cwcarter
15-07-2016, 02:19 PM
I see recently on here a few threads of motor height and set ups not behaving like they should and I'm just in the process of this as well and thought I'd share what I have done so far.
So new Merc 115 CT fitted. This is mounted at standard height from the installation manual..cav plate even with bottom of boat.
First tests at this height were terrible. Very rough, porpoising, bow high. I had the family (3 people) up front and could not go at speed without violent porpoising. Move them out back the porpoising was improved but rode bow high and rough.
I do have bennett trim tabs and using these I can greatly improve the ride, but for testing purposes until the handling is where I want it these are omitted from use. Other problems experienced was very little usable trim and slow to plain. Just didn't feel right.
Looking at the video below you can see how rough it was with the camera shake, this was the calmest day of testing compared to the next 2 days.
I had to use the tabs to get a max RPM read out the porpoise was so bad.
Running a Mercury Enertia 18P tops were 40mph at 6000rpm.
https://youtu.be/qDLxCjRlLNI
Motor lifted one hole. Inch above bottom of boat not keel extrusion.
Well its like driving a different boat. Heaps more usable trim, smooth, you can hear it sounds happier. I could get it to porpoise on high trim out. Boat still was bow high getting on plane and at plane also the prop would blow out slightly in chop.
Mercury Enertia 18P, 40mph at 6100RPM.
https://youtu.be/KBS487aLWjg
Getting better but still not happy. I think the motor height is correct and going any higher would cause excessive prop blowout offshore.
Now I was focusing on the weight issue. Being a centre console and most of its weight aft of centre of the hull then you add everyone trying to shelter behind the 1 metre wide console you have a bum heavy boat.
The weight issue is there and there's not much I can do about it. I will not be adding weight up front to compensate like some posts I've read.
I went on the search for a four blade prop and came across a Powertech SFS4 to provide stern lift and more bite.
This prop is a smaller diameter prop then the Enertia and has quite a lot of cupping.
The first thing I noticed with the 4 blade is the smoothness and the lack of clunk shifting. The heavy Enertia clunked and chattered quite well.
Yes the prop did improve stern lift and increased trim range even more. Plaining was easy and this prop holds great but more stern lift wanted.
Powertech SFS4 17P, 40mph at 6000rpm.
Notice the speed and revs are all perfect but handling wise big improvements have been made over the tests.
https://youtu.be/gUQslE6uFqc
Happy with prop selection and using tabs for extra lift is great but I find using the the tabs in choppy/confused seas a bit clunky at times and often press the wrong button with adverse effects.
Other things I would like is better slow tracking and even slower plaining.
The next search is for a decent foil. I had an SE sport on my last boat and it was night and day different.
My selection list was between SE sport, True Tracker and Permatrim. After speaking to Scott on here I settled with the permatrim due to being thinner and more fuel efficient at slow speeds.
Yet to trial, waiting for weather to clear.
113569113570
So new Merc 115 CT fitted. This is mounted at standard height from the installation manual..cav plate even with bottom of boat.
First tests at this height were terrible. Very rough, porpoising, bow high. I had the family (3 people) up front and could not go at speed without violent porpoising. Move them out back the porpoising was improved but rode bow high and rough.
I do have bennett trim tabs and using these I can greatly improve the ride, but for testing purposes until the handling is where I want it these are omitted from use. Other problems experienced was very little usable trim and slow to plain. Just didn't feel right.
Looking at the video below you can see how rough it was with the camera shake, this was the calmest day of testing compared to the next 2 days.
I had to use the tabs to get a max RPM read out the porpoise was so bad.
Running a Mercury Enertia 18P tops were 40mph at 6000rpm.
https://youtu.be/qDLxCjRlLNI
Motor lifted one hole. Inch above bottom of boat not keel extrusion.
Well its like driving a different boat. Heaps more usable trim, smooth, you can hear it sounds happier. I could get it to porpoise on high trim out. Boat still was bow high getting on plane and at plane also the prop would blow out slightly in chop.
Mercury Enertia 18P, 40mph at 6100RPM.
https://youtu.be/KBS487aLWjg
Getting better but still not happy. I think the motor height is correct and going any higher would cause excessive prop blowout offshore.
Now I was focusing on the weight issue. Being a centre console and most of its weight aft of centre of the hull then you add everyone trying to shelter behind the 1 metre wide console you have a bum heavy boat.
The weight issue is there and there's not much I can do about it. I will not be adding weight up front to compensate like some posts I've read.
I went on the search for a four blade prop and came across a Powertech SFS4 to provide stern lift and more bite.
This prop is a smaller diameter prop then the Enertia and has quite a lot of cupping.
The first thing I noticed with the 4 blade is the smoothness and the lack of clunk shifting. The heavy Enertia clunked and chattered quite well.
Yes the prop did improve stern lift and increased trim range even more. Plaining was easy and this prop holds great but more stern lift wanted.
Powertech SFS4 17P, 40mph at 6000rpm.
Notice the speed and revs are all perfect but handling wise big improvements have been made over the tests.
https://youtu.be/gUQslE6uFqc
Happy with prop selection and using tabs for extra lift is great but I find using the the tabs in choppy/confused seas a bit clunky at times and often press the wrong button with adverse effects.
Other things I would like is better slow tracking and even slower plaining.
The next search is for a decent foil. I had an SE sport on my last boat and it was night and day different.
My selection list was between SE sport, True Tracker and Permatrim. After speaking to Scott on here I settled with the permatrim due to being thinner and more fuel efficient at slow speeds.
Yet to trial, waiting for weather to clear.
113569113570