Practically, it shouldn't be a big deal. But, it is illegal and you can get tagged with a fine for it. I have no idea if an officer would cite you for 5hp over, but if you got someone on a bad day you might end up paying.

HP ratings are based on the measuerments of the hull. The formula uses hull length, beam width, transom height to reach an HP limit. That's how for the example mentioned above the Reatta hits 130 HP. That's also why my Lund hull is 16'10" for example, not 17' on the nose, but to reach the max and hit the 115 HP number, which by no coincidence is a commonly made HP motor.

Removing the Coast Guard plate is illegal as is overpowering a boat. Simple as that. You're only asking for trouble and potentially worse regarding insurance, etc.

DNR conservation officers will use this formula to figure out your max. hp rating if the tag is missing.If your motor is too much hp for the boat, you get a citation.They will then tag you for not having the coast guard tag.Sheriff's deputies, who are on water patrol, will use the formula,too. Coast Guard, and Coast Guard Auxilary boats, will enforce this as well.You will not only get a ticket, but also a tow back to shore, and your trip will be over until the infraction is corrected.

Hull design also plays a part as well as length and beam. Not only would your insurance company leave you hanging, but how about a lawsuit by the guy that got hurt or killed in ANY accident you have, not to mention living with that for the rest of your life. Believe it or not, the NMMA and coast guard came up with HP ratings for a reason.

if it was me I would not worry about it, when it comes to insurance, I always handle the boat much different depending on who is riding with me, Slower wifey/kids, wide open till you see god then back her down a notch with my buddy. how ever the torque curve may twist it up a bit and that would be my biggest concern. it happened to me, weakend rivots and started to leak, a duck boat and the only motor I had at the time.

Personally, I would not have a problem with it on my boat.

The Merc "Classic 50" and 45 (80's vintage) are the same motor.

5hp diff is just a drop in the bucket.

Sometimes weight is more of an issue, like putting a 4 stroke on an older boat. You can have the same hp, but the 4 stroke might be to heavy for your transom. Some manufactures (Alumacraft) actually had to go to a 25" transom to handle the weight of the new 4 strokes.

I was thinking the same. Depending on the manufacturer going from a 40 to a 50 may mean 50+ lbs more weight. Evinrude, Suzuki, and Honda 40 and 50 hp weight the same though. The Mercury and Yamaha 50 hp are 4 cyl compared the the 40's which are 3 cyl.

Personally I'd be concerned with the weight, especially for a 4 stroke, and therefore stick with a 40 hp. BTW the Yamaha is the lightest by nearly 30 pounds.

Thanks to all for the input on this. I should have mentioned my boat is a 1993 Alumacraft Lunker 16' which isn't as wide as the new ones. Insurance? Does my auto insurance cover me when I'm rovin'?

All the new rating plates I've seen mention net wieght as well as horsepower and usually number of people--has something to do with level flotation.

The difference in speed is not the issue. Alot of it has to do with the weight of the motor. It plays into the calculation of total weight/gear/persons the boat can handle.

I know that if you try and purchase a motor from a dealer and they see you are going over the hp rating, they will not install the motor.

Ins. is another issue if you are doing this.

Yeah, but if you stacked all that weight on the transom it would stick up like a buoy

put reflective tape on her and your good to go for night fishing

SS I personally have had a very scary experience by doing what Dtro and some of the other guys say is no big deal. Here is what happened I had a 14' lund just a little fishing boat and the tag said it was rated for 14HP and when I saw a 20HP on a garage sale for a price I couldnt pass up I quickly replaced the ol 5 HP Johnson and the first time out was awesome with four of us in the boat, but the second time nearly cost me and my son our lives. We were out on a little local lake and I had her going about half throttle and and I took my hand off the motor for a quick second and it usually ran nice and straight and all of a sudden we started whipping violently back and forth and we bounced off the sides of the boat and had lost all control of the boat and eventually just before my boy flew out of the boat I regained control by killing the engine and I will never do that again. Granted it was a small boat, but just goes to show your better off staying on the lower side of things Bigger isn't always better.

And Dtro if just the carbs are bigger it's not going to have any effect on the horsepoer output? Hmmmmm let me think about that.

actually some of the bigger motors use the same block and just bore it a little bigger for the higher CC's.

I would stick with the 40. Back in the day, i had an old 78' 16' Ranger with the tri hull and i came with a 35 johnson. I ended up burning out that motor (which is a story in itself) so i bought a 50 mariner to put on it. That boat was a tank, but with that 50 on there that thing was a rocket. For a 16' lunker, a 40 would do you just fine and for a cheaper price too. imo.

A Lunker isn't the strongest hull to begin with. If you took out any supports when you added the casting deck or tank it'll have more flex then it already had. Next is hull shape, with a relatively flat bottom it'll pound on a chop.

Heres where you'll really feel the added hp and weight over a hulls rating. Slower speed turns will get hairy. That extra hp and weight will heal the boat over a lot.

A newer 40 hp will be close in hp to an older 45 hp. The jump from 30hp to 40hp will be a very noticeable change and I think you'd be more then happy with that. If I saw a 50 hp on the Lunker I'd be doing a double take for sure. Would a CO also?