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Author Topic:   New Motor for Montauk
TRIDENT posted 09-19-2000 02:43 PM ET (US)   Profile for TRIDENT   Send Email to TRIDENT  
I know this has been discussed before, but now it is my Whaler that needs a new engine.
I have narrowed it down to either a 70 or 90 HP 2-stroke Tohatsu or a 70 HP 4 stroke Suzuki. I need to know what the top end speeds will be with each engine, or an educated guess if anyone has an opinion. I can get the Tohatsu 90 for $4,800 with controls and a stainless prop along with a spare aluminum prop. Any opinions as to the best course of action?
Outraged posted 09-19-2000 07:42 PM ET (US)     Profile for Outraged  Send Email to Outraged     
TRIDENT, You need to decide what your main use for the boat will be. A four stroke would be great if your main use is fishing.It would be a more quiet motor& a bit more fuel efficent. The down side is it will be a heavier motor. So, if speed is more of a concern,a two stroke might be your choice. As far as top speed goes, I had a `71 Nauset for a while(17`) with a 100 h.p. Johnson on it, and with two people on board we could top out at about 42 mph all trimmed up. Hope this info helps you in your decsion making process.
Ed Stone posted 09-19-2000 09:49 PM ET (US)     Profile for Ed Stone  Send Email to Ed Stone     
Its hard to beat that deal on the tohatsu.
Just add rigging and a hour meter.
If you could get close to the same deal
on the 4-stroke that would make for a tough
Good luck!
Hoop posted 09-19-2000 11:42 PM ET (US)     Profile for Hoop  Send Email to Hoop     
I checked just the other day. Top end speed on my Evinrude 70 hp four stroke on my Montauk is at 5200 rpm with an aluminum prop and is about 29.5 mph. I figure a SS prop might raise the speed a couple of mph. The real benefit of the engine is not speed, its the "peace and quiet" and the Lake-Tahoe-compliant emissions. You can actually have a conversation at 4500 rpm. Hoop
jimh posted 09-20-2000 01:36 AM ET (US)     Profile for jimh  Send Email to jimh     
Unless the price was excessive compared to the other choice, I would go with the Suzuki.


--Montauk hull can tolerate the extra weight

--Warranty on Suzuki is excellent (6 years!)

--Low noise operation is a big plus

--Low pollution operation is a plus

--Improved fuel economy is a plus

The other factor is: will you be happy with just 70 HP on the transom?


TRIDENT posted 09-20-2000 12:03 PM ET (US)     Profile for TRIDENT  Send Email to TRIDENT     
I currently have a 1985 Mercury Inline 6 115HP on it. I have seen steady speeds of 47 MPH on my GPS with that setup. I don't really need to go that fast, but 40 MPH would be nice because sometimes I have long runs and can't wait to fish! I guess the 70 4 stroke may not get me there as fast as I want, darnit.
dgp posted 09-20-2000 01:11 PM ET (US)     Profile for dgp  Send Email to dgp     
Hoop, at 5200 RPM you're at the bottom end of the WOT range for your 70 HP Evinrude 4 stroke; it's rated up to 5800 RPM. Work with your dealer to reprop it to get maximum rated RPM. You'll certainly see better than 30 MPH. Don
stagalv posted 09-20-2000 02:15 PM ET (US)     Profile for stagalv  Send Email to stagalv     
Yes, I also thought 30mph was quite slow for the 17 with a 70hp 4 stroke. Having a tach and experimenting with different prop sizes can make a world of difference.
TRIDENT posted 09-20-2000 03:42 PM ET (US)     Profile for TRIDENT  Send Email to TRIDENT     
What do ya'll think would be the maximum speed from a 70 HP 4 stroke? How about a 70 HP 2 stroke? A 90 HP 2 stroke? Many thanks for the replies...
lhg posted 09-20-2000 07:44 PM ET (US)     Profile for lhg    
I would say that 70HP on a Montauk ought to do about 38MPH and that 90 ought to do about 45. Speeds will vary with engine trim position, engine brand, installation height on transom, choice of prop and weight of equipment on boat. But those are ball-park numbers for a good installation.
Hoop posted 09-20-2000 11:11 PM ET (US)     Profile for Hoop  Send Email to Hoop     
Hmmmm ... and I would have thought that the dealer would have know what the right prop should be! Don and others, thanks for the advice about re-propping. I would really like to get the boat speed up above 30 mph at a minimum. That would mean a lower pitch prop? (Higher pitch, more travel at a given RPM, less torque; lower pitch, less travel, more RPM, more torque?) Hoop
lhg posted 09-21-2000 01:22 AM ET (US)     Profile for lhg    
Hoop: Changing your prop should help a little, but I'm sure it's not going to get you up to the 35-38 range you should be in. Assuming your Montauk is pretty standard, and not "overweight" for some reason, you might have the engine checked out. Something could be wrong with the engine. If I'm not mistaken, people are indicating their Montauks run around 32-34 with a Merc/Yamaha 50HP 4-stroke. DonP, am I correct?

Back in the late 70's, BW used to indicate boat speeds with various HP's. They show a Montauk with a 70/75HP engine to run about 35mph, and that was for the powerhead rated engines of those days. You should at least get that speed. There must be other guys reading this with 70's on Montauks. Maybe they'll report in.

dgp posted 09-21-2000 08:23 AM ET (US)     Profile for dgp  Send Email to dgp     
Larry, you're correct, I averaged 34 MPH with the Mercury 50 HP four stroke. This average is based on two runs, both with and against a 10 MPH wind. My dealer had to go down in pitch size and up in diameter to get to the rated 6000 RPM (WOT). This is a Mercury SS Vengeance prop.
Hoop, if you go to the "Montauk w/ 50HP four stroke" topic in this section you'll see all my performance results. Don
Clark Roberts posted 09-22-2000 08:55 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Hoop, you're getting some good advice! I agree with Larry that you should be in the mid-thirties range...maybe high 30's... let me say this, "power is power" and generally doesn't matter whether is a steam engine or a hampster on a treadmill... two stroke/four stroke or whatever! What matters is the weight, the prop, the set-up height on transom, engine tune, condition of hull bottom surface...etc...etc... Would suggest that you raise engine at least one mounting hole and check that you are actually getting full wide open throttle (WOT)! Take air box off and look straight down carb throat... with EFI check throttle body butterfly or box valve and have the injector timing checked... get the rpm up to Max rating by selecting prop that will allow with light load... if using 87 octane go up one grade to 89... that's about it but will probably think of something else... by way of comparison ... there is a Newport here with 50 Evinrude and a Montauk with 50 Merc and both run 35mph easily.... I have driven a Whaler Test boat ... 17 std with 50 Merc 4 stroke at 36mph... Keep fiddling .. Happy Whalin'... Clark... Spruce Creek Navy
RWM posted 09-22-2000 06:52 PM ET (US)     Profile for RWM  Send Email to RWM     
Timely subject for me. I'm adjusting to sticker shock looking to repower my 1977 Montaulk. I'm used to my old reliable? 90 Merc, but corrosion finaly took it's toll. I'm using a little Marine-tex to get throught the season, and I ran it WOT today at an apparent 45 MPH. I really don't need that much speed and frequently run at 25 MPH which is fine on the ocean and bay water I run on. My question is...once I decide on a motor it appears I'm also in for new controls, wiring harness, tank and other stuff. I'm used to doing some of my own work and would hate to pay the dealer since I would expect all this to add over $1000 to the price of the engine. Anyway, gulp, am I really looking at $6-7,000 for all the above and maybe I should do all my console wiring too, and new guages, and new switches and......yikes, I'm out of control.
whalernut posted 09-22-2000 08:04 PM ET (US)     Profile for whalernut  Send Email to whalernut     
RWM, I am going through the same delema as you. My 85h.p. Johnson still runs well, but would love a quiet,clean,slow trolling 4-stroker. Sticker shock is keeping me at bay until my current engine gives up the ghost! Regards-Jack Graner.
masbama posted 09-22-2000 10:40 PM ET (US)     Profile for masbama  Send Email to masbama     
I'm in the same boat (pardon the bad pun).
I have a '77 Montauk and I want to repower in the spring with a Yam. or Johnson 90 2 stroke. I'm guessing total with new controls, tanks,console and other wiring will be 6 grand on a 23 year old boat. Sticker shock indeed. The selling price after repowering would not recoup the new motor cost. Decisions!
Hoop posted 09-23-2000 10:16 AM ET (US)     Profile for Hoop  Send Email to Hoop     
Thanks, guys! I'm also thinking that my GPS speed was into the incoming current of 1 to 2 knots. I'll definitely talk to the dealer.

Clark, the engine manual is very clear about the mounting height of the engine, to the effect that the antiventilation plate should be even with and not higher than the very bottom of the boat. I could see how a Doel-Fin could help deflect the water to ensure satisfactory flow to the water intake vents. I recall your having posted somewhere else in this forum that you recommend Doel-Fin.

Here's what the manual says, "The resulting position of the antiventilation plate must be no higher than the boat's bottom and no lower than 2 in. below it." Later on, the manual says, "higher than recommended - serious powerhead damage could result from inadequate cooling or an over-revving propeller. Propeller ventilation (slippage) often occurs, resulting in poor boat performance. On a specialty hull, non-planing hull, or on a boat with a curved transom, these guidelines might not apply. See Dealer for special installation information." Raising my engine would result in the antiventilation plate being about 3/4 of an inch above the bottom of the boat.

You would still recommend raising the engine 3/4 of an inch above the bottom of the boat?

Barry posted 09-23-2000 12:33 PM ET (US)     Profile for Barry  Send Email to Barry     
My Mercury outboard manual says basically the same thing. "Proper transom height is important for best boating performance. The gear housing anti-ventilation plate should be parallel to the boat bottom and flush to 1.5" below boat bottom."

It then says, "Running the engine while trimmed down may cause undesirable spray on some boats. If so, and you do not wish to run trimmed further out, raise the engine on the transom by one bolt hole (3/4" increase in height)."

And finally that "raising the outboard higher than standard on the transom will:

A. Decrease steering torque.
B. Increase top speed as the engine is raised, due simply to a reduction in gear housing drag.
C. Improve boat handling and stability."

The Merc 90 on my '74 Montauk is mounted so the plate is about 1" to 1-1/2" ABOVE the boat bottom.


Clark Roberts posted 09-23-2000 05:04 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Hoop, I can't argue with manufacturer's recommendations but they are interested in the safest position re: product warranty and liability... You have to use your own judgement and make sure that mounting does not compromise flow of water to cooling water pick up on motor... testing is always part of setting up a motor properly.. that's why there are several mounting hole positions.. Yes, I recommend raising an engine as high as practical... what's practical ? You will get varying opinions on this subject.... Happy Whalin'... Clark
Dick posted 09-25-2000 09:12 PM ET (US)     Profile for Dick  Send Email to Dick     
Motor mounting is critical. I have a 1999 Montauk with a Merc 50hp 4 stroke mounted up one hole. Trimmed out with just me onboard it will do 38 mph with a 13 pitch Merc SS Vengance prop. The speed is averaged between my GPS and speedo.
triblet posted 09-25-2000 10:12 PM ET (US)     Profile for triblet  Send Email to triblet     
Your GPS will probably be more accurate
than your speedo. With SA off, probably
+- .2 MPH.

And you need to make runs in both directions
and average to compensate for wind and

Chuck Tribolet

FISHNFF posted 09-30-2000 01:41 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
I have a 1998 Alert Commercial hull with my previous Montauk console modified with a fiberglass box and plexiglas windshield just shy of 6' tall. About as aerodynamic as a brick! A 1996 75 Merc 2 stroke, Doel-fin, and a 19" Ballistic SS prop pushes me to 35.3knts with 1 group 24 battery and 10 gallons of fuel in console. With 3 aboard, 17 gallon bait tank, and 22 gallons of fuel drops me to 31knts and more porpoising when trimming out.
david in boston posted 10-02-2000 11:04 AM ET (US)     Profile for david in boston  Send Email to david in boston     
I put a 2000, 70 hp tohatsu on my montauk last spring and am very happy with it. lots of power. 40+mph, good on gas, light, very reliable. I got it online for $3800. +$150 for the optional binnacle mount cotrols. (no sales tax) I think 70 hp is plenty of power for a 17"whaler. I've had the whole family in my boat (2 adults, 3 kids) water sking with no problem. Its a great engine. David
Lanny posted 10-03-2000 05:44 PM ET (US)     Profile for Lanny  Send Email to Lanny     
Any ideas on how I would mount a tower for water skiing and wakeboarding into the floor of my montauk. The tower needs to be approx. 5-6 feet tall and be able to withstand the force/ weight of the towed rider. In all liklihood, I'll have to drill a large area into the floor/hull to be able to have a sturdyt/reinforced tower.ONE IDEA I HAD WAS TO MOUNT a car rim to the floor and let the interior area of the rim support the tower and much of the force from the towing. Any thoughts?
Hoop posted 10-21-2000 02:28 PM ET (US)     Profile for Hoop  Send Email to Hoop     
Just an update regarding my Evinrude 70hp 4-stroke on my Montauk. In my posting above I was running into a current, by wife and I and our 2 dogs (40 lb for the two of them) on aboard.

The update: with me alone, with the standard aluminum prop that came with the boat, playing with trim ... trimming the motor way up at high speed (I was surprised how high I could trim it and still get mph speed increase) ... I got up to around 35 to 36 GPS-measured mph at 5500 rpm at slack water.

With the suggestions above, including raising the motor on the transom by one hole and shifting to a SS prop, I do think I could get a bit more speed. In any event, I'm feeling much better about boat speed.

Hoop, San Jose, CA

RWM posted 10-21-2000 10:51 PM ET (US)     Profile for RWM  Send Email to RWM     
Hoop - Thanks for the info on the 70 Evinrude. I just bought a leftover 2000 and will mount it this winter. This is a "deal" motor and it will simply be dropped on my Montauk sans prop. Can you tell me which prop you would recommend? Also (FYI) I'm going to be restoring my 1979 model with new wiring, controls and guages etc...this site has given me the courage to take it on. My plan is to source the components and parts by mailorder using Shoreway, and picking up other stuff at West Marine...I'm thinking about the weight of my new engine (replacing a '77 Merc 90) and am wondering if anyone with a heavy motor places their gas tank in front of the console instead of under the seat to balance weight..Happy Whaling...and for me...Busy winter!...Bob M.
Hoop posted 10-22-2000 10:38 AM ET (US)     Profile for Hoop  Send Email to Hoop     
Bob, I don't know the prop size, I'm embarrassed to say. I looked at it a minute ago and couldn't find any readable information on it. I'll have to research. Hoop
triblet posted 10-22-2000 10:44 AM ET (US)     Profile for triblet  Send Email to triblet     
Your new motor weighs about the same as
my Evinrude 2-stroke 90, and less then
a 90 Ficht. No need to move the gas tank
from it's nicely protected position under
the seat.

Chuck Tribolet

RWM posted 10-22-2000 05:18 PM ET (US)     Profile for RWM  Send Email to RWM     
I read the "Offshore" article about repowering (as mentioned in another thread). The Suzuki 70 4-stroke had a 13"x15" stainless for the test. Max RPM shown was 5700 which should be near WOT. Highlighted was that minimum planing speed was 14.5 knots (16.7 MPH). That was with 3 people on board and a full tank. That minimum planing speed seems way too fast (I hope) and assume that either a different prop, different engine height, or lower trim might have helped. On the other hand the Mercury 60 (with a 14 x 12 prop) held a plane at only 8 knots. The difference cannot be explained by weight only so I'm leaning towards prop, height, or trim as the difference. Since I use my boat on choppy ocean bays I want to be able to plane at relatively low speeds. Right now I'm guessing a larger diameter prop and lower pitch will help me do this with my new Evinrude 70 4-stroke..Bob M.
scottfarm1 posted 11-21-2000 09:50 PM ET (US)     Profile for scottfarm1  Send Email to scottfarm1     
96 montauk with 96 75hp 2 stroke merc--between 38 and 40mph

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