1974 MONTAUK 17 Re-power Suzuki DF90

Optimizing the performance of Boston Whaler boats
nlbounds
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1974 MONTAUK 17 Re-power Suzuki DF90

Postby nlbounds » Mon May 18, 2020 1:31 pm

I plan to buy a new SUZUKI DF90 engine for my 1974 MONTAUK 17 to replace a Johnson 70-HP engine. The DF90 weighs about 100-lbs more than the Johnson 70-HP.

Q1: Are there concerns about the weight of a DF90 on a MONTAUK 17?

Q2: Did Boston Whaler state a maximum engine weight for a 1974 MONTAUK 17 boat?

biggiefl
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Re: 1974 MONTAUK 17 Re-power Suzuki DF90

Postby biggiefl » Mon May 18, 2020 3:31 pm

All your answers are here I believe: http://www.continuouswave.com/forum/vie ... f=4&t=5435
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

jimh
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Re: 1974 MONTAUK 17 Re-power Suzuki DF90

Postby jimh » Mon May 18, 2020 5:25 pm

nlbounds wrote:Q2: Did Boston Whaler state a maximum engine weight for a 1974 MONTAUK 17 boat?
No. Boston Whaler did not specify a maximum engine weight in 1974 for their MONTAUK 17 boat. In 1974 federal regulations compelled Boston Whaler to only state a maximum horsepower for the engine. You can find the specifications for a c.1974 MONTAUK 17 in the REFERENCE section. See either of these two articles:

Dimension and Production Information
http://continuouswave.com/whaler/refere ... tions.html

--or--

The 16/17-foot Hull
http://continuouswave.com/whaler/reference/16-17/


nlbounds wrote:Q1: Are there concerns about the weight of a DF90 on a MONTAUK 17?


The weight of an outboard engine on any boat is always a concern. From that general precept you can infer that the weight of a DF90 engine on a MONTAUK 17 is a concern.

What is the weight of the engine you plan to buy? You never really tell the readers the actual engine weight.

A better way to ask if the DF90 engine's weight will be a problem would be to clearly state the DF90 engine weight. To tell us that the DF90 weighs more than some other engine does not give any real information about the weight of a DF90. Readers would have to already know how much the other engine weighs in order to figure out how much the DF90 weighs. Instead of leaving this to the readers to figure out, just tell the readers how much the engine you plan to buy weighs.

Is the engine you plan to buy a Suzuki DF90 or a DF90a? The two models are different.

A MONTAUK 17 boat made in 1974 was designed to use engines made in 1974. The boat is rated for 100-HP. A reasonable inference can be made about the weight of a 100-HP engine in 1974 by looking at the weight of older outboard engines. An article has collected the weight of older outboard engines. See

Weight of Older Outboard Engines
http://continuouswave.com/ubb/Forum3/HTML/011042.html

In c.1974 it would be very common that a MONTAUK 17 would be rigged by a dealer with an OMC V4 100-HP engine. From the article on the weight of older outboard engines, you will find this information about OMC V4 100-HP engines:

V4 1632 cc platform, 85/88/90/100/115 HP

20 inch shaft, elec. start, man. tilt -- 288 lbs
20 inch shaft, elec. start, trim/tilt -- 301 lbs
25 inch shaft, elec. start, trim/tilt -- 311 lbs


From that historical data, a reasonable inference can be made that an outboard engine of about 300-lbs would be the heaviest engine used in 1974 on a MONTAUK 17 boat.

Now, if you would just tell us how much the engine you plan to buy actually weights, we could then compare its weight to the 300-lbs that was anticipated to be the engine weight in c.1974. From that comparison some judgements or opinions could be provided.

There can be no dispute that a boat made in 1974 or possibly late in 1973 is now, in 2020, 46- to 47-years-old. There is no reasonable basis to presume or think or infer that the strength of the wood and fiberglass laminate in the transom of a 47-year-old boat is now greater and stronger than it was back in 1973 or 1974. The truth is quite the opposite: one can reasonably assume that after 47-years of exposure to weather, water, and sunlight, and to the forces of normal use of a boat, it is more likely that the strength of the wood and fiberglass in the transom is not a great as it was in 1973 or 1974.

This leads to the reasonable conclusion that the maximum engine weight that should be used on a c.1974 MONTAUK 17 should not exceed about 300-lbs.

biggiefl
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Re: 1974 MONTAUK 17 Re-power Suzuki DF90

Postby biggiefl » Tue May 19, 2020 10:36 am

"This leads to the reasonable conclusion that the maximum engine weight that should be used on a c.1974 MONTAUK 17 should not exceed about 300-lbs."

FALSE! Many people had 300lb engines as well as a small kicker engine and batteries in the stern of those boats exceeding that weight by over 100lbs back in the day.

The engine, as we have been discussing for weeks on the thread I linked, is 347lbs I believe. From the last set of pics most of us have concurred that the static trim of the smirkless 16 is more than appropriate with the new Suzuki DF90 engine.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

jimh
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Re: 1974 MONTAUK 17 Re-power Suzuki DF90

Postby jimh » Tue May 19, 2020 10:50 am

biggiefl wrote:Many people had 300-lbs engines as well as a small kicker engine and batteries in the stern of those boats exceeding that weight by over 100-lbs back in the day.


The weight of a battery is not in question. We are discussing the weight of the main propulsion engine on a 1974 MONTAUK 17, not the combined weight of auxiliary engines and batteries and other gear in the stern of the boat.

jimh
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Re: 1974 MONTAUK 17 Re-power Suzuki DF90

Postby jimh » Tue May 19, 2020 10:58 am

Since we have never been told the weight of the engine that is planned to be used, I will assume it will be a SUZUKI DF90a. I looked up the specifications. If the engine that is going to be purchased will be a current model SUZUKI DF90a with long shaft, the engine weight is 343-lbs according the the manufacturer's specification.

If we compare 343-lbs to the weight of a c.1975 OMC V4 100-HP at 301-lbs, we see the proposed engine weighs more. The increase is 42-lbs. This is an increase in the engine weight of by a factor or 343/301= 1.139 or a 14-percent increase in engine weight.

Whether or not an increase in engine weight by 42-lbs or 14-percent is to be a concern is left to the individual to decide. But there is no doubt that the DF90a will weigh more than an older V4 100-HP engine weighed when engine of that type were commonly used on 1974 MONTAUK 17 boats.

Can we make a reasonable inference that even 47-years later the transom of the MONTAUK 17 boat in 2020 is sufficiently strong to tolerate an engine weight that is 14-percent higher than the typical engines used when the boat is new? Again, that is left to the individual to decide.

I don't see any way to endorse the notion that a 47-year-old transom is now completely suitable for engines of more weight than were generally used when the boat was new. Also, there is no basis to know the strength of the 47-year-old transom. It might have cracked laminate and rotten wood. Or it might in as-new condition.

biggiefl
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Re: 1974 MONTAUK 17 Re-power Suzuki DF90

Postby biggiefl » Tue May 19, 2020 1:56 pm

"I don't see any way to endorse the notion that a 47-year-old transom is now completely suitable for engines of more weight than were generally used when the boat was new. Also, there is no basis to know the strength of the 47-year-old transom. It might have cracked laminate and rotten wood. Or it might in as-new condition."

Absolutely TRUE.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll: