Pulling to port

[strakeryrius]

Regular forumites will know that I recently had the bad luck to run into a large and hard submerged object. One major rebuild of the starboard engine and both legs was completed about a month ago. The absolutely %$*&^ weather in July has prevented me using her much, but today we managed to get out.

The boat is pulling pretty hard to port., So much so that I had to steer about a point to starboard to stay in a straight line - it did this on all points of sailing so wasn't just the wind. It's doing it at virtually all speeds from as low as 5 knots, and at planing speeds the requirement to steer starboard is causing the boat to heel alarmingly to starboard, so that it was too hairy to do more than 17 - 20 knots.

What's odd is that the port trim tab seems to be stuck down, while the starboard is stuck up - which ought to make the boat steer to starboard. Its certainly not helping at all with the alarming heel to starboard.

Two other oddities that may be symptoms - the bilge is contaminated with some sort of oil, and its not from the engines as they haven't lost a drop. Also when I put her into astern to back into my berth I noticed that the leg trim indicator jumped from -4 to 0 and then back again when I came out into neutral.

Now putting all of this together I'm starting to see a pattern, but just in case I'm barking up the wrong tree can anyone else suggest what they think might be wrong?

 

[Kawasaki]

imho, if the Port trim tab is stuck down you will veer to Port.
The oil present could be the 'leg fluid' leaking also causing the leg to muck about?

 

[Philiz]

What's odd is that the port trim tab seems to be stuck down, while the starboard is stuck up - which ought to make the boat steer to starboard. Its certainly not helping at all with the alarming heel to starboard.

Two other oddities that may be symptoms - the bilge is contaminated with some sort of oil, and its not from the engines as they haven't lost a drop. Also when I put her into astern to back into my berth I noticed that the leg trim indicator jumped from -4 to 0 and then back again when I came out into neutral.
(

I'd have thought just the opposite. If your port trim tab is stuck in the down position it will cause drag on the portside which will cause it to pull to port.

Do you know why the trim tabs are stuck? If they're hydraulic the contamination in the bilge might be hydraulic fluid or oil maybe oil from the leg(s) which may expalin your trim indicator jumping. Did trim work okay prior to that? I presume the props are correctly matched and engine revs are equal.

 

[omega2]

pulling

Do the legs have small fins on the ends of the cavitation plates, if so adjust them to Port a little at a time a check the bias.

 

[Pendana]

Also, check the the toe-in of the legs, think it should be -1"

Eddie

 

[Elessar]

In theory....
At planing speeds, if the boat heels right it will turn right.
At displacement speeds if the boat heel right it will turn left.
(this is why planing boats are esy to steer on the plane and unstable needing lots of correction at low speed)

So a stuck down port tab should cause a veer to spd at planing speeds even though this is counter intuitive.

But......

The effect happens all the way from 5 knots.

Its clear, forget the theory and fix the tab before trying anything else!

Then sea trial with the legs fully in. If there is a trim hydraulic leak as you are suggesting it won't have any impact.

 

[SeaDave]

In theory....
At planing speeds, if the boat heels right it will turn right.
At displacement speeds if the boat heel right it will turn left.
(this is why planing boats are esy to steer on the plane and unstable needing lots of correction at low speed)

So a stuck down port tab should cause a veer to spd at planing speeds even though this is counter intuitive.

From your above rules, the opposite should be true, ie veering in the opposite direction to stuck down tab - at DISPLACEMENT speeds, not planing.

 

[Elessar]

From your above rules, the opposite should be true, ie veering in the opposite direction to stuck down tab - at DISPLACEMENT speeds, not planing.

nope.

left tab stuck down = left hand of boat up = heel to right

thus left hand tab stuck down = veer to left at displacement speeds and veer to right at planing

 

[SeaDave]

DOh!

 

[Elessar]

DOh!

Doh indeed. I was convinced you were right and had to type the reply twice, it is confusing.
Just add in cross wired bennet trim tabs for added amusement.

And anyway if its happening from 5 knots the theory is pants anyway!!

 

[strakeryrius]

Thanks to everyone who has contributed their two ha'porth to this thread. I spoke to my engine bods this morning who have finally sent someone down to fix the trim tabs - they said it was two loose connections causing them both to fail simultaneously, but they are going to sea trial to see what is going on with the steering.

I suspect that the tabs are just an extra complication, and that the oil in the bilge is from the leg(s) trim pumps and the current behaviour of the legs attitude is the actual cause of the problem with the steering. I'll update after I have tried her out - hopefully this weekend.