I need help please I will love you for ever!

andrewcoon

Petty Officer 2nd Class
Joined
Aug 21, 2011
Messages
130
heres the deal its a 16ft starcraft with a johnson 100 I have a bad right pull. NOTE It does not have the tab to adjust the torque. It does fine to about 25mph but after that the bow goes down and the boat pulls almost flips very scary. the engine is trimmed all the way out and remember at 25+ the bow lowers kinda like a nose dive and it torques please help i need it seams that it just torques when the bow lowers also it is trimmed all the way up. would a hydrofoil help? PLEASE HELP if you help i will love you for ever. P.S. the skeg broke and their is only about 3 inches of it left. Remember its an old engine their is no way move a fin above the prop. Okay so again here are the factors:

at 25mph bow lowers in the water and boat pulls

its trimmed all the way up

Its NOT the boat its the engine

This is very dangerous i need to fix as this could injure or perhaps kill someone.

Thanks so much!:D
 

kfa4303

Banned
Joined
Sep 17, 2010
Messages
6,094
Re: I need help please I will love you for ever!

Hi andrew. It sounds like you have a couple issues going on. The right pull is probably to what is call "torque steering". Essentially, the clockwise (right handed) spinning of the motor is causing the boat to pull to the right. It usually doesn't help that most helms and/or tiller positions are also on the right hand side of the vessel, which just tilts the craft to the right and further compounds the problem (like when you lean left or right on a skateboard, or bike, to get it to go where you want, especially if you're alone in the boat with not weight to counter balance you. For this reason some boats have the helm on the port (left) side of the vessel so as to counteract the natural tendency for the boat to want to pull right, and so the captain turns to the righ (i.e into on coming traffic to speak to passengers, rather than away from oncoming obstacles as is the case with starboard mounted helms) . Also, the 100 hp motor (more than some cars) you're running is an awful lot for a 16' boat. I'm not sure what your boat is rated for, but you might want to check. More is NOT always better, as you can see. As a result of having such a large, powerful motor, there is a tremendous amount of torque generated when it gets up to speed. I only run a 20 hp motor on my 14' runabout/ski boat and it's plenty. I can't imagine having, or needing 5 times that much power, but I'm kind of a speed wuss.
The bobbing up and down you described is indeed dangerous and is usually called "porpoising" (i.e. nose of vessel moving up and down like a porpoise). This effect is usually do to an improper balance between the weight distribution fore and aft in the boat coupled with the way the motor is trimmed. Again the fact that you have a 100hp motor on the back of a relatively small boat means you have a tremendous amount of weight aft in the vessel. As a result, it essentially wants to do a wheelie when it gets up to speed. Think of a drag racer standing up at the starting line. Unless there is enough weight forward in the boat, the problem will persist. You may need to add quite a bit of ballast up front in the boat to counteract this effect. Cinder blocks and/or lead shot may be your best bet. You could always get a smaller lighter motor (maybe 50-75hp range) which should weigh quite a bit less and still give good power. You can also try trimming the motor in towards the transom a bit more. With it trimmed all the way out (away from the transom) it just wants to push down the back end even more. Generally, people start with the motor trimmed all the way in, then adjust it to find the sweet spot once the boat is on plane. Every boat's "sweet spot" is unique and varies with load, hull and engine size, etc... Give these tricks a try and let us know what you find.

P.S.
Don't worry about the skeg too much. It's main job is to protect the prop, which it sounds like it did. You can either replace the lower half of the gear case, or have it welded back on, if you still have the broken piece.
 

andrewcoon

Petty Officer 2nd Class
Joined
Aug 21, 2011
Messages
130
Re: I need help please I will love you for ever!

its not porpoising at 25+ its just finishing coming out of the hole. It came original with a 100hp the boat is very heavy so i belive the 100 is not too big. You know what the prop is dinged, is that the problem???

And my fathers first car was only like 70hp haha
 

Numlaar

Chief Petty Officer
Joined
Jul 9, 2009
Messages
633
Re: I need help please I will love you for ever!

Hi Andrew,

That's some great basic information, but I think we would need some more info to go on, as well as a picture of the lower unit condition, and to see how it's mounted in relation to the bottom of the boat...

I had a boat that did the same thing, and it was because they had the motor mounted 5" too low....

When you say the engine is trimmed "all the way out"... what do you mean? (up or down), is it in as far as it will go or tilted up to some degree?

Just based on the symptoms you are describing, it seems to me that the motor may be tilted in (down), too much...

Remember the more you tilt the motor in/down, the more it brings the nose (bow), of the boat down as well, trim it up, and the bow lifts up...

You may need to experiment with it a bit, and try to get the trim/tilt angle set to where it rides the best...

generally what i recommend is, all the way down when you first take off, this gets you up and onto plane fastest, them trim it up until you just start to get the bouncing (porpoising) motion, then trim it back down just until that goes away... that should get you to the correct position for motor height in relation to how your boat handles... once you get a feel for it, you can better decide where your motor should be trimmed to take off.

If you are missing the "trim tab" which helps with steering correction, you need to replace this ASAP, also if you are missing a portion of the skeg, I would remove the lower, and have a new one re-welded on.

A ding in the prop may or may not need to be addressed immediately, it depends on how bad it is, and whether or not you get vibrations from it.... obviously, you want to get it fixed, but I would address the other 2 lower unit issues first.

About the hydrofoil question, that is a big debate by a lot of people, I will leave that one alone... but they are supposed to help a boat get on plane quicker...
 

andrewcoon

Petty Officer 2nd Class
Joined
Aug 21, 2011
Messages
130
Re: I need help please I will love you for ever!

Okay It never had trim tabs its too old, its trimmed all the way out and I have another lowerunit but I cant figure out how to take it off. At this point i have it for sale for 500.
 
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