Help Tuning a Powercat

[Ad Hoc]

....The captain made an assumption the boat pulling to the right. I have been too nervous to let go! I got you stuck in my bad grammar.

Aaahh.. not so easy to diagnose with a changing narrative!

 

[fallguy]

I did not notice a pull one way, but he said I might not unless I let go of the wheel. It is hydraulic steering and surprisingly easy to steer..

I do apologize for my grammar, but I have never said a notable pull. The Captain told me two right turning props would push the boat to the right.

 

[fallguy]

Normally with hydraulic steering, there are s.c. block valves that prevent rudder cylinders to force oil through the steering pump. The valves only open when the pump is moved. In this case you don't have to hold the wheel when checking. If the system is lacking block valves, I recommend that they are fitted. When you apply the "brute force", the maximum in/out movement of the cylinder ram is about +/- 3 mm.

Any pictures/drawings of the wet parts of the hulls??

The steering system is all Seastar with a liquid tie bar.

I can take some pictures tomorrow of the beaching keels as I am headed that way for other reasons.

I am sorry for the grammar and poor explanation to all. I kind of figured it would not go well because I am explaining with so much speculation. Please keep in mind I really hadn't a clue I could even fix the issue until I spoke with my friend Tuesday. And honestly the section of river is really narrow to let the boat do its will with lots of bridges and timber and other hazards.

I will check, but have to believe the Seastar system has block valves.

Thanks. Dan

 

[fallguy]

Seastar helm pumps all have what they call a lock valve, so that means the steering is not feeding back into the wheel. But that would not mean the boat is not working off in one direction. More testing is needed I see.

Thanks to everyone for input.

I may need to run 45 miles downriver to some bigger, wider river..

 

[SolGato]

How did you go about setting the toe on the motors?

Since your motors are spaced so far apart and installed on a catamaran, I have to wonder if perhaps motor alignment may be causing your issue at high speed similar to alignment issues one might experience in a lightweight sports car and what some might describe as a twitchiness requiring constant input.

On a mechanical tie bar setup, it’s easy to start by disconnecting one motor to find where they naturally want to point, then adjust accordingly and fine tune from there.

Imagine there must be an adjustment on your setup.

You might document current setting and make a change in the opposite direction and see if there is any improvement.

 

[fallguy]

How did you go about setting the toe on the motors?

Since your motors are spaced so far apart and installed on a catamaran, I have to wonder if perhaps motor alignment may be causing your issue at high speed similar to alignment issues one might experience in a lightweight sports car and what some might describe as a twitchiness requiring constant input.

On a mechanical tie bar setup, it’s easy to start by disconnecting one motor to find where they naturally want to point, then adjust accordingly and fine tune from there.

Imagine there must be an adjustment on your setup.

You might document current setting and make a change in the opposite direction and see if there is any improvement.

Thanks. I have a liquid tie bar. But am wondering if you are onto something because the description is accurate.

I did not set any toe. I just tried to get the motors the same, but seems it may need some attention.

I wonder whether I can make any assumptions running one engine at a time? Or rather, have an idea what to expect or not..

 

[baeckmo]

I made a notice on the toe in/out issue in a previous posting. Now also realizing you have a "liquid link", I can only say that these are notorious for instability, you better get rid of it and arrange a solid parallell link. Until then, and with a test as per Ad Hoc, all further speculations are just a waste of time!

 

[fallguy]

I made a notice on the toe in/out issue in a previous posting. Now also realizing you have a "liquid link", I can only say that these are notorious for instability, you better get rid of it and arrange a solid parallell link. Until then, and with a test as per Ad Hoc, all further speculations are just a waste of time!

The hydraulic cylinders I have were like $1600 and the liquid connection about $300, so I have like $2k into cylinders and the ltb system. Making a stainless tie bar would interfere with fishing lines.

I realize now that any toe out or toe in is done by me with the liquid adjustments.

So, time for some experiments. Pictures are a nogo as there are good sized snowbanks around the hulls atm.

Thanks for ALL comments.

please stand by, I will toe in and toe out with the ltb; see if there is any notable pulls; take some pictures, add the bow extensions and report back here in say 6 months

 

[baeckmo]

A Bowden wire can replace the straight tie-bar between the engines, and be led around the tunnel; it is still a "stiff" connection compared to the "liquid tie bar".

 

[fallguy]

I did go to the marina today. Here are pictures of the bottom sans the planned bow extensions which it is too cold to do now.

Special thanks to @adhoc who is doing much.

 

[fallguy]

The transoms were built at 14 degrees, so I have been running the engines tilted up a bit; not sure this is accurate position as it looks perhaps all the way down atm.

The snow defines the boat exterior to offer perspective.

 

[baeckmo]

Ok, these images say a lot!

• First it shows the bow down trim, increasing the lateral area forwards. The positive trim you notice when making speed is NOT the bow rising, but the rear sinking due to wave shape and low pressure on the flat bottom "rocker". Hull beam is reducing aft and there is no/low side force acting to compensate for pressure peaks forward.
  
• Second it shows practically vertical sides from stem and going aft; when yawed, these lines will have a lateral pressure peak forwards (roughly like a symmetrical wing section where the pressure point occurs about 1/3 from the leading edge).
• Third, there is no skeg or fin area aft at all, and the beaching shoes will leave an unstable trailing wake, in which the engine fins don't have lateral authority, ie they do not "steer".
• On top of them all, it seems that the engines have been trimmed down too far (here I'm judging from the video you have shared earlier). Note that with the "rocker" bottom shape, the flow leaving the bottom is inclined upwards. For the outboards to have a neutral trim impact with these lines, they must be trimmed out so that the AV plate has about the same inclination as the hull bottom aft!
• The combined effects of these properties make the hull inherently instable on course.

The good news are that it is quite easy to correct most of the faults causing the problem, but the measures must be applied together with whatever Ad Hoc is planning for the bow.

 

[fallguy]

A Bowden wire can replace the straight tie-bar between the engines, and be led around the tunnel; it is still a "stiff" connection compared to the "liquid tie bar".

Very interesting. But I believe this means new cylinders...

Ok, these images say a lot!

• First it shows the bow down trim, increasing the lateral area forwards. The positive trim you notice when making speed is NOT the bow rising, but the rear sinking due to wave shape and low pressure on the flat bottom "rocker". Hull beam is reducing aft and there is no/low side force acting to compensate for pressure peaks forward.
  
• Second it shows practically vertical sides from stem and going aft; when yawed, these lines will have a lateral pressure peak forwards (roughly like a symmetrical wing section where the pressure point occurs about 1/3 from the leading edge).
• Third, there is no skeg or fin area aft at all, and the beaching shoes will leave an unstable trailing wake, in which the engine fins don't have lateral authority, ie they do not "steer".
• On top of them all, it seems that the engines have been trimmed down too far (here I'm judging from the video you have shared earlier). Note that with the "rocker" bottom shape, the flow leaving the bottom is inclined upwards. For the outboards to have a neutral trim impact with these lines, they must be trimmed out so that the AV plate has about the same inclination as the hull bottom aft!
• The combined effects of these properties make the hull inherently instable on course.

The good news are that it is quite easy to correct most of the faults causing the problem, but the measures must be applied together with whatever Ad Hoc is planning for the bow.

I am very grateful for this reply. More than you know.

As for the trim, if I trimmed up much higher than in the videos, I started to send the rooster up with loss of thrust and speed. I can do a series of videos, but 8.5" will likely change much. The shower is caused by the jackplate which I used to get 25" legs on 20" transoms.

I also plan to close off the jackplates because the water coming off the transoms is hitting the bottom and parting odd.

After we make changes to the bows, and close the plate bottoms, I have to do some testing.

One challenge is the narrow river. It is 45 miles to get to wide water enough to really get a bit more daring. Quite a bit of the river where we are is only 100 yards wide, so in the channel, I have 50 yards to shore, so 30 feet per second means I'm onshore in 5 seconds... A few spots are wider, but hazard areas...

If not for overseas kindness, I would be sitting here quite sick about my boat being 8.5" neg trim which I spent about 12,000 hours building.

Dan

Happy New Year!