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02-27-2021, 08:49 PM #1Junior Member
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Tunnel hull pulling extremely hard to the right despite cambered skeg.
I have and older 22' Rapid Craft tunnel that I had set up with an Evirude 300XP which pulled just slightly to the right as it should but got lighter at high speed -- easy enough to hold and steer with one hand. I swapped it for a new Mercury 300r with a 33" Bravo prop and took it for a test run today. It pulls extremely hard to the right despite having a cambered skeg. No trim tabs of course as they wouldn't matter with this type of boat and the last motor didn't have them and was fine. I have to hold both hands on the wheel not to go flying off to the right and literally cannot turn the boat left far enough to turn around while on plane. I don't have power steering but my last motor didn't have it either and was heavier. The problem only gets worse with the trim higher and worse with increased speed. I would guess that I am using 40-50lbs of force to keep the boat straight. My arms were jello after five miles. I've had many boats before this and none were 10% as bad! Has anyone had this issue before?
As an aside. My motor overheats at idle. Yep! Brand new made in December 2020 with correct oil/level and water circulating through and out the side pisser and she gets to 205F before the alarm sounds and warning that it's over heating before the temperature continues rising. I shut it off at 212. Runs fine 134F at cruise though. $29,000 installed. Thanks Mercury!
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02-28-2021, 07:11 AM #2Screaming And Flying!
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Dang, that sucks. For the torque, the 4 stroker has a lot of skeg. That should help, but needs a torque tab. Might have to test some diff props to start also. I would guess a sticky t-stat for overheat. 4 stroke experts will chime in and help on set up. Lot of guys running them now and have experience.
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02-28-2021, 07:48 AM #3Team Member
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Mercury should fix the idle overheating under warranty. It’s no fun to have an early problem, but too soon to damn the motor. From what I have read here the 300Rs need different props. You could see what Wildman is using on his Liberators with 300Rs.
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02-28-2021, 02:36 PM #4
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03-03-2021, 01:01 AM #5
Sounds like you may have blown the gasket under the water pump. After that they overheat at idle try trimming all the way under it may help slightly.
24 Twister
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03-03-2021, 01:54 AM #6
Some props pull more than others. That sounds excessive though. Post some pictures of the lower, etc.
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03-03-2021, 05:36 AM #7
Idle temp problem is all Mercs but steering torque could be several things. Engine to high, To much trim, Skeg to small or no torque tab on skeg. Is it a swept back skeg or straight? Maybe wrong prop? Need pictures and running vid if possible.
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03-03-2021, 07:12 AM #8
Which way is the curve?
always can play with some bondo to see what works ?
Last edited by CUDA; 03-03-2021 at 07:14 AM.
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03-03-2021, 09:08 AM #9Supporting Member
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Run a 5 blade cleaver for the propeller like everyone is doing with cat hulls for best results. The gasket under the water pump will blow out if the motor was run low at speed and over pressured (replace it with a 450 kit is my advise). I have not run a boat without power steering for many years now but compare the skeg size of your old motor Vs. your new and the answer will become vary apparent that you are most likely running too low and causing all of these issues.
Hope this helps
Joe
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03-03-2021, 07:02 PM #106000 RPM
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You never said what prop u ran on the XP? Aanother thought, maybe a 20'' xp doesnt sit exactly same height as a merc 20"". you could actually not be at the same as the rude...
Last edited by KIRCHNER; 03-03-2021 at 07:12 PM.
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