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Author Topic:   170 Montauk Re-power, Yamaha F70

pflugrad posted 11-10-2013 11:15 PM ET (US)
I plan to repower my 2004 Boston Whaler 170 Montauk from its current 2004 Mercury 60 FourStroke ELPT EFI BIGFOOT to a Yamaha F70. I would appreciate any advice and lessons learned from anyone who has repowered a 170 Montauk with a Yamaha F70. My main reasons for this repower are:
--current 2004 Mercury 60 has over 1,600 hours and maintenance costs are increasing; prefer higher reliability
--seeking slightly more power with only a little more weight.
frontier posted 11-11-2013 01:00 AM ET (US)
How does your 170 perform with 60 HP Merc Bigfoot?
It was a factory engine option in 2004 but most were equipped with the Mercury 90 2-Stroke or 90 4-stroke.
I am very tempted with the F70 Yamaha also. My local Yamaha dealer says they have proven out to be great, trouble free engines since they came out in 2010. Close in weight and performance to the classic, excellent 90 HP Yamaha 2-stroke.
We've had a F60 Yamaha on a classic 17 Montauk, but it weighs 500# less than a 170.
Peter posted 11-11-2013 07:00 AM ET (US)
When you say you are "seeking slightly more power", what do you mean by that? Higher top speed or a motor that does not get bogged down easily by added weight?
Sorry, but there is no way a 60 cubic inch 70 HP 4-stroke will be close in performance to a 70 cubic inch 90 HP 2-stroke. The 70 4-stroke isn't going to have anything close to the 90 2-stroke low and mid-range torque.
PeteB88 posted 11-11-2013 02:31 PM ET (US)
I can't imagine any Montauk without more power. I mean 70HP is go to power for Classic 15s! I'd be thinking, well, more power. Not only is it fun but you can punch it up to a quick planing configuration, throttle back and not have to run the living guts out of your outboard at or near WOT just to maintain nice cruising speed. And you have reserve power to get you out of trouble or stay ahead of a storm. It's your boat and I have no idea how you use it - some people just cruise along slow, pontoon boat style, maybe that's you. Get the 90, I'd go Yamaha or ETEC if repowering my guess is 90 will keep value up especially with new motor.
Peter posted 11-11-2013 03:58 PM ET (US)
With the same displacement, same number of cylinders, but lower profile with more low end and midrange grunt than a Mercury FourStroke 90, the recently announced E-TEC 90 HO might be the perfect motor for the Montauk 170.
frontier posted 11-11-2013 05:05 PM ET (US)
One of the things that makes the F70 Yamaha such a great engine with excellent low and mid range torque is the use of the High Thrust lower unit (2.33 to 1 gear ratio). That also allows it to swing a lot bigger and wider range of props.
OMCrobert posted 11-11-2013 05:49 PM ET (US)
I would wager that you dont see any increase in performance over the 60hp Mercury Bigfoot with a new Yamaha 70hp.
With no real increase in displacement and that is a heavy boat to start with. If you are hoping for an increase in performance, I would look at a 90hp.
Peter posted 11-11-2013 06:22 PM ET (US)
The F70 has a higher redline 6300 versus 6000 for the T60 but both motors use the 2:33 gear ratio. I believe the Merc Bigfoot does too. I bet the F70 would swing the same propeller that the current Bigfoot swings on the Montauk 170 and the only real difference will be the top speed.
I think the Montauk 170 should be able to hold a 400 lb outboard on its transom without any problem so I wouldn't let weight be a limitation on repower choices.
mkelly posted 11-11-2013 09:08 PM ET (US)
Go with the F90. It was made for that boat. You won't have to run it too hard. [A Yamaha F90 has] 28-percent more displacement; [an F90 is] 100-lbs heavier [than a Yamaha F70, but the added weight is] well worth it. Make sure to pay attention to propeller; customize it for what you want, which may be good [acceleration from a standing start] with a little sacrifice on top end.
jimh posted 11-12-2013 08:37 AM ET (US)
I was initially surprised that a 170 MONTAUK was sold with only 60-HP on the transom. That seems like marginal power for the boat. I had to refer to my original article about the 170 MONTAUK from 11 years ago (2002)
http://continuouswave.com/whaler/reference/170Montauk/
to see that there was an option for only 60-HP. If you are accustomed to running the boat with only 60-HP, then an increase to 70-HP is probably going to feel like an improvement, although it probably won't be a dramatic change.
The switch to Yamaha from the Mercury-brand engine will be expensive because of rigging costs.
pflugrad posted 11-12-2013 11:19 AM ET (US)
Thanks to all for thoughtful and useful advice! I would still like to hear from anyone who actually runs a Yamaha F70 four stroke on 170 Montauk.
Here is additional information regarding my boating experience vs needs:
1. My 10 year experience with the Merc 60 Four Stroke Big Foot on my 2004 170 Montauk is that it powers me fine but is insufficient power with 2-3 friends on board. So I want more power to occasionally take more people on the boat. Also a little more speed would be useful going from fishing hole to fishing hole on the Chesapeake Bay.
2. I store the boat in my garage on a trailer with a swing tongue AND it barely fits (I need to twist the boat on an angle). I calculate that I could get the Yamaha F70 in the garage but not a Merc 90 Four Stroke!
3. The advice received to date is mixed on whether I would actually get more power (moving from a Merc 4 60 stroke to a Yamaha F70)?
So I remain conflicted. My Merc 60 slightly under-powers my needs but the Merc 90 or Yamaha 90 is physically too big for my garage.
I want to stay with a four stroke so I haven't studied the ETEC option seriously.
Again, I welcome and value your opinions....but are their any "Yamaha F70 on a 2004 170 Montauk" continuous wave readers? How can I find them?

Peter posted 11-12-2013 03:27 PM ET (US)

quote:
My 10 year experience with the Merc 60 Four Stroke Big Foot on my 2004 170 Montauk is that it powers me fine but is insufficient power with 2-3 friends on board. So I want more power to occasionally take more people on the boat.
This tells me that you have insufficient displacement. An F70 will not solve the problem. If you are limiting your choices to a Yamaha 4-stroke and wish to limit the HP, then you should consider the Yamaha F75 instead of the F70 for this application. The larger displacement will give you more load carrying capacity which is what you are really seeking.
frontier posted 11-12-2013 03:42 PM ET (US)
The Yamaha F75 and F90 are the same size and weight (1596 cc and 366#). That's why you don't see very many F75's around.
Because garage fit is a big issue, the F70 seems like it might work.
I, too, am very interested to see results from a 170 Montauk with a F70 on it.
I was happy with an F60 on a classic Montauk.
Maybe the F70 on a heavier 170 would be OK for his use.
frontier posted 11-12-2013 08:14 PM ET (US)
Take a look at this performance test on the Yamaha website ("Performance Bulletins" at yamahaoutboards.com):
Boat & motor - Sundance B18 with Yamaha F70LA.
Factory boat weight 1355 (170 Montauk is 1400#), weight as tested: 2108#.
2 people on board.
Top speed: 36.4 MPH @ 6250 RPM
Cruising speed: 21.1 MPH @ 4000 RPM (2.4 GPH).
Sounds pretty good to me.
OMCrobert posted 11-12-2013 08:32 PM ET (US)
I dont think you will find anyone that has repowered the 170 Montauk [with a Yamaha F70] for the above outlined reasons. The 60hp on the 170 is a rare duck and if anyone has repowered they most likely went with a 90hp or another Mercury product due to the rigging.
I would be shocked if you can find someone that has repowered a 170 with a F70 Yamaha.
What about modifying your trailer with a hinged swing tongue to allow for a larger engine?
I think everyone agrees that you will not see any significant increase in performance if any with the F70.
We are trying to talk you out of it as I dont think you will be happy with the ROI.
PeteB88 posted 11-13-2013 03:28 AM ET (US)
Hey, we're your buddies: 90. Forget 70 or 60. Go ETEC, everyone I know who owns those motors love them. Kick a hole in your garage if you have to, you will love that set up, a whole new boat my guess especially if you are concerned about performance with more passengers.
jimh posted 11-13-2013 09:26 AM ET (US)
That the performance of your Boston Whaler 170 MONTAUK powered by a 60-HP four-stroke-power-cycle engine declines when three additional people are aboard is not at all surprising. On a small boat like a Boston Whaler 170 MONTAUK, the addition of three people represents a considerable increase in the boat weight. A 170 MONTAUK with a 60-HP engine and one person probably weighs about 1,950-lbs. If you add 600-lbs (or three people) to the boat, the weight increases about 30-percent. The predicted top speed for the boat drops to about 29-MPH from 33.5-MPH. This suggests that the boat may be difficult to get onto plane, and probably cannot be held on plane easily at slower planing speeds with the heavier load.
You might want to read the lengthy and profusely illustrated CETACEA article about the 170 MONTAUK at
http://continuouswave.com/whaler/cetacea/cetaceaPage58.html
This article details the owner experience of one of the first 170 MONTAUK boats delivered by Boston Whaler. It also describes the replacement of the original 90-HP engine with a 115-HP engine.
Peter posted 11-13-2013 09:37 AM ET (US)
Another factor to consider -- resale. If a point in time comes when you are selling the 170 Montauk, the boat will be far easier to sell with a 90-HP (or larger) outboard than a 60 or 70-HP outboard. The 60- or 70-HP outboard limits the boat's versatility and will thus limit the potential buying pool.
masbama posted 11-14-2013 09:33 PM ET (US)
The f70 on the pre 170 montauk would be a good fit. Lighter hull and what not.

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Author	Topic: 170 Montauk Re-power, Yamaha F70
pflugrad	posted 11-10-2013 11:15 PM ET (US) I plan to repower my 2004 Boston Whaler 170 Montauk from its current 2004 Mercury 60 FourStroke ELPT EFI BIGFOOT to a Yamaha F70. I would appreciate any advice and lessons learned from anyone who has repowered a 170 Montauk with a Yamaha F70. My main reasons for this repower are: --current 2004 Mercury 60 has over 1,600 hours and maintenance costs are increasing; prefer higher reliability --seeking slightly more power with only a little more weight.
frontier	posted 11-11-2013 01:00 AM ET (US) How does your 170 perform with 60 HP Merc Bigfoot? It was a factory engine option in 2004 but most were equipped with the Mercury 90 2-Stroke or 90 4-stroke. I am very tempted with the F70 Yamaha also. My local Yamaha dealer says they have proven out to be great, trouble free engines since they came out in 2010. Close in weight and performance to the classic, excellent 90 HP Yamaha 2-stroke. We've had a F60 Yamaha on a classic 17 Montauk, but it weighs 500# less than a 170.
Peter	posted 11-11-2013 07:00 AM ET (US) When you say you are "seeking slightly more power", what do you mean by that? Higher top speed or a motor that does not get bogged down easily by added weight? Sorry, but there is no way a 60 cubic inch 70 HP 4-stroke will be close in performance to a 70 cubic inch 90 HP 2-stroke. The 70 4-stroke isn't going to have anything close to the 90 2-stroke low and mid-range torque.
PeteB88	posted 11-11-2013 02:31 PM ET (US) I can't imagine any Montauk without more power. I mean 70HP is go to power for Classic 15s! I'd be thinking, well, more power. Not only is it fun but you can punch it up to a quick planing configuration, throttle back and not have to run the living guts out of your outboard at or near WOT just to maintain nice cruising speed. And you have reserve power to get you out of trouble or stay ahead of a storm. It's your boat and I have no idea how you use it - some people just cruise along slow, pontoon boat style, maybe that's you. Get the 90, I'd go Yamaha or ETEC if repowering my guess is 90 will keep value up especially with new motor.
Peter	posted 11-11-2013 03:58 PM ET (US) With the same displacement, same number of cylinders, but lower profile with more low end and midrange grunt than a Mercury FourStroke 90, the recently announced E-TEC 90 HO might be the perfect motor for the Montauk 170.
frontier	posted 11-11-2013 05:05 PM ET (US) One of the things that makes the F70 Yamaha such a great engine with excellent low and mid range torque is the use of the High Thrust lower unit (2.33 to 1 gear ratio). That also allows it to swing a lot bigger and wider range of props.
OMCrobert	posted 11-11-2013 05:49 PM ET (US) I would wager that you dont see any increase in performance over the 60hp Mercury Bigfoot with a new Yamaha 70hp. With no real increase in displacement and that is a heavy boat to start with. If you are hoping for an increase in performance, I would look at a 90hp.
Peter	posted 11-11-2013 06:22 PM ET (US) The F70 has a higher redline 6300 versus 6000 for the T60 but both motors use the 2:33 gear ratio. I believe the Merc Bigfoot does too. I bet the F70 would swing the same propeller that the current Bigfoot swings on the Montauk 170 and the only real difference will be the top speed. I think the Montauk 170 should be able to hold a 400 lb outboard on its transom without any problem so I wouldn't let weight be a limitation on repower choices.
mkelly	posted 11-11-2013 09:08 PM ET (US) Go with the F90. It was made for that boat. You won't have to run it too hard. [A Yamaha F90 has] 28-percent more displacement; [an F90 is] 100-lbs heavier [than a Yamaha F70, but the added weight is] well worth it. Make sure to pay attention to propeller; customize it for what you want, which may be good [acceleration from a standing start] with a little sacrifice on top end.
jimh	posted 11-12-2013 08:37 AM ET (US) I was initially surprised that a 170 MONTAUK was sold with only 60-HP on the transom. That seems like marginal power for the boat. I had to refer to my original article about the 170 MONTAUK from 11 years ago (2002) http://continuouswave.com/whaler/reference/170Montauk/ to see that there was an option for only 60-HP. If you are accustomed to running the boat with only 60-HP, then an increase to 70-HP is probably going to feel like an improvement, although it probably won't be a dramatic change. The switch to Yamaha from the Mercury-brand engine will be expensive because of rigging costs.
pflugrad	posted 11-12-2013 11:19 AM ET (US) Thanks to all for thoughtful and useful advice! I would still like to hear from anyone who actually runs a Yamaha F70 four stroke on 170 Montauk. Here is additional information regarding my boating experience vs needs: 1. My 10 year experience with the Merc 60 Four Stroke Big Foot on my 2004 170 Montauk is that it powers me fine but is insufficient power with 2-3 friends on board. So I want more power to occasionally take more people on the boat. Also a little more speed would be useful going from fishing hole to fishing hole on the Chesapeake Bay. 2. I store the boat in my garage on a trailer with a swing tongue AND it barely fits (I need to twist the boat on an angle). I calculate that I could get the Yamaha F70 in the garage but not a Merc 90 Four Stroke! 3. The advice received to date is mixed on whether I would actually get more power (moving from a Merc 4 60 stroke to a Yamaha F70)? So I remain conflicted. My Merc 60 slightly under-powers my needs but the Merc 90 or Yamaha 90 is physically too big for my garage. I want to stay with a four stroke so I haven't studied the ETEC option seriously. Again, I welcome and value your opinions....but are their any "Yamaha F70 on a 2004 170 Montauk" continuous wave readers? How can I find them?
Peter	posted 11-12-2013 03:27 PM ET (US) quote: My 10 year experience with the Merc 60 Four Stroke Big Foot on my 2004 170 Montauk is that it powers me fine but is insufficient power with 2-3 friends on board. So I want more power to occasionally take more people on the boat. This tells me that you have insufficient displacement. An F70 will not solve the problem. If you are limiting your choices to a Yamaha 4-stroke and wish to limit the HP, then you should consider the Yamaha F75 instead of the F70 for this application. The larger displacement will give you more load carrying capacity which is what you are really seeking.
frontier	posted 11-12-2013 03:42 PM ET (US) The Yamaha F75 and F90 are the same size and weight (1596 cc and 366#). That's why you don't see very many F75's around. Because garage fit is a big issue, the F70 seems like it might work. I, too, am very interested to see results from a 170 Montauk with a F70 on it. I was happy with an F60 on a classic Montauk. Maybe the F70 on a heavier 170 would be OK for his use.
frontier	posted 11-12-2013 08:14 PM ET (US) Take a look at this performance test on the Yamaha website ("Performance Bulletins" at yamahaoutboards.com): Boat & motor - Sundance B18 with Yamaha F70LA. Factory boat weight 1355 (170 Montauk is 1400#), weight as tested: 2108#. 2 people on board. Top speed: 36.4 MPH @ 6250 RPM Cruising speed: 21.1 MPH @ 4000 RPM (2.4 GPH). Sounds pretty good to me.
OMCrobert	posted 11-12-2013 08:32 PM ET (US) I dont think you will find anyone that has repowered the 170 Montauk [with a Yamaha F70] for the above outlined reasons. The 60hp on the 170 is a rare duck and if anyone has repowered they most likely went with a 90hp or another Mercury product due to the rigging. I would be shocked if you can find someone that has repowered a 170 with a F70 Yamaha. What about modifying your trailer with a hinged swing tongue to allow for a larger engine? I think everyone agrees that you will not see any significant increase in performance if any with the F70. We are trying to talk you out of it as I dont think you will be happy with the ROI.
PeteB88	posted 11-13-2013 03:28 AM ET (US) Hey, we're your buddies: 90. Forget 70 or 60. Go ETEC, everyone I know who owns those motors love them. Kick a hole in your garage if you have to, you will love that set up, a whole new boat my guess especially if you are concerned about performance with more passengers.
jimh	posted 11-13-2013 09:26 AM ET (US) That the performance of your Boston Whaler 170 MONTAUK powered by a 60-HP four-stroke-power-cycle engine declines when three additional people are aboard is not at all surprising. On a small boat like a Boston Whaler 170 MONTAUK, the addition of three people represents a considerable increase in the boat weight. A 170 MONTAUK with a 60-HP engine and one person probably weighs about 1,950-lbs. If you add 600-lbs (or three people) to the boat, the weight increases about 30-percent. The predicted top speed for the boat drops to about 29-MPH from 33.5-MPH. This suggests that the boat may be difficult to get onto plane, and probably cannot be held on plane easily at slower planing speeds with the heavier load. You might want to read the lengthy and profusely illustrated CETACEA article about the 170 MONTAUK at http://continuouswave.com/whaler/cetacea/cetaceaPage58.html This article details the owner experience of one of the first 170 MONTAUK boats delivered by Boston Whaler. It also describes the replacement of the original 90-HP engine with a 115-HP engine.
Peter	posted 11-13-2013 09:37 AM ET (US) Another factor to consider -- resale. If a point in time comes when you are selling the 170 Montauk, the boat will be far easier to sell with a 90-HP (or larger) outboard than a 60 or 70-HP outboard. The 60- or 70-HP outboard limits the boat's versatility and will thus limit the potential buying pool.
masbama	posted 11-14-2013 09:33 PM ET (US) The f70 on the pre 170 montauk would be a good fit. Lighter hull and what not.