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Author Topic:   MONTAUK: Re-power with 60-HP 4-stroke
hanksaper posted 09-19-2004 03:25 PM ET (US)   Profile for hanksaper   Send Email to hanksaper  
I am planning to replace my 2003 90-HP 2-stroke Yamaha on my older MONTAUK with a 2005 60-HP 4-stroke EFI YAMAHA. Does anyone have any suggestion regarding prop size, or performance?

Thank you.


jimh posted 09-19-2004 04:07 PM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the performance expected, boat speed varies as the square root of horsepower. In dropping from 90 to 60 the horsepower will decrease by

60/90 =0 .666

Therefore the speed will decrease by

0.666^0.5 = 0.81

If you could reach 30-MPH you will now be able to reach only 24-MPH.

However, this analysis does not account for the increase in weight. Speed is inversely proportional to weight. Your old motor weighs about 261 lbs. The new motor weighs about 237 lbs. This is a ratio of

261/237 = 1.10

Therefore the boat's performance should change by a factor of

0.81 X 1.10 = 0.88

If this holds true, then if the boat went 30-MPH previously it ought to now be able to go 26.4 MPH.

You can predict the performance using the calculations explained in the REFERENCE section article on Propellers. See:

Propeller Basics: Part 2

A number of performance predictions have been computed for most all Boston Whaler hulls when equipped with maximum rated horsepower. The calculations include allowances for fuel, crew, and engine weight. See:

Performance Prediction

jimh posted 09-19-2004 04:30 PM ET (US)     Profile for jimh  Send Email to jimh     
Well, wait a minute. After I clicked SUBMIT I gave this some more thought. The weight calculation is not correct. It has to account for the total weight changed, and certainly the boat is not going to be ten percent lighter if only the engine is ten percent lighter. Thus, scratch that figure. There will be some improvement from the reduced weight, but not as much as I showed above.

The total weight of a MONTAUK will be in the vicinity of 1750 lbs. The weight change of the lighter motor will be 24 lbs. This is a ratio of roughly

1750/1725 = 1.015

This means the increase in speed due to weigh decrease will be very small, and the total speed potential from the aggregate of the horsepower decrease and weight decrease will be now something like

0.81 X 1.015 = 0.82

So if the boat used to go 30-MPH it will now go 24.65 MPH.

The Yamaha website has dozens of performance bulletins. One of these shows the 60-HP four-stroke on a 15-foot Edgewater. It can barely get the boat up to 30-MPH, even cranking to 6,000 RPM.

Ouch! My 1976 Mercury 2-stroke 50-HP (powerhead rated, not propeller shaft horsepower) used to push my SPORT-15 around at 35-MPH.

Based on these numbers, I wonder what the four-stroke 60-HP motor will do on the Montauk? I know there are many happy reports from the 70-HP four-stroke Suzuki owners.

Dick posted 09-19-2004 05:18 PM ET (US)     Profile for Dick  Send Email to Dick     

I had a 1999 Merc 50HP 4 stroke on my 99 Montauk. Loaded with 24 gallons of fuel, stern seat, down riggers, 2 batteries and trolling motor. I would max out at 33 mph per the GPS. I was very happy with the combination.
The 60 4 stroke should be a good set up.


home Aside posted 09-19-2004 07:30 PM ET (US)     Profile for home Aside  Send Email to home Aside     
What made you decide to make the change ? and What are you asking for the Yamaha 90 2 stroke ?


erik selis posted 09-20-2004 04:42 AM ET (US)     Profile for erik selis  Send Email to erik selis     
I often go out fishing in my buddy's 17-foot Alert. He has the Mercury 60-hp 4-stroke EFI on it and the set-up runs great. (Check out the pictures in my profile).
I don't have any WOT performance figures but I can say that she runs more than fast enough for our purpose (fishing and getting to the fishing spots at a reasonable speed). I would estimate it to be close to what Dick mentioned.
In the 3 years that we have used this boat-motor combination (they were new) we have never encountered any mechanical problems what-so-ever. The motor starts first time, every time, under all conditions. It sips fuel and is very quiet. We run it both in fresh and salt water during all seasons. Even when it's freezing outside the motor starts first time and keeps running....It's truly a great engine and boat.


daveweight posted 09-20-2004 06:06 AM ET (US)     Profile for daveweight  Send Email to daveweight     
Erik, do you launch North in The Netherlands or do you take the longer route West.
erik selis posted 09-20-2004 07:03 AM ET (US)     Profile for erik selis  Send Email to erik selis     
Dave, we always launch out of Breskens in the South-West of the Netherlands. Right at the river outlet of the Wester-Schelde.


elaelap posted 09-27-2004 11:32 AM ET (US)     Profile for elaelap  Send Email to elaelap     
Smirkless 16'7" Katama with 50 hp Yamaha four stroke High Thrust motor, super quick on plane at low speeds and WOT 6000 rpm = 30 mph/GPS. Loved this combo. The current owner of the boat/motor, CW member Steve/17 Bodega, also reports being pleased with the combination...he's even waterskiied behind the boat, which I never tried.


17 bodega posted 09-28-2004 10:34 AM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Very true. I was on two ski's but still not bad. Isn't the high thrust 60 the same powerhead as the 50? What is the difference in the two motors? Your smirked Montauk will not go as fast as my lighter smirkless hull. I would love to hear your performance numbers if you end up buying the motor. I love mine.


LHG posted 09-29-2004 07:43 PM ET (US)     Profile for LHG    
The entire powerhead of the Yamaha 60 4-stroke is 100% made by Mercury, and is now the same as the Mercury 60 Hp EFI. Previously the Yamaha only had carburators. Yamaha also buys their 30 and 40 Hp engines from Mercury.

The 50 HP Yamaha is the older joint venture engine, with block and internals made by Mercury, and heads/valve train by Yamaha. This engine is often referred to a Merc-aha. Mercury's 50EFI is no longer using this powerhead, but instead the newer one used for this 60.

I'm wondering if Yamaha's new 50 EFI will no longer use this older powerhead, and instead buy the new one from Mercury, like the other hp ranges?

For performance indications on a Montauk, one might look at the 150 Whaler performance figures, since these two boats weigh the same.

I would estimate about 36-37 MPH

Moe posted 09-29-2004 10:28 PM ET (US)     Profile for Moe  Send Email to Moe     
> I'm wondering if Yamaha's new 50 EFI will no longer use this older powerhead, and instead buy the new one from Mercury, like the other hp ranges?

Last I checked, the Yamaha website shows their standard foot 50HP using the larger displacement EFI powerhead, but the High Thrust 50HP still using the smaller, joint venture powerhead. That could be a web mistake though.

Given the classic Montauk is about the same weight as the 150 Sport (50 lbs heavier than the 150), but a bit narrower, I'd think the 60HP Mercury BigFoot EFI would perform about as Larry says, and would be a good choice. I'd only recommend the Yamaha High-Thrust 60HP if it's cheaper AND has the Mercury EFI now. I'd definitely chose the larger gearcase with the lower (higher numerically) 2.33:1 gearing.


erik selis posted 09-30-2004 02:17 AM ET (US)     Profile for erik selis  Send Email to erik selis     
Larry & Moe,

I don't think the Merc 60 4-stroke EFI reaches a top of 37mph. I think more like the low 30's.

I will check it on the GPS on Saturday when we go out in the Alert. I will also check for the exact prop size and come back with the info.


LHG posted 09-30-2004 05:59 PM ET (US)     Profile for LHG    
Erik - Remember that the Alert is a heavier hull than the recreational Montauk.
Moe posted 09-30-2004 07:09 PM ET (US)     Profile for Moe  Send Email to Moe     
On the 150 Sport, it reaches 33 mph with 400+ lbs of people, 12 gallons of fuel, all the stuff we bring, and the bimini up. I believe kshoaps saw 36-37 mph on his 150, solo, and in fresh water. I'd have to believe the classic 17 would have to do at least as well.


erik selis posted 10-01-2004 02:46 AM ET (US)     Profile for erik selis  Send Email to erik selis     
Larry, it's true that the Alert is heavier than the Montauk. We also have a 25 gal.fuel tank in the back. With the 2 of us in the boat (400lbs), lots of fishing gear, 2 anchors, 2 batteries, electrical trolling motor...I guess you have made a good point.

Moe, I don't really know for sure if you can compare the 150 to the 17-ft Montauk. The 150's hull is very similar to the 170's hull. True, the 150 weighs about the same as the 17-ft Montauk but the 170 weighs more than an 18-ft Outrage. Let's say you would put a 90-hp on a 18-ft Outrage. I'm pretty sure you wouldn't get the same performance figures as you would with the heavier 170.

I think the overall shape of the 150's hull will allow higher performance with equal power compared to the 17-Montauk. This would not be the case with the 16.7 smirkless hull IMO.


Moe posted 10-01-2004 12:32 PM ET (US)     Profile for Moe  Send Email to Moe     
> I think the overall shape of the 150's hull will allow higher performance with equal power compared to the 17-Montauk...IMO.

Perhaps. I agree on the hull shape, but the 150 Sport is much wider than the 17 Montauk, especially at the bottom. More lift, but more drag.


erik selis posted 10-02-2004 04:18 PM ET (US)     Profile for erik selis  Send Email to erik selis     
Checked the WOT speed today on the 17-Alert with Mercury 60-hp, 4-stroke EFI.

Conditions: wind 3 beaufort (+/-7kn)
Load: +/- 750lbs (2-people, 50 liters gas, anchors, fishing gear...)

WOT gave us 51km/h (31.8 mph).

Prop: 10 1/2"x 13p Mercury Black Max.

We took this reading with the wind coming from the starboard side. There was on current to take into account.


Hoosier posted 10-06-2004 08:09 AM ET (US)     Profile for Hoosier  Send Email to Hoosier     
I get 29 mph (GPS) in my 86 Montauk using a Honda 50 and a composite prop. That's fully loaded, 450 lbs of people, 25 gal of gas and maybe 100 lbs of fishing stuff.
Moe posted 10-06-2004 10:03 AM ET (US)     Profile for Moe  Send Email to Moe     
31.8 mph is about what we get in the 150 Sport with 60HP BigFoot, with two people, 12 gallons gas, two anchors/chain in the well, all the other gear we carry, and the 50 lbs of cooler, ice, and drinks in the bow behind the anchor locker. The motor is trimmed up way past vertical at max rpm/speed.

Moving the cooler to the stern bumps that up to 33 mph with the motor only a bit up past vertical at max rpm/speed. Load distribution makes a big difference.


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