I have a boat rated at 45HP max on the coast guard specs. I'm currently using a 30 hp motor. I have added a built in gas tank/casting deck since purchasing the boat which has added some weight. 45's are hard to come by and I would really like to put a 50 HP on there. What are the repercussions for having an overpowered boat? Is it possible to get a new rating for the boat? Any knowledge is appreciated.

I think the difference in a 45-50 is minimal at best. I would not recommend overhorsepowering, but in this case, I think you would be fine with a 50.


The only thing I would be worried about is some sort liability thing if anyone ever got hurt.

I can see no reason to not put any size motor on that boat you want to...as long as you are not concerned about insurance. The coast guard tag is easily removed and the boat registered as home built as there is no title on boats in many states. I guess the only other consideration is your and your passengers safety. (Can the hull physically handle the added weight and speed the larger engine will supply.) The short answer is no the boat cannot be re-rated and with the added weight in all likelyhood it would probably drop due to the fact that the boat now weighs more.

I personally think you would be better off going with a 40 hp motor than going higher than the manufacture's rating states. I know you want to go as fast as possible, but those tags are there for a reason. Generally a boats transom can hang a larger engine than what the tag says, but the hull and boat as a whole is most likely not able to take the extra forces. There is a lot of engineering that goes into hull and boat design and safety factors are a part of engineering for a reason. I don't really think it is legal to simply take the tag off and register it as a home made boat if it was factory produced. I will search through some of my books and find that tidbit of info this weekend.

Agree with dtro. Should be fine being your not going over board on the amount of hp added and you have the wieght to offset. And your bennifit maybe torque added to youe performance. May not see much added to top end. Out of the hole will be better.

Some boats are rated for speed and weight. If you add excessive horsepower you stand a chance at exceeding the limits of the boat. Porpoising that leads to chiming(chiming is when boat dances to one side of hull to the other) is a factor at higher speeds. The boat may become out of control. Some hull designs are not meant to go over a set speed. Ive been in boats that were overpowerd and it gets scary and dangerous.

Also remember that a lot times added horsepower (5-10hp difference) is merely a larger carb. 35 and 40 are essentially the same outboard in most cases, just a different carb.

dtro-I'm not following your logic here
"35 and 40 are essentially the same outboard in most cases, just a different carb"

This is the case with the Merc Optimax 135, 150 and 175. Essentially the same just different sized carbs/injectors; does that mean I can put the 175 on a 1700 explorer? I think not!

The manufacturer plate is there for safety not to increase someones motor sales.

Horsepower ratings sometimes seem a bit fishy to me. Take for instance the Ranger 1750 Reata. It's rated up to 130hp. But wait a minute! Nobody makes a 130hp motor....so how'd they come up with that! Probably some computer and engineering calcs and not field testing. If a boat's hull isn't designed to take on an added 5hp, then that boat has some serious problems! I wouldn't want to be in a boat like that.

Going 5hp over the limit from a practical standpoint probably won't be a problem at all. I mean really...put a 5hp motor on the back of a 16' or 17.5' boat and how much added weight and torque does it produce? Not much I'd guess. However, as mentioned, the insurance and liability is another thing. If it waives your insurance, that aint good! Better to stay under than go over IMO, but some of the hp ratings like the 1750 Reata don't make sense.

Apples/Oranges

Your trying to compare a 35/40 to a 135/175.......come on now

I think with every situation an individual needs to [PoorWordUsage] what the risks might be. Nobody went ahead and said, "yeah sure hang that 50 on there". There could be possible repercussions to slapping a bigger motor on there.
IMO, I wouldn't have a problem with doing it to my boat.

Do we know if that rating was based upon the horsepower at the engine or the prop, or merely a weight issue?

I am sure you put some of the bigger motors on the dyno, there would a + or - of at least 5 hp between them. Heck, a 45hp motor maybe really putting out 48hp or even 50hp. You might have a 50 running at 43hp or 55hp.

I have also heard about what dtro said. I think it has to something with the 9.9hp to a 10hp. What a wopper that is

I guess I would do it if I got the 50hp at a deal. Take it easy and see what it does.

For about 10 years my fishing buddy has had a 60 on a Lund Alaskan that is rated for a 50 and has had no negative effects on performance or the boat.

I've heard from a couple of old timers that the 9.9 came about when restrictions were put on lakes in some national parks that banned motors 10 hp and up.
The manufacturers just slapped 9.9 decals on thier 10 horses to make them legal.

The 9.9 and the 15 are the same motor with different carburation. I dont think that the couple horse power over that the 50 would give you would do any harm. You can get the same performance change on some motors with a prop change. Just use your common sense when you run it and you should be good to go.

Not to highjack this topic, but what about if you wanted to increase HP? I have a 15 HP mariner, would there be a chance I could get a carb and have it be a 20HP??

Your boat will handle the small difference with no problem, but one of the main concerns of this is liability in case of accident. Insurance might not cover if they see boat was overpowered, even if by few HPs.

Regarding motors with different HP many have same block and powerhead, just carburation or fuel injection are modified.
In the case of Opti 135, 150, and 175, yes they are the same motor with different fuel injection setups.

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?

I agree that you would be happy with a newer 40hp. For some reason I thought a 40hp is what you were using, and now that you say you have a Lunker, the 40hp would be ideal.

Goldtip, that must be a pretty small boat to be only rated for a 14hp max. My plain Jane 14ft is rated for a 35hp. Also, I never recommended overpowering, just said that I wouldn't have a problem if it was my boat, bumping up 5hp if I had a real hard time finding anything close to the max.

You need to get boat insurance. It's not all that spendy and worth it to have it.

I guess I will go with the 40 horse if I still can't find a 45. Also that motor may be more ideal for trolling at lower speeds. The knowledge available from so many people on this topic has been SO helpful. Thanks.

Andy

The newer lunkers are rated for 50 hp
but there are the wider ones

I'll agree about what was said comparing a 30 HP to a 40 HP. Someone mentioned on here about the engines being "completely different animals" or something to that regard. That is an understatement from what I have seen personally. Of course, my boat isn't very long, but it is a bit bulky (1425 Classic SS)...

-Gregg B.

I always figured the rating was for our protection. The boat's hull design, length, depth, water displacement, and transom design must all go into the calculation.

Just because a boat's transom doesn't rip off from the motor torque doesn't mean it's safe to use the extra power. There might be issues such as stearing and handling for example. Insurance could be the least of your worries.

Bob

A 40hp 2 stroke should do you just fine. 4 stroke may be too heavy. Most boats' ratings are pretty close to good common sense, although there are some exceptions somewhere I suppose. Check into putting some hydro-stabilizers on the cav-plate...they knock your speed down about 1% but the stability of the motor greatly improves.

The bottom line, in my opinion anyway, is that it's over the rated HP. If any incident happens between you and anything else one of the things insurance looks for is if the motor hp is over the rated hp. If so, claim denied, regardless of what the situation was or who was at fault.

It's the same reason a dealer won't hang a motor over the rated hp on a boat.

Will an accident happen? Hopefully not. But, who plans to have an accident?

marine_man

To the original poster Ssminner, I think the basic question here is not a horsepower numbers issue but rather one of "desired performance". Assuming you need a new motor, do your homework and get the operational features that you want in a 40 HP model. It will be more than enough for that hull. Most fishing boat designs are very low performance and sluggish to begin with and your money is best spent on the best all around motor for what you want to do. Remember that weight on the transom is a critical factor in determining high speed response so look for a lighter motor. The two strokes excel here but the technology is outdated.

The most important thing that you can do is to select the right prop. Your dealer can help here and see if you can try out a couple on the water. Keep in mind that more pitch does not always mean more speed and it usually reduces overall performance. Set your trim neutral to negative and check the hole shot. You want the nose of the boat to come up quickly and then drop back level. If the motor has power trim raise it while at WOT until you see a rooster tail about 3' high and see how it feels (more trim just uses energy to throw water into the air and will slow you down). The handling should still be nimble and responsive with no torque steer. Do a couple of high speed turns and see if the prop loses grip, if so, try another.

IMHO on that hull increasing to a 50 HP motor would probably be a waste of money and as said above, illegal.