Boat handling problems.

[kind_cir]

Got a 4m tinny fitted with a 30 hp tiller, and it's hard to steer and burries the nose when pushed past cruise speed with engine trimmed out.

Things I have discovered are:

Engine is too low by 30mm and can't go higher. ( mounted 20 mm higher allready)
Transom is 20.5 inches, and leg is 22.5in

Would the motor being to low cause the nose down attitude ?
I was thinking the cav plate being too low would cause excessive lift in the stern at speed.

Now if I were to lift the engine higher, it would need a jack pate or modified transom. So what should one do ?

[Troy Wood]

Is it hard to steer in both directions?
The easiest and cheapest way to raise the transom to add a piece to the transom.
We do this all the time. As for running on the nose, The three main things to look at are,
Trim angle which you already have adjusted, weight distribution thru the boat, the third being
To check to see if there is a hook thru the bottom of the hull.

[astro66]

adjust your trim...if the nose is down your trimmed in to far....i take it has tilt and trim? if its manual lift move the pin out one hole...

[johncar]

So long as the cav plate is running somewhere near parallel to the keel it shouldn't cause that nose burying issue if it is a little deep. It seems common to have engines a little deeper on lighter tinnies to avoid ventilation.

It would seem more likely a distortion in the bottom as in the bottom should be flat or convex to be normal. As Troy said check for a hook bottom.
Some pics can be helpful.

[kind_cir]

Is it hard to steer in both directions?
The easiest and cheapest way to raise the transom to add a piece to the transom.
We do this all the time. As for running on the nose, The three main things to look at are,
Trim angle which you already have adjusted, weight distribution thru the boat, the third being
To check to see if there is a hook thru the bottom of the hull.

The hull looks all good, and there is nothing I can see that is irregular. There is, 25 lt of fuel, battery and me at the stern, and nothing of weight in the bow. I can put someone, and esky ect in the front and it seems to perform the same, maybe a little more spray from the front.

It dosen't realy burry the nose tha bad, it just seems to realy level out at WOT and throw more spray up front. At cruise it sits slightly higher in the bow and the spray disappears at the front.

Steering sux both directions...

[kind_cir]

So long as the cav plate is running somewhere near parallel to the keel it shouldn't cause that nose burying issue if it is a little deep. It seems common to have engines a little deeper on lighter tinnies to avoid ventilation.

It would seem more likely a distortion in the bottom as in the bottom should be flat or convex to be normal. As Troy said check for a hook bottom.
Some pics can be helpful.

String line off the bottom of the hull tells me the cav plate is level with the bottom of the boat but cav plate sits 30mm lower, and motor is trimed out to last hole. Trim the motor in one hole at a time and the angle of the cav plate changes and is no longer level with the bottom of the hull.


Wasn't the weather great today.... Had boated 3 jewies just before sun up, but it shut down as hundreds mad their way to the water.

[astro66]

my brooker felt like it was burying the nose at wot but after checking and getting a mate to drive past so i could have a look i could see it was all good...wasnt hard to steer though....
dont move the trim in...that will make it worse...to bring the nose up you need to go out....maybe if its really bad you will have to wedge the motor out...
does it have a foil on it?
is it hard to steer at slower speeds?

[Fed]

String line off the bottom of the hull tells me the cav plate is level with the bottom of the boat but cav plate sits 30mm lower, and motor is trimed out to last hole.

Do you mean parallel with the bottom of the boat but 30mm lower?

You want the cav plate to run parallel with the surface of the water so if it's parallel to the bottom of the boat then it's trimmed in too far.

It does seem strange to have a transom angle Vs motor trim combination that can't get enough trim.

Don't worry about the depth, here's a little mental exercise...
If your prop was 10 feet below the hull your boat would do a backflip.

[kind_cir]

Do you mean parallel with the bottom of the boat but 30mm lower?

You want the cav plate to run parallel with the surface of the water so if it's parallel to the bottom of the boat then it's trimmed in too far.

It does seem strange to have a transom angle Vs motor trim combination that can't get enough trim.

Don't worry about the depth, here's a little mental exercise...
If your prop was 10 feet below the hull your boat would do a backflip.

With the motor trimmed out as far as it can go it sits parallel with the bottom of the hull. Now if I trim it in one hole then it does not sit parallel with the bottom and it gets worse the more I trim it in.

I am going to raise the engine this weekend, and see how it goes. That should fix the tight steering and give me more top end. Then if it still wants to run level/nose down, I will get hold of some wedges to give us more positive trim.

[johncar]

Seems like a good plan, yes if you can just achieve parallel at full trim out, it probably isn't enough and the boat is behaving as expected but having said that it depends a bit of other factors like your hull design and weight distribution too.
The engine running deep though tends to give more bow lift as Fed said and in fact I recently dropped my engine one hole to achieve exacly that.
If your cav plate is level with the keel at full trim out and parallel as you said I doubt that you will need to raise it but so long as you don't do anything real permanent it can't hurt to try. It would seem that the wedges might be the go.
Not sure what the go with the steering is though but it should get a bit lighter if you can get some more trim out, also check your steering tube has nice new grease etc but it should get harder to steer as you apply more power. Always hard to tell from the lounge roon whats going on.

[Gon Fishun]

Have you checked the vertical angle of the motor compared to horizontal of the hull, when it is at rest in the water. Maybe the transom is not allowing enough angle for the motor, and as the other guys have suggested, you may have to fit wedges.

[Fed]

My money is on a hooked hull.

[Gon Fishun]

Whats the outcome K-C? waiting with baited breath.