How Would this Motor Work On An 18' Holiday?

[Laker99]

I'm looking for a 1974 or so 18' Holiday OB. How well do you think this 1985 Merc 115 would push it? I know the boat is rated for a 140HP. I have heard that in 1984 Merc went with prop rated horsepower rather than at the head and that this year motor was probably the old 125HP. I wouldn't be out to set any speed records and would hope it could run upper 30's. I'm kind of a 3000 RPM guy so it doesn't inhale fuel. The 18' Holiday is 900 pounds. Curious to hear what you think. I have this motor from a rotted out fiberglass boat and trailer I bought for $500. Sold the trailer for $300 so I have this motor for about $200 and my labor to cut up the hull and take it to the dump.

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[GA_Boater]

Started a new thread for you, Laker. Questions like this get lost in the CL/Ebay thread.

 

[Laker99]

Thanks. Sorry about that.

 

[Watermann]

That Merc would be a perfect companion to the 18' Holiday. :thumb:

Be sure to loose that fin thing from the LU though.

 

[jbcurt00]

Not sure if Mercury was still underrating their OBs in 1974, but no matter, I think a 1974 Merc 115 would push you along just fine on plane, no problem.

 

[64osby]

We run a 90 JohnnyRude on the 21" Mariner, High 30's all day long. The dry hull weighs 900. That Merc would work just fine.

Hope you find a nice Tin hull.

 

[pckeen]

I thought the 18' Holidays were rated for 120. We ran a 70s 115 Johnson on our 68' 18' Holiday and it ran fine. Then we upgraded to a 1 year old 90 Yamaha, and it ran even better. That 115 is perfect for your boat.

 

[Laker99]

Sounds like the 85 Merc 115 will be a good fit. I think I am going to decal it up like a 1974 motor. And, yes, I have already ditched the hydrofoil off the lower unit!

 

[roscoe]

Rumor has it that the 115 was based off the 140, and put out more than 115 indeed.
115 I6 pushed my 18SS at 42 mph.
It is not a very fuel efficient engine though, and I've had several of them.

 

[achris]

That was the last of the in-line 6s... Still my favourite engines. But, they have a couple of little things you need to know about.

Firstly, NEVER overload them. They'll pop a piston. Make sure when you do the prop test, you push it right up to the top of the range. If it's the 'power ported' block and pistons, 5500-6000. If it's not power ported, then 5000-5500....
Second. Merc coated the inside of the water jackets on those blocks, in an effort to fight corrosion, but that means heat can't get out quite as fast, and the middle cylinders tend to get a little warmer. We found we needed to open up the main jets in the carbs one size to just bring the crankcase temps down a little....

Good luck with it....

Chris.......

 

[smokeonthewater]

FWIW... That hull is rated for a flywheel rated 140 and that merc is a PROP rated 114.... it just happens to be 140 hp at the flywheel or in other words that motor IS the max hp that the boat was intended to run.