose maybe I should have asked my original question a little differently. Are today’s modern 90s more/less/or the same power as the power from the “classic” Mercury’s? We all know that just because a motor carries a label of 90 that it doesn’t necessarily put out a true 90 horse power. As long as its performance falls within in a certain range the manufacture is allowed to round off. In the late 80s I always suspected that Mercury produced an engine that put out a few more ponies over its rating- just to have an edge over the competition. This is pure speculation on my part, however. Still, I never got beat with the Merc powering my Whaler.

Looking at today’s Mercury 2 stroke offering I see it only has 93 CI, but maybe it accelerates better than the engines of old? The 4 stroke has 106 CI, but it’s a 4 stroke, so how good could the low end torque be compared to my 2 stroke? Both motors are heavy, which counts for nothing once on a plane, but means the world when you’re pulling a skier out of the water. Remember where the extra weight is placed. Suzuki makes a 100, but it’s a 4 stroke too and weighs a ton, so the hole shot may not be better than a 2 stroke 90? The Evinrude 90 has a displacement of only 79 CI, so clearly it’s no performer for pulling skiers. As far as repowering with a 115 is concerned- that’s a no go. I’ve moved back to Florida, which doesn’t permit doing such a thing, and I’d have insurance problems to boot- I checked into it when it was still legal. Great idea though.

So am I just going to have to hang up my skies- or feet- when my motor gives up the ghost or do today’s 90s out perform the 90 of yester year?

Much thanks,

Al

WT posted 07-21-2010 01:36 AM ET (US)     Profile for WT  Send Email to WT     
If a new Montauk with 90 hp two stroke didn't cut the mustard back in 1989. I doubt a 90 hp motor today would cut the mustard especially with the increase in weight.

A new 90 outboard would cost at least $7,000 out the door.

An option would be to sell the Montauk and get a ski boat. I don't know where you live, but around Sacramento you can buy tons of ski boats, CHEAP. Tons of repossessions. A 19 foot ski boat with a Corvette V8 would have gobs of torque.

Warren

WT posted 07-21-2010 01:56 AM ET (US)     Profile for WT  Send Email to WT     
Or re-power your Montauk with a new 90 hp outboard and get two props. One for everyday use and one for extreme water skiing conditions. In theory, it would take less than 5 minutes to swap out props.

jimh posted 07-21-2010 08:26 AM ET (US)     Profile for jimh  Send Email to jimh     
I am not an angler.
russellbailey posted 07-21-2010 01:14 PM ET (US)     Profile for russellbailey  Send Email to russellbailey     
As an avid skier, it is hard for me to imagine that you would not find sufficient a 90 hp 2000-something conventional OMC 2-stroke (I think they were all called Johnson in this time frame). I tend to think a 90 hp convention 2-stroke Mercury would also be comparable. Both of these engine families are inexpensive used, simple, lightweight and dependable. Compared to a modern engine, they are also a bit smoky and loud, but not moreso than your current engine.

With a 15" SST prop on one of these, they will yank you out of the water with a Montauk.

I have not barefooted behind a Montauk, but I did sort-of (I would not say proficient) behind our Striper 15 Evinrude 70. The load on the engine for a deepwater start was dramatic, and I was wishing for a 90 at the time.

I would suspect that the 90 you tried was either a weak engine or just not propped right.

It is hard to imagine finding a stronger accelerating <=100 hp engine for a Montauk than one of these choices.

Tohsgib posted 07-21-2010 01:49 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Go with a 115 E-Tec.
Buckda posted 07-21-2010 02:19 PM ET (US)     Profile for Buckda  Send Email to Buckda     
I would look for another used 100 HP two stroke in good condition and store it in my garage until I needed it. It will cost about $1,000, and you can then just run the heck out of the current engine.

For $500 you could buy an old "donor" engine to keep your current one running.

As WT stated, if 90 wasn't enough HP in 1989, it won't be enough in 2010 or whenever you blow up your current motor.

Incidentally, we towed skiers last week behind the Mercury engine that I learned how to ski behind - (same motor) - a 1974 Mercury 500 4-cylinder 50 HP. It runs as well today as it did back then. Very little smoke, smooth and powerful.

Take care of that '89 - it will to strong service for years to come.

Lame Duck posted 07-21-2010 10:05 PM ET (US)     Profile for Lame Duck  Send Email to Lame Duck     
Thanks, everyone. The suggestion about locating a used 100 and preserving it in my garage may be the best solution yet. My hat’s off to you, Bucda. Still pulling skiers with the same motor after 36 years! I’d love to say that I’m looking forward to doing the same, but I’ll be surprised if it happens. I’ve moved back to Florida- no more fresh water boating- and the Whaler will be swinging from davits in fair weather and foul. We get a lot of salt spray where I live, which, as you all know, is tough on boats, motors and everything in between.

Al

Tohsgib posted 07-22-2010 10:27 AM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Where in FL...e-mail me to be on our FL Whaler club rendezvous list.
Buckda posted 07-22-2010 10:35 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Al -

One more thing then - consider looking in Northern freshwater states like MN, WI, IN, OH, MI and PA. Lots of these boats see maybe 50 hours a season - if they're lucky. The further north you go, the fewer hours are likely on the motors.

Buckda posted 07-22-2010 10:47 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Here's that motor with the third generation of users on board:
http://www.facebook.com/photo.php?pid=31518250&l=7c2979a3e5& id=1383963684

That's a 1968 Starcraft that is still doing duty. She has a fresh coat of paint and some new wood, but looking good.

And here it is towing that third generation of water dogs... http://www.facebook.com/photo.php?pid=31518252&l=cc7f3a0775& id=1383963684

Lame Duck posted 07-22-2010 08:31 PM ET (US)     Profile for Lame Duck  Send Email to Lame Duck     
Those are great pics, Buckda. The one of the Ski Bob really takes me back. My kids were real clowns on that thing.

Tohsgib, I'm in St. Pete. Don't know how to find your email address, but mine is z200@ptd.net.

Al

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