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Just got a 2014 ShadowCast 18' with a 30 hp Tohatsu and breaking it in just has 6 hours and now at 10-11 mph its making a suction noise from the motor is there something I'm doing wrong or sometime I can do to stop it of doing this I didn't want to going faster.
 

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My 15hp may have had the same "suction noise"... Did you check if it was pumping water. Mine would not spurt out water and was not pissing water continually. I would run the motor with some earmuffs and move the water hose that runs to the piss hole around to see if it was kinked slightly.
 

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u might be in the "unsweet" spot ------ the hull  is squatting and plowing water away from the motor
resulting in the prop sucking air

or call Mel at the shop
 

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That gurgling/growling sound is normal at mid range speeds on the shadowcast 18. It's not a mechanical problem with the motor. It's a result of water being forced/sucked through the tunnel to the prop. This isn't going to negatively impact performance whatsoever. However, if you are using the stock prop you are likely experiencing cavitation as well especially as you make a turn or trim it up, you will lose speed and hear the rpms increase as the prop starts slipping. Highly recommend an aftermarket prop with cup. A 4 blade powertech works best on this hull and eliminates the cav issue. Difference in perf with stock prop vs aftermarket prop is night and day. Congrats on your new skiff.
 

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Thanks I been wanting a skiff for a while now and was tried of hiring guides and going on friends boats so I been looking and reading lots of reviews on Akona and they are good people to deal with. But I just got a little worried first tunnel hull for me I'll call them and order a aftermarket 4 blade powertech prop tomorrow. thanks again I'll post some pics some.
 

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I have the 4 blade that will fit your motor. Twokids has run my prop on his boat with good results. PM me before you order it from powertech. I can save you some money, I don't need it anymore.
 

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You can also order the prop from Ankona, not sure what price differential is, shop for best price between Ankona and prop listed above. I also get the sucking sound, it is coming from the upper water pickup on the underside of the cavitation plate on the motor. I am looking at adding a Shaw Wing or the Bob's Machine Shop Cavitation plate to try to eliminate this. basically, you can't trim the motor up at all.
 

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You can also order the prop from Ankona, not sure what price differential is, shop for best price between Ankona and prop listed above.  I also get the sucking sound, it is coming from the upper water pickup on the underside of the cavitation plate on the motor.  I am looking at adding a Shaw Wing or the Bob's Machine Shop Cavitation plate to try to eliminate this.  basically, you can't trim the motor up at all.
Interesting... I've not experienced the same performance issue as you wrt trimability. Curious as to which prop/pitch you are running?  I've used an SRA3 11p and SRA4 10p and am able to trim the motor significantly past the sweetspot without loss of water pressure or cavitation. I've experimented and trimmed it up into rooster tail territory, at which point I start losing stream before the cupped prop loses bite. When you say you can't trim the motor up at all, what is happening performance wise when you do? At all speeds? In straight line runs or only in turns?
 
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