Johnson 70hp - How fast does it push your boat?

[Mark42]

Trying to figure out what sort of performance a 1990's or 2000's 3 cylinder Johnson 70 hp will push my 16' Bayliner. So if you have a 70 hp Johnson on your boat, I would really like to hear how fast it goes, and what size boat the motor is on!

Thanks much!

Mark.

 

[JB]

Re: Johnson 70hp - How fast does it push your boat?

After carefully optimizing the rigging and trim my JohnnyRude 70 would push my Boston Whaler Sakonnet 16 to just under 40mph with just me aboard.

 

[wtxmale]

Re: Johnson 70hp - How fast does it push your boat?

had 1984 70hp johnson on 15'6" blazer bass boat,,prop was a SS 17 pitch,,ran 45 with one person

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

Wow, those are good numbers. Right now the tired old 85hp Force is only able to muster 32 mph with me, wife and two small kids. Earlier this year it was able to do 38-40 mph. I know the compression is down on all cylinders, but they are still all the same. Just wear I guess, because it starts and runs well.

If the 1985 Force 85 hp is actually rated 85hp at the crank, and not the prop, then accounting for the change in hp rating, plus wear and tear, I would think a 70 hp Johnson/Evinrude could push the boat to 35 mph. Don't forget the hard top adds a bit of wind resistance, and probably a big vacuum behind the cabin.

The 16' Bayliner cuddy was factory listed as weighing 1150 lbs boat and motor. Add 100 lbs of gear, 150 lbs for a full 17 gal fuel tank, and about 50 lbs for the hard top (net gain). That gives a total weight of 1450lbs. Also, the 70hp will save about 20 lbs over the old Force, so that would help.

What do you think? Similar, better or worse performance with a good running 70hp Jonnyrude?

 

[Faztbullet]

Re: Johnson 70hp - How fast does it push your boat?

In 1974 Johnson set a speed record with stock 70hp on 14ft Allison of 70mph!!!

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

Oh, darn.... It appears that the 85 hp Force I have is rated under the newest rating system. That means I really am losing 15 hp when using the Johnson 70 hp. Still..... The compression on the Force is in the low acceptable range, and that means loss of HP no matter how you look at it. I doubt the Force is really producing 85 hp today. It's a 25 year old motor that never had rings or bearings replaced.

To that end......

How well does your boat perform with a FULL load? The light/near empty numbers are great. Very encouraging. But how well does your boat do with a full load, IE 4 adults, or other similar load? Do you drop 10, 15, or 20 mph when loaded?

Right now, the boat does not lose more than 3-5 mph when fully loaded.

Please help me decide if the Johnson 70 is a good choice for me by posting your experience.

Thanks so much...

Mark.

PS, If you have a Johson/Evinrude 70hp service manual, please check the WATT rating on the HP. HP is often listed in Watts, and that makes comparison easier.

 

[ezmobee]

Re: Johnson 70hp - How fast does it push your boat?

What's your Capri rated for? I still think one of those 3 cly 90HP Yamaha's would be sweet for your boat.

 

[Home Cookin']

Re: Johnson 70hp - How fast does it push your boat?

70 on a 17' Key West DC--a flat "bay boat" hull. I'd estimate 35.

 

[JB]

Re: Johnson 70hp - How fast does it push your boat?

That bilgeliner is a barge compared to the other boats mentioned, and the difference between bolted on and fine tuned rigging is often as much as 8-10mph.

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

What's your Capri rated for? I still think one of those 3 cly 90HP Yamaha's would be sweet for your boat.

I agree, and have been looking for a good one. A 1998 C90 is listed as weighing 255lbs on NADA, and the 85 Force F85 (no tilt/trim) is listed as 249, so its a wash. I always thought the Force weighed 285, but that is with tilt/trim. Anyway, the Yamaha is what I have my eye on.

70 on a 17' Key West DC--a flat "bay boat" hull. I'd estimate 35.

The Bayliner will take a little more HP to get the same speed as your Key West, because of the hull shape, but 35 isn't bad at all.

That bilgeliner is a barge compared to the other boats mentioned, and the difference between bolted on and fine tuned rigging is often as much as 8-10mph.

Now, now, JB. No need to call my boat brand names. Now you went and hurt my feelings. ...... JK!

Hey, its a 16' boat with a stepped deep V hull, so yes it will take more HP to keep in on plane than a flats boat, but that is true of any V hull. At at under 1300 lbs boat and motor, its fairly light. (oe spec is 1149 boat and motor, so I added 150lbs for upgrades). Its just unusual to find such a deep V on such a small boat. But that's what makes it ride so nice in the chop. I go out in water that my MFG just couldn't handle because the MFG is a shallow V .

I think the 70 Johnson would work, but my preference is the 90 yamaha. Thought I found a good C-90 on ebay, but close up photos shows welding on the gear case, lots of deep pitting on the gear case and a welded on stud on the powerhead. Don't like that the motor had to be welded back together and all that pitting. So its now off my list... Darn!

 

[Boss Hawg]

Re: Johnson 70hp - How fast does it push your boat?

Had a '87 70hp Johnson behind a 15' Starcraft fiberglass bassboat & with normal load + 2 people under ideal water conditions it'd hit 35 :redface:

BTW- LOVED that motor

 

[whofan]

Re: Johnson 70hp - How fast does it push your boat?

I have a 1650 Lund fisherman. My 2000 Johnson 70 will push it 30 mph with a 17 in prop.
Max hp rating for my boat is 90hp.

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

I have a 1650 Lund fisherman. My 2000 Johnson 70 will push it 30 mph with a 17 in prop.
Max hp rating for my boat is 90hp.

Everyone pay attention! This is a member who knows how to respond to a question. Gives boat, year, HP, and PROP!!!!!

Way to go my friend. Way to go....

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

I've been checking the boats that came with 70hp Johnsons, and as many as I could from the members who posted their boats above. The bottom line is that the boats with the 70hp typically weigh 400 to 600 lbs LESS than my boat, and typically are not deep V hulls.

So it appears that the Johnson 70hp will barely be able to reach 30mph with a full load, and could be detrimental to safe performance in extreme adverse conditions.

I will continue to look for a 90 Yamaha, and may have to settle for the obese 90hp Johnson/Evinrude V4 (weighing in at 70 lbs more than the Yamaha).

Oh well. I've got time on my side now that its the end of the season in the north east.

 

[jay_merrill]

Re: Johnson 70hp - How fast does it push your boat?

65hp Johnson "triple" on a 17.5 foot Glassmaster trihull .... 29 statute mph by GPS. Its a heavy boat, with a lot more weight than your boat and 5 less hp - I would expect your boat to do about 35 mph, or better.



???

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

65hp Johnson "triple" on a 17.5 foot Glassmaster trihull .... 29 statute mph by GPS. Its a heavy boat, with a lot more weight than your boat and 5 less hp - I would expect your boat to do about 35 mph, or better.



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How heavy is "a lot more weight" than my boat? I'm estimating 1300 lbs boat and motor. No people, gear, etc. Do you have a good idea what the boat weighs now or what the original spec for the weight is? Also is that trihull a shallow V or deep V?

I was surprised to find that the 16-17' center/side console boats typically only weigh 600 to 800 lbs. So they have a lot less wind resistance, and weigh a lot less than my boat, giving the 35+ mph speeds.

I'm afraid that when I add 700 lbs of people and gear, the 70 hp will just not cut it. The old 85hp has a struggle when the boat is loaded as it is, even with trim tabs. And the boat is dry as a bone (I know, I cut inspection holes with deck plates to keep an eye on the foamed under-deck. Dry, dry, dry.)

Thanks!!!!

 

[jay_merrill]

Re: Johnson 70hp - How fast does it push your boat?

My boat is about 2,000 pounds loaded in my typical configuration, which includes boat, motor, 24 gallons of gas, three coolers which double as seats/storage, gear and my big ole fat butt. If I take a guest or a couple of models for a photo shoot, its heavier.

As for configuration, I'd call it a shallow V.

My last trihull was also a Glassmaster and had a pair of 1958 ERude 35hp motors on it at one point. Those motors really only deliver something a little less than 30hp to the props and the dual engine setup results in more drag than a single engine installation. I had 14" pitch props on the motors for this boat.

Since this boat was 15.5 ft in length, I would say that its closer to your boat in weight. If I remember correctly, the empty weight was about 800 pounds. Add 300 pounds of motors, 24 galllons of gas, gear, etc. and the operating weight would be about the same as your boat.

With probably no more than 58hp total HP to the props, plus the added drag, that boat probably ran at least in the mid 30s range. I never checked it via GPS, but it was considerably faster than my present boat.

You mentioned that your 85hp Force used to push your boat at 38-40 mph and that it is rated at the powerhead, not the prop. If the 70hp that you want to put on it is rated at the prop, I see no reason why you shouldn't get about 35 mph out of it, as long as you prop it correctly.



???

 

[Bigprairie1]

Re: Johnson 70hp - How fast does it push your boat?

I can't help you with any direct experience Mark...but those 70hp motors are pretty good according to legend. (Are they not of the 'looper' variety, explained to me a while back?)
Anyhow, I don't think you are going to see a world of difference no matter how you cut it on that choice tho' on that boat vs. the 85 Force.
What about bumping up to a 85hp Johnson or maybe a 100 or 115hp?
Those would get that boat humming I'm sure.
BP
Note: Just what is your compression right now on the Force?....100-ish psi? or?

 

[Mark42]

Re: Johnson 70hp - How fast does it push your boat?

I can't help you with any direct experience Mark...but those 70hp motors are pretty good according to legend. (Are they not of the 'looper' variety, explained to me a while back?)
Anyhow, I don't think you are going to see a world of difference no matter how you cut it on that choice tho' on that boat vs. the 85 Force.
What about bumping up to a 85hp Johnson or maybe a 100 or 115hp?
Those would get that boat humming I'm sure.
BP
Note: Just what is your compression right now on the Force?....100-ish psi? or?

Compression was 120 on all 3 cylinders when I checked two years ago. The Force service manual lists the compression spec as 145-165, so it's down on power.

But I think the 90 Yamaha or 90 Johnson is the better choice over the 70 Johnson. Boats max hp rating is 90.

At any rate, I need power tilt/trim, and the Force does not have it. And parts are getting harder to find, getting more expensive, and I want something more reliable.

BTW, been looking at a few used motors lately. Anything under about $5000 is a mess, or 25 years old. I already have a 25 year old motor.

 

[jay_merrill]

Re: Johnson 70hp - How fast does it push your boat?

I'm a die-hard OMC guy, but have to admit that the 3 cylinder, 90hp yammies intrigue me. I have heard that some of the early models had some oil injection issues, but once that problem was worked out in later models years, the motors supposedly became pretty "bullet-proof."

I have also heard that they are very good on fuel in general and especially in comparison to OMC v-4s. I would think that this would be an excellent choice for your boat and I bet you would gets speeds in the 40 mph range.

Stray to Yamaha if you must - we will forgive you in the Johnson/Evinrude forums!



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