Prop Pitch were to go

[Don Weaver]

Hello, I'm new to this board. I have a problem with the prop set up on my new boat. It's a Alumacraft 20ft tunnel hull with a F115 Four stroke Yamaha on a 10" power Jack plate and a 17 pitch prop. My problem is I think a need a higher pitch prop,right now when I'm a the lowest setting on the jack plate and trimed in all the way at 3/4 troddle I'm pushing 5600 rpms and running 43 mph by my GPS. The book states they WOT is between 5000 and 6000 rpm. At this point I'm not sure what my WOT rpm's are I don't want to push it much and cause problem with my motor. It only has 15 hrs. on it. I'm thinking I need to step up to a 19 or 20 pitch. To get the rpms down. I really don't care much about top in speed 43 is fine. But think I need to get the rpms down to at least 5600 to 5800 at WOT. The weigh of the rig is about 1600 to 1800 loaded. One thing I'm not sure I should try is take it out and go to WOT to see were the top end of the RPMs are. I have a good hole shot the boat stays just about level on take off due to the pontoons on back. It's a new motor and I just want ot make sure I get maney years of service out of it.

 

[Hooty]

Re: Prop Pitch were to go

Hey Tracker,<br /><br />Welcome to iboats.<br /><br />If it were me, I would prop it to the maximum rpm. Four stroke engines forgive lugging better then two stroke engines. Trim the engine up and out and run it wfo. If it looks like it's going to go over the 6000 rpm max., throttle back and think about proping up.<br /><br />c/6<br /><br />Hooty

 

[Don Weaver]

Re: Prop Pitch were to go

Hey Hooty I never owned a four stroke. So your saying running 6000 will not hurt it. the last motor I had was a two stroke and I blew the lower unit out running 5600. That was a bass boat with a 115 everrude on it and it was push by a 23 double cupped prop. that was the way it ws set up and it's WOT ran at 5600. this four stroke is new to me and a just didn't want to hurt it. I didn't think I should push 6000 day in and day out when running that I would want to drop back off the top end and use that a WOT rpm. It's in the sho p new doing the ten hour check up and adding some stuff to the hull. I guess a see what game plan they come up with. I was hope to learn a lettle before I pick it up and jsut took what set up they gave me.

 

[Forktail]

Re: Prop Pitch were to go

Hey Tracker. You might want to read the manual for break-in procedure if you want the outboard to last.<br /><br />If you followed break-in procedure, you should've run the engine at WOT for short durations of one minute every 10 minutes for a complete hour...on just its second hour of use.<br /><br />This engine has a break-in period of 10 hours. You're a little late on opening her up. And how the heck do you know if you're at 3/4 throttle if you haven't gone WOT? You might be surprised at how little throttle is left, especially at the speeds you're seeing.<br /><br />Propping is simple. The operating range is 5000-6000 rpm. If WOT exceeds 6000 rpm, then you need more pitch to bring it down. If it can't make 5000 rpm then you need less pitch to bring it up. Anything in between works. The 17 sounds about right.<br /><br />Most people prop for max rpm which will usually give you max speed and economy. I prefer to increase pitch slightly, dropping down from max rpm, because most outboards make their max hp slightly below max rpm.<br /><br />Open her up. These F115's are tough and can take continuous WOT running (hours and hours on end). That's what they're designed to do. Mine do it just fine.

 

[Don Weaver]

Re: Prop Pitch were to go

Hey, Forktail Thanks I did see 6000 in the break in but I back it off and from that point on I never taken it over 5800 I wasn't sure what it would have went too I may have screw up on the break in if so then keeping at or below 5800 now wouldn't be a bad idea would you think? From Three hour on I have been trying to keep it between 5600 and 5800 I would think red line it is good I could be wrong this is new to me If they are as tuff as you make hem sound then I think I'm ok.<br /><br />Don