Hull cleaning to gain rpm
Hey guys
Been a fair while off here but Ive got a boating/engine query for those more experienced than I.
Ive got a 4.8m glass center console that was new in early 2012. The original run in the river over in SE Queensland was great with good revs and went like a scalded cat. Engine is a 2011 90 etec.
Fast forward to now and Ive got some RPM loss in the order of 400-500 rpm. Have been chasing my tail with spark plugs, fuel lines, throttle cable adjustments, carbon cleaning, VST filters etc but wondering just how much RPM I would actually lose with the bottom of the hull being fairly dirty and having a few scratches and such on it. The wobble rollers have a heap of road grime on them and thats now on the hull. A couple of gelcoat chips and a few scratches as well. A Lowrance side scan transducer, and TM150 transducer hang off the back also. Ive heard over time that gelcoat becomes porous and will hold water? It probably does need a clean, sand and wax and some new rollers to stop the dirt going straight back onto it. In saying all this, the motor sat for a long time during the arrival of a young family and has less than 300 hours on it. Quite possibly it has gummed up/carboned up from little use and not much time spent having it running at WOT.
Have been onto a few mechanics in perth and back locally and not many can seem to put a finger on anything mechanically wrong. So my question here is can the fouling and increased surface area on the old gelcoat on the hull be causing this sort of thing?
Fish for thrills....
ranmar850
Posts: 2702
Date Joined: 12/08/12
It doesn't take much
I dropped both speed and rpm over the course of a few months from new. TM transducers will have an effect, even seawater intake scoops being added. Weight, too--how much weight have you added since firsr sea trials? Your intial response would probably be, not much, then you start thinking. Everything matters. Sea trials are usually pretty bare, then you start adding fishing gear, safety gear, list goes on. Actual hull finish will have an effect, everything is cumulative. Old anti fouling can be the worst, although I am guessing you are not. Actual chips and scatches? Add everything up.
My new boat seatrialled in my river at 38 knots and 5500 rpm. (14.5x17P) Very little room for experimentation, as it is short ( and 8 knot limit
, had to do it pre-sunrise) Engine recommended RPM range was 5200-5800. Over the next six months, I added fishing gear, a water bladder and pump, 305mm drumwinch, fridge,outrigger bases, and a scoop strainer for the deck hose/bait tank. RPM went down to a bare 5000-5200, 34-35 knots, sometimes less. So I was well over-propped. Going down an inch in pitch early on had just resulted in a loss of speed, and no rpm gain,so I went to a 15 x 15. Got 5600, and same speed, so better. I believe it was just a cumulative effect of weight and drag added.
Brad Y
Posts: 260
Date Joined: 03/02/12
Cheers mate. Yes I did
Cheers mate. Yes I did initially add in weight, batteries and bits and pieces. But even now I can empty the boat totally bar the two sounders and stereo added and the safety gear. It’s still nowhere near where I was. I will give the hull a clean up and replace the rollers, but its just weird now that I can hit 4950rpm and not be at full WOT throttle lever position. And to top it off there is a bloke over east running the same motor as me with the heavier and longer 5.5m version of my hull getting good revs with a larger prop... honestly it baffles me!
Fish for thrills....
holth
Posts: 812
Date Joined: 09/10/06
Ask the question over on
Ask the question over on www.etecownersgroup.com
If there's no prop damage, your not going to drop those rpms from some scratches on your hull. Is there water trapped in hull.
Im thinking this is a motor problem, have heard afew stories of this from my time as an etec owner and on the etec forums.
From memory the optimum wot rpms on a 90hp is 5200rpm. What's your wot rpms before and now.
Brad Y
Posts: 260
Date Joined: 03/02/12
Ive booked it in with
Ive booked it in with Muhling Marine on Monday. It’s a weird one thats for sure. Just a few things that make me doubt the motor is all. The support down south isnt great for evinrude motors which is a shame as although the 4 strokes are so user friendly and popular, I really like the 2 stroke DI motors. Fingers crossed they find something and I dont waste their time and my money anymore!
Fish for thrills....
Mark_M
Posts: 158
Date Joined: 10/04/15
:-)
http://www.fishwrecked.com/forum/marine-spray-painting
Just do it Brad :-)