Transom Weight for Older 17-footer

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Transom Weight for Older 17-footer

Postby Ruby » Sat Mar 12, 2016 7:31 am

Is a Yamaha 90 four-stroke-cycle outboard too much [transom weight] for an older 17-footer hull?

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Phil T
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Re: Transom weight for an old 17

Postby Phil T » Sat Mar 12, 2016 1:28 pm

Not necessarily.

Are we discussing a pre-1980 16'7 model or a smirked 17' model? What is the interior? Where is the battery located?
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1992 Outrage 17, 1992 Evinrude 115

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Re: Transom weight for an old 17

Postby pcrussell50 » Sat Mar 12, 2016 4:08 pm

I have a Yamaha-made Mercury 90 FourStroke on a newer classic (1998) smirked 17. It is a HEAVY setup, no question about it.

Since I bought the boat in early 2011, I ran dual batteries stored in the center console. Recently, I took them out, and just use one battery that I put in front of the console where the cooler seat would be. That way, I keep the battery indoors on a trickle charger when I'm not using the boat.

The boat is set up for deck space, and fishing, and has no seats, so it's pretty light, however, it does have trim tabs that adds back some weight. I can't help thinking that the designers of this hull never intended it to have a nearly 400lb motor on the back. The 90-HP outboard engines of the time, were probably at least a 100-lbs lighter, and that was for 90-HP. A 75-HP engine would be lighter still.

Other than being a little slow, top speed around 32 mph, the extra weight is mostly unobtrusive. I have read here that it's worthy of consideration that the extra weight might make the boat more prone to capsizing if you're fighting a big fish abeam, in rough seas, but I've never caught a big fish in this boat, or put much weight in the gunwales in a rocking sea to put that theory to the test.

For those who question the "Yamaha-ness" of the Mercury labelled motor, I get it serviced at the Yamaha dealer, using Yamaha parts. It is a Yamaha, no matter the paint color and logo on the cowl.


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Re: Transom weight for an old 17

Postby Ruby » Mon Mar 14, 2016 10:32 am

The hull is around 1970, modified Montauk layout, fuel tanks under console, battery by the transom

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Re: Transom weight for an old 17

Postby goldstem » Mon Mar 14, 2016 1:10 pm

[An outboard engine weight of] 400-lbs does seem a bit heavy for the old 16/17 boats, smirked bow or not. The old OMC V4 engines were about 320-lbs, they were about the maximum engine weight the hull really wants. Current four-stroke-cycle outboard engines of about 250-lbs engine weight run very well.

[For a 17-foot boat that is] lightly-loaded a 50 or 60-HP outboard engine [of four-stroke-cycle design will produce a top boat speed of] 34-MPH, and [permit] cruises all day in the [range of 25 to 29-MPH]. That would be my choice.

Now you will hear from the crowd that thinks that anything less than 120-percent of maximum rated HP is under-powered.

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Re: Transom weight for an old 17

Postby contender » Mon Mar 14, 2016 10:15 pm

I have a 1975 hull with a 1985 140 looper (evinrude) engine, weight about 320 lbs. never a problem....

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Re: Transom weight for an old 17

Postby rlboeri » Tue Mar 15, 2016 10:40 am

I have a 1988 Montauk, so it may not be the same, but I contacted Chuck Bennett at Boston Whaler regarding transom weight on my boat. He indicated that the engineers at Whaler would not recommend anything over 330 pounds for it. Thought that I would pas it along.


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Re: Transom weight for an old 17

Postby Buckda » Tue Mar 15, 2016 12:43 pm

We have a 2006 Mercury 90 HP fourstroke on a 1972 Katama at camp. It is terrible. I'm currently looking for a classic 21' Outrage to hang that motor on, and considering moving our 50 HP Honda to the Katama from the pontoon boat it is currently on.

400 LBS is too much weight on the transom - wet feet in a following sea, terrible handling, and the bow sits so high that the wind reallyl blows the boat around so it has terrible manners at the dock. I inherited this setup when I got to this job and can't wait to fix it.

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Re: Transom weight for an old 17

Postby Whal » Wed Mar 16, 2016 7:58 am

[I concur with] what Buckda said; he is exactly right I know from first-hand experience. I changed to a 257-lb Yamaha F70 and my boat handles like a sports car-- the lighter the better, and 400-lb is too heavy.

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Re: Transom Weight for Older 17-footer

Postby jimh » Wed Mar 16, 2016 1:11 pm

One ought to give some regard to the strength of the transom on a boat that is now coming into its 46th-year. Considering that when the boat was first designed and first constructed, the intent was the outboard engine on the transom would weigh about 300-lbs, the notion that 46-years later the hull can hold an engine that weighs over 400-lbs seem to make a lot of assumptions. In my mind, the first bad assumption is the transom strength is as good as it was 46-years-ago. Most structures that are 46-years-old and immersed in water have some deterioration.

The second assumption is that increasing the engine weight by a factor of one-third to 400-lbs from 300-lbs will not cause any significant change in the boat's handling or behavior. This cannot be true. On a small and relatively light boat, adding 100-lbs to the transom is bound to cause a change in the behavior of the hull, and, as Bucka so succinctly described, not good changes.