90hp on a 20' 200hp rated boat?

[444]

Here is the boat I've got but with a non-running outboard(needs full rebuild):

http://www.classicglastron.com/1986_Glastron_CVX20sprint-intim.html

I've got an excellent condition 1986 Mercury 90hp inline 6 I could borrow off my other boat so I could at least get this hull in the water. The CVX's boat hull was designed and rated back in the days of measuring HP at the crank, and I know before Merc went to prop HP ratings, my exact same motor was rated at 115 crank HP. I know it's a good bit below even the 70% of rated power rule but I've always heard how the Merc I-6's made such good power... I read an old magazine review saying this hull did 62mph with a late 70's 200hp Evinrude on it. If I could at least pull someone on a tube at 25 with the driver and one passenger without wringing the motor right out I would be happy for the time being. Right now I have that 90hp on a 78 Glastron GT150 (small 15' boat) hull and it pulls someone on a tube at an acceptable speed with not much throttle but it's a lot less boat. My question is will the 90 get the job done for a while until I get the V6 ready? Or do you think it will be a total dog, not want to plane and not be worth the effort of unbolting the 90 from the GT150?

 

[5150abf]

Re: 90hp on a 20' 200hp rated boat?

That should surely pull a tube, a 90 is decent sized engine.

Just because it is rated for 200 doesn't mean it won't work with less, look at bass boats, some are rated for 250-300 horse but will work fine with a 90 or 150.

And it is the engine you have so why not use it.

 

[mpsyamaha]

Re: 90hp on a 20' 200hp rated boat?

i would think the 90 should plane the boat with the right prop. obviously wont be a speed demon, but it should work.

 

[lprizman]

Re: 90hp on a 20' 200hp rated boat?

not worth the effort,,,sure to dissapoint

 

[Frank Acampora]

Re: 90hp on a 20' 200hp rated boat?

Yes, the inline six is a strong engine, but that only goes so far. Even at 115 HP, there is only so much you can do. The 90 by consensus is conservatively rated by Merc, and will plane the boat --BUT--a skier, especially a slalom skier will have trouble. Correctly propped, you are probably looking at about 25 MPH top end without a skier and less with. AND: Even if he does get up, on a hard turn, the skier will be able to out-accelerate the boat and actually end up in front of it (to the side) with a slack line. (Yes, I have done that.)

Now, I am an experienced slalom skier and have deepwatered behind a little 55 --BUT-- (there's that little word again) I tried behind a 16 foot Glastron with a "Tower of Power" 115. With 4 people in the boat, it was unable to accelerate fast enough to pull me up.

 

[DuckHunterJon]

Re: 90hp on a 20' 200hp rated boat?

FWIW, my boat is a 20', with a 200 Merc on it and it will do about 65 mph. My guess is the 90 would push it along on plane, proably around 35 - 40 mph - plenty to cruise, but pulling will be limited. This is just my guess based on the water drag increasing as a function of speed (I believe it's a cubic fuction) so hitting 60 requires much more than twice the HP to hit 30 mph. In the end, if you have the motor and the time, give it a whirl.

 

[ezmobee]

Re: 90hp on a 20' 200hp rated boat?

I think it will plane it ok. Won't be fast but should get the job done. My buddy has a 90 on a 21' Starcraft Chieftain with a cuddy that's rated for like 175 or something. It planes nicely and gets you there but top speed is like 26MPH.

 

[jp10]

Re: 90hp on a 20' 200hp rated boat?

You bought Batman's boat?

 

[jayhanig]

Re: 90hp on a 20' 200hp rated boat?

Here is the boat I've got but with a non-running outboard(needs full rebuild):

http://www.classicglastron.com/1986_Glastron_CVX20sprint-intim.html

I've got an excellent condition 1986 Mercury 90hp inline 6 I could borrow off my other boat so I could at least get this hull in the water.

If you decide to do this, please come back and tell us how it did. We can then determine who's right and who's wrong about this.

In the woodworking world, people always have a tendency to call the other man's tool crap, even though they've neither owned one or even used one. I have a table saw that's been great for me even though it was denigrated by several others, none of which had ever used one.

This way, everybody can learn something.

 

[Charlie in TX]

Re: 90hp on a 20' 200hp rated boat?

I think it will be ok.

I have a '88 McKey Craft rated at 160hp. It has a '88 90hp Johnson. Top speed of 30. Pulls a tube (raft type) with 3 people pretty easy.

Back in my younger days, my buddy had that boat in a 18 footer with a 100hp rude. It pulled 4 skiers often. Easily pulled a para-sale. All much harder to pull than a tube.