150 Montauk: Speed with 90-HP

Optimizing the performance of Boston Whaler boats
Jack Slote
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150 Montauk: Speed with 90-HP

Postby Jack Slote » Fri Jun 21, 2019 6:35 pm

Hi, I have a 2015 150 MONTAUK with the stock engine, Mercury 60-HP.

[Top boat speed is] about 35 [MPH] with just me and light fuel load.

Q1: If [the engine were changed to a] 90-HP, how will [a 150 MONTAUK perform?]

Q2: [What will the] top [boat] speed be [with 90-HP?]

macfam
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Re: 150 Montauk Upgrade

Postby macfam » Sat Jun 22, 2019 8:01 am

Yes, you’ll go faster with a 90. That’s the ONLY upside I see. Otherwise the resale value drops, and there is too much weight aft. For my money, if I wanted to go faster, I’d get a 170 MONTAUK with a 90-HP.

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Phil T
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Re: 150 Montauk Upgrade

Postby Phil T » Sat Jun 22, 2019 12:41 pm

Ever since I got a demo ride the year it was introduced, I have thought the Montauk 150 is underpowered. The Montauk 150 weights the same as a classic Montauk 17 of 950 lbs yet has a max hp rating 40hp less.

With a transom weight limit of 305 lbs. I would consider a E-TEC 90 at 320lbs. I would test the added weight in the rear before you do anything.

With 30% more horsepower I would estimate a WOT speed of 45 with a 90hp. How the hull will handle that is a separate question.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

jimh
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Re: 150 Montauk Upgrade

Postby jimh » Sun Jun 23, 2019 11:54 am

Boat speed for moderate V-hull boats is proportional to horsepower to the 0.5 exponent.

If power increases to 90 from 60, then speed would increase by

( 90/60 )^0.5 = 1.22

If the boat speed were “about 35” with the 60-HP, then with the 90-HP the boat speed should increase to

35 x 1.22 = “about 42”

This assumes no weight increase. Any increase in weight reduces the boat speed.

jimh
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Re: 150 Montauk Upgrade

Postby jimh » Sun Jun 23, 2019 11:57 am

The hull of any particular boat may not be suitable for operating at unlimited increase in speed. There may be a good reason that Boston Whaler limits the horsepower rating of some models differently from other models if analyzed only on a boat weight to power comparisons.

In the particular case of a 150 MONTAUK the weight of a larger engine and the effect of that on overall weight distribution might have been influential.

biggiefl
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Re: 150 Montauk: Speed with 90-HP

Postby biggiefl » Fri Jul 12, 2019 11:07 am

I agree with Jim on top speed being around 42. Weight should not be a problem as I have run a heavy engine on a jackplate on a classic 17-footer--which everyone said was too heavy but it ran like a dream. Actually ran smoother than the 130-lbs-lighter setup due to stern weight.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll: