My Boat Pushes at Full Speed

[Gouch]

I have a 1981 Peterbrough Fury, with a 90 HP Mercury Outboard (1980 I think). First of all, the owner previous to me, put the 90 HP after he burned out his 50 HP. The boat is only rated for a 50 HP. <br /><br />My problem is that when it is at full speed, I can feel the back end of the boat being pushed. Is there anything I can do to fix this problem???????<br /><br /> It will also list, depending on how gear is stored.<br /><br />How far down should the Cavitation Plate be down from the transom bottom?????

 

[Jdeagro]

Re: My Boat Pushes at Full Speed

Explain "pushed".<br /><br />Is it running bow up or bow down at speeds?

 

[Dhadley]

Re: My Boat Pushes at Full Speed

With the outboard mounted on the transom, thats the whole idea -- it pushes the boat forward. Or do you mean when drafting and its the boat behind thats pushing you? Oh wait -- thats stock cars. Whats a stock car doing that close to you? How'd you get in front of the stock car with your boat?

 

[Boomyal]

Re: My Boat Pushes at Full Speed

If it's pushin the bow down, get one of those water bladders that they use for wake boardin, load it up and place just forward of the transom.

 

[RTW2112]

Re: My Boat Pushes at Full Speed

Take the 90hp off and put a motor on that is rated for the boat. You're running a motor almost twice the hp that the boat is rated for, that's very unsafe to you and any other boaters around you.

 

[Capn Mike]

Re: My Boat Pushes at Full Speed

RTW is so right....not sure what you mean by being "pushed", but instability created by over-powering is the reason why manufacturers rate boats for maximum horsepower.<br />The previous owner's motor didn't burn out because it was underpowered....go back to a 50 and see what happens.

 

[roscoe]

Re: My Boat Pushes at Full Speed

Sounds like way too much power, probably chinewalking.

 

[Gouch]

Re: My Boat Pushes at Full Speed

What I mean by pushing is that it feels like the motor is pushing the back end of the boat over. Very similar to when you do a burn out with a car. The back end of the car kicks out. <br /><br />What is Chinewalking????????

 

[hammlfam]

Re: My Boat Pushes at Full Speed

What is Chinewalking you ask???? Please read the following post. TOPIC Am I missing something.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=006841 <br /><br />Once you've read that, you will know what Chinewalking is all about.

 

[hammlfam]

Re: My Boat Pushes at Full Speed

duplicate post. sorry

 

[Dhadley]

Re: My Boat Pushes at Full Speed

Are you saying that the boat runs crooked thru the water?

 

[Gouch]

Re: My Boat Pushes at Full Speed

Yes. It seems to run slightly crooked. The bow and stern are not inline. It will also sometimes list to one side under speed. Usally to the left side (facing forward). I believe that my prop turns to that side.

 

[JasonJ]

Re: My Boat Pushes at Full Speed

You are definatly running with too much power. What is the hull design? Shallow V, Deep V, flat bottom semi V, tri-hull?. How long and wide is the boat? The different hull designs will react differently to excess speed. I personally would try to find a motor that is 50 horse. Not only do you have too much power, but you also have too much weight. The more the motor weighs, the less payload you can safely carry. Thats less people, coolers, whatever. There are plenty of people out there who overpower their boats, but it isn't wise. If the boat is listing to the left while at speed despite you sitting on the right side, it is because all that prop torque is causing the list.

 

[snohomishbaddawg]

Re: My Boat Pushes at Full Speed

Could be the boat is not handeling the torque from the prop. The big motor may also be alittle off center. I would definately look at powering down. There is reason you don't put a V-8 on a bicycle!

 

[Jdeagro]

Re: My Boat Pushes at Full Speed

Gouch;<br /><br />Sounds like the prop torq is cuasing you problems. The bigger motor has a larger prop and the boat design may not be adequate in resisting the torq of a larger motor. Does the bow run high when cruising?

 

[Gouch]

Re: My Boat Pushes at Full Speed

The hull is a deep vee and the boat length is 15 1/2'.

 

[Gouch]

Re: My Boat Pushes at Full Speed

The bow also runs high when cruising. I really have to set the trim properly to get the right combination. If I do, then the boat will not list and I don't get the pushing feeling. If I go faster than 30 mph, then everthing changes.

 

[JasonJ]

Re: My Boat Pushes at Full Speed

Generally, having the boat ride on the aft 1/3rd is fairly ideal, the rest of the boat should be just out of the water. It shouldn't be pointed at the sky however. While I still feel you are overpowered, I am running 125 horses on a 16.5 length boat. It is, however, rated for 145 horsepower, so I am well within spec. Part of the reason your boat has such a low horsepower rating also is because the heavier motor eats up too much of your weight capacity, and also may prevent the boat from staying at the surface if it gets swamped (assuming it has floatation foam). If you are planning to keep the motor, there is no law that says you need to be running wide open all the time. You may want to try to set it up for optimal cruising at the expense of all out speed. Do you have power trim? The cavitation plate should be within 1 inch of the very bottom of the boat. Normally I would say for you to have it mounted a bit above the bottom of the keel, but I have the feeling you are already going too fast with not enough boat around you, don't need to add to it. If you have power trim, then you need to always be adjusting it based on speed and water conditions anyway. There isn't really a magic one position that does it all, which is why power trim was developed. Anyway, good luck and use caution...

 

[Gouch]

Re: My Boat Pushes at Full Speed

Jason, <br /><br />I do have Power trim. I have to use it a lot when I cruise. When I go about 30 -35 Mph, the boat handles nice. That is usally sking range.<br /><br />I do have to adjust the trim based on the speed. If the boat list's to the port side, then I need to adjust the trim. <br /><br />One thing I do find, it that I always have to adjust the trim so much. It seems like the prop is only doing half it's job. It seem like it is out of the water too much. Would lowering the motor help????????

 

[JasonJ]

Re: My Boat Pushes at Full Speed

Does the prop ever cavitate or simply blow out? How close is the cavitation plate to the bottom? I could say that it may just be the extra weight of the motor, but a 90 horse merc (I am assuming it is the 3 cylinder variant) isn't going to weigh a huge amount more than a 50 horse, they would be within 75 pounds of each other, depending on the 50 horse. How far out are you trimmed when you get this sensation that the prop is half way out of the water? A deep V hull can handle more power than other hull designs, but I still stick with the belief that the hull is being overpowered. You could try shifting some weight around to see if it helps much, but I am thinking you may just not have an optimal motor/boat combo.