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Post by The Lone Ranger on Nov 6, 2009 2:24:00 GMT -1
Hey Shawn,
I have a question about propping my boat. I recently bought a 2006 Nitro - 17.9 feet with 115 Optimax. The fella that owned it had less experience than me (if that's possible!) It has a 22 pitch Lazer prop. According to the manual, top running rpm is 51k - 57k with optimal performance in the top half of that range. The boat is a slug getting out of the hole and pulls very hard to the right as it's getting out.....once up on plane, it's fine and runs about 55.5k rpm flat out. Problem is getting there. I also notice hard pulling to the right when I decelerate from plane. My limited knowledge of propping problems says this may be too much pitch on the prop....I'm thinking I may need to go down to a 19 pitch....any advice would be appreciated!
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Laugh44
Executive Member
Posts: 786
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Post by Laugh44 on Nov 6, 2009 2:48:05 GMT -1
trim your motor up after you are on plane and you will eliminate the pulling. don't trim it too far...you don't want it to come out of the water. You will see an increase in speed as you do this also.
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Post by Mike Bucca on Nov 6, 2009 6:09:50 GMT -1
Bob, not sure if this is your problem but also make sure your motor is trimmed down all the way before trying to get out of the hole. Then trim up like Scott says once you get on plane and the steering should loosen up.
Mike
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Post by leapnlineman on Nov 6, 2009 10:47:00 GMT -1
I'm not saying this is the problem but I have noticed on my boat that when the weather cools down it becomes harder to steer as well. However it is a sign to me that the grease on the steering linkage needed to be tended to. I believe that the old grease becomes a little harder and thus the steering becomes harder. When I start to notice that every year I just reaply more fresh grease and the problem goes away.
Any single prop boat will tend to pull to the right due to the clockwise rotation of the prop. Just like a single prop plane or air boat will need a touch of left rudder to overcome the torque of the prop rotation. I have a 115 Johnson with a 21 pitch prop so I would think that your prop is about the right pitch for your motor.
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Post by pbmang on Nov 6, 2009 13:38:05 GMT -1
In general for every step in pitch with a prop you can count on a 300 - 500 RPM difference. This typically doesn't matter if you are stepping up or down in pitch. I would say if you are turning 5550 and the max recommended is 5700, then you are pretty close to where you need to be. If anything you could stand to gain a few RPM's on the top end but not much. Also, now that we are coming into the winter months, the colder air will allow your motor to run a little higher RPM's as well. I know there is about a 400 rpm difference between summer/winter for my boat. There are a few things that can help you out. First, do you have a jackplate? If so, you can slowly move it up to increase your speed/RPM's. When you do this, you will need to keep an eye on your water pressure to make sure you stay within your recommended minimum. With the jackplate you will reach a point where you are either losing too much water pressure or not gaining speed. Once you get there, bump it down a notch and you are where you need to be. If you don't have a jackplate, then don't worry about this... As far as the boat being slow out of the hole, a boat that is almost 18ft long with a 115 seems underpowered to me. Most 18ft. boats are rated for a 150, and if that is the case your are pretty underpowered and that will cause the slowness you are experiencing coming out of the hole. There should be a Coast Guard plaque on the boat that will have the max weight/persons/horse power recommended for the boat. Check that out and see if you are indeed underpowered. With that said, you should be able to make it better. Some props come with exhaust holes on the hub (called PVS holes). The point of those holes is to allow ehaust to come out of the hub around the actual blades of the propeller. What this does is when you first take off, there is less water for the blades to "bite" into, and the prop can spin easier. This will allow your motor to get up in RPM's quicker and come out of the hole faster. Once you are moving, the pressure of the water coming around the lower unit basically plugs the holes and all of the exhaust flows though the center of the hub and does not interfere with the blades. These holes are how bigger boats are able to run high pitched props (I run a 27) and still come out of the hole fast. From what I have read, I think optimally you want to be able to spin about 3000 - 3500 RPM's fairly easily when coming out of the hole (depending on the motor). I'm guessing your prop does not have any PVS holes in it, but most "prop guys" can add them to any prop for a fee. Then, you take plugs with different sized holes in them and can adjust the amount of exhaust that flows around the blades. That way you can fine tune it to your application. Lastly, like has been said above, the boat is pulling to the right because of the rotation of the prop. I'm guessing you have cable steering because boat with hydrolic steering don't have this issue (unless something is wrong with the system). I would agree with Ray that you should check and make sure everything is well greased and turning smoothly (no binding). Having a boat pull when you are taking off/coming off plane is normal with cable steering. There is also a small "fin" looking thing just above your propeller. First, check to make sure it is there and also see if it is turned a bit. You should be able to rotate it left and right (have to loose a bolt first). That is there to help alleviate the pull as well. I don't know a thing about adjusting them, so I would talk to a mechanice first on that one. Hope this helps
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Post by The Lone Ranger on Nov 6, 2009 15:10:37 GMT -1
Thanks everyone for the replies. No, don't have a jackplate and the boat could very well be underpowered as you said - it's rated for a 150 and has a 115 on it. I'll also go out and make sure everything is greased the way it should be - although I'm pretty sure it is...Mike, I did have motor all the way down on hole shot and gradually increased trim (up) as boat was getting onto plane......once there, speedo says 51 mph which is way fast enough for me even if speedo is not accurate .........fact of the matter may be that boat is just underpowered therefore the sluggish hole shot....ALSO - my 225 lb son was sitting in the co pilot seat.....first time I've ever had anyone in the boat with me and seems to me that when I'm in it by myself it's a "little" quicker coming up.....oh well - I think what I'll do is wait until I have an opportunity to be with ya'll in a tournament or something and ask you to take it out for a spin and an opinion....I may be looking for too much out of the equipment I've got......thanks again for all the replies!
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Post by pbmang on Nov 6, 2009 15:27:22 GMT -1
If you are rated for a 150, then technically you are underpowered. That will be more evident the more weigh in the boat, regardless of what is causing it. Something else to consider would be getting a 4 blade 21 pitch prop. The 4 blade will help to come out of the hole faster, but you will lose a bit on the top end. Since it doesn't sound like you are concerned with top speed, that might be the best solution. A 4 blade is better at carrying a load, but the more blades you add to a prop, the less efficent it will run (causing a loss in top speed). That might be the best/easiest solution for getting a good holeshot.
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Post by The Lone Ranger on Nov 6, 2009 20:05:00 GMT -1
Pbmang, you're absolutely right.....I ran faster on plane yesterday (once up there) than I was comfortable with and it would not bother me at all to lose a little top end speed. I went out today and greased everything as suggested and noted that my current hub does in fact have the PVS holes and there are plugs in them (with their own holes). I suspect you are right......"under motored" is a good way to put it.....I know Nitro put these boats out at the dealer with the 115's on them and the guy I bought it from didn't upgrade. Given the alternatives, a four blade prop may be the answer - even a little bit of improvement would be great given I'm just not in the market to trade in a practically new 115 on a 150. Thanks for your answers, by the way!
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Post by pbmang on Nov 6, 2009 20:11:37 GMT -1
Since you have the PVS plugs, you can just pull one all the way out or take a drill bit and enlarge one a tad and see if you have a difference. The worst that could happen is you would have to get a new plug (which are pretty cheap). I would try try popping one out first and see what happens. Never know, it might be just right with one plug removed. Also, glad I could help I've been in the same situation as you when I first got my boat except I was looking for more top end.
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Post by The Lone Ranger on Nov 6, 2009 20:19:37 GMT -1
I'll give it a shot!
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Post by groundloop on Nov 8, 2009 23:22:04 GMT -1
Just like a single prop plane ......will need a touch of left rudder to overcome the torque of the prop rotation. Right rudder. I was a flight instructor and with a student pilot in the plane we're all like stuck records - right rudder..... right rudder..... right rudder...... right rudder..... 'till they finally get tired of hearing it and get it right. ;D But yes, it's the same effect - one side of the prop is at a slightly higer angle of attack and is getting a bigger bite than the other.
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Post by leapnlineman on Nov 9, 2009 0:08:55 GMT -1
I stand corrected. You are absolutly RIGHT! Bet your glad you don't fly with me.
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