BIG motor on a 18' checkmate. Opinions please

[cosblock 300]

First post, hi to all.

Anyways, I have the chance to buy a rare 1983 Mercury 300 black max for a good price. It runs good (I heard it) but I don't know if I should put that much motor on a 18'6" checkmate. I realize that I won't be able to insure this setup and thats ok with me. Does anyone have any thoughts or experiences?

-Jeff

 

[CFronzek]

Re: BIG motor on a 18' checkmate. Opinions please

Although motor size discussions always involve horsepower the calculation of maximum motor size has a lot to do with motor weight.
As you mount more and more weight on the transom it sinks deeper into the water. This can become a safety question particularly when the boat is at rest. Also a big change in the weight bias rearward can make for "unususal" handling at high speeds.
There is also the question of how much additional abuse your tansom will take but that's a question that only an engineer could answer.
Since you didn't supply any numbers a best guess would be that you could get away with increasing the weight and/or the horsepower by 20% over the allowable limit but you might have to shift some weight forward to keep the boat on an even keel.

 

[walleyehed]

Re: BIG motor on a 18' checkmate. Opinions please

The checkmate is designed for high HP and good speeds...seldom does anyone follow guidlines for this type of set-up.
You need to discuss this with Dhadley...he runs many of this style and can answer about anything you need to know....It may be Monday before you hear from him though.

 

[cosblock 300]

Re: BIG motor on a 18' checkmate. Opinions please

thanks for the replies. the boat is rated for 185 hp but I figure that has alot to do with weight bias like cfronzek mentioned. I think the 300 weighs about 100 lbs more than my black max 150 does. I could counter that by putting 100 lbs of ballast in the front storage cubby hole (it's a bowrider). If anyone knows actual weights please post. I'm guessing the 150 weighs ~420lbs and the 300 weighs ~540lbs. They are both 1983-84 models.

walleyehed thanks for the contact, I may send him a pm.

-Jeff

 

[walleyehed]

Re: BIG motor on a 18' checkmate. Opinions please

He'll be around Monday, and is the only one on this forum that I know of, that will pretty much know the ins and outs. I know he has some experience with checkmates and several others of simular design.

 

[Solittle]

Re: BIG motor on a 18' checkmate. Opinions please

Shusssh - gota keep a low profile on you plan lest the lawyers find out ifn you have any kind of accident. They will clean your clock.

 

[tashasdaddy]

Re: BIG motor on a 18' checkmate. Opinions please

nada says the 150hp is 375 lbs, and 300hp is 565lbs. better beef up the ransom with some weight distribution plates. i'd also get a 200lbs person to sit on top of the 150hp and see how the boats sits in the water. its and easy test, to see if you have enough freeboard left on the transom. no point getting swamped.

 

[deejaycee_2000]

Re: BIG motor on a 18' checkmate. Opinions please

oooooo, how did I miss this post ......... i've done exactly what you wanto do now, I put a 375hp johnny/rude offshore racing outboard on a 24 ft bayliner speedboat ..... that thing scares the $@£% out of me ..... even for me, runs like hell but a whole lot of fun (heavy on fuel) ... I wouldn't take it out on a windy day though .... on a 18'6 bowrider, i would say go for it, you can reinforce the transom with stainless steel cover plates ..... seeing that you can't insure the setup, put as many empty coke bottles in the bow as possible ..... have fun ...

 

[Texasmark]

Re: BIG motor on a 18' checkmate. Opinions please

I agree with dee. Not just dead weight but when you let the hammer down on that 300 it's like peeling a bannana in terms of torque on top of your transom/motor mount.

Mark

 

[cosblock 300]

Re: BIG motor on a 18' checkmate. Opinions please

Thanks for the feedback guys.

So would the 300 use roughly twice the fuel of the 150? That is an unfortunate factor for me with the price of gas these days.

 

[walleyehed]

Re: BIG motor on a 18' checkmate. Opinions please

Likely a bit more than double..depending on how you run it.

 

[deejaycee_2000]

Re: BIG motor on a 18' checkmate. Opinions please

Fuel wise .... I would say in 15min you can easily burn 25 litres (6.6 gallons) of fuel ... here in South Africa fuel costs .... R7 per litre that is about $1 per litre (about $3.75 per gallon) a 2litre coke is still more expensive if you look at it that way ...

 

[cosblock 300]

Re: BIG motor on a 18' checkmate. Opinions please

Wow thanks guys. I may just pass on the 300. As tempting as it is, that fuel cost may be the breaking point for me...Maybe!

Thanks again,
-Jeff

 

[phatmanmike]

Re: BIG motor on a 18' checkmate. Opinions please

those 300 mercs drank LOTS of fuel!

plus, i wouldnt put that much weight on that boat. its just not meant to be!

 

[Silvertip]

Re: BIG motor on a 18' checkmate. Opinions please

Look at it this way. It takes a given amount of fuel to make a given amount of horsepower regardless of engine size or design. Put a decimal point one position left in the horsepower rating and you'll be very close to the amount of fuel you'll burn per hour at wide open throttle. Your 150 would be 15 gal/hr and the 300 would be 30. Those work out pretty close in the tests I've seen where fuel flow monitors are used. Note that I said "wide open throttle". Fuel consumption is a great deal less if you cut it back a little. But when you have all that HP why would you want to do that??? d

 

[AlanR]

Re: BIG motor on a 18' checkmate. Opinions please

I had a Johnson V8 3.6 Gt (its in my avatar) It did about 103 mph + (if you had the balls to get it that high) she'd keep going. She was a real rocket ship and im kicking my self for selling it but then i Look at how much gas I was going threw on a weekend it just didnt fit into my buget. My hydrostream was rated for a 140 or 150 i dont remeber but it was around there and the 300 did just fine on it. I accutly had a guy sit on top of my 300 while driving to get more bounce out of it and it still did just fine. I think youd be alright with the 300 on your check mate, just watch out for full speed (if you get there) and your gas price's i was going threw about 700 buxs easy in a good weekend of boating.

I hope you go with the 300 there really a wicked motor. Just if you can afford the gas bill

 

[Dhadley]

Re: BIG motor on a 18' checkmate. Opinions please

Depending on which Checkmate it is, it may handle funny at certian speeds. They are great boats but some were not meant to go real fast. Not compated to a Hydrostream or an Allison (of the same era). I think you saved yourself a lot of hassel by passing on the motor. Your 150 will do just fine. And then some probably.

Just for kicks, check on the cost of a piston for that 300. And availability.

 

[AlanR]

Re: BIG motor on a 18' checkmate. Opinions please

Yeh people sell the 300's and 250's motors cheap because there so thirsty on fuel

 

[waterinthefuel]

Re: BIG motor on a 18' checkmate. Opinions please

Dude, if you do it, get a video of that thing. And be careful, the sound barrier is 750mph at sea level. Going over that can result in some hefty fines!

 

[AlanR]

Re: BIG motor on a 18' checkmate. Opinions please

Dude, if you do it, get a video of that thing. And be careful, the sound barrier is 750mph at sea level. Going over that can result in some hefty fines!

LOL!!! My hydro with the 3.6 GT v8 would only do 112 mph+ It might do more but im a BIG baby and got scared. I should have taken a video of it. It was a scarey machine